Lepton Number Violation and Lepton Flavour Violation

B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6th December, 2012 1

Search for Majorana neutrinos in B-decays ,lepton flavour violation in - --+ ,and baryon number violation with LHCb

Lepton Number Violationand Lepton Flavour Violation

54 institutions, 15 countries

LHCb collaboration

B. Adeva, University of Santiago de Compostela Discrete Symmetries Lisbon 6th December, 2012

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SEARCH FOR LEPTON NUMBER VIOLATION IN B DECAYS


Search for Lepton Number Violation at LHCb

Phys. Rev. D 85, 11204 (2012) arXiv:1201.5600v2 b

du

c

¯

W-

W-

N

-

-

a)

b)

c)

Virtual Majorana neutrino

Resonant neutrino production

Also resonant production

Impressive limits to date from nuclear 0- decay on electrons: O(1025) years.Yet heavy quark mesons could undergo the same process with muons:

Vcb

Vub

Annihilation

New

Pioneered by Mark II


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Limits from B-factories

Belle results on B D+l-l- Based on 772106 BB events at (4s), collected withthe Belle detector at KEKB

BaBar results on B h+l-l- with h=K, Based on 471106 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


Analysis general aspects

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

Phys. Rev. D 85, 112004 (2012)

B- J/ K- J/ +- B- (2s) K- (2s) + - J/

Total efficiency + - K- : 0.99 0.01 % Total efficiency + - + - K- : 0.078 0.002 %


Majorana neutrinos B- +- -

B- +- -

K// misid rates from D* +D0(K-+) K0

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

Phys. Rev. D 85, 112004 (2012)


Majorana neutrinos B- D+(*)- -

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)

Phys. Rev. D 85, 112004 (2012)

Limits determined using

and taking the vaue in which such probability is 0.05 (95 % C.L.)

obsNN

B)(SN

obs N!

eB)(S)NP(N

Total systematics : 8.8 % (D+ ) , 8.2 % (D*+)Dominated by branching ratios of normalization channels and trigger efficiencies

6 evts 6.9 1.1 backg. 5 evts 5.9 1.0 backg.


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-)

Phys. Rev. D 85, 112004 (2012)

B- D0+- -

D0 reconstructed via decay to K

MN spectra consistent with polynomial backgs. estimated from sidebands

MN


Mass-dependent Majorana neutrino limits

2 D. Delepine, G. Lopez Castro, and N. Quintero, Phys. Rev. D84 (2011) 096011, arXiv:1108.6009.

A model dependent calculation2

was used for B- D0 +-- , but the mode +-- is more sensitive.

For B- D+(*)- - , limits on the coupling require calculation of hadronic form factor (as for 0 decay) .

Phys. Rev. D 85, 112004 (2012)

B- +- - B- Ds+- - B- D0+- -

Upper limits (95% C.L.) are set at each MN mass by searching a signal within 3N in small steps.


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Limits on Majorana coupling |V4 |

B LHCb

B- +--

Mass dependent upper limits on the coupling |V4 | of a 4th generation Majorana neutrino to a muon and virtual W 1.

1 A. Atre, T. Han, S. Pascoli, and B. Zhang, JHEP 05 (2009) 030, arXiv:0901.3589.

Phys. Rev. D 85, 112004 (2012)


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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)

Summary on LNV in B decays


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SEARCH FOR LEPTON FLAVOR AND BARYON NUMBER VIOLATION


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- --+ 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--+


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current status - --+

But can also set limits a hadron colliders …

- --+ yet to be observed Current experimental limits (at 90% C.L.):


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- --+ 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%)

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

Systematics cancel in ratio of efficiencies


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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

5s 10)12.033.1()(KK)(

π)(KK)(D

B

B

B

Background subtracted


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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

- --+ signal and background discrimination


- --+ 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


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


- 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


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 |V4| 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 - p-+ and - p--

Only up to 1.0 fb-1 used by LHCb, currently 3.0 fb-1 on tape


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THANKS


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BACKUP


Mass and lifetime acceptance for on-shell Majorana neutrinos

B- +-- B- Ds+-- B- D0 +--

Finite neutrino lifetimes ignored so far (except for off-shell production)Sensitivity is lost for lifetimes longer than 10-10s to 10-11s.

Neutrino mass acceptanceMass resolution


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production at LHCb


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Event selection


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--+ mass binning


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Limits from B factories


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Differences between the analyses


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Binning optimisation


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Differences between - p( -+ and - p--


- p( -+ and - p-- at LHCb

Documents

Lepton Number Violation and Lepton Flavour Violation