Upload
annabella-parsons
View
219
Download
2
Tags:
Embed Size (px)
Citation preview
Bs Mixing at the Tevatron
Md. Naimuddin(on behalf of CDF and D0 collaboration)
University of DelhiRecontres de Moriond
19th March, 2006
03/19/2006 Md. Naimuddin 2
– Introduction to Mixing
– Why study Mixing
– Fermilab Tevatron
– Data Taking
– CDF and D0 Detectors
– Analysis strategy
– Bs mixing at CDF
– Bs mixing at D0
– Results and Conclusions
OUTLINE
03/19/2006 Md. Naimuddin 3
Mixing: The transition of neutral particle into it's anti-particle, and vice-versa
Introduction
First observed in the K meson system.
In the B meson system, first observed in an admixture of B0 and Bs
0 by UA1 and then in B0 mesons by ARGUS in 1987.
These oscillations are possible because of the flavor-changing term of the Standard Model Lagrangian,
..,,2
chW
b
s
d
Vtcug
L
L
CKML
03/19/2006 Md. Naimuddin 4
1)1(2
11)1(
)(2
11
23
2242
32
AiA
AiA
iA
VVV
VVV
VVV
tbtstd
cbcscd
ubusud
Where VCKM is the CKM matrix;
Wolfenstein parametrisation- expansion in ~ 0.22
0*** tbtdcbcdubud VVVVVV
CP violation in the Standard Model originates due to a complex phase in the CKM matrix (quark mixing).
iubub eVV || i
tdtd eVV ||1
*
*
*
*
cbcd
tbtd
cbcd
ubud
VV
VV
VV
VV
Introduction
(0,0) (0,1)
(,)
*ubud
*tbtd
VV
VVarg
*cbcd
*tbtd
VV
VV
*tbtd
*cbcd
VV
VVarg
*cbcd
*ubud
VV
VVarg
*cbcd
*ubud
VV
VV
(0,0) (0,1)
(,)
*ubud
*tbtd
VV
VVarg
*cbcd
*tbtd
VV
VV
*tbtd
*cbcd
VV
VVarg
*cbcd
*ubud
VV
VVarg
*cbcd
*ubud
VV
VV
03/19/2006 Md. Naimuddin 5
Mixing in B mesons
Light and Heavy B mesons mass eigenstates differ from flavor eigenstates:
B|qB|pB| L
B|qB|pB| H
122 qp
2LH MM
m
2
LH
LH MMm HL
Time evolution of
B0 and states
mtte
BBPt
cos2
cosh2
)(
mtte
BBPt
cos2
cosh2
)(
In case 0,
0B
mttP temu cos1
1, 2
03/19/2006 Md. Naimuddin 6
2*2
22222
6
/tbtddBdBdB
WttFd VVBfm
π
)mηF(mmG=Δm
standard model Expectation:Δms= 14 - 28ps-1 Δmd=
0.5ps-1
measurement of Δms/Δmd
Vts/Vtd
constrain unitary triangle
f2BdBBd = (228+30+10 MeV)2
|Vtd| from md limited by ~15%
consider ratio
2
22
2
2
2
2
td
ts
B
B
td
ts
BB
BB
B
B
d
s
V
Vξ
m
m=
V
V
Bf
Bf
m
m=
Δm
Δm
d
s
dd
ss
d
S
Determine |Vts|/|Vtd| ~ 5% precision
02.021.12 035.0014.0
Why Bs mixing is important
K mixing direct & indirect CPVBd mixing heavy top mass mixing neutrino mass 0
Bs mixing ????
03/19/2006 Md. Naimuddin 7
Fermilab Tevatron
Highest Luminosity achieved: 1.7x1032 cm/s2
Expected: 2 – 3 x 1032 cm/s2
03/19/2006 Md. Naimuddin 8
Data TakingExcellent performance by the Tevatron and we are doubling our data set every year.
Data taking efficiency is ~ 85%.
We already have collected about 10 times of run 1 data.
0
200
400
600
800
1000
Luminosity used in the currentanalysis
CDF
CDF
D0
Pb-1
03/19/2006 Md. Naimuddin 9
CDF Detector
• Solenoid 1.4T• Silicon Tracker SVX
• up to ||<2.0• SVX fast r-
readout for trigger• Drift Chamber
• 96 layers in ||<1• particle ID with
dE/dx• r- readout for
trigger• Time of Flight
• →particle ID
03/19/2006 Md. Naimuddin 10
D0 Detector
• 2T solenoid• Fiber Tracker
• 8 double layers• Silicon Detector
• up to ||~3• forward Muon +
Central Muon detectors• excellent coverage
||<2• Robust Muon
triggers.
03/19/2006 Md. Naimuddin 11
We need to:
Reconstruct the Bs signal. Know the flavor of the meson at it’s production time (Flavor tagging) and get D2
Proper decay length resolution
Analysis strategy
(t)N(t)N
(t)N(t)N(t)A
mixunmix
mixunmixmix
N
NNε WR
Measuring Bs oscillations is much more difficult than Bd oscillations because of the fast mixing frequency.In order to measure,
N
NND WR
2
22
2
tsm
eysensitivit DNBSS
Reconst-ruction
Flavor tagging
Propertime
tmΔcos*D s
03/19/2006 Md. Naimuddin 12
2
22
2
tsm
eysensitivit DNBSS
Semileptonic modes collected by the two track trigger
Reconst-ruction
Flavor tagging
Proper time
03/19/2006 Md. Naimuddin 13
More than 2300 Bs signal candidates in 765 pb-1
Reconst-ruction
Flavor tagging
Proper time
2
22
2
tsm
eysensitivit DNBSS
)(0 KDB BsDs-()+
03/19/2006 Md. Naimuddin 14
Currently using only semileptonic decay of the Bs
Bs Ds X (Ds ) ( K+K-)
Reconst-ruction
Flavor tagging
Proper time
2
22
2
tsm
eysensitivit DNBSS
26,710±560
7,422±281
5,601±102
1,519±96
Untagged Tagged
03/19/2006 Md. Naimuddin 15
Soft Lepton Tagging ( or e):• Charge of the leptons provides the flavor of b.Jet Charge Tagging:• Sign of the weighted average charge of opposite B jet provides the flavor of b.Same Side(Kaon) Tagging (New at CDF)• B meson is likely to be accompanied by a close K/ • particle Id helps
b-hadron
Trigger leptonFragmentationpion
B
PV D
neutrino
LxySoft lepton
Jet charge
0 b<jetQ
0 b>jetQ
Opposite side Same side
e or
Reconst-ruction
Flavor tagging
Proper time
2
22
2
tsm
eysensitivit DNBSS
03/19/2006 Md. Naimuddin 16
Reconst-ruction
Flavor tagging
Proper time
2
22
2
tsm
eysensitivit DNBSS
Opposite side Tagging: )%014.0020.055.1(2 D
Same side Kaon Tagging:
%3.28 2.32.4
D %0.4 9.0
2.12
D
03/19/2006 Md. Naimuddin 17
Reconst-ruction
Flavor tagging
Proper time )%21.048.2(
06.0
08.02
D
2
22
2
tsm
eysensitivit DNBSS
Using only Opposite side e, , secondary vertex or jet charge for tagging
Tagger tuned using Bd mixing measurement
md = 0.506±0.020±0.014 ps-1
03/19/2006 Md. Naimuddin 18
Easier to calculate for Hadronic decays
Proper decay time given as :
TB
xy P
mLct Reconst-
ruction
Flavor tagging
Proper time
2
22
2
tsm
eysensitivit DNBSS
KP
mLct
TB
xy *
TB
TlD
P
PK s
Distance from PV to SV in transverse plane
Boost meson back to its rest frame
Due to missing neutrino, it becomes little tricky in semileptonic sampleMissing momentum increased ct error ( ct)
Proper decay time given as:
where
from MC
03/19/2006 Md. Naimuddin 19
2
22
2
tsm
eysensitivit DNBSS
Reconst-ruction
Flavor tagging
Proper time
Best estimate of errors used in track fitting, any additional scaling determined from data
Scale factor = 1.17 +/- 0.02
(largest systematic)
Pull of J/ vertex from the primary vertex for prompt J/ s
03/19/2006 Md. Naimuddin 20
Fitting procedure
Amplitude Fitting approach: Introduce amplitude
Fit for A at different ms
Traditionally used for Bs mixing search Easy to combine experiments
tmADtP s cos1~)(
Likelihood approach:
Search for min, which minimizes the –ln(L),
where min is the estimator of the true frequency.
Difficult to combine the results from different experiments.
)(ln)(ln)( minmin LLL
03/19/2006 Md. Naimuddin 21
Amplitude fit method
• Fit to data - free parameter
• Obtain as a function of
• Measurement of gives and otherwise
• At 95% CL• sensitivity • excluded
• Systematics is given by
A
A
AsysA AA
1
t)]m(A±[Γe=p sΓt cos1
2
1
sm
smA 0
A
1 1.645 =A1 1.645 <+A A
A 1
03/19/2006 Md. Naimuddin 22
Bs mixing limit
Limit: ms > 8.6 ps-1 @ 95% confidence
Sensitivity: 13.0 ps-1 @ 95% confidence
03/19/2006 Md. Naimuddin 23
Bs mixing limit
Dominant sources of systematic uncertainty:Scale factor, K factors and Sample composition
Limit: ms > 14.8 ps-1 @ 95% confidence
Expected Limit: 14.1 ps-1 @ 95% confidence
A clear deviation of 2.5 from 0 can be seen at
ms~19 ps-1
03/19/2006 Md. Naimuddin 24
Likelihood scan
ms < 21 ps-1 @ 90% CLMost probable value of ms = 19 ps-1
Resolution K-factor variation by 2% BR (BsDsX) ccbar contamination BR (BsDsDs)
Syetematics
03/19/2006 Md. Naimuddin 25
Probability for this measurement to lie
in the range
16 < ms < 22ps-1
Given a true value:
ms > 22 ps-1: 5.0%
ms = 19 ps-1: 15%
Simulate ms = infinity by randomizing flavor
tagging variable
Consistent results from parameterized MC studies
Significance Test
03/19/2006 Md. Naimuddin 26
CKM fit without new D0 result
03/19/2006 Md. Naimuddin 27
Disclaimer:
Produced only yesterday by CKM group so I don’t have much information about the inputs.
CKM fit with new D0 result
03/19/2006 Md. Naimuddin 28
CONCLUSIONS Excellent performance of the Tevatron.
Development of Same Side Kaon Tagger which will ease the total tagging power by about 2.5 (CDF)
D0 has excellent opposite side tagger performance.
CDF preliminary:
D0 Final (hep-ex/0603029, submitted to PRL):
We are on the edge of Bs mixing measurement and entering into the precision era.
Limit: ms > 8.6 ps-1 @ 95% confidence
Sensitivity: 13.0 ps-1 @ 95% confidence
ms < 21 ps-1 @ 90% CLMost probable value of ms = 19 ps-1
Likelihood scan
Limit: ms > 14.8 ps-1 @ 95% confidence
Expected Limit: 14.1 ps-1 @ 95% confidence
Amplitude Scan
03/19/2006 Md. Naimuddin 29
FUTURE IMPROVEMENTS
CDF:
Improved selection in hadronic modes using Neural Networks
Use semileptonic events from other triggers.
Improve vertex resolution.
Use same side Kaon tagger.
Several major improvements are expected in the future:
More data: On track for 4-8 fb-1 of data by 2009.
D0:
More decay modes (DsK*K, 3, Ks, Bse Ds X )
Use of same side tagging.
Use of hadronic modes.
Additional Layer of silicon.
Proposal to increase the bandwidth.
03/19/2006 Md. Naimuddin 30
• Back-up slides
03/19/2006 Md. Naimuddin 31
Backup-1
Time evolution follows from a simple perturbative solution to the schrondinger’s equation
(t)B|
B(t)|iΓMiΓM
iΓMiΓM
(t)B|
B(t)|
22222121
12121111
dt
di
Eigenvalues are, LHLHLH
im ,,, 2
B|B|
q/p1q/p1B|B|
2
qpB| L
Bεq/p1
q/p1
Measure of the amount by which |BL> and |BH> differ from CP eigenstates
In case 0,
03/19/2006 Md. Naimuddin 32
In the limit of no CP violation in mixing (q/p =1), unmixed and mixed decay probabilities become
mttP temu
cos11
,
These oscillations can be used to measure the fundamental parameters of the standard Model and have other far reaching effects such as breaking the matter anti-matter symmetry of the Universe.Constraining the CKM matrix redundantly using different measurements of the angles/sides is a sensitive probe of New Physics
Backup-2
03/19/2006 Md. Naimuddin 33
Backup-3
03/19/2006 Md. Naimuddin 34
Backup-4
03/19/2006 Md. Naimuddin 35
Backup-5
03/19/2006 Md. Naimuddin 36
Backup-6
03/19/2006 Md. Naimuddin 37
Backup-7
WA+CDF+D0
03/19/2006 Md. Naimuddin 38
Comparison with other experiments at ms=15 ps-1
Backup-8