Lake Louise Winter Institute 2008 1

Outlook: Introduction LHCb performance Radiative decays: CP violation BsΦγ Backward-forward Asymmetry BK*μμ Branching ratio of very rare Bsμμ Conclusions

Prospects for rare B decays in LHCbJose A. Hernando

(CERN, on leave Universidade de Santiago de Compostela, Spain)

[On behalf of the LHCb collaboration]

Lake Louise Winter Institute 2008 2

LHCb experiment and conditionsLHCb experiment and conditions

Luminosity range 2-5 1032 cm-2s-1 Nominal integrated luminosity 2 fb-1 / year (107s)

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)

Total 10 fb-1

•P. Vazquez

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Rare B decaysRare B decays

LHCb Physics CP violation in B system: using tree and penguins processes (NP) Rare B decays: test FCNC (bs)

•V. Gligorov

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. bsγ) strongly limit extensions of SM• Indirect search of new particles: “visible” via loops

Experimental observables: ratios, asymmetries, branching ratios to leptons

•bsγ Radiative decays:

•BK*γ, BsΦγ

•ΛbΛγ, ΛbΛ*γ

•Bρ0γ, Bωγ

bsll :•BK*μμ,

•B+K+μμ, B+K+ee

Bqll

Bsμμ

LFV Bqll’

BsμeACP(t) (BsΦγ) AFB(BK*μμ)

β(Bsμμ)

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BsBsΦΦγγ

Motivation:Inclusive BR in agreement with SM LHCb can perform exclusive measurementsAnd test the γ polarization

In SM is bsγ is predominantly (at 0(ms/mb) left handed

CP violation in the mixing and decay depends on the γ polarizationMeasured in BK*(Ksπ0)γ ACP at Belle[3], BaBar (SK*γ = -0.08 ±0.31±0.05) [4]

LHCb can measure time-dependent CP asymmetry of BsΦγ

,)2/cosh()2/sinh(

)sin()cos()(tt

tmStmCtAss

ssCP

[1]NNLO

•[2]HFAG

•[1] hep-ph/0607258

•[2] arXiv/0704.3575 hep/ex

•[3] hep-ph/0507057, Phys.Rev D72,051103

•[4] arXiv/0708.1614 hep/exp

•[5] hep-ph/0410036

[5] SM: C~0, S~-0.1±0.1%, AΔ ~ sin2ψ

Ψ fraction of “wrong” polarization

ACP(t) (BsΦγ)

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AACPCP(t)(t) for B for BssΦΦγγ

Full detector simulationmain background bb (37 M)

Selection Et(γ) > 2.8 GeV,

Yields (2 fb-1):Total efficiency ~ 0.3%

Background bb inclusive: B/S ~ 0.55 @ 90 CL

Issues: Acceptance function a(t) σ(t) as function of topology

•MC stats: 37 M bb events

2 fb-1

σ(AΔ) 0.20

σ(S,C) 0.11

2 fb-1

BK*γ 72 k

BsΦγ 11 k

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AAFBFB(B(BKK**μμμμ))

Motivation:BR in agreement with SM β(BK*μμ) 1.22+0.38

-0.3210-6

But NP can show us in angular distributionsAFB asymmetry vs m2

μμ

Decay described with 3 angles (θl,Φ,θK*)

AFB of μ in θl vs m2μμ

SM zero point well predicted:SM: [1] 4.36+0.33

-031 GeV2

BaBar and Belle [2] Measurements

•[1] hep-ph/0412400

•[2] hep-ph/0603018

AFB

M2 (GeV2)

BELLE ’06

m2

[GeV2]

AFB(m2μμ) theory illustration

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AAFBFB(B(BKK**μμμμ))

Yields Efficiency ~ 1%

Background B/S 0.5+0.2 @ 90% CL bb: bμ,bμ bb: bμ,c (cμ)

Issues Acceptance function a(θl,m2

μμ,)

Sensitivity 0.07 fb-1 competitive with BaBar & Belle

An example 0.5fb-1 experiment

An example 0.1fb-1 experiment

M2 (GeV2)

AFB2 fb-1

BK*μμ 7.3 k

0.5 fb-1 2 fb-1 10 fb-1

σ(s0) 0.8 GeV2 0.5 GeV2 0.3 GeV2

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ββ((BsBsμμμμ))

Motivation Bsμμ very rare

Helicity suppress (mμ/mB)2

SM well predictedSM: β(Bsμμ) = (3.55±0.33) x 10-9

Very sensitive to (pseudo) scalar operators MSSM ~ tan6β/M4

A

MSSM (NUHM) fit favor large tanβ ~ 30μ g-2 results (deviate from SM 3.4 σ)

Current limits [2] CDF BR < 4.7 10-8 90% CL @ 2fb-1

[3] D0 BR < 7.5 10-8 90% CL •[1] arXiv:0709.0098v1 [hep-ph]

•[2] arXiv:0712.1708v1 [hep-ex]

•[3] arXiv:0705.300v1 [hep-ex]

•[1]

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ββ((BsBsμμμμ))

Small signal and large background, but Efficient trigger: ~1.5 kHz inclusive μ. Di-μ Mass resolution: σ ~20 MeV Vertexing: GL: Combine geometrical variables

Background: Main background (bμ,bμ, bμ , bcμ ) Bhh, small compared with bμ,bμ Bc+J/Ψμν dominant of exclusive, but still small

Analysis: Divide (GL, Mass) space in N bins Expected events/bin for signal, signal+bkg

Yield : Total efficiency ~10% (all GL values) S ~30 events, Bkg ~ 83 @ 2fb-1 (GL>0.5)

Control channels: Signal description: Bhh ~200 k @ 2fb-1

background (from sidebands)Normalization: B+J/Ψ K+ 2 M @ 2fb-1

Red: signalBlue: bb inc.Black: b μb μGreen: Bc+ J/Ψμν

•GL (geometry)

•Mass (MeV)

Bs μμ

Bs KK

• arb

itrar

y un

its

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10-7

2x10-8

(~0.05 fb-1)

5x10-9

(~ 0.4 fb-1)

Integrated luminosity (fb–1)

BR

(x10

–9)

Uncertainty in background prediction

Expected final CDF+D0 limit

SM prediction

90% CL imit on BR (only bkg is observed)

[1] arXiv:0709.0098v1

SM agreement2 fb–1 3 evidence6 fb–1 5 observation

Exclusion:0.1 fb–1 BR < 10-8 0.5 fb–1 < SM

ββ((BsBsμμμμ))

•[1]

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ConclusionsConclusions

LHCb finishing installation, getting ready for 1st 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

Bsμμ excluded at SM value with 0.5 fb-1 AFB(B K*μμ) σ(s0) ~0.8 GeV2 @ 0.5 fb-1

And above 2 fb-1 Bsμμ evidence if SM 2 fb-1, observation 6 fb-1

BK*μμ σ(s0) ~0.5 (0.3) GeV2 @ 2 (10) fb-1

other observables: A(2)T, FL

BsΦγ ACP asymmetry >2 fb-1

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Particle ID

π-K separation:Kaon ID ~ 88%Pion mis-ID ~ 3%

μ ID Bqhh (~0.5%)2

(mu-ID eff 95%)

LHCb expected performanceLHCb expected performance

Mass resolution

Vertexing

σ(Mass) Bsμμ ~20 MeVBK*μμ ~14 MeVBsΦγ ~90 MeV

σ(proper time) BsΦγ ~50-110 fs

Trigger: 1MHz @ L0 2 kHz @ HLTB signature : “large” Pt and displaced tracksHLT: ~ 1.5 kHz μ + di-μ inclusive sample

efficiency (L0xHLT)Bsμμ ~90 %BK*μμ ~70 %B Φγ ~40 %

•P. Vazquez

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AA(2)(2)T T ,F,FTT (B (BK*K*μμμμ))

Other observables [1] in BK*μμExpresed in terms of transversity amplitudesFit individual angular distributions (θl,Φ,θK*) vs m2

μμ

20

2

||2

202 )(

AAA

AqFL

2

||2

2

||2

2)2( )(AA

AAqAT

2 fb-1

Asymmetry AT(2) Longitudinal polarization FL

SM NLOMSSM tan=5MSSM tan=5

2 fb–1 10 fb–1

AT(2) 0.42 0.16

FL 0.016 0.007

AFB 0.020 0.008

Sensitivity with

•[1] hep-ph/0612166

An example 2 fb-1 experiment