CMS / ATLAS production: quarkonia, cross section ... - Beauty 2009

CMS / ATLAS production: 

quarkonia, cross section, correlations 

Valery P. Andreev 

University of California, Los Angeles 

on behalf of the CMS and ATLAS Collaborations 

12 th International conference on B-physics at Hadron Machines 

BEAUTY09, Heidelberg, Germany 

7-11 September 2009

• Introduction 

Outline 

• LHC: schedule, ATLAS/CMS detectors 

• onia production at LHC 

– triggers 

– cross sections 

– polarization 

• b production at LHC 

– b tagging 

– cross sections 

– high luminosity run (P T reach) 

– correlations 

• conclusions 

BEAUTY09, 7-11 Sept. 2009 

2 

Valery Andreev, UCLA

Heavy Flavor study prospects 

in ATLAS and CMS vs luminosity 

• Cross sections for beauty, charm, onia 

Prompt and indirect J/Ψ, exclusive B decays 

• Onia production study 

– polarisation, correlations, Υ 

− 

• bb correlations 

• Life time of B hadrons 

• high P T b production cross section 

• B s oscillations 

• CP violation 

• FCNC rare decays (B µµK, B s µµ, …) 

BEAUTY09, 7-11 Sept. 2009 3 

Valery Andreev, UCLA 

Ο ( 10 pb -1 ) 

Ο ( 100 pb -1 ) 

Ο ( 1 fb -1 ) 

Ο ( 10 fb -1 )

A.Grelli, EPS09 

Heavy Flavour production 

• b production at hadron colliders 

– Huge cross section 

– in other SM processes (top, Z, …) 

– Challenge for perturbative QCD 

– Tevatron measurements are on top 

of NLO QCD calculations 

– New physics searches: 

• b jets as a signal feature (SM Higgs, 

SUSY decay chains, …) 

• b jets as a background 

• onia production at hadron colliders 

– prompt quarkonia production not yet 

understood 

– Color Singlet Model, Color Octet 

Mechanism, NRQCD, ... 

– polarisation measurements challenging 

theory as well 



General-purpose detector 

Onion structure: 

• Tracker 

• Calorimeters 

• Muon system 

Precise 

e, µ, γ, jets, E T 

Efficient 

b tagging, τ detection 

The CMS detector 



The ATLAS detector 

General-purpose detector 

Toroids 

Tile CAL 

2T solenoid 

LAr CAL 

TRT and Si tracker 

Muon detector 



LHC schedule 2009-2010 

http://lhc-commissioning.web.cern.ch/lhc-commissioning/luminosity/09-10-lumi-estimate.htm 



Quarkonia production measurement 

at LHC (CMS) 

• low luminosity (start-up) conditions 

– Lowest possible trigger thresholds, if any 

• Double-muon trigger with P T > 3 GeV/c, |η| < 2.4 

• Single muon trigger with threshold P T > 3,5,9 GeV/c – depends on lumi 

– open-muon trigger at start-up 

• Displaced dimuon vertex trigger 

– Take advantage of already aligned by cosmics tracker 

• close to ~ 100 pb -1 collision data alignment scenario 

• Expectation for 10 pb -1 

– 250k J/Ψ 

– 60k b J/Ψ X 

– 60k Υ " 

Helpful in detector calibration and trigger/tracker/muon chambers commissioning 



Quarkonia production measurement 

• Trigger (dimuon) 

– Topological dimuon trigger 

at LHC (ATLAS) 

ATLAS, CERN-OPEN-2008-020 

– µ6µ4 µ 1: P T > 6 GeV/c µ 2: P T > 4 GeV/c 

OR 

• µ4µ4 at start-up 

– single muon trigger P T > 6 GeV/c (µ4 at start-up) 

– dimuon trigger seeded by single muon, extended region of interest 

• off-line: mass and vertex cuts 

J/ψ with CMS ATLAS 

trigger 2µ3 µ6µ4 

mass res.(MeV) 30 54 

yield/10pb -1 250k 150k 

ATLAS 

µ 1 µ2 



µ 1 

no vtx and cτ cut Prompt 

J/ψ and ϒ 

production

J/ψ production study (CMS) 

PAS BPH-07-002 

3 pb -1 3 pb -1 

Inclusive J/ψ cross 

section: 

1-D fit to mass spectra 

Prompt vs 

non-prompt (BJ/ψ X): 

2-D fit to mass spectra 

and pseudo-proper 

decay length 

• Systematics dominated 

already at start-up 

Systematics at ~15% level 

• Competitive with Tevatron 

starting with the first 

picobarns 



J/ψ and ϒ production (ATLAS) 

no vtx and cτ cut 

• 10 pb-1 estimate 

• prompt fraction selected 

by vertexing, cut on 

pseudo-proper time 

Polarisation as discriminant between 

models 



€ 

t = Lxy • MJ / Ψ 

J / Ψ 

pT •c

Quarkonia polarization analysis 

ATLAS 

α parameter: 

+1 – transverse polarization 

- 1 – longitudinal 

0 – unpolarized 

efficiency depends on polarisation 

CMS 

Tevatron: no model to describe cross section and polarization at the same time 



B-production / QCD aspects 

• present status of the production phenomenology at hadron colliders 

– The shape of transverse momentum and angular distributions as well as the 

azimuthal angular correlations in a reasonable agreement with perturbative 

QCD 

– The observed cross-sections are larger than QCD predictions 

– The agreement between experiment and theory has improved due to the 

evolution of latter mostly a consequence of improved experimental inputs 

• More precise parton density function, up-to-date α s 

• Improvement on fragmentation effects estimate 

– The agreement is not complete, to improve the phenomenological 

description requires new experimental input (LHC) 

Review on R=σ b/σ NLO , 

F.Happaher, P.Giromini,F.Ptohos PRD 73, 014026 (2006) 

• experiment is 

systematically 

above NLO QCD 

prediction 



• ATLAS/CMS 

– |η| < 2.5/2.4 

• Tracker/muon detector 

acceptance 

– high-P t muon trigger 

– b-tagged jet trigger 

• LHCb 

– Forward spectrometer 

• 1.9 < η < 4.9 

– much softer p t triggers 

There is an overlap 

B acceptance 

CMS study: much higher P t 

can be reached 

BEAUTY09, 7-11 Sept. 2009 Valery Andreev, UCLA 14

CMS PAS-BTV-07-003 (2008) 

B tagging 

• most performing: 

Combined Secondary 

Vertex algorithm 

(high luminosity run) 

• different misalignment 

scenarios studied 

• SoftMuon algorithm: 

• efficiency < 20 % 

(B branching ratio) 

• robust against 

misalignment 

BEAUTY09, 7-11 Sept. 2009 Valery Andreev, UCLA 15

CMS Analysis: Inclusive b production 

CMS Note 2006/120, V.P. Andreev, D.B. Cline, S. Otwinowski 

• B production total cross section 

• Differential cross sections dσ/dp t’ dσ/dη 

– Selection 

• b-tagged jet 

• semileptonic b-decays into muons 

– Luminosity: 10 fb -1 

• The most energetic b tagged jet as 

the reconstructed B-particle candidate 

• the rate of b jets is a direct measurement of 

the b production with only small fragmentation 

systematics 



Event selection 

Trigger 

Level-1: High Level Trigger: 

“single µ”, “muon + b-jet”, 

p t >14 GeV/c, |η| < 2.1 P t µ >19GeV/c, Et jet >50GeV, |η| < 2.4 

ε = 18 % ε = 60 % 

• B-tagged jet: E t > 50 GeV, |η| < 2.4 

ε = 65 % (barrel), 55 % (endcap) 

• Muon associated with B-tagged jet 

ε = 75 % 

Off-line selection 



B-jet resolution/B-tag efficiency 

P t > 170 GeV/c 

σ = 12.9 % σ = 5.7 % 

B tag: 

inclusive secondary vertex in jets 



Fit results 

QCD events MC: 230 

Muon P t w.r.t. the closest B jet 

b 

c 

udsg 



Nb =5250 (56 % 

Nc = 2388 (26% 

Nudsg= 1740(18% 

--------- 

9378 events 

Fit: 

Nb =5222 ± 501 

Nc = 2050 ± 728 

Nudsg =1778 ±341 

--------- 

9050 events

B hadron 

– P t > 50 

GeV/c 

– | η | < 2.4 

b-quark P t reach 

statistical 

systematic 

We can reach 1.5 TeV as the highest measured B hadron P t 



B production at LHC, P T reach 

Extended P t reach 

CMS analysis summary 

• ~16 M b events to be selected with 10 fb -1 

• b purity in a range from 70 % to 55 % 

• up to 1.5 TeV B-hadron P t reach 



Exclusive B production 

CMS PAS-BPH-09-001 (2009) 

10 TeV 

B + J/ψ K + 

B 0 J/ψ K *0 



Differential cross sections 

can be measured with 

statistical precision better 

than 10 % for 10 pb -1 

luminosity (early data)

B production mechanisms at LHC 

PYTHIA MC prediction @ LHC 

hep-ph/0003142 

σbb = 465 µb ( ~ 500 µb ) 

Pair creation (LO) : 

~50 µb 

Gluon splitting (NLO) : 

~190 µb 

Flavor excitation (NLO) : 

~220 µb 

• Both, ATLAS and CMS, will 

measure bb-correlations 

• Δϕ bb as discriminating variable 

• B → J/ψ X + B → µ 

• Δϕ bb = φ J/Ψ - φ µ 

• b-jet + B → µ 

• Δϕ bb = φ b-jet - φ µ 

• b-jet + b-jet 

• Δϕ bb = φ b-jet – φ b-jet 



CMS PAS-BPH-08-004 (2009) 

_ 

bb correlations 

B → J/ψ X + B → µ 

• bb fraction extracted by simultaneous 3D unbinned maximum LH to 

J/ψ invariant mass, J/ψ transverse flight length, µ impact parameter 

• Expected total uncertainty between 15 and 25 % for 50 pb -1 



Conclusions 

• data on b production and quarkonium need to be yet 

reconciled with theory 

• ATLAS and CMS have an intense program for the QCD test 

in Heavy Flavor production at LHC energies 

• correlations and polarization measurements are foreseen to 

investigate in detail production mechanisms 

• HF measurements important for New Physics search 

Eagerly looking forward to the first LHC collision data 

this year !

CMS / ATLAS production: quarkonia, cross section ... - Beauty 2009

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