A Short Introduction Into the Physics at the Antiproton Decelerator at CERN

A short introduction into the physics at the Antiproton Decelerator at CERN

Michael Doser March 10, 2015 11:23 World Scientiﬁc Review Volume - 9.75in x 6.5in Schopper˙v3 page 11

cooling and storing a minute number of antiprotons in ICE, a 9 order of magnitude improved lower limit on the lifetime of antiprotons could be obtained [58]. This fundamental advance allowed CERN’s antiproton complex (figs. 4 and 5) consisting of the antiproton production target, the Antiproton Accumulator (AA) and the Antiproton Collector (AC) and the low energy antiproton ring (LEAR) - THE ANTIPROTON ACCUMULATOR,COLLECTOR AND DECELERATOR RINGS and relying on the Proton Synchrotron which produces 26 GeV/c protons, to be proposed [59] and rapidly built (AA start-up in 1980, LEAR began operation in 1982, AC from 1987 onwards). !"#$%"&$'(#'%)$'*+%The development",-(%(+'./01'%)$'#"-2%',*-%"3!$',)42"32'$5,$-"&$+%',$-#(-&$6'7"%)'%)$'*"6'(#'2%(3)*2%"3' of antiproton trapping and electron cooling techniques by 3((!"+89'Gabrielse:;<' 2%",=!*%$2' et al. "6$+%"3*!' [60] in 1986 6$3*4 at' !"#$%"&$2' CERN’s #(-' dedicated *+%",-(%(+2' antiproton *+6' ,-(%(+21' experimental ,-*3%"3*!!4' facil- "+#"+"%$' 3(&,*-$6'7"%)'%)$'-$>="-$6'6*42'(#'*33=&=!*%"(+'%"&$?';-"(-'%('@:A1'%)$'$5,$-"&$+%*!!4'!(7$-'!"&"%' ity LEAR finally allowed carrying out precision experiments on trapped and cooled #(-'*+%",-(%(+2'7*2'(+!4'BCD'E2'F6$-"G$6'#-(&'H=HH!$'3)*&H$-'%-*3I2J?'K$2,"%$'#*"%)'"+'%)$(-41'"%'7*2'*' +"8)%&*-$'antiprotons %(' !*=+3)' and *' &=!%"&"!!"(+ working towardsL6(!!*-' ,-(M$3%' the study "+' 2=3)' of antihydrogen *' 2"%=*%"(+?' <(' atoms -$&(G$' first 6(=H%21' at LEAR *' 3-=6$' *+%",-(%(+',-from(6=3%"(+'%*-8$%'7*2'"+2$-%$6'"+%('%)$'%-*+2#$-'!"+$'H$%7$$+';N'*+6'@:A1'7)"3)'3(+G$-%$6' 1986 to 1996, and - since 2000 - at the unique Antiproton Decelerator (AD) BD'O$PQfacility!' ,-(%(+2' (transformed F%)$' &*5"&=&' from &(&$+%=&' the AC), %-*+2#$-*H!$' which hosts "+' all %)$' existing !"+$J' %(' C experiments'O$PQ!' *+%",-(%(+2' requir- F%)$' &*5"&=&'ing 2%(-*H!$' trapped "+' antiprotons. @:AJ?' @+' %)"2' Confinement 7*4' *' H$*&' of (#' antiprotons CRD' *+%",-(%(+2' in ion 3(=!6' traps for H$' 2%seconds(-$6' *+6' (or 7*2' 2%(3)*2%"3*!!4'3((!$6'"+'@:A?'S(=-'6*42'!*%$-1'TD'7$-$'2%"!!'3"-3=!*%"+8?'<)"2'$2%*H!"2)$6'*'+$7'!(7$-'days) opened up major improvements in the determination of the antiproton’s mass, !"&"%'#(-'%)$'6$3*4charge, but'!"#$%"&$'(#'UC')'*%'-$2%1'*+'"&,-(G$&$+%'H4'/'(-6$-2'(#'&*8+"%=6$'*+6'*'-$!"$#'#(-' also of its magnetic moment (although it took until 2012 to surpass the %)(2$'7)('+$$6$6'&(-$'%)*+'M=2%'#*"%)precision achievable in antiprotonic'"+':;

The ﬁrst facility capable of producing antiprotons at CERN was the Proton Synchrotron; completed in 1959; meson spectroscopy with antiprotons (from 1965) and exotic atoms incorporating them

stochastic cooling (proposed in 1968 by S. van der Meer, published in 1972);

successfully tested in the Initial Cooling Experiment (ICE) in 1978 '

!"#$%&''Y*4(=%'(#'Fig. 4.%)$' Layout:AZ['*33$!$-*%(-2'"+'B/TB?'YAVZ1'2%"!!'=+6$-'3(+2 of the CERN accelerators in 1981. LEAR, still%-=3%"(+'"+'B/TB1'"2'*!2('2)(7+ under construction in 1981, is' also :(+2%-=3%"(+'shownAntiproton [58]. From (#' %)$'Accumulator 2000 VV' onwards,H$8*+' "+' the(AA), B/\/?' AA Antiproton was @+' V,-"!'transformed B/TB1' Collector into %)$' the #"-2%' Antiproton(AC) ,-(%(+ and]*+%",-(%(+' Decelerator, low energy 3(!!"2"(+2' and antiproton ring (LEAR): now houses at CERN all experiments worldwide relying on low energy antiprotons. (33=--$6'"+'%)$'@NZ1'*%'CAA start-up 'in^' C1980W'O$P?'<)$'N;N'#(!!(7$6'(+'%)$')$$!21'7"%)'3(!!"2"(+2'*%'C, LEAR began operation in 1982, AC from 1987'^ 'C\Uonwards'O$P'(+' BD'_=!4'B/TB?'<)$'#"-2%'`'6*%*'7$-$'%*I$+'"+'B/TC'*+6'%)$'6"23(G$-4'(#'%)$'`'*+6'a'7*2'*++(=+3$6'"+' B/TU?' @+' (-6$-'AD start %(' 2*%"2#4' in 2000 %)$', $G$-ELENAL"+3-$*2"+8' commissioning *,,$%"%$' (#' in *+%",-(%(+' 2018: looking =2$-21' %)$'at another V+%",-(%(+' very :(!!$3%(-' active decade with antiprotons FV:J' .BC0' 7*2' H="!%' *-(=+6' %)$' VV' "+' B/TX?' S-(&' B/T\' (+1' "%' H((2%$6' %)$' *33=&=!*%"(+' -*%$1' $G$+%=*!!4' H4' *+' (-6$-' (#' &*8+"%=6$?' V#%$-' *' !*2%' 3(!!"6$-' -=+' "+' B//B1' %)$' N;N' -$%=-+$6' %(' *+' *33$!$-*%(-L(+!4' !"#$?' <)$' Y(7' A+$-84' V+%",-(%(+' Z"+8' FYAVZJ' 3(+%"+=$6' %(' %*I$' H$*&' #-(&' %)$' V:QVV'=+%"!'$+6'B//X?'@+'B//\1'%)$'VV'7*2'6"2&*+%!$6'*+6'%)$'V:'3(+G$-%$6'"+%('%)$'V+%",-(%(+' K$3$!$-*%(-'FVKJ1'%(',-(G"6$'!(7L$+$-84'*+%",-(%(+2'"+'*'2"&,!$-'7*4'.BU0?'

&! ()*+",-%./%*0-%120-3-%% <)$'WD'b$P'Y"+*31'%)$'TDD'b$P'c((2%$-'*+6'%)$'CW'O$P';N'FS"8?'CJ'7$-$',=2)$6')*-6'%('6$!"G$-'*+' "+%$+2$',-(%(+' H$*&' (+' %)$' ,-(6=3%"(+'%*-8$%?'<)$' H=-2%' (#'*+%",-(%(+2' $&$-8"+8' *-(=+6' U?W'O$PQ!'

22 space for future overview of AD facility (anti)atomic physics experiments

ELENA: extraction ALPHA-g ASACUSA of antiprotons at PUMA? 100 keV; ALPHA GBAR trapping efﬁciency ATRAP BASE goes from ~1% at I & II AD to O(100%); _ AEgIS 107 p /100s physics at the AD _ _ H / pHe _ Gravity w/ H Spectroscopy

ALPHA ALPHA-g GBAR ASACUSA AEgIS ATRAP

ACE BASE PUMA Nuclear Matter-Antimatter physics interactions Symmetries_ ( p / p ) antihydrogen _ H spectroscopy (1s-2s, GS HFS, others?) _ ALPHA: continuous formation and trapping of H _ ASACUSA: continuous formation and beam of H* _ H for WEP tests _ _ AEgIS: pulsed formation and beam of H* (H) _ ALPHA-g: release of trapped H _ GBAR: formation, trapping and cooling of H+ Schematic overview: AEgIS (Antimatter Experiment: gravity, Interferometry, Spectroscopy) Physics goals: measurement_ of the gravitational interaction between_ _ matter and antimatter, H spectroscopy, antiprotonic atoms (pp, pCs), Ps, ...

¡ Anti-hydrogen formation via Charge exchange_ process with Ps* • o-Ps_ produced in SiO2 target_ close to p; laser-excited to Ps* • H temperature defined by p temperature → Schematic¡ Advantages: overview_ ¡ Pulsed H production (time_ of flight – Stark acceleration) ¡ Narrow and well-defined H n-state distribution ¡ Colder production than via standard process possible positronium 4 _ converter ¡ Rydberg Ps & σ ≈ � 0 � → H position-sensitiformationve enhanced e+ detector Ps Ps grating 1 grating 2 laser excitation Ps* Ps* H* H* H beam

antiproton accelerating trap electric field H* atomic L L beam

pulsed production_ beam gratings produce periodic pattern on detector; of H* formation measure gravity-induced vertical shift of fringes Physics goals: measurement_ of the gravitational interaction between matter and antimatter, H spectroscopy, ... _ AEgIS experiment

Development of nuclear emulsions with 1 m spatial SETUP resolution for the AEgIS experiment M. Kimura on behalf of the AEgIS collaboration. Albert Einstein Center for Fundamental Physics, Laboratory for High Energy Physics, University of Bern Contact e-mail: [email protected] Chamber for Ps Chamber for Ps experiments experiments The AEgIS experiment Emulsion in high vacuum Positron accumulator The goal of the AEgIS experiment (CERN AD6) is to test the Weak Experiments with emulsions under 1T trap Equivalence Principle (WEP) using antihydrogen . The gravitational sag high vacuum have not been of a beam will be measured with a precision of 1% on g/g by means of performed so far. We therefore tested Positron trap a moiré deflectometer and a position sensitive annihilation detector. The their behavior in respect to such required position resolution should be a few m to achieve the 1% goal. conditions. Water loss in the gelatine can produce cracks in the emulsion 5T trap OVC Thin metal window UHV layer compromising the mechanical

stability (m level needed). Therefore

TOF Target for Ps we developed glycerine treatment to Moiré deflectometer avoid this effect. Glycerine can Fig. 3. Emulsion films after 3.5 days in the production and vacuum chamber without glycerine Position detector _ efficiently prevent the elasticity loss treatment (A) and with treatment (B). Fig.1 Left: Schematic view of the AEgH formationIS detectors. Right: g/g vs. number of in the emulsion (see fig. 3). particles for a position sensitive detector resolution of 1 m (red) and 10 m (blue). Nuclear emulsions Emulsion properties after glycerine treatment Positron PositronPositron transfer line Nuclear emulsions are photographic film with extremely high spatial Since the glycerine treatment changed the composition of the emulsion accumulator resolution, better than 1 m. In recent experiments such as OPERA, large layer, we investigated : source area nuclear emulsions were used thanks to the impressive developments • The detection efficiency per AgBr crystal with 6 GeV/c pions in automated scanning systems. For AEgIS, we developed nuclear • The background in terms of the fog density Antiproton line -5~ -7 Positron Antiproton line emulsions which can be used in ordinary vacuum (OVC, 10 mbar). (the number of noise grains per 103 m3) trap This opens new applications in antimatter physics research.

Fig. 4. Left: Crystal sensitivity vs. glycerine concentration. Fig. 2. Left: AgBr crystals in emulsion Right: Fog density vs. glycerine layers observed by SEM. content for films kept in vacuum : A minimum ionizing track (MIP) of Right for 3.5 days (square), compared a 10 GeV/c pion 1 m to atmospheric pressure(dots).

UHV/OVC separation Bare emulsion gratings (12 m slit, 40 m pitch, separated by 25 mm). The antiproton (2 m titanium) SUS 20 m data is being analyzed and preliminary results are encouraging.

Fig. 5. Left: Schematic view of the

Janusz detector setup. chamber SUS 20 m Upper right: Emulsion holder. MC

-5 Flange 1 m (10 mbar) Lower right: Emulsion detector attached to Gate valve Gate Gate valve Gate 5 T / 1 T the vacuum flange by a crossed bar frame. magnet Emulsion 10 m Turbo pump 5 films

Vacuum flange The 3D tracking and annihilation vertex reconstruction were performed at the University of Bern. Annihilation stars were observed together with Fig. 7. Left: Holder of the miniature moiré deflectometer. Phase (rad) tracks from nuclear fragments, protons, and pions. From the measured Right: Simulated intensity distribution of reconstructed vertices with position resolutions of 1 m (red) and 10 m (blue). impact parameters a spatial resolution of ~1 m on the vertical position of the annihilation vertex can be achieved. Glass-based films with highly sensitive emulsions

p Preliminary Annihilation products from annihilating will be isotropically distributed. Since (A) Impact MIP tracks at large incident angles parameter

reduce the track finding efficiency in our

SUS automatic scanning system, we are 100 m 200 m (B) Impact parameter resolution (m) presently investigating new emulsions 44 m 50 m with increased sensitivity. They were Fig.6. Left: A typical antiproton annihilation vertex in the emulsion layer. developed at Nagoya University (Japan) Fig.8. A 10 GeV/c pion track in the reference Middle: Definition of the impact parameter. and then coated onto glass substrates in film (A) and in a highly sensitive one (B). Right: Impact parameter resolution with a window of 20 m stainless steel (SUS). Bern. Glass is well suited for highest position resolutions thanks to its superior Reference environmental stability (temperature and humidity), as compared to plastic. Tab.1. Comparison between the reference C. Amsler et al., ‘A new application of emulsions to measure the films (OPERA) and the new emulsions gravitational force on antihydrogen’., JINST (in press), arXiv:1211.1370. (Nagoya University). ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms5538 NATURE COMMUNICATIONS | DOI: 10.1038/ncomms5538 ARTICLE he precise measurement of forces between objects As indicated in Fig. 1b, the position of the moire´ pattern is shifted deflectometergives experiencing deep insight no acceleration. into the fundamental Thus, light interactions provides andthe emulsionin the presence detector of a isforce removed, with respect developed to the geometric and analysed shadow with by symmetries of nature. A paradigm example is the the requiredT absolute zero-force reference. The only prerequisite an automatic microscope availableF at2 one2 of the participating comparison of the motion of matter in the gravitational field, Dy k t at ; 1 is that the Talbot length (or a multiple integer of it) is matched to institutions to determine the location¼ m of¼ single annihilations. Thisð Þ testing with high precision that the acceleration is material- the distance between the gratings and the detector. With1–4 that, the facilitywhere wasF initiallyrepresents developed the force for component the detection along of the neutrino- grating independent, that is, the weak equivalence principle . Although || 13 absoluteindirect shift of experimental the antimatter evidence pattern suggests can be that directly the weak accessed equivalenceinducedperiod,t-leptonsm is bythe the inertial OPERA mass experiment of the test. The particle, developmenta is the and systematicprinciple also errors holds can for be antimatter significantly5–7, a directreduced observation as the forof emulsionacceleration detectors and t is for the the time application of flight between presented the two here, gratings. which It moire´ deflectometerantimatter is still and missing. Talbot–Lau First attempts interferometer in this direction use the haveinvolvesis important operation to in note vacuum, that the is described shift has two in refs contributions. 20,21. The same gratings.recently been We reported would by like the to ALPHA stress collaboration that Talbot–Lau8, who used Aftervelocity removal of the ofparticle the emulsionafter the second detector grating the in pattern the direction of the of interferometrythe release is also of antihydrogen possible for from matter a magnetic waves such trap toas exclude atoms theTalbot–Lauthe acceleration interferometry is non-zero with and the light particle was is alsorecorded accelerated in a in 17,18 and moleculesabsolute valueif theirof the de gravitational Broglie wavelength acceleration is oflong antihydrogen enough. tosubsequentthe second measurement. half of the For moire this´ purpose,deflectometer. the grating The holderrelevant be 100 times larger than for matter. An alternative approach iswas homogenouslyparameter for precision illuminated measurements by an incoherent is the sensitivity,light source that (red is, 9 Experimentalfollowed implementation by the GBAR. The collaboration experiment, which was performed is based onlight-emittingthe minimal diode detectable with spatial acceleration diffuser).amin. For This a can wavelength be estimated of by considering the maximal signal S to noise2 ratio possible in this within thesympathetic AEgIS apparatus cooling designed of positive to produce antihydrogen antihydrogen ions and for theirl 640 nm, the Talbot distance is LTalbot 2d /lE5 mm. Thus, subsequent photodetachment. One of the specified10,19 goals offor¼ ourscenario. setup Since (L 25 the mm), influence we analyse of a pattern the¼ fifth shift rephasing is most sensitively of the a future measurement of the gravitational acceleration .A detected at the¼ steepest gradient of the pattern the visibility beam ofthe antiprotons AEgIS collaboration with a broad (antihydrogen energy distribution, experiment: delivered gravity,light waves. The light pattern was directly recorded at the plane of interferometry, spectroscopy) is the direct detection of thetheu emulsion(Smax S withmin)/( aSmax high-resolutionSmin) should flatbed be maximized charge-coupled and the by the AD at CERN, is realized after the 5.3 MeV antiprotons are 10,11 periodicity¼ À minimized.þ The noise of the signal is intrinsically transmittedgravitational through acceleration degrader foils using with an a antihydrogen total thickness beam of device scanner (2.7 mm resolution). To align the antiproton and combined with a moire´ deflectometer12, a device with high limited for classical particle sources to the shot noise which scales 225 m (170 m of aluminium and 55 m of silicon). The light measurement in the experiment reported here, an m sensitivitym for acceleration measurements.m as 1/pN, where N is the number of detected particles. independent spatial reference is implemented. For that12 purpose simulatedHere, distribution we present has the a mean successful energy realization of 106 keV of such and a a device root for Consequently, the minimal detectable acceleration is given by we installedffiffiffiffi an additional2 transmission grating in direct contact mean squared value of about 150 keV (see Methods). After amin d= 2put pN . It is important to note that this device antiprotons. This has been achieved using slow antiprotons fromwith the¼ detector plane. Contact grating and moire´ deflectometer traversingthe a Antiproton 3.6-m long Decelerator tube within (AD) two homogeneous at CERN, the magnetic technology of works even for a very divergent source of particles as shown in (see Fig. 1a)ÀÁ wereffiffiffiffi simultaneously illuminated: first with fields ofemulsion 5 T and 1 detectors T, the antiprotons developed enter for recent the deflectometer. high-energy neutrinoWe Fig. 1a, and thus is an ideal device for the highly divergent beam 14 antiprotons and subsequently with light. In each case, the pattern estimateexperiments the mean13 deand Broglie a novel wavelength referencing to be 8.8 method10 À employingm, of antihydrogen atoms that is expected in the AEgIS apparatus. GRAVITY MEASUREMENTÂ - behind the contact grating is a simple shadow withoutDevelopment any force of nuclear emulsions with 1 m spatial whichProofTalbot–Lau implies that interferometry the concept of14,15 of with classicalprinciples light. paths The observation for the is trajectoriesconsistent of the antiprotons with a force is applicable at the 500 for aN our level gratings acting with on thedependence,Talbot–Lau and interferometry thus can be used with as lighta reference as absolute for alignment. reference. resolution for the AEgIS experiment a periodicity of 40 m. antiprotons.m This demonstration is an important prerequisite To determine the magnitude of the fringe pattern shift, M. Kimura on behalf of the AEgIS collaboration. PROOF TheOF gratingfor future PRINCIPLE holder studies is ofcompact the gravitational (25 mm distance acceleration between of antimatter the Antimatterknowledge fringe of the patterns undeflected. With fringe the position emulsion (indicated detector, as the grey gratings)building so that on the an antihydrogenpassive stability beam. of the relative positions positionstrajectories of the in Fig.annihilation 1b) is required. vertices Due can to the be neutrality detected and withAlbert high aEinstein Center for Fundamental Physics, Laboratory for High Energy Physics, University of Bern Contact e-mail: [email protected] between the gratings for the long measurement time of 6.5 h is typicalspeed resolution of photons, of 2 itmm is favourable(see Fig. 2a). to measure The fragments this position produced inde- Mini-Moiréensured. setup The slit arrays are manufactured in silicon by reactive by thependently annihilation with light of antiprotons so that the lead action to aof characteristic forces is negligible. star- The AEgIS experiment Emulsion in high vacuum •Mini-moiréion etching,Results leadingdeflectometer to a 100-mm thick silicon membrane with a shapedUnlike pattern, the case which ofclassical can be observed particles describedwith the microscope above, geometric (an ❖ slit widthMoire of´ 12deflectometermm and a periodicity. The principle of d used40 mm. in Low-energy the experimentexamplepaths is are depicted not applicable in Fig. 2a). forThe visible goal first of light observationthe AE asgIS diffraction experiment of such at(CERN an the AD6) is to test the Weak Experiments with emulsions under ~100 keV antiprotonsantiprotonsreported hitting# here the is slit visualized array annihilate in Fig.¼ 1a.on the A divergent surface of beam the ofannihilationgratings has star to succeeded be taken into shortlyEquivalence account. after Figure Principle the discovery 1c (WEP) depicts using theof antihydrogen the cor- . The gravitational sag high vacuum have not been Challenges: • distancearray 25 andantiprotons mm do not reach enters the the detector. moire´ setup For this consisting measurement, of three the equallyantiprotonresponding using light emulsions field pattern22. Thisof a where allows beam the will for distance be verymeasured robust between with anda precision the of 1% on g/g by means of performed so far. We therefore tested ❖ a moiré deflectometer and2 a position sensitive annihilation detector. The their behavior in respect to such 7 hour exposurefinal# pattern,spaced that elements: is, the two annihilation gratings and positions a spatially of resolving antiprotons emulsionhigh-qualitygratings is particle given by identification, the Talbot length whichLTalbot makes2d this/l. Thisdetector con- • slit 12 μm, detector.pitch The40 two μ gratings with periodicityμm thickd define the classical figuration is known as Talbot–Laurequired position interferometer resolution¼ 14 should, which be a few is m to achieve the 1% goal. conditions. Water loss in the gelatine after passing two gratings,m, is detected100 by an emulsion detector. practically background-free. In addition, this15 detector can detectDevelopment of nuclearcan produce emulsions cracks in the emulsion with 1 m spatial trajectories leading to a fringe pattern with the same periodicity at based on the near-field Talbot effectOVC —theThin rephasing metal window of the ❖ The moire´ deflectometer and the annihilation detector are the arrival of antiprotons over a large area and thus is compatible layer compromising the mechanical Bare emulsion behindthe position deflectometer of the detector. If the5 # transit time of the particles pattern in discrete distances behindUHV a grating illuminated with mounted in a vacuum chamber (10 mbar) on the extraction with an upscaling of the grating area necessary for experiments stability (m level needed).g Therefore DEFLECTOMETER• p ̄ beam E~(100±150)through the deviceRESULT keV is known, traversingÀ absolute force measurements light. The final pattern is not a classical distribution, but an resolution for the AE IS experiment p TOF Pulsed formation: line of the AEgIS apparatus. After theMeasurement: exposure to antiprotons, 16with a divergent antihydrogen beam. we developed glycerine treatment to ̄ Temperature:❖ are possible by employing Newton’s second law of mechanics . interference pattern and coincides with the pattern of the moire´ avoid this effect. Glycerine can Alignment1T magnetof gratings using light and Moiré deflectometer M. Kimura on behalf of the AE IS collaboration.Fig. 3. Emulsion films after 3.5 days in the g vacuum chamber without glycerine Position detector efficiently prevent the elasticity loss treatment (A) and with treatment (B). abcFig.1 Left: Schematic view of the AEgIS detectors. Right: g/g vs. number of in the emulsion (see fig. 3). single grating Moiré pattern Contact pattern Albert Einstein Center for Fundamental Physics, Laboratory for High Energy Physics, University of Bern • light reference: a Moiré b particles for a position sensitive detector resolution of 1 m (red) and 10 m (blue). Contact Matter moiré Contact e-mail: [email protected] Talbot-Lau_ Nuclear emulsions Emulsion properties after glycerine treatment •Pattern observed Nuclear emulsions are photographic film with extremely high spatial Since the glycerine treatment changed the composition of the emulsion Submitted for publication The AEgIS experiment Emulsion in high vacuum ❖ cooling of p resolution, better than 1 m. In recent experiments such as OPERA, large layer, we investigated : Antiproton fringes observed# area nuclear emulsions were used thanks to the impressive developments • emulsion detector • The detection efficiency per AgBr crystal with 6 GeV/c pions 1 Thein automated goal of thescanning AEg systems.IS experiment For AEgIS (CERN, we developed AD6) nuclear is to test the Weak Experiments with emulsions under _ 40 m • The background in terms of the fog density • Shift between p and µ -5~ -7 ̄ Equivalenceemulsions which Principle can be used (WEP) in ordinary using vacuum antihydrogen (OVC, 10 mbar). . The gravitational sag high vacuum3 have3 not been ❖ 0.8 (the number of noise grains per 10 m ) sympatheticSmall uncertainty cooling due of top distortion # 50 60 This opens new applications in antimatter physics research. 25 mm c of a beam will be measured with a precision of 1% on g/g by means of performed so far. We therefore tested 0.6 40 Light interference50 light observed a moiré deflectometer and a position sensitive annihilation detector. The their behavior in respectFig. to4. such: Crystal sensitivity vs. Left _ 40 to ~❖ mK through anions 25 mm 30 glycerine concentration. Shift of fringes detected # 0.4 30 required position resolution shouldFig. be 2. a Left few: AgBr crystalsm to in achieve emulsion the 1% goal. conditions. Water loss in the gelatine Hits Hits Right: Fog density vs. glycerine 20 layers observed by SEM. A. Kellerbauer & J. Walz, New J. Phys. 8 (2006) 45 position (mm) 20 can produce cracks in thecontent emulsion for films kept in vacuum y 0.2 OVC Thin metal window : A minimum ionizing track (MIP) of 10 10 Right for 3.5 days (square), compared UHV a 10 GeV/c pion layer compromising the mechanical Δy=9.8±0.9(stat)±6.4(syst)❖ μm 0 0 0 1 m to atmospheric pressure(dots). _ Consistent with the force from0 0.2stray 0.4 0.6 field 0.8 1 perpendicular0 20 40 60 aato the+d /2gratinga+d period0 d/2 d stability (m level needed). Therefore ParasiticWarring measurementset al, PRL 102 (2009) primordial 043001 to convergex position (mm) to thex position optimal (µm) detector/deflectometery position configurationy position TOF we developed glycerine treatment to avoid this effect. Glycerine can La E. Jordan et al., PRL 115FigureARTICLE (2015) 2Figure | Antiproton 113001 1 | Moire fringe´ deflectometer pattern. (a for) The antiprotons. spatial pattern(a) A divergent of the antiprotons antiproton (highlighted beam impingesNATURE as blue on two COMMUNICATIONStracks) subsequent as detected gratings Exposure by | thatDOI: theMoire restrictemulsion 10.1038/ncomms5538 ́ ofdeflectometer nuclear the detector transmitted emulsions to stopping antiprotons Proof of principle using a miniature moiré deflectometer Fig. 3. Emulsion films after 3.5 days in the • consistent with residualparticlesAghion, to well-defined S. et 2al. trajectories. Nature This Communications leads to a shadow fringe pattern5, 4538 as indicated (2014) in b, which is shifted in the presence of a force (blue trajectories). vacuum chamber without glycerine in an exemplary area of 1 mm . The annihilation of an antiproton leads to a clear signal from which the annihilationWe vertex performed can beexposures extracted with withPosition stopping a detector antiprotons in June and December, We irradiated emulsionefficiently films with antiprotons prevent thepassing elasticity through aloss small C. MalbrunotFinally, the antiprotons — PSAS are detected 2014 with— aRio spatially de resolvingJaneiro, emulsion May detector. 26th To2014 infer the force, the shifted position of the moire21 ´ pattern has to be treatment (A) and with treatment (B). precision of 2 mm by reconstruction analysing the emitted secondary particles. The image enlargement shows an exemplary2012. The annihilationemulsion detector star. (consistedb) The of sandwiches each made out with moiré deflectometer. Thein thesimulation emulsion below (see shows fig. as an3). example the E.#Widmann 21 Fig.1 Left: Schematic view of the AEgIS detectors. Right: g/g vs. number of _ fringe patterncompared after with transmissiona the expected through pattern the without moire´ deflectometer force. (c) This setup is achieved revealsb using a visibility light and as near-field high as (71 interference,±10) %. Since the10 shift lessfilmsparticles thanof on which five one for double is antiproton a negligible. position sided issensitive plastic A detected grating substrates detector in resolution (68 x 68 xof 0.3 1 mmm (red3) . ) and 10 m (blueexpected). interference pattern at the emulsion layer, generated by a pair of B, E fields direct contact with the emulsion is used to reference the antimatter and120 the light measurements. 120 per lattice period, the pattern shown is obtained by binning the vertical positionsMoiré modulo the extracted periodicityContactUHV/OVC of the separation fringe pattern. The solidBare emulsionblack gratings (12 m slit, 40 m pitch, separated by 25 mm). The antiproton (2 m titanium) SUS Emulsion properties after glycerine treatment m) P. Yzombard et al., PRLline denotes114, 213001 the expected distribution. (c) The pattern behind a grating placedm) directly on the emulsion detector (‘contact’) is a simple20 m shadowNuclear that is emulsions data is being analyzed and preliminary results are encouraging. µ µ

2 NATURE COMMUNICATIONS80 | 5:4538 | DOI: 10.1038/ncomms553880 | www.nature.com/naturecommunications Fig. 5. Left: Schematic view of the

C2 smeared out due to the ﬁnite resolution of the detection. The few background events are consistent with independently observedJanusz grating defects. This detector setup. μ & 2014 Macmillan Publishers Limited. All rights reserved. Nuclear chamberemulsions are photographicSUS 20 m film with extremely high spatial Since the glycerine treatmentMC changed the composition of the emulsion • sensitivity of m Upper right: Emulsion holder. pattern is used as a reference with no force dependence since the transit time is zero. The position of the moire´ fringe pattern-5 (indicatedFlange as offset a) is 1 m (10 mbar) Lower right: Emulsion detector attached to Gate valve Gate 40 40 resolution, bettervalve Gate than 1 m. In recent experiments such as OPERA, large layer, we investigated : 1 5 T / 1 T

position ( the vacuum flange by a crossed bar frame. measured using light. position ( y

y magnet traps, Ps production target area nuclear emulsions were used thanks to the impressive developments Emulsion • The detection efficiency per AgBr10 m crystal with 6 GeV/c pions reached Turbo pump 5 films 0 0 _ in automated scanning systems. For AEgIS, we developed nuclear H formation region: p Penning NATURE COMMUNICATIONS | 5:4538 | DOI:0.8 10.1038/ncomms5538 | www.nature.com/naturecommunications 3 Note: beam experiments 0 40 80 120 0 40 80 120 Vacuum flange • The background in terms of the fog density emulsions which can be used in ordinary vacuum (OVC, 10-5~ -7 mbar). & 2014 Macmillan Publishers Limited.xAll position rights (µ reserved.m) xThe position 3D tracking (µm) and annihilation vertex reconstruction were performed at (the number of noise grains per 103 m3) 0.6 Thisthe Universityopens new of Bern. applications Annihilation in stars antimatter were observed physics together research. with Fig. 7. Left: Holder of the miniature moiré deflectometer. Phase (rad) have a weak dependence c 50 • H̅ beam case tracks from nuclear fragments, protons, and pions. From the measured Right: Simulated intensity distribution of reconstructed vertices 9.8 µm with position resolutions of 1 m (red) and 10 m (blue). 0.4 40 impact parameters a spatial resolution of ~1 m on the vertical position of Fig. 4. Left: Crystal sensitivity vs. Ps* (n=15, ~ µs) the annihilation vertex can be achieved. τ of gravity measurement−4 on position (mm) glycerine concentration. • velocity *10 y 30 Fig. 2. Left: AgBr crystals in emulsion Glass-based films with highly sensitive emulsions Light Right: Fog density vs. glycerine 0.2 Hits layers observed by SEM. ~1700 nm 20 p Annihilation products from annihilating content for films kept in vacuum (transverse) temperature Antiprotons Right: APreliminary minimum ionizing track (MIP) of (A) for 3.5 days (square), compared 10 a 10 GeV/c pion will be isotropically distributed. Since • distance * 40 0 to atmospheric pressure(dots). Impact MIP tracks at large incident angles Ps (n=3) 0 0.2 0.4 0.6 0.8 1 0 1 m parameter (→ figure of merit is the reduce the track finding efficiency in our x position (mm) 0 d/2 d −10 SUS automatic scanning system, we are y position 100 m 200 m (B) • Force 10 Impact parameter resolution (m) presently investigating new emulsions flux into gravity-sensitive 44 m 50 m Figure 3 | Comparison between photon and antiproton patterns. (a) The spatial positions of the detected_ antiprotons (blue Exposure dots) are comparedof nuclear with theemulsions to stopping antiprotonswith increased sensitivity. TheyProof were of principle using a miniature moiré deflectometer 205 nm subsequently recorded light pattern (measured intensity indicated by the red shading). The Talbot–Lau fringe pattern providesFig.6. Left the: A zero-forcetypical antiproton refe annihilationrence, vertex in the emulsion layer. developed at Nagoya University (Japan) Fig.8. A 10 GeV/c pion track in the reference Ps (n=2) Aghion, S. et al. Nature Communications 5, 4538 (2014) Middle: Definition of the impact parameter. and then coated onto glass substrates in film (A) and in a highly sensitive one (B). detector) as long aspresented flight here for the same exemplaryprinciple detector area with tenestablished annihilations as in Fig. 2a. with (b) The antiproton p; displace- and light measurements are aligned by We performedRight: Impact exposures parameter resolution with with astopping window of 20 antiprotonsm stainless steel (SUS). in June and December,Bern. Glass is well suitedWe for irradiated highest emulsion films with antiprotons passing through a small overlaying the two patterns obtained with the contact grating._ The result of this procedure is visualized on the right,2012. where The the emulsion annihilation detector positions consisted of sandwiches each made outposition with resolutions thanksmoiré to itsdeflectometer superior . The simulation below shows as an example the 2 E.#Widmann of all antiprotons are folded into an area of 80 80 mm . The moire´ and Talbot–Lau pattern22 depicted on the left, without any further alignment, can be 3 times are ~ ms or longer mentÂ of p annihilation vertices10Reference films(blue on five double sided plastic substrates (68 x 68 x 0.3 mm environmental) . stabilityexpected (temperature interference and pattern at the emulsion layer, generated by a pair of compared to determine a shift. (c) The data is projected onto the y axis for quantitative analysis. A relative shift between moire´ and Talbot–Lau humidity), as compared to plastic. Tab.1. Comparison between the reference C. Amsler et al., ‘A new application of emulsions to measure the gratings (12 m slit, 40 m pitch, separated by 25 mm). The antiproton pattern indicates that a force is present. The observed mean shift of 9.8 mm is consistent with a mean force ofUHV/OVC 530 aN. separation Bare emulsion films (OPERA) and the new emulsions o-Ps ( 142 ns) (2 gravitationalm titanium) force on antihydrogenSUS ’., JINST (in press), arXiv:1211.1370. (Nagoya University). τ = dots) measured relative to light (red) 20 m data is being analyzed and preliminary results are encouraging.

Fig. 5. Left: Schematic view of the

_ The pattern of 146 antiprotons detected for the grating in Janusz detector setup. dedicated experiments 1 100 aN direct contact with the emulsion is depictedS. Aghion in Fig. et 2c. al.,"A The highmoiré deﬂectometer for antimatter", chamber SUS 20 m Upper right: Emulsion holder. MC

-5 Flange 1 m (10 mbar) Lower right: Emulsion detector attached to Gate valve Gate pulsed formation of H @ end 2018 visibility implies that the periodicity isNature well-deﬁned Communications in an area as 5 (2014) 4538 valve Gate to establish laser-coolinglarge as 15 6 mm2 since the data collapses onto one fringe by 0.8 5 T / 1 T the vacuum flange by a crossed bar frame. magnet taking the detectedÂ position modulo the extracted periodicity d of Emulsion 10 m Turbo pump 5 films464 aN Ps(2s) beam formation under way of anionic systems underthe pattern. Toway extract the periodicity, we employ the Rayleigh 0.6 23 24 Vacuum flange S. Aghion et al., Phys. Rev. A 98, 013402 (2018) test that is also widely used in astronomy . The periodicity d

and manyVisibility more... and the relative rotation a of the pattern is found by maximizing 0.4 The 3D tracking and annihilation vertex reconstruction were performed at Fig. 7. : Holder of the miniature moiré deflectometer. Phase (rad) n 2 n 2 the University of Bern. Annihilation stars were observed together with Left 2 2p 2p 2154 aN Right: Simulated intensity distribution of reconstructed vertices Z2 sin y cos y ; 2 tracks from nuclear fragments, protons, and pions. From the measured ¼ n d Á i þ d Á i ð Þ 0.2 Simulation with position resolutions of 1 m (red) and 10 m (blue). "# i 1 ! i 1 ! impact parameters a spatial resolution of ~1 m on the vertical position of X¼ X¼ Measurement where n is the total number of antiprotons and yi y0 cos a 0 the annihilation vertex can be achieved. ¼ Á 1 2 3 4 x0 sin a depicts the antiproton’s projected coordinate. This 10 10 10 10 0 d/2 d Glass-based films with highly sensitive emulsions leadsþ Á to an inferred periodicity of 40.22±0.02 mm, which is Force (aN) y position consistent with the expected emulsion expansion of B1% and the p Preliminary Annihilation products from annihilating Figure 4 | Monte Carlo simulation. A detailed simulation study based on will be isotropically distributed. Since (A) nominal periodicity of 40 mm. It is interesting to note that the the expected energy distribution of the antiprotons (see Methods) shows analysed area corresponds to 368 slits and, on average, only in Impact MIP tracks at large incident angles the visibility for increasingly large forces. As the observed pattern in the parameter every second slit an antiproton is detected. presence of a force is an ensemble of differently shifted patterns reduce the track finding efficiency in our In Fig. 2b, the observed moire´ pattern for antiprotons is shown. corresponding to different transit times t the visibility consequently SUS automatic scanning system, we are The 241 events associated with antiproton annihilations were 100 m 200 m (B) decreases. The measured fringe pattern exhibits a visibility of (71±10) % Impact parameter resolution (m) presently investigating new emulsions accumulated during the 6.5-h run of the experiment. The 44 m 50 m and is consistent with the result of this simulation. The error bar on the with increased sensitivity. They were Rayleigh tests on sub-segments of the detected patterns reveal measured visibility is determined via resampling; the error bar on the Fig.6. Left: A typical antiproton annihilation vertex in the emulsion layer. developed at Nagoya University (Japan) Fig.8. A 10 GeV/c pion track in the reference local distortion due to the expansion/shear of the emulsion and measured force includes the systematic error bound and the one sigma allow the identification of regions with negligible distortion. Middle: Definition of the impact parameter. and then coated onto glass substrates in film (A) and in a highly sensitive one (B). statistical error bound. The observed high visibilityRight: Impact excludes parameter that the resolution fringe with a window of 20 m stainless steel (SUS). We have restricted the areas to two-thirds of their initial size, pattern is shifted by more than one period and sets an upper limit for a Bern. Glass is well suited for highest which ensures a position uncertainty due to shear to be smaller force present without the necessity of referencing. position resolutions thanks to its superior ± than 1.2 mm. Reference environmental stability (temperature and humidity), as compared to plastic. Tab.1. Comparison between the reference Absolute deflection measurement. To determine the absolute For the quantitative analysis,C. we Amsler extract et the al., orientation ‘A new application of the of emulsions to measure the films (OPERA) and the new emulsions position of the antiproton fringe pattern (parameter a in Fig. 2b), antimatter (Rayleigh test) and lightgravitational patterns (Fourierforce on transforma-antihydrogen’., JINST (in press), arXiv:1211.1370. (Nagoya University). we conduct a comparison with the measurement with light. tion as the data is discrete in space). We find that the relative The results are represented in Fig. 3a,b where the detected angle of the two antiproton patterns, which are 15 mm apart, intensity is indicated by the red shading. The alignment is deviates from the angle measured between the two corresponding achieved by overlaying the contact patterns as depicted on the light patterns by Dy 0.92±0.27 mrad. right of Fig. 3b. The moire´ pattern can now be directly compared This observation¼ is consistent with independent systematic with the Talbot–Lau pattern (left of Fig. 3b) to extract a possible studies of the distortion of emulsions on this large scale25. It is deflection. important to realize that this angle implies an intrinsic systematic

4 NATURE COMMUNICATIONS | 5:4538 | DOI: 10.1038/ncomms5538 | www.nature.com/naturecommunications & 2014 Macmillan Publishers Limited. All rights reserved. other physics topics: positronium (spectroscopy, inertial sensing in metastable beams) antiprotonic atoms (with radioisotopes: PUMA @ AD/ISOLDE) _ - antiprotonic molecules (H2 , others ?)

_ Rydberg atoms (with p instead of e-) - laser cooling of anionic systems (C2 ) 2

wave atom interferometer [8] to measure their vertical thus selecting Ps populations emitted after di↵erent per- displacement with a position-sensitive detector. Grav- manence times in the target [28, 29] and consequently ity (or any other force acting on the atoms) can then be with di↵erent velocities [30, 31]. worked out if the average velocity of the atoms is known In our experiment, Ps is formed when 7 ns bursts [3, 8]. of 107 e+, prepared in the AE¯gIS e+⇠system (see All the suggested schemes involve laser excitation to [16,⇠ 32, 33] for a detailed description of the apparatus) long-lived excited states to overcome the lifetime limita- are electro-magnetically transported and implanted at tion of the 13S ground state (142 ns) where Ps is nor- 3.3 keV into a Si (111) p-type crystal where nanochan- mally produced. An e↵ective and widely adopted choice nels were previously produced via electrochemical etch- consists in laser-exciting the atoms to the Rydberg lev- ing and thermal oxidized in air [16, 33]. Ps produced in- els, where lifetimes spanning from tens of s up to several side the converter out-di↵uses into vacuum through the ms can be obtained [9, 10]. Atoms in Rydberg states are, nanochannels loosing a fraction of its emission energy by in general, sensitive to electric field gradients [11] which collision with the walls. The Si target was kept at room can modify their trajectories. This is due to their large temperature and e+ were implanted into it with a spot of 32 2 1 electrical polarizability (up to 10 Cm V for Ps 3 mm in size. Measurements previously performed on in n = 15) [12, 13]. Ps Rydberg⇠ sublevels with large elec- identical⇠ e+–Ps converters indicated a wide angular emis- trical dipole can be guided and focused [12, 13] while the sion of Ps from the nanochannels [16, 33]. A schematic Development of nuclear emulsions with 1 m spatial selective excitation to sublevels with low dipole moment of the experimental chamber is illustrated in Fig. 1. hasS beenETUP proposed [14] as a method to minimize the de- resolution for the AEgIS experiment flection of Rydberg Ps in interferometric measurements with physical gratings [15]. PbWO4 detector M. Kimura on behalf of the AEgIS collaboration. An alternative way to produce a beam of long-lived Ps 38 2 1 with lower electrical polarizability ( 10 B=0TCm V ) B=1T Albert Einstein Center for Fundamental Physics, Laboratory for High Energy Physics, University of Bern ⇠ 3 positroniumconsists in laser exciting the atoms to their 2 S + Contact e-mail: [email protected] metastable level [15], whose lifetime is 1.14 s in vac- e /Ps converter uum and in the absence of electric field [16]. A beam Chamber for Ps of 23S Ps atoms (of known average velocity) has been experiments + The AEgIS experiment Emulsion in high vacuum shown to be suitable for improving the inertial sensitiv- e ity in proposed matter-wave interferometric layouts [8]. The goal of the AEgIS experiment (CERN AD6) is to test the Weak Experiments with emulsions under Moreover, the availability of 23S Ps with average veloc-Positron+ accumulator 5 1 e Equivalence Principle (WEP) using antihydrogen . The gravitational sag high vacuum have not been ity < 10 ms would allow keeping the interferometer UV / IR lasers1T trap compact in length (L . 1 m), thus easing the control of of a beam will be measured with a precision of 1% on g/g by means of performed so far. We therefore tested thermal and vibrationalPositron noise [17]. trap a moiré deflectometer and a position sensitive annihilation detector. The their behavior in respect to such 3 Producing fast 2 S Ps with energies of several eV has required position resolution should be a few m to achieve the 1% goal. conditions. Water loss in the gelatine already been demonstrated via e+ collisions with solid _ 3 1cm can produce cracks in the emulsion [18–20] or gaseous targets [21, 22]. 2 S Ps atoms with 5T trap OVC Thin metal window a beam Maxwellian distribution at around 600 K (av- pUHV layer compromising the mechanical 5 1 erage speed > 1.4 10 ms ) were also produced via 1cm stability (m level needed). Therefore Doppler-free two photon· excitation of ground-state atoms TOF we developed glycerine treatment to of Ps desorbed from metallic surfaces [23–25] and 13S– Figure 1: Schematic of the experimental chamber with 23S two photon excitation of Ps emitted from porous sil- example Monte Carlo in-flight and collision annihilation Moiré deflectometer avoid this effect. Glycerine can Fig. 3. Emulsion films after 3.5 days in the 3 icon [26]. Production of 23S Ps via single photon excita- distributions for an 1 S Ps population (light and dark efficiently prevent the elasticity loss vacuum chamber without glycerine 3 Position detector tion of ground-state atoms to mixed 23S–23Pinelectric red dots) and for a 2 S Ps population (yellow and blue treatment (A) and with treatment (B). 3 Fig.1 Left: Schematic view of the AEgIS detectors. Right: g/g vs. number of in the emulsion (see fig. 3). fields [15] and the single photon excitation of ground- dots). The line-shaped annihilations distribution of 2 S particles for a position sensitive detector resolution of 1 m (red) and 10 m (blue). Energy state atoms to 33P levels with subsequent radiative decay atoms is due to the UV laser Doppler selection. to 23S [16] have been recently demonstrated. The reduc- Emulsion properties after glycerine treatment tion of the 23S lifetime in electric fields due to Stark In the target region, e+ are guided by a 25 mT mag- Nuclear emulsions mixingPositron has also been studied [16]. Positron transfernetic field line and focused by an electrostatic lens formed by Nuclear emulsions are photographic film with extremely high spatial Since the glycerine treatment changed the composition of the emulsion In the present work we investigate the feasibility of a the last electrode of the transfer line set at 3000 V and resolution, better than 1 m. In recent experiments such as OPERA, large layer, we investigated : Rydberg source of metastable 23SPswithdefined and tunable the target kept at ground potential (see Fig. 1 for the ge- source 3 1 area nuclear emulsions were used thanks to the impressive developments velocity in the absence1640~1700 of electric field.The2 nm Slevel ometry), inducing an electric field of about 300 V cm • The detection efficiency per AgBr crystal with 6 GeV/c pions is populated by spontaneous radiative decay of laser- in front of the converter. Since this electric field shortens in automated scanning systems. For AEgIS, we developed nuclear • The background in terms of the 3 3 3 -5~ -7 fog density excited 3 P Ps atoms. The tuning of the 2 SPsvelocity considerably the 2 S lifetime [13, 16], for the present mea- emulsions which can be used in ordinary vacuum (OVC, 10 mbar). 3 3 n=3 Antiproton3 3 line (the number of noise grains per 10 m ) is achieved by varying the delay of the 1 S–3 P excitation surements the focusing electrode was switched o↵ 5ns This opens new applications in antimatter physics research. pulse1312 between nm 20 ns and 65 ns from the e+ implantation after the e+ implantation using a fast switch with⇠ a rise n=2 1.1 μs time in a nanochannelled silicon e+–Ps2 converterns [27], time of 15 ns (from 3000 V to 0 V). ⇠ Fig. 4. Left: Crystal sensitivity vs. glycerine concentration. 205 nm Fig. 2. Left: AgBr crystals in emulsion Right: Fog density vs. glycerine 243 nm layers observed by SEM. content for films kept in vacuum : A minimum ionizing track (MIP) of Right for 3.5 days (square), compared a 10 GeV/c pion n=1 142 ns 1 m to atmospheric pressure(dots).

Exposure13 of nuclear emulsions to stopping antiprotons Proof of principle using a miniature moiré deflectometer We performed exposures with stopping antiprotons in June and December, We irradiated emulsion films with antiprotons passing through a small Efﬁcient Rydberg positronium production pulsed H production E.#Widmann 2012. The emulsion detector consisted of sandwiches each made out with moiré deflectometer. The simulation below shows as an example the 10 10 films on five double sided plastic substrates (68 x 68 x 0.3 mm3) . expected interference pattern at the emulsion layer, generated by a pair of 3 3 x3 over spontaneous decay Efﬁcient 2 S positronium production by stimulated decay from the 3 P level UHV/OVC separation Bare emulsion gratings (12 m slit, 40 m pitch, separated by 25 mm). The antiproton (2 m titanium) SUS data is being analyzed and preliminary results are encouraging. 3 20 m

Velocity selected production of 2 S metastable positronium beam of meta-stable Ps Fig. 5. Left: Schematic view of the

Janusz detector setup. chamber SUS 20 m Upper right: Emulsion holder. MC

-5 Flange 1 m (10 mbar) Lower right: Emulsion detector attached to

3 valve Gate Gate valve Gate further manipulations, enhanced 2 S production, formation of “intense” 5 T / 1 T the vacuum flange by a crossed bar frame. magnet Emulsion 10 m ongoing work on: metastable Ps beam for inertial sensing, high resolution state-selective Turbo pump 5 films Vacuum flange imaging, test bed for interferometry, spectroscopy, ... The 3D tracking and annihilation vertex reconstruction were performed at the University of Bern. Annihilation stars were observed together with Fig. 7. Left: Holder of the miniature moiré deflectometer. Phase (rad) tracks from nuclear fragments, protons, and pions. From the measured Right: Simulated intensity distribution of reconstructed vertices with position resolutions of 1 m (red) and 10 m (blue). impact parameters a spatial resolution of ~1 m on the vertical position of the annihilation vertex can be achieved. Glass-based films with highly sensitive emulsions

p Preliminary Annihilation products from annihilating will be isotropically distributed. Since (A) Impact MIP tracks at large incident angles parameter

reduce the track finding efficiency in our

_ , or even potentially potentially even or , _ p Stefan Meyer Institute e - (and other exotic) other (and • Atom Exotic atomf par negativ stopping of • • • orbits withn~ energ energ energ ionization (normal capture inhigh-lying end whenkinetic slo E. Ξ

Widmann ticles inmatter (Rydberg states, cascades, binding energies, lifetimes) energies, binding cascades, states, (Rydberg : the deeply bound states' energy levels and lifetimes lifetimes and energy states' bound deeply the levels : and and wing do _ y y

Figure 1 presents the measured spectra for antiprotonic hydrogen and deuterium. 6 6 The total number of Lα events detected is about 2 10 for hydrogen and 10 for deuterium. × Table 1 shows the calculated electromagnetic energies for the Balmer and Lyman transitions in antiprotonic hydrogen and deuterium [4]. For the Kα transition, the difference between the measured energy and the calculated electromagnetic energy is the strong interaction shift ε1s.

3. Results

The three CCDs chips have been analysed separately. For the detection efficiency calibration, we have done a measurement with a 4 mbar nitrogen target.Antiprotonic At this Hydrogen: From Atomic Capture to Annihilation 69 pressure, the stopping efficiency of the antiproton beam is the same as in 20 mbar hydrogen. The intensity of each transition in the pN system is the same (circular 600 , 100, I transitions). In the case of antiprotonic hydrogen, a spin averaged analysis has first La been performed to determine the repulsive shift ε1s and the width Γ1s of the Kα

transition. The results obtained for each CCD were statistically compatible and were, - - -Lp v, LOO + 456 therefore, averaged (weighted mean): 2 3 0 ε = 706.4 18.2eV, Γ = 1054 65 eV. 1s − ± 1s ± the simplest antiprotonic atoms: protonium U 200 1 Approximately 20000 Kε1sα =X-rays−706 have.4±18 been.2 eV, recorded. Γ1s =1054 Thus,±65 taking eV into account the detector efﬁciency, we deduce that only 1% of the 2p level population reaches the 1 , ground state. Our results04 are compatible with the weighted mean of those obtained 3D → 2P by the preceding LEARL experiments2P6 → 1S 8 PS17410 and12 PS17514 (ε1s16 = 18730 20 20 eV and − ± 456 caveat: internal bremsstrahlung! Γ1s = 1122 57 eV) [5–7]. ± M. Augsburger et al., Hyperﬁne Interactions 118 (1999) 59–62

1, 600 v, - c i 5 LOO : 0 U 200 : x -ray energy

Fig. 2. Energy spectrum of X-rays emitted by protonium atoms formed in H, gas at NPT and annihilating OL x-. x- 4- into two charged pions and neutral particles. The peak at low energies is due to the Balmer series of L 6 8 10 12 --1L 16 18 20 the pp-atom. The solid line represents an absolute bremsstrahlung calculation. ENERGY (keV) x -ray energy Ftg Y X-ray spectrum of protonium (Cold gas experiment using a gas 01 Fig. 2. Energy spectrum of X-rays U.emitted Schaefer by protonium et al., Nucl.atoms Phys.formed A495 in H, (1989)gas at NPT 451 and annihilating scintillation proportional detector) The solid line correspond to the best fit into two charged pions and neutral particles. The peak at low energies is due to the Balmer series of Figure 2.taking Expanded into view account of the antiprotonicthe shape of hydrogen the background spectra from from one CCD. D, runs The (dashed) solid lines and show a ﬁt the pp-atom. The solid line represents an absolute bremsstrahlung calculation. 10-3 10-2 10-1 1 10 10-3 10-2 10-1 1 to the spin averaged Kα line, the dotted curves are from a ﬁt to the triplet/singlet splitting. IO two lines for (K, and K, X-rays) PRESSURE [atml PRESSURE lalml 11. - Fig. Cascade of protonium in HLgas. The data are from the three cade. At low gas pressure contamination lines show up due to experiments and Ref. [3]. The solid line represents an absolute calculation, the dotted lines two extreme variations of the calculated Auger effect. imperfect gas tightness of the target. The data obtained by using the GSPD have a better signal/background ratio (Fig. 9). 4. Protonium atoms: Interpretation They show unambiguously the presence of the Lyman series of antiprotonic hydrogen [ 131. 4.1. The atomic cascade The results of the three experiments on line intensities are 3.3. The inverse-cyclotron experiment summarized in Fig. 1 1. All line intensities depend crucially on The third experiment uses a very clever trick to stop anti- target density. The solid line represents the results of a cas- protons at very low densities [14]. Antiprotons enter an cade model which was developed recently by G. Reifenroether and the author [15]. In this model the trajectories of pp atoms x -ray energy bti inverse cyclotron and lose some energy in moderation foils. During their circular path in H, they continue to lose energy, colliding with hydrogen atoms are followed by the Classical Fig. 3. Energy spectrumCharged of particlesX-rays emitted accelerated by protonium in the atoms.annihilation An X-ray emit enhancing inner bremsstrahlungtrigger is used. focussing is provided by the cyclotron magnetic field and its Trajectory Monte Carlo Method applied to the three-body The line represents radiationa fit taking withinto aaccount sizeable the yieldBalmer in series the X-rayof the energyyjp-atom, regionthe bremsstrahlung, below 10 keV(solid line), contributions from the Lyman series of the pp-atom (dashed tine), and a (small) constant x -ray energy bti gradient. The path in H, can thus be made very long and the system p, p, H atom. During the collision the electric field as background. Fig. 3. Energy spectrum of X-rays emitted by protonium atoms. An X-ray enhancing trigger is used. gas density correspondingly very small. The antiprotons a function of the collision time is determined (Fig. 12) as well The line represents a fit taking into account the Balmer series of the yjp-atom, the bremsstrahlung, (solid spiral inwards until they come to rest in the center of the as the local electron density. These calculations are carried line), contributions from the Lyman series of the pp-atom (dashed tine), and a (small) constant background. cyclotron where they form protonium atoms. The atomic out for some values of principal and orbital angular momen- transition lines are observed in Si(Li) detectors (Fig. lo). The tum quantum numbers and then interpolated for any value of three experiments give compatible results [6]: the K, X-ray (n, I). The knowledge of the electric field strength allows to transition is shifted by (-0.72 i 0.04)keV and broadened to a strong interaction width of (1.11 f 0.07) keV.

H ~ atom

200 1 .- _r_-

Ftg 12. Collision process between the pp atom and a hydrogen atom The pp starts with a center-of-mass velocity z, and an impact parameter b The Fig. 10. Energy spectrum observed by the inverse cyclotron collaboration. A nearest distance between pp and H is rmin.which result in a maximum electric strong K, line is seen above a smooth background. field E,,,

Phjsica Scripta T34 the simplest antiprotonic atoms: ... and deuteronium

D. Gotta / Protonium X-ray spectroscopy 41 D. Gotta, Hyperﬁne Interactions 118 (1999) 35–43

Figure 4. Line_ shapes of the Lα transitions in antiprotonic hydrogen and deuterium (from [33]). The solid lines shownIn pD in the pH¯because spectrum correspond of the to the predictionmore of frequent [11] taking into account the experimental _ annihilationresolution. from For the p hyperfine levels pattern as of ¯pDcompared see text. to pH, 3.3.no The 2pclear multiplet evidence in antiprotonic was hydrogen found for the ground The results from various calculations for the pure electromagnetic interaction_ [28, 35,36]state are differing transition by up to 12 (1% meV for of the 2p mean population energy of the Lα intransition pH) and Line up shapes of the Lα transitions in antiprotonic hydrogen and deuterium (from [33]). The solid lines shown in the ̄pH spectrum correspond to the to 20% for the hyperfine level splitting. In common to all calculations is the large value 3 prediction of [11] taking into account the experimental resolution. For the for the electromagnetic splitting of more than 200 meV for the 2 P0 hyperfine state.hyperfine pattern of ̄pD see text. As a matter of fact, the line profile of the 3d–2p transition in antiprotonic hydrogen So: the direct measurement of the 2p-level3 exhibited a shoulder at the high energy side, which was interpreted as the 2 P0 Astate. re-measurement of the Lyman transitions with the forthcoming generation 3 3 1 Thewidth 3 close-lying was components the only 2 P2,2 possibilityP1,and2 P1 were at not all resolved to (figure 4).of CCD detectors is desirable and should be able to improve the accuracy by 3 The 2 P0 state plays a particular role. A strong and_ attractive interaction, result-a factor of 5. Such an experiment requires a continuous antiproton beam of ing indetermine a large hadronic hadronic shift and broadening effects of the in order pD. of 100 meV, is mandatorythe order of 105/s, which, however, will not be available in the near future. for meson-exchange models used for the construction of the real part of the NN potential [8,9,11]. The large attraction was confirmed by the experimental result of 3 3 ε(2 P0) = (+140 25) meV and Γ(2 P0) = (130 50) meV, where the value of ± ± 3 +203 meV [28] for the electromagnetic splitting of the 2 P0 state has been used. 3 3 1 The measured mean shift of the group (2 P2,2 P1,2 P1)wascompatiblewithzero and the mean broadening of the order of the spin-averaged 2p-level width Γ2p as predicted [31,33].

3.4. The 2p multiplet in antiprotonic deuterium

For pD,¯ the results of the two calculations for the electromagnetic hyperﬁne splitting differ much more than for pH.¯ In one case, the electromagnetic interaction dominates the splitting of the 2p level and the 3d–2p line shape should form ap- 4 4 4 proximately a “doublet” structure formed by the sub-states ( P3/2, P1/2, P1/2)and 4 2 2 ( P5/2, P3/2, P1/2)[35].Theothercalculationpredictsmuchsmallerseparationsof the sublevels [28]. It is then sufﬁcient to describe the line shape by one Lorentzian only, which is found to be in much better agreement with experiment. 5

is the 366 nm laser excitation rate for H(2p) ml = 1,ms = 1/2,mi = 1/2 H(30d)| m =0 ,m = ±1/2,m = ±1/2 i!, because we | l s ± i ± i have used circular polarized light. Npi is the population lost due to photoionized H. ⌘L is then deﬁned as the _ _ population transfer eciency from H to H(30d) by

AEgIS : an improved pp (and pd) production method ⌘L = N30d/NH at t = 100 ns. This parameter is maximized scanning over the laser intensities and pulse delays, see Fig. 3 b). Figure 3 c) shows the result,5 where the time depending populations of the states are plotted in Fig. 3 d). Here we find that 16% of the H are _ _ _ is the 366 nm laser excitation⇠ rate for H(2p) mexcitedl = 1 to,ms H(30d)= 1/2 mainly,mi = limited1/2 by the Lyman-alpha • co-trap H (or D ) and p H(30d)|laserm =0 power ,m and= ±1 width./2,m = ±1/2 i!, because we | l s ± i ± i in a Penning trap have used circular polarized light. Npi is the population lost due to photoionized H. ⌘L is then defined as the population transfer eciency from H to H(30d) by B. Pn limitations from crossed fields in Penning ⌘ = N /N at t = 100 ns. This parameter is _ L 30d H traps • photo-ionize H maximized scanning over the laser intensities and pulse delays, see Fig. 3 b). Figure 3 c) shows the result, where 4 the timeThe depending precedent populations discussion of the deals states (especially are plotted the Pn cross in Fig.section 3 d). Hereformation we find and that Pn radiative16% of lifetime the H andare annihi- FIG. 3. (color online) a) Level scheme of the relevant statesexcitedlation) to H(30d) with mainly Pn in limitednlm ⇠state. by the Unfortunately Lyman-alphaFigure 3 a) the sketches Pn the relevant levels of H and H | i • laser-excite H → H*(30) of H and H at 5 T. The continuum of H is marked in graylaser poweris formed and width. in a complex electric andin magnetic the Paschen-Back field envi- regime at B=5 T showing the with the possible ionizations from the excited states. The ronment. Indeed, formed Pn will beuncoupled exposed to basisthe trap-n, l, s, m ,m for each state, where ml, ms states and E are labeled and the binding energy ping magnetic field but also to several electric fields: time| l si (BE) of H. The three lasers are shown with the 121 nm the level splitting is E = µBB(ml +2ms). Thus + constant electric fields (due to the trapping potential in and 366 nm laser driving and transitions, respectively.B. Pn limitations from crossed fields in Penning • charge-exchange reaction: axial E and radial E direction)for butml also= timel, vary- .., 0,..,l and ms = 1/2 the splitting _ _ The solid lines represent the addressed states. b) Excita- ax trapsrad ± _ ing electric fields (from stochastic Coulombcaused by collision a change with of ml = 1 or ms = 1/2is H*(30) + p → pp(n) + e tion eciency ⌘L versus 366 nm laser parameters for a beam ± ± waist of wL =1mmandGaussianintensitypulseshapes p, p,¯ e,H,H⇤ as Ecol) and a motionalE field=11.2Em GHz.= v B For. the 121 nm we will use specifica- 2 2 The precedent discussion deals (especially the Pn cross ⇥ Ii = Ii,max exp( 4ln2(t Ti) /⌧i )fori =1064, 121, 366 It is beyond the scope of this articletions to study that in have detail been the achieved in [47] of a laser energy of section formation and Pn radiative lifetime and annihi- FIG.with 3. (color peak online) intensity a)I Leveli,max, scheme FWHM of the intensity relevant pulse states durationlation)e↵ withect of Pn the in externalnlm state. fields Unfortunately and we190 will nJ simply the at Pn a give pulse sim- duration of 16 ns, which results in a ⌧i and pulse delay Ti with respect to the 121 nm; I1064,max = ple argument| in orderi to estimate the modification of its of H and H at 5 T.± The continuum0 of H is marked in gray is formed in a complex electric and magnetic field envi- • (detect fluorescence & annihilation2.5MW/cm (2π, I , π=755W/cm)) 2, ⌧ = ⌧ =10ns, linewidth of ⌫L 27 MHz. For the other two lasers with the possible ionizations121,max from the excited1064 states.366 The ronment.internal Indeed, states formed and Pn especially will be exposed concerning to the its trap- annihilation.⇡ ml, m⌧121s states=16nsand and ETare1064 labeled= 20 and ns. the c) Lasers binding intensities energy ver- The Hamiltonian for Pn in E and Bwefields will is fix expressed the pulse as duration to typical 10 ns giving 2 ping magnetic field but also to several electric fields: time sus time for I366,max =0.12 MW/cm and T366 = 5ns.d) (BE) of H. The three lasers are shown with the 121 nm H = H0 + HZeeman + HDiamagneticlinewidths+ HStark and of is44 dis- MHz. The H transitions get Doppler + constant electric fields (due to the trapping potential in and 366Populations nm laser drivingof the bound and electronic transitions, levels respectively. and of dissociated cussed in the appendix V (the formulasbroadened are also at valid⇡ the for plasma temperature, which gives at TheH solid from lines eq. represent 3 versus time the addressed with an insert states. showing b) Excita- the H(30d)axial Eax and radial Erad direction) but also time varying electricH and fields Ps (frombecause stochastic of the reduced Coulomb mass).T collision=100 Neglecting with K a transition sec- FWHM of ⌫ = 17.9 GHz tionstate eciency resulting⌘L versus in ⌘L 366=0 nm.163 laser at 100 parameters ns. for a beam p D,121 p, p,¯ eond,H, orderH⇤ as magneticE ) and a interactions motional field (HEDiamagnetic= v B.= 0), Pn waist of wL =1mmandGaussianintensitypulseshapes col andm ⌫D,⇥ 366 =5.9 GHz. Because this broadening is 2 2 It is beyondhas no the first scope order of this Zeeman article e↵ toect study (HZeeman in detail= the 0) and the Ii = Ii,max exp( 4ln2(t Ti) /⌧i )fori =1064, 121, 366 larger than the hyperfine splittings between m = 1/2 e↵ect ofHamiltonian the external eigenstates fields and we are will thus simply the Stark give sim- eigenstates i withatomic peak intensity populationsIi,max, given FWHM by: intensity pulse duration states of E =1.3 GHz for the H(1s) and of 55± MHz ⌧i and pulse delay Ti with respect to the 121 nm; I1064,max = ple argument(assuming in order a quantization to estimate the axis modification along the electric of its HF field): 2 2 2.5MW/cm, I121,max =755W/cm, ⌧1064 = ⌧366 =10ns, lm for the H(2p),jm all m hyperfine substates are addressed. N˙ = N , internalnkm states= and especiallynlm C n concerning1 m+k n 1 m itsk annihilation.where C is i H pd H l , j1m1,j2m2 ⌧121 =16nsand T1064 = 20 ns. c) Lasers intensities ver- The Hamiltonian| i for| Pn ini E2and2B fields2 2 is expressed as ˙ 2 sus timeN1s for=IA3662p,maxN2p=0+.12pd MW/cmNH and1s2pT(366N1=s 5ns.d)N2p), the standard Clebsch-Gordan coecient producing, up H = H0 + HZeemanP + HDiamagnetic + HStark and is dis- Populations of the bound electronic levels and of dissociated to the first order a level shift of E(1) = 3 nkm E(see¯ N˙ = A N + (N N ) cussed in the appendix V (the formulas are alsoSt valid2 for H from2 eq.p 3 versus2p time2p with1s2 anp insert1s showing2p the H(30d) H andeq. Ps because 7) [51]. of This the reduced formula mass). can be Neglecting use to estimate sec- the state resulting in2⌘pL30=0d (N.1632p atN 10030d ns.) pi,2p N2p, Additionally the influence of crossed E and B fields on ond orderannihilation magnetic lifetime interactions of the (HDiamagnetic Stark states= because0), Pn of the ˙ H have to be18 considered,3 1 which Hamiltonian is discussed N30d = A30d N30d + 2p30d (N2p N30d) pi,30d N30hasd, nos firstor orderp annihilation Zeeman e↵ rateect (H⌫aZeeman(ns)=5= 0).3 and10 the n s , 14 3 1 ⇥ ˙ Hamiltonian⌫a(np)=4 eigenstates.3 10 aren thuss the[4]. Stark Ratesin the eigenstates from appendix higher values V. For this case of E B, the energy atomicNpi populations= pi,2p N given2p + by:pi,30d N30d. (3) ⇥ 10 3 1 ? (assumingof lPn a quantizationones such as theaxis⌫ alonga(nd) the10spectra electricn s field): ofare H have negligi- been experimentally studied in [48] and 8 1FIG. 2. a) Formation5 cross1 section to producelm Pn fromp ¯ with3 ⇡ (Pnjm) 2l N˙ Here= A2p N=6.3, 10 s and A30d =2.6 10 s are thenkm ble= (ratenlm variesC n about1 m+k n as1 nmk (whereR /a C ) [52].)is In a very H pd H l , theoretically0 j1m1,j2m2 in [49, 50]. In first order perturbation of the Einstein A coe⇥cients fromH(n=1) the usingH(2p)⇥ the and Langevin the H(30d)| crossi rough section| estimation andi 2 with we2 can H(n=2)2 assume2 ⇤ that the Clebsch-Gordan (1) 1 3 N˙ = A N + N (N N ), the standard Clebsch-Gordan coecientfields producing, the levelup shift is then E = ml( B¯ + nE¯)(see 1s 2p 2p pd H and1s2p H(n=30)1s 2 usingp eq. 1 versus theP collision energy. The 2 2 state, respectively, andpd is the photodetachment rateto thecoe firstcient order is a on level the shift order of of 1E/n(1)and=eq.3 thatnkm 7). theE(see¯ For Stark H(2p) eigen- in m = 1 the radial trapping field of N˙ 2p = A2p N2p + 1s2p (N1reds N dots2p) show the findings for H(n=2) from [30] and the or- St 2 l of H. Because the decay of H(30d) populates a lot of states contains more or less all l m quantum numbers eq. 7) [51]. This formula4 can be use totypically estimate upthe to 104 V/m (see sec. II B) thus causes a level levels with2p30d ( aN2 negligiblep N30d)ange probabilitypi, curve2p N2p, the of reachingfit using H(2p) theannihilation valuesandc1=6 thus lifetime. that3 10 the of the annihilationa.u. Stark and states rate because for a Stark of the eigenstate ⇥ 1 ˙ within the considered time,c2=6 we neglected.9 a.u. this The part. plot includes1s2p with them ionization= 0 is roughly thresholds given by shift⌫18a( ofns3)n0.51 MHz,and for which is smaller than the contribution N30d = A30d N30d + 2p30d (N2p N30d) pi,30d N30d, s or p annihilation rate ⌫a(ns)=5.3 ⇠10 n⇠s , is the 121 nm laser excitation(right axis) rate and for the probability four tran- distributiona m = function114 state3 by (PDF)1 ⌫ (np for)n 1⇥fromwhereas the for magneticm = 2 field and can be neglected compared ˙ ⌫a(np)=4.3 10 n s [4]. Ratesa from higher values Npi = pi,2p N2p + pi,30d N30d. (3) ⇥ ⇠ 10 3 1 ± sitions H(1s) ml =0,msa= Maxwellian1/2,mi = at1 100/2 KH(2p) (leftof axis).l onesthe b) radiative such Radiative as the transition⌫ lifetime(nd) rate10 of inton stop-statesare the negligi- Doppler is larger than line broadening for plasma temperatures | ± ± i! Pn a ⇡ ml = 1,ms =8 1/2,m100i = 1/n2Pn 5 and12001 for di2p↵30erentd thelPnd-statestates annihilation including3 black rate(Pn (see) 2l Fig. 2 e). The first net Here A2p =6.3 10 s and A30d =2.6 10 s are the ble (rate varies about as n (R /a0 ) [52].)>1K. In a very | ⇥ ± ± i⇥  ⇤ Einstein A coecients frombody the H(2p) radiation and the at H(30d) 10 K. c) nroughPn distribution estimation we resulting can assume from thatp ¯ the Clebsch-Gordan state, respectively, and iscapture the photodetachment by either H(n=20) rate withcoecientnPn is on=735,H(n=30)with the order of 1/n and that the Stark eigen- pd h i of H. Because the decay ofn H(30d)Pn =1288orH(n=40)with populates a lot of statesn containsPn = 1825 more integrated or less all l overm quantum numbers h i h i levels with a negligible probabilitycollision of energies reaching for H(2p) 100 K usingand thus fit parameters that the annihilation in [23]. d) ratelPn for a Stark eigenstate From1 this we see that after the 1064 nm addresses the within the considered time, wedistribution neglected this corresponding part. 1s2p towith Pnm formation= 0 is roughly from H(n=30). given by e) ⌫a(ns)n and for 1 ⇠ three H states separated by 22.4 GHz with approxi- is the 121 nm laser excitation rate for the four tran- a m = 1 state by ⌫a(np)n whereas for m = 2 For initial Pn(n=300) and di↵erent lPn,withall⇠ mPn statis- ± sitions H(1s) m =0,m = 1/2,m = 1/2 H(2p) the radiative transition rate into p-statesmately is larger the than same cross section, all four mi H(1s) hyper- | l s ±ticallyi populated,± i! the time before annihilation occurs is cal- ml = 1,ms = 1/2,mi = 1/2 and 2p30d the d-state annihilation rate (see Fig. 2 e).fine The states first net get populated. Then, due to Doppler broad- | ± ±culatedi in a field free environment. Similar, f) shows the ening at 100 K the 121 nm laser addresses all H(1s) sub- annihilation time for initial Pn(n=1000) and di↵erent lPn for a perturbation electric field of Ep =1 V/cm using ⌫St,x from states. To find the overall transfer eciency, we can cal- eq. 4. culate the cross sections and the excitation and photoionization rates using standard expressions for the radial wavefunctions of H and their overlaps for bound-bound and bound-continuum transitions (see appendix V). The A. H excitation to Rydberg H excitation rates include the Doppler broadening at the plasma temperature. Both the 121 nm and 366 nm laser To create Rydberg H from ground state H and to can cause photoionization from the excited states. The calculate a value for ⌘L, several laser excitation paths photoionization rates for the 121 nm laser from H(2p), are possible [44], where we concentrate on a scheme us- pi,2p, is calculated from the sum of the rates coupling ing single photon excitations and a Lyman-alpha laser. to the l = 0 and l = 2 continuum states. Similarly, the First a pulse laser at 1064 nm photodetaches H from photoionization rate from H(30d) caused by the 121 nm the ground state to the H(1s) state, overcoming the bind- and the 366 nm laser as pi,30d constitute of the sums ing energy of BE=0.7542 eV [45]. The photodetachment of the individual photoionization rates that couple to the 17 2 cross sections is given by =4 10 m [46]. Sub- continuum states with l = 1 and l = 3. The e↵ect of 1064 ⇥ sequently, a laser at 121 nm excites the atoms to the the laser interaction with the H and H atom can then H(2p) state, from where, a third laser at 366 nm ad- be semiclassically described as solutions to a set of Ein- dresses the H(2p) H(30d) transition. stein rate equations for the time dynamics of the involved ! further physics opportunities _ Probing the diffuse neutron halo at the nuclear surface with p

nuclear physics: the PS209 experiment The PS209 experiment at LEAR investigated a range of 34 different nuclei, from 40Ca to 238U via both techniques Neutron density distributions can be sampled in (heavy) nuclei by correlating measurements of their: Antiprotonic atoms – strong interaction effects • antiprotonic x-ray cascade (annihilation radius, energy shifts)

strongstrong interaction effects for lowest-lying bound states _ ↓ pPb+ widens and shifting shifts p levels of energy levels, change in lifetime of the state, change in transition probabilities (intensities) in the experiment we measure:

Γlow - directly from the line shape ε - determining w.r.t. athe pure line energy QED reference value

Γup - indirectly from the intensity balance annihilation radius, energy shifts

• with a radiochemical determination of the same nuclei (annihilation on n / p) (in AEgIS : perhaps through TOF mass spectroscopy ?)

after they have been exposed to antiproton capture and annihilation (and are consequently one mass unit lighter). A. Trzcinska et al., Phys. Rev. Lett. 87 (2001) 082501 A. Trzcinska et al., Hyperﬁne Interact (2009) 194:271–276

ANTIPROTONIC ATOMS 44 1

T" et . e 3 Cont r i but i ons to the tota l er ror for the 4 - . 3 t rans i t i on wi dth i n x ' 60 ( i n eV)

4 ~ 3 p-D2 ' 60 ! ' d l ' d! '~° dI ' ~, d! ' , df

detector 1 300 83 150 30 100 200

detector 2 348 66 l 50 l 40 100 238 438 H . POTH et a l .

OMUIn I tYwl on Auger e l ect ron, respect i ve l y . The ca l cu l at i on of I ' x and T" °" i s st ra i ght forward, but at tent i on has to be pa i d to the fact that the movement of the p-N system around T i ts cnuclearommon physics:c.m. g i ve isotopics a non-n eeffectsg l i g i b l e Zt ) . c cont r i but i on Th i s c .m . cor rect i on T F enhances the rad i at i on and Auger wi dths by the factor 0

C M+ntpZ~12 F - p b è ' . ' C M+m~ ' _ where M i s the nuc l ear mass and mp the ant i proton mass . In the nuc l e i d i scussed p18O here , Z~n can be put equa l to Z to a good approx i mat i on Z1 ) . In tab l e 4, co l umn 3, a l so the l ' P va l ues for P, Cl , K, Sn, I , and Pr are l i sted . They are ca l cu l ated f rom _ p-b p16 T~ 4 O

Compar i son between measured and ca l cu l ated ( i n bractets) st rong i nteract i on e f ï eds " 1 " f~ "2 i 0 Y " " K 7 j "0 " " " K} 14 1n 1K 1" " ~ rw F i g . 1 . The ~' °U~' sU 7{ - ray apxt rum . Last observab l e 5-4 4-3 Nuc l eus l ' ,P (eV) In the case of oxygen cascade , st rong chemi ca l et%cts were observed . The resu l ts t rans i t i on of the re l at i ve i ntens i t i es of the l i nes , norma l i zed to the i ntens i ty of the 5 ~ 4 t rans i - Z 16 t i on, are g i ven i n tab l e 2 for C160s and HZ 0 (co l umns 2 and 3) . The i ntens i t i es of , for examp l e , do = 3 t rans i t i ons d i f fer by as much as a factor of two . In the 16 1 2 3 4 case of ZH 2 0 the i nner l eve l s of the energy l eve l scheme (1 < n-1) apparent l y are much more st rong l y popu l ated than i n CO z . One st ra i ght forward exp l anat i on wou l d be a t ransfer of the ant i proton between the deuteron and the oxygen atom, wh i ch N 4 ~ 3 0.1310 .03 205170 popu l ate3s 1pr5e f0erent i a l l y the i nner l eve l s . In sp i te of the l arge d i f%rences i n the (0 .10) (144) (ca-scad3es1, )the Yl P va l ue for 16 0 i s the same for the measurements i n CO Z and ZHZO . ' 60 4 - . 3 0.6410 .11 Th i s behav i our i s , of course , expected and g i ves add i t i ona l conf i dence i n the method 320 f 150 of-d1er2i v4i ng1t3h i 6s rat i o f rom the measured data . In co l umn 4 of tab l e 2, the re l at i ve 1 " (0 .62) ' (480) ' ) (i n-te1ns1i t i1es)o~f the ZHz O X- ray cascade are g i ven . Wi th i n the exper i menta l er rors ' °O 4 -+ 3 0.8010 .12 5501240 th-es1e 8nu9mb1er4s2co i nc i de wi th the re l at i ve i ntens i t i es of 16 0, g i ven i n co l umn 3 ; th i s shows that the de-exc i tat i on process i n sH 16 0 and ZH 1 "O i s i dent i ca l . (1 .05) ' ) (659) ' ) ( -167) ' ) Z Z P S ~ 4 1 .1410 .25 (1 .42) S 5 ~ 4 3.0410 .70 6501100 -60 140 (2 .20) (673) ( - 79) CI 5 ~ 4 8.0 12 .2 (6 .77) K 5 ~ 4 26 .8 17 .0 (24.3) Sn 8 -y 7 3.1 11 .8 H. Poth et al., Nucl. Phys. A 294 (1978) 435 (41 .53) I 8 ~ 7 9.9 17 .7 (22 .6) Pr 8 ~ 7 24 .7 156.9

' ) Ft ted on l y to the . data of ` 60/ ' °O .

444 H . POTH et a l .

br , , = 240 f 100 eV,

b l / ' s l = _p .34 f 0.20 . (1) .

I f ruP ~ rx+r~°~, as i s the case here , the b l l l s l can be re l ated to the re l at i ve d i f ference i n the upper wi dth by 81/ l s l = -br P/16r p . The data show thanucleart the i sphysicsotope e f fects seen for the f i rst t i me i n st rong i nteract i on i n ant i proton i c atoms are stat i st i ca l l y s i gn i f i cant and remarkab l y l arge . _ analyze p-N interaction in terms of optical potential 4. Campar i aoa between data and ca l ca l at i o~ Aposs i b l e ansat z for the st rong p-N i nteract i on i s an opt i ca l potent i a l of the form

ρ18 ρ16 n / n where P i s the roduced p-nuc l eus mass , ~! i s the nuc l eon mass , mP i s the ant i proton mass , pP ( r ) and po( r ) are the d i st r i but i ons of protons and neut rons i n the nuc l eus , and A~ and A~ are comp l ex numbers wh i ch descr i be the e f fect i ve i nteract i on between the l ow-energderivey ant shiftsi prot o/ nwidths, and ofth thee p atomicrotons levelsand neut rons of the nuc l eus. ρ18 ρ16 Si mi l ar ansät ze were t(onlyr i ed visiblefor p i cinn ilastc a nobservabled kaon i c transitionatoms an ofd wtheer ecascade)ab l e to reproduce p / p the gross features of the data sat i sfactor i l y . In both cases a re l at i on between A°~ and` ρ18 the f ree scat ter i ng amp l i tude A cou l d be found z2-Z' ) . n ρ16 To der i ve sh i f ts and wi dths of the l eve l s f rom the opt i ca l potent i a l , the express i on n for Ys , i s i nt roducedcomparei nto th withe D i rmeasurementac equat i on a nρdn(r),i n ρtepg(r)ra distributionsted numer i ca l l y . QED and other cor rect i ons were computed i n per turbat i on theory . The numer i ca l i ntegrat i on of the equat i on y i e l ds the comp l ex energy va l ue E- i 2 r . of the l eve l s as a funct i on of the parameters A~ , APôt , and the d i st r i but i ons pp, po . As for kaon i c r [fm] i t turns out that on l y the ta i l s of the nuc l ear d i st r i but i ons g i ve i mpor tant i a0 atoms , _ F i g . 3. Nuc l eon d i st r i but i ons for ' 60 and and the i r rat i on . cont r i but i ons . p-atoms test essentially the large-r region of nuclear density The i dea beh i nd the ana l ys i s of the data presented here i s to ga i n i nformat i oH.n Poth et al., Nucl. Phys. A 294 (1978) 435 . The ana l ys i s i s sp l i t i nto two par ts on the ¢N i nteract i ons tak i ng p l ace i n nuc l e i 3 (a) The ansat z , as i nt roduced above , i s shown to be use fu l for the nuc l e i under i nvest i gat i on. Hy ad j ust i ng the parameters of the ansat z so that the data are reproduced, a l east -squares f i t va l ue for the sum (A~+A~) i s deduced f rom 160/1s0 nuc l e i wi th po( r ) x pv( r ) . (b) The st rong i nteract i on e f fects i n are s i g_ n i f i cant l y d i f ferent . Th i s d i f%rence i s a l most comp l ete l y due to thEe two add i t i ona l neut rons of 1 s0. Thus the 160/ t s0 data are used to get an i ndependent va l ue for Apt and, together , wi th the resu l t f rom (a) , a l so for Ate . For both par ts of the ana l ys i s a re l i ab l e i nput for the proton and neut ron rad i a l dens i ty d i st r i but i ons 1s0 i s needed . For 160, and S these d i st r i but i ons were determi ned as descr i bed be l ow. ~0 t 2 3 i R~ A;~ F i g . 4. A contour p l ot of Re Aâ , Im . !â ; the mi n i mum i s at x~ = . 0.75, the c i rc l es cor respond to X~ z X'+ I , X = +2, and X +3 . heavierAEgIS : antiprotonicheavier antiprotonic atoms atoms

• established method: capture in gas/solid; Stark mixing upon collisions, practically immediate annihilation, from high-n s-states

• proposed method: trapped anion together with antiprotons, photo-detachment of electron, excitation into a Rydberg state, lifetime O(ms), possibly even trappable (large dipole) ...

→ spectroscopy of Rydberg antiprotonic atoms → clean cascade (vacuum → no Stark mixing) _ → controlled annihilation (à la ASACUSA pHe) AEgIS : measts with pulsed-formed antiprotonic atoms passing these neutral beams of antiprotonic atoms through gratings (optical gratings required for Rydberg atoms) may allow testing the WEP for a range of matter - antimatter systems (purely antimatter, purely leptonic, purely baryonic, ...)

Schematic overview _ _ Ps* •+ these p → beams H*(30) are long-lived+e+ • annihilations can be induced spectroscopically positronium converter • sensitive probes position-sensitifor inertialve e+ sensing detector Ps Ps Ps* beam _ grating 1 grating 2 laser pCs* beam excitation _ pd* beam Ps* _ Ps* pp* beam H* H* H beam

antiproton accelerating trap electric field H* atomic L L beam

antiproton accelerating trap electric field H* or intense atomic L L thermal source beam

Physics goals: measurement_ of the gravitational interaction between matter and antimatter, H spectroscopy, ... AEgIS : measts with pulsed-formed antiprotonic atoms passing these neutral beams of antiprotonic atoms through gratings (optical gratings required for Rydberg atoms) may allow testing the WEP for a range of matter - antimatter systems (purely antimatter, purely leptonic, purely baryonic, ...) + Cs* + e → _Ps* Schematic overvie•w these_ beams are long-lived+ Ps Ps* + p → H*(30) +e Ps • annihilations can be induced + e spectroscopically Cs positronium converter Ps • sensitive probes position-sensitifor inertialve e+ sensing detector Ps Ps Ps* beam _ grating 1 grating 2 laser pCs* beam excitation _ pd* beam Ps* Ps* _ Ps* Ps* pp* beam H* H* H beam

antiproton accelerating trap electric field H* or intense atomic L L thermal source beam

Schematic overvie•w these beams are long-lived Ps Ps • annihilations can be induced + _ _ e Cs* +spectroscopically p → pCs*(30) +e+ Cs positronium converter Ps • sensitive probes position-sensitifor inertialve e+ sensing detector Ps Ps Ps* beam _ grating 1 grating 2 laser pCs* beam _ excitation _ pCs* pd* beam Ps* Ps_* _ Ps* Ps*_ pCs* pp* beam p _ H* H beam H* Cs _ _ pCs* * antiproton accelerating pCs trap electric field H* or intense atomic L L thermal source beam

Schematic overvie•w these beams are long-lived Ps Ps • annihilations can be induced + e spectroscopically Cs positronium converter _ _ Ps • sensitive probes position-sensitifor inertialve+ H* + p → pp*(2000)detector +e e+ sensing Ps Ps Ps* beam _ grating 1 grating 2 laser pCs* beam __ excitation _ ppCsp** pd* beam Ps* Ps_*_ _ Ps* Ps*_ ppCsp** pp* beam p H* __ H* H beam CsH __ __ pppCs** pp** antiproton accelerating pCs trap electric field H* or intense atomic L L thermal source beam

Schematic overvie•w these beams are long-lived Ps Ps • annihilations can be induced + e spectroscopically Cs positronium converter Ps • sensitive probes position-sensitifor inertialve e+ sensing detector Ps Ps Ps* beam _ grating 1 grating 2 laser pCs* beam __ excitation _ ppCsp** pd* beam Ps* Ps_*_ _ Ps* Ps*_ ppCsp** pp* beam p H* __ H* H beam CsH __ __ pppCs** pp** antiproton accelerating pCs trap electric field H* or intense atomic L L thermal source beam

Physics goals: measurement_ of the gravitational interaction between matter and antimatter, H spectroscopy, ... 500 500 Minimally ionizing Heavily ionizing 400 Data 400 Data Antiprotonic atoms – anninihaltion Entries MC (CHIPS) Entries MC (CHIPS) 300 MC (FTFP) 300 MC (FTFP) MC (FLUKA) MC (FLUKA) 200 200 target 100 100 [10 µm] 0 0 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 p ends its life in the atomAEgIS annihilating :nuclear with fragmentation a peripheral processes nucleon (p or n) Multiplicity Multiplicity

_ Copper. 2017 JINST 12 P04021 p-induced nuclear fragmentation 700 700 600 600

Entries 500 Entries 500 400 400 π n 300 300 200 200 100 100 0 0 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 _ Multiplicity Multiplicity p π tracking,Silver. dE/dx, no PID 500 200500 200 Minimally ionizing Heavily ionizing 3.5 Minimum ionizing FTFP 400 Data 400 3Data Cu CHIPSAu Entries Entries p Entries 150 Entries 150 MC (CHIPS) 2.5MC (CHIPS) FLUKA 300 MC (FTFP) 300 MC (FTFP) Data π MC (FLUKA) 100 2MC (FLUKA) 100 200 200 1.5 100 50100 1 50 Average multiplicity 0.5 0 0 0 0 0 0 1 2 3 4 5 6 7 8 0 01 12 23 34 45 560 671078 208 30 040 1 502 603 470 5 806 907 8100 Multiplicity MultiplicityMultiplicity AtomicMultiplicity number 2017 JINST 12 P04021

3.5 2017 JINST 12 P04021 Copper. HeavilyGold. ionizing FTFP 3 CHIPS very little experimental700 information 700 FLUKA Figure 8. Reconstructed multiplicity distributions2.5 for annihilations in copper, silverData and gold foils for MIPs 600 600 2

available given the veryEntries 500 low energy(left) and HIPs (right).Entries 500 The colored histograms1.5 show the Monte Carlo predictions by CHIPS, FTFP and 400 FLUKA. The error bars400 of the histograms account1 for uncertainties in the dE dx classification. (10‘s of MeV) and short range of the Average multiplicity / 300 300 0.5 200 200 0 fragments (only some data on p, d, t, 0 10 20 30 40 50 60 70 80 90 100 3 4 100 100 Atomic number 0 0 He, He) W. Markiel et al. Nucl. Phys.0 A485(1988)1 2 3 445-4604 5 6 7 8 0 1 2 3 4 5 6 7 S.8 Aghion et al., 2017 JINST 12 P04021 Multiplicity Figure 9. Particle multiplicityMultiplicity from antiproton annihilations as a function of atomic number for MIPs (top) Averageand HIPs multiplicity (bottom). for MIPs Average multiplicity for HIPs DataSilver. CHIPS FTFP FLUKA Data CHIPS FTFP FLUKA 200 200 +0.07 +0.09 +0.08 +0.09 +0.14 +0.11 Copper 1.07 0.07 tracks0.98 using0.09 emulsion1.59 0. detectors14 0.83 with0.11 a vertex1.54 position0.07 resolution1.46 0.07 at the0.60 level0. of10 a few1.68 microme-0.08 ± ± Silver 1.02 0.06 ters,1.04 which+0.08 allowed1.64 the+0.09 separation0.73+ between0.07 1.71 minimally0.07 and1.33 highly+0. ionizing09 0.51 particles.+0.14 The1.87 fragment+0.09 Entries 150 ± Entries 150 0.09 0.13 0.09 ± 0.08 0.09 0.07 multiplicities+0.10 we measured+0.09 were not+0.07 well reproduced by the di+erent0.11 models+ used0.13 in Monte+0. Carlo11 Gold 0.92 0.09 1.21 0.11 1.75 0.13 0.81 0.11 1.60 0.09 1.04 0.09 0.39 0.09 1.60 0.06 100 ± 100simulation with the exception of FLUKA, which is± in good agreement with the particle multiplicities for both minimally and heavily ionizing particles. Future measurements with more materials are Table 1. Measured average multiplicity and Monte Carlo predictions by CHIPS, FTFP (GEANT4) and 50 50needed to gain a better understanding of antinucleon annihilations also on low-Z materials, and FLUKA. Statistical errors and uncertainties in the background estimation are combined and reported for each to obtain a full description in terms of particle types, multiplicities, as well as energy, for a more 0 set of data. The errors in0 the predictions account for uncertainties in dE dx classification. 0 1 2 3 4 5 6 7 8 complete0 1 benchmarking2 3 4 5 of6 Monte7 Carlo8 simulations. / Multiplicity Multiplicity Gold. Acknowledgments Figure 8. Reconstructed multiplicity distributions for annihilations in copper, silver and gold foils for MIPs This work was supported by the Swiss National Science Foundation Ambizione grant (left) and HIPs (right). The colored histograms show thePZ00P2_154833; Monte Carlo predictions Istituto Nazionale by CHIPS, di Fisica FTFP Nucleare; and a Deutsche Forschungsgemeinschaft re- FLUKA. The error bars of the histograms account for uncertainties in the dE dx classification. search grant; an excellence/ initiative–6– of Heidelberg University; European Research Council under the European Unions Seventh Framework Program FP7/2007-2013 (Grants No. 291242 and No. 277762); Austrian Ministry for Science, Research, and Economy; Research Council of Norway; Bergen Research Foundation; John Templeton Foundation; Ministry of Education and Science of the Russian Federation and Russian Academy of Sciences; and the European Social Fund within the Average multiplicity for MIPs framework ofAverage realizing multiplicity the project, infor support HIPs of intersectoral mobility and quality enhancement of research teams at Czech Technical University in Prague (Grant No. CZ.1.07/2.3.00/30.0034). The Data CHIPS FTFP FLUKA Data CHIPS FTFP FLUKA authors would like to acknowledge the contributions by the mechanical workshop at LHEP. +0.07 +0.09 +0.08 +0.09 +0.14 +0.11 Copper 1.07 0.07 0.98 0.09 1.59 0.14 0.83 0.11 1.54 0.07 1.46 0.07 0.60 0.10 1.68 0.08 ± ± Silver 1.02 0.06 1.04+0.08 1.64+0.09 0.73+0.07 1.71 0.07 1.33+0.09 0.51+0.14 1.87+0.09 ± 0.09 0.13 0.09 ± 0.08 0.09 0.07 +0.10 +0.09 +0.07 +0.11 +0.13 +0.11 Gold 0.92 0.09 1.21 0.11 1.75 0.13 0.81 0.11 1.60 0.09 1.04 0.09 0.39 0.09 1.60 0.06 ± ± –8– Table 1. Measured average multiplicity and Monte Carlo predictions by CHIPS, FTFP (GEANT4) and FLUKA. Statistical errors and uncertainties in the background estimation are combined and reported for each set of data. The errors in the predictions account for uncertainties in dE dx classification. /

–6– end of overview of physics opportunities

status and CHALLENGES CHALLENGES

Physics and techniques: _ • H formation rate • beam formation • inertial sensing (gratings) _ _ • pulsed formation of antiprotonic atoms (pCs, pp, ...) • stimulated de-excitation of Rydberg states • sympathetic cooling of antiprotons • theory (atomic physics, plasma physics)

Experimental implementations:

• experiment control system (LabView) =/ DCS • electronics (DAC, sequencers, ampliﬁers, FPGA’s) • detectors (ﬂuorescence detection) • manpower & automation • ... EXCEL editor

data base RT-Labview sequencer DAC + ampliﬁer electrodes ~ μs custom power supplies voltages SPI bus lasers, pulsers, ~ ns transfers e- gun triggers electron gun control

signal / detectors analysis actuators, MCP voltage LabView meta- phase I visual language editor/ “salvage” display “syntax” check spare modules data base RT-Labview sequencer DAC + ampliﬁer electrodes ~ μs voltages custom power supplies SPI bus lasers, ~ ns pulsers, triggers transfers - e gun electron gun control

signal / detectors analysis actuators, MCP voltage LabView meta- phase II visual language editor/ “compartementalize” display “syntax” check new data base modules RT-Labview sequencer DAC + ampliﬁer electrodes ~ μs voltages standard power supplies RS485 bus lasers, master pulsers, status ~ ns transfers - sequencer triggers e gun lasers electron gun control current source

signal / detectors analysis actuators, MCP voltage