High-pT QCD and Heavy Quarks Vadim Oreshkin on behalf of CMS - - PowerPoint PPT Presentation

High-pT QCD and Heavy Quarks

Vadim Oreshkin

• n behalf of CMS collaboration

Petersburg Nuclear Physics Institute HSQCD 2014 Gatchina, Russia The 1th of July, 2014

Outline Part I. High QCD Dijet production cross section at 8 TeV 1. 3-jet production cross section at 7 TeV, determination 2. Colour coherence 3. Inclusive three- and four-jet Events: topological distributions 4. Part II. Heavy quarks

• ver

production cross-section ratio 1. branching fractions 2. Peaking structures in the J/ψφ mass spectrum 3. prompt J/ψ pair production 4.

This is only a small fraction of all results. For more results, see: https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSMP https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsBPH

pT αs χb2 χb1 → μμ B(s)

Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 2/14

Part I. QCD Importance of QCD measurements at CMS: test pQCD predictions in previously unexplored energy region 1. constrain PDF and determine 2.

• btain input for MC tuning

3. understand the main background to many new physics searches 4.

αs

Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 3/14

Dijet production cross section at 8 TeV

CMS-PAS-SMP-14-002

dijet mass spectrum corrected for detector effects (unfolded) measured cross section agree with the prediction of pQCD at NLO 1. 5 different PDF sets were used: CT10, MSTW2008NLO, NPDF2.1, ABM11, and HERAPDF1.5 2. dijet-mass range: 0.35 TeV to 5.5 TeV 3. experimental and theoretical uncertainties are

• comparable. So these results can be used to contrain

PDF fits 4.

Experimental and theoretical uncertaintie for different bins of experimental: 5% at low , 20% at high theoretical: PDF variation - 30%, choice of scale - 5%-10% for , 40% - for outer bins and for high dijet masses

| | ymax Mjj Mjj < 1.5 ymax ymax

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3-jet production and determination

CMS-PAS-SMP-12-027

Double differential cross section as function of and : Agreement between NLOxNP predictions and data for all PDFs except for AMB11 PDF 1. size of uncertainties allows for contraining PDF and determining 2. By adding as a free parameter and fitting to data, is determined 1. using different regions of allows testing its running 2. behaviour vs Q is consistent with the dependence predicted by RGE and extends to 1 TeV region 3.

αs

m3 ymax = ( + + m2

3

p1 p2 p3)2 | | = max(| |, | |, | |) ymax y1 y2 y3 αs ( ) αs MZ α( ) MZ m3

Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 5/14

Colour coherence

EPJC 74 (2014) 2901 (CMS-SMP-12-010)

2 leading jetsx with back-to-back topology color-connectedness of the third jet close to dijet event plane angle in plane Effect of colour coherence:

Results: none of the MC describe the data satisfactorily Pythia 6 has the weakest effect Pythia 8 has stronger effect Madgraph ( exact LO ME) better Herwig++ best in central region

β (η, ϕ)

2 → 3

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Inclusive 3- and 4-jet events: topological dists

CMS-PAS-QCD-11-006 The topology of the multijet events and kinematics of the outgoing partons are studied to test higher order QCD and to get a deeper insight to the underlying physics. Topological and kinematical variable are measured for 3- jet and 4-jet events Three-Jet events: invariant mass of the 3-jet subsystem scaled energies of the jets ordered with respect to energies in c.m.s determined by angles between jets Four-jet events: invariant mass of the 4-jet subsystem Bengtsson-Zerwas Angle: angle between planes containing the two leading jets and the two non-leading jets Natchmann-Reiter Angle: angle between the momentum vector difference of the two leading jets and two non-leading jets

1 + 2 → 3 + 4 + 5 = , + + = 2 xi 2Ei s345 − − − √ x3 x4 x5 1 + 2 → 3 + 4 + 5 + 6 cos = θBZ ( × ) ⋅ ( × ) p⃗

3

p⃗

4

p⃗

5

p⃗

6

| × || × | p⃗

3

p⃗

4 p⃗ 5

p⃗

6

cos = θNR ( − ) ⋅ ( − ) p⃗

3

p⃗

4

p⃗

5

p⃗

6

| − || − | p⃗

3

p⃗

4 p⃗ 5

p⃗

6 Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 7/14

Inclusive 3- and 4-jet events: topological dists

CMS-PAS-QCD-11-006

Mass distributions: Pythia 8 gives best description Herwig++ has largest deviations (>15%) Angular distribution: best described by Herwig++ Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 8/14

Part II. Heavy quark measurements measurements are limited to muon signal because of too high QCD background 1. high precision measurements of muons 2. excellent resolution of tracker- converted low energy photons 3. vertex displacement id 4. flexible high level trigger expoits vertex, mass and momentum constraints variety of triggers to cover 5. different processes resistance to pile-up : constant HLTSingleMuon trigger cross section achieved 6.

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production cross-section ratio

CMS-PAS-BPH-13-005 Process of interest: 1. decays into two muons 2. converts into in the bulk of detector 3.

Invariant mass of a candidate is calculated through: kinematic fit with contraints 1. 2. Challenges to detector performance: small difference btw. and masses 1. small production cross section 2. Candidate invariant mass spectrum for one of four bins:

Main systematic uncertainties:

signal parametrisation 1. limited size of MC sample 2. uncertainty on the ratio of the branching fractions 3.

Results: Red curve - theoretical prediction from PRD 86 (2012) 074027. Conclusion: The ratio dies not show a significant dependence on the transverse momentum.

χb2 χb1

(1P) → Υ(1S) + γ χn Υ γ e+e−

m( ) = 0 e+e− m(μμ) = m(Υ(1S)) χb1 χb2 (Υ) pT

Υ(1S)

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Rare decays: branching fractions

CMS-PAS-BPH-13-004

Likelihood function: S/(S+B) distribution:

CMS experimental result: with significance upper limit: with 95% C. L. Joint CMS + LHCb result: with significance with significance Comparison to other experiments:

→ μμ B(s)

B( → μμ) = 3.0 × Bs

+1.0 −0.9

10−9 4.3σ B( → μμ) < 1.1 × Bd 10−9 B( → μμ) = 2.9 ± 0.7 × Bs 10−9 > 5σ B( → μμ) = 3.6 × Bd

+1.6 −1.4

10−10 < 3σ

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Peaking structures in the J/ψφ mass spectrum

CMS-PAS-BPH-11-026

Process: Candidate reconstruction (based on 2 muon and 3 kaon tracks from b-vertex): J/ψ candidate: 1. φ candidate: lowest-mass pair of , GeV 2. B+ yield as a function of (sort of projection of the Dalitz plot):

fitting procedure: Unbinned likehood fit (UML) peaks: S-wave BW convolved with Gaussian continuum: 3-body Phase space B+ yield calculation in each interval: UML fit to mass with constraint on 1. Gaussian with predefined mean and width corresp. to 2. corrected for efficiency determined from MC(Srelative, since Branching fraction are not measured) 3. Two peaking structures observed: MeV (significance > 5σ) MeV Angular analysis would help to elucidate the nature of these structures.

→ J/ψ(→ )ϕ(→ ) B± μ+μ− K +K − K ± μ+μ− K −K + 1.008 < m < 1.034 Δm

Δm = m( ) − m( ) μ+μ−K +K − μ+μ− Δm m(J/ψϕK) Δm B± = 4148.0 ± 2.4(stat) ± 6.3(syst) m1 = 4313.8 ± 5.3(stat) ± 7.3(syst) m2

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prompt J/ψ pair production

CMS-PAS-BPH-11-021 higher-pT: first-time probe of color-octet J/ψ states 1. more central rapidity than LHCb 2. Event selection and candidate reconstruction final state 1. trigger: unprescaled 3-muon trigger with dimuon mass close to mass of J/ψ 2. candidate search: 2 J/ψ candidates based on 3. cuts that maximise coverage of the J/ψ P.S. within muon acceptance 4. topological cuts: tranverse decay length of leading J/ψ cm and separation between two J/ψ 5. DPS or SPS production? Model-independent Monte Carlo calculation of efficiencies: J/ψ momenta borrowed from data. no evidence for

(signal search interval 9.15-9.64 GeV, sidebands: 8.68-9.16 GeV, 9.64-10.12 GeV)

should be suppressed according to NRQCD non-zero population in predicted by DPS models Total cross section (in dedicated P.S. window):

J/ψJ/ψ → 4μ μ+μ− ∈ (−0.05, 0.1) δd < 8 → J/ψJ/ψ ηb |Δy| ∈ (2.6, 4.4) ⇐ σ(pp → J/ψJ/ψ + X) = 1.49 ± 0.07(stat) ± 0.13(syst) nb

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Summary

Part I. High QCD Dijet and 3-jet production: pQCD NLO predictions are tested 1. strong coupling constant determined by fitting to data 2. Colour coherence: all MC underestimate effect of colour coherence, Herwig++ is most close to data 3. 3- and 4-jet Events: having different shower models, Pythia 6, Pythia 8 and Herwig++, describe angular and mass distributions with different extent of success 4. Part II. Heavy quarks

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production: measured and provide important inputs to constrain future studies

• f quarkonium production.

1. Branching fractions of are measured 2. Peaking structures in the J/ψφ mass spectrum: two peaks found 3. prompt J/ψ pair production: no evidence for found (as predicted by NRQCD), non-zero population at large found as predicted by DPS models 4.

pT χb2 χb1 → μμ B(s) → J/ψJ/ψ ηb Δy

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