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Electroweak Physics at Electroweak Physics at the LHC the LHC Precision Measurements and New Precision Measurements and New Physics Physics PY898: Special Topics in LHC PY898: Special Topics in LHC Physics Physics By Keith Otis By Keith Otis 4/13/2009 4/13/2009

Electroweak Physics at the LHC Precision Measurements and New Physics

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Electroweak Physics at the LHC Precision Measurements and New Physics. PY898: Special Topics in LHC Physics By Keith Otis 4/13/2009. Outline. Electroweak Parameters W-Mass Top-Mass Electroweak Mixing Angle Drell-Yan Forward-Backward Asymmerty in Z Decays (A FB ) - PowerPoint PPT Presentation

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Page 1: Electroweak Physics at the LHC Precision Measurements and New Physics

Electroweak Physics at the LHCElectroweak Physics at the LHCPrecision Measurements and New PhysicsPrecision Measurements and New Physics

PY898: Special Topics in LHC PhysicsPY898: Special Topics in LHC Physics

By Keith OtisBy Keith Otis

4/13/20094/13/2009

Page 2: Electroweak Physics at the LHC Precision Measurements and New Physics

OutlineOutline

Electroweak ParametersElectroweak Parameters W-MassW-Mass Top-MassTop-Mass Electroweak Mixing AngleElectroweak Mixing Angle

Drell-YanDrell-Yan Forward-Backward Asymmerty in Z Decays (AForward-Backward Asymmerty in Z Decays (AFBFB)) Triple Gauge Boson CouplingsTriple Gauge Boson Couplings

Charged TGCsCharged TGCs Neutral TGCsNeutral TGCs Anomalous Quartic CouplingsAnomalous Quartic Couplings

Heavy LeptonsHeavy Leptons

Page 3: Electroweak Physics at the LHC Precision Measurements and New Physics

Electroweak ParametersElectroweak Parameters The main parameters of EW theory are measured to very high The main parameters of EW theory are measured to very high

precision.precision. The mass of the W (MThe mass of the W (MWW) is known with an uncertainty of 0.03%) is known with an uncertainty of 0.03%

MMWW= 80.428 ± 0.039 GeV UA2/CDF/D0, 80.376 ± 0.033 GeV LEP 2= 80.428 ± 0.039 GeV UA2/CDF/D0, 80.376 ± 0.033 GeV LEP 2 SM predicts 80.375 ± 0.015 GeVSM predicts 80.375 ± 0.015 GeV

The uncertainty in the mass of the Top (mThe uncertainty in the mass of the Top (mtt) is 0.7%) is 0.7% mmtt= 170.9 ± 1.8 GeV= 170.9 ± 1.8 GeV SM predicts 171.1 ± 1.9 GeVSM predicts 171.1 ± 1.9 GeV

The uncertainty on the electroweak-mixing angle (The uncertainty on the electroweak-mixing angle (θθww) is 0.07%) is 0.07% cos(cos(θθww)= M)= Mww/M/Mzz

The LHC will be able to improve on these in a relatively short period The LHC will be able to improve on these in a relatively short period of time.of time.

Page 4: Electroweak Physics at the LHC Precision Measurements and New Physics

Tevatron: 2 TeVTevatron: 2 TeV

LHC: 10-14TeVLHC: 10-14TeV

LHC @ 10LHC @ 103333 Luminosity Luminosity 150 Hz W150 Hz W 50 Hz z50 Hz z 1 Hz tT1 Hz tT

10 pb10 pb-1-1 of Luminocity of Luminocity 150k W→e150k W→eνν 15k Z→ee15k Z→ee 10k tT10k tT

Page 5: Electroweak Physics at the LHC Precision Measurements and New Physics

W-MassW-Mass

W→W→llvv signature signature Isolated charged lepton pT > Isolated charged lepton pT >

25 GeV |25 GeV || < 2.4| < 2.4 Missing transverse energy Missing transverse energy

ETMiss > 25 GeVETMiss > 25 GeV No jets with pT > 30 GeVNo jets with pT > 30 GeV Recoil < 20GeVRecoil < 20GeV

For an integratedFor an integrated luminosity of 1 luminosity of 1 fbfb−1−1, 4 million events with , 4 million events with W→W→llvv (ℓ (ℓ = e or = e or μμ) decays are expected.) decays are expected.

)(

direct

indirect

Summer 2005 result

68% CL68% CL

Page 6: Electroweak Physics at the LHC Precision Measurements and New Physics

W mass extractionW mass extraction

The W mass is extracted from the The W mass is extracted from the measured pmeasured pll

TT distribution or from the distribution or from the

Jacobian peak observed in the transverse Jacobian peak observed in the transverse mass of the lepton-neutrino system, Mmass of the lepton-neutrino system, MWW

TT..The W mass is obtained by comparing the The W mass is obtained by comparing the

measured distributions with template measured distributions with template distributions generated from data (Z distributions generated from data (Z events) or MC.events) or MC.

Page 7: Electroweak Physics at the LHC Precision Measurements and New Physics

MC Template method

Source Source MMW W (MeV)(MeV) MMTTee(W)(W) PPTT(e)(e)

StatisticsStatistics 22 22

BackgroundBackground 55 55

Lepton E-p scaleLepton E-p scale 44(15)(15) 44(15)(15)

Lepton E/p resolutionLepton E/p resolution (5)(5) (5)(5)

Recoil modelRecoil model 55

Lepton identificationLepton identification 88 88

Total InstrumentalTotal Instrumental <20<20 <20<20

ppTTWW 55

Parton distribution Parton distribution functionsfunctions

33((10)10) 33((10)10)

W widthW width 11(7)(7) 11(7)(7)

Radiative decaysRadiative decays 1010 1010

Based on 10fb-1 of data corresponding to ~10M Wl

Fit MT(W) or pT (e) to Z0 tuned MC

Z-Samples play a crucial role in reducing systematics and theoretical uncertaintiesRequires further study

ATLAS

W-mass: ATLAS

Page 8: Electroweak Physics at the LHC Precision Measurements and New Physics

Scaled observables

Use Z events as templatesUse Z events as templates Scaled observable using Scaled observable using

weighting fnweighting fn Morphing using kinematic Morphing using kinematic

transformationtransformation Limited by Z-statisticsLimited by Z-statistics

Detector and theoretical effects Detector and theoretical effects cancel at least partiallycancel at least partially

Pt(l) better than MT as it is not Pt(l) better than MT as it is not sensitive to Esensitive to ETT systematics systematics But needs PBut needs PTT(W) to be (W) to be

understoodunderstood

CMS

Scaled pScaled pTT(l ) (l )

WWee

““Morphed” mMorphed” mTT

WW

StatisticalStatistical 1515 1515

InstrumentalInstrumental <20<20 <30<30

PDFPDF <10<10 <10<10

WW <15<15 <10<10

PPTT(W)(W) 3030 ----

Systematic uncertainties (MeV) on W-mass for 10fb-1

PT(W) needs to reduced ET-systematics

W-mass: CMS

Page 9: Electroweak Physics at the LHC Precision Measurements and New Physics
Page 10: Electroweak Physics at the LHC Precision Measurements and New Physics

New Physics?New Physics?

tW MM 2107.0• For equal contribution to MH uncertainty:

• MW is a fundamental SM parameter linked to

the top, Higgs masses and sinW.

Mt < 2 GeV MW < 15

MeV

rGM

WF

EMW

1sin

1

2

Mar 06

LEP2+Tevatron MW=30MeVTevatron run2 (2fb-1) 30MeV combined

Can get MH/MH~30%Important cross-check with direct measurements

Page 11: Electroweak Physics at the LHC Precision Measurements and New Physics

W-mass summaryW-mass summary

A number of methods have been studiedA number of methods have been studied Direct measurement of MDirect measurement of MTT p pTT(l)(l)

Z-events used to tune W MCZ-events used to tune W MC scaled observable pt(l), ‘morphing’scaled observable pt(l), ‘morphing’

Z-events used as a templateZ-events used as a template Systematics greatly improved using Z-samplesSystematics greatly improved using Z-samples All methods are giving All methods are giving MMww in range of 20MeV per channel in range of 20MeV per channel

per variable, so combined <15MeV per experiment seems per variable, so combined <15MeV per experiment seems to be achievable for 10fbto be achievable for 10fb-1-1

Need to understand correlationsNeed to understand correlations Main issues at EMain issues at ETT for M for MTT and P and PTT(W) for p(W) for ptt(l)(l) MMW W ~10MeV looks possible~10MeV looks possible Requires Requires MMtt<1GeV for EW fits<1GeV for EW fits

Page 12: Electroweak Physics at the LHC Precision Measurements and New Physics

Top MassTop Mass

Top quark pairs, mainly produced via gluon fusion, yields a production cross-section of 833 pb, at next to leading order, 100 times higher than at Tevatron.

The "golden" channel is the semi-leptonic channel:tT→Wb+WB→ (lv)b+(jj)B

Page 13: Electroweak Physics at the LHC Precision Measurements and New Physics

Top MassTop Mass Golden Channel event selection:Golden Channel event selection:

Isolated high pIsolated high pTT lepton, E lepton, EmissmissTT and at and at

least 4 jets, two of which are b-least 4 jets, two of which are b-tagged.tagged.

This gives a signal efficiency of ~5% This gives a signal efficiency of ~5% with a signal to background ratio of with a signal to background ratio of the order 10.the order 10.

Primary backgroundsPrimary backgrounds The main backgrounds are single top The main backgrounds are single top

events, mainly reduced by the4 jet events, mainly reduced by the4 jet cut, fully hadronic t T events, reduced cut, fully hadronic t T events, reduced by the lepton requirements, W+jet by the lepton requirements, W+jet and Z+jet events and Z+jet events

Page 14: Electroweak Physics at the LHC Precision Measurements and New Physics

Finding the Top MassFinding the Top Mass

Reconstruction of the hadronic side of the decay is done Reconstruction of the hadronic side of the decay is done by minimization procedure.by minimization procedure. This minimization constrains the light jet pair mass to MThis minimization constrains the light jet pair mass to Mww, via , via

corrections to the light jet energies.corrections to the light jet energies. After trying all possible jet combinations the one minimizing the After trying all possible jet combinations the one minimizing the

χχ22 is kept. is kept. The b-jet closest to the hadronic W is associated to the chosen The b-jet closest to the hadronic W is associated to the chosen

pair.pair. The three jet invariant mass is then fitted with a Gaussian plus a The three jet invariant mass is then fitted with a Gaussian plus a

polynomialpolynomial The Result: MThe Result: Mtt= 175.0±0.2(stat.)±1.0(syst.) GeV, for an input = 175.0±0.2(stat.)±1.0(syst.) GeV, for an input

mass of 175 GeV and 1 fbmass of 175 GeV and 1 fb−1−1..

Page 15: Electroweak Physics at the LHC Precision Measurements and New Physics

Drell-YanDrell-Yan

As discussed in As discussed in previous weeks this is previous weeks this is where a heavier where a heavier neutral gauge boson neutral gauge boson (Z’) would show up(Z’) would show up

AAFB FB of the leptons from of the leptons from

ZsZs

Page 16: Electroweak Physics at the LHC Precision Measurements and New Physics

Drell YanDrell YanImportant benchmark process:• Measure cross-section• parton-parton luminosity functions• constrain PDFs• measure sin2W

• Deviations from SM

Page 17: Electroweak Physics at the LHC Precision Measurements and New Physics

Need to define direction

At the Tevatron -- well defined

At LHC no asymmetry wrt beamAssume that there is a Q-qbar collision quark direction from y(ll)Requires measurement at high y(ll)

Determination of sinDetermination of sin22θθeffeffleptlept(M(MZZ

22 ))

AFB = b { a - sin2θefflept( MZ

2 ) } Measure Afb with leptons in Z0 DY events

Q q

q q

Can fit with Mt to constrain MHa, b calculated to NLO QED and QCD.

Page 18: Electroweak Physics at the LHC Precision Measurements and New Physics

Determination of Determination of sinsin22θθeffeff

leptlept(M(MZZ22

))y cuts – ey cuts – e++ee--

((||y(y(ZZ))|| > 1) > 1)

ATLAS ∆AATLAS ∆AFBFB

(Stat)(Stat)

ATLAS ATLAS ∆sin∆sin22θθeffeffleptlept

(Stat)(Stat)

||y( y( ll1,21,2 ) )|| < 2.5 < 2.5 3.0 x 103.0 x 10-4-4 4.0 x 104.0 x 10-4-4

||y( y( ll11 ) )|| < 2.5 + < 2.5 +

||y( y( ll22 ) )|| < 4.9 < 4.92.3 x 102.3 x 10-4-4 1.4 x 101.4 x 10-4-4

Can be further improved by combining Z decay channels

[%]

Systematics: PDF, lepton acc. (~0.1%), radiative correction calculations

Current error on world average 1.6x10-4

sin2θeff =0.23153±0.00016

Page 19: Electroweak Physics at the LHC Precision Measurements and New Physics

Associated Production of Gauge Associated Production of Gauge BosonsBosons

Page 20: Electroweak Physics at the LHC Precision Measurements and New Physics

Triple gauge boson Triple gauge boson couplingscouplings

, ,, Z1 ZZg

s ~ grows

s ~ grows

SM gauge group SU(2)LxU(1)Y

WW and WWZ couplings(charged TGCs)

Couplings described by 5 independent parameters

s ~ grows

All are zero in SM

Any deviations is a signal of new physics

Page 21: Electroweak Physics at the LHC Precision Measurements and New Physics

Anomalous couplings in Anomalous couplings in WWWW

Most sensitive measurement is looking for high pMost sensitive measurement is looking for high pTT Zs or Zs or ss

30fb-1

~3000 evts

ATLASCMS

Page 22: Electroweak Physics at the LHC Precision Measurements and New Physics
Page 23: Electroweak Physics at the LHC Precision Measurements and New Physics
Page 24: Electroweak Physics at the LHC Precision Measurements and New Physics

Charged TGC predictionsCharged TGC predictions

95% CL 30fb95% CL 30fb-1-1 (inc syst) (inc syst)

-0.0035<-0.0035<<+0.0035<+0.0035

-0.0073<-0.0073<ZZ<+0.0073<+0.0073

-0.075<-0.075<<+0.076<+0.076

-0.11<-0.11<ZZ<+0.12<+0.12

-0..86<-0..86<gg11ZZ<+0.011<+0.011

Results expected to be ~x10 better than LEP/Tevatron

Results are statistics limited(except for g1

Z )

Page 25: Electroweak Physics at the LHC Precision Measurements and New Physics

2,45,43,1 , hfh

2

3

s ~ grows

All are zero in SM

2

5

s ~ grows

Neutral TGCsNeutral TGCs

No tree level neutral couplings in SM

Leads to 3-5 order of magnitude improvement compared to LEP

95% CL 100fb95% CL 100fb-1-1 (inc syst) (inc syst)

-6.5x10-6.5x10-4 -4 <h<h3030ZZ<+6.4x10<+6.4x10-4-4

-1.8x10-1.8x10-6 -6 < h< h4040ZZ

< +1.7x10< +1.7x10-6-6

CMS

Page 26: Electroweak Physics at the LHC Precision Measurements and New Physics

Quartic CouplingsQuartic Couplings

Page 27: Electroweak Physics at the LHC Precision Measurements and New Physics

Anomalous Quartic Anomalous Quartic couplingscouplings

Look for W, low production threshold at Mw

S/B~1

ATLAS 30fb-1 e-~14 events(~x4 for l+/-)

Page 28: Electroweak Physics at the LHC Precision Measurements and New Physics

Heavy LeptonsHeavy Leptons

““Evidence grows for charged heavy lepton Evidence grows for charged heavy lepton at 1.8-2.0 GeV”- Physics Today (1977)at 1.8-2.0 GeV”- Physics Today (1977)

Current limits: mCurrent limits: mL(±)L(±) >100.8GeV >100.8GeVNeutral Heavy Lepton Mass LimitsNeutral Heavy Lepton Mass Limits

Mass m> 45.0 GeV, 95% CL (Dirac)Mass m> 45.0 GeV, 95% CL (Dirac)Mass m> 39.5 GeV, 95% CL (Majorana)Mass m> 39.5 GeV, 95% CL (Majorana)

Page 29: Electroweak Physics at the LHC Precision Measurements and New Physics

Heavy LeptonsHeavy Leptons Relic abundance of the leptons must not “over-close” the universe.Relic abundance of the leptons must not “over-close” the universe.

Can’t provide more than the critical energy density (10Can’t provide more than the critical energy density (10-5-5GeV cmGeV cm--

33)) A stable, charged lepton must have a low enough relic abundance A stable, charged lepton must have a low enough relic abundance

for it not to have been detected in searches for heavy isotopes in for it not to have been detected in searches for heavy isotopes in ordinary matterordinary matter

The mass and lifetime of the new leptons musts not be such that The mass and lifetime of the new leptons musts not be such that they would have been detected in a previous collider experiment.they would have been detected in a previous collider experiment.

There are no theoretical constraints found for lifetimes less that ~10There are no theoretical constraints found for lifetimes less that ~1066 s even for masses up to the TeV scale.s even for masses up to the TeV scale.

Only limits are the experimental onesOnly limits are the experimental ones

Page 30: Electroweak Physics at the LHC Precision Measurements and New Physics

Heavy LeptonsHeavy Leptons

Where do we look for heavy Leptons?Where do we look for heavy Leptons?Drell-YanDrell-YanOther mechanismsOther mechanisms

pp→pp→γγ→γγ→LL++LL--

pp→Zpp→Zγ→γ→LL++LL--

Mechanisms for introducing new leptonsMechanisms for introducing new leptonsNew fermionic degrees of freedomNew fermionic degrees of freedom

Vector Singlet Model (VSM)Vector Singlet Model (VSM)Vector Doublet Model (VDM)Vector Doublet Model (VDM)Fermion-mirror-fermion Model (FMFM)Fermion-mirror-fermion Model (FMFM)

Page 31: Electroweak Physics at the LHC Precision Measurements and New Physics

Heavy LeptonsHeavy Leptons

In these new models:In these new models:Exotic leptons mix with the standard leptons Exotic leptons mix with the standard leptons

through the standard weak vector bosons and through the standard weak vector bosons and according to the Lagrangiansaccording to the Lagrangians

Page 32: Electroweak Physics at the LHC Precision Measurements and New Physics

LL±± Detection Detection

Time-of-FlightTime-of-FlightHeavy particlesHeavy particlesDetectable in both the central tracker and Detectable in both the central tracker and

muon chambersmuon chambersUse measured momentum and time delay to Use measured momentum and time delay to

reconstruct the massreconstruct the mass

Page 33: Electroweak Physics at the LHC Precision Measurements and New Physics

LL±± Detection Detection

Imperfections in the time and momentum Imperfections in the time and momentum resolutions will cause a spread in the resolutions will cause a spread in the mass peakmass peak

Bunch crossing identificationBunch crossing identificationMuons from D-Y and heavy quark decaysMuons from D-Y and heavy quark decays

For a background signal to look like a heavy lepton neutral current For a background signal to look like a heavy lepton neutral current two opposite charge muons would have to be mis-identified at the two opposite charge muons would have to be mis-identified at the same time.same time.

Make pMake pTT cut at 50 GeV to eliminate heavy quark decays cut at 50 GeV to eliminate heavy quark decays

Page 34: Electroweak Physics at the LHC Precision Measurements and New Physics
Page 35: Electroweak Physics at the LHC Precision Measurements and New Physics

LL±± Detection Detection

Detection at the LHC is entirely cross Detection at the LHC is entirely cross section limited.section limited.

Page 36: Electroweak Physics at the LHC Precision Measurements and New Physics

LL±± Detection Detection

Detection of up to 1TeV should be Detection of up to 1TeV should be possible a the LHCpossible a the LHC

Page 37: Electroweak Physics at the LHC Precision Measurements and New Physics

Leptons vs. SleptonsLeptons vs. Sleptons

Study the angular distributionStudy the angular distribution

Page 38: Electroweak Physics at the LHC Precision Measurements and New Physics

Leptons vs. SleptonsLeptons vs. Sleptons

Page 39: Electroweak Physics at the LHC Precision Measurements and New Physics

Heavy Lepton SummaryHeavy Lepton Summary

Assuming standard model couplings and Assuming standard model couplings and long lifetime:long lifetime:We can detect heavy charged leptons in We can detect heavy charged leptons in

intermediate scale models up to 950 GeV with intermediate scale models up to 950 GeV with 100 fb100 fb-1-1

Above 580 GeV it’s hard to distinguish them Above 580 GeV it’s hard to distinguish them from scalar leptonsfrom scalar leptons

Page 40: Electroweak Physics at the LHC Precision Measurements and New Physics

SummarySummary

The Electroweak sector, while one of the The Electroweak sector, while one of the better understood sectors of the SM, still better understood sectors of the SM, still holds important information and even holds important information and even some exciting new physics at the LHCsome exciting new physics at the LHC

Page 41: Electroweak Physics at the LHC Precision Measurements and New Physics

Backup slides

Page 42: Electroweak Physics at the LHC Precision Measurements and New Physics
Page 43: Electroweak Physics at the LHC Precision Measurements and New Physics

2.5

Constraining gluon PDF with Ws

• Many W+Z measurements have pdf uncertainties• at LHC Q2~MZ

2 corresponds to sea-sea collisions depends on gluon from gqq• Need to improve understanding of gluon

Page 44: Electroweak Physics at the LHC Precision Measurements and New Physics

ZEUS to MRST01 central value difference ~5%ZEUS to CTEQ6.1 central value difference ~3.5% (From LHAPDF eigenvectors)

W Rapidity Distributions for W Rapidity Distributions for different PDFsdifferent PDFs

CTEQ6.1M MRST02

GOAL: syst. exp. error ~3-5%

~ ±5.2% @y=0~ ±8.7% @y=0 ~ ±3.6% @ y=0

ZEUS-S

Page 45: Electroweak Physics at the LHC Precision Measurements and New Physics

• At Detector level reflects generator level distributions ~8% PDF uncertainty at y=0 remains

CTEQ61

MRST01 ZEUS-S

CTEQ61

MRST01 ZEUS-S

e- rapidity e+ rapidity

Generator Level

ATLASDetector Levelwith sel. cuts

Error boxesare the Full PDF Uncertainties

Electron distributions

Page 46: Electroweak Physics at the LHC Precision Measurements and New Physics

First measurements of W and ZFirst measurements of W and Z

W3.3%~ Z%3.2~

W and Z cross-sectionsFor ~1fb-1 data, systematics dominate

(CMS)tracker efficiency

Main theoretical contributionPT(W/Z) LO-NLO ~2%

ET

Initial luminosity uncertainty ~10%, reduced to 5%

ATLAS

-reconstruction efficiency from 20pb-1 Z

Barrel and endcapTo 0.5% in 0.2 bins

Page 47: Electroweak Physics at the LHC Precision Measurements and New Physics

Minimum bias and Underlying Event

Tevatron

● CDF 1.8 TeV

PYTHIA6.214 - tuned dN/ddN/dηη ((ηη=0=0))

NNchch jet- jet-

pptt=20GeV=20GeV

1.8TeV (pp)1.8TeV (pp) 4.14.1 2.32.3

14TeV (pp)14TeV (pp) 7.07.0 7.07.0

increaseincrease ~x1.8~x1.8 ~x3~x3

~80%~200%

LHC prediction

Tevatron

PYTHIA6.214 - tuned

● CDF 1.8 TeV

MB onlyUE includes radiation and small impact parameter bias

LHC

Page 48: Electroweak Physics at the LHC Precision Measurements and New Physics

First measurements at the LHC ?First measurements at the LHC ?Charged particle density at Charged particle density at = 0 = 0

(Only need central inner tracker and a few thousand pp events)

LHC?

• Min bias events are also crucial for intercalibration CMS require 18M events to intercalibrate ECAL in at 2%• ATLAS studies of use of MB events to study L1 trigger rates

Page 49: Electroweak Physics at the LHC Precision Measurements and New Physics

Measuring the minimum bias events at ATLASMeasuring the minimum bias events at ATLAS

dNch/d

dNch/dpT

Black = Generated (Pythia6.2)Black = Generated (Pythia6.2)

Blue = TrkTrack: iPatRecBlue = TrkTrack: iPatRec

Red = TrkTrack: xKalmanRed = TrkTrack: xKalman

Only a fraction of tracks reconstructed,:Only a fraction of tracks reconstructed,:

limited rapidity coveragelimited rapidity coverage

Measure central plateauMeasure central plateau

can only reconstruct track pcan only reconstruct track pTT with with

good efficiency down to ~500MeV, but good efficiency down to ~500MeV, but most particles in min-bias events have most particles in min-bias events have ppTT < 500MeV < 500MeV

Hard extrapolation.Hard extrapolation. Reconstruct tracks Reconstruct tracks with:with:

1) pT>500MeV1) pT>500MeV 2) |d2) |d00| < 1mm| < 1mm 3) # B-layer hits >= 13) # B-layer hits >= 1 4) # precision hits >= 4) # precision hits >=

88

pT (MeV)

Page 50: Electroweak Physics at the LHC Precision Measurements and New Physics

UE uncertaintiesUE uncertaintiesTra

nsvers

e <

Nch

g >

PYTHIA6.214 - tuned

PHOJET1.12

x 3

LHC

x1.5

Extrapolation of UE to LHC is unknownDepends on• Multiple interactions• Radiation• PDFs

CDF definition of UE

Page 51: Electroweak Physics at the LHC Precision Measurements and New Physics

Ra

tio

<N

Tra

ckR

eco>

/<N

Tra

ckM

C>

Leading jet ET (GeV)

ReconstructinReconstructing the g the

underlying underlying eventevent

Njets > 1, |ηjet| < 2.5, ET

jet >10 GeV,

|ηtrack | < 2.5, pT

track > 1.0 GeV/c

ATLAS DC2 Simulated data

Analyse with first data(a la CDF)Need to ensure overlap between MB and jet triggerRequire ~20M MB events to get pt

jet~30GeV