Physics Division Gauge-boson Physics Gauge-boson Physics at the LHC at the LHC Matt Dobbs Lawrence Berkeley Laboratory, USA Hadron Collider Physics 2004 Michigan State U.
Dec 21, 2015
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.
Matt Dobbs Hadron Collider Physics 2004 3
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
Matt Dobbs Hadron Collider Physics 2004 4
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
Matt Dobbs Hadron Collider Physics 2004 5
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
Matt Dobbs Hadron Collider Physics 2004 7
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)
Matt Dobbs Hadron Collider Physics 2004 8
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
Matt Dobbs Hadron Collider Physics 2004 9
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)
Matt Dobbs Hadron Collider Physics 2004 10
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
Matt Dobbs Hadron Collider Physics 2004 11
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…
Matt Dobbs Hadron Collider Physics 2004 12
Matt Dobbs Hadron Collider Physics 2004 13
Physics Division
Weinberg Angle: sinWeinberg Angle: sin22θθWWWeinberg Angle: sinWeinberg Angle: sin22θθWW
Matt Dobbs Hadron Collider Physics 2004 15
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%)
Matt Dobbs Hadron Collider Physics 2004 16
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
Matt Dobbs Hadron Collider Physics 2004 17
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
Matt Dobbs Hadron Collider Physics 2004 19
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
Matt Dobbs Hadron Collider Physics 2004 20
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
Matt Dobbs Hadron Collider Physics 2004 21
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
Matt Dobbs Hadron Collider Physics 2004 22
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
Matt Dobbs Hadron Collider Physics 2004 23
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
Matt Dobbs Hadron Collider Physics 2004 24
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!..
Matt Dobbs Hadron Collider Physics 2004 25
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
Matt Dobbs Hadron Collider Physics 2004 26
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
Matt Dobbs Hadron Collider Physics 2004 27
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