# Presentation: 465665

## γ from B0(s)→h+h’-

- γ from B0(s)→h+h’-

**G. Volpi (Univ. and INFN Pisa)**
**on behalf of the CDF Collaboration**
**CKM 2008, Rome Oct. 09, 2008**

## Introduction

- Angle γ=arg(Vub*)‏: the least known of CKM matrix
- In 1999 Fleischer proposed of using time-dependent asymmetries of flavor tagged Bd→ππ and Bs→KK decays to measure , under assumption of U-spin symmetry.
- Bs→KK was not yet observed, ∆ms not yet measured, low-BR and tagging.
- CDF started the B→hh analysis with above measurement of  as ultimate goal.
- Necessary intermediate steps: untagged measurement of decay-rates (BR and CP-violating asymmetries in flavor-specific modes)
- Proved to be very prolific analysis:
-  observation of Bs→KK [**Phys.Rev.Lett.97:211802,2006**],
-  observation of Bs→Kπ, observation of Λb→pπ/K.
- Besides their intrinsic interest, these intermediate results provided already powerful constraints on gamma, especially when combined among them and with other observables.
- This talk describes the current status of the B→hh analysis at CDF, its impact on the inferring gamma and the near-future plans

- gamma from  B(s)->hh

- CKM 2008 - G. Volpi

## Triggering on Bhh in p-pbar collisions

- Trigger performance is crucial

- Reject light-quark background
- Two oppositely-charged tracks
- Transverse opening angle;
-  pT1 ,  pT2;
-  pT1+ pT2.
- Reject multi-prongs and backgrounds
- B  impact parameter.

- gamma from  B(s)->hh

- CKM 2008 - G. Volpi

## B->hh sample 

- B->hh sample

- Further observables:
- 3D Vertex chi-square
- Isolation:
- Effective in reducing light-quark background, 85% efficient. (analog of event shape at e+e-)‏

- 3 sets of cuts:
-  Loose: optimize for ACP(B0K+-)
- (good for all three “large modes”)‏
-  Tight: optimize for B0sK-+
- (good for all “rare modes”)‏
- Tight+Pt cut for the Λb

**# evts: 6059±159**

- gamma from  B(s)->hh

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## Challenge of the Analysis

- Several overlapping signals contribute to a single unresolved peak.
- Challenge is to determine the sample composition.
- Signal separation needs to combine kinematic and PID into ML fit.
- Determining sample composition gives the relative BRs and CP violatings after correcting for detector acceptance  and selection efficiency

- gamma from  B(s)->hh

- CKM 2008 - G. Volpi

## Signal composition

- Correlation between arbitrary  mass assignment and signed momentum imbalance distinguish modes function of α variable

- dE/dx parameterized using D*+(-)→D0π+(-) sample

**dE/dx residual**

**1.5****σ**

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- CKM 2008 - G. Volpi

## Unbinned Log-likelihood fit

- Unbinned ML fit using 5 observables

- Signal shapes:  from MC and analytic  formula Background shapes: from data sidebands

- sign and bckg shapes from D0   K-π+

- fraction of jth mode, to be determined by the fit

- mass term

- PID term

- momentum term

***α***

***p******tot***

**2.1****σ**** sep  KK/****ππ**

- 

- K

- 

- K

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## Fit results

- Determination of sample composition provides
- Observation of new Bhh mode: Bs→Kπ
- First observation of Λb→ph decays: Λb →pπ and Λb→pK
- Unique sample of Bs→KK
- B-factories-like samples of Bd →ππ and Bd→Kπ

- A wealth of measurements is extracted
- BR(Bs→Kπ) and ACP(Bs→kπ)
- Improved BR(Bs→KK)
- BR(Λb→pπ) and ACP(Λb→pπ)
- BR(Λb→pK) and ACP(Λb→pK)

- All BR are measured relative to the reference mode Bd → Kπ to cancel common systematic uncertainties

- Constrains on gamma!

- gamma from  B(s)->hh

- CKM 2008 - G. Volpi

## Impact on γ angle

- Measured BR(Bs→Kπ) e ACP provide important inputs to constrain gamma.
- Recent update by Chiang, Gronau, and Rosner on γ angle
- Phys.Lett.B664:169-173,2008
- U-spin simmetry
- SU(3) breaking correction
- γ and δ not in perfect agreement with other determinations
- γ=60° obtained only assuming:
- Br 42% greater (need a better determination of fs/fd)‏
- Large difference between (δs-δd)>20°

- gamma from  B(s)->hh

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## Impact on gamma (2)

- We update the measurement:
- This is the largest Bs→KK sample available (1300 cands), using HFAG 2008 we derive a BR
- Systematic uncertainties are large mostly due to the fs/fd uncertainty
- This is the sample on which the time-dependent measurement will eventually be carried out.

- Update

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## Other results

- B0 CP competitive with B factories
- Lipkin-Gronau proposed a model-independent SM test based on combining B0 and B0s differential rates
-  First world measurements of BR and ACP of 2-body charmless B baryon decays:

**SM=-1**

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## Prospects

- 2.7 fb-1 data sample ready (sample enriched of 2.1 times)
- Updated measurements expected soon
- It is less than half of the expected integrated luminosity goal

**Present untill this point**

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## B0s DCPV resolution projections

- B0s DCPV resolution projections

- Assuming SM hypothesis  Gronau-Lipkin relation true

- 5σ are not so far away...

- Using 2.7 fb-1 >3σ

- Yield Factor

- gamma from  B(s)->hh

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## Time-dependent asymmetries

- Ingredients for a time-dependent             ACP(t) ready:
- large samples (2700 ev in ~3 fb-1)
- tag dilutions calibrated, xs measured
- Can have (ACP) ~0.2÷0.15 in runII(translate to sensitivity on  ~ 10 deg.)‏
- This resolution allows tests for NP.
*[**R. Fleischer, Phys. Lett. B459, 306  (1999)]*
*[Baek et al, JHEP 0612:019,2006]*

- BR determination could improve o factor 2 or better
- UT angle determination also possible from ACP(t) determination

- ACP(Bs→KK_)_

- 1/fb

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- CKM 2008 - G. Volpi

## Summary and outlook

- CDF analysis of B→hh modes proved very successful:
- several new modes observed
- results complementary (Bs and Λb) or competitive (B0) with B factories.
- Already provided several important constraints on gamma (mainly through Bs→Kπ) that are currently used in combination with external information to shrink the allowed parameter space.
- This is only the beginning (i.e. 1/fb, and time-integrated). Soon updater on 2.7/fb.
- The final goal is the determination of gamma through time-dependent analysis of Bs→KK and Bd->ππ CP-violating asymmetries.
-  Will require the full run II statistics but all ingredients are in place.

- gamma from  B(s)->hh

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## Backup slides

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## CDF and Tevatron (backup)

- Tevatron exceeded design performance
- New Record L = 318 1030cm-2/s-1
- CDF main features:
- Good central tracking precision
- 6 silicon layer
- COT chamber
- pT/pT = 0.0015 pT
- Good Particle Identification:
- dE/dx in COT
- TOF

**Main Injector**
** ****& Recycler**

**Tevatron**

******p source**

**Booster**

**CDF**

**DØ**

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## B Physics @ Tevatron

- At Tevatron, large b production cross section
- Tevatron experiments CDF and DØ enjoy rich B Physics program
- Plethora of states accessible: B0s, Bc, Λ0b, Ξb, Σb...
- complement the B factories physics program
- Total inelastic cross section at Tevatron is ~1000 larger that b cross section
- large backgrounds suppressed by triggers that target specific decays.

- Flavor Creation (annihilation)** **

- q

- b

- q

- Mechanisms for b production in pp collisions at 1.96 TeV

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- CKM 2008 - G. Volpi

## Signal separation

- The variables used to separate the signals are:
- Mass in two-pion hypothesis
- Charged momentum unbalance: α=(1-p(1)/p(2))∙q(1)‏
- where p(1)<p(2)‏
- p(tot) = p(1)+p(2)‏
- dE/dx residual normalized to a kaon deposit:

- The plot shows the Mass as function of α variable

- dE/dx parameterized using D*+(-)→D0π+(-) sample

- gamma from  B(s)->hh

- CKM 2008 - G. Volpi