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

High-pT QCD and Heavy Quarks Vadim Oreshkin on behalf of CMS collaboration Petersburg Nuclear Physics Institute HSQCD 2014 Gatchina, Russia The 1th of July, 2014

α s p T χ b 2 χ b 1 → μμ B ( s ) Outline Part I. High QCD 1. Dijet production cross section at 8 TeV 2. 3-jet production cross section at 7 TeV, determination 3. Colour coherence 4. Inclusive three- and four-jet Events: topological distributions Part II. Heavy quarks 1. over production cross-section ratio 2. branching fractions 3. Peaking structures in the J/ψφ mass spectrum 4. prompt J/ψ pair production 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 Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 2/14

α s Part I. QCD Importance of QCD measurements at CMS: 1. test pQCD predictions in previously unexplored energy region 2. constrain PDF and determine 3. obtain input for MC tuning 4. understand the main background to many new physics searches Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 3/14

y max y max < 1.5 M jj M jj y max | | Dijet production cross section at 8 TeV CMS-PAS-SMP-14-002 dijet mass spectrum corrected for detector effects Experimental and theoretical uncertaintie for different bins of (unfolded) experimental: 5% at low , 20% at high 1. measured cross section agree with the prediction of theoretical: PDF variation - 30%, choice of scale - 5%-10% for pQCD at NLO , 40% - for outer bins and for high dijet 2. 5 different PDF sets were used: CT10, masses MSTW2008NLO, NPDF2.1, ABM11, and HERAPDF1.5 3. dijet-mass range: 0.35 TeV to 5.5 TeV 4. experimental and theoretical uncertainties are comparable. So these results can be used to contrain PDF fits Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 4/14

= ( |, | m 3 α s + m 2 3 p 1 p 2 p 3 ) 2 | | = max(| |, | |) + y max y 1 y 2 y 3 α s ( ) α ( ) M Z m 3 y max 3-jet production and determination CMS-PAS-SMP-12-027 Double differential cross section as function of and : 1. Agreement between NLOxNP predictions and data for all PDFs except for AMB11 PDF 2. size of uncertainties allows for contraining PDF and determining 1. By adding as a free parameter and fitting to α s M Z data, is determined 2. using different regions of allows testing its running 3. behaviour vs Q is consistent with the dependence predicted by RGE and extends to 1 TeV region Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 5/14

β 2 → 3 ( η , ϕ ) Colour coherence EPJC 74 (2014) 2901 (CMS-SMP-12-010) Results: 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: 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 Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 6/14

5 × ) ⋅ ( × ) p ⃗ 3 p ⃗ 4 p ⃗ 4 p ⃗ 6 | × || | ( = ) − ) ⋅ ( − ( θ NR cos p ⃗ 6 p ⃗ 5 p ⃗ p ⃗ 3 × θ BZ 3 − 5 p ⃗ 6 | − || | 1 + 2 → 3 + 4 + 5 p ⃗ 3 p ⃗ 5 p ⃗ 6 p ⃗ = = − cos 1 + 2 → 3 + 4 + 5 + 6 x 5 x 4 x 3 √ − − , s 345 2 E i x i = 2 + + p ⃗ 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: Four-jet events: invariant mass of the 3-jet subsystem invariant mass of the 4-jet subsystem scaled energies of the jets ordered with respect to energies Bengtsson-Zerwas Angle: angle between planes containing in c.m.s the two leading jets and the two non-leading jets determined by angles between jets 4 p ⃗ Natchmann-Reiter Angle: angle between the momentum vector difference of the two leading jets and two non-leading jets 4 p ⃗ 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: Angular distribution: best described by Herwig++ Pythia 8 gives best description Herwig++ has largest deviations (>15%) Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 8/14

Part II. Heavy quark measurements different processes 1. measurements are limited to muon signal because of too high QCD background 2. high precision measurements of muons 6. resistance to pile-up : constant HLTSingleMuon trigger cross 3. excellent resolution of tracker- section achieved converted low energy photons 4. vertex displacement id 5. flexible high level trigger expoits vertex, mass and momentum constraints variety of triggers to cover Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 9/14

χ b 1 χ b 2 (1 P ) → Υ(1 S ) + γ χ n Υ γ e + e − m ( ) = 0 χ b 2 m ( μμ ) = m (Υ(1 S )) χ b 1 e + e − (Υ) p T Υ(1 S ) over production cross-section ratio CMS-PAS-BPH-13-005 Main systematic uncertainties: Process of interest: 1. 1. signal parametrisation 2. decays into two muons 2. limited size of MC sample 3. converts into in the bulk of detector 3. uncertainty on the ratio of the branching fractions Invariant mass of a candidate is calculated through: kinematic fit with contraints Results: 1. 2. Challenges to detector performance: 1. small difference btw. and masses 2. small production cross section Candidate invariant mass spectrum for one of four bins: Red curve - theoretical prediction from PRD 86 (2012) 074027. Conclusion: The ratio dies not show a significant dependence on the transverse momentum. Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 10/14

−0.9 B ( 4.3 σ 10 −9 B d +1.0 B s × → μμ ) = 3.0 B ( B ( s ) → μμ 10 −9 → μμ ) = 2.9 ± 0.7 × → μμ ) < 1.1 × B s 10 −9 > 5 σ B ( → μμ ) = 3.6 × B d +1.6 −1.4 10 −10 < 3 σ B ( Rare decays: branching fractions CMS-PAS-BPH-13-004 Likelihood function: CMS experimental result: with significance upper limit: with 95% C. L. Joint CMS + LHCb result: with significance with significance Comparison to other experiments: S/(S+B) distribution: Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 11/14

m ( J / ψϕK ) B ± = 4313.8 ± 5.3(stat) ± 7.3(syst) m 1 = 4148.0 ± 2.4(stat) ± 6.3(syst) B ± → J / ψ (→ ) ϕ (→ ) μ + μ − Δ m μ + μ − 1.008 < m < 1.034 Δ m Δ m = m ( ) − m ( ) μ + μ − Δ m m 2 Peaking structures in the J/ψφ mass spectrum CMS-PAS-BPH-11-026 Process: μ + μ − K + K − K + K − K ± fitting procedure: Candidate reconstruction (based on 2 muon and 3 Unbinned likehood fit (UML) kaon tracks from b-vertex): peaks: S-wave BW convolved with Gaussian 1. J/ψ candidate: continuum: 3-body Phase space 2. φ candidate: lowest-mass pair of , K − K + B+ yield calculation in each interval: GeV 1. UML fit to mass with constraint on B+ yield as a function of (sort of projection of the Dalitz plot): 2. Gaussian with predefined mean and width corresp. to 3. corrected for efficiency determined from MC(Srelative, since Branching fraction are not measured) Two peaking structures observed: MeV (significance > 5σ) MeV Angular analysis would help to elucidate the nature of these structures. Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 12/14

∈ (−0.05, 0.1) δd < 8 μ + μ − J / ψJ / ψ → 4 μ → J / ψJ / ψ η b |Δ y | ∈ (2.6, 4.4) ⇐ σ ( pp → J / ψJ / ψ + X ) = 1.49 ± 0.07( stat ) ± 0.13( syst ) nb prompt J/ψ pair production CMS-PAS-BPH-11-021 1. higher-pT: first-time probe of color-octet J/ψ states 2. more central rapidity than LHCb Event selection and candidate reconstruction 1. final state 2. trigger: unprescaled 3-muon trigger with dimuon mass close to mass of J/ψ 3. candidate search: 2 J/ψ candidates based on 4. cuts that maximise coverage of the J/ψ P.S. within muon acceptance 5. topological cuts: tranverse decay length of leading J/ψ cm and separation between two J/ψ DPS or SPS production? Model-independent Monte Carlo non-zero population in predicted by DPS calculation of efficiencies: J/ψ momenta borrowed from data. models Total cross section (in dedicated P.S. window): 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 Vadim Oreshkin High-pT QCD and heavy quarks (CMS) slide 13/14