Lifetime Difference ( = 1/ ) in the B s System
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Transcript of Lifetime Difference ( = 1/ ) in the B s System
February 2006 Kin Yip 1
Lifetime Difference (Lifetime Difference ( = 1/ = 1/ ) in the B ) in the Bs s SystemSystem Lifetime Difference (Lifetime Difference ( = 1/ = 1/ ) in the B ) in the Bs s SystemSystem
Avdhesh Chandra, UCR
Kin Yip, BNL
Daria Zieminska, IU
D Winter Physics WorkshopFebruary 21, 2006
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Old (PRL 2005) and New Analyses
PRL 95, 171801 (2005) ~0.45 fb-1
Triggers v13 and lower1- and 2-muon triggers
unbiased in cReco p14
1-angle analysis~500 signal events
Winter 2006 ~0.9 fb-1 (?) [ D Note 4810 ]
Triggers v14 and lower1- and 2-muon triggers, unbiased in c and track pT
(173 trigger names)
Data sample: CSskim p17fix + p17.09 (4%) (SKIM_2MU)
Compared to 2005 PRL • Improved track energy loss • Rematched muons• “adaptive” vertexing• Same kinematic cuts, slightly tigther quality cuts
3-angle () analysis~1000 signal events
CKM Matrix and Unitarity triangle
1)1(
21
)(21
23
22
32
AλiηρAλ
Aλλλ
iηρAλλλ
‘bd’ (THE unitary triangle) Large effort in B physics Mainly at B factories
’bs’ (A ‘squashed’ unitary triangle)
s, small in SM
Interesting to check how small/big s really is.
Currently: Tevatron domain
Relates quarkmass and weak eigenstates
SM: CP-violating processes solely related to one phase in CKM.
tbtstd
cbcscd
ubusud
VVV
VVV
VVV
(1,0)
(0,0)
()
*
*
cbVcdV
tbVtdV
*
*
cbVcdV
ubVudV
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Bs System and CP violation
cbcs
cbcs
tbts
tbtsi
VV
VV
VV
VVec CP violating
weak phase
In Standard Model, λ (0.03), very small. Much larger measurement of a striking signal of new physics in
Bs – Bs mixing.
oddeven
oddeven
B)2
1(B)
2
1(B
B)2
1(B)
2
1(B
H
L
ss
ss
ii
ii
ee
ee
m = MH ML > 0; = L - H (> 0 in Standard Model)
Any dependence on mt cancels in untagged samples.
s SM)
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Untagged Bs Decay
Bs J/, Pseudoscalar Vector Vector decay
Three waves: S, P, D, or ┴
Both CP-even and CP-odd present, but separated in angular distributions
S, D (Parity, CP even) :linear combination of
P (Parity, CP odd) : ┴
R ┴ ┴(t=0)|
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Bs Lifetime Difference
• We measure TWO distinct lifetimes (or, equivalently, and by fitting time evolution and angular distributions in untagged Bs Jdecays.
• If CP is conserved, they can be interpreted as the lifetimes of the two Bs mass eigenstates.
• We discuss the sensitivity to a free CP violating angle
D0 p17fix/p17.09
History:
CDF (PRL 2004) fit used 3 angles, 203 events
D0 (PRL 2005) used 1 angle, θ, 513 events
Nsignals = 978 45
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Some selection cuts
Bs candidate mass
J/ candidate mass
Non-J/ meson mass
Bs pT
J/ pT
pT
J/, 2
K± pT
SMT hits each track (incl. fdisk)
SMT+CFT hits on track
B candidate decay length error
5.0 < M(J/,) < 5.8 GeV
2.9 < M(+,-) < 3.3 GeV
1.01 < M(K+,K-) < 1.03 GeV
> 6.0 GeV
> 4.0 GeV if || < 1.0
> 1.5 GeV
< 10.0
> 0.7 GeV
>1
>7
< 0.006 cm
Total number of Bs J candidates: 21380 (PRL 2005: 9699)
CSG p17fix + p17.09
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Data
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Untagged Bs Decay Rate in Time & Angles
Arg[A||(0┴andArg[A0(0)A┴(0)] are CP-conserving strong phases
No dependence on mt
correction for acceptances, kinematic cuts
Detector Acceptance (MC & data)
G(cos ) = 1 + Bcos2 + Ccos4
H(cos ) flat distribution
F() = 1 + J cos(2) + K cos2(2)
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Maximum Likelihood FitSimultaneous fit to mass, proper decay length and 3 angles
using an unbinned maximum log-likelihood method
30 parameters: 1 fsig = signal fraction
2 signal mass, width
3 A , |A0|2-|A|||2, 1 strong phase
1 c = c / , = (LL+ HH) /2) /2
1 = = LL - - HH
3 bkg mass (1 prompt, 2 long-lived)
1 (ct ) scale
6 bkg ct shape
4 bkg transversity (2 prmpt + 2 long-lived)
4 bkg angle φ (2 prompt + 2 long-lived)
2 bkg angle ψ (1 prompt + 1 long-lived)
2 bkg “interference” (1 prompt + 1 bkg)
])1([1
i
bcksig
N
i
i
sigsig ff FFL
set
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Full (chain) MC TestInput: (close to PRL 2005 results)
cL = 370 µm cH = 460 µm|A┴| = 0.4 with ~9K events (~10 current stats)
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Data:Fit projections in signal regions
transversity)
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Fit projection (lifetime)
All events
Background mass region
Signal mass region
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Results (3-angle fit)
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Cross-check: 1-angle fit
This analysis PRL (2005)
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Comparisons:
D ’06 – errors statistical only
0.140.06
1.580.09
0.220.13
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Systematics
One “outlyer” treat its effect as systematic uncertainty Event Run #: 210344 Event #:23385781 unlikely signal or background Signal: mass 2.3 from peak, lifetime 8.5 x mean Bkg: 10.2 x mean for “right slope long”
1 - 2
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Sensitivity to CP violation
So far, we have assumed CP to be conserved, i.e., no interference between CP-even and CP-odd terms, and
the two physical Bs states, L and H, are orthogonal
CKM (Standard Model) : λ 0.03
Allowing for a free requires an assumption on strong phases 1 2,our fit does not converge with all 3 phases free
With 1 free and 2 = 0, we obtain = -0.9 ± 0.7CP-violating angle consistent within statistical uncertainty of ± 0.7.
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Summary
NNewew results based on X2
New analysis based on ~1 fb-1 data
Statistical uncertainty on the CP-violating angle 0.7
Bd J/ K analysis is in progress