γ from b 0 (s) →h + h’ -
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γ from B 0 (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 - PowerPoint PPT PresentationTRANSCRIPT
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
CKM 2008 - G. Volpi gamma from B(s)->hh 3
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.
CKM 2008 - G. Volpi gamma from B(s)->hh 4
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
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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
CKM 2008 - G. Volpi gamma from B(s)->hh 6
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
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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
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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!
CKM 2008 - G. Volpi gamma from B(s)->hh 9
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
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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.
60 103.51.424.4 ±±=KKBB +s
Update016.0020.0347.0)(
)(0
0
KBBf
KKBBf
d
ss
CKM 2008 - G. Volpi gamma from B(s)->hh 11
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
CKM 2008 - G. Volpi gamma from B(s)->hh 12
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
Assuming SM hypothesis Gronau-Lipkin relation true
5σ are not so far away…
Using 2.7 fb-1 >3σ
Yield Factor
CKM 2008 - G. Volpi gamma from B(s)->hh 14
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
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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.
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Backup slides
CKM 2008 - G. Volpi gamma from B(s)->hh 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
Main Injector
& Recycler
Tevatr
onp source
BoosterCDF 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, 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
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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