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 measurements

And 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 polarization

Measured 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

tmStmCtA

ss

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 distributions

AFB asymmetry vs m2μμ

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

AF

B

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)

AF

B2 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 predicted

SM: β(Bsμμ) = (3.55±0.33) x 10-9

Very sensitive to (pseudo) scalar operators

MSSM ~ tan6β/M4A

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 @ 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

itra

ry u

nit

s

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10-7

2x10-8

(~0.05 fb-1)

5x10-9

(~ 0.4 fb-1)

Integrated luminosity (fb–1)

BR

(x1

0–9)

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 MeV

BK*μμ ~14 MeV

BsΦγ ~90 MeV

σ(proper time)

BsΦγ ~50-110 fs

Trigger: 1MHz @ L0 2 kHz @ HLTB signature : “large” Pt and displaced tracks

HLT: ~ 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 amplitudes

Fit individual angular distributions (θl,Φ,θK*) vs m2μμ

2

0

2

||

2

2

02 )(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