QCD 与强子物理研讨会， 2010 年 8 月 4 － 10 日，威海

Prospects of Flavor Physics at the LHC

高原宁清华大学高能物理研究中心

2010/8/6 1Y. Gao, Prospects of flavor physics at the LHC

Outline(very selective view of the field)

• Early results from the LHC experiments

• LHC as a B factory

• Remarks on flavor physics

• Status and prospects - CKM matrix - Bs mixing - Rare decays

• Conclusion

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LHC is running…

• ~400 nb-1/experiment delivered to ATLAS, CMS , LHCb• Date collected with high efficiencies (> 90%) • Much more underway…

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LHCb operation

Quarkonia production

• Signals seen from data !

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Quarkonia production

• J/ in central region

• J/ in forward region

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CMS preliminary : (4≤pT≤30GeV/c and |y| <2.4)

BR(J/ψ→µ+µ−)·σ(pp→J/ψ + X) = (289.1 ± 16.7(stat) ± 60.1(syst)) nb

LHCb preliminary : (pT≤10GeV/c and 2.5<y <4)

σ(pp→J/ψ + X) = (7.65 ± 0.19(stat) ± 1.10(syst) +0.87

-1.27 ) b

Data favor neither color singlet nor color octet model.

Quarkonia production

• 1s, 2s and 3s→μ+μ-

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σ(pp →Υ(1S)X)·B(Υ(1S)→µ+ µ−)=(8.3±0.5±0.9±1.0)nb(Assuming no polarization and integrated over |y| <2.0)

bb cross-section • bb in central region

• bb in forward region

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CMS preliminary : (4≤pT≤30GeV/c and |y| <2.4)

BR(J/ψ→µ+µ−)· σ(pp→bX→ J/ψX’) = (56.1 ± 5.5(stat) ± 7.2(syst) )nb

LHCb preliminary : (pT≤10GeV/c and 2.5<y <4)

σ(pp→ bX→ J/ψX’) = (0.81 ± 0.06(stat) ± 0.13(syst) ) b

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bb cross-section • bb cross-section from BD0X, with D0 K - correlate D0 with of right (wrong) sign

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Fully reconstructed B events

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Flavor physics at hadron colliders

Tracking• We need good Vertexing Particle Identification

Flavor program at LHC• LHC is also a b-factory

• Next generation of flavor program

• 40% Bu , 40% Bd, 10% Bs, 10% b-baryons

Bs is very hard at (Super-)B factories, but may be crucial for NP…

LHCb Experiment

It is not very easy to realize MFV in theoretical models

Tracking at ATLAS, CMS and LHCb

It is not very easy to realize MFV in theoretical models

Hadron ID

It is not very easy to realize MFV in theoretical models

Remarks on flavor physics

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• It is not easy to reconcile the 2 points: - The SM is very successful in describing quark mixing - New physics TeV

Minimal Flavor Violation (MFV)

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• In the Standard Model

• MFV Hypothesis

Yukawa coupling is unique source of flavor symmetry breaking also beyond the SM

It is not very easy to realize MFV in theoretical models

CKM Matrix

• At first sight the global CKM fit shows an excellent consistency.

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CKM Matrix

• Closer inspection shows some tensions …

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CKM Matrix • The sin2 & Br(B) tension: closer look

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CKM Matrix

• LHCb will measure in trees and loops

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Bs mixing

• Recent results from CDF & D0

- Bs J/ : 2.1 sigma -> 1.0 sigma

-> measures sin2s

- D0 observed a 3.2 sigma anomalous in like-sign dimuon charge asymmetry

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Bs mixing

• At LHCb, PID may help event selection and flavor tagging

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Bs mixing

• Prospects

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Bs,d →μ+μ−

• Very small in SM,

could be enhanced, e.g. in MSSM

• Current CDF (World’s best) limit

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10

9

10)1.01.1()(Br

10)3.06.3()(Br

d

s

B

B

.).%95(101.9: Expected

.).%95(106.7)(Br

.).%95(103.3: Expected

.).%95(103.4)(Br

9

9

8

8

LC

LCB

LC

LCB

d

s

Bs,d →μ+μ− at LHCb

• Ways to enhance S/B

- Vertexing - Invariant mass - Muon ID

• Using control samples

• So far data consistent with MC background predictions

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Bs →μ+μ− at LHCb

• LHCb roadmap

c.f. MC studies at 14 TeV

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B K* +-

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B K* +-

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B K* +-

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• Measurements seem favor • LHCb sensitivity:

0.1 fb-1 ~ B Factories

1.0 fb-1 ~ 4 sigma exclusion of SM (Assuming Belle central value)

Conclusion

• Flavor programs at LHC (and Super B Factories) will provide further precise measurements on CKM matrix elements, (very) rare decay rates which are sensitive to new physics beyond the Standard Model.

• Theory – Experiment interplay is essential to maximize the potential of these (expensive) programs.

• Complementary to experiments at high energy frontier, flavor physics will help us to explore features of the new physics, hopefully in near future.