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Transcript of 1 Heavy Quarks at the Tevatron CDF DO Bottom Barbro Åsman Stockholm University For the CDF and D 0...
1
Heavy Quarks at the Tevatron
CDF
DOBottom
Barbro Åsman
Stockholm University
For the CDF and D0 Collaborations TO
P
Proton
Proton LISHEP 06
Rio de Janeiro
2
Golden Eggs
Mixing:
Bs, Bd
New particles:
X(3872), Xb,
Pentaquarks, …
Mass measurements:
Bc, b, Bs, …
Production properties:
(b), (J/y), …
B and D
Branching ratios
Rare decay searches:
Bs -> µ+µ-,
D0 -> µ+µ- , …
CP Violation
Lifetimes:
, b, Bs, Bc ..SURPRISES!?
3
HOW ?
Measuring b(udb) Lifetime
Lxy
PV
cLxy MB
PT
b
p
p
p
B0K0
WHY ? A ~2 Differance between theory and
experiment for (b)/(B0). Theory =
0.86 ± 0.05
xy-plane
4
b LifetimeExtract lifetime with unbinned likelihood fit to proper decay length and mass event information.
(b)=1.45 + 0.14 – 0.13 ± 0.02 (sys) ps
b)/(B0) = 0.944 ± 0.089
(b)=1.22 + 0.22 – 0.18 ± 0.04 (sys) ps
b)/(B0) = 0.87 +0.17
-0.14 ± 0.03
5
Bc Contains Two Heavy Quarks
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/e
6
Results
(Bc) = 0.474 + 0.073– 0.066 ± 0.033 (sys) ps
Bc)= 0.448 +0.123 – 0.096 ± 0.121 (sys) ps
Bc
Lxy
XY - plane
e
cLxy MB *K PT (vis)
Where K = PT(vis) / PT(B)
is given from MC
7
Review of B0 SystemIn the B0 system: physical mass eigenstates = flavor eigenstates
where:= H- L (lifetime difference)
= (H+ L)/2
m = mH- mL (mass difference)
BL = B0 + B0
BH = B0 - B0
Time evolution of the two states is governed by the time-dependent Schrödinger equation and in the limit
m
Prob (B0 -> B0) = ½ e-t(1+cosmt)
Prob (B0 -> B0) = ½ e-t(1-cosmt)
oscillation frequency( md , ms)
Ignoring CP violation
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Extract from Bs K+K- lifetime
• Measurement of Bs -> K+K- lifetime (=L) in 360 pb-1
• Mass fit and lifetime fit:
•Extraction of (CP)/(CP):
•This measurement gives cL = 458 ± 24 ± 6 µm
•HFAG average gives weighted average: (L2 +H
2) /(L + H)
•Extract H
•Thus derive =-0.080 ± 0.23 (stat) ±0.03 (syst)
9
BS lifetime and Bs
0 -> J/
= 1.53 ± 0.08 +0.01 -0.04 ps
= 0.15 ± 0.10 +0.03 -0.04 ps
Gives rise to both CP-even and CP-odd
final states
10
Summary of
11
Bd and Bs Mixing
00H
00L
BqBpB
BqBpB
W W
b
d(s)
d(s)t
Vtb
Vtb Vtd(s)
Vtd(s)t b
md = (lots of QCD) x Vtd
ms = (lots of QCD) x Vtsms/md = (much less QCD ) x Vts /
Vtd
Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb
V =
Vud Vub* + VcdVcb* + VtdVtb* = 0
VtdVtb*VcdVcb*VudVub*
VcdVcb*-
1
= Vtd
Vts
12
Analysis StrategyBs oscillations is more difficult than Bd oscillations because of the fast mixing frequency
In order to measure m:
Reconstruct the Bs signal
Know the flavor of the meson at its
production time (Flavor tagging) and
getD2 (tagging power)
Calculate Proper length resolution
S = signal events D2 = tagging pow er S/B = signal/background t = proper time resolution
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Reconstruction Currently only using semileptonic decay of the Bs
Bs -> Ds X (Ds -> μD±: 7,422±281
μD±: 7,422±281
μDs: 26,710±560μD±: 1,519±96
μDs: 5,601±102
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Flavor Tagging
Soft lepton
Soft Lepton Tagging ( 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
Ds
Bs
b-hadronJe
t Char
ge
P.V.
Tagging SideVertexing Side
Secondary Vertex Charge
T
TEV p
qpQ
15
Cross Check of Tagging On a Bd sample
D2 = (2.48 0 ±.21 +0.08 -0.06 ) %
Tagger tuned using Bd mixing measurement
md = 0.506 ± 0.020 ± 0.014 ps-1
B0B+
)()(
)()()(
tNtN
tNtNtA
oscoscno
oscoscno
16
Bs Lifetime
Ds
Bs XY plane Lxy
cLxy MB *K PT (lD)
Where K = PT(lD) / PT(B)
is given from MC
17
Amplitude Fit Method
Prob (B0 -> B0) = ½ e-t(1+Acosmt)
Fit to data – A free parameter
Prob (B0 -> B0) = ½ e-t(1-Acosmt)
Fit for oscillations amplitude A
for a given m
Expect A = 1 for frequency = true ms
Expect A = 0 for frequency = true ms
If no signal observed :
Exclude ms value at 95% C.L.
In region where A+1.65A < 1
Sensitivity at 95% C.L. is at ms
value for which 1.65A=1
Bd
Bs
18
Bs Mixing Limit
ms > 14.8 ps-1 @ 95% CL
Uppgrade to an event by event fit
19
Log Likelihood Scan
ms < 21 ps-1 @ 90% CLMost probable value of ms = 19 ps-1
With the assumption A = 1
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Top
p p
t
t
b
b
W
l
q
q
Branching Ratios
Production Cross Section
Top Mass
Top Charge
Top Lifetime
W
Rare/non SM Decays
W Helicity
Resonance Production
Top
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TOP PAIR PRODUCTION
~85% ~15%q
t
t
q t
t
Standard model pair production via the strong interaction
Discovered in Run I
= 6.77 ± 0.42 pb for mtop = 175 GeV
22
TOP DECAY
20%
14.6%
14.6%1.2%2.4%
46%
1.2%
DILEPTON [ ee, mm, em,+ 2 b jets ] Small BR ~ 5%Smallest background
LEPTON + JETS[ e, m + 4 jets (2 b jets) ]Large BR ~ 30%Moderate background
ALL HADRON[ 6 jets (2 b jets) ] Large BR ~ 46% Larges background
23
DILEPTON CROSS SECTION
Signal Selection :
2 high PTLeptons
2 high PT Jets
Large missing ET
Veto invariant mass =
Z Background :Physics (from MC) :
Z /g *→ , Dibosons
Instrumental (from Data):
Faked Missing ET and
Faked Leptons
24
DILEPTONS
8.3 ± 1.5(stat) ± 1.0(syst) ± 0.5(lumi) pb
8.6. +2.3-2.0 (stat) +1.2 -1.0
(syst) pb
Results (Topological
cuts): ee, and ecombinedCDF 750 pb-1 preliminary
D0 350 pb-1 preliminary
Result (b-tag):
lepton + Track/b-tagging
7.1+2.6-2.2 (stat)±1.3 (syst) pb
D0 350 pb-1 preliminary
Combined with etopological)
8.6+1.9-1.7 (stat)±1.3 (syst) pb
Primary Vertex
Secondary Vertex Displace
d Tracks
Promt Tracks
Lxy
d0
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Lepton+Jets Cross SectionBackgrounds Physics : W+Jets Instrumental: QCD Multijet
Signal Selection 1 high PT Leptons 4 high PT Jets (2 b-
jets) Missing ETTopological /Kinematics Analyses
6.7+1.4-1.3 (stat)+0.9
-0.8 (syst) pb
6.0± 0.6 (stat) ±0.9 (syst) pb
Likelihood Discriminant
Neural Network
26
Lepton+Jets Cross SectionSecondary Vertex Tag
8.2± 0.9 (stat)+0.9-0.8 (syst)
pb 8.2± 0.6 (stat) ±1.0 (syst) pb
27
Summary of Cross Section
28
t-channel
Single Top
q
q'
W t
b
u d
b t
W
tb
qq' s-channel
Top production via the Weak Current
SM : pb ± 8% = 1.98 pb ± 8%
A lot of background : W + jets, ttbar etc
29
Selecting Single Top
b
S channel: - W
- High PT lepton - Missing ET
-2 b – jets - At least 1 b-tagged jet
T channel: - W
- High PT lepton - Missing ET
-2 b – jets - At least 1 b-tagged jet
- 1 extra jet
t
W
b
l
pp
q
30
Single Top SearchLikelihood Discriminant Method Separate Single top from Backgrounds
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
31
Top Mass Measurement
3232
Why Interesting?Top mass is fundamentel parameter
Top mass can constrain the Higgs mass
trough the loop diagrams:
W W
W W
b
t
H
Top mass can probe new physics
33
jet
jet
jet
jet
e/μ
b-tag jet
jet
jet
jet
b-tag jet
b-
tag
jet
jet
jet
Hard to Measure • Complicated events
– 12 ways to interpret 4 jets
• Reconstruction of jet energy scale is
distorted by:
additional interactions
electronic noise
pileup from previous buch-crossing
energy deposition outside jet cone
different response for different particles
20% of b-jets have muon and neutrino
• Background contamination
•
lepton
34
Top Mass MethodologyTEMPLATES
One mass per event from kinematic fit.
Create templates using event simulated with different Mtop values +
background.
Perform maximum likelihood fit to extract final mass.
MATRIX ELEMENTBuild likelihood directly from PDFs,matrix element(s), and transferfunctions that connect quarks and
jets.
Integrate over unmeasured quantities
Calibrate measured mass and error using simulation.
35
CDF Template Method
Four samples with different S/B and sensitivity to top:
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.
- top masses equal
-reconstructed W near MW
Reconstructed W mass to calibrate JES
36
CDF Result
173.4+-2.5(stat+JES)+-1.3(syst).
37
D0 Matrix Element Method
x: reconstructed lepton and jets kinematics JES from MW constraint. Signal and background probabilities: from differential cross-sections All events are combined in a likelihood
-ln L(mtop;JES)=-lnΠ Pevt(xi;mtop;JES)
Maximal use of information in each event:
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
38
Top Mass in Dilepton Events
Pros: Fewer combinationsCons: Unconstrained kinematics: 2 neutrinos in final
state Small branching fraction (5%)
CDF: 700 pb-1
164.5 ± 4.5 (stat.) ± 3.1 (syst.) GeV/c2
D0: 370 pb-1
177 ± 11 (stat.) ± 4 (syst.) GeV/c2
39
Top Mass Result
40
Are the other Properties of the Top Quark as Expected?
Top Charge
W-t-b
41
Top Charge
t
b
W
l
+2/3
-1/3
+1
+1
0
t
b
W
l
-4/3
-1/3
-1
-1
0
Standard Model
Exotic 4th Generation
Assiciate lepton + b-jet to a top quark
Kinematic fit for the ttbar hypothesis
Determine charge of the b-jet
PT weighted sum of tracks in the b-jet
Analys method
42
Top Charge II
D0 RunII (365pb-1)
- 17 candidate events with two tagged b-jets,
lepton, missing ET, 4 jets or more.
- 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 charge.
- excluded the hypothesis of an exotic quark
with charge = -4/3 e at 95% confidence level.
43
With top quark samples we can measure it directly as “R”:
The relative rates of ttbar events with 0/1/2 b-tags is very sensitive to R
Top Decay Properties We said tWb, but really 100%?
Indirect measurement using the CKM matrix:
• implies |Vtb| is 0.998 @ 90% CL
R BR(t Wb)
BR(t Wq)
Vtb2
Vtd2 Vts
2 Vtb2
R = 1.03+0.19-0.17 (stat +
syst)
R > 0.64 @ 95% CL
Vtb > 0.80 @ 95% CL
R = 1.12+0.27-0.23 (stat +
syst)
R > 0.61 @ 95% CL
Vtb > 0.78 @ 95% CL
44
ConclusionLots of Exciting Results are pouring out from CDF and DO!
What I have shown is just theTop of the iceberg
And there are much more in the pipeline
Look forward to many more exciting results soon!