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Heavy Quarks at the Tevatron

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Heavy Quarks at the Tevatron. Barbro Åsman Stockholm University. For the CDF and D 0 Collaborations. TOP. CDF. Proton. Bottom. DO. Proton. LISHEP 06 Rio de Janeiro. Golden Eggs. Lifetimes: DG , L b , B s , B c. SURPRISES!?. B and D Branching ratios. Production properties: - PowerPoint PPT Presentation

Text of Heavy Quarks at the Tevatron

Bild 1CDF
DO
Bottom
TOP
Proton
Proton
Rio de Janeiro
*
experiment for t(Lb)/t(B0). Theory = 0.86 ± 0.05
xy-plane
t(Lb)/t(B0) = 0.944 ± 0.089
t(Lb)/t(B0) = 0.87 +0.17-0.14 ± 0.03
Unique system with two heavy quarks of different flavor
Probes heavy-quark theories in the region between the cc and bb
Decays in 3 different ways: b or c decays or bc annihilation
Low production rate B+,B0: 40%,
Bs,B baryons: 10%, Bc~ .05%
Reconstruct Bc J/yen
m
Bc
Lxy
where: DG = G H- GL (lifetime difference)
G = (GH+ GL)/2
Dm = mH- mL (mass difference)
Time evolution of the two states is governed by the time-dependent Schrödinger equation and in the limit DG << D m
Prob (B0 -> B0) = ½ e-G t(1+cosDmt)
Prob (B0 -> B0) = ½ e-G t(1-cosDmt)
oscillation frequency
( Dmd , Dms)
• Measurement of Bs -> K+K- lifetime (=tL) in 360 pb-1
• Mass fit and lifetime fit:
•Extraction of DG (CP)/G(CP):
•HFAG average gives weighted average: (tL2 +tH2) /(tL + tH)
•Extract tH
*
Gives rise to both CP-even and CP-odd
final states
Dms/Dmd = (much less QCD ) x Vts / Vtd
Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb
-
Analysis Strategy
Bs oscillations is more difficult than Bd oscillations because of the fast mixing frequency
In order to measure D m:
Reconstruct the Bs signal
production time (Flavor tagging) and
get eD2 (tagging power)
Calculate Proper length resolution
Bs -> Ds m X (Ds -> f p ) (f -> K+ K- )
μD±: 7,422±281
μD±: 7,422±281
μDs: 26,710±560
μD±: 1,519±96
μDs: 5,601±102
Soft Lepton Tagging (m or e ):
Charge of the leptons together with the jet charge gives the flavor of b
Jet Charge Tagging :
Sign of the weighted average charge of opposite B jet gives the flavor of b
b-hadron
Dmd = 0.506 ± 0.020 ± 0.014 ps-1
B0
B+
Fit to data – A free parameter
Prob (B0 -> B0) = ½ e-G t(1-AcosDmt)
Fit for oscillations amplitude A
for a given Dm
If no signal observed :
Exclude Dms value at 95% C.L.
In region where A+1.65sA < 1
Sensitivity at 95% C.L. is at Dms value for which 1.65sA=1
Bd
Bs
Uppgrade to an event by event fit
*
Most probable value of Dms = 19 ps-1
With the assumption A = 1
*
Discovered in Run I
*
Small BR ~ 5%
Large BR ~ 30%
Large BR ~ 46%
*
s = 8.6. +2.3-2.0 (stat) +1.2 -1.0 (syst)  pb
Results (Topological cuts):
CDF 750 pb-1 preliminary
D0 350 pb-1 preliminary
D0 350 pb-1 preliminary
Combined with em (topological)
Primary Vertex
Secondary Vertex
Displaced Tracks
Promt Tracks
Missing ET
Likelihood Discriminant
Neural Network
*
SM : s = 0.88 pb ± 8% s = 1.98 pb ± 8%
A lot of background : W + jets, ttbar etc
q
q'
W
t
b
u
d
b
t
W
t
b
q
q'
T channel:
- 1 extra jet
Dzero limits with 370 pb-1
95% C.L.: s < 5.0 pb t < 4.4 pb
CDF limits with 695 pb-1
95% C.L.: s < 3.2. pb t < 3.1 pb
*
Top mass can constrain the Higgs mass
trough the loop diagrams:
W
W
W
W
b
t
H
distorted by:
additional interactions
electronic noise
20% of b-jets have muon and neutrino
• Background contamination
Create templates using event simulated
with different Mtop values + background.
Perform maximum likelihood fit to
extract final mass.
matrix element(s), and transfer
Integrate over unmeasured quantities
using simulation.
0 b-tag 4 jets > 21 GeV
1 b-tag 3 jets > 15 GeV , 4th : 8 GeV < Et < 15 GeV
1 b-tag 4 jets > 15 GeV
2 b-tag 3 jets > 15 GeV , 4th > 8 >GeV
-Use assignments with lowest χ2
to reconstruct top mass.
*
JES from MW constraint.
differential cross-sections
-ln L(mtop;JES)=-lnΠ Pevt(xi;mtop;JES)
Calculating event-by-event probability to be signal or background,
based on the respective matrix elements:
Pevt(x;mtop; JES) = ftop*Psgn(x;mtop; JES) + (1-ftop) * Pbkg(x;JES)
Mtop = 170.6 ± 4.4 (stat.) ± 1.7 (syst.) GeV/c2
JES = 1.03 ± 0.03
Pros:
Small branching fraction (5%)
D0: 370 pb-1
177 ± 11 (stat.) ± 4 (syst.) GeV/c2
*
Are the other Properties of the Top Quark as Expected?
Top Charge
Kinematic fit for the ttbar hypothesis
Determine charge of the b-jet
PT weighted sum of tracks in the b-jet
Analys method
- two entries per event for top and anti-top.
- discriminate b and b with jet charge algorithm
- calibrate Monte Carlo with data using two jet
heavy flavor sample with opposite jet tagged
with m charge.
with charge = -4/3 e at 95% confidence level.
*
measure it directly as “R”:
The relative rates of ttbar events
with 0/1/2 b-tags is very sensitive to R
We said tWb, but really 100%?
Indirect measurement using the CKM matrix:
implies |Vtb| is 0.998 @ 90% CL
R = 1.03+0.19-0.17 (stat + syst)
R > 0.64 @ 95% CL
Vtb > 0.80 @ 95% CL
R > 0.61 @ 95% CL
Vtb > 0.78 @ 95% CL
Conclusion
Lots of Exciting Results are pouring out from CDF and DO!
What I have shown is just the
Top of the iceberg
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