PoS(ICRC2015)346 , 8 , 7 , 10 , 9 http://pos.sissa.it/ , C. Williams , K. Mulrey 3 , C. Hast 6 9 , B. Rotter 1 , T. Liu 2 , A. Vieregg , P. Gorham 13 7 , J. Lam 2 , A. Romero-Wolf , J. Clem , B. Strutt 5 6 7 . , K. Kuwatani 10 , P. Chen 2 , D. Seckel 9 , B.F. Rauch 13 , K. Jobe 12 , K. Borch 3 , R. Nichol 14 1 , H. Schoorlemmer 2 , K. Bechtol , R. Hyneman 2 , A. Zilles , 2 1 11 ∗ , C. Naudet 6 [email protected] Speaker. We report on the first observationsondary of cascade by radio a emission magnetic from field transversein in currents previous dense induced experiments media. in in Only a ice, the sec- because Askaryan silica the effect sand radio has detection and been of in observed ultra-high rock energyemission cosmic salt. from rays extensive (UHECRs) air These relies showers. measurements on In models are orderat of to important radio validate SLAC the National models we Accelerator performed an Laboratorytarget experiment placed in in 2014 a magnetic using field, a yielding results high within density 36% of polyethylene the (HDPE) model predictions. ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. SLAC National Accelerator Laboratory, Menlo Park, CA,Karlsruher 94025, Institut USA. für Technologie, Institut fürPhysics Kernphysik Dept., , College 76021 of Karlsruhe, William Germany. &Dept. Mary, Williamsburg of VA Physics 23187, and USA. Astronomy, UniversityKarlsruher College Institut London, für London, Technologie, United Institut Kingdom. für Experimentelle Kernphysik, 76128 Karlsruhe, Dept. of Physics and Astronomy, Univ. of California, Los Angeles, LosDept. Angeles, CA of 90095, Physics, University of Chicago,Dept. Chicago, of IL, Physics USA. and Astronomy, Univ.Dept. of of Kansas, Physics, Lawrence, Washington KS Univ., 66045, St.Dept. USA. Louis, of MO Physics, 63130, Grad. USA. Inst. of Astrophys.,& Leung Center for CosmologyDept. and of Particle Physics, Univ. of Delaware,Dept. Newark, of DE Physics, 19716, Stanford USA. University, Stanford,Dept. CA, of 94305, Physics USA. and Astronomy, Univ. of Hawaii, Manoa, HI 96822, USA. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA, c

T. Huege J. Nam K. Belov SLAC T-510: A beam-line experiment foremission radio from particle cascades in thea presence magnetic of field 11 12 13 14 Germany. The 34th International Cosmic Ray Conference, 30 July- 6 August, 2015 The Hague, The Netherlands D. Saltzberg 2 USA. 3 4 5 6 Astrophysics, National Taiwan University, Taipei, Taiwan. 7 8 9 10 1 E-mail: S. Wissel PoS(ICRC2015)346 ∼ 90 cm ]. The 4 ∼ K. Belov eV primary 18 , occurs 10 × max 4 X ∼ ]. In recent years, radio detection 3 eV [ 20 10 × ] treat each shower particle as an independent 6 , 2 5 ]. Such emission has been already measured in ac- 8 shows the schematics of the experiment and the target layout. 1 ]. The Lorentz force also acts on charges in the shower, generating 11 , 10 , 9 800 A current of reversible polarity. This allows us to create a mostly vertical ∼ 3 pC mean charge measured at the target, which corresponds to a ± 12” rectangular bricks of pure polyethylene with an index of refraction of 1.53. The target × in the forward direction to form a trapezoidal side cross-section. The purpose of the slope is to The experiment, SLAC T-510, was performed inside End Station A building at SLAC National Detectors utilizing air fluorescence and ground counting techniques have accumulated signifi- 4” ◦ × 8 . cosmic particle energy. The beambetween current the is beam measured pipe by exit an andwas integrated the charge obtained target transformer entrance. by placed The making systematic a uncertaintyand in series does the of beam not successive charge exceed measurements 3%. at different Fig. places along the beam into the target. The showers arewith induced 131 in the target by 4.35 GeV and 4.55 GeV electron bunches is 396 cm long by 60contains cm almost wide all by the 97 shower cm9 particles. tall The at upper the layer highest bricks point.avoid internal are Simulations reflection shaped show of to that the create the emerging target athe radiation at target slope the 12 of target cm boundary. above The thethat electron floor allows beam us through enters to a reduce 1.2 the overall cm length thick of lead the target. plate. The The shower lead maximum, provides pre-radiation A vertical magnetic fieldcarrying is up formed to by 15 water cooled coils aligned along the beam axis each Accelerator Laboratory in January–February, 2014. A2” 1500 kg HDPE target was constructed from a time-variable transverse current, the Hallsive current, air and shower subsequent induced radiation. bymagnetic In an field case UHECR and of particle, can an be this exten- calledto radiation geomagnetic validate will radiation. the be new The correlated formalisms SLAC with basedfrequency T-510 experiment emission the on from is Earth’s first secondary designed principles cascades by in conducting a measurements controlled of laboratory environment. the radio 2. Experimental setup radio detection technique relies ondeveloped models formalisms based of on radio first emission principles from [ extensive air showers. Newly celerator experiments [ cant statistics on UHECRs with energies as high as 3 SLAC T-510 experiment 1. Introduction emerged as a viableenergy method of that the can UHECRs provide andical round-the-clock the composition calorimetric shower and measurements development inelastic of profile, cross-sectiontechnique the which of is can the dictated be primary not used particles. onlypossibility to by to The obtain potentially resolve need chem- lower discrepancies for deployment in an and theand ground-based alternative operating data observatories costs, obtained reported successful using but detections traditional also of methods. by the UHECRs a Balloon–borne using radio [ radiator, summing up the emissionby from an all observer. This particles approach inpurpose does the of not cascade separate simplicity to different we components obtain discuss of thembuilt the up the separately. signal in emission, Askaryan received the but radiation shower for due forms the toa from pair time-varying a production, current charge positron along excess absorption the and shower Compton axis scattering, [ creating PoS(ICRC2015)346 K. Belov . In three separate 2 3 5 cm grid at the beam height across the whole target × UHF, VHF (bicone) antennas and HDPE target. T-510 experiment schematics with target details. Figure 2: Figure 1: measurements four linearly polarized 200–1200 MHz horn antennas sensitive to both polarizations magnetic field of up toa 970 more G uniform at magnetic the field, beamplate. the height coils We around measured are the the assembled shower magnetic in maximum. field two in In staggered a order layers 5 to on create a 4” thick steel area. The variation on the magneticat field does the not beam exceed 15% height. alongIn the We beam order estimate line to inside the suppress the B-field reflections, target pieces the uncertainty of target to ANW-79 floor absorber be are is 5.7% placed linedat at at with both the an every sides exit RF measured of surface the absorbing location. target of blanketANITA around experiment, and the the bicone several shower target. or maximum log-periodic and The dipole signal antennas is (LPDAs), see received Fig. by quad-ridged horns borrowed from the SLAC T-510 experiment PoS(ICRC2015)346 K. Belov ] altered to 12 ˇ Cerenkov ring. ˇ Cerenkov angle. In ]. The systematic uncertainty 2 2 m apart and two high frequency ∼ ] during the final stage. The simula- 5 . The change in impedance from free space to E 4 ˇ Cerenkov ring shows that the effect is reproduced e f f h = V shows the expected magnitude of the electric field, “radio 3 ]. 1 ]. The second stage of simulations is done after the experiment using the actual 6 20% charge imbalance, the whole shower is deflected to one side in the magnetic field, ∼ system is accounted for in the effective antenna height. The antenna cross-talk is removed Ω The simulations of the T-510 experiment are performed using GEANT4 code [ ˇ between the models does nottra exceed 3% in in the the 30–1400 peak-to-peak MHz amplitudesfootprint” range. or if in Fig. a the 970 frequency spec- Gcoherence of vertically the oriented emission magnetic from field the is individual applied. particles of The the pattern cascade is at formed the due to 3. Radio emission models beam parameters, measured magnetic fieldtion and A the building. actual experimental Refraction setradiation and up demagnification are inside effects the also at End taken the Sta- formalism, into target the account surface radio at as emission well the is as final also transition stage. modeled using In Ref. addition [ to the previously mentioned include emission from each charged-particle track.mal to The the incident electric electron field beam was 13are simulated m from performed on the in a target entrance. grid two nor- The stages. simulationsthe for The optimal the experimental preliminary experiment set stage up, was including done thestrength choice before and of the the the experiment target expected to material, signal. requiredprimary determine magnetic particles The field and nominal the parameters beam of chargefollowing were the Ref. used beam [ at such this as stage. the The energy radio emission of is the implemented tions are performed using a smallerthe number beam of charge. electrons The per simulations bunch and are the described results in are details scaled in up Ref. to [ the presence of a magnetic field the Askaryan effect manifests an asymmetry in the changing the relativistic timing andpeak-to-peak causing voltages the on different observed sides asymmetry. of A the detailed analysis of the SLAC T-510 experiment were mounted in a vertical lineantennas to sensitive probe to the shape 50–300 of MHz the were wave front, mounted two vertically linearly polarized bicone Due to a LPDA antennas mounted in the sameto fashion 3 as GHz. the The bicone antennas antennas areof cover hung the the from frequency a data range crane up taking soCerenkov they consists cone can about be of 13 moved moving m in away all the12 from directions antennas m the The beginning above majority vertically of the to the beam target,the axis. sample and exit at a of The heights the DAQ slice varying beam system from pipe of is 0 toto-shot triggered the register charge to transition calibration. by expected radiation an Waveforms from (TR). S-Band the The UHF horn TRsampled horns signal antenna at are also placed recorded 5 provides near on the GSa/s, 2.0 shot- GHz whilerecorded oscilloscopes, the at waveforms 10 from GSa/s the onUHF VHF horn 3 antennas, antennas GHz LPDAs, in oscilloscopes. and this S-banddeconvolving paper. the We horn The signal only are electric with report the field frequency-dependent the at effectivethe the measurements height cable face of done loss of the with according quad-ridge the horns to the antennasa and the is 50 equation reconstructed by for the horizontally polarized component bycurrent averaging the flowing waveforms through with the opposite magnetic polarityprocessing coils. in can the The be details found about in the [ experimental setup and the data PoS(ICRC2015)346 K. Belov ]. Askaryan 11 . It is also not , 4 ˇ Cerenkov cone is 10 , 9 ˇ Cerenkov ring is caused by refraction at the 5 , 131 pC charge, 4.35 GeV energy. illustrates that signal polarity flips with the reversal of the max X 5 . Fig. 4 , confirms the coherent emission model. While the response of the 6 and shows very good agreement between the models and the measured “magnetic” 6 The magnitude of the electric field in a grid 13 m from the entrance of the beam on target. In the absence of the magnetic field in the target, SLAC T-510 experiment was able to ob- ˇ Cerenkov cone where the measurements were done. The introduction of the vertical magnetic horn antennas goes down to 200region MHz, where we the only antenna use calibration the is frequencies more above uncertain. 300 MHz to exclude the emission is inherently radially polarized,the and it appeared as afield vertically polarized in signal the on target top resultscomponent of in the of induction the of electric Halltively currents field rotating in is the the polarization added cascade. vector. to As Ascomponent predicted the a by depends vertically result, the linearly a models, polarized on the horizontal Askaryan magnitude thesurprising of component, that magnetic the the effec- field horizontal Askaryan strength, and see “magnetic”shown signal in left scales the plot linearly right in with plot the Fig. in beam Fig. charge, which is signal in three separate frequencyis bands. seen The in narrowing of the the plots cone in at Fig. higher frequencies, which magnetic field direction. Ashown scan in Fig. in the vertical direction across the top of the Figure 3: Simulated at 970 G magnetic field around very well by our models. The elliptical form of the serve the Askaryan signal confirming observations by previous experiments [ 4. Results SLAC T-510 experiment upper flat tapered surface of themensions. target. The internal The reflections ring from is theinside cut target the walls off as End on well Station both as sides A thelations. due reflections building from to are The the the very structure reflections fixed difficult target inside touncertainty. di- the account for target and ended are up left being out the for largest these contributor simu- to the systematic PoS(ICRC2015)346 K. Belov ˇ Cerenkov cone for the ˇ Cerenkov cone may be ˇ Cerenkov cone shape is also measured and is in 6 ] and also confirmed that the emission scales linearly 11 , 10 , 9 The electric field peak amplitude (left) and intensity (right) at the top of the SLAC T-510 confirmed the Askaryan radiation for particle cascades in dense media that was with the beam charge.currents We induced observed in the the expected target by emissionthat cascade component this particle magnetic due deflection component in to scales an transverse linearly applieddicted with electric magnetic by field field the strength and in models, found agreement the withfield polarity models. of polarity, As the confirming pre- emission the signal time-varying reversesnent. with Hall The the magnetic current change current nature induction of manifests of theemission itself magnetic the from as the magnetic the shower. polarization emission The vector absolute compo- rotationels amplitude of to of the within the total 36% measured with electric the largestreflections field systematic agrees show uncertainty with up coming mod- from as reflections a infiltering delayed the the target. signal, reflections The altering out by the windowing pulsewe the shape signal decided would and to introduce frequency include a content. the biasfor in reflections future Because the work. in power The spectrum, the frequency systematic dependence error of the instead and leave the improvements very good agreement with the models. A slight asymmetry of the observed reported by previous experiments [ Figure 4: vertically polarized (black, squares solid)for and different horizontally magnetic polarized fields. channels (scaled by 3 left; by 9 right) 5. Discussion due to diffraction effects in thewithin the target that measurement range are as seen welleffects at are as different also due angles difficult to at to the the model reflections,of top and as radio and they they at emission are exhibit the from left a bottom out extensive delay of air rate. this showers, These discussion. the By SLAC validating T-510 experiment the models provides a framework SLAC T-510 experiment PoS(ICRC2015)346 K. Belov 7 Radio emission beam patterns for magnetic emission as measured in a vertical slice aligned with Impulse dependence on magnetic field and polarity. Simulated: magenta – 250 G, green – 500 G, The authors thank SLAC National Accelerator Center for providing facilities and support and Figure 6: the beam in three frequency ranges. for measuring the energy UHECRs using radio technique. Acknowledgments especially Janice Nelson and Carl Hudspethsible. for Work supported their in support part and by dedication Department that of made Energy contract T-510 pos- DE-AC02-76SF00515, the Taiwan Figure 5: yellow – 750 G, red – 970 G. Data: black. DC offset added to visually separate the impulses. SLAC T-510 experiment PoS(ICRC2015)346 AIP , , see K. Belov (Nov, 2011). Observations of 84 ´ Geant4 simulation c, D. Walz, and (2014), no. 5 520–529. 44 ˇ cinovi ˇ Phys. Rev. E Cerenkov emission from charge , ˇ Cerenkov radio pulses from (Mar, 2001) 2802–2805. ´ c, P. Mio ˇ ci Jun, 2010 86 Braz J Phys (Mar., 1995) 144–150. , 81 (2012), no. 6 325 – 341. 441 35 General description of electromagnetic radiation ApJ Monte carlo simulations of radio pulses in , (Jul, 2005) 023002. 8 72 (Oct, 2007) 171101. Phys. Rev. D Phys. Rev. Lett. , , 99 Simulating radio emission from air showers with coreas Astropart. Phys. , (Jan, 1992) 362–376. (2003), no. 3 250 – 303. (1962) 441. Electromagnetic pulses from high-energy showers: Implications for Phys. Rev. D 45 , 14 506 Phys. Rev. Lett. Detection of a cosmic ray with measured energy well beyond the expected , Phys. Rev. D , (2013), no. 1 128–132. Excess Negative Charge of an Electron-Photon Shower And Its Coherent Radio Modelling of radio emission in the SLAC T-510 Experiment using microscopic Geant4 Measurements, system response, and calibration of the SLAC T-510 Experiment Accelerator measurements of the askaryan effect in rock salt: A roadmap toward teraton Observation of the askaryan effect: Coherent microwave 1535 , see contribution 660 of this conference. Soviet Physics JETP The renaissance of radio detection of cosmic rays , Nucl. Instrum. Meth. A , C. G. Larsen, E. C. Loh,Tang, and M. S. Z. B. Luo, Thomas, M. H. Salamon, J. D. Smith, P. Sokolsky, P. Sommers, J. K. K. contribution 826 of this conference. simulations spectral cutoff due to cosmic microwave radiation processes based on instantaneous charge acceleration in “endpoints” electromagnetic showers in the time domain atmospheric showers using ZHAireS D. Williams, Emission asymmetry in high-energy particle cascades toolkit neutrino detection Conf. Proc. the askaryan effect in ice D. Williams, underground neutrino detectors [2] A. Zilles et al., [1] S.Wissel et al., [6] Alvarez-Muñiz, Jaime and Romero-Wolf, Andrés and Zas, Enrique, [3] D. J. Bird, S. C. Corbato, H. Y. Dai, J. W. Elbert, K. D. Green, M. A. Huang, D. B. Kieda, S. Ko, [4] T. Huege, [5] C. W. James, H. Falcke, T. Huege, and M. Ludwig, [7] J. Alvarez-Muñiz, W. R. Carvalho Jr., and E. Zas, [8] G. A. Askaryan, [9] D. Saltzberg, P. Gorham, D. Walz, C. Field, R. Iverson, A. Odian, G. Resch, P. Schoessow, and SLAC T-510 experiment Ministry of Science and Technologyers. under project Part number of MOST103-2119-M-002-002 the andTechnology, under research oth- a was contract carried with out the National at Aeronautics the and Jet Space Administration. Propulsion Laboratory,References California Institute of [12] S. Agostinelli, J. Allison, K. Amako, J. Apostolakis, H. Araujo, P. Arce,[13] et al., E. Zas, F. Halzen, and T. Stanev, [14] T. Huege, M. Ludwig, and C. W. James, [10] P. W. Gorham, S. W. Barwick, J. J. Beatty, D. Z. Besson, W. R. Binns, C. Chen, et al., [11] P. W. Gorham, D. Saltzberg, R. C. Field, E. Guillian, R. Milin