Prospects for rare B decays in LHCb Jose
Prospects for rare B decays in LHCb Jose A. Hernando (CERN, on leave Universidade de Santiago de Compostela, Spain) [On behalf of the LHCb collaboration] Outlook: § Introduction § LHCb performance § Radiative decays: CP violation Bs Φγ § Backward-forward Asymmetry B K*μμ § Branching ratio of very rare Bs μμ § Conclusions Lake Louise Winter Institute 2008 1
LHCb experiment and conditions • P. Vazquez Luminosity range 2 -5 1032 cm-2 s-1 Nominal integrated luminosity 2 fb-1 / year (107 s) Total 1012 bb produced/year B, Bs, B+ But large backgrounds and small BR 0(10 -6)of relevant decays 10 MHz visible interaction (1% bb) Lake Louise Winter Institute 2008 10 fb-1 2
Rare B decays • V. Gligorov ØLHCb Physics § CP violation in B system: using tree and penguins processes (NP) § Rare B decays: test FCNC (b s) Ø Rare B decays § FCNC has a pivotal roll: • They are suppressed in SM, only realized via boxes or penguins • NP can show up as the same level of SM • Present results (i. e. b sγ) strongly limit extensions of SM • Indirect search of new particles: “visible” via loops § Experimental observables: ratios, asymmetries, branching ratios to leptons • b sγ Radiative decays: b sll : Bq ll • B K*γ, Bs Φγ • B K*μμ, Bs μμ • Λb Λγ, Λb Λ*γ • B+ K+μμ, B+ K+ee • B ρ0γ, B ωγ ACP(t) (Bs Φγ) AFB(B K*μμ) Lake Louise Winter Institute 2008 β(Bs μμ) LFV Bq ll’ Bs μe 3
![Bs Φγ [1]NNLO • [2]HFAG Motivation: Inclusive BR in agreement with SM ACP(t) (Bs](http://slidetodoc.com/presentation_image_h2/ae4196df5491b5bea6b6da806e376269/image-4.jpg "Bs Φγ [1]NNLO • [2]HFAG Motivation: Inclusive BR in agreement with SM ACP(t) (Bs")
Bs Φγ [1]NNLO • [2]HFAG Motivation: Inclusive BR in agreement with SM ACP(t) (Bs Φγ) LHCb can perform exclusive measurements And test the γ polarization In SM is b sγ is predominantly (at 0(ms/mb) left handed CP violation in the mixing and decay depends on the γ polarization Measured in B K*(Ksπ0)γ ACP at Belle[3], Ba. Bar (SK*γ = -0. 08 ± 0. 31± 0. 05) [4] LHCb can measure time-dependent CP asymmetry of Bs Φγ • [1] hep-ph/0607258 • [2] ar. Xiv/0704. 3575 hep/ex • [3] hep-ph/0507057, Phys. Rev D 72, 051103 • [4] ar. Xiv/0708. 1614 hep/exp • [5] hep-ph/0410036 [5] SM: C~0, S~-0. 1± 0. 1%, AΔ ~ sin 2ψ Ψ fraction of “wrong” polarization Lake Louise Winter Institute 2008 4
ACP(t) for Bs Φγ • MC stats: 37 M bb events Full detector simulation main background bb (37 M) Selection Et(γ) > 2. 8 Ge. V, Yields (2 fb-1): Total efficiency ~ 0. 3% 2 fb-1 B K*γ 72 k Bs Φγ 11 k Background bb inclusive: B/S ~ 0. 55 @ 90 CL Issues: Acceptance function a(t) σ(t) as function of topology 2 fb-1 σ(AΔ) 0. 20 σ(S, C) 0. 11 Lake Louise Winter Institute 2008 5
AFB(B K*μμ) AFB(m 2μμ) theory illustration Motivation: BR in agreement with SM β(B K*μμ) 1. 22+0. 38 -0. 3210 -6 But NP can show us in angular distributions AFB asymmetry vs m 2μμ Decay described with 3 angles (θl, Φ, θK*) AFB of μ in θl vs m 2μμ SM zero point well predicted: AFB m 2 [Ge. V 2] SM: [1] 4. 36+0. 33 -031 Ge. V 2 Ba. Bar and Belle [2] Measurements BELLE ’ 06 • [1] hep-ph/0412400 • [2] hep-ph/0603018 Lake Louise Winter Institute 2008 Mmm 2 (Ge. V 2) 6
2 fb-1 Yields Efficiency ~ 1% B K*μμ 7. 3 k AFB(B K*μμ) An example 0. 1 fb-1 experiment Background B/S 0. 5+0. 2 @ 90% CL bb: b μ, b μ bb: b μ, c (c μ) Issues An example 0. 5 fb-1 experiment Acceptance function a(θl, m 2μμ, ) Sensitivity 0. 07 fb-1 competitive with Ba. Bar & Belle σ(s 0) 0. 5 fb-1 2 fb-1 10 fb-1 0. 8 Ge. V 2 0. 5 Ge. V 2 0. 3 Ge. V 2 Lake Louise Winter Institute 2008 Mmm 2 (Ge. V 2) 7
β(Bs μμ) Motivation Bs μμ very rare Helicity suppress (mμ/m. B)2 SM well predicted SM: β(Bs μμ) = (3. 55± 0. 33) x 10 -9 Very sensitive to (pseudo) scalar operators MSSM ~ tan 6β/M 4 A MSSM (NUHM) fit favor large tanβ ~ 30 μ g-2 results (deviate from SM 3. 4 σ) Current limits [2] CDF BR < 4. 7 10 -8 90% CL @ 2 fb-1 [3] D 0 BR < 7. 5 10 -8 90% CL • [1] ar. Xiv: 0709. 0098 v 1 [hep-ph] • [2] ar. Xiv: 0712. 1708 v 1 [hep-ex] • [3] ar. Xiv: 0705. 300 v 1 [hep-ex] Lake Louise Winter Institute 2008 8
β(Bs μμ) Efficient trigger: ~1. 5 k. Hz inclusive μ. Di-μ Mass resolution: σ ~20 Me. V Vertexing: GL: Combine geometrical variables Background: Main background (b μ, b μ , b c μ ) B hh, small compared with b μ, b μ Bc+ J/Ψμν dominant of exclusive, but still small • arbitrary units Small signal and large background, but Red: signal Blue: bb inc. Black: b μb μ Green: Bc+ J/Ψμν • GL (geometry) Analysis: Divide (GL, Mass) space in N bins Expected events/bin for signal, signal+bkg Yield : Bs μμ Total efficiency ~10% (all GL values) S ~30 events, Bkg ~ 83 @ 2 fb-1 (GL>0. 5) Bs KK Control channels: Signal description: B hh ~200 k @ 2 fb-1 background (from sidebands) Normalization: B+ J/Ψ K+ 2 M @ 2 fb-1 Lake Louise Winter Institute 2008 • Mass (Me. V) 9
β(Bs μμ) 10 -7 BR (x 10– 9) 90% CL imit on BR (only bkg is observed) 2 x 10 -8 (~0. 05 fb-1) Expected final CDF+D 0 limit Uncertainty in background prediction 5 x 10 -9 (~ 0. 4 fb-1) SM prediction • [1] Integrated luminosity (fb– 1) Exclusion: 0. 1 fb– 1 BR < 10 -8 0. 5 fb– 1 < SM [1] ar. Xiv: 0709. 0098 v 1 SM agreement 2 fb– 1 3 evidence 6 fb– 1 5 observation Lake Louise Winter Institute 2008 10
Conclusions LHCb finishing installation, getting ready for 1 st collisions Rare B decays in LHCb will constrain extensions of SM or find NP Already with first “year” data 0. 1, 0. 5 fb-1 Bs μμ excluded at SM value with 0. 5 fb-1 AFB(B K*μμ) σ(s 0) ~0. 8 Ge. V 2 @ 0. 5 fb-1 And above 2 fb-1 Bs μμ evidence if SM 2 fb-1, observation 6 fb-1 B K*μμ σ(s 0) ~0. 5 (0. 3) Ge. V 2 @ 2 (10) fb-1 other observables: A(2)T, FL Bs Φγ ACP asymmetry >2 fb-1 Lake Louise Winter Institute 2008 11
LHCb expected performance Trigger: 1 MHz @ L 0 2 k. Hz @ HLT Mass resolution B signature : “large” Pt and displaced tracks HLT: ~ 1. 5 k. Hz μ + di-μ inclusive sample efficiency (L 0 x. HLT) Bs μμ ~90 % B K*μμ ~70 % B Φγ ~40 % σ(Mass) Bs μμ ~20 Me. V B K*μμ ~14 Me. V Bs Φγ ~90 Me. V • P. Vazquez Particle ID Vertexing σ(proper time) Bs Φγ ~50 -110 fs π-K separation: Kaon ID ~ 88% Pion mis-ID ~ 3% Lake Louise Winter Institute 2008 μ ID Bq hh (~0. 5%)2 (mu-ID eff 95%) 12
![A(2)T , FT (B K*μμ) Other observables [1] in B K*μμ Expresed in terms](http://slidetodoc.com/presentation_image_h2/ae4196df5491b5bea6b6da806e376269/image-13.jpg "A(2)T , FT (B K*μμ) Other observables [1] in B K*μμ Expresed in terms")
A(2)T , FT (B K*μμ) Other observables [1] in B K*μμ Expresed in terms of transversity amplitudes Fit individual angular distributions (θl, Φ, θK*) vs m 2μμ Asymmetry AT(2) Longitudinal polarization FL 2 fb-1 SM NLO MSSM tan =5 Sensitivity with 2 fb– 1 10 fb– 1 AT(2) 0. 42 0. 16 FL 0. 016 0. 007 AFB 0. 020 0. 008 An example 2 fb-1 experiment • [1] hep-ph/0612166 Lake Louise Winter Institute 2008 13
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