PoS(EMC2006)007
http://pos.sissa.it Metadata, citation and similar papers at core.ac.uk at papers similar and citation Metadata, oscillations clearly indicating that the the the most powerful tool to determine the ently ently running DBD experiments briefly different flavours is different from zero. will be reviewed with special emphasis to The results already obtained in this lepton discover if neutrino is indeed a Majorana f it is a massless Dirac particle different from from f different it Dirac a is particle massless peculiar and interdisciplinary nature of these mass, is discussed. The question is related to on-NonCommercial-ShareAlike Licence. Licence. on-NonCommercial-ShareAlike century century di Milano-Bicocca and Istituto Nazionale di Fisica di Nazionale Istituto and di Milano-Bicocca
1 [email protected] Speaker Neutrinoless Neutrinoless double beta decay (DBD) is at present violating process will be reported and the discussed. two The future second generation experiments pres searches will be stressed in their exciting particle aim to The problem of the nature of the neutrino, namely i of the namely neutrino, the of nature The problem its its antineutrino or a Majorana particle with finite the recent results showing the difference presence between the of squared mass neutrino of neutrinos of effective value of the mass of a Majorana neutrino. those already partially approved. In conclusion the 1 Copyright owned by the author(s) under terms the Commons owned author(s) by the Copyright Creative Attributi the of
Ettore Fiorini Neutrino: Dirac or Majorana? G.P.S.Occhialini,Universita’ Fisica di Dipartimento Nucleare, Sezione di Milano-Bicocca Milano-Bicocca di Sezione Nucleare, ,Italy Milano 20126 3, Scienza della Piazza E-mail:
the XXI of Physics the and legacy Majorana's Ettore Italy of Catania, University 2006 October, 5-6
CORE Provided by CERN Document Server Document CERN by Provided PoS(EMC2006)007 Ettore Fiorini Ettore Fiorini
(Fig.2) tically in 1937 when Ettore Majorana been proposed in general only one year eat eat physicists (Fig.1) is double beta decay ppert Mayer [1] o neutrino mass. The most powerful tool to tally different from its antineutrino and this etween etween the neutrino and its antiparticle, the servation of the lepton number. In the Dirac
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The mystery on the nature of neutrino started prac Neutrino: Dirac or Majorana? or Dirac Neutrino: discriminate between the hypothesis of these two gr Fig.2 M.Goeppert Mayer and Enrico Fermi Fermi Fig.2 M.Goeppert and Enrico Mayer Introduction Introduction suggested the possibility of a certain “equality” b antineutrino: this would obviously violate the con hypothesis on the contrary the neutrino would be to would make “unnatural” the possibility of a non-zer (DBD) in its neutrinoless mode. This rare decay has theafter Fermi theoryEnrico of Fermi by Maria Goe Fig.1 P.A.M. DiracEttoreFig.1Majorana P.A.M. and PoS(EMC2006)007 (1) (2) (3) ission of Ettore Fiorini Ettore Fiorini
ucleus (A,Z) to its isobar (A,Z+2) , the author was essentially interested in oron” after our great Ettore. Our interest trinos) are emitted . This process does not oint of view, in neutrinoless DBD the two ed. The result is that this process occurs ince the energy of the nuclear recoil is years for a nucleus, even if its isobar of tes tes the lepton number with the emission of 0 times thetimes 0 electron mass” ocess would strongly dominate on the two : 17 normally called “neutrinoless” DBD even if etically forbidden (Fig.3) or at least strongly represents therefore the strongest tool to test s. Two electrons are emitted in three possible 0 ndard Model and has been found in ten nuclei.
3
) χ e e - disintegration the probability of simultaneous em β ν +(1,2,3.. + + 2 - - -
(A,Z) (A,Z+1) (A,Z+2) From the Fermi theory of In the first channel two neutrinos (in fact antineu
In this first fundamental paper, published in 1935 “ DBD consists in the spontaneous transition from a n (A,Z) (A,Z+2)=> + 2 e (A,Z) (A,Z+2)=> + 2 e (A,Z) (A,Z+2)=> + 2 e Neutrino: Dirac or Majorana? or Dirac Neutrino: violate the lepton number, it is allowed by the Sta We will not consider the second channel which viola double of decay beta Fig.3 : The scheme one or more massless Goldstone particles named “Maj will be concentrated on the third process which is also in process (2) no neutrino is emitted. This pr neutrino channel if lepton number is violated ; it lepton number conservation. From the experimental p electrons would share the total transition energy s the nuclear physics aspect of the decay claimed and two electrons (and two neutrinos) has been calculat when the single beta transition to (A,Z+2) is energ sufficiently rarely to allow an half-life of over 1 atomic number different by 2more were stable by 2 hindered by a large change in the spin-parity state channels PoS(EMC2006)007 > > called the Ettore Fiorini Ettore Fiorini ν >. While the ν
related to properties of two neutrino and of the neutrinoless many peaks appear due to radioactive nt regions would definitely prove the tal point of view there is a even more ectrum ectrum of the sum of the two electron above mentioned term 4 > > and therefore the rate of neutrinoless DBD is cor ν The value of calorimetric one. It consists in the isotopic methods consisting in storing for aches (Fig.6). In the search search for DBD : the indirect and the rino or neutrinoless decay, decays to s s have to be used to optimize the of the nucleus (A,Z) to search for an produced by DBD. This method was very gnetic field could be present and help to U) U) and in searching later the presence of a electron energies. geochemical its discovery in various nuclei, but could not 238 ng the DBD candidate nucleus (e.g. radiochemical 5 Xe Xe in a Xenon TPC, scintillator or ionization 136 approach the sheets of the DBD source are interle Th). Th). > from neutrino a The upper results.to refers curve > from oscillations 238 ν detector ≠ source Experimental approach scheme of the of of differentscheme neutrinos flavours “inverse masses from called hierarchy” refershierarchy”while “normal lower the to The most common indirect approach is the 1. There are two different experimental approaches to Direct Direct experiments are based on two different appro Neutrino: Dirac or Majorana? or Dirac Neutrino: direct one. 1.1 experimentsIndirect resolution measurement the in of of the thetwo sum Fig.5 : The value Ettore Fiorini Ettore Fiorini of thermal sourcee detector detector y of diamagnetic - scheme of these - er er particles and for e e capacity is proportional to detector one detector ≠ particle particle Incident Incident 6 - Thermal sensor Thermal - e e absorber absorber crystal bath bath detector” or “calorimetric” and thedetector” or “source Neutrino: Dirac or Majorana? or Dirac Neutrino: or cryogenic detectors, also amply adopted in searches on Dark Matt direct measurement of the neutrino mass in detectors is shown in Fig. 7. An single absorber is made by a crystal , possibl beta decay. The and dielectric type, kept at low temperature where its heat a thermalFig.7 of Scheme detector 1.3 Thermal detectors A new approach [5] based on the direct detection of DBD is the use “source a = direct the beta experiment: to ways decay perform Fig.6 : double The two heat PoS(EMC2006)007 res. As a Ettore Fiorini Ettore Fiorini n any other thermal sensor. bers bers of masses up eased eased by a particle heat heat capacity could Ge Ge . This evidence is 76 the the FWHM resolution is already excellent. In erg-Moscow collaboration led by absorber of ~ 760 grams the grams 760 ~ absorber of 2 this process in orted in Table I with the corresponding as as indicated the existence of neutrinoless ies on nuclear matrix elements are taken into detector 2 7 line line α α αα Po Po 210 Present Present results and future experiments spectroscopy with a 760 grams TeO spectroscopy a 760 grams with α 2. Neutrino: Dirac or Majorana? or Dirac Neutrino: 2.1 resultsPresent The present results [6] on neutrinoless DBD are rep limits on neutrino mass, where the large uncertaint account. It can be seen that so far no experiment DBD, h with the exception H.Klapdor-Kleingrothaus of who claims the existence of a subset amply debated in the international arena. of the Heidelb Fig.8: the cube of the consequence in a ratio cryogenic set-up like between a dilution refrigerator the this become so low that the operating increase of temperature due to the energy and rel the in Debye the absorber can temperatu be detected and measured by means The resolution of of a these detectors, suitable even if still in their infancy, X-ray spectroscopy made with bolometers of a milligram or less can be as low as 3 detector. In eV, the region of neutrinoless more DBD the resolution than with absor an order diodes. Ge better that of to or thancomparable a kg is of magnitude better than i TeO ina shown Fig.8 , obtained with In the spectrum resolution isMeV at 3.2 keV! ~ . FWHM 5.4 PoS(EMC2006)007 ) ν ν νν .2-1. -2.9 1.1 ? -3 24 24 21 22 25 25 23 23 23 25 10 24 ) ) )) × y ( ( ( ( ( ν ν νν 0 7.7 Τ >2x10 >1.2x10 >1.2x10 >1.4x10 >1.9x10 >1.6x10 1.2x10 >1.x10 >4.6x10 >1.7x10 > Τ ΤΤ bolometric scintillator tracking Technique scintillator ionization Ionization ionization tracking tracking scintillator geochem 8 69 91 Enrich Enrich (%) 87 87 87 97 95-99 83 ββ ββ ββββ 2995 3034 3034 2529 2529 2476 3367 Q 4271 2039 2039 2039 9.2 9.6 7.5 34 33.8 8.9 5.6 % 0.19 7.8 7.8 7.8 NEMO 3 NEMO 3 NEMO Solotvina Bernatovitz Cuoricino DAMA Irvine Experiment IV Elegant Heidelberg-Moscow IGEX al Klapdor et neutrinoless DBD Table on Present results I: Nd Cd Te Te Mo Xe Ge Se Ca Ge Ge Neutrino: Dirac or Majorana? or Dirac Neutrino: 2.2 3NEMO and CUORICINO Nucleus 150 116 128 130 136 76 82 100 48 76 76 PoS(EMC2006)007 Laboratory Ettore Fiorini Ettore Fiorini Se (Fig.10 and Table I) 82 Mo and 100 ivity on neutrino mass comparable to the aly at a depth of ~ 3800 meters of water remely good results on two neutrino DBD NEMO 3 CUORICINOand presented as evidence by Klapdor et al. hannel of 9 ν ν νν 0 detector experiment (Fig.9) presently running in a ≠ It is a source Neutrino: Dirac or Majorana? or Dirac Neutrino: Fig.9 : Scheme and properties 3 Fig.9 NEMO : Scheme of Two experiments are presently running with a sensit evidence reported by H.Klapdor Klingrothaus et al : NEMO 3 , alreadyare approaching valuethe of neutrino mass 3 Fig. NEMO 10: Results of of various nuclei. The limits on the neutrinoless c situated in the Frejus tunnel between France and It equivalent (m.w.e). This experiment has yielded ext PoS(EMC2006)007 del del Ettore Fiorini Ettore Fiorini to search for neutrinoless 2 less less DBD experiment . It is agnitude larger than in any other under a overburden of rock of ~ 3500 r a peak in the region of neutrinoless DBD tals tals of natural TeO y the span of evidence coming from the claim 10 Is at present the most sensitive running neutrino Te. Te. Its mass of 40.7 kg is more than an order of m 130 Neutrino: Dirac or Majorana? or Dirac Neutrino: installation and CUORE NazionaleinLaboratorio the CUORICINO Fig. 11 : The Gran Sasso (Fig.13) setting a limit that covers almost entirel of H.KlapdorKleingrothaus et al. CUORICINO mounted in the Laboratori Nazionali del Gran Sasso m.w.e. (Fig.11). It consists in a column of 62 crys cryogenic set-up (Fig.12). No evidence is found fo DBD DBD of PoS(EMC2006)007 Te) x y x Te) Ettore Fiorini Ettore Fiorini 130 (Jul 0.02 c/keV/kg/y 0.02 ± DBD MT = 5.87 (kg (kg MT5.87 = b = 0.18 0.18 = b Energy ted in Table II with the techniques to be detail . Only two of them have been approved Klapdor 0.1 – 0.9 Klapdor 11 > .18 -.9 ν y 24 TeDBD Q-value Q-value 18±.01 c /kev/ kg/ a 18±.01 130 Te) > 2.4x 10 Te) up 130 ( A A list of proposed future experiments [6] is repor 0 peak 1/2 Copile- 60 adopted and the expected background and sensitivity = + 40.7 kg of cm3 44 crystalsTeO2 18 crystals cm3 5x5x5 3x3x6 Background . CUORICINO and of results 12: Mounting CUORICINO spectrum neutrinolessFig.13:Theinregion of the 2.3 Future experiments Neutrino: Dirac or Majorana? or Dirac Neutrino: T T , 142501 (2005) 142501 , anticoincidence spectrum 95 [1] PRL. PoS(EMC2006)007 16-22 29-54 50-94 65-? . They are logical Tracking Scintillation Scintillation Scintillation Ionization Scintillation Tech Bolometric Ionization Ionization Ionization Tracking Tracking Tracking 27 28 27 26 27 27 26 27 27 28 26 lassical” detection of neutrinoless periments, respectively. GERDA, being carried out by the Majorana 1x10 3x10 3x10 1x10 T (year) T 1.8x10 2x10 4x10 1x10 2x10 1.3x10 1.7x10 few others will be briefly described ng to be mounted in the Gran Sasso 0 35 . 20 Back c/y 3.5 3.85 .6 .4 1 .55 3.8 xperiment: its underground location has not yet 12 80 - - - % 34 90 90 90 90 65 85 ββ 1730 2805 3367 2995 2476 3034 3367 4271 4271 Q 2533 2039 2039 2039 22 7.5 5.6 8.7 8.9 9.6 5.6 .19 .19 % 34 7.8 7.8 7.8 d Gd Cd Xe Mo Nd Te N Se Ca Ca Ge Ge Ge 160 115 150 82 136 100 150 48 48 Nucleus 130 76 76 76 Ge Ge in a calorimetric approach with Germanium diodes 76 Table DBD experiments II: Future on neutrinoless GERDA and Majorana Both these experiments (Fig.14) are based on the “c SNOLAB+ Candles CARVEL GSO COBRA EXO EXO Moon-3 DCBA-2 Majorana GENIUS Supernemo CUORE CUORE GERDA Name Name Neutrino: Dirac or Majorana? or Dirac Neutrino: DBD DBD of continuations of the Heidelberg-Moscow and already approved in IGEX its ex preliminary version, is goi Underground Laboratory. An intense R&D activity is and partially funded : Gerda and CUORE. These and a here. collaboration in view of the installation of this e been decided. PoS(EMC2006)007 f Mo 100 Ettore Fiorini Ettore Fiorini d laboratory in Europe. h planes of scintillating fibers. The y in Japan. The set-up is made (Fig.15) of hold interactions of solar neutrinos on 13 detector experiment mainly intended to search for detector approach to search for neutrinoless DBD o ≠ ≠ Se, Se, to be installed in a not yet decided undergroun is also a source 82 is is based on the source Rb. 100 SUPERNEMO SUPERNEMO MOON MOON and Majorana Fig. 14: GERDA Mo Mo to be installed in the Oto underground laborator Neutrino: Dirac or Majorana? or Dirac Neutrino: neutrinoless DBD of 100 thin sheets of enriched molybdenum interleaved wit leading to Fig.15. MOON experiment is also intended to detect the low thres PoS(EMC2006)007 Ettore Fiorini Ettore Fiorini Ba, Ba, but with a totally new 136 a a large mass of enriched Xenon Xe- 136 Xe. Xe. Due to the large mass it will be , but with a considerably different 136 th the help of LASER beams single Ba++ f f liquid or gas Xenon and the underground boratory in USA. atter atter particles (WIMPS) liquid Xenon experiment without Ba tagging DBD of EXO 14 XENON is an experiment to be carried out in Japan with also intended to search for neutrinoless DBD of XENON EXO Neutrino: Dirac or Majorana? or Dirac Neutrino: approach: to search for DBD events by detecting wi ions produced by the process (Fig.17) The option o location has not yet been decided, but a kg litre Fig. 16. SuperNEMO Fig. 16. SuperNEMO based on scintillation to search for neutrinoless also used to for search a in interactions of Dark M is going soonto operate in the WIPP underground la The system is similar to the one geometry (Fig.16) adopted by NEMO 3 PoS(EMC2006)007 ic he one of Ettore Fiorini Ettore Fiorini 650 nts) will be consist in 988 47s metastable 3/2 8) . The experiment has already been . sso Laboratory and by the Italian Institute D 4 allows many other interesting, but expensive, ation has been already prepared in Gran Sasso 15 CUORE CUORE Te Te has been chosen for CUORE due to its high isotop 1/2 130 P 2 arranged in 19 columns practically identical to t 2 493 1/2 S (for Cryogenic Underground Observatory of Rare Eve 2 CUORE Neutrino: Dirac or Majorana? or Dirac Neutrino: abundance, but the versatility of thermal detectors of Nuclear Physics and the basement for its install doublebeta active materials. CUORICINO, with a total mass of about 750 kg (fig.1 approved by the Scientific Committee of the Gran Sa (Fig.19) . As shown in Table III crystals of natural TeO EXO taggingin Fig. 17: Ba++ PoS(EMC2006)007 Ettore Fiorini Ettore Fiorini “ hat hat the difference keV keV nd the measurement s s different zero.from valid and is strongly 3368 2038.7 " 3034 " 2804 " 2528 " 4272 Transition energy 16 7.44 " 9.63 " 7.49 " 34 " 5.64 " .0187 % Isotopic abundance 4 3 4 2 3 2 F O F PbO WO GaO Ge Nd Te Conclusions Ca 76 Cd Nd Mo 48 150 130 116 3. 150 100 Compound After 70 year the brilliant hypothesis of Ettore Majorana is still supported by the discovery of neutrino oscillations which between squaredthe masses of two neutrinos of different flavours i implies t As a consequence at least one of the neutrinos has to be massive a Neutrino: Dirac or Majorana? or Dirac Neutrino: Fig.18 : CUORE neutrinoless for Table thermal candidates 3: Possible DBD PoS(EMC2006)007 n a erence Ettore Fiorini Ettore Fiorini physics to sent the most rino rino is a Majorana beta decay involve PoS(EMC2006)010 help in understanding : Yuri Zdesenko, Rev. h the sensitivity in the , 83 (1984). , 83 (1984). PoS(EMC2006)003. 224 17 , 512 (1935 48 , 6 (2005). S.R. Elliott and J. Engel, J. Phys.G: Nucl. Part. 7 , 663 (2002); F.T. Avignone III, G.S. King III,and Yu. G. Zdesenko, 74 , 183 (2004); hepph/0405078, and the resport by S.Elliotto to the recent 30R Mod. Phys. New New Journal of Physics, Phys. Neutrino-2006 Conference )Santa Fe JulyNeutrino-2006 2006. Conference )Santa Fe "Ettore Majorana's legacy and the Physics of he XXI century"XXI PoS(EMC2006)003 he legacy and the of "Ettore Physics Majorana's see Aalseth The Neutrino Matrix; C. al.,arXiv:hep-ph/04123000 et also 5] E. Fiorini and T. Ninikoski, Nucl. Instrum. and Meth. E. Instrum. 5] Fiorini Nucl. and Ninikoski, T. [6] [6] For reviews of future experiments on Neutrinoless DBD see [ Neutrino: Dirac or Majorana? or Dirac Neutrino: and N. Cabibbo, "Neutrino oscillations", proceedings of the conference Cabibbo, "Ettore and "Neutrino of N. oscillations", proceedings the legacy century", Majorana's the of XXI Physics and [3] MultidivisionalAPS [3] Neutrino Study, Neutrino Joint Study on the of Physics: future the of conference Maiani,:The L. 70 years proceedings [4] neutrino, after, Majorana legacyMajorana's "Ettore Physics and the the century", of XXI of of the neutrino mass becomes imperative. Double powerful beta tool decay to is obtain at this pre result particle. and also to clarify if the The future neut second generation experiments being designed , proposed and already i few case under construction will allow in a oscillations.neutrinoby the predicted mass of results few years to reac Due to their peculiar interdisciplinarity experiments different on double fields of physics radioactivity, material sciences , geochronology etc. It could even from nuclear, subnuclear in theasymmetry Universe. the particle-antiparticle and astroparticle Therefore you Ettore! thank References M. Goeppert-Mayer, Phys. Rev. [1] [2] N. Cabibbo: N. Cabibbo, "Neutrino oscillations", n proceedings of the conf