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Recent results of the CMS experiment
QFTHEP2015The 22th International Workshop on High Energy Physics and Quantum
Field Theory, Samara (Russian Federation)
Dr. Bora Akgün – Rice University(on behalf of CMS Collaboration)
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Outline
25 June 2015
• CMS - Data Collection• Selected Results• Vector Bosons – arXiv:1505.06520, arXiv:1503.05467• Quarkonia – PRL 114 (2015) 191802, arXiv:1501.07750• Rare Decays – Nature 522 (2015) 68• Top Physics – arXiv:1505.04480• SUSY – arXiv:1502.06031• Exotica – arXiv:1502.04994• What to expect from Run2 and beyond
• Summary
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Data Collection
25 June 2015
• Results presented in this talk have been produced with LHC Run-1 data collected by CMS experiment
• CMS Public Results twiki• https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResults
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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CMS Standard Model Summary Plot
25 June 2015
Great agreement btw theory and measurements
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Vector Bosons
25 June 2015
• W and Z can be measured very accurately through their leptonic decays, photon energies precisely measured in the electromagnetic calorimeter
• Z and photons used for calibration of jets, Z used as a candle to determine lepton efficiencies
• Vector boson plus jets are major backgrounds in beyond standard model searches and excellent testing ground for QCD NLO predictions
• Diboson processes (ZZ and γγ) are major SM backgrounds for Higgs measurements
• WZ and ZZ w/ Zνν major contribution to backgrounds in searches w/ large missing transverse energy (e.g. SUSY)
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Z+jets / Photon+jets
25 June 2015
Z+jets
Photon+jets
• V+jets are major backgrounds in beyond standard model searches and excellent testing ground for QCD NLO predictions
arXiv:1505.06520
njet≥1
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Z+jets / Photon+jets
25 June 2015
• The ratio of Z + jets to γ + jets• Both simulations reproduce the shape
of the ratio better than the individual distributions in all selections
arXiv:1505.06520
njet≥1
njet≥2
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Production cross-section for ZZllνν
25 June 2015
• ZZllνν production cross section measured • Using a profile likelihood fit to the reduced-ET
miss • Main backgrounds
• DY, WZ, WW,W+jets,top• σ(ppZZ) = 5.2+1.5
-1.4(stat)+1.4-1.1(syst)±0.2(lumi)pb at 7 TeV
• σ(ppZZ) = 6.9+0.8-0.8(stat)+1.8
-1.4(syst)±0.3(lumi)pb at 8 TeV
• Theory calculations w/ NLO QCD and NLO EW
• σ(ppZZ) = 6.2+0.3-0.2 at 7 TeV
• σ(ppZZ) = 7.6+0.3-0.3 at 8 TeV
arXiv:1503.05467
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Production cross-section for ZZllνν
25 June 2015
• ZZγ and ZZZ expected to be null at the tree level• Enhancement in ZZ production rate compared to SM indicate the existence
of anomalous boson couplings
arXiv:1503.05467
• No observation of new physics stringent limits on the relevant Anomalous Triple Gauge Coupling (ATGC) parameters
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Charmonium spectrum
25 June 2015
cross sections and polarizations
cross section ratio
observation, cross section
observation with > 5σ
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Prompt ψ(ns) cross-sections
25 June 2015
• Yields are corrected for efficiency and acceptance on an event-by-event basis
PRL 114 (2015) 191802
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Prompt ψ(ns) cross-sections
25 June 2015
• Yields are corrected for efficiency and acceptance on an event-by-event basis
• Four polarization scenarios are considered • PT reach is extended compared to previous measurements • FKLSW band is obtained in a fit to previous data w/ essentially PT <
30 GeV and extrapolated to higher PT values
PRL 114 (2015) 191802
un-polarized scenario
un-polarized scenario
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Bottomonium spectrum
25 June 2015
cross sections and polarizations cross section ratio
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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ϒ(ns) differential cross-sections
25 June 2015
• Acceptance calculated w/ polarization values measured by CMS (PRL 110 (2013) 081802)
• PT reach is extended compared to previous measurements
arXiv:1501.07750
ϒ(2S), ϒ(3S) scaled by 0.1, 0.01, respectively
NRQCD
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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ϒ(ns) production ratios
25 June 2015
arXiv:1501.07750
• Exponential fit – 10 < PT < 20 GeV• Power-law fit – PT >20 GeV• Change in ratios occur at the same PT range
in which dσ/dPT also changes behavior
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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BS0μ+μ- and B0μ+μ-
25 June 2015
• SM predicts small branching fractions for BS0μ+μ- and B0μ+μ-
• Direct flavor-changing neutral currents not possible in SM, theories beyond SM predict larger branching fractions
Nature 522 (2015) 68
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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First observation - BS0μ+μ- (CMS
& LHCb)
25 June 2015
• Weighted distribution of dimoun mass-spectrum, superimposed in a combined fit• First observation of BS
0μ+μ- (6.2σ) and evidence for B0μ+μ- (3.2σ)
Nature 522 (2015) 68
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Combined result - BS0μ+μ- (CMS
& LHCb)
25 June 2015
• Likelihood in BS0μ+μ- vs B0μ+μ- branching ratio plane
• BR: BS0μ+μ- = 2.8+0.7
-0.6 * 10-9 (0.76+0.20-0.18 * SM)
• BR: B0μ+μ- = 3.9+1.6-1.4 * 10-10 (3.7+1.6
-1.4 * SM)
Nature 522 (2015) 68
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Top mass measurements
25 June 2015
• The most massive particle known to date
• Very short lifetime shorter than hadronization timescale
• The only elementary high mass particle that has color• EWK, QCD and flavor physics
• Combined top mass using all CMS Run-1 data• 172.38±0.10(stat.) ±0.65(syst.) GeV
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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ttbar production cross-section at 7/8TeV
25 June 2015
• ttbar production cross-section measured w/ different channels at 7 and 8 TeV
• ttbar is a major background for many processes
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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ttbar differential measurements
25 June 2015
• MC generators predict harder dilepton mass and lepton PT spectrum than observed in data• Powheg+Herwig6 provide a satisfactory agreement • 8 TeV results are input for future MC tuning
arXiv:1505.04480
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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SUSY searches
25 June 2015
• SUSY, popular BSM theories• Solves the hierarchy
problem• Provides a suitable
dark matter candidate• SUSY corrections
allow for high energy unification of strong and electroweak couplings
• Searches involve typically the presence of large missing transverse energy and multijets
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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SUSY search w/ two leptons, jets and ET
miss
25 June 2015
arXiv:1502.06031
• The invariant mass distribution of the two-lepton system can exhibit an excess that increases with the di-lepton mass, followed by a sharp decrease, if the two leptons originate from the decay of a neutral particle decayed from a bottom squark-antisquark production
1. Mass difference btw Χ20 and Χ1
0 fixed to 70 GeV
2. Mass of the slepton chosen to lie halfway btw the masses of Χ2
0 and Χ10
• Lepton pair from the decay of an o-shell Z boson from gluino pair production
1
2
3
3.
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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SUSY search w/ two leptons, jets and ET
miss
25 June 2015
Mll> 20 GeVNjets ≥ 2
arXiv:1502.06031
Low mass significance: 2.6σNo evidence for a statistically
significant signal
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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SUSY search w/ two leptons, jets and ET
miss: setting limits
25 June 2015
arXiv:1502.06031
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Exotica: Narrow high-mass resonance decaying to Z and H
25 June 2015
arXiv:1502.04994• A search for a highly massive ( ≥ 0.8TeV) and narrow
resonance decaying to Z and H bosons that decay in turn to merged dijet and ττ final states• τ decaying leptonically and hadronically
• Advanced reconstruction techniques in boosted topology• Main backgrounds (simulated in MC)• Z+jets/W+jets• Ttbar, single-t• ZZ,WW,QCD
• Main source of uncertainty: limited MC statistics for signal efficiencies and background estimation
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Exotica: Narrow high-mass resonance decaying to Z and H
25 June 2015
arXiv:1502.04994
• From a combination of all possible decay modes of the τ leptons, production cross sections in [0.9-27.8fb] depending on the resonance mass [0.8-2.5TeV], are excluded at a 95% CL
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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What have we been doing lately?
25 June 2015
• Finishing analyses w/ 2012 data • Many results and publications (≥400), more to come..
• Long Shutdown (LS) – 1: 2013-2015• Fixes and upgrades to CMS detector
• Pixel detector taken out, misbehaving channels (~5%) fixed and installed back to CMS• w/ an additional part - pilot system w/ upgrade
electronics and readout• Muon detectors
• New stations (CSC/RPC) to complete redundancy, new electronics for triggering
• Narrower beampipe• Preparation for upgrade pixel detector in 2017
• Re-commissioning of the detector for Run-2
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Detector Improvements for Run 2
25 June 2015
Muons• Completion of forward detector
• 4th layer in ME• RPCs to |η|=4
Tracker • at -200C• Pixel Pilot System
New Beam pipe
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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13 TeV Collisons
25 June 2015
• June 3rd: First collisions at the new center of mass energy
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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What to expect in Run-2?
25 June 2015
• EW & Quarkonia• Improve on precision w/ higher statistics
• Top• Increase mass precisions w/ better jet energy scale
systematic uncertainties• Use boosted reconstruction techniques to perform
differential cross-section measurements• Improve precision on ttZ, ttW, ttH cross-sections
• Higgs• Look for deviations from SM w/ higher precision
• SUSY• Discovery?
• ??
Recent Results of the CMS Experiment - bora.akgun@cern.ch
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Summary
25 June 2015
• Only a small portion of results out of the rich long list of measurements performed by CMS
• In general predictions provide a good description of data• CMS is ready for Run-2 data taking (already started)• Sophisticated reconstruction techniques, analysis tools,
analysis methodologies and interpretation approaches have been developed and matured during the previous years
• Exciting times ahead of us
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