C. K. Mackay EPS 2003

Electroweak Physics and the Top Quark Mass

at the LHC

Kate Mackay

University of Bristol

On behalf of the Atlas & CMS Collaborations

EPS Aachen, July 2003

C. K. Mackay EPS 2003

Outline

The Atlas and CMS Detectors

W Mass Measurement of the W mass Errors on W mass measurement

Top Physics Top Quark Mass measurements Errors on top mass measurement Single top quark production

Triple Gauge Boson Couplings WW ZZ and Z

Summary

C. K. Mackay EPS 2003

The Atlas DetectorInner Detector:Silicon pixels and stripsTransition radiation trackerEM Calorimeter:Sampling Pb/LAr

Hadron Calorimeters:Barrel: Fe/Scintillating

tiles

Endcaps: Cu & W /LArMuon Spectrometer:Drift tubes & Cathode strip Tubes, resistive plate

chambers

Magnet: 2T Solenoid

)(

%10

GeVEE

03.0)(

%50

GeVEE

%32 Tp

C. K. Mackay EPS 2003

The CMS DetectorInner Detector:Silicon pixels and strips

Preshower:Lead and silicon strips

EM Calorimeter:Lead Tungstate

Hadron Calorimeters:Barrel & Endcap: Cu/Scintillating sheets

Forward:Steel and Quartz fibre

Muon Spectrometer:Drift tubes, cathode strip chambers and resistive platechambers

Magnet: 4T Solenoid

%2)(

%5

GeVEE

%5)(

%65

GeVEE

C. K. Mackay EPS 2003

Precision of the W MassThe W mass is known with a precision

of

± 34 MeV from LEP2 and the Tevatron -

What is the motivation for improving

at the LHC? Higgs mass estimation Radiative corrections

For equal weights in a 2 test:

If Mt ~ 2 GeV at the LHC, we

require

MW ~ 15 MeV

W Transverse Mass Distribution including

expected detector resolution

rGM

WF

W

1sin

1.

2

)cos1(2 TlT

WT ppM

Measurement of the W mass is performed in

the leptonic channels using the transverse

mass:

tW MxM 2107.0

C. K. Mackay EPS 2003

Precision of the W MassCuts:

Isolated charged lepton pT > 25 GeV || <

2.4

Missing transverse energy ETMiss > 25 GeV

No jets with pT > 30 GeV

Recoil < 20GeV

Sources of Uncertainty: Statistical uncertainty

pp W + X = 30 nb (l= e,)

W ll 3 x 108 events

< 2MeV for 10 fb-1 Systematic Error

Detector performance

Physics

Source MW

(MeV)

Statistics 2

E-p scale 15

Energy resolution 5

Recoil model 5

Lepton identification 5

pTW 5

Parton distribution functions

10

W width 7

Radiative decays 10

Background 5

Total 25

Reduces the error on log MH from

0.2 to 0.1

1 year, 1 lepton species: 25 MeV

Combining lepton channels: 20 MeV

Combining experiments: 15 MeV

C. K. Mackay EPS 2003

Top Mass Together with MW helps to

constrain the SM Higgs mass

tt production: main background to new physics processes: production and decay of Higgs bosons and SUSY particles

Top events used to calibrate the calorimeter jet scale

Precision measurements in the top sector provide information of the fermion mass hierarchy

At low luminosity:

Semi-leptonic: best channel for top mass

measurement (pure hadronic channel can

also be used)

Error dominated by systematic errors: Jet energy scale Final state gluon radiation

tt leptonic decays

(t bW)

Single lepton

W l, W jj

29.6 %

2.5 x 106 events

Di-lepton

W l, W l

4.9 %

400,000 events

eventsxpbttppNLO6108833)(

--

qqbblWbbWtt

C. K. Mackay EPS 2003

Top Mass Measurements

Predicted error on the top mass measurement from the semi-leptonic channel of 1.3 GeV

(Di-leptonic channel: 2 GeV)

C. K. Mackay EPS 2003

Single Top Quark Production Probe the t-W-b vertex

Direct measurement of the CKM matrix element Vtb

(t) |Vtb|

New Physics – heavy Vector Boson W’

Source of high polarized tops

Background: tt-, Wbb-, Wjj

Tevatron: (t) ~ (t-) LHC: (t) ~ 1.5 (t-)

LHC provides a new scenario for

single top quark production.

(pb) D0 CDF LHCWg <22 <13 245Wt - - 60W* <17 <18 10

For each process: |Vtb|2

Systematic errors: B-jet tagging, luminosity,

theoretical (dominates Vtb measurements)

Process S/B S/√B Vtb/Vtb

Statistical

Vtb/Vtb

Theory

W-g 4.9 239 0.51% 7.5%

Wt 0.24 25 2.2% 9.5%

W* 0.55 22 2.8% 3.8%

C. K. Mackay EPS 2003

WW VertexParameters and are related to

physical properties of the W boson.

They are CP-conserving couplings and

relate to the electric quadrupole

moment of the W (QW) and its

magnetic dipole moment (W)

In the SM =1 ( = 0) and

=0 at

tree level.

Anomalous contribution is enhanced

at high √s

Observing the anomalies: pT distribution Radiation zero (,l) MT distribution Angular distribution W

Shaded = SM Clear = = 0.01

C. K. Mackay EPS 2003

Limits on W pT Cuts: () > 100 GeV, (l) > 25

GeV,

pT miss > 50 GeV

Jet veto R(,l) > 0.7

MT (l ,pT miss) > 90 GeV

LHC Limits for 10 fb-1 and 100 fb-1

C. K. Mackay EPS 2003

ZZ & Z VerticesAnomalous couplings are hV

i (i = 1-4, V

=

Z, )

hV3 and hV

4 are the CP-conserving couplings

and hV1 and hV

2 are the CP-violating couplings

relating to the transition moments of the Z

Observing the anomalies: pT distribution MT distribution

C. K. Mackay EPS 2003

ZZ & Z Vertices Main Backgrounds

Z + JetZ

Cuts

|,l | < 2.4

pT > 100 GeV

pTl > 25 GeV

R(,l) > 0.7MT (ll) > 100 GeV

Predicted Limits = 1 TeV

= 3 TeV

Typically order of magnitude improvement

hZ3 hZ

4

10 fb-1 ± 2.0 x 10-2 ± 8.2 x 10-4

100 fb-1 ± 7.8 x 10-3 ± 3.6 x 10-4

hZ3 hZ

4

10 fb-1 ± 2.3 x 10-3 ± 1.9 x 10-5

100 fb-1 ± 1.5 x 10-3 ± 8.5 x 10-6

C. K. Mackay EPS 2003

Summary LHC: precision measurements, unexplored kinematic

regions, high-statistics (W, Z, b, t factory)

W Mass: Measured with a precision of ~ 15 MeV

(Combining lepton channels and both Atlas and CMS)

Top Mass: Measured with a precision of ~ 1.3 GeV

Higgs Mass:

Together MW and Mt improve error on log MH ~ 50%.

Triple Gauge Couplings: WW: Anomalies clearly observed in pT() distribution ZZ: Anomalies clearly observed in pT() and MT(ll) distribution Predicted Limits: ~ order of magnitude improvement