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Rare B decays at LHCb

DISCRETE '08,   11–16 December 2008, València. Rare B decays at LHCb. Hugo Ruiz On behalf of the LHCb Collaboration. Institut de Ciències del Cosmos. Introduction. In the SM, b  s only through loops (FCNC) which implies: Processes are rare

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Rare B decays at LHCb

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  1. DISCRETE '08,   11–16 December 2008, València Rare B decays at LHCb Hugo Ruiz On behalf of the LHCb Collaboration Institut de Ciències del Cosmos

  2. Introduction • In the SM, b  s only through loops (FCNC) which implies: • Processes are rare • Powerful to find/constrain NP! • Operator Product Expansion allows parametrizing effect of new physics throughout different b  s observables : • Observables are functions of C’s. • Branching ratios (BR) • Polarizations • Angular distributions • Three examples for LHCb: B0  K*(K+p-)m+m- Bs  f(K+K-)g Bs m+m-

  3. Three interesting rare decays t m+ m+ m+ g g Z, Z, m- m- m- NP? in @ LHCb BR(SM) BR exp Bsfg g polarization • (57+18-12+12-11) 10-6 Belle’08 Largetheory errors on exclusive BRs angular distributions (1.22+0.38-0.32)·10-6 B factories B0K*m+m- TeVatron @ 90% CL (2 fb-1) < 4510-9 (3.35±0.32)·10-9 helicity suppressed BR Bsm+m-

  4. LHCb overview VELO: s(IP) ~ 14mm + 35mm/pT s(t) ~ 40-100 fs L = 2(5)·1032 , 2fb-1/year 10 MHz visible interaction 10 KHz bb (1012 bb / year) Tracking: e = 95% p>5 GeV, 1.9<h<4.9 s(p)/p ~ (0.4 + 1.5 p/TeV)% s(m[Bs →mm]) ~ 20 MeV s(m[K*m+m-]) ~ 15 MeV ECAL: s(E)/E ~ (9.4/√E ⊕ 0.83)% s(m[Bs → fg]): 90 MeV MC: Full sim, pile-up & spillover Photos for FSR in signal Muon, RICH: k-ID: 88% for 3% p misID m-ID: 95% for 5% p/k misID

  5. Bs  fg

  6. g polarization in Bs  fg • SM @ LO: O7 B0XsgR, B0XsgL, tan y AR/AL~ ms/mb ~ 0 • NLO (gluon interchange, etc..) tan y ~ 0.1[1] • SM extensions (left-right-symmetric [2] , unconstrained MSSM [3]) predict large tan y while no change on inclusive BR (bsg) • Interference mixing-decay gives access to g polarization: • In the SM: C=0, S=sin 2y sin f, AΔ=sin 2y cos f, cos f  1(mix + CP odd weak phases) • B-factories: ACP@ BdK*(Ksπ0)g:C=-0.03±0.14, S=-0.19±0.23 [HFAG] • LHCb can study Bsfg: DGs≠0, it probesAΔas well as CandS !! _ B0 XsgR(L) B0 no flavour tagging required XsgL(R) flavour tagging required • [1] B. Grinstein et al, Phys. Rev. D 71,011504 (2005), Phys. Rev. D 73, 014013 (2006) • [2] R. N. Mohapatra et al, Phys. Rev. D 11 (1975) 566; (1979) 334. • [3] H. E. Haber et al, Phys. Rept. 117 (1985) 75.

  7. Bs→fg at LHCb e(t) • Acceptance function: e=e (t) • because of IP, vertex displacement cuts @ trigger and selection • Bd→K*(K+p-)g useful x-check • Selection: e 0.3% • eL0  85% , eHLT 80% • ETg>2.7 GeV • Main background: BXf+ p0 • Bs → fp0< 4% CALO • B → K*0g < 0.3% RICH Yields and purities: Belle: O(1 Bs→fg)/day at U(5S)

  8. Bs→fg at LHCb • b) Background “lifetime” vs mass: •  checked that parameter resolutions are robust under bkg lifetime, B/S, st • Other analysis issues: a) st depends on qf-Bs • Precision on ACP parameters: • Fix ms, Gs, DGs, acceptance, e tagging, background “lifetime” Leftmassside-band Rightmassside-band st(ns) cos qf-Bs •  event-by-event errors used in fit  sy  0.1

  9. B0  K*m+m-

  10. Angular distributions in B0  K*m+m- • Decay described by ql, f, qKand q2  mmm2 • Some observables have low theoretical error • Ex: AFB of ql vs q2 in 1 < q2 <6 GeV2low systs. • For 0 x-ing point s0, cancellation of form factors, • s0SM= 4.36+0.33-0.31 GeV2 [1] BELLE ~230 K*llevts(657M BB) BaBar ~60 K*ll evts (384 M BB) compatible with BR(bs g) right handed weak currents q2(GeV2) CDF ~20 K*mm events (0.9fb-1) [1] M Beneke et al, Eur Phys J C 41 173-188, 2005

  11. B0  K*m+m- at LHCb eL0  90% eHLT 75% • Selection: • Background: • Developed 4 methods, with increasing: • Sensitivity to NP, model independence • Requirementsin terms of statistics, control of acceptance functions ~230@BELLE effect on asymmetry, ex: but can be modeled from mass side-bands

  12. B0  K*m+m- at LHCb AFB An example 0.1fb-1 experiment • Counting AFB in bins of q2 • Precision from linear fit, incl. bkg: • @ 0.07 fb-1 competitive with B-facts • Unbinned AFB vs q2 • No need to assume linearity • Remove dependence on bin-size, fit range s(s0SM) q2(GeV2) AFB forward backward q2(GeV2)

  13. Bd→K*mm at LHCb AT(2) LHCb, 2fb-1 3. Fitting projections on ql, f, qK*: • FL, AT, AFB model-indep. functions of C7, C9, C10. • s(s0) factor ~2 better 4.Full angular analysis: • Requires  2fb-1, full acceptance correction • Can form any observable • Eg [2]: SM SUSY [1] q2(GeV2) AT(4) LHCb 10fb-1 SUSY, large-gluino + positive mass insertion  1s, 2s LHCb SM with theory error bands vs [1] Kruger et al, Phys.Rev.D71:094009, 2500 [2] Egede et al, arXiv:hep-ph/0807.2589 q2(GeV2)

  14. Bs m+m-

  15. Bs m+m- • SM: BR = (3.35±0.32)·10-9 [1] • TeVatron • @ 90% CL (~2 fb-1) < 45·10-9 • final (8 fb-1): < 20·10-9 6x BR! • MSSM: • Ex: Non-Universal Higgs Masses framework (generalization of CMSSM) [2] • bs , Mh>114.4 GeV, (g-2) @ 3.4 from SM, WMAP dark matter density BR(Bs+-)~20x10-9 Excluded @ 95% if BR (Bs m+m- ) < 10-7 20·10-9 NUHM 5·10-9 68%  95% [1] arXiv:hep-ph/0604057 (2006) [2] arXiv:0709.0098

  16. Arbitrary normalization Bs m+m-analysis • Selection e  6% • Categorization of signal likelihood: • Geometry: combination of IPS, B lifetime, isolation, B IP, DOCA • Invariant mass • m identification • Exclude/observe BR from distrib. in 3D bins, use CLs method [1] • BR reach 20% better than in simple cut analysis ( eL0 95% , eHLT 90%) Bs m+m- Bkg, L ~ 0.05 fb-1 Geometry likelihood (*) In many bins! [1] A. L. Read, http://doc.cern.ch/yellowrep/2000/2000-005/p81.pdf

  17. Bs m+m-: calibration • For normalization of BR, use control channels instead of MC • Bs BRs measured with large errors (>20%)  use Bd, B+ • Then the largest syst. (13%) comes from additional factor: • Useful channels: Ex: Calibration of geometry likelihood Bs  m+m- [HFAG] B(s)  h+h- TRIGGERED ON OTHER B Geometry likelihood < 6% per bin for 0.5fb-1 (bkg incl.)

  18. Bs m+m-: performance Discovery 90%CL limit (only bkg observed) BR (x10–9) BR (x10–9) Expected final CDF+D0 limit 5 observation Uncertainty from MC stats on bkg SM prediction 3 evidence SM prediction  L dt (fb–1)  L dt (fb–1) Exclusion 0.25 fb–1 BR < 10-8 2 fb–1 BR < SM Discovery (@ SM BR): 3 fb–13 evidence 10 fb–15 observation

  19. Conclusions • LHCb ready to exploit the B factory known as LHC • With 2fb-1 integrated luminosity: • Bs→μμ: BR exclusion down to SM value • 5s observation at SM value with 10 fb-1 • Bd→K*μμ: σ(s0) ~ 0.5GeV2 • Start having sensitivity to other observables with more complex fits • Bs →fg:from CP asymmetry,sy/y 10% • Rare B decays in LHCb will constrain extensions of SM or find NP

  20. Back-up

  21. More rare decays • Radiative : • Polarization through ancular distributions: • Lb → L0γ, Lb →L*γfor tany, @ 3s >20-25% each with 10fb-1 • B±→ fK±g for cos2y • B → r0g, B → wg for b  d • Other bsll observables: • B+ → K+lldirect CP asymmetry in B  K*m+m-, B+  K+m+m- • small in SM <~0.01, statistical error with 10/fb: ~0.01 • B+ → K+ll for ratio e+e- / m+m- (RK) • SM prediction 0.1% theoretical uncertainty, 4% @ LHCb after 10fb-1 • Bs →fm+m-, Bs/Bd, ¼, flavour tagging  1/15 • Lb→ Lm+m-not yet studied • b  dll: • Bs → K*m+m-, Bs/Bd, ¼, |Vtd/Vts|2=0.2082 ~ 1/25 • Lepton Flavour Violation : Bq → ll’

  22. G(B Km+m-)/G(B Ke+e-)

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