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The COMPACT MUON SOLENOID Experiment: Electroweak and Top Physics

The COMPACT MUON SOLENOID Experiment: Electroweak and Top Physics . Fermilab Joint Experimental-Theoretical Physics Seminar March 25, 2011. Jeffrey Berryhill FERMILAB For the CMS Collaboration. The COMPACT MUON SOLENOID Experiment: Electroweak and Top Physics .

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The COMPACT MUON SOLENOID Experiment: Electroweak and Top Physics

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  1. The COMPACT MUON SOLENOID Experiment:Electroweak and Top Physics Fermilab Joint Experimental-Theoretical Physics Seminar March 25, 2011 Jeffrey Berryhill FERMILAB For the CMS Collaboration

  2. The COMPACT MUON SOLENOID Experiment:Electroweak and Top Physics Fermilab Joint Experimental-Theoretical Physics Seminar March 25, 2011 Jeffrey Berryhill FERMILAB For the CMS Collaboration

  3. LHC Data 2010 statistics: Started 7 TeVpp collisions March 30. 47 pb-1 delivered , ~90 % in October alone Peak instantaneous luminosity: 2.1*1032 cm-2 s-1 36-40 pb-1 for CMS analysis for all results shown 2011 expectations: 5-10*1032 cm-2 s-1 930 bunches/beam 1-3 fb-1 delivered This week: 2.7*1032 cm-2 s-1 200 bunches/beam ~10 pb-1delivered A year from now, we may have 100X more data than shown today!

  4. The CMS detector Tracker coverage |h| < 2.5 Electron coverage |h| < 2.5 Muoncoverage |h| < 2.4 Efficient muon (electron) triggering down to 9 (17) GeV at L = 2E32 3.8 T solenoid + 76000 crystal ECAL + 200 m2 silicon = percent level lepton momentum resolution at high PT HCAL/HF coverage |h| < 5.0

  5. CMS Jets and Missing ET Most all of the Jet and Missing ET reconstruction here uses Particle Flow (PF) technique: All tracks/energy deposits sorted into charged/neutral hadron, electron, photon, or muon candidates Resulting set of corrected particles input to jet clustering, MET determination, HT, MT, etc. Significant improvement over traditional “CaloJets” for ~low-medium ET jets with tracker coverage Anti-kT clustering with R=0.5 used everywhere here JES of PF jets known to 3-4% PF MET FWHM in dijets ~10 GeV PF JET JES Dijet PF MET

  6. CMS b-Tagging Two classes of discriminators w/ 2-3 operating points each: Track counting: requires minimum number of tracks (2 or 3) exceeding some IP significance Simple secondary vertex: requires SV with 2 or 3 tracks, discriminant based on 3D flight distance “Loose” operating point for track counting has ~80% efficiency, ~10% mistag rate Efficiency well-modeled to 5% level.

  7. CMS Winter 2011 Results: Electroweak • Electroweak physics results • https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsEWK • Single boson production • W and Z inclusive cross sections • Z ds/dy , ds/dPT, ds/dm • Z AFB and weak mixing angle • W asymmetry • Z to tau tau • W to tau nu • Multi-boson production • Wg, Zg production and couplings • WW production and couplings • Boson + jets production • W,Z+jets : ds/dNjet and multiplicity ratios • Z + b • W polarization at high PT

  8. W and Z Production at the LHC • Occurs through admixture ofvalence/sea quark annihilation and sea/sea annihilation, at HERA-like parton x (10-5 to 10-2) • 4X higher cross sections than Tevatron, with stronger sea-sea component (lower x). • W sxBR(W→ln) ~ 10 nb per channel, 60/40 W+/W- • Z sxBR(Z→ll) ~ 1 nb per channel • W production in pp collisions is globally charge asymmetric: • pp has 2X more u-dbar than d-ubar collisions due to uud valence quark content of p • Sea quark-sea quark charge symmetric production dilutes W+/W- ratio from 2 to about 1.4 • Theory uncertainties at few percent level CTEQ, Phys.Rev.D82:074024,2010

  9. W and Z Cross Sections Provide a precision test of NNLO predictions and PDFs Alternatively, tests understanding of lepton efficiency, luminosity Z Selection: Two isolated electrons (muons), PT > 25(20) GeVdilepton mass 60-120 GeV Lepton scale and resolution calibrated to the Z peak (scale factor w/ MC < 1%) Lepton efficiencies known to 1% per lepton 20000 Z’s lumi, theory dominant err.

  10. W and Z Cross Sections W Selection: One isolated electron (muon), PT > 25 GeV, |h|<2.5(2.1) Dilepton veto No MET or MT cut Fit PF MET to extract W signal: Background from param. shape (e) or non-iso template (mu) Signal shape matched to Z lepton scale, resolution, efficiency, and Z recoil data 280000 W’s lumi, theory dominant err. PF MET, muons PF MET, electrons

  11. W and Z Cross Sections Excellent agreement with NNLO FEWZ+MSTW08 predictions Competitive estimator of luminosity Ratios test QCD to 2% level!

  12. Z rapidity shape Z rapidity shape sensitive to PDFs, especially at high rapidity HF shower shape used to identify electrons in 3.0 < |h| < 5.0 and extend Z acceptance Data agree with POWHEG NLO+CT10

  13. Z PT Z PT sampled from 0 to 600 GeV, sensitive to non-perturbative QCD effects at lowest PT higher-order perturbative QCD at highest PT POWHEG+Z2 deviates from data at both lowest and highest PT

  14. Z PT PYTHIA describing well low PT recoil for recent UE tunes FEWZ NLO correctly describes high PT tail

  15. Drell-Yan Differential Cross Section Drell-Yan spectrum measured from 15 GeV to 600 GeV in dimuon mass Leading (2nd) muons with PT > 16 (7) GeV, |h| < 2.1 (2.4) NNLO FEWZ + MSTW08 agrees well with mass shape

  16. Z Forward-Backward Asymmetry Z axial vector coupling to fermions produces small angular asymmetry on-shell Z/g* interference gives large, mass-dependent asymmetries defines forward (>0) and backward (<0) hemispheres. Significant distortions from FSR/mass resolution effects AFB vs. mass measured in 11 mass bins, 40-600 GeV, dielectrons and dimuons POWHEG+CT10 gives a good description of the uncorrected AFB vs. M

  17. Weak Mixing Angle Measurement A multi-dimensional unbinned likelihood fit of dilepton rapidity Y, M(mm), cosq* Acceptance*eff (G) and mass/FSR resolution ( R(s) ) convolved with LO generator level distribution P(ideal), with mixing angle a fit parameter Fit 12000 dimuon candidates, M = 60 to 120 GeV |h*| < 2.3 PT* > 18 GeV 2X improvement over traditional extraction from AFB

  18. W asymmetry Charge asymmetric production of W’s in pp sensitive to sea quarks at low x Measure A as a function of lepton h: 6 bins of h measured Statistical error 3-5% per bin Systematics 0.7-1.5% per bin Two different lepton PT cuts tested Two PDF scenarios tested: CT10W MSTW2008 Both include full weight of Tevatron W asymmetry data We now have the capability to further constrain contemporary PDFs

  19. Measurement of Z to tt Major background of tau searches Important control sample for tau ID, trigger, and reconstruction Selection: HPS Tau ID (“Hadron Plus Strip”): PF particles clustered into 1 and 3-prong taus with p0’s collected in an ECAL strip, eff. ~ 70% e or mu PT > 15 GeV HPS tau PT > 20 GeV MT < 50 GeV Signals in et, mt, em, and mm decay modes.

  20. Z to ttCross Section Tau ID efficiency is known to only 23% from control samples. Simultaneous fit to all four modes constrains both eff. and s.BR s.BR = 0.99 ±0.06 (stat) ±0.08 (syst) ± 0.04 (lumi) in agreement with Z →ee and mm Tau ID agrees with MC efficiency within a scale factor 0.96±0.07

  21. H to tt MSSM, tanb-enhanced Higgs production and decay to tt Bump hunt in tt mass Already improves upon recent Tevatron limits W to tn With HPS tau ID, can harvest 175 W’s in 18 pb-1 with ~50% purity 1 HPS tau, PT > 30 GeV PF MET > 35 GeV

  22. Wg, Zg Production Probes (anomalous) triple gauge boson couplings (aTGC) WWg, ZZg, Zgg Selection: W or Z selection in e or mu channels as above, and Photon with ET > 10 GeV, |h| < 2.5 and DR(l,g) > 0.7 with leptons Wg : PF MET > 25 GeV, Zg: MZ > 50 GeV Photon fake rates from jet samples, norm. from isolation-inverted Wg,Zg candidates About 500 Wg, 120 Zg expected. Good agreement with SM predictions SM = 49±4 pb SM = 9.6±0.4 pb

  23. Wg, Zg Production Charge-signed rapidity difference in good agreement with SM expectations aTGC limit setting, using observed photon ET spectrum, for Wg (left) and Zg (right)

  24. WW Production Direct test of WWg and WWZ gauge couplings and H decaying to WW LHC SM WW cross section is 43 pb, 3.7X Tevatron Selection: exactly 2 leptons, PT > 20 GeV Projected MET: If Df(l,MET) < p/2, use component of MET transverse to lepton direction use MET otherwise Projected MET > 20 (35) GeV for em (mm) Jet Veto: No PF jets with ET > 25 GeV and |h| < 5.0 Top veto: No b-tags or soft muon tags Z veto in ee, mm: No MZ±15 GeV, nor M < 12 GeV No jet veto No top veto No Z veto 13 events observed Background = 3.3±1.2 em/mm/ee = 10/1/2

  25. WW Production With WW leading lepton PT spectrum, derive limits on aTGCs With kinematic BDT of WW candidates, derive limits on s·BR(H→WW) Exclude 2.2X SM Higgs160 @95% CL Exclude 4-gen Higgs [144,207] @95% CL

  26. W, Z + jets Production Important test of QCD and recent NLO predictions Important background for numerous searches Selection: W lepton PT > 20 GeV, PF MT > 20 GeV Z leading (2nd) lepton > 20 (10) GeV, 60 < MZ <120 GeV PF jets > 30 GeV and |h| < 2.4 DR > 0.3 with electrons ET corrected for average pileup Z signal extracted with MZ fit W signal extracted with MT fit in N-tag categories

  27. W, Z + jets Production Inclusive >= Njet shapes in agreement with MadGraph predictions Systematics 10(30)% for N = 1(4), jet energy scale and lepton efficiency dominant Njet unfolding corrections via SVD methods estimated from MadGraph

  28. W, Z + jets Production Tests of Berends-Giele scaling: N jet/(N+1)jet ratios predicted to be roughly constant (a) with n, with a small linear correction term of slope b. W,Z B-G scaling in both lepton channels consistent with MadGraph prediction

  29. Z + b jet Production An important background for Higgs searches Tests schemes for heavy flavor QCD MEs (fixed flavor, variable flavor) Z + >= 1 b-tag PF jet, jet PT > 25 GeV, |h| < 2.1 65 events selected w/ 83% purity, 2 double-tag events w/ 80% purity Z+c/u/d/s content from fit to tagging discriminant shape Confirmed with high-efficiency lower-purity tagging selection Measure HF fraction ee Data 0.054±0.016 MCFM 0.043±0.005 MadGraph 0.051±0.007 mm Data 0.046±0.014 MCFM 0.047±0.005 MadGraph 0.053±0.007

  30. W Polarization in W + jets In pp collisions qgW+jet production has a charge-dependent polarization Possible robust discriminator against W+jets for searches At high PT, polarization angle cosq* is highly correlated with Lp: Selection: MT > 50 (30) GeV for e (mu), PT(W) > 50 GeV, Njet <=3, 14k candidates Fit dN(±)/dLp for longitudinal fraction f0(±), left-right transverse fractional difference fL(±)-fR(±)

  31. W Polarization in W + jets Largest systematics: W recoil energy scale W recoil resolution Lepton energy scale Significant transverse polarization observed. W’s are left handed! Non-zero f0 inconclusive. Charge differences not significant

  32. CMS Winter 2011 Results: Top • Top physics results • https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsTOP • top dilepton cross section • top lepton+jets cross section (tagged/untagged) • M(top) • top charge asymmetry • M(tt) • single top evidence

  33. Top Dilepton Cross Section LHC top pair cross section is 160 pb, about 20X Tevatron Selection: Two isolated leptons, muon (electron) PT > 20 GeV ±15 GeV Z mass veto for ee/mumu 1-4 PF jets PT > 30 GeV, |h| < 2.5, DR < 0.4 lepton overlap veto No MET cut for emu, for ee/mumu: PF MET > 30 (50) GeV for >2 (=1) jets Simple counting experiment in Njet/Ntag bins 79 tops expected >=1 jet >=1 tag 86 tops expected >=2 jet >=0 tag

  34. Top Dilepton Cross section systematic uncertainties (%), by channel Combine nine categories: ee/mumu/emu in three jet/tag categories: = 1 jet >= 0 tag >= 2 jet >= 0 tag >= 1 jet >= 1 tag Combined cross section: 14% precision with no dominant systematic ingredient b-tag efficiency inferred from double-tag/single-tag ratio

  35. Top lepton + jets cross section (untagged) One isolated lepton, muon (electron) PT > 20 (30) GeV, |h| < 2.1 (2.5), dilepton veto >=3 PF jets, PT > 30 GeV, |h| < 2.4, No MET cut ~700 top candidates expected, =3 jet bin 20% top purity, >= 4 jet bin 50% top purity

  36. Top lepton + jets cross section (untagged) 2D likelihood fit to MET and M3 (3-jet mass with highest P) in =3, >=4 jet bins, e/mu separately. Signal + 5 background yields floating. 22% precision, 14% statistical, JES largest systematic Six (!) different variations on the untagged analysis are consistent with this result.

  37. Top lepton + jets cross section (tagged) Same lepton selection as untagged, BUT >=1 PF jets, PT > 25GeV, |h| < 2.4, PF MET > 20 GeV 1D LH fit to vertex massin 1,2,3,4, or >=5 jets, 1 or >=2 tagged jets, e or mu channels = 18 categories Inspired by CDF l+jetsxsec :arXiv:1103.4821 All normalizations and nuisance parameters (JES, Q2, btag eff., etc.) floating in the fit!

  38. Top Lepton+Jets (tagged) Fit >= 4 jet >= 1 tag 80% purity >= 4 jet >= 2 tag 90% purity

  39. Top Lepton+Jets (tagged) Results Cross-checked by 4 other analyses which use explicit IP and soft muonb-tagging Interesting best fit nuisance parameters B-tag efficiency scale factor: 0.975±0.045 Jet energy scale shift: +0.6±0.6 s W + jets Q2 scale shift: -0.25±0.45 s W+bx scale factor: 1.9±0.6 X “SM” W+cx scale factor: 1.4±0.2 X “SM” “SM” = MadGraph scaled to W+jets NLO Soft muon tags Electron only Mu Ele Combined result 13% precision, largest systematics reducible

  40. Top Cross Sections 12% precision obtained All measurements consistent with the SM and with each other CMS ATLAS

  41. First LHC top mass measurement Use top dilepton events first: highest purity, least number of jets, cross section and event selection established six months ago Based on improved versions of Tevatron methods CDF MWT doi:10.1103/PhysRevD.73.112006 D0 KIN doi:10.1103/PhysRevLett.80.2063 • KINb method: • many solutions per lepton-jet pairing upon variation of jet PT, MET direction, Pz(tt), and their resolutions. • B-tagging used for jet-lepton assignment wherever possible • Choose combination with the largest number of solutions (75% success). • 1D Likelihood fit to reconstructed top mass

  42. First LHC top mass measurement • AMWT method: • many solutions per lepton-jet pairing upon variation of jet PT, MET direction, Pz(tt), and their resolutions, Each assigned a weight • MAMWT is Mtop hypothesis with largest average weight • 1D LH fit to MAMWT over 3 b-tagging categories Dominant systematics are JES and b-JES Agrees with world average top mass ATLAS l+jets preliminary : 169.3±4.0±4.9

  43. Top charge asymmetry Top pair angular production asymmetries of the type observed by CDF/D0 are a possible indicator of BSM top production interfering with SM production. Symmetric gg top production dominant at LHC, so SM asymmetries are more diluted than Tevatron tops. Angular variable with best resolution at CMS is |h(t)| - |h(tbar)|. Construct asymmetry tops +,- determined from sign of |h(t)| - |h(tbar)| SM AC = 0.0130(11) Anti-tops Event selection follows untagged lepton+(>=4) jets Top pair jet assignments and neutrino Pz from a chi2 minimization W+jets asymmetries studied in W+1,2 jet events

  44. Top charge asymmetry Raw charge asymmetry consistent with 0 at 3% level After background subtraction, efficiency correction, and rapidity diff. unfolding, Largest systematics: JES and lepton efficiency shape Differential cross section in agreement with simulation predictions

  45. Top pair mass spectrum A variety of BSM top production models sensitive to tt mass spectrum Jet-parton assignment via multi-term kinematic chi2 minimization M(tt) resolution improved 10-50% via kinematic fit 2 lepton species * 4 jet/tag categories studied simultaneously Good agreement obtained with SM Mtt prediction

  46. Top pair mass spectrum Reference model: leptophobictopcolor Z’ 7 pb UL obtained for MZ’ = 1 TeV

  47. First Evidence for Single Top at LHC At LHC, single top cross section is 60 pb, about 20X higher than at the Tevatron. t-channel is dominant over s-channel, tW Evidence seen in two different approaches: t-channel 2D Analysis: Select W + =2 jet + =1 tag (~200 events), signal extraction with 2D LH fit to Cos qlj , angle between lepton and recoil jet in top rest frame (signal is ~ 1+ cosq) |hlj|, rapidity of the recoil jet (signal is more forward) Background shapes, rel. norm from control samples, total norm floating 3.7s evidence

  48. Single Top BDT Analysis: Inspired by D0 single top analysis doi:10.1103/PhysRevD.78.012005 similar selection to 2D analysis, but >=1 tag allowed, Df(j1,j2) > 3.0 disallowed 37 ingredients in BDT discriminant: Lepton, jet kinematics and their correlations W, top kinematics and correlations Global event shape and energy Most important: lepton momentum, Wbj mass, bj PT, b PT, mtop Description of backgrounds validated by background-enriched control samples Muon channel Electron channel

  49. Single Top BDT Analysis: Signal extracted by 1D LH fit to BDT Muon channel Electron channel 3.5s evidence Nuisance parameters (background norms) floating W+HF, tt scale factors constrained to lepton+jetstt analysis

  50. Single Top Cross Section Consistent with SM and each other 36% precision on single top cross section Largest systematics: V+jets Q2, JES, b-tag efficiency ATLAS preliminary : (1.6s excess)

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