Prospects for Rare B Decay Studies at LHCb B physics @ LHC Pythia - PowerPoint PPT Presentation

Prospects for Rare B Decay Studies at LHCb

B physics @ LHC Pythia production cross section bb correlation p T of B hadron Large gain from lower 100 µ b p T thr. 230 µ b η of B hadron • B phys @ pp machine @ 14 TeV: – σ (bb ̅ ) ~ 500 µ b : 5 ⋅ 10 4 bb ̅ /s @ L = 10 32 – Reduced by factor ~2 @ 8 TeV – Huge background from pp to be suppressed B physics become difficult when Lumi increases: pp interaction #/crossing increases (>>1) resulting in a dirtier environment! 29/07/09 A. Sarti 2

Why going for ‘Rare’ ➡ LHC (+LHCb) ⇒ largest B factory (+ dedicated B det.) ever built: – Every kind of ‘b-hadrons’ are produced: B d , B s , B u , B c , Λ b , ... – The statistics collected will permit to measure BRs in the 10 -3 to 10 -9 range! ➡ Rare decays are a way to probe New Physics processes in an indirect way (virtual particles) contributing to ‘suppressed’ modes trough loops or penguin diagrams – FCNC processes (b → d and b → s) are particularly suited for SM extension searches: the SM rate is highly suppressed (can occur only trough box or penguin diagrams) and NP effect can show up with significant contributions! ➡ Rare decays covered in this talk: – Leptonic: B → µµ , Semileptonic: b → sll, Radiative: B → s γ , Two body: B → hh 29/07/09 A. Sarti 3

(semi)leptonic and radiative decays O perator P roduct E xpansion allows parametrizing effect of new physics throughout different b → s observables : introduce effective Hamiltonian H with new operators O’ i and/or modified Wilson coefficients C’ i Rare B decays give a number of opportunities to constrain these contributions: From G. Hiller [hep-ph/0308180] 29/07/09 A. Sarti 4

B s → µµ ➡ B s → µµ very rare – Effective FCNC +Helicity suppression ~ (m µ /m b ) 2 ➡ SM predictions [G. Isidori e P. Paradisi – B(B s → µµ) = (3.5±0.5) x 10 -9 Phys Lett. B639, 499 (2006)] – B(B d → µµ) = (1.0±0.2) x 10 -10 ➡ Very sensitive to NP with large tan β – MSSM ~ tan 6 β /M 4 A – Large tan β favoured by b → s γ , (g-2) µ , B → τν , etc. Upper limit on BR(B s → µµ) plays crucial role Limit from TeVatron at 90% CL: Current (~2 fb -1 ): <47•10 -9 Expected final (8 fb -1 ): <20•10 -9 ~ 6 times higher than SM! 29/07/09 A. Sarti 5

Bs → µµ analysis ➡ Analysis Strategies – LHCb Combine geometrical information into a likelihood (GL); Divide 3D (GL, Mass, PID) space in N bins and evaluate expected events/bin for signal and signal+bkg ➡ Trigger ~1.5 kHz inclusive µ B s → µµ ➡ Control & normalization channels B s → KK – J/ ψ K + , J/ ψ K * , h + h - : selected with same set of cuts → efficiencies ≃ for all channels and reduced systematics ➡ Performances B s → KK PDF before and after PID cut – Di-µ mass resolution ~20 MeV/c 2 correction extracted from B → h + h - control sample Mass (MeV) ‏ 29/07/09 A. Sarti 6

Yields (S,B) ‏ ➡ Background Background – Main background (b → µ & b → µ, b → µ & b → c → µ) – B → hh << b → µ & b → µ Signal – B c+ → J/ Ψ µ ν dominant of excl. but still small ➡ Event yields [1 nominal year] : – S ~21, B ~ 180 +140-80 @ 2fb -1 in the most sensitive regions ( Δ m<60MeV/c 2 , GL>0.5) ➡ Normalization channel: B + → J/ ψ K + – 2M events @ 2fb -1 ➡ Control channels: – Signal description: B → hh ~200 k @ 2fb -1 – background (from sidebands) ‏ 29/07/09 A. Sarti 7

Results 3 σ observation (sig + bkg is observed) ‏ Uncertainty in background prediction 2009 data 90% CL imit on BR 8 TeV (only bkg is observed) ‏ 14 TeV ➡ LHCb potential LHC (limit) summary: – With 0.1 fb -1 → Improve current limit ATLAS < 7x10 -9 (10 fb -1 ) from Tevatron CMS < 14x10 -9 (10 fb -1 ) – Tevatron final limit reached with ~0.2 fb -1 LHCb < 3.5x10 -9 (~2 fb -1 ) – With 3 fb -1 → measure SM BR at 3 σ 29/07/09 A. Sarti 8

Systematics α ➡ The BR depends on the calibration ch (cal) – BR cal = 5.97±0.02 [1.88±0.07] 10 -5 when using B + → J/ ψ (µ + µ - )K + [B d → K + π - ] – The estimate of α • α TRA (J/ ψ (µ + µ - )K + ) ≃ 0.6 Ratio of tracking efficiency (REC*SEL|REC) from data $! ! 2(4$5#$6789:/;<=$%2(4$5#$:>>6?$9;@;A! ! • α TRI (K + π - ) ≃ 0.4 Ratio of trigger efficiency $ . BAC=DC?D$E=C9F/;/ ! $ ! ! 3 "( 1<':/A$E=C9F/;/ $ (TRIG|SEL) from data ( / 01%$0 5:A$E=C9F/;/ – The main contribution comes from f cal /f B0s ~13% ! - "( ➡ Sensitivity estimated also using robust and cut analysis ! 2 "( ( ()* ()+ (), ()- " ")* ")+ "), ")- * ! " #$%&' ! 29/07/09 A. Sarti 9

b → sll decays ➡ Inclusive decay difficult to access at hadron collider. – Good prospects for excl decays (B → K ℓℓ , K* ℓℓ ). ➡ Hadronic uncertainty reduced in: – Forward-backward asymmetry A FB and s 0 – Invariant mass distributions – Transversal asymmetries – Ratio of µµ and ee modes ➡ Ex. from SM (*) BR(B d  K* µµ )=(1.22 +0.38 -0.32 ) x10 -6 and s 0 =s 0 (C 7 ,C 9 )=4.39 +0.38 -0.35 GeV 2 ➡ NP could contribute @ SM levels – modify BR and angular distributions: sensitivity to SUSY, gravitation exchange, extra- dimensions 29/07/09 A. Sarti 10 (*) Beneke et al hep-ph/0412400

B d → K * µµ BELLE 657M BB arXiv: 0904,0770 ➡ BR = (1.22 +0.38-0.32 )10 -6 agrees to within ~30% with SM (B fact.) – Measure A FB as a function of the µµ invariant mass and determine s 0 . ➡ Signal selection: q 2 µµ IM after selection – Cuts: trk quality, p, p T + B flight lenght, PV pointing and Fisher – Trigger: ε L0 ∼ 90%, ε HLT ∼ 75% ➡ Background: – b → µ, b → µ dominant contribution, symmetric in θ l ⟹ scales A FB – b → µ, b → c → µ significant contribution, asymmetric θ l ⟹ effect on A FB depends on θ l shape S/2$ ‐1 B/2$ ‐1 ε (%) B/S S/√S+B
 Cuts 4
k 1
k 0.7 0.3 60 – Non-resonant NOT included in B Fisher 8
k 3
k 1.4 0.3 80
 estimate (so far) Expected 1k ev. Bfact + Tevatron 29/07/09 A. Sarti 11

Selection and yields ➡ Already with O(100) pb -1 competitive with A FB (s) ‏ L= 0.1 fb –1 , 400 evts B factories results! (BFact @ 2ab -1 ∼ 450) – L = 0.5 fb –1 σ (s 0 ) = ±0.8 GeV 2 – L = 2 fb –1 σ (s 0 ) = ±0.46 GeV 2 – L = 10 fb –1 σ (s 0 ) = ±0.27 GeV 2 ⟹ at the level of present theoretical precision ➡ Other handles come into play with higher s = m 2 µµ [GeV2] statistics (better understood detector) L= 0.5 fb –1 2k evts A FB (s) ‏ – q 2 distribution of B s → Φ µ + µ - and A FB in Λ b → Λ 0 µ (BFact @ 2ab -1 ∼ 450) + µ - decays – Full angular analysis • Fitting A T , A FB , F L instead of cut & count s = m 2 µµ [GeV2] 29/07/09 A. Sarti 12

Angular analysis & R k ➡ Angular analysis F L (s) ‏ doable with L ≥ 2fb -1 – Achieves a ~2 reduction of σ (s 0 ) – Requires acceptance correction s = m 2 µµ [GeV 2 ] ➡ NP contribution can be probed also by measuring R k LHCb expects 10k ee and 20k µµ events in 10fb -1 achieving σ (R k )/R k ~ 4% 29/07/09 A. Sarti 13

Radiative decays ➡ Current exp. status (B factories): – BR(B d → X s γ ): rate in agreement with SM, 5% relative error – CP asymmetry A CP (t) [ Γ (B ̅ )- Γ (B)/sum] in B d → K*(K s π 0 ) γ : C=-0.03±0.14, S=-0.19±0.23 [HFAG] B 0 X s γ R(L) ➡ In the SM: C=0, S=sin 2 ψ sin φ , A Δ =sin 2 ψ _ cos φ , where φ (s,d) is the sum of mix and X s γ L(R) B 0 CP odd weak phases, while ψ is related to the decay rate to polarized photon states ➡ LHC experiments can perform time dependent measurement in Bs → φγ and Λ decays – As ΔΓ s ≠ 0, B s → φγ decay probes A Δ as well as C and S (with φ s small A Δ reduces to sin 2 ψ ) Br (B s → φγ ) = (57 +18-12+12-11 ) 10 -6 Belle’08 Br (B s → φγ ) = (43°±14) 10 -6 (theo) 29/07/09 A. Sarti 14

Yields B s → φγ ➡ B → K *0 γ – A CP < 1% in SM, up to 40% in σ ~ 90 MeV/c 2 B s → φγ SUSY: can be measured in σ ~ 80 fs LHCb at <% level. – direct CP-asymmetry, calibration channel for B s → φγ ➡ B s → φγ – No mixing-induced CP asymmetry in SM, up to 50% in SUSY. – Main background: B → X φ + π 0 • B s → φπ 0 < 4% CALO • B → K *0 γ < 0.3% RICH ➡ Λ b → Λ 0 γ , Λ b → Λ * γ – Right-handed component of photon polarization O(10%) in SM. Can be higher BSM. Measured from angular distributions of γ and hadron 29/07/09 A. Sarti 15

CP parameters resolution tan ψ can be measured >20% with Λ b → Λ 0 γ and Tagging 0.5$ ‐1 2$ ‐1 F.Legger & T.Schitienger, LPHE 2006-003,LHCb 2006-013 >25% with Λ b → Λ ∗ γ at 3 σ in 5 years (L = 10fb -1 ) σ (A Δ ) No 0.3 0.22 σ (S,
C)
 Yes 0.2 0.11 NP can modify r Equivalent of 13mins of simulated BB events – already see a peak! True K* γ signal events Combinatorial background 3 σ evidence of right-handed Photon polarization component to 21% with 10 fb –1 Mode Parameter Value L B s → φγ sin2 ψ σ ≈ 0.2 2fb -1 Λ b → Λ 0 γ / Λ b → Λ * γ tan ψ σ ≈ 0.07( Λ 0 )/0.08( Λ * ) 10fb -1 B 0 → K S π 0 γ Bfact sin2 ψ σ =0.4 Sep 2008 29/07/09 A. Sarti 16