Standard Model Results From CMS

Standard Model Results From CMSMatt Herndon

University of Wisconsin – MadisonFermilab joint experimental theoretical seminar

2Matthew Herndon, Wisconsin, FNAL 2013

• Measurements are from 7 TeV and 8 TeV pp collisions

• I concentrate on newer measurements and some prospects

• All results shown can be found at:

Integrated Luminosity

https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResults



3

QCD Measurements

• LHC/CMS Advantages• Multiple energies• Excellent detectors and techniques for object reconstruction.

• CMS routinely uses particle flow• CMS starting to use Jet Substructure techniques

• Large integrated luminosity and datasets• Control of Jet energy scale uncertainties in absolute and ratio

measurements• Allows

• Differential cross sections to high jet multiplicities• Multiple differential cross sections• Measuring the evolution of as

• Constraint of PDFs• Probes in low cross section corners of the phase space.• Searches for new physics using dijets, multijet masses• Searches for new physics with boosted jets using jet

substructureMatthew Herndon, Wisconsin, FNAL

2013

4

Differential Jet Measurements

• Jet cross sections

• Global PDF sets show good agreement with the data• PDF sets not including high energy collider

data have difficulty with high pt jet data• At 13-14 TeV these analyses will test our

understanding of the data for early searches using jet data.CMS PAS SMP-12-012Phys. Rev. D 87 (2013) 112002

Matthew Herndon, Wisconsin, FNAL 2013

https://cdsweb.cern.ch/record/1547589

http://arxiv.org/abs/1212.6660

5

3 Jet Mass, 2/3 Jet Ratio

• 2-3 Jet ratios and 3 jet mass are used to extract as (also (s ttbar))

• Not competitive with world average as(mZ)• Complete NNLO calculation would improve

extrapolation• Evolution of as to the highest region of Q• Non global PDFs continue to have trouble with

high pT jet data CMS PAS QCD-11-003 CMS PAS SMP-12-027


CMS PAS TOP-12-022


http://cds.cern.ch/record/1562985

http://arxiv.org/abs/arXiv:1307.1907

6

Jet Substructure

• Allows efficient detection of boosted W, Z, top• Grooming techniques improve data/simulation agreement• Also improves response vs. pile up• Essential in high mass resonance searches (already done at

CMS) and in aTGC and aQGC searches where sensitivity is on the high pT tail of the vector boson pT distributionsJHEP 05 (2013) 090

• Jet Subtructure techniques• Identify massive objects decaying hadronically in

boosted topologies.• W, Z top


http://arxiv.org/abs/arXiv:1303.4811

7

W & Z Precision Measurements

• Combination of several factors have made unprecedented precision measurements possible in a Hadron collider environment.• The capabilities and performance of the LHC experiments• The development sophisticated experimental techniques to

treat collider data• The existence of inclusive and differential calculations of cross

sections at NLO and now NNLO precision• The integration of matrix element MCs with parton shower

generators in a consistent way at NLO (work to move to NNLO)• These factors allow an exciting program of measurements with

sensitivity to essential issues.• pQCD tests at NLO and NNLO• Tests of matrix element + parton shower techniques to high jet

multiplicity• PDF sensitivity• Test of Electroweak predictions for asymmetries and

polarizations• Differential distributions for transverse momentum, rapidity,

and jets• Associated production of vector boson and heavy flavor jets• Vector boson fusion and scattering


8

W & Z Cross Sections

• Measurement of total W and Z cross sections.• pQCD test from ratio of 7 TeV to 8 TeV cross sections and

W/Z, W+/W- • PDF sensitivity

• Comparable experimental and theory uncertainty

• 2-3% systematic and 5% luminosity uncertainty

• Expect extrapolation to 13-14 TeV to be good

CMS PAS SMP-12-011JHEP 10 (2011) 132Matthew Herndon, Wisconsin, FNAL

2013

https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSMP12011


9

W and Z Cross Sections

• Cancelation of systematic errors in ratio- both experimental and theoretical- Removes largest experimental uncertainty,

luminosity

CMS PAS SMP-12-011

JHEP 10 (2011) 132

• W/Z ratio at 8 TeV: ~1.5 sigma difference all PDF sets• 2% experimental systematic uncertainty.• Present at 7 TeV and in W+ and W- separately

• With better precision discrepancies are found (look further for the source)Matthew Herndon, Wisconsin, FNAL

2013



10

W+ and W- Cross Sections

• Expect 2:1 ratio form valence quarks in valance-sea annihilation, diluted by sea-sea

• Agrees with theory predictions• Tested at 2% level driven by experimental systematic uncertainty.


luminosity

CMS PAS SMP-12-011



11

Z pT at 7 and 8 TeV

• pT of Drell Yan (Z) production:

• 60 < ml l< 120 GeV

• Agreement with NNLO calculations

• Matrix Element + PS generators• Madgraph slightly better

at high qT – includes multiple hard emission

• Resbos improves low qT region

• V+jets important for VV scattering

Phys. Rev. D 85, 032002 (2012)CMS PAS SMP-12-025





Z Forward Backward Asymmetry

• Z forward Backward asymmetry– Measured as a function of mass in four rapidity bins– Sensitivity to new physics such as new neutral vector

bosons which would modify vector coupling of the leptons at high mass • Also measure the weak

mixing angle.

• Good agreement with theory: POWHEG+CT10

• Many sources of experimental uncertainty are statistics driven. Raw statistics and Tracker alignment.

• Expected to be competitive with world average (with improved PDFs)

Phys.Lett. B718 (2013) 752-772



W Charge Asymmetry• Study of ratios of kinematic variables

between W+ and W- production– Cancellation of systematic uncertainties in the

ratio maximizing sensitivity to PDF– Valance-sea interaction and asymmetry

increase at high y– Provides significant constraint on the global

PDF fit

• Good agreement with several PDF sets (initially excluding MSTW in both electrons and muons)

• MSTW fit now introduces new degrees of freedom for valance x distribution improving the agreement

• Continue to improve PDFs in preparation for 13-14TEV

Phys.Rev.Lett. 109 (2012) 111806

CMS PAS SMP-12-021


http://cds.cern.ch/record/1563576?ln=en

14

Z + jets

• Z + 1j rapidity• Azimuthal correlations, Event

shapes• Test of NLO theory and

Matrix Element + parton shower MCs

• Individual Z and jet rapidities look good

• Combined distributions show deviations.

• Combined rapidity, Event thrust

• Test vs. newer theory tools

• V(V)+jets important for VV scattering

CMS PAS SMP-12-004Phys. Lett. B722 (2013) 238





VBF Z Production

• σ(μμ+ee) = 154 ± 24 (stat.) ± 46 (syst.) ± 27 (th.) ± 3 (lum.)fb

• VBFNLO 166 fb• Same topology as VBF Higgs

and longitudinal vector boson scattering. Benchmark for EWSB studies

• EW VBF production of Z + jets• Dominant background from standard DY

production• Uses multivariate (BDT) discriminant to extract

signal• Includes a gluon vs. quark jet likelihood

discriminant • Measures WWZ TGC

CMS PAS FSQ-12-019


16

W + c-Jet

• W+c‐jet production• Sensitive to strange PDF of the proton.• W charge the same as initial s quark• Strange anti-strange PDF should be

~symmetric• Analysis uses charm hadron

reconstruction to identify charm jets.

• Fair agreement with PDF fits

• Competitive sensitivity to strange PDF compared to neutrino scattering experiments

CMS PAS SMP-12-002



17

Z + b-Jets

• Production of Z + 1 or 2 b jets

• Good agreement with predicted cross section across jet bins

• Key distributions for ZH analysis look good

CMS PAS SMP-13-004



18

W + 2b-Jets

• Production of W + 2 central b jets• History of disagreement in

V+hf between theory and experimental data. Critical background for Higgs searches

• Double tags events to remove W+c and constrain top contribution from high jet multiplicity region.

• Good agreement with predicted cross section

CMS PAS SMP-12-026

• Disagreement with V+b states localized to V+1b. Populated by merged low angle gluon splitting. Controlled in Higgs by data driven background estimates

CMS PAS EWK-11-015Matthew Herndon, Wisconsin, FNAL

2013


https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsEWK11015


Other V (+ jets) Results

• Active program in V (+jets) (not shown here)– Photon + jets, Photon + Jets rapidities– W differential vs. n jet cross section– W polarization at large pT– DY cross section– Z differential vs. n jet cross section– Z tautau


• Fundamental test of Standard Model• Multiple vector boson interactions due to the gauge structure

of the Standard Model• Test of QCD techniques in VV+jets

• Probe for new physics• Indirect search for tree or loop effects of massive new

particles in Anomalous Triple Gauge Couplings (TGC) and Quartic Gauge Couplings (QGC)

• Quartic coupling especially sensitivity to EWSB including non SM contributions

Multiboson Production

QGCTGC

EWSB

21

γγ Production

• Highest statistics diboson mode

• Probes phase space regions where NNLO prediction is important

• Differential NNLO prediction available

• Best agreement with is with NNLO theory

• Other predictions agree in phase spaces where they are expected to do well

CMS PAS SMP-13-001



22

Wγ, Zγ Production

• Wγlνγ, Zγ llγ ννγ• Differential with γ in charged lepton modes• Minimum γ ET > 15 GeV• Also missing ET and γ with high ET in

Zγ ννγ• Agreement with NLO

theory (MCFM NLO, BAUR)

• Don’t strongly confirm ATLAS excess

• Need differential measurements including nJet and jet kinematics

• Confirm our understanding of VV+jets for VV scattering or triple gauge boson production

CMS PAS SMP-12-020

CMS PAS EWK-11-009




23

Wγ, Zγ aTGC

• aTGC searches• Exploit expected high transverse momentum of

vector boson if there is aTGC using γ Et distribution• Good sensitivity due to higher branching ratios in in Zγ ννγ

• Zγ ννγ dominates sensitivity.

• aTGC limits on ZZγ and Zγγ are worlds best• Limits on WWγ approaching LEP sensitivity• -0.38 < |Dkg| < 0.29 and -0.050 < |lg| < 0.037

CMS PAS SMP-12-020

CMS PAS EWK-11-009




24

aTGC – interesting yet?

• Are these aTGC limits interesting yet?• Useful to consider aTGC in effective field

theory• Essentially the same as looking for weak

force effect well below the mass scale of the W and Z

• h ≈ cmV2/L2

• Natural assumption for coupling constant c: order 1

• Assumption new physics scale. 1 to 3 TeV• Therefore h3 = 1x10-4 to 1x10-3 interesting

• h4 described by higher dimension operator but limits 100x more stringent

• At level of interesting sensitivity. Also higher order effects will become important



WW Production

• Signal: dileptons (e and μ) and missing ET

• Cross sections at 7 and 8 TeV• Apply jet veto to reduce top backgrounds

• Cross sections high at 1-1.5σ level compared to NLO• σ(WW 7 TeV) = 52.4 ± 2.0(stat.) ± 4.5(sys.) ± 1.2(lum.) pb,

MCFM: 47.0±2.0 pb• σ(WW 8 TeV) = 69.9 ± 2.8(stat.) ± 5.6(sys.) ± 3.1(lum.) pb,

MCFM: 57.3±2.0 pb• Expect contributions at 5% level from H WW and other processes

jet veto adds systematic uncertainty

Removing 0 jet veto should be possible. Expand to 1 jet

Phys. Lett. B 721 (2013) 190CMS PAS SMP-12-005




WW aTGC

• aTGC search• Exploit expected high transvers momentum of

vector boson using leading lepton pT distribution

• Limits Limits on WWγ and WWZ approaching LEP sensitivity• -0.21 < |Dkg| < 0.22• -0.048 < |lZ| < 0.048• -0.095 < |gZ

1| < 0.095

CMS PAS SMP-12-005



WZ Production

• Signal: trileptons (e and μ) and missing ET

• Cross sections at 7 and 8 TeV• Sample pure enough to allow jet analysis

CMS PAS SMP-12-006

• Highest cross section very low background VV mode

• Interesting for testing theory predictions

• Approximate NNLO available

• Collinear radiation effects along a hard object can increase the hard cross section

• Matrix element + PS at NLO available

hep-ph/1209.4595




WW+WZ Production

• WW + WZ production in semileptonic decays• Signal: leptons (e and μ) and missing ET and two jets consistent with a

W or Z• Cross sections at 7• Apply jet veto to reduce top backgrounds

• First observation of WW+WZ: 2700 candidates

• Cross section in agreement with theory• σ(WV 7 TeV) = 68.89 ± 8.71 (stat) ±

9.70 (syst) ± 1.52 (lumi) pb• MCFM NLO : 65.6 ± 2.2 pb

• Also used to search for higher mass resonance produced in associated with a W boson

• No evidence of a resonance and limits placed on several models

Eur. Phys. J. C 73 (2013) 2283Phys. Rev. Lett. 109 (2012) 251801




WW+WZ aTGC

• aTGC search• Exploit expected high

transverse momentum of vector boson using hadronically decaying vector boson pT distribution

• Weak sensitivity to gZ1. Set to SM value. • Limits Limits

on WWγ and WWZ • approaching

LEP sensitivity• Continuing

this analysis requires using jet substructure

Eur. Phys. J. C 73 (2013) 2283

Probably not sensitive to NP yet. Will reach sensitivity with 13-14 TeV data or 8 TeV combination



ZZ Production

• ZZ production in charged leptonic decays (e, μ and tau) • Cross sections at 7 and 8 TeV. Also Z 4l

• Cross sections in agreement with theory• σ( ZZ 7 TeV) = 6.2 ± 0.8 (stat.) ± 0.4 (sys.) ± 0.1

(lum.) pb• MCFM NL) : 6.3 ± 0.4 pb• σ(ZZ 8 TeV) = 7.7 ± 0.5 (stat.) ± 0.4 (sys.) ± 0.3

(lum.) pb• MCFM NLO : 7.7 ± 0.4 pb

Phys. Lett. B 721 (2013) 190

JHEP 12 (2012) 034

JHEP 01 (2013) 063

CMS PAS SMP-13-005






ZZ aTGC

• aTGC search• Exploit expected high

transvers momentum of vector bosons using the 4l mass.

• World leading sensitivity to ZZγ and ZZZ

CMS PAS SMP-13-005

• Very near interesting region for NP sensitivity


32

Summary of Cross Sections



• Many places you might look for new physics• In the context of SM measurements?• Look for deviations in the EWSB sector

• Compatibility with precision SM measurements with the observed Higgs boson– mt, mW

• Longitudinal vector boson scattering

Where to Next


• Has the LHC finally surpassed the Tevatron?– CMS: 0.56%(with 8 TeV), Best CMS measurement in 7

TeV l+jets– LHC: 0.54%– Tevatron: 0.50% (Tevatron result is still a moving

target)

Top Mass

CMS PAS TOP-13-005JHEP 12 (2012) 105

CMS PAS TOP-13-003





Top Mass Projections

JHEP 12 (2012) 105

• Substantial improvement in top mass possible.

• Good sensitivity from orthogonal methods with different limiting factors

• 200 MeV sensitivity– Doesn’t address issue of

defining the top pole mass

• The W mass?– Not studied in detailed– Currently limited by PDF

uncertainty at 10 MeV level. Data may allow improved PDFs

CMS PAS FTR-13-017




mT vs mW

• LHC gets halfway to ILC type sensitivity.– Multiple

orthogonal methods of top mass reconstruction may improve sensitivity in combination

– Large datasets may improve PDF uncertainty in Wmass

• Could be sensitivity to indicate non SM behavior

Where to look next?

37

QGC and Vector Boson Scattering

• Vector boson scattering interactions in the SM– Double triple gauge couplings, t and s channel– Quartic gauge coupling: WWγγ, WWZγ, WWWW, WWZZ– t channel scattering via a Higgs

• Standard model expectation is precisely predicted given the Higgs mass– All scattering contributions individually rise quickly with

CM energy and violate unitarity. – Unitarity conserved by interference effects.

• New physics in scattering– Often described in generalized context of anomalous

quartic gauge couplings (aQGCs)– Exchange of new heavy particles such as extra scalars

(Higgs) is a direct window on non-SM electroweak symmetry breaking contributions.

– NP would modify the interference and alter the differential cross section as a function of scattering CM energy.

• Also triboson productionMatthew Herndon, Wisconsin, FNAL 2013


WWγ+WZγ (a)QGC

• Signal: leptons (e and μ) and missing ET, dijet, photon• Search for SM WWγ+WZγ Production• aQGC Search for WWZγ, WWγγ, aQGC

• Not sensitive to SM rate or likely aQGC

CMS PAS SMP-13-009

• σ(WVγ) < 241 fb, 3.4x σSM

Many studies of aQGC done. Now also some complete analysis!Expect that most scattering and 3Vstates accessible at 13-14TeV.SM or aQGC



Search for gg WW and aQGC

• gg WW in Central exclusive production• Signal: dileptons (eμ) and missing ET with central track

veto• Use pTeμ to search for aQGC.

• Expect 2.2 ± 0.5 signal events, 0.84 ± 0.13 background. Observe 2

• σ(gg WW) < 8.4 fb, SM: 3.8 ± 0.9 LEP

CMS PAS FSQ-12-010

Near interesting region for SM and NP sensitivity

https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsFSQ12010

40

WZ Scattering and aQGC

• Discovery potential for SM EWK WZ scattering and aQGC– WZ events in leptonic decays with forward scattering jets

CMS PAS FTR-13-006



• Impressive number of SM results from the CMS– Precise tests of the Standard Model at TeV scale– Agreement with theory in most cases– Starting to set serious constraints on electroweak parameters

and PDFs– Measurements are challenging NLO and NNLO predictions– Analysis approaching new physics sensitivity in the gauge

sector• Still much of the LHC data at 8 TeV to be analyzed

– More results with improved precision and new topics expected soon, stay tuned!

• 13-14 TeV data will have strong sensitivity to new physics.– Though predicated on the excellence of theory predictions and

experimental effort to validate them

Summary


Backup

43

W and Z Cross Sections


luminosity

• W/Z ratio at 8 TeV: ~1.5 sigma difference all PDF sets• 2% experimental systematic uncertainty.• Present at 7TeV and in W+ and W- seperately also• With better precision discrepancies are found

CMS PAS SMP-12-011

JHEP 10 (2011) 132




44

Drell-Yan Cross Sections

• Doubly differential in dσ/dM and rapidity in mass bins

• dσ/dM from 15 to 1500 GeV

• Rapidity from 0 to 2.4 in 6 mass bins

• Comparisons with:• FEWZ + PDF

sets• Agreement in

dσ/dM and y.• Low mass sensitive

to PDF and integration issues.

• Understanding low mass dilepton pairs important for Higgs

JHEP 10 (2011) 7

CMS PAS SMP-12-011





W Charge Asymmetry

• W charge asymmetry results both testing and then constraining PDFs– CMS and ATLAS results added in

NNPDF2.2 reducing uncertainty.– Again improving PDFs in preparation for

13-14TEV

Nucl.Phys. B855 (2012) 608-638 NNPDF Collaboration


Standard Model Results From CMS

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