Lepton number violation and basic neutrino properties Andrea Giuliani CNRS/CSNSM, Orsay, France
Outline The neutrino mass scale Single beta decay and neutrino mass Double beta decay: neutrino mass and LNV Double beta decay: experimental status and prospects Double beta decay: open issues 2
The absolute neutrino mass scale Cosmology , single and double b decay measure different combinations of the neutrino mass eigenvalues, constraining the neutrino mass scale In a standard three active neutrino scenario: cosmology 3 S S M i simple sum pure kinematical effect i=1 1/2 b decay 3 S M i M b incoherent sum 2 |U ei | 2 real neutrino i=1 3 double b decay |S M i |U ei | 2 e i a | M bb coherent sum i virtual neutrino i=1 Majorana phases
M b 4
Direct n mass measurement use E 2 = p 2 c 2 + m 2 c 2 → m 2 ( ν) is the observable Use low Q-value beta-like processes and study endpoint of electron or g spectrum MAC-E-filter Spectrometers KATRIN Q 18.6 keV 3 H 3 He + e - + n e CRES PROJECT 8 187 Re 187 Os + e - + n e Bolometers Q 2.5 keV NUMECS HOLMES ECHO 163 Ho + e - 163 Dy* + n e Q 2.8 keV g In red, projects located in EU
KATRIN concept Thanks to Ch. Weinheimer
KATRIN status Thanks to Ch. Weinheimer
KATRIN and light sterile neutrinos Reactor neutrino anomaly Thanks to Ch. Weinheimer
How to improve KATRIN Ho-embedding cryogenic bolometers (ECHO, HOLMES, NUMECS) Interesting new results from ECHO Technology starts to be scalable But : many orders of magnitude to go to achieve required satistics Systematics? Project 8 Measure the coherent cyclotron radiation from tritium b electrons Detection of single electron succesfull But : is the experiment scalable? Systematics? Thanks to Ch. Weinheimer
How to improve KATRIN: time of flight TOF spectrum is sensitive to neutrino mass The difficulty is to measure START without disturbing electron energy at the 10 meV level Interesting possibility: use Project8 technology for START measurement Thanks to Ch. Weinheimer
M bb LNV 11
Neutrinoless double beta decay ( 0n2b ): standard and non-standard mechanisms 0n2b is a test for « creation of leptons »: 2n 2p + 2e - LNV This test is implemented in nuclear matter: (A,Z) (A,Z+2) + 2e - Energetically possible for 40 nuclei Only a few are experimentally relevant Standard mechanism: neutrino physics 0n2b is mediated by light massive Majorana neutrinos (exactly those which oscillate) 0n2b Non-standard mechanism: BSM, LNV Not necessarily neutrino physics
Neutrinoless double beta decay ( 0n2b ): standard and non-standard mechanisms 0n2b is a test for « creation of leptons »: 2n 2p + 2e - LNV This test is implemented in the nuclear matter: (A,Z) (A,Z+2) + 2e - Energetically possible for 40 nuclei Only a few are experimentally relevant Standard mechanism: neutrino physics 0n2b is mediated by light massive Majorana neutrinos (those which oscillate) 0n2b Non-standard mechanism: BSM, LNV Not necessarily neutrino physics
Why it is important to test LNV L and B are accidentally conserved in the SM Effective theory: 9 5 dim 5 dim 4 dim 6 dim 9 Majorana Proton LNV mass term, decay Seesaw LNV Light Majorana n L Baryogenesis (Leptogenesis) B (L) violation Heavy Majorana N R B, L often connected in GUTs GUTs have Majorana neutrinos and seesaw
Why it is important to test LNV L and B are accidentally conserved in the SM Effective theory: 9 5 dim 5 dim 4 dim 6 dim 9 Majorana Majorana Proton LNV mass term, mass term, decay Seesaw LNV LNV Light Majorana n L Baryogenesis (Leptogenesis) B (L) violation Heavy Majorana N R B, L often connected in GUTs GUTs have Majorana neutrinos and seesaw
Standard mechanism How 0 n -DBD is connected to neutrino mixing matrix and masses in case of process induced by light n exchange ( mass mechanism ). Axial vector Phase Nuclear coupling constant neutrinoless space Effective matrix elements Double Beta Decay Majorana mass rate 1/ t = G(Q,Z) g A 4 |M nucl | 2 M bb 2
Standard mechanism How 0 n -DBD is connected to neutrino mixing matrix and masses in case of process induced by light n exchange ( mass mechanism ). Axial vector Phase Nuclear coupling constant neutrinoless space Effective matrix elements Double Beta Decay Majorana mass rate 1/ t = G(Q,Z) g A 4 |M nucl | 2 M bb 2 Neutrino physcis Experiments Calculable Nuclear theory Controversial M bb = | | U e1 | 2 M 3 | 2 M 1 + e i a 1 | U e2 | 2 M 2 + e i a 2 | U e3 |
M bb vs. lightest n mass [eV] S. Dell'Oro et al., Phys. Rev. D90, 033005 (2014) M lightest [eV]
Status 76 Ge 136 Xe 130 Te Ge Cuoricino + CUORE-0 GERDA-I claim KamLAND + EXO T 10 25 y [eV] Here and next slides g A = 1.269 (no quenching) See later for discussion M lightest [eV]
Current-generation experiments Even the most ambitious of the current generation experiments – GERDA, CUORE, EXO-200, KamLAND-Zen, SNO+ SuperNEMO demonstrator – can arrive at best (time scale 2018-2020) here T 10 26 y [eV] g A = 1.269 (no quenching) M lightest [eV] 20
Strategic milestone ? [eV] T 10 27 y g A = 1.269 (no quenching) M lightest [eV] 21
Strategic milestone ? [eV] T 10 27 y O O (1 ton) + zero background g A = 1.269 (no quenching) M lightest [eV] 22
Factors guiding isotope selection Phase space: G(Q,Z) Q 5 Q is the crucial factor Background Nine Magnificent 23
Isotope choice and nuclear matrix elements 1/ t = G(Q,Z) g A 4 |M nucl | 2 M bb 2 J. Barea, et al. Phys. Rev. C91,034304 (2015) R. G. H. Robertson, Mod. Phys. Lett. A 28, 1350021 (2013) Kotila, J. et al. Phys.Rev. C85 (2012) 034316
Isotope and background End-point of 222 Rn-induced radioactivity End-point of natural g radioactivity 25
Current-generation experiments Future proposed TODAY efforts 40 kg – 76 Ge nEXO 110 kg – 136 Xe GERDA+MAJORANA 29 kg – 76 Ge 200 kg – 130 Te 7 kg – 82 Se CUPID LUCIFER LUCINEU 7 kg – 100 Mo 160 kg – 130 Te NEXT-NEW BEXT NEXT-100 100 kg – 136 Xe PANDA X 7 kg – 82 Se SuperNEMO 5 kg – 100 Mo AMoRE 70 kg – 100 Mo AMoRE 320 kg 600 kg – 136 Xe Adapted from NLDBD-NSAC document Europe-based 26 (April 2014)
Possible routes to 1 ton Collaborations are already thinking to improve/upgrade their technology in view of 1 ton set-up In order to select the best(s) technology(ies) for 1 ton, it is necessary to get the complete scenario of the current generation experiments and demonstrators Wait 2-3 years for a sensible decision 27
Possible routes to 1 ton Fluid-embedded source way ❶ Low energy resolution 250 keV FWHM SNO+ ( 130 Te 200 kg) – SNO+ ( 130 Te 800 kg) Scalability 80 keV FWHM KamLAND- Zen → KamLAND2 -Zen (1 ton 136 Xe , higher energy resolution, 214 Bi line not resolved pressurized Xe) from 0 n 2 b 136 Xe signal EXO- 200 → nEXO (5 ton liquid 136 Xe TPC) NEXT- 100 → BEXT (1-3 ton high pressure 136 Xe TPC) Extreme background demand Crystal source way ❷ (10 -4 counts/keV/kg/y at 2 MeV) High D E GERDA 2 → GERDA +MAJORANA → 1 ton 76 Ge (Ge diodes) CUORE CUPID (1 ton 130 Te or 100 Mo or 82 Se ) (bolometers) LUCIFER, LUMINEU, LUCINEU AMoRE ( 100 Mo 100 kg) AMoRE ( 100 Mo 10 kg) Cryogenics It is problematic to reach the 1 ton scale with the External source Crystallization approach ( SuperNEMO ), but the use of a high promising isotope 28 as 1 50 Nd could partially compensate for the lower mass In red, projects located in EU
Impact of enrichment cost Price/ton [M$] 80 Adapted from A. Barabash J. Phys. G: Nucl. Part. Phys. 39 (2012) 085103 nEXO – 5 tons – sensitivity: 5-16 meV in 10 y (no barium tagging) CUPID 130 Te – 0.54 tons – sensitivity: 6-15 meV in 10 y Not always really 1 ton: CUPID 100 Mo – 0.21 tons – sensitivity: 6-17 meV in 10 y 29
Down-selection process in the US http://science.energy.gov/~/media/np/nsac/pdf/docs/2016/NLDBD_Report_2015_Final_N ov18.pdf 2-3 years time scale NSAC recommandations:
Strategic milestone [eV] T 10 27 y O O (1 ton) + zero background nEXO, CUPID, GERDA+MAJORANA, AMoRE final, KamLAND-Zen2 Time scale > 2020 g A = 1.269 (no quenching) M lightest [eV] 31
Strategic milestone [eV] T 10 27 y O O (1 ton) + zero background nEXO, CUPID, GERDA+MAJORANA, AMoRE final, KamLAND-Zen2 Time scale > 2020 g A = 1.269 (no quenching) M lightest [eV] 32
g A quenching 1/ t = G(Q,Z) g A 4 |M nucl | 2 M bb 2 1.269 Free nucleon J. Barea et al. and Ejiri et al. realized that g A is quenched in 2n2b decay g A = 1.25 Often taken in the calculations (confrimed by b -like processes) J. Barea et al., Phys. Rev. C 87, 014315 (2013) 1 Quark E. Ejiri et al., Physics Letters B 729 (2014) 27 – 32 J. Kotila et al., Phys. Rev. C 85, 034316 (2012) Evaluate M 2n eff from experiments Compare M 2n eff (exp) with M 2n (theo) Observe that M 2n eff (exp) < M 2n (theo) Rescale g A to explain the difference g A,eff 0.6 – 0.8 (depending on model)
Recommend
More recommend
