icfp 2005, taiwan colin gay, yale university b mixing and lifetimes from cdf colin gay, yale...
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ICFP 2005, Taiwan Colin Gay, Yale University
B Mixing and Lifetimesfrom CDF
Colin Gay, Yale Universityfor the
CDF II Collaboration
ICFP 2005, Taiwan Colin Gay, Yale University
Outline
• Status of B lifetimes• Bs “lifetime” and lifetime difference• Bs mixing
ICFP 2005, Taiwan Colin Gay, Yale University
State of Lifetime
• Heavy Quark Expansion predicts
0B B Bs b
• B+, B0 in ok shape
• b a bit below expectation
• Bs on edge
/(B0) Expt /(B0) Theory
B0 1.528 ± 0.009 ps
B+ 1.643 ± 0.010 ps 1.076 ± 0.008 1.06±0.02
Bs 1.405 ± 0.045 ps 0.920 ± 0.030 1.00±0.01
B1.232 ± 0.072 ps 0.806 ± 0.047 0.86±0.05
ICFP 2005, Taiwan Colin Gay, Yale University
Lifetime/Mixing samples
Semileptonic Hadronic
• Easy to trigger ()• 100s–1000s events•Eg
• High pt lepton•Missing complicates• ~2k-100k evts•Eg
• Low pt lepton + displaced track• ~8k events• Eg
• Two displaced tracks• ~500-10k events• Eg
/ basedJ
lifeti
me
Unbia
sed t
rig
ger
lifeti
me
bia
sed t
rigger
0 *0
/
/
/
/s
b
B J K
B J K
B J
J
s sB l D X
s sB l D X
0
0
s s
B D
B D
B D
Mixing
ICFP 2005, Taiwan Colin Gay, Yale University
Measuring Lifetime
• For fully reconstructed (hadronic) modes
0 pct ct ct
p
Vertex resolution(~constant)
Momentum resolution(proportional to ct)
~ (30 ) (c.f. ~ 450 )ct O ct
~ (15%)p Op
• For semileptonic modes, missing neutrino causes
=> Resolution poor at large decay time
Important effect for Bs mixing
xy B
T
L MLc
p
Flight distance
Boost
properdecaylength
ICFP 2005, Taiwan Colin Gay, Yale University
Fully Reconstructed J/ X
• Easy to trigger on, large samples, unbiased in lifetime• Fully reconstructed modes • Excellent vertex and momentum resolution
• CDF Fully reconstructs•J/+•B+ J/K+
•B0 J/K*, J/Ks
•Bs J/b J/
0 462 15 4B
c m 460.8 4.2PDG m
For example:
• See summary followingfor detailed results
1155§39 signal
ICFP 2005, Taiwan Colin Gay, Yale University
Lifetimes from hadronic decays
• To get large samples of fully reconstructed hadronic decays, we use events recorded via the Secondary Vertex Trigger• Requires 2 tracks with impact
parameters between 120m and 1mm • Trigger has intrinsic lifetime bias• Events have excellent momentum and
vertex resolutions
• Final states reconstructed:• B± D0± (D0K) N=8380 evts• B0 D± D±K) N=5280 evts D± 3(D±K)N=4173evts• Bs Ds ± (Ds) N=465 evts Ds 3 (Ds) N=133 evts
B- ct-efficiency
B- D0-
• Larger statistics than J/ modes
• Larger systematics due to• Trigger Efficiency curve • Larger backgrounds
ICFP 2005, Taiwan Colin Gay, Yale University
Lifetimes from hadronic decays
B+
Bs
Bs
(B+) = 1.661±0.027±0.013 ps (Bs) = 1.598±0.097±0.017 ps(B0) = 1.511±0.023±0.013 ps
ICFP 2005, Taiwan Colin Gay, Yale University
Lifetime with high-pt Semileptonic sample
0sB
sD
W
b cl
s
l
s
• Trigger on 8 GeV lepton• Reconstruct• High statistics, but missing
neutrino -> “K” factor
lB Dl X
(B+) = 1.653±0.029±0.032 ps
(Bs) = 1.381±0.055±0.046 ps
(B0) = 1.473±0.036±0.054 ps
KDp
BmLct
sTxy
)(*
ICFP 2005, Taiwan Colin Gay, Yale University
B Mass & Lifetime Difference
12 12* *12 122
M M iH
M M
• Second order weak diagram gives non-zero matrix element• In basis have a non-diagonal Hamiltonian
B H B
B B
• Recall Eigenstates are:
b s
bs
0sB 0
sB, ,u c t , ,u c t
*tsV
tbV
tbV
*tsV
W
W
, 12 1222Im( ) iH L M
, 12 122Re( ) iH LM M M
/ 2
/ 2
m
12
12
|
|
(| | )
(| | )
Hs
L
s s
s ss
B B
B B
B
B12
1( )L H
L H
ICFP 2005, Taiwan Colin Gay, Yale University
Bs “lifetime” meaning
but SL SLH L H L
12
| ( ) (| ( ) | ( ) )H Ls s sB t B t B t
• E.g. lifetime measured in SL decays dominates the average
22 22
2
2
11
1L H
SL L L H HL H s
f f
sB
s d
2
22
2
1
1SL d d
1.47 0.05
1.53 0.01
FS
d
Unphysical value =>most likely / 0
• With the constraint (HQE says equal to 1%)
• When a significant exists,lifetime measurements aresample composition dependent
• Measured lifetime iswhere = fraction of light state
meas L L H Hf f Lf
ICFP 2005, Taiwan Colin Gay, Yale University
Extracting both Bs lifetimes
• In previous cases, the sample composition, and hence relation of depends upon the unknown
• In the case of the hadronic decays, there is the additional effect that the trigger turn-on affects the short-lived component of the Bs more than the long-lived
• There is a decay in which one can measure, simultaneously, the light-heavy sample composition AND each components’ lifetime:
• S,D wave amplitudes = Parity Even, (CP Even)• P wave amplitude = Parity Odd, (CP Odd)
• Since the mass eigenstates of the Bs system are
12
(| | )Hs s sB B B CP odd
12
(| | )Ls s sB B B CP even
Disentangle different L-componentsof decay amplitudes => isolate two B states
/sB J
• See D0 talk for details
ICFP 2005, Taiwan Colin Gay, Yale University
Two Lifetimes
0.160.13
0.580.46
1.05 0.02ps
2.07 0.03ps
L
H
0.19 -10.24
0.250.33
0.47 0.01 ps
0.65 0.01
s
s
s
CP-odd fraction ( ) ~ 22%H
0.140.11
0.390.43
1.23 ps
1.52 ps
L
H
0.270.400.21
s
s
+ Recent D0: 1.42±0.04±0.06 psSL
ICFP 2005, Taiwan Colin Gay, Yale University
The two Lifetimes
Constraint helpslow statistics H
0.080.09
1.21 0.08ps
1.68 ps
L
H
( 1.53 0.009) d
Note that L d
ICFP 2005, Taiwan Colin Gay, Yale University
Experiments vs. Theory
Flavor-specific“lifetime” (SL) CDF
D0
( 1%)S d
TheoryPreferred
Theory:
ICFP 2005, Taiwan Colin Gay, Yale University
Combined CDF/D0 Fit
-1
0.090.11
0.0430.047
0.23 0.08ps
0.33
11.405 ps
s
s
s
s
ICFP 2005, Taiwan Colin Gay, Yale University
Lifetimes: CDF Summary
J/ modes Hadronic modes Semileptonic modes HFAG 2005
B0 1.539±0.051±0.008 1.511±0.023±0.013 1.473±0.036±0.0541.528 ± 0.009
B+ 1.662±0.033±0.008 1.661±0.027±0.013 1.653±0.029±0.0321.643 ± 0.010
Bs 1.369±0.100±0.009 1.598±0.097±0.017 1.381±0.055±0.0461.405 ± 0.045
B 1.25±0.26±0.10 1.232 ± 0.072
ICFP 2005, Taiwan Colin Gay, Yale University
Mixing Analysis Strategy
•Just like a lifetime measurement, but look for change of B particle to antiparticle
•Mixing
•Bs or Bs at production?• Initial state flavor tagging (calibrated on B0)• Tagging dilution D=1-2w, w=mistag prob.• Effective sample N D2 (D2~1%)
• Bs or Bs at decay?• Decays are self-tagging (eg )
• Reconstruct proper decay time
mteN
BBdt
dN
mteN
BBdt
dN
t
t
cos12
cos12
/000
/000
Kaon
s sB D
• Fit Asymmetry (Nunmixed-Nmixed)/ N to D*A*cos(m t) at fixed m
• Expect A=1 for m ~ ms
• Limit (95% CL): m such that A+1.645A = 1
ICFP 2005, Taiwan Colin Gay, Yale University
Flavor Tagging + Signals
•Opposite side tagging• Use the other B in the event• Semileptonic decay (b l-)• (1) Muon, (2) Electron
• Use jet charge (Qb = -1/3)
• (3) Jet has 2ndary vertex
• (4) Jet contains displaced track
• (5) Highest momentum Jet
• Calibrated on B0 Opposite side B
Reconstructed B
Fragmentation track
0sB
K
K
bjetQ
• Hadronic (eg ): • Less signal yield• Excellent pT resolution• Good sensitivity at higherms
•Semileptonic (eg ): • Higher signal yield• Poor pT resolution• Good sensitivity at lower ms.
0sB
sD
W
b cd
s
u
s
ss DB0
lss lDB 0
0sB
sD
W
b cl
s
l
s
ICFP 2005, Taiwan Colin Gay, Yale University
CDF Limit (Semileptonic Mode)
• Bs ! Dsl X l=e/(360 pb-1)
• Ds !
• Opposite side:
• e, tag
• Jet Charge
• 7800 events
• D2 = (1.43§0.09)%
ICFP 2005, Taiwan Colin Gay, Yale University
CDF Limit (Hadronic mode)
1
1Limit: 0.0 @95% CLSensitivity: 0.4
sm ps
ps
• Bs ! Ds (360 pb-1)
• Ds !
• Opposite side:
• e, tag
• Jet Charge
• ~900 events
• D2 = (1.13§0.08)%
ICFP 2005, Taiwan Colin Gay, Yale University
Potential Improvements
• Increase statistics • Additional Decay Modes, More Data
• Increase tagging power
• Same Side Kaon Tagging increase D2 by 1-3%
• Lifetime resolution improve 10-20%
StatisticsR
esolution
Statistics
ICFP 2005, Taiwan Colin Gay, Yale University
Conclusion
• Bs mixing search at the Tevatron is an ongoing affair• Expect improvements in technique and statistics• Observation likely still some time away
• Lifetime ratios in reasonable agreement with theory• Bs the exception?
• Lifetime difference observed. Higher than predicted, but errors still large
• In addition, the mean width differs by ~2.7 from prediction
• Could it really be that • Will repeat J/ analysis with x4 data
• Both CDF and D0 are statistics limited
~ 1.1 ?s d