Gauge-boson Physics at the LHC

Physics Division

Gauge-boson Gauge-boson PhysicsPhysics at the LHCat the LHC

Gauge-boson Gauge-boson PhysicsPhysics at the LHCat the LHC

Matt DobbsLawrence Berkeley Laboratory,

USA

Hadron Collider Physics 2004Michigan State U.

Matt Dobbs Hadron Collider Physics 2004 2

OutlineOutline LHC Physics EnvironmentLHC Physics Environment

ATLAS and CMS DetectorsATLAS and CMS Detectors

Precision Gauge Boson PhysicsPrecision Gauge Boson Physics W-massW-mass AAFB FB and sin and sin22θθWW

Di-bosonsDi-bosons Triple Gauge-boson CouplingsTriple Gauge-boson Couplings

Tri-bosonsTri-bosons

Challenges ahead:Challenges ahead: Monte Carlo ToolsMonte Carlo Tools Experimental measurements – PDFs, energy scales, Experimental measurements – PDFs, energy scales,

etc.etc.


Large Hadron Large Hadron ColliderCollider

ProcessProcessEvents/Events/10 fb10 fb-1-1

TevatronTevatron

2 fb2 fb-1-1

ZZ→e→e++ee-- ~10~107-87-8 10105-65-6

WW→e→e±±vv ~10~108-98-9 10106-76-7

t anti-tt anti-t ~10~1077 5x105x1033

EETT>100 GeV >100 GeV

JetsJets 10101010 10106-76-7

14 TeV proton-proton 14 TeV proton-proton collisions collisions

broad-band q & g broad-band q & g collidercollider,, scales →few TeVscales →few TeV

Low L→ Low L→ 2x102x103333/cm/cm22/s/s precision physicsprecision physics

High L →High L →10103434 /cm /cm22/s/s(~23 interactions/crossing)(~23 interactions/crossing)

300 fb300 fb-1-1 in in ≤ 10 ≤ 10 yearsyears


Inner Detector

Tracking in range || < 2.5Silicon Pixels, Strips & TRTEM Calorimetry

Fine granularity up to || < 2.5Pb/LAr AccordianHadronic Calorimetry

Barrel: Fe/Scintillating tilesEndcaps: Cu & W / LArFine Muon Spectrometer:/pT ~ 7 % at 1 TeVCovers < 2.7Magnet2T solenoid plus air core toroid

The ATLAS DetectorThe ATLAS Detector

)(

%10

GeVEE

03.0)(

%50

GeVEE

01.0%05.0 )( GeVTT

PP


The CMS DetectorThe CMS Detector Inner DetectorInner Detector::

Silicon pixels and stripsSilicon pixels and stripsPreshower:Preshower:Lead and silicon stripsLead and silicon stripsEM CalorimeterEM Calorimeter::Lead TungstateLead Tungstate

Hadron CalorimetersHadron Calorimeters::Barrel & EndcapBarrel & Endcap:: Cu/Scintillating sheetsCu/Scintillating sheets

Forward:Forward:Steel and Quartz fibreSteel and Quartz fibreMuon SpectrometerMuon Spectrometer::

/pT ~5% at 1 TeV(combined)Drift tubes, cathode strip Drift tubes, cathode strip chambers and resistive chambers and resistive

plateplatechamberschambersOne MagnetOne Magnet: : 4T Solenoid4T Solenoid

%2)(

%52

GeVEE

%5)(

%65

GeVEE

005.0%015.0 )( GeVTT

PP

Physics Division

W-MassW-Mass W-MassW-Mass


Mass(W)Mass(W) electroweak fitelectroweak fit

Higgstop MM

W

F

EMW

GM

ln,

2

2

scorrection radiative1sin

1

2

LHCat GeV5.1

007.0

topW MM

MeV15 require WMsuch that MW is not the

dominant error in EW fit. constrains MHiggs & consistency check

(LEP2: 42 MeV, Tev RunI: 59 MeV)


Measuring Mass(W)Measuring Mass(W) Measured with MMeasured with MTRANTRAN of Leptonic Channels of Leptonic Channels

)cos1(2 TlT

WT ppM

MTRAN very sensitive to detector effects

vs.

PTl± very sensitive to

higher order corrections

+ detector effects

Finite PT(W)

PT(W)=0

Baur, hep-ph/0304266


Measuring Mass(W)Measuring Mass(W)SourceSource CDF Run IbCDF Run Ib ATLAS or CMSATLAS or CMS W→ W→ l l νν , one lepton species , one lepton species

30K evts, 84 30K evts, 84 pbpb-1-1

60M evts, 10fb60M evts, 10fb--

11

StatisticsStatistics 65 MeV < 2 MeV

Lepton scaleLepton scale 75 MeV75 MeV 15 MeV15 MeV most serious most serious challengechallenge

Energy resolutionEnergy resolution 25 MeV25 MeV 5 MeV5 MeV known to 1.5% from Z known to 1.5% from Z peakpeak

Recoil modelRecoil model 33 MeV33 MeV 5 MeV5 MeV scales with Z statisticsscales with Z statistics

W widthW width 10 MeV10 MeV 7 MeV7 MeV ∆∆ГГWW≈≈30 MeV (Run II)30 MeV (Run II)

PDFPDF 15 MeV15 MeV 10 MeV10 MeV

Radiative Radiative decaysdecays

20 MeV20 MeV <10 MeV<10 MeV (improved Theory (improved Theory calc)calc)

PPTT(W)(W) 45 MeV45 MeV 5 MeV5 MeV PPTT(Z) from data, (Z) from data,

PPTT(W)/ P(W)/ PTT(Z) from theory(Z) from theory

BackgroundBackground 5 MeV5 MeV 5 MeV5 MeV

TOTALTOTAL 113 MeV113 MeV ≤ ≤ 25MeV 25MeV Per expt, per lepton Per expt, per lepton speciesspecies

Combining channels and CMS data, expect Combining channels and CMS data, expect ΔΔMMWW ≈ 15 MeV ≈ 15 MeV expect improvements from using Mexpect improvements from using MTRANTRAN(W)/M(W)/MTRANTRAN(Z) (Z)


W-mass: ChallengesW-mass: Challenges 0.03% knowledge of lepton energy 0.03% knowledge of lepton energy

scalescale calibrate with 6 million Zcalibrate with 6 million Zll++ll-- events events

tracker material to 1%tracker material to 1% overall alignment to 1 μmoverall alignment to 1 μm B-field knowledge to 0.1%B-field knowledge to 0.1% muon E-loss to ¼%muon E-loss to ¼%

(CDF/D0 achieved 1% despite small (CDF/D0 achieved 1% despite small Z samples)Z samples)

Well constrained PDFsWell constrained PDFs active program for measuring PDFs active program for measuring PDFs

at LHC from Day 1at LHC from Day 1 new LHC-HERA workshopnew LHC-HERA workshop

mitigate some theory errors by mitigate some theory errors by using W/Z ratio methodsusing W/Z ratio methods but MC model of but MC model of ppppZZllll is further is further

behind in some cases (no multi-behind in some cases (no multi-photon corrections)photon corrections)

ZZll ≠ Wll ≠ Wlνlν Theory modeling of radiative decays Theory modeling of radiative decays

and recoiland recoil

ATLAS: C. Marques, Lisbon

CTEQ6 ERROR PDFsRMS = 9.8 MeV

-20

-15

-10

-5

0

5

10

15

20

600 605 610 615 620 625 630 635 640PDF

Me

V

Shift on W mass = 550 MeV / 1%

80

80.5

81

0.01 0.1 1

Error on Lepton Scale/%

Mas

s G

eV


The State of the Art TodayThe State of the Art TodayQCDQCD EWEW StyleStyle

RESBOS-ARESBOS-A resummed resummed PPTT(W)(W)

Final State Final State NLO(NLO(ααQEDQED))

Distr. onlyDistr. only

WGRAD2WGRAD2 nonenone complete complete NLO(NLO(ααQEDQED))

Distr. onlyDistr. only

MC@NLOMC@NLO NLO(NLO(ααSS) + all ) + all orders orders parton parton showershower

nonenone Event Event GeneratorGenerator

(some -1 (some -1 evts)evts)

& other codes too!..& other codes too!..

• confused? a word from our sponsors…

Physics Division

Weinberg Angle: sinWeinberg Angle: sin22θθWWWeinberg Angle: sinWeinberg Angle: sin22θθWW


Measuring sinMeasuring sin22θθWW with A with AFBFB

At the Tevatron, defining AAt the Tevatron, defining AFBFB is easy. is easy.

But for symmetric proton-proton beams (LHC), But for symmetric proton-proton beams (LHC), there is no asymmetry WRT the beams.there is no asymmetry WRT the beams.

pp

Proton BeamAntiProton Beam

e-

e+

θFB

Proton BeamAntiProton

Beam

Z°/γ

)(sinA 2FB Z

lepteff

BF

BF Mab

known to NLO in EW, QCD(effects can be as large as 30%)


Measuring sinMeasuring sin22θθWW with with AAFBFB Instead, we “sign” the forward direction by the lInstead, we “sign” the forward direction by the l++ll- -

boost.boost.

Measure asymmetry in charged lepton direction WRT Measure asymmetry in charged lepton direction WRT CMS boost directionCMS boost direction

Asymmetry increases at high Y(lAsymmetry increases at high Y(l++ll--))

Proton Beam

Z°/γ

Proton Beam Proton Beam

Z°/γ

Proton Beam


Measuring sinMeasuring sin22θθWW with with AAFBFB

Statistical precision using 100 fbStatistical precision using 100 fb-1-1

Performance issue:Performance issue: increasing forward lepton tagging acceptance greatly improves increasing forward lepton tagging acceptance greatly improves

measurementmeasurement

Systematic PDF uncertainty is most challenging.Systematic PDF uncertainty is most challenging.

CutsCuts AAFBFB (%) (%) Δ Δ AAFBFB (%) (%) ΔΔ sin sin22θθeffeff(M(MZZ))

Both eBoth e±±, |, |ηη||<2.5<2.5

0.770.7744

0.0200.020 0.000660.00066

One eOne e±±, |, |ηη||<2.5<2.5

other other ee±±,|,|ηη||<4.9<4.9

1.981.98 0.0180.018 0.000140.00014for comparison, ΔΔ sin sin22θθeffeff=0.00053 combining 4 LEP expts and e,μ,τ channels [CERN-EP/2001-098]

ATLAS-PHYS-2000-018

CMS IN 2000/35

Physics Division

Triple Gauge-bosonTriple Gauge-bosonCouplingsCouplings

Triple Gauge-bosonTriple Gauge-bosonCouplingsCouplings


Probing theProbing the Triple Gauge-boson Triple Gauge-boson CouplingsCouplings

non-abelian SU(2)non-abelian SU(2)LL×U(1) ×U(1) YY gauge group gauge group (foundation of (foundation of SM!)SM!)

WWWWγγ WWZ WWZ couplingscouplings most-general C & P conserving WWZ,WWmost-general C & P conserving WWZ,WWγγ

vertices are specified by just vertices are specified by just 5 parameters5 parameters::

model independent parameterizationmodel independent parameterization

Probe tool:Probe tool: sensitive to low energy remnants of new physics sensitive to low energy remnants of new physics operating at a higher scaleoperating at a higher scale

complementcomplement to direct searches to direct searches

S.M. in the ZERO , Δκ ,Δκ ,g

s like grow

Z

s like grow

Z1Z

big advantage for LHC


95% C.L. for Wγ95% C.L. for Wγ binned max. likelihood fit to binned max. likelihood fit to

PPTT(V) distribution(V) distribution sensitivity comes from a few sensitivity comes from a few

events in the high Pevents in the high PTT(V) tail(V) tail

ATLAS


TGC Limits vs. Integrated TGC Limits vs. Integrated LuminosityLuminosity

typically order of magnitude better than LEP/TeVa [ [O(.10-.20), 95% C.L.]•Statistics will dominate LHC measurements (except for Δ g1)

sensitivity derived from a few events in the high PT(V) tail

•Dominant systematics are theoretical: neglected higher orders and pdf’s

confidence limit

systematic contribution

ATLAS95% C.L., 30 fb95% C.L., 30 fb-1-1, Syst. Incl., Syst. Incl.

-0.0035 < λ-0.0035 < λγγ < +0.0035 < +0.0035

-0.0073 < λ-0.0073 < λZZ < +0.0073 < +0.0073

-0.075 < Δκ-0.075 < Δκγγ < +0.076 < +0.076

-0.11 < Δκ-0.11 < ΔκZZ < +0.12 < +0.12

-0.0086 < Δg-0.0086 < Δg11ZZ < 0.011 < 0.011


Limits vs. Form Factor Limits vs. Form Factor ScaleScale

new form factor new form factor strategy is introducedstrategy is introduced

rather than imposing rather than imposing an arbitrary form an arbitrary form factor in the model,factor in the model,

the limits are the limits are reported as a reported as a function of a mass function of a mass scale cutoffscale cutoff

unitarity limitexpt limit

expt limit

unitarity limit

ATLAS


Neutral TGC’sNeutral TGC’s no tree level neutral no tree level neutral

couplings in SMcouplings in SM

typically 3-5 orders of typically 3-5 orders of magnitude improvement magnitude improvement in limits at LHC over LEP.in limits at LHC over LEP.

53 s like grow

2,4

s like grow

4,51,3

s like grow

Z

s like grow

Z1Z

hfh

, Δκ ,Δκ ,g

Zγ


The State of the Art TodayThe State of the Art TodayNLONLO(QCD)(QCD) lepton lepton

corr.corr.anomaloanomalousus

TGC’sTGC’s

stylestyle

Baur Baur et. al.et. al. yesyes

φ-slicingφ-slicingalmosalmostt

yesyes distributions distributions onlyonly

Dixon/Dixon/Kunst/Kunst/SignerSigner

yesyes

subtractsubtractyesyes yesyes distributions distributions

onlyonly

MCFMMCFM yesyes

subtractsubtractyesyes nono distributions distributions

onlyonly

MC@NLOMC@NLO yes + yes + parton parton shower(!)shower(!)

no(!)no(!) no(!)no(!) event event generator generator (some -1 evts)(some -1 evts)

& other codes too!..& other codes too!..


Tri-boson ProductionTri-boson Production

sensitive to quartic gauge-boson couplings sensitive to quartic gauge-boson couplings (QGC’s)(QGC’s)

Events for 100 fb-1

(M(MHIGGSHIGGS=200 GeV)=200 GeV)

no branching no branching ratios, no ratios, no

cutscuts

pure leptons,pure leptons,

PPTT > 20 GeV , |η| > 20 GeV , |η| < 3< 3

pppp WWW WWW (difficult, 3 ν’s)(difficult, 3 ν’s) 3192531925 180180

ppppWWZ WWZ (difficult, 2 ν’s)(difficult, 2 ν’s) 2091520915 3232

ppppZZWZZW 63786378 2.72.7

ppppZZZ ZZZ 48834883 0.60.6

ppppWWγγγγ, preferred due to thresholds and BR’s., preferred due to thresholds and BR’s.“gold-plated” channelswould require full LHCdata set

van

der

Bij

, G

hin

cu

lov

hep

-ph

/9909409


Tri-boson ProductionTri-boson Production pppp Wγγ Wγγ

σ x BR(Wσ x BR(Wl,νl,ν)) √√s > Ms > MWW production threshold production threshold σ = 1.96 fb (μσ = 1.96 fb (μ±±,e,e±± after efficiency, detector effects) after efficiency, detector effects) WWγγ WWγγ couplingscouplings

Eboli, Gonzalez-Garcia, Lietti, Phys Lett D63, 2001

W2GRAD (Baur, Stelzer)

ATL-PHYS 2003-051


ConclusionsConclusions CMS & ATLAS are under construction.CMS & ATLAS are under construction. LHC physics potential includes LHC physics potential includes competitive competitive

precisionprecision electroweak measurements: electroweak measurements: sinsin22θθWW, mass(W), mass(W)

Order of magnitude and better improvement Order of magnitude and better improvement in anomalous TGC limits in anomalous TGC limits precision arena for precision arena for diboson productiondiboson production

Challenges include:Challenges include: Detector performance: lepton energy scale, Detector performance: lepton energy scale,

forward taggingforward tagging More precise measurement of PDFsMore precise measurement of PDFs

no good no good prediction of LHC precisionprediction of LHC precision exists. exists. Theory: next-generation codes need QCD + QEDTheory: next-generation codes need QCD + QED

Gauge-boson Physics at the LHC

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