Lepton Number and Lepton Flavour Violation

Transcription

1 Lepton Number and Lepton Flavour Violation Search for Majorana neutrinos in B-decays, lepton flavour violation in τ - µ - µ - µ + and baryon number violation with LHCb seen Paul Seifert's talk today LHCb collaboration 54 institutions, 15 countries B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

2 Introduction Lepton Number Violation No known symmetry associated with Lepton Number Conservation. Gauge symmetry is behind electric charge conservation. New Physics models such as those with Majorana neutrinos, or LR symmetric models with doubly charged Higgs boson can violate LN conservation. LHCb has searched for B - π + µ - µ - and B - K + µ - µ - Phys. Rev. Lett. 108, (2012) Such decays have previously been searched for: - Ξ- pμ - μ - HyperCP D. Rajaran et al. Phys. Rev. Lett. 94, (2005) - B he + μ -, he + e +, he + μ +,hμ + μ + h=π,k,ρ,k* CLEO K.W. Edwards et al. Phys. Rev. D65, (2002) - 0νββ excellent review: J. J. Gomez-Cadenas et al. Riv. Nuovo Cimento 35, 29 (2012) - pp (e + e +,e + μ +,μ + μ + ) + X, high mass SS dileptons ATLAS G. Aad et al. J. High Energy Phys. 10 (2011) 107. B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

3 LHCb detector overview and performance Search for B - π + µ - µ -, B - K + µ - µ -, B - D s+ ( ϕ(k + K - )π + )µ - µ - B - D + (K - π + π + )µ - µ -, B - D *+ (D 0 π + )µ - µ -, B - D 0 (K - π + )π + µ - µ -

4 B-Vertex Measurement B 0 J/Ψ (μ + μ - ) K + Primary vertex B + d~1cm K + μ + μ - σ(τ) ~40 fs Proper-time resolution σ t = 40 fs Vertex Locator (VELO) Vertexing: trigger on impact parameter measurement of decay distance (time)

5 Momentum and Mass measurement : Tracker OT IT TT TT LHCb 8276 signal [LHCb-CONF ] TT and Inner Tracker: silicon micro-strips ~ 200 μm pitch. 12 m 2 of silicon 4 layers with (0º, +5º, 5º, 0º) stereo angle. Outer Tracker: drift chamber with 5 mm diameter straws gas Ar/CO 2 /O 2 (70:28.5:1.5). Resolution: p/p = % (2 100 GeV/c). B s J/ψ φ selection (J/ψ µ + µ, φ K + K ): σ(m B ) = 7 MeV/c 2 (LHCb). ~ 20 MeV/c 2 (ATLAS/CMS) yields/pb -1 and S/B lower.

6 Particle Identification RICH: K/π identification using Cherenkov light emission angle Bs Ds K π +,K + Primary vertex B s b tag D s K + K π K K : ± 0.06% π K : 3.94 ± 0.02% RICH1: 5 cm aerogel n=1.03, 4 m 3 C 4 F 10 n= Pure sources of K and π given by D *+ D 0 π +, D 0 K - π + RICH2: 100 m 3 CF 4 n=1.0005

7 Particle identification: Calorimeters and L0 trigger e h ECAL (inner modules): σ(e)/e ~ 8.2% / E + 0.9% Calorimeter system : Identify electrons, hadrons, π 0,γ Level 0 trigger: high E T electron and hadron

8 Muon identification and L0 trigger µ Muon system: Level 0 trigger: High P t muons pure muon sample from J/Ψ μ + μ - μ-id requirement applied to only one Primary vertex d~1cm B + K + μ + μ -

9 Search for Lepton Number Violation at LHCb Impressive limits to date from nuclear 0ν-ββ decay on electrons: O(10 25 ) years. Yet heavy quark mesons could undergo the same process with muons: a) b u W - W - N µ- µ- c d Phys. Rev. D 85, (2012) arxiv: v2 Virtual Majorana neutrino Resonant neutrino production b) V ub Annihilation c) New V cb Also resonant production B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

10 Limits from B-factories Belle results on B D + l - l - Based on BB events at ϒ(4s), collected with the Belle detector at KEKB BaBar results on B h + l - l - with h=k,π Based on BB events at ϒ(4s), collected with the BaBar detector at SLAC Event selection similar to other B analysis. B mass and energy calculated in center of mass system using E beam constraint B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

11 Phys. Rev. Lett. 108, (2012) Phys. Rev. D 85, (2012) Search for the decays B - π + µ - µ -, B - D s+ µ - µ -, B - D + µ - µ -, B - D *+ µ - µ -, B - D 0 π + µ - µ - using 0.41 fb -1 Neutrinos are assumed to have a very narrow width compared to detector resolution. Limits calculated asuming phase space, and also as function of neutrino mass Signal yields are normalised to B channels with known branching fractions with the same number of muons in 3-body and 5-body final states B - J/ψ K - J/ψ µ + µ - Analysis general aspects B - ψ(2s) K - ψ(2s) π + π - J/ψ Total efficiency µ + µ - K - : 0.99 ± 0.01 % Total efficiency µ + µ - π + π - K - : ± % B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

12 Majorana neutrinos B B - π + µ - µ - K/π/µ misid rates from D * π + D 0 (K - π + ) K 0 s and J/ψ µµ Peaking background from misid B - J/ψ K - and B - J/ψπ - (2.5 evts) Combinatorial background from fit to the sidebands (5.3 evts) Many systematics cancel in ratio to normalisation channel B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

13 Majorana neutrinos B - D +(*) - - Phys. Rev. D 85, (2012) B - D + µ - µ -, B - D* + µ - µ - Total efficiencies are ± % and ± % D + reconstructed via decay to Kπ π, D *+ reconstructed via D 0 ( Kπ)π Any value of M N (virtual neutrinos) 6 evts 6.9 ± 1.1 backg. 5 evts 5.9 ± 1.0 backg. Total systematics : 8.8 % (D + ), 8.2 % (D *+ ) Dominated by branching ratios of normalization channels and trigger efficiencies Limits determined using P(N N obs ) = N N obs N (S+ B) e N! (S+ B) and taking the vaue in which such probability is 0.05 (95 % C.L.) B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

14 Mass and lifetime acceptance for on-shell Majorana neutrinos Finite neutrino lifetimes ignored so far (except for off-shell production) Sensitivity is lost for lifetimes longer than s to s. B - π+µ - µ - B - D s+ µ - µ - B - D 0 π+µ - µ - Mass resolution Neutrino mass acceptance B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

15 Systematic uncertainties for B - DX - - B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

16 Systematic uncertainties for B B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

17 B - D s+ - - and B - D B - D s+ µ - µ - D s reconstructed via decay to KKπ Heavy neutrino can decay to D s+ µ - D s + decay tracks form a vertex with µ - candidate then a detached vertex with second µ - (B - ) B - D 0 π + µ - µ - D 0 reconstructed via decay to Kπ M N spectra consistent with polynomial backgs. estimated from sidebands M N Phys. Rev. D 85, (2012) B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

18 Mass-dependent Majorana neutrino limits B - π + µ - µ - B - D s+ µ - µ - B - D 0 π + µ - µ - Phys. Rev. D 85, (2012) Upper limits (95% C.L.) are set at each M N mass by searching a signal within ± 3σ N in small steps. For B - D +(*) µ - µ -, limits on the coupling require calculation of hadronic form factor (as for 0νββ decay). A model dependent calculation 2 was used for B - D 0 π+µ - µ -, but the mode π+µ - µ - is more sensitive. 2 D. Delepine, G. Lopez Castro, and N. Quintero, Phys. Rev. D84 (2011) , arxiv: B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

19 Limits on Majorana coupling V 4 Phys. Rev. D 85, (2012) B - π+µ - µ - Mass dependent upper limits on the coupling V µ4 of a 4th generation Majorana neutrino to a muon and virtual W 1. B πµµ LHCb 1 A. Atre, T. Han, S. Pascoli, and B. Zhang, JHEP 05 (2009) 030, arxiv: B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

20 Summary on LNV in B decays a BaBar,Phys. Rev. D 85, (2012) b CLEO, Phys. Rev. D 65, (2002) c Belle, Phys. Rev. D 84, (R), (2011) d LHCb, CERN-PH-EP , arxiv: (2012) e LHCb, Phys. Rev. Lett (2012) B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

21 Summary of LNV and LFV at LHCb neither lepton number violation nor lepton flavour violations observed yet heavy quark and lepton decays provide good probes for Lepton Number & Flavour Violation. Excellent sensitivity achieved at B factories. LHCb extends knowledge on forbbiden B decays in LNV processes to , establishing best limits on the coupling V µ4 of a 4th generation N to µw, using B πµµ LHCb is approaching B factories for τ µµµ first measurement at hadron colliders: < % C.L. LHCb has set limits ( 10-7 ) for the first time on (B L) = 0 decays τ - p µ - µ + and τ - pµ - µ - Only up to 1.0 fb-1 used by LHCb, currently 3.0 fb-1 on tape B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

22 THANKS B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,

23 Limits from B factories B. Adeva, University of Santiago de Compostela 3 rd Workshop Flavour Physics LHC era Valencia 6 th February,