CDF B Physics

Run-I Results and Run-II Prospects
KEK Workshop
Feb 9, 2000
Fumihiko Ukegawa
Institute of Physics, Univ. of Tsukuba• Introduction• Selected Run-I Results
mixing, sin(2β), rare decays• Run-II Prospects (x 20 more data)• Conclusion

Introduction

Why B Physics at a Hadron Machine?
Because the production rates are high.
σ (bb) ~ 1 nb at(4S)

6 nb at Z0
pp → bb x via
strong interaction
σ ~ 10 µb at 1.8 TeV

Need to trigger on B decays, though.
So far relied on leptons:• Single leptons (e, µ)– B → l+X• Di-leptons

pT > 8 GeV/c<pT(B)> ~ 20 GeV/cpurity ~ 40%(µµ, eµ)pT > 2 GeV/c– B → J/ X, J/ → + - <pT(B)> ~ 10 GeV/cpurity ~ 20% (J/ψ)– b → e X, b →X’

Run II will employ impact parameter trigger.
→ can collect all-hadronic final statessuch as B0 → π+π-, B0s → Ds- π+.

CDF Detector (Run I)• Silicon microstrip detector

Impact parameter
σ = (13+40/pT) µm• Central trackingchamberσ(pT) /pT ~ 0.001 pT• Lepton detection
Collected ~ 110 pb-1 in 1992 - 96.

J/→Signal• ~ 250 k J/ →+ -Decay length dist.

+ -.

• Mass resolution ~ 15 MeV/c2.
• ~ 20% from B decays, others direct /c → J/γ.

Run-I CDF B physics results
B hadron properties• Mass measurements of B0s andb.

• Lifetime measurements of B+, B0, B0s,
• B0-B0 oscillations and flavor tagging.
• sin(2β) from B0/B0 → J/ K0S.
• Bc meson.
• Rare decay searches (FCNC decays)– B → K(*) l+ l-, B0, B0s → l+ l-.

b.

Run-I results (continued)
QCD studies• Inclusive b and B production.
• bb production correlations.
• b-quark fragmentation fractions, fu, fd, fs …
• Onium production (J/ , )– Prompt and non-prompt (from B, χc ) production– Production polarization

I cannot cover all results today. Please visit
http://www-cdf.fnal.gov/physics/physics.html

B0-B0 Oscillations• 2nd order weakinteraction.
• Decay probability:−t /1PB 0 →B 0 (t ) = e
2−t /PB 0 →B 0 (t ) = 21 e

(1 + cos ∆mt)

Unmixed(1− cos ∆mt)

Mixed

• Oscillation frequency = m = mH - mL :∆mq ∝ |Vtq|2• ∆ms /∆md → |Vts| / |Vtd| with less theory
uncertainty

Ingredients for B0-B0
Oscillation Measurements• Proper decay time

• Decay flavor (B0 → l+X vs B0 → l-X)

• Production flavor, b or b ? Flavor tagging
Flavor tagging is the hardest part.
Conventional approach:
identify the flavor of the other B
semileptonic decay leptons,kaons, jet charge
infer the flavor of the signal B

Flavor Tagging (cont’d)Exploit charge-flavor correlation witha nearby pion (Gronau, Nippe, Rosner).
Example: D*+ → D0 π+.
Since B* → B π, use pions from
B**→ B π (resonant) orFragmentation b → B π(non-resonant).
The correlations are the same
if it is resonant or not.

Tagging Dilution

No tag is perfect. e.g. for lepton tag:
• Leptons from b → c → l+ ν s• B0, B0s mixes.
• Fakes.
Probability of misidentification W
Dilution D = 1 - 2W.
Oscillation amplitude reduced by a factor D.
(unmixed - mixed) / total = cos(∆m t)→ D cos(∆m t)
2Tag effectiveness = εD ,ε is the efficiency of the tag.

Proper decay time and decay flavor: signal side
• l- with inclusive charm vertex(Secondary vertices)High stat, lower B0 content
B-, B0, B0s, b, … , charm, fakes• l- with exclusive D reconstruction
Low stat, high B0 content
e.g. B0 → l- ν D*+ X, D*+ → D0π+.
Charge of the lepton
identifies the decay flavor :−+b → l c, b → l c .

CDF Mixing Measurements• Combination of signal and tags.
• Six measurements so far.
Trigger• single lep• single lep• single lep• dilepton• dilepton

SignalTag• l + incl. charm • jet Q + lepton•l+D• same-side pion•DX• lepton• l + incl. charm • lepton (e , )•l+D• leptonTag lepton can be part of trigger

Mixing from l- D(*) and same-side pion tag
Charm signal near l(a)

(c)

(b)

(d)

Asymmetry = (RS-WS) / Total
(a)

(b)

(c) + (d)(a) D0 → K- π+. (b) D+ → K- π+ π+.
+0.078−1∆m = 0.471−0.068 ± 0.034ps+0+(c) D* → D π ,D0 → K- π+, K- π+ π+ π-.
(d) D*+ → D0 π+, D0 → K- π+ π0.

D(B+) = 0.27±0.03±0.02
D(B0) = 0.18±0.03±0.02

Mixing from l- D*+ and lepton tag
Charm signal near l(a)(c)

Asymmetry = (RS-WS) / Total(b)m(D0π+) - m(D0)D*+ → D0 π+, followed by(a) D0 → K- π+,(b) D0 → K- π+ π+ π-.
(c) D0 → K- π+ π0.

−1∆m = 0.516 ± 0.099 +0.029
ps−0.035

W = 0.325±0.033±0.012→ D = 0.350±0.070.

CDF competitivewith e+e-|Vtd| = (8.6±0.2±0.2±1.7) X 10-3
∆mdmtop

theoryCP Violation in B0/B0 → J/ K0S
CP viol. ⇔ Γ( i → f ) ≠ Γ( i → f )A(t ) ≡

Γ (B0 → J / K 0S ) − Γ(B 0 → J / K 0S )0

Γ (B → J /00K S ) + Γ(B → J /0K S)= − sin(2 ) sin(∆mt )• Now the amplitude is the quantity of interest.
• Final State = J/ K0S → µ+µ- π+π- “Trivial”• Initial State, B0 or B0 ? Flavor Tagging• Decay Time: Not necessary at CDF, but helps.

B0/B0 → J/ K0S~ 400 signal ev. / 110 pb-1

precise lifetime info

Not as precise[ Mass(J/ψ K0S) - M(B0) ] / σ
Apply flavor tags, count B0 vs B0.
Extract raw asymmetry = D sin(2β)
Divide it by dilution.

Apply 3 Flavor Tagging
Methods• Same-side “pions”• Leptons• Jet charge
Measure tag dilution
from ~ 1000 B+ → J/ K+decays.
Tagε(%) D(%) εD2(%)
SST 70 17±3 2.1±0.5(For SST, extrapolation
Lepton 6.5 63±15 2.2±1.0
of lepton-D meas.)
Jet Q 45 22±7 2.2±1.3
Total
6.3±1.7

Asymmetry Precise lifetime sample:
Asymmetry = [ N(B0) - N(B0) ] / tot

Asymmetry vs. time.

Less precise
lifetime sample:
Time-integrated
Asym x (1+xd2) / xd
= sin(2β)

sin(2β) = 0.79

+ 0.41- 0.44(stat + syst).

Constraints on the unitarity triangle

sin(2β) → β: four solutions, β1, β2, β1+π, β2+π (β2=π/2-β1).
1 σ bound

1 σ boundNot much constraint now, but should be interestingin Run-II, where we expect ±0.08 in sin(2β).

Rare Decays• B → K(*) l+l– b → s FCNC transition– |Vts|– SM predicts B.R. ~ 10-7 to 10-6.
– New physics could enhance it.
– Has yet to be observed.

l+l- can be resonant, e.g. J/ , (2S).
→ Indistinguishable from b → ccs
Look at non-resonant mass region.

B+ → K+ µ+ µ-

B0 → K*0 µ+ µ-• 4 candidates• 0 candidate• BR < 5.2 X 10-6 @90% CL • BR < 4.0 X 10-6 @90% CL• SM: few X 10-7
• SM: ~ 10-6
Expected signal ~ 0.5 event each.
Should see a few signal events in Run II.

More Rare Decays: B0, B0s → l+l• Vtd for B0, Vts for B0s• Helicity suppressed• B.R. highly suppressed:
SM predictions:– B0 → µ+ µ- (1.5±1.4) x 10-10– B0s → µ+ µ- (3.5±1.0) x 10-9
– B0 → e+ e- (3.4±3.1) x 10-15– B0s → e+ e- (8.0±3.5) x 10-14

Rare Decays B0, B0s → µ+µOne candidatein the overlap regionof B0 and B0s mass
windows.
B.R. < 8.6 x 10-7 for B0
B.R. < 2.6 x 10-6 for B0s
both @ 95% C.L.
Also looked for
decays to e+ µ- , e- µ+
B.R. < 4.5 x 10-6 for B0
B.R. < 8.2 x 10-6 for B0s
Still long way to go...

B Physics in CDF Run II

Two Major Goals:

I. Precisison sin(2β) from B0/B0 → J/ K0S
II. B0s - B0s Oscillation → ms / md

|Vtd| / λ |Vts|

Can be the first meaningful test of the unitarity triangle.

Summary• CDF does B physics pretty well.
• Run I results cover virtually all aspectsof B physics.
• Run II should produce more interesting
results, in particular– sin(2β) precision of ±0.08.
– ∆ms up to 40 ps-1.