Lepton Number Violation and Lepton Flavour Violation Search
Lepton Number Violation and Lepton Flavour Violation Search for Majorana neutrinos in B-decays , lepton flavour violation in - - - + , and baryon number violation with LHCb collaboration 54 institutions, 15 countries B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 1
SEARCH FOR LEPTON NUMBER VIOLATION IN B DECAYS B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 2
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: b Wa) - c N Wu Phys. Rev. D 85, 11204 (2012) ar. Xiv: 1201. 5600 v 2 Virtual Majorana neutrino - ¯d Resonant neutrino production b) V ub Annihilation Pioneered by Mark II c) New Vcb Also resonant production B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012
Limits from B-factories Belle results on B D+l-l. Based on 772 106 BB events at (4 s), collected with the Belle detector at KEKB Ba. Bar results on B h+l-l- with h=K, Based on 471 106 BB events at (4 s), collected with the Ba. Bar detector at SLAC Event selection similar to other B analysis. B mass and energy calculated in center of mass system using Ebeam constraint B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 4
Analysis general aspects Phys. Rev. D 85, 112004 (2012) Search for the decays B- + - - , B- Ds+ - - , B- D*+ - - , B- D 0 + - 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/ + - Total efficiency + - K- : 0. 99 0. 01 % B. Adeva, University of Santiago de Compostela B- (2 s) K- (2 s) + - J/ Total efficiency + - K- : 0. 078 0. 002 % Discrete Symmetries Lisbon 6 th December, 2012 5
Majorana neutrinos B- + - Phys. Rev. D 85, 112004 (2012) B- + - K/ / misid rates from D* +D 0(K- +) K 0 s 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 B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 6
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 D 0( 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. ) B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 7
B- Ds+ - - and B- D 0 + - B- Ds+ - Ds reconstructed via decay to KK Heavy neutrino can decay to Ds+ decay tracks form a vertex with - candidate then a detached vertex with second - (B-) B- D 0 + - D 0 reconstructed via decay to K MN spectra consistent with polynomial backgs. estimated from sidebands MN Phys. Rev. D 85, 112004 (2012) B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 8
Mass-dependent Majorana neutrino limits B- + - - B- Ds+ - - Upper limits (95% C. L. ) are set at each MN mass by searching a signal within 3 N in small steps. For B- D+(*) - - , limits on the coupling require calculation of hadronic form factor (as for 0 decay). A model dependent calculation 2 was used for B- D 0 + - - , but the mode + - - is more sensitive. Phys. Rev. D 85, 112004 (2012) 2 B- D 0 + - - D. Delepine, G. Lopez Castro, and N. Quintero, Phys. Rev. D 84 (2011) 096011, ar. Xiv: 1108. 6009. B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012
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 4 th generation Majorana neutrino to a muon and virtual W 1. 1 A. Atre, T. Han, S. Pascoli, and B. Zhang, JHEP 05 (2009) 030, ar. Xiv: 0901. 3589. B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 10
Summary on LNV in B decays a Ba. Bar, 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, ar. Xiv: 1201. 5600 (2012) e LHCb, Phys. Rev. Lett. 108 101601 (2012) B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 11
SEARCH FOR LEPTON FLAVOR AND BARYON NUMBER VIOLATION B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 12
- - - + 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 - - + B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 13
current status - - - + yet to be observed Current experimental limits (at 90% C. L. ): But can also set limits a hadron colliders … B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 14
- - - + analysis strategy Inclusive cross section is 79. 5 8. 3 b at s = 7 Te. V in LHCb acceptance 1. 0 fb-1 collected in 2011 8 1010 produced mainly from Ds- - decays (78%) Systematics cancel in ratio of efficiencies f. Ds is the fraction of from Ds , from LHCb cross-section measurements and LEP/B-factory branching fractions B(Ds ) from ar. Xiv: hep-ex/1201. 2401 are the efficiencies to select signal and normalisation events, calculated from MC NDs from data , B(Ds ( ) is known B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 15
D-s ( + -) - decays in data B(Ds ( ) ) from: Very efficient 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 B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 16
- - - + signal and background discrimination Two multivariate classifiers, M 3 body and MPID Use boosted decision trees with adaptive boosting Trained on signal and background MC M 3 body includes : vertex and track fit quality, vertex displacement, vertex pointing, vertex isolation and p. T Calibrated on D-s - data MPID includes : information from RICH, ECAL, HCAL and muon chambers Calibrated on J/ data B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 17
- - - + background fits Aaaaa 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 B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 18
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 B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 19
- p - + and - p - - at LHCb - - - + analysis adapted at LHCb to search for - p - + 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 - p - + - p - - 90 % C. L. 3. 4 x 10 -7 4. 6 x 10 -7 95% C. L. 4. 5 x 10 -7 6. 0 x 10 -7 First limits obtained from these channels, similar to those at B-factories from - h- h= , K B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 20
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 4 th 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 - p - + and - p - Only up to 1. 0 fb-1 used by LHCb, currently 3. 0 fb-1 on tape B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 21
THANKS B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 22
BACKUP B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 23
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 -10 s to 10 -11 s. B- + - Mass resolution B. Adeva, University of Santiago de Compostela B - D s + - - B- D 0 + - Neutrino mass acceptance Discrete Symmetries Lisbon 6 th December, 2012
production at LHCb B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 25
Event selection B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 26
- - + mass binning B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 27
Limits from B factories B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 28
Differences between the analyses B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 29
Binning optimisation B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 30
Differences between - p - + and - p - - B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 31
- p - + and - p - - at LHCb B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6 th December, 2012 32
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