γ from B 0 (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

CKM 2008 - G. Volpi gamma from B(s)->hh 2

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


Triggering on Bhh in p-pbar collisions

Trigger performance is crucial

SVT

Reject light-quark background Two oppositely-charged tracks Transverse opening angle; pT1 , pT2; pT1+ pT2.

Reject multi-prongs and backgrounds

B impact parameter.


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-)

allpBp

=ITcone

T

3 sets of cuts:

Loose: optimize for ACP(B0K+-)

(good for all three “large modes”)

Tight: optimize for B0sK-+

(good for all “rare modes”)

Tight+Pt cut for the Λb

# evts: 6059±159


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


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

1.5σ


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 termmomentum term

αptot

2.1σ sep KK/ππ

K

K


Fit results

Determination of sample composition provides

1. Observation of new Bhh mode: Bs→Kπ

2. First observation of Λb→ph decays: Λb →pπ and Λb→pK

3. Unique sample of Bs→KK

4. B-factories-like samples of Bd →ππ and Bd→KπA wealth of measurements is extracted

1. BR(Bs→Kπ) and ACP(Bs→kπ)2. Improved BR(Bs→KK)

3. BR(Λb→pπ) and ACP(Λb→pπ)

4. 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!


60 100.80.75.0 ±±=πKBB +s

Updated using BR

From HFAG 2008

60 100.90.75.3 ±±=πKBB +s

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/f

d)

– Large difference between (δs-

δd)>20°

0.080.150.390 ±±=πKBA +sCP


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.

60 103.51.424.4 ±±=KKBB +s

Update016.0020.0347.0)(

)(0

0

KBBf

KKBBf

d

ss


Other results

• B0 CP competitive with B factories–

• Lipkin-Gronau proposed a model-independent SM test based on combining B0 and B0

s differential rates

• First world measurements of BR and ACP of 2-body charmless B baryon decays:– –

0.080.410.83

00

00

±±=πKBΓπKBΓ

πKBΓπKBΓ+

s+

s

++

60 101.50.75.6 ±±=pKΛB b

60 100.90.63.5 ±±=pπΛB b

SM=-1

0.0090.0230.0860 ±±=πKBA +CP

05.017.003.0)( 0 pA bCP

03.017.037.0)( 0 pKA bCP


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


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


Time-dependent asymmetries

Resolutionuncertainty

(D2 = 5.3%)Ingredients for a time-dependent

ACP(t) ready: large samples (2700 ev in ~3 fb-1)

tag dilutions calibrated, xs

measuredCan 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


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.


Backup slides


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

Tevatr

onp source

BoosterCDF DØ


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, Λ0

b, 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 b

bg

gFlavor Creation (gluon fusion)

b

Flavor Excitationq q

bg

b

b

Gluon Splitting

g

g g

b

Mechanisms for b production in pp collisions at 1.96 TeV


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

γ from B 0 (s) →h + h’ -

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