b 0 s j/ lhc review nicolò magini university and infn, firenze for the atlas, cms and lhcb...
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BB00s s J/ J/
LHC reviewLHC review
Nicolò MaginiUniversity and INFN, FirenzeFor the ATLAS, CMS and LHCb
collaborations
Oxford, 28th September 2006Beauty 2006
The 11th International Conference on B-Physics at Hadron Machines
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OutlineOutline
B0s mesons and the B0
s J/ decay
Reconstruction and selection with LHC detectors
Analysis and parameter extraction
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ss
ss
BB00ss
BB00ss
BB00s s mixingmixing
BBss are too heavy to be produced at are too heavy to be produced at (4s)(4s) B factories B factoriesstudied with high statistics at hadron collidersstudied with high statistics at hadron colliders
CDFCDF and and D0D0 results on mixing results on mixing
Standard Model prediction for ssssssss
ss
ms = 17.77 ± 0.10 ± 0.07 ps-1 17 ps-1 < ms < 21 ps-1 @ 90% CL
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BBs s J/ J/ ++--KK++KK--
CP violating weak phase
SM predicts s = 2s ~ O(0.03)
s
b t
t Vcb
V*cs
Vtb
Vtb Vts*
Vts*
BR(BsJ/ )=(9.3±3.3)x10-4
BR(J/+-)=(5.93±0.06)%BR (K+K-)=(49.2±0.6)%
s
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New physics in New physics in ss
Present measurements still allow for almost arbitrary NP contributions to ss
Measuring s will greatly constrain flavour violation in NP models
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BBss J/ J/
BBss decay products are both decay products are both JJPCPC = 1 = 1---- states statesThe final state hasThe final state has CP = +1CP = +1 ifif L = 0,2L = 0,2 andand CP = -1CP = -1 ifif L = 1L = 1
The two contributions with opposite CP can be separated with an The two contributions with opposite CP can be separated with an angular analysisangular analysis of the final decay products of the final decay products
ℓ+
ℓ-
K+
K-
p p
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Angular distributionsAngular distributions
Time evolution is a function of the transversity amplitudes A0(t), A||(t) (CP = +1) and A(t) (CP = -1)
Known functions of the three angles describing decay product kinematics in the transversity basis
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Angular distributions - Angular distributions - taggedtagged
The distributions depend on 8 independent parameters
• Amplitudes |A||(0)|,|A(0)| - Strong phases 1, 2
• Width difference ΔΓs = (ΓH - ΓL) - Average width Γs = (ΓH+ΓL)/2
•Mass difference Δms - Weak phase s
moduli2
interference
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Angular distributions - Angular distributions - untaggeduntagged
Remarkable feature: If s≠0 the distributions are still sensitive
to the weak phase s
Terms with ms cancel: not necessary to resolve the very fast oscillations
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B Physics at LHC B Physics at LHC
b production atb production at LHCLHCLuminosityLuminosity
2x102x1033 33 cmcm-2-2ss-1 -1 (ATLAS, CMS 2009)(ATLAS, CMS 2009)
2x102x1032 32 cmcm-2-2ss-1 -1 (LHCb)(LHCb)
0.5 mb 0.5 mb about about 101066 (10 (1055) ) bb pairs/sec bb pairs/sec
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The detectorsThe detectors CMSCMS
LHCbLHCb
Dedicated forward detectorRICH for PIDTriggering VELO
ATLASATLAS
Multipurpouse central detectors
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Trigger selectionTrigger selection
Di-muon trigger at L1
Decay chain reconstruction with fast/regional tracking at HLT (lifetime biased)
ATLAS/CMSDetails in talks by J. Kirk and E. Rodrigues
ATLAS : pT () > 6,3 GeV/c
CMS : pT () > 3,3 GeV/c
LHCb
Di-muon trigger at L0
L1/HLT: lifetime unbiased single & di-muon streams + lifetime biased J/ stream
LHCb : pT() > 1.5 GeV/c
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KK++
KK--ss
Offline Offline reconstructionreconstruction
reco with tracker + ID with muon detector
K reco with tracker - ID only in LHCb
Common 4-track vertex
p(B0s) // L
Flavour tagging
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Kinematic fittingKinematic fittingConstraints applied
Common 4 track vertex J/mass constraintVertex pointing constraint
CMS
Mass resolution = 14 MeV/c2
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Proper time Proper time resolutionsresolutionsCMS - t = 77 fs
LHCb - <terr> = 36.0 fs
ATLAS - t = 84 fs
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Event yieldsEvent yieldsSignal Background (B/S)
ATLAS (10 fb-1) 106000 0.30
CMS (10 fb-1) 109000 0.33
LHCb (2 fb-1) 131000 0.12
Background is mostly combinatorial for LHCb,
combinatorial + B0J/K*0+-K±+ for ATLAS/CMS
( ) ( )
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Angular analysisAngular analysis Goal: extract from the angular
distributions of the decay products the parameters of interest (e.g. s/s , s)
In principle: single maximum likelihood fit to extract the parameters simultaneously from all available data
In practice: many parameters, complicated distributions use different multi-step approaches to fitting
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First step: untagged First step: untagged fitfit
Example: CMS measurement of s/s , s
Angular distributions to extract
signal
BdJ/K* bkg
Combinatorial bkg
t– selection efficiency as function of proper time & angles
Gs(m,mss– mass resoultion (gaussian)
Maximum likelihood fit with P.D.F.
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Selection efficiencySelection efficiency (t,)
As a function of proper time
As a function of angles
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Results – untagged Results – untagged analysisanalysis
Statistical error for 100k evts (NSEL with Lint = 10 fb-1)
Systematical errors for 13k evts (NSEL with Lint = 1.3 fb-1)
Main source is modeling of proper time bias need control samples to measure in data
CMS also evaluated Angular Moments analysis, results only slightly worse than MLH fit
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Next step: tagged fitNext step: tagged fit Example: LHCb one-angle distribution
analysis
Flavour tagging methods used: OS l, OS K, OS Vtx charge, SS K Performance =57%, tag=33% eff=6.6%
ms and tag determined using BsDs as control sample
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Results: tagged Results: tagged analysisanalysis
LHCb also combines other lower statistics decays to CP eigenstates (no angular analysis)
Could also add J/ e+e- channel (not included here, statistics 1/6 of J/ +-)
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Results - summaryResults - summary
s/s (stat err) s (stat err)
ATLAS (10 fb-1) 0.03 0.08
CMS (10 fb-1) 0.015 0.072 (untagged)
LHCb (2 fb-1) 0.0092 0.022
Results for one year at nominal low luminosity
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ConclusionsConclusions
Any large NP effect will be seen “soon”
SM value of s will be found at 3 within 5 years data taking at LHCb
ATLAS & CMS can also give good contributions to the measurement
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AcknowledgementsAcknowledgements
M. Smizanska, J. Catmore for the ATLAS collaboration
V. Ciulli, N. Magini, L. Wilke, T. Speer, K. Prokofiev, S. Shulga, T. Ilicheva for the CMS collaboration
J. Van Hunen, L. Fernandez for the LHCb collaboration