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Lepton Number Violation and Lepton Flavour Violation

Lepton Number Violation and Lepton Flavour Violation

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Lepton Number Violation and Lepton Flavour Violation

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  1. Lepton Number Violationand Lepton Flavour Violation Search for Majorana neutrinos in B-decays , lepton flavour violation in- --+ , and baryon number violationwith LHCb LHCb collaboration 54 institutions, 15 countries

  2. SEARCH FOR LEPTON NUMBER VIOLATION IN B DECAYS

  3. Search for Lepton Number Violation at LHCb Impressive limits to date from nuclear 0- decay on electrons: O(1025) years. Yet heavy quark mesons could undergo the same process with muons: Phys. Rev. D 85, 11204 (2012) arXiv:1201.5600v2 Virtual Majorana neutrino a) Resonant neutrino production b) Vub b c - Annihilation Pioneered by Mark II W-  N c) W- New - ¯ Vcb ¯ u d Also resonant production

  4. Limits from B-factories Belle results on B  D+l-l- Based on 772106 BB events at (4s), collected with the Belle detector at KEKB • BaBar results on B  h+l-l- with h=K, • Based on 471106 BB events at (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 Ebeam constraint

  5. Analysis general aspects Phys. Rev. D 85, 112004 (2012) • Search for the decays • B-  +- - , B-  Ds+- - , B-  D+- - , B-  D*+- - , B-  D0+- - • 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/ K- J/  +- B- (2s) K- (2s)  + - J/ Total efficiency + - K- : 0.99  0.01 % Total efficiency + - + - K- : 0.078  0.002 %

  6. Majorana neutrinos B-  +- - Phys. Rev. D 85, 112004 (2012) • B-  +- - • K// misid rates from D* +D0(K-+) • K0s and J/   • Peaking background from misid • B-  J/ K- and B-  J/- (2.5 evts) • Combinatorial background from • fit to the sidebands (5.3 evts) • Many systematics cancel in ratio to • normalisation channel

  7. Majorana neutrinos B-  D+(*)- - Phys. Rev. D 85, 112004 (2012) • B-  D+- - , B-  D*+- - • Total efficiencies are 0.099  0.007 % and 0.066  0.005 % • D+ reconstructed via decay to K  , D*+ reconstructed via D0( K) • Any value of MN (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 and taking the vaue in which such probability is 0.05 (95 % C.L.)

  8. B-  Ds+- - and B-  D0+- - • B-  Ds+- - • Ds reconstructed via • decay to KK • Heavy neutrino can • decay to Ds+- • Ds+ decay tracks form a • vertex with - candidate • then a detached vertex • with second - (B-) • B-  D0+- - • D0 reconstructed via • decay to K • MN spectra consistent • with polynomial backgs. • estimated from sidebands MN Phys. Rev. D 85, 112004 (2012)

  9. Mass-dependent Majorana neutrino limits B-  +- - B-  Ds+- - B-  D0+- - • Upper limits (95% C.L.) are set at • each MNmass by searching a signal • within  3N in small steps. Phys. Rev. D 85, 112004 (2012) • For B-  D+(*)- - , limits • on the coupling require calculation • of hadronic form factor • (as for 0 decay) . • A model dependent calculation2 • was used for B- D0+-- , but • the mode +-- is more sensitive. 2 D. Delepine, G. Lopez Castro, and N. Quintero, Phys. Rev. D84 (2011) 096011, arXiv:1108.6009.

  10. Limits on Majorana coupling |V4 | Phys. Rev. D 85, 112004 (2012) B-+-- B   LHCb Mass dependent upper limits on the coupling |V4 | of a 4th generation Majorana neutrino to a muon and virtual W 1. 1A. Atre, T. Han, S. Pascoli, and B. Zhang, JHEP 05 (2009) 030, arXiv:0901.3589.

  11. Summary on LNV in B decays a BaBar,Phys. Rev. D 85, 071103 (2012) b CLEO, Phys. Rev. D 65, 111102 (2002) c Belle, Phys. Rev. D 84, 071106(R), (2011) d LHCb, CERN-PH-EP-2012-006, arXiv:1201.5600 (2012) e LHCb, Phys. Rev. Lett. 108 101601 (2012)

  12. SEARCH FOR LEPTON FLAVOR AND BARYON NUMBER VIOLATION

  13. - --+ physics • - --+ possible with neutrino • oscillations, but highly suppressed • BR << 10-40,as well as -  -  • Rates enhanced by various new • physics scenarios e.g. • MSSM + massive neutrinos, • suppressed by MSUSY scale (instead MN) • RPV SUSY, Littlest Higgs, etc. • Predicted branching fractions • for some models close to • current experimental limits for • some regions of parameter • spaces • both scalar and pseudoscalar • Higgs bosons are involved in • - l--+

  14. current status - --+ • - --+ yet to be observed • Current experimental limits (at 90% C.L.): • But can also set limits a hadron colliders …

  15. - --+analysis strategy • Inclusive  cross section is 79.5  8.3 b at s = 7 TeV • in LHCb acceptance • 1.0 fb-1 collected in 2011  8  1010  produced •  mainly from Ds- - ̅ decays (78%) Systematics cancel in ratio of efficiencies • fDsis the fraction of  from Ds , from LHCb cross-section • measurements and LEP/B-factory branching fractions • B(Ds  ̅ ) from arXiv:hep-ex/1201.2401 •  are the efficiencies to select signal and normalisation events, calculated from MC • NDs  from data , B(Ds () is known

  16. D-s   (+-) - decays in data • B(Ds  ()) from: • Veryefficient trigger • Negligible contribution of non-resonant events in data (< 2%) • NDs   = 45 520  920 from a gaussian fit to data • (1020) reconstructed with a low background level Background subtracted

  17. - --+signal and background discrimination • Two multivariate classifiers, M3body and MPID • Use boosted decision trees with adaptive boosting • Trained on signal and background MC • M3body includes : vertex and • track fit quality, vertex displacement, • vertex pointing, vertex isolation • and  pT • Calibrated on D-s  -data • MPID includes : information • from RICH, ECAL, HCAL • and muon chambers • Calibrated on J/   data

  18. - --+background fits • Background estimate in signal • region from data sidebands • 4 highest (left), and second 4 • highest (right) bins merged • Combinatorial, + (--) + • and backgrounds from heavy • meson decays Aaaaaaaaa

  19. Limits on - --+ • Limit calculated using • CLs method • (J. Phys. G: Nucl. Part. Phys. 28 2693) • First  LFV result at a • hadron collider • Detailed in • LHCb-CONF-2012-015 • Further improvements • expected in 2012

  20. - p̅-+ and - p-- at LHCb •  - --+ analysis adapted at LHCb to search for  - p̅-+ and •  - p--with- flux normalised to the control sample: D-s  (+-) - • LHCb-CONF-2012-027 • Both violate baryon/lepton number and lepton flavour , with  (B –L) = 0 • Observed numbers of events consistent with background expectations First limits obtained from these channels, similar to those at B-factories from -   h- h=,K

  21. Summary • 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 10-6…-8, establishing best limits on the coupling • |V4| of a 4th generation N to W, using B   • LHCb is approaching B factories for   • first measurement at hadron colliders • LHCb has set limits ( 10-7)for the first time on  (B –L) = 0 • decays - p̅-+and - p-- Only up to 1.0 fb-1 used by LHCb, currently 3.0 fb-1 on tape

  22. THANKS

  23. BACKUP

  24. 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 10-10s to 10-11s. Mass resolution Neutrino mass acceptance B-+-- B- Ds+-- B- D0+--

  25.  production at LHCb

  26. Event selection

  27. --+ mass binning

  28. Limits from B factories

  29. Differences between the analyses

  30. Binning optimisation

  31. Differences between - p̅ -+ and - p--

  32. - p̅-+ and - p-- at LHCb