Neutrinoless Double Beta Decay and Lepton Number Violation

Transcription

1 Neutrinoless Double Beta Decay and Lepton Number Violation Manfred Lindner M. Lindner, MPIK PPC2015 1

2 Q 76 Zn β - 76 Ga S Single and Double Beta Decay Mass parabolas of special nuclei: double beta decay = very rare è single β-decay forbidden è certain even-even nuclei: 76 Ge, odd-odd 76 Kr β + 76 Rb even-even β - 76 Br EC Q ββ = 2039 kev 76 Ge 76 As β - β + 76 Se Z Double beta decay = 2 simultaneous single β-decays: 2n à 2p +X ; q x = -2 ; energy Q ββ goes ~ into X if m X <<GeV transition probability looks like 2 nd order perturbation ß à intermediate state inherent NME uncertainty ß à overlap of nuclear wave fcts. with quarks M. Lindner, MPIK PPC2015 2

3 The Standard Picture of Double Beta Decay SM 2νββ 2νββ decay seen for diff. isotopes (Kirsten, ) T 1/2 = O( years) è up to Τ Universe 0νββ decay Majorana mass 0νββ 2νββ decay T 1/2 > O(10 25 y) observe 2νββ look for 0νββ signal at Q ββ large amount of 76 Ge nuclei extreme low backgrounds! è signal = Majorana mass M. Lindner, MPIK PPC2015 3

4 m ee : The Effective Neutrino Mass Use known mixings and Δm 2 à Allowed m ee vs m 1 plots 0νββ by Majorana masses à limits on m ee cosmology à limit on m M. Lindner, MPIK PPC2015 4

5 76 Ge and 136 Xe Results ν 76 T 1/2 ( Ge) [yr] Ge combined GERDA Phase I claim (2004) 68% C.L. GERDA How model dependent? - T 1/2 is model independent - Ge / Xe comparison à NME s - NME ratios better known à NME ratio has spread! à at best one is right - Full NME uncertainty and model assumptions come back for Majorana mass limits EDF ISM IBM-2 pnqrpa SRQRPA-B SRQRPA-A QRPA-B QRPA-A SkM-HFB-QRPA ν ( Xe) [yr] EXO-200 (new result) KamLAND-Zen T 1/2 KK claim strongly disfavoured directly by Ge & indirectly by Xe è See experimental talks: V. Wagner (GERDA) M. Koga (Kamland-Zen) Y.-R. Yen (EXO) K.R. Rielage (Majorana) M. Lindner, MPIK PPC2015 5

6 More general: L Violating Processes 2νββ Search unchanged SM 2νββ decay 0νββ decay 0νββ BSM interpretation changes: T 1/2 > O(10 25 y) 0νββ some ΔL=2 operator M. Lindner, MPIK PPC2015 6

7 Standard Model: Double Beta Decay Processes + è 2 electrons + 2 neutrinos 2νββ Majorana ν-masses or other ΔL=2 physics: è 2 electrons 0νββ Majorana neutrino masses SM+Higgs + triplet SUSY SUSY important connections to LHC and LFV sub ev Majorana mass ß à TeV scale physics M. Lindner, MPIK PPC2015 7

8 Interference of ΔL=2 Operators Usually with interferences = overall phase space factor ß à determined by parameters of new physics m ε ~ (Λ new ) -5 m 0νββ = 1 ev ç è Λ new ~ TeV M. Lindner, MPIK PPC2015 8

9 m ee m ee m ε ç growing m ε à shifts of masses, mixings and CP phases à sensitivity to TeV physics à cancellations possible à upper bounds for ε and m ee M. Lindner, MPIK PPC2015 9

10 Does 0νββ Decay imply Majorana Masses? Standard picture: Majorana neutrinos è 0νββ observation of 0νββ è Majorana neutrinos wrong! Correct picture: observation of 0νββ è some ΔL=2 operator must exist which allows the decay è much broader than m ν The usual rescue: The `Schechter-Valle Theorem Any ΔL=2 operator which mediates the decay induces via loops Majorana mass terms è unavoidable! è Majorana nature of neutrinos!? M. Lindner, MPIK PPC

11 The Schechter-Valle Theorem induced Mass - any ΔL=2 operator which leads to 0νββ decay induces via loops a Majoarana mass - assume a 0νββ signal è how big is the induced mass? Dürr, ML, Merle 4 loops è δm ν = ev è very tiny (academic interest) è cannot explain observed ν masses and splittings è explicit Dirac neutrino mass operators required Extreme possibility: - 0νββ = L violation = other BSM physics - neutrino masses = Dirac (plus very tiny correction) M. Lindner, MPIK PPC

12 Neutrino Mass Terms & L Violation Simplest possibility: assume 3 right handed singlets (1 L ) ν L g N ν R x <φ> = v ν R x ν R Majorana L / è c 0 m ν c D L ( ν ) L ν R md MR ν R like quarks and charged leptons è Dirac mass terms (including NMS mixing) +9+ new ingredients: è SM+ 1) Majorana mass = scales 2) lepton number violation 6x6 block mass matrix block diagonalization M R heavy è 3 light ν s Or: add scalar triplets (3 L ) ν L ν 3 L or fermionic 1 L or 3 L è left-handed Majorana mass term: M. Lindner, MPIK PPC2015 x x ν L 1,3 ν L x x è M L LL _ c 12

13 Both ν R and new singlets / triplets: è see-saw type II, III m ν =M L - m D M R -1 m D T Higher dimensional operators: d=5, Radiative neutrino mass generation _ è M L LL c Extra gauge groups, SUSY, extra dimensions, è neutrino masses can/may solve two of the SM problems: - leptogenesis (BAU) - kev sterile neutrinos as (WDM) è assumptions = new physics ß à connections to LFV, LHC,... è think of other realizations of L violation è interesting options... M. Lindner, MPIK PPC

14 Overall Situation L-violation is among the most interesting topics We know only some mixings and Δm 2 ç è many models & details (neutrinos and other BSM) Generic expectation (assumption): - m D = O(EW scale) - M R = O(high L-violating scale) è see-saw variants based on two scales è light active ν s + heavy steriles (leptogenesis ) Other scenarios... expectations could change drastically è nothing new at the LHC = just the SM M. Lindner, MPIK PPC

15 SM:Triviality and Vacuum Stability Λ(GeV) 126 GeV < m H < 174 GeV SM does not exist w/o embeding - U(1) copling, Higgs self-coupling λ Landau pole ML GeV is here! è λ(m pl ) ~ 0 - EW-SB radiative - just SM? Holthausen, ML, Lim (2011) triviality allowed vacuum stavility ln(µ) è RGE arguments seem to work è we need some embeding ç è no BSM physics observed! è just a SM Higgs Λ M. Lindner, MPIK PPC

16 Holthausen, ML, Lim Is the Higgs Potential at M Planck flat? Buttazzo, Degrassi, Giardino, Giudice, Sala, Salvio, Strumia 2-loop α s error difference 1à 2 loop Notes: - remarkable relation between weak scale, m t, couplings and M Planck ß à precision - strong cancellations between Higgs and top loops à very sensitive to exact value and error of m H, m t, α s = (7) à currently 1.8σ in m t - other physics: DM, m ν axions, Planck scale thresholds SM+ ç è λ = 0 è top mass errors: data ç è LO-MC è translation of m pole à MS bar è be cautious about claiming that metastability is established M. Lindner, MPIK PPC

17 Is there a Message? λ(m Planck ) ~ 0? è flat potential at M planck è flat Mexcican hat at the Planck scale è if in addition µ 2 = 0 è V(M Planck ) ~ 0? (Remember: µ is the only single scale of the SM) è conformal symmetry as potential solution to the HP è combined conformal & EW symmetry breaking è Realizations & implications for neutrino masses M. Lindner, MPIK PPC

18 Conformal Symmetry as Protective Symmetry - Exact (unbroken) CS è absence of Λ 2 and ln(λ) divergences è no preferred scale and therefore no scale problems - Conformal Anomaly (CA): Quantum effects explicitly break CS existence of CA à CS preserving regularization does not exist - dimensional regularization is close to CS and gives only ln(λ) - cutoff reg. è Λ 2 terms; violates CS badly à Ward Identity Bardeen: maybe CS still forbids Λ 2 divergences è CS breaking ß à β-functions ß à ln(λ) divergences è anomaly induced spontaneous EWSB NOTE: asymmetric logic! The fact the dimensional regularization kills a Λ 2 dependence is well known. Argument goes the other way! M. Lindner, MPIK PPC

19 Looking at it in different Ways Basics of QFT: Renormalization ß à commutator - [Φ(X),Π(y)] ~ δ 3 (x-y) è delta funtion è distribution - freedom to define δ*δ è renormalization ç è counterterms - along come technicalities: lattice, Λ, Pauli-Villars, MS-bar, Reminder: Technicalities do not establish physical existence! Conceptually most clear à BPHZ-renormalization è Symmetries are essential! Question: Is gauge symmetry spoiled by discovering massive gauge bosons? è NO ß à Higgs mechanism è non-linear realization of the underlying symmetry è important consequence: naïve power counting is wrong Gauge invariance è only log sensitivity M. Lindner, MPIK PPC

20 Implications Gauge invariance è only log sensitivity If conformal symmetry is realized in a non-linear way è protective relic of conformal symmetry è only log sensitivity ß à reflects anomaly there is nothing more No hierarchy problem, even though there is the the conformal anomaly = logs ß à β-functions Dimensional transmutation due to log running like in QCD è scalars can condense and set scales like fermions è use this in Coleman Weinberg effective potential calculations ß à most attractive channels (MAC) ß à β-functions M. Lindner, MPIK PPC

21 Let s try to implement the idea M. Lindner, MPIK PPC

22 Why the minimalistic SM does not work Minimalistic: SM + choose µ= 0 ß à CS Coleman Weinberg: effective potential è CS breaking (dimensional transmutation) è induces for m t < 79 GeV a Higgs mass m H = 8.9 GeV This would conceptually realize the idea, but: Higgs too light and the idea does not work for m t > 79 GeV Reason for m H << v: V eff flat around minimum ß à m H ~ loop factor ~ 1/16π 2 AND: We need neutrino masses, dark matter, M. Lindner, MPIK PPC

23 Realizing the Idea via Higgs Portals SM scalar Φ plus some new scalar ϕ (or more scalars) CS à no scalar mass terms the scalars interact è λ mix (ϕ + ϕ)(φ + Φ) must exist è a condensate of <ϕ + ϕ> produces λ mix <ϕ + ϕ>(φ + Φ) = µ 2 (Φ + Φ) è effective mass term for Φ CS anomalous à breaking à only ln(λ) è implies a TeV-ish condensate for ϕ to obtain <Φ> = 246 GeV Model building possibilities / phenomenological aspects: - ϕ could be an effective field of some hidden sector DSB - further particles could exist in hidden sector; e.g. confining - extra hidden U(1) potentially problematic ß à U(1) mixing - avoid Yukawas which couple visible and hidden sector à phenomenology safe due to Higgs portal, but there is TeV-ish new physics! M. Lindner, MPIK PPC

24 Realizing the Idea: Examples for other Directions SM + extra singlet: Φ, ϕ Nicolai, Meissner, Farzinnia, He, Ren, Foot, Kobakhidze, Volkas, SM + extra SU(N) with new N-plet in a hidden sector Ko, Carone, Ramos, Holthausen, Kubo, Lim, ML, (Hambye, Strumia), SM embedded into larger symmetry (CW-type LR) Holthausen, ML, M. Schmidt SM + colored scalar which condenses at TeV scale Kubo, Lim, ML Since the SM-only version does not work è observable effects: - Higgs coupling to other scalars (singlet, hidden sector, ) - dark matter candidates ß à hidden sectors & Higgs portals - consequences for neutrino masses M. Lindner, MPIK PPC

25 Conformal Symmetry & Neutrino Masses ML, S. Schmidt and J.Smirnov No explicit scale è no explicit (Dirac or Majorana) mass term à only Yukawa couplings generic scales Enlarge the Standard Model field spectrum like in R. Foot, A. Kobakhidze, K.L. McDonald, R. Volkas Consider direct product groups: SM HS Two scales: CS breaking scale at O(TeV) + induced EW scale Important consequence for fermion mass terms: è spectrum of Yukawa couplings TeV or EW scale è interesting consequences ß à Majorana mass terms are no longer expected at the generic L-breaking scale à anywhere M. Lindner, MPIK PPC

26 3 0 N _ ( ν L ν c ) R Implications for Neutrino Mass Spectra _! # " 3x3 matrix 3xN NxN ML m D m D MR $! &# %" c ν L ν R $ & % Usually: M L tiny or 0, M R heavy à see-saw & variants light sterile: F-symmetries... Now: M L, M R may have any value: è diagonalization: 3+N EV è 3x3 active almost unitary M L =0, m D = M W, M R singular M L = M R = 0 M L = M R = ε M R =high: see-saw singular-ss Dirac pseudo Dirac active sterile M. Lindner, MPIK PPC

27 Examples Yukawa seesaw: SM + ν R + singlet è generically expect a TeV seesaw BUT: y M might be tiny è wide range of sterile masses è including pseudo-dirac case è suppressed 0νββ Radiative masses è pseudo-dirac case M. Lindner, MPIK PPC or The punch line: all usual neutrino mass terms can be generated à suitable scalars à no explicit masses all via Yukawa couplings à different numerical expectations

28 Another Example: Inverse Seesaw SU(3)c SU(2)L U(1)Y U(1)X P. Humbert, ML, J. Smirnov è light ev active neutrino(s) è two pseudo-dirac neutrinos; m~tev è sterile state with µ kev è tiny non-unitarty of PMNS matrix è tiny lepton universality violation è suppressed 0νββ decay ç! è lepton flavour violation è tri-lepton production could show up at the LHC è kev neutrinos as warm dark matter à M. Lindner, MPIK PPC

29 M. Lindner, MPIK PPC

30 General Implications of CISS The usual expectation that sterile mass terms are automatically very heavy is no longer fulfilled VEVs heavy, but Yukawa couplings may be anything è various ev-evidences may or may not be correct è any sterile mass natural: ev, kev, MeV, GeV, TeV, è cosmology avoid thermalization and HDM è interesting theoretical and phenomenological options: -TeV improved EW fits (Z-width, NuTeV, A LR, Akhmedov, Kartavtsev, ML, Michels, J. Smirnov ; Antusch, Fischer è - kev è warm dark matter è very interesting but. M. Lindner, MPIK PPC

31 Experimental Challenges for 0νββ The required background level: typical material 30Bq/kg ~10 12 cts/ton/year now cts/ton/year x cts/ton/year x cts/ton/year M. Lindner, MPIK PPC

32 Extreme Radiopurity Requirements Materials have unavoidably impurities of unstable elements è select cleanest raw materials è screening Processing can clean materials, but also introducse new impurities è careful planning & screening Transport and activation è go underground Rn emanation from U and Th in all materials à Rn222 decays è Further improvements are very challenging and there are limitations M. Lindner, MPIK PPC

33 γ and Rn Screening Facilities γ-screening stations underground lab 4 GEMPIs New: GIOVE è extensive task for GERDA, XENON and other experiments Rn Screening Facilities ß à 222Rn emanation: Gas counting systems (LNGS, MPIK) sensitivity = few atoms/probe è typ. sensitivity: few µbq/m2 ICPMS: M. Lindner, MPIK PPC

34 Sensitivity & Background (for a Majorana Mass) 1000 without background N A = Avogadro s number W = atomic weight of isotope ε = signal detection efficiency M = isotope mass t = data taking time è 100 with background N = N + N background è ton-scale à c = cts/kev/kg/yr ; ΔE = ROI M. Lindner, MPIK PPC

35 Goals and hard Facts: Testing IH è 17 mev è ~ y Effort: 1ty= 200kg*5y 10ty = 1t * 10y Ge 76 lead time: O(100) kg/y à by then the MH should be known and may be NH M. Lindner, MPIK PPC

36 Summary Ø lepton number violation is a very important topic! Ø goes beyond neutrino masses Ø big new 0νββ experiments à search for L-violation are very hard (ultra low background) and expensive (large quantities of very special material) will take many years (complexity, R&D) while expectations will change: Ø LHC results/limits ß à ν mass terms (SUSY, W R, nothing) Ø sterile neutrinos may be confirmed Ø the mass hierarchy will be known Ø indications for other L-violation? è the 50 mev goal is uncertain and very hard to reach ç è effort & time scales M. Lindner, MPIK PPC