Measurement of γ from B(s) → hh Decays at CDF

1. γ from B0(s)→h+h’- G. Volpi (Univ. and INFN Pisa) on behalf of the CDF Collaboration CKM 2008, Rome Oct. 09, 2008

2. gamma from B(s)->hh Introduction • Angle γ=arg(Vub*)‏: the least known of CKM matrix • In 1999 Fleischer proposed of using time-dependent asymmetries of flavor tagged Bd→ππand 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

3. gamma from B(s)->hh SVT 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.

4. gamma from B(s)->hh 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-)‏ # evts: 6059±159 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

5. 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

6. Signal composition 1.5σ dE/dx residual Correlation between arbitrary mass assignment and signed momentum imbalance distinguish modes function of α variable dE/dx parameterized using D*+(-)→D0π+(-) sample gamma from B(s)->hh

7. gamma from B(s)->hh Unbinned Log-likelihood fit Unbinned ML fit using 5 observables fraction of jth mode, to be determined by the fit 2.1σ sep KK/ππ mass term PID term momentum term K  ptot α K  Signal shapes: from MC and analytic formula Background shapes: from data sidebands sign and bckg shapes from D0  K-π+

8. 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) Constrains on gamma! All BR are measured relative to the reference mode Bd →Kπ to cancel common systematic uncertainties gamma from B(s)->hh

9. Updated using BR From HFAG 2008 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

10. gamma from B(s)->hh 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

11. 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 gamma from B(s)->hh

12. gamma from B(s)->hh 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

13. gamma from B(s)->hh B0s DCPV resolution projections • Assuming SM hypothesis  Gronau-Lipkin relation true Using 2.7 fb-1 >3σ Yield Factor • 5σ are not so far away…

14. gamma from B(s)->hh (D2 = 5.3%)‏ Resolution uncertainty Time-dependent asymmetries • BR determination could improve o factor 2 or better • UT angle determination also possible from ACP(t) determination ACP(Bs→KK) • 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] 1/fb

15. gamma from B(s)->hh 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.

16. gamma from B(s)->hh Backup slides

17. 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 CDF DØ Booster Tevatron p source Main Injector & Recycler gamma from B(s)->hh

18. gamma from B(s)->hh g b b g b g b b g Flavor Creation (gluon fusion)‏ b g g Gluon Splitting q b q Flavor Excitation 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. Mechanisms for b production in pp collisions at 1.96 TeV q b q Flavor Creation (annihilation)

19. 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