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THE COMPACT MUON SOLENOID EXPERIMENT: ELECTROWEAK AND TOP PHYSICS JEFFREY BERRYHILL FERMILAB FOR THE CMS COLLABORATION FERMILAB JOINT EXPERIMENTAL-THEORETICAL.

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Presentation on theme: "THE COMPACT MUON SOLENOID EXPERIMENT: ELECTROWEAK AND TOP PHYSICS JEFFREY BERRYHILL FERMILAB FOR THE CMS COLLABORATION FERMILAB JOINT EXPERIMENTAL-THEORETICAL."— Presentation transcript:

1 THE COMPACT MUON SOLENOID EXPERIMENT: ELECTROWEAK AND TOP PHYSICS JEFFREY BERRYHILL FERMILAB FOR THE CMS COLLABORATION FERMILAB JOINT EXPERIMENTAL-THEORETICAL PHYSICS SEMINAR MARCH 25, 2011

2 THE COMPACT MUON SOLENOID EXPERIMENT: ELECTROWEAK AND TOP PHYSICS JEFFREY BERRYHILL FERMILAB FOR THE CMS COLLABORATION FERMILAB JOINT EXPERIMENTAL-THEORETICAL PHYSICS SEMINAR MARCH 25, 2011

3 LHC Data 2010 statistics: Started 7 TeV pp collisions March 30. 47 pb -1 delivered, ~90 % in October alone Peak instantaneous luminosity: 2.1*10 32 cm -2 s -1 36-40 pb -1 for CMS analysis for all results shown 2011 expectations: 5-10*10 32 cm -2 s -1 930 bunches/beam 1-3 fb -1 delivered This week: 2.7*10 32 cm -2 s -1 200 bunches/beam ~10 pb -1 delivered A year from now, we may have 100X more data than shown today!

4 The CMS detector Tracker coverage |  | < 2.5 Electron coverage |  | < 2.5 Muon coverage |  | < 2.4 Efficient muon (electron) triggering down to 9 (17) GeV at L = 2E32 3.8 T solenoid + 76000 crystal ECAL + 200 m 2 silicon = percent level lepton momentum resolution at high PT HCAL/HF coverage |  | < 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 Electroweak physics results https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsEWK Single boson production W and Z inclusive cross sections Z d  /dy, d  /dPT, d  /dm Z AFB and weak mixing angle W asymmetry Z to tau tau W to tau nu Multi-boson production W , Z  production and couplings WW production and couplings Boson + jets production W,Z+jets : d  /dNjet and multiplicity ratios Z + b W polarization at high PT CMS Winter 2011 Results: Electroweak

8 W and Z Production at the LHC Occurs through admixture of valence/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  xBR(W→l ) ~ 10 nb per channel, 60/40 W + /W - Z  xBR(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 Z Selection: Two isolated electrons (muons), PT > 25(20) GeV dilepton 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. Provide a precision test of NNLO predictions and PDFs Alternatively, tests understanding of lepton efficiency, luminosity

10 W and Z Cross Sections W Selection: One isolated electron (muon), PT > 25 GeV, |  |<2.5(2.1) Dilepton veto No MET or MT cut PF MET, electrons PF MET, muons 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.

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 < |  | < 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 (2 nd ) muons with PT > 16 (7) GeV, |  | < 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/  * 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(  ), cos  * 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 |  *| < 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  : 6 bins of  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  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  0 ’s collected in an ECAL strip, eff. ~ 70% e or mu PT > 15 GeV HPS tau PT > 20 GeV MT < 50 GeV Signals in e , , e , and  decay modes.

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

21 H to  MSSM, tan  -enhanced Higgs production and decay to  Bump hunt in  mass Already improves upon recent Tevatron limits W to  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 W , Z  Production Probes (anomalous) triple gauge boson couplings (aTGC) WW , ZZ , Z  Selection: W or Z selection in e or mu channels as above, and Photon with ET > 10 GeV, |  | 0.7 with leptons W  : PF MET > 25 GeV, Z  : MZ > 50 GeV Photon fake rates from jet samples, norm. from isolation-inverted W ,Z  candidates About 500 W , 120 Z  expected. Good agreement with SM predictions SM = 49±4 pb SM = 9.6±0.4 pb

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

24 WW Production Direct test of WW  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  (l,MET) <  /2, use component of MET transverse to lepton direction use MET otherwise Projected MET > 20 (35) GeV for e  (  ) Jet Veto: No PF jets with ET > 25 GeV and |  | < 5.0 Top veto: No b-tags or soft muon tags Z veto in ee,  : 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 e  /  /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  ·BR(H→WW) Exclude 2.2X SM Higgs 160 @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 (2 nd ) lepton > 20 (10) GeV, 60 < MZ <120 GeV PF jets > 30 GeV and |  | < 2.4  R > 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 (  ) with n, with a small linear correction term of slope . 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, |  | < 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 ee Data 0.054±0.016 Measure HF fraction MadGraph 0.051±0.007 MCFM 0.043±0.005  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 cos  * 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 Significant transverse polarization observed. W’s are left handed! Non-zero f0 inconclusive. Charge differences not significant Largest systematics: W recoil energy scale W recoil resolution Lepton energy scale

32 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 CMS Winter 2011 Results: Top

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, |  | < 2.5,  R < 0.4 lepton overlap veto No MET cut for emu, for ee/mumu: PF MET > 30 (50) GeV for >2 (=1) jets 86 tops expected >=2 jet >=0 tag 79 tops expected >=1 jet >=1 tag Simple counting experiment in Njet/Ntag bins

34 Top Dilepton Combined cross section: 14% precision with no dominant systematic ingredient b-tag efficiency inferred from double-tag/single-tag ratio 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

35 Top lepton + jets cross section (untagged) One isolated lepton, muon (electron) PT > 20 (30) GeV, |  | < 2.1 (2.5), dilepton veto >=3 PF jets, PT > 30 GeV, |  | < 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 > 25 GeV, |  | < 2.4, PF MET > 20 GeV 1D LH fit to vertex mass in 1,2,3,4, or >=5 jets, 1 or >=2 tagged jets, e or mu channels = 18 categories All normalizations and nuisance parameters (JES, Q 2, btag eff., etc.) floating in the fit! Inspired by CDF l+jets xsec :arXiv:1103.4821

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

39 Top Lepton+Jets (tagged) Results Electron only Combined result Interesting best fit nuisance parameters B-tag efficiency scale factor: 0.975±0.045 Jet energy scale shift: +0.6±0.6  W + jets Q 2 scale shift: -0.25±0.45  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 Cross-checked by 4 other analyses which use explicit IP and soft muon b-tagging Ele Mu Soft muon tags 13% precision, largest systematics reducible

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

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 M AMWT is Mtop hypothesis with largest average weight 1D LH fit to M AMWT 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 |  t)| - |  tbar)|. Construct asymmetry tops Anti-tops +,- determined from sign of |  t)| - |  tbar)| SM A C = 0.0130(11) Event selection follows untagged lepton+(>=4) jets Top pair jet assignments and neutrino Pz from a chi 2 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 chi 2 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: leptophobic topcolor 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  lj, angle between lepton and recoil jet in top rest frame (signal is ~ 1+ cos  )  lj |, rapidity of the recoil jet (signal is more forward) Background shapes, rel. norm from control samples, total norm floating 3.7  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,  (j 1,j 2 ) > 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 Nuisance parameters (background norms) floating W+HF, tt scale factors constrained to lepton+jets tt analysis 3.5  evidence

50 Single Top Cross Section Largest systematics: V+jets Q 2, JES, b-tag efficiency 36% precision on single top cross section Consistent with SM and each other ATLAS preliminary : (1.6  excess)

51 The Standard Model: How am I doing? Phil Harris, Moriond EWK 2011

52 Conclusions In less than one year of 7 TeV operation, CMS has realized full-fledged electroweak and top physics research programs Precision W and Z studies Multiboson observation W,Z + jets studies Double and single top production Top properties Already several instances of beyond-the-Tevatron insights and sensitivity with 1/200 of the luminosity We are perhaps ~1% of the way through the initial 7 TeV LHC run. Fully operational machine for discoveries of all varieties!

53 Conclusions In less than one year of 7 TeV operation, CMS has realized full-fledged electroweak and top physics research programs Precision W and Z studies Multiboson observation W,Z + jets studies Double and single top production Top properties Already several instances of beyond-the-Tevatron insights and sensitivity with 1/200 of the luminosity We are perhaps ~1% of the way through the initial 7 TeV LHC run. Fully operational machine for discoveries of all varieties! CMS DETECTOR

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