b 0 s j/ lhc review nicolò magini university and infn, firenze for the atlas, cms and lhcb...

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

Beauty 2006, Oxford28th September 2006

BB00ss J/ J/ LHC review LHC review Nicolò Magini 2

OutlineOutline

B0s mesons and the B0

s J/ decay

Reconstruction and selection with LHC detectors

Analysis and parameter extraction



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



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



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



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



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



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



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



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



The detectorsThe detectors CMSCMS

LHCbLHCb

Dedicated forward detectorRICH for PIDTriggering VELO

ATLASATLAS

Multipurpouse central detectors



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



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



Kinematic fittingKinematic fittingConstraints applied

Common 4 track vertex J/mass constraintVertex pointing constraint

CMS

Mass resolution = 14 MeV/c2



Proper time Proper time resolutionsresolutionsCMS - t = 77 fs

LHCb - <terr> = 36.0 fs

ATLAS - t = 84 fs



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

( ) ( )



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



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.



Selection efficiencySelection efficiency (t,)

As a function of proper time

As a function of angles



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



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



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/ +-)



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



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



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



ReferencesReferences

CMS-NOTE 2006/121 LHCb NOTE 2006/047 and

L. Fernandez, PhD Thesis ATLAS Physics and detector

performance TDR. Vol. II

b 0 s j/ lhc review nicolò magini university and infn, firenze for the atlas, cms and lhcb...

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