Transcript Prospect for bs measurement at LHC

Prospect for bs
measurement at LHC
Alessia Satta on behalf of the LHCb
collaboration + some Atlas and CMS results
Physics at LHC, 3rd october 2008
Content
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Introduction
Analysis strategy
LHC prospects
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Alessia Satta INFN
2
bs angle in one slide
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the CKM unitarity
triangle in Bs system
V V * 
Possible to extract b s   arg ts * tb 
from CPV in Bs if b  VcsV cb 
ccs decay GOLDEN
decay
MODE J/yf
Bs
SM predicts a very
mixing
small value:
2bs=0.037±0.002
W, ?
b
B0
s
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s
u,
c,
t
W,?
u,
c,
t
s
B 0s
b
+
Alessia Satta INFN
b
B 0s
s
W
f=CP(f)
decay
Bs
c Ψ,hc
c
s 3Φ , h
s
Interesting !
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Tevatron result is
larger that SM
prediction by 2.2 s
(arXiv:0808.1297)
Exciting for NP
searches but not easy
to settle down by
tevatron alone: room
for LHC
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Alessia Satta INFN
CDF Probability of
5 s observation
8 fb (2010)
6 fb (2009)
bs
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Formulas of decay rate
A0, A║, A┴ : transition
 Bs in
J/yf
amplitudes
a givensum
polarization
CP +/-state
of
•f(ρ):
Angular
angular analysis to
decouple
distribution
for a the
giveneigenstates
polarization
state still
Untagged analysis
some sensitive to bs
T U V :Time dependence
If P anti P (U,V)+ (U,V)
h=1-1
Tagged analysis sensitive
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to cos(2b) sin(2b)
–
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Analysis in a nutshell
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Fit time dependent angular
distribution
• Large statistics is mandatory
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Large sbb , good trigger
• Good signal background separation
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–benefit a lot for dimuon in final state
• Good time resolution
• Good tracking (angular resolution)
• Good tagging (for tagged analysis)
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Beauty in LHC experiment
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General purpose
experiment
|h|<2.5 , s=100mb
B physics mainly first
years (L=1033)
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230 mb
s =100 mb
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Gain in low Pt
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B dedicated
experiment
Forward spectrometer
to max. bb in
acceptance
1.9<h<4.5 s=230mb
Locally reduced L to
maximize events with
one interaction
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Trigger
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Crucial since only 1% of stot is b production and
decay chain of interest has BR 3*10-5
Hardware and sw levels for all experiments:
• L0 rate 1MHz (LHCb) ~100kHz (ATLAS CMS)
• HLT rate 2kHz (LHCb) ~100Hz (ATLAS CMS)
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ATLAS and CMS general purpose so limited
bandwidth for b physics ( O(10%))
All experiments have a dimuon trigger to select
signal events
• ATLAS /CMS Pt and Mass based cut + IP, rate ~Hz
• LHCb : 600Hz of IP unbiased dimuon trigger signal
recostruction as offline (loser cut) noIP . Very high
efficiency on selected events of trigger ( ~ 70%)
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Signal reconstruction
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Standard cuts : Pt, invariant mass, PID,
vertex quality, B pointing to primary
vertex, B decay length (only ATLAS &
CMS)
PID
• Similar muon ID performance for ATLAS CMS
and LHCb
• ATLAS and CMS no Kaon pid capability, LHCb
has 2 Riches that ensures good K identification
e(KK)~80% e(p->K)~ 3%
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Signal and background
L (fb-1) ev
B/S
Background
ATLAS 10
90k
0.18
long lived B
CMS
10
109k
0.25
long lived B
LHCb
2
114k
2.0
1.8 prompt*
+0.2 long lived
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Proper time resolution
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Need to resolve fast Bs oscillation: bs
extraction sensitivity ~ exp(-0.5*st2
Dms2)
Atlas 83fs CMS 77fs LHCb 39fs
• LHCb vertex detector close to IP (0.8cm
wtr 4.4cm)
• LHCb P resolution a factor 2 better
• LHCb trigger collects 600Hz unbiased
dimuon (also) to calibrate proper time
on data
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Tagging
Kaon from fragmentation
Primary
vertex
“Same side”
Signal B
~1cm
D
vertex charge
Tagging B
kaon
(K±)
“Opposite side”
lepton (m±, e±)
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Sensitivity goes as e(1-w)2
ATLAS : e, m Qjet 4.6%
CMS : NA
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e(1-2w)2
Muon
0.8
Electron
0.4
K (OS)
1.5
K (SS)
2.1
Q vertex
1.1
Combined
6.2
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Tagging from data
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LHCb plans to extract the mistag fraction
from control sample with large statistics
Opposite Side is extracted from B+J/y K+
or BdJ/y K*
• Common selection as much as possible with
signal sample to avoid phase space bias to
opposite b
• Large statistics is expected:in 2 fb-1
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650k Bd J/y K*
1 million for B+ J/y K*
Same Side
• From Bs->Dsp
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Acceptance proper time and angles
Theory
Selected events
No bias from selection
Theory
Selected events
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A common
selection with
BdJ/Y K*
allows to test
the acceptance
on data (650kev/2fb)
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Theory
Selected events14
Systematic studies
s(bs) vs mistag fraction
0.04
s(bs) vs Prompt bkg fraction
0.035
Angular
resolution is
very good and
has negligible
impact on bs
error
0.03
0.025
0.02
0.015
0.01
0.005
0
1.4
1.8
s(bs) vs proper time resoltuion
2.2
2.6
0.04
0.035
0.03
0.025
0.02
s(bs) vs long lived bkg fraction
0.015
0.01
0.005
0
0.2
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0.5
0.8
Crucial : mistag
and proper time
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1.1
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Sensitivity
ATLAS
CMS
LHCb
L (fb-1)
10
10
2.0
Yield (k)
90
109
114
B/S
0.18
0.25
2.0
s(MBs) (MeV) 16.5
14
17
st (fs)
83
77
39
Eff(tag) (%)
4.6
NA
6.2
s(2bs)
0.08
NA
0.03
Even with fraction of one year nominal luminosity good sensitivity
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More channels in LHCb
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Other bccs decay
can be added
• Low yield ,
experimental
signature more
difficult, larger
background ,
degradation of
proper time
resolution for Ds Ds
• No angular analysis
is required
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Decay
mode
J/Yhgg
J/Yhppp0
J/Yh’pph
J/Yh’rg
hcf
Ds Ds
All
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Events
in 2fb-1
8.5 k
3k
2.2 k
s(2bs)
4.2 k
3k
0.08
0.108
4k
0.133
0.046
0.109
0.142
0.154
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Summary
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All experiments will collect large
sample of golden mode decay for bs
measurement
Great potential to improve
significantly the existing
measurement
• even with fraction of nominal year
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Spares
CPV in Bs  ccs (s)
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Golden mode :J/y(mm)f(K+K)
• Large BR
• Clean experimental signature
• Easy to trigger
• Sum of even and odd CP eigenstates
 angular analysis
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total
even
background
odd
Other modes J/yh, J/y h’, hC f, Ds Ds
• Low yield , experimental signature more difficult, larger
background , degradation of proper time resolution for Ds Ds
• No angular analysis is required
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Sensitivity study
Due to limited MC statistics
• we use the full Monte Carlo to estimate all the
relevant quantities:
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yield, background fraction, mass, proper time/ angle
distributions, resolutions and acceptances
• and plug them in hundreds of toy MC to estimate
the sensitivity to 2 bs (and the others
parameters), through an unbinned maximum
likelihood fit:
• 6 observables:: proper time,, 3 angles,, tagging
answer =0,,+1,,1,mass
• 8 physical parameterrs:: 2bs,, Gs, DGs,
R(T)
R(0), d(T),d(0)
• + detector parameters (resolutions, acceptances,
tagging)
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CMS time and angular acceptance
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