1

Electroweak physics at LHC

Marina Cobal, University of Udine‘IFAE’, Torino Apr 14 - Apr 16, 2004

P 2

Outline

Introduction

W mass measurement

Top mass measurement

EW single top quark production: measurement of Vtb.

AFB asymmetry in dilepton production: sin2θefflept(MZ

2).

Conclusion.

P 3

TOTEM

ALICE : heavy ions,p-ions

ATLAS and CMS :pp, general purpose

LHCb : pp, B-physics

27 km ring 1232 dipoles B=8.3 T

LHC and experiments

pp (mainly) at s = 14 TeV Startup in April 2007

Initial/low lumi L~1033 cm-2 s-1

2 minimum bias/x-ing “Tevatron-like” environment

10 fb-1 /year Design/high lumi L=1034 cm-2 s-1

after ~ 3 years ~ 20 minimum bias/x-ing

fast ( 50 ns) radhard detect 100 fb-1 /year

P 4 ATLAS cavern

Huge activities in construction of both CMS and ATLAS

CMS yoke

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What we know

No observable directly related to mNo observable directly related to mHH. Dependence through radiative corrections. Dependence through radiative corrections.

Example: mExample: mWW=m=mWW((mmtt22,,log(mlog(mHH))))

SM(17 parameters)

mfermions (9)

mbosons (2)

VCKM (4)GF (1)

mH

predictions

from n, decays

not discovered yet

from directmeasurements

from meson decays

(down to 0.1% level)

t t m mtt22 H H ln(m ln(mHH/m/mWW))

By making precision measurements (already interesting per se):By making precision measurements (already interesting per se):• • one can get information on the missing parameter mone can get information on the missing parameter mHH• • one can test the validity of the Standard Modelone can test the validity of the Standard Model

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Where we are

At the Tevatron run II: At the Tevatron run II: mmt t 2.5 GeV ; 2.5 GeV ; mmW W 30 MeV 30 MeV mmHH/m/mH H 35% 35%

What can we expect/should be our goal at LHC?What can we expect/should be our goal at LHC?

Uncertainties on mUncertainties on mtt, m, mWW are the dominating ones in the ew fit are the dominating ones in the ew fit

Each “observable” Each “observable” (A(Aqq, A, All, ,

RRqq, R, Rll, , , m, sin, m, sinWW,…) ,…) can can

be calculated as a function be calculated as a function of: of: hadhad, , ss(m(mZZ), m), mZZ, m, mtt,,mmHH

P 7

Predictions

LHC

TeVatron1034

1033

<1032

Luminosity

[cm-2s-1]

100

10

0.3

∫L

[fb-1/y]

14 LHC (high lum)

14 LHC (low lum)

2 TeVatron

√s

[TeV]

processprocess (pb)(pb) Events/sEvents/s Events/yEvents/y

bbbb 55101088 101066 10101313

ZZeeee 1.51.5101033 ~3~3 101077

WWℓℓℓ=e,μℓ=e,μ 33101044 ~60~60 101088

WWWWeeXX 66 1010-2-2 101055

tttt 830830 ~1.7~1.7 101077

HH(700 GeV/c(700 GeV/c22)) 11 221010-3-3 101044

--

--

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• mtop and MW: equal weight in the EW fit if MW 0.007 mtop

at LHC: mtop 2 GeV gives the precision

• Methods: same as at the Tevatron, with Wl decays

but LHC statistics is higher

Wl 60 M reconstructed @ low L (x10 RunII)

PTl spectrum

R=MTW / MT

Z spectrum

MTW

MW measurement at the LHC

year 2004: MW 30 MeV , year 2007: MW < 30 MeV (Lep2+Tevatron)

MW : 15 MeV

Pile-up , theo. know. of PTW

Small syst, sample /10

Best choice for low lum phase

upp

T

l

T

(missing p(missing pTT))

e

Wbeam line

u

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W mass : fit exp. shape to MC sample with different Values of MW

stat. error negligible

syst. error: MC modelling of the physics

and the detector responses

Mw measurement: Transverse Mass

,)cos1(2 , elppM l

P

TlT

TW

missT

Use Transverse mass to

cope with unmeasured PL

PTW

spectrumPDFW widthW rad. decaysBackground

ZllLHC dataZll,R,CDF/D0Theory, MC

Lep. E/p Lep. res.Recoil

Zll, E/p for e

Zll, E/p for e

Zll

physics detector

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Advantages of LHC

Profit from Tevatron experience:

Many potential hidden sources of systematics from the detector description in the simulations (+pile-up, + radiation)

use data samples for in-situ calibrations !

Advantages of the LHC:

Huge statistics of signal & control samples like Z leptonic decays:

Larger production cross-section for the control process Larger production cross-section for the control process ZZ(e/(e/)(e/)(e/) (6 millions/y/exp)) (6 millions/y/exp)

granularity + acceptance + resolution are bettergranularity + acceptance + resolution are better

Error from control samples at the LHC < than at the TevatronError from control samples at the LHC < than at the Tevatron

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Detector systematics

0.02% on lepton E/p scale precision needed0.02% on lepton E/p scale precision needed

ZZee, Zee, Z mass reconstruction mass reconstruction leptonic decays of leptonic decays of , J/, J/

~15 MeV/y-e-l can be reached~15 MeV/y-e-l can be reached

… … and ~1-2% uncertainty in E+p resolution and ~1-2% uncertainty in E+p resolution

Z width reconstructionZ width reconstruction beam tests data beam tests data

~5 MeV/y-e-l can be reached~5 MeV/y-e-l can be reached

Recoil modelling (UE + detector)Recoil modelling (UE + detector)

determine response/resolution of the recoil (+UE) from Zdetermine response/resolution of the recoil (+UE) from Z data data ~5 MeV/y-e-l can be reached~5 MeV/y-e-l can be reached

low extrapolation error Zlow extrapolation error ZWW

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Physics systematics

ppTT(W)(W) use puse pTT(Z) from Z(Z) from Z, use p, use pTT(W)/p(W)/pTT(Z) to model MC.(Z) to model MC.

~5 MeV/y-e-l can be reached~5 MeV/y-e-l can be reached

Uncertainties on the parton density functionsUncertainties on the parton density functions Compare different models, constrain pdfs through Z+W dataCompare different models, constrain pdfs through Z+W data

~10 MeV/y-e-l can be reached~10 MeV/y-e-l can be reached

W width W width use measurement of use measurement of

<10 MeV/y-e-l can be reached<10 MeV/y-e-l can be reached

Radiative decaysRadiative decays constrained through Wconstrained through W? ?

<10 MeV/y-e-l, theory work needed<10 MeV/y-e-l, theory work needed

BackgroundBackground checks on Z and Wchecks on Z and W (composition similar to Tevatron)(composition similar to Tevatron)

<5 MeV/y-e-l should be reached<5 MeV/y-e-l should be reached

)(

)(

ZBR

WBRR

Z

W

Implicit SM assumption

to determine W From LEP

From theory

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Mw measurement: errors

MW , Wl one lepton species low lum , per exp., per yearsource CDF RunIb LHC

30K evts,84pb-1 60M evts,10fb-1

Statistics

Lepton scale

Energy resolution

Recoil model

Lepton id.

PTW

PDF

W width

Radiative decays

Background

65 MeV

75 MeV

25 MeV

37 MeV

----------

15 MeV

15 MeV

----------

20 MeV

5 MeV

<2 MeV

15 MeV

5 MeV

5 MeV

5 MeV

5 MeV

10 MeV 7 MeV

<10 MeV

5 MeV

TOTAL 92 MeV < 25 MeV

Combining channels and exp., should reach MW 15 MeV

Much better!

Internal calibration from Internal calibration from Z data mainly. Z data mainly. Need excellent control of Need excellent control of energy flow+ p scaleenergy flow+ p scale

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Mtop measurement: production

Cross section determined to NLO precision Total NLO(tt) = 834 ± 100 pb Largest uncertainty from scale variation

Compare to other production processes:

Top production cross section approximately 100x Tevatron

Opposite @ FNAL

32121 10~ ; ˆ xxxsxs

~90% gg~10% qqProcess N/s N/year

Total collected before start LHC

W e 15 108 104 LEP / 107 FNAL

Z ee 1.5 107 107 LEP

tt 1 107 104 Tevatron

bb 106 1012-13 109 Belle/BaBar ?

H (130) 0.02 105 ?

LHC is a top factory!

Low lumi

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MTop from lepton+jet

Br(ttbbjjl)=30%for electron + muon

Golden channel Clean trigger from isolated lepton

The reconstruction starts with the W mass: different ways to pair the right jets

to form the W jet energies calibrated using mW

Important to tag the b-jets: enormously reduces background

(physics and combinatorial) clean up the reconstruction

Lepton side

Hadron side

Typical selection efficiency: ~5-10%:

•Isolated lepton PT>20 GeV

•ETmiss>20 GeV

•4 jets with ET>40 GeV

•>1 b-jet (b40%, uds10-3,

c10-2)

Background: <2%

W/Z+jets, WW/ZZ/WZ

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Lepton + jet: reconstruct top

Hadronic side W from jet pair with closest invariant mass to MW

Require |MW-Mjj|<20 GeV

Assign a b-jet to the W to reconstruct Mtop

Kinematic fit Using remaining l+b-jet, the leptonic part is

reconstructed |mlb -<mjjb>| < 35 GeV Kinematic fit to the tt hypothesis,

using MW constraints

j1

j2

b-jet

tW-mass Selection efficiency 5-10%

Borjanovic et al., SN-ATLAS-2004-040

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Mtop systematics

Method works: Linear with input Mtop

Largely independent on Top PT

Biggest uncertainties: Jet energy calibration FSR: ‘out of cone’ give

large variations in mass B-fragmentation

Verified with detailed detector simulation and realistic calibration

Source of uncertainty

Hadronic Mtop (GeV)

Fitted Mtop (GeV)

Light jet scale 0.9 0.2

b-jet scale 0.7 0.7

b-quark fragm 0.1 0.1

ISR 0.1 0.1

FSR 1.9 0.5

Comb bkg 0.4 0.1

Total 2.3 0.9

Challenge:

determine the mass of the top around 1 GeV accuracy in one year of LHC

P 18 Alternative mass determination

Select high PT back-to-back top events: Hemisphere separation

(bckgnd reduction, much less combinatorial) Higher probability for jet overlapping

Use the events where both W’s decay leptonically (Br~5%) Much cleaner environment Less information available from two ’s

Use events where both W’s decay hadronically (Br~45%) Difficult ‘jet’ environment Select PT>200 GeV

Mtop

Various methods all have different systematics

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Use exclusive b-decays with high mass products (J/) Higher correlation with Mtop Clean reconstruction (background free) BR(ttqqb+J/) 5 10-5 ~ 30% 103 ev./100 fb-1

(need high lumi)

Mtop from J/

Different systematics (almost no sensitivity to FSR)

Uncertainty on the b-quark fragmentation function becomes the dominant error

M(J/+l) Mtop

M(J/+l)

MlJ/

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Commissioning the detectors Determination MTop in initial

phase Use ‘Golden plated’ lepton+jet

Selection: Isolated lepton with PT>20 GeV Exactly 4 jets (R=0.4) with

PT>40 GeV Reconstruction:

Select 3 jets with maximal resulting PT

Signal can be improved by kinematic constrained fit Assuming MW1

=MW2 and MT1

=MT2

PeriodStat Mtop (GeV)

Stat /

1 year 0.1 0.2%

1 month 0.2 0.4%

1 week 0.4 2.5%No background

included

Calibrating detector in comissioning phase

Assume pessimistic scenario:

-) No b-tagging

-) No jet calibration

-) But: Good lepton identification

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Commissioning the detectors

Signal plus background at initial phase of LHC

Most important background for top: W+4 jets Leptonic decay of W, with 4 extra ‘light’ jets

Alpgen, Monte Carlo has ‘hard’ matrix element for 4 extra jets(not available in Pythia/Herwig)

ALPGEN:

W+4 extra light jets

Jet: PT>10, ||<2.5, R>0.4

No lepton cuts

Effective : ~2400 pb

With extreme simple selection and reconstruction the top-peak should be visible at LHC

L = 150 pb-1

(2/3 days low lumi)

measure top mass (to 5-7 GeV) give feedback on detector performance

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Single top production

Direct determination of the tWb vertex (=Vtb)

Discriminants:- Jet multiplicity (higher for Wt)

- More than one b-jet (increase W* signal over W- gluon fusion)- 2-jets mass distribution (mjj ~ mW for the Wt signal only)

Three production mechanisms:

Main Background [xBR(W→ℓ), ℓ=e,μ]: tt σ=833 pb [ 246 pb] Wbb σ=300 pb [ 66.7 pb] Wjj σ=18·103 pb [4·103 pb]

Wg fusion: 245±27 pbS.Willenbrock et al., Phys.Rev.D56, 5919

Wt: 62.2 pbA.Belyaev, E.Boos, Phys.Rev.D63, 034012-3. 7

+16.6 W* 10.2±0.7 pbM.Smith et al., Phys.Rev.D54, 6696

Wg [54.2 pb]

Wt [17.8 pb]

W* [2.2 pb]

1) Determination of Vtb

2) Independent mass measurement

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Signal unambiguous, after 30 fb-1:

Complementary methods to extract Vtb

With 30 fb-1 of data, Vtb can be determined to %-level or better(experimentally)

Single top results

Detector performance critical to observe signal Fake lepton rate b and fake rate id Reconstruction and vetoing of

low energy jets Identification of forward jets

Each of the processes have different systematic errors for Vtb and are sensitive to different new physics heavy W’ increase in the

s-channel W* FCNC gu t increase in the

W-gluon fusion channel

ProcessVtb

(stat)Vtb

(theory)

Wg fusion 0.4% 6%

Wt 1.4% 6%

W* 2.7% 5%

Process Signal Bckgnd S/B

Wg fusion 27k 8.5k 3.1

Wt 6.8k 30k 0.22

W* 1.1k 2.4k 0.46

P 24 Drell-Yan production at the LHC

Goals:• Measure pdf• Determine parton lumi• Measure sin2W

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From AFB in p-pZ, l+ l-

at the Z pole, AFB comes from interference

of the V and A components of the couplings

[hep/ph9707301]

At pp collider, forward direction not naturally defined BUT

- Always from sea softer: direction given by the sign of y(ll)

- Asymmetry increase with y(ll)

sin2leff measurement

q

AFB = b { a - sin2θefflept( MZ

2 ) }

a and b calculated to NLO in QED and QCD.

• sin2θefflept is one of the fundamental parameters of the SM!

• precise determination will constrain the Higgs mass and check consistency of the SM.

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• Main sys. effect: uncertainty on pdf, lepton acceptance (~0.1%), radiative correction

To reach World Average precision, need to use full calorimeter coverage (e channel only) - Z + - ||<2.

- Z e+ e- ||<2.5 jet rejection factor 1000

- Z e+ e- 2.5<||<5 jet rejection factor 10 - 100

σ ( Z → l +l - ) ~ 1.5 nb (for either e or μ)

y cuts – e+e- ( | y(Z) | > 1 )

∆AFB ∆sin2θefflept

| y( l1,2 ) | < 2.5 3.03 x 10-4 4.0 x 10-4

| y( l1 ) | < 2.5; | y( l2 ) | < 4.9

2.29 x 10-4 1.41 x 10-4

L = 100 fb-1

( statistical ) ( statistical )

Can be further improved: combine channels/experiments.

[%]

sin2leff measurement

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Conclusions:

LHC will allow precision measurements: unexplored kinematic regions, high-statistics (W, Z, b, t factory);

MW can be measured with a precision of 15 MeV (combinig e/μ and ATLAS

+ CMS);

Mtop: ~ 1 GeV (combined with ∆mW~15 MeV, constrains MH to ~ 25%);

EW single top production: direct measurement of Vtb; measurement of top

polarization (Wg with statistical precision of ~ 1.6%);

sin2θefflept( MZ

2 ) can be determined with statistical precision of 1.4x10-4

(competitive to lepton collider measurements!)

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 lepton E,p scale

goal ~0.02% mandatory for MW

• knowledge of ID material to 1%• precise alignment (<1m)• precise magnetic fields maps (<0.1%)• differents sub-detectors concerned

  jet energy scale (light jets / b jets)

goal ~1% mandatory for Mtop

coverage ||<2.5 ||<5 e, , jets

ATLAS & CMS: crucial parameters

ATLAS

CMS

Stan Bentvelsen Moriond-QCD 2004 29

Backup

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MW & Mtop measurement -

2 fb-1 of RunII(per experiment)

10 fb-1 of LHC(per experiment)

From D. Glenzinski (CDF), ICHEP2002

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tt Cross Section at 14TeV

total Td dp

NNLO: uncertainty from scale (mt/2, 2mt) < 3% !!!

(N.Kidonakis, hep-ph/0401147)

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Consequences from Mtop

Assuming total uncertainty on W-mass of 15 MeV Combined LHC prospect Very challenging measurement!

Repeat the Electro-Weak fit changing the uncertainties: Mtop=1 GeV MW =15 MeV Same central values

SM constraints on MHiggs:

Summer 2003 values:Chances to rule out SM!58

3791 Hm ((mmHH/m/mH H 53%)53%)

221863 Hm ((mmHH/m/mH H 32%)32%)

Thanks to M.Grunewald

direct

EXCLU

DED

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High Pt sample

The high pT selected sample deserves independent analysis: Hemisphere separation (bckgnd reduction, much less combinatorial) Higher probability for jet overlapping

Use all clusters in a large cone R=[0.8-1.2] around the reconstructed top- direction Less prone to QCD, FSR,

calibration UE can be subtracted

j1

j2

b-jet

t

Statistics seems OK and syst. under control

R

Mtop Mtop

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Top mass from hadronic decay

Use events where both W’s decay hadronically (Br~45%) Difficult ‘jet’ environment

(QCD, Pt>100) ~ 1.73 mb (signal) ~ 370 pb

Perform kinematic fit on whole event b-jet to W assignment for combination

that minimize top mass difference Increase S/B:

Require pT(tops)>200 GeV

Source of uncertainty

Hadronic Mtop

(GeV)

Statistics 0.2

Light jet scale 0.8

b-jet scale 0.7

b-quark fragm 0.3

ISR 0.4

FSR 2.8

Total 3.0

3300 events selected:

(tt) = 0.63 %

(QCD)= 2·10-5 %

S/B = 18

Selection

6 jets (R=0.4), Pt>40 GeV

2 b-tagged jets

Note: Event shape variables like HT, A, S, C, etc not effective at LHC (contrast to Tevatron)

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Alternative methods

Continuous jet algorithm Reduce dependence on MC Reduce jet scale uncertainty

Repeat analysis for many cone sizes R

Sum all determined top mass:robust estimator top-mass

Determining Mtop from (tt)? huge statistics, totally different systematics

But: Theory uncertainty on the pdfs kills the idea 10% th. uncertainty mt 4 GeV Constraining the pdf would be very precious… (up to a few % might not be a dream !!!)

Luminosity uncertainty then plays the game (5%?)

Luminosity uncertainty then plays the game (5%?)

P 36Triple gauge boson couplings

• TGC of the type WWγ or WWZ provides a direct test of the non-Abelian structure of the SM (EW symmetry breaking).

• This sector of the SM is often described by 5 params: g1

Z, κγ, κZ, λγ and λγ

(SM values are equal to g1Z =

κγ = κZ = 1 and λγ = λγ = 0,

tree level).

• Anomalous contribution to TGC is enhanced at high √s (increase of production cross-section).

• It may also indicate hints of new physics: new processes are expected to give anomalous contributions to the TGC.

• New physics could show up as deviations of these parameters from their SM values.

W TGC vertex

W γ/Z

L = 30 fb-1 L = 30 fb-1

∆g1Z = 0.05

λ1 = 0.01

▓ SM▓ SM

Parameters Statistical (95% C.L.)

Systematic (95% C.L.)

∆g1Z - 0.0064

+ 0.010±0.0058

∆κZ- 0.10+ 0.12

±0.024

λZ- 0.0065+ 0.0066

- 0.0032+ 0.0031

∆κγ- 0.073+ 0.076

- 0.015+ 0.0076

λγ ±0.0033 ±0.0012

Systematic uncertainties:

• At the LHC, sensitivity to TGC is a combination of the very high energy and high luminosity.

• Uncertainties arising from low pT background will be quite small: anomalous TGC signature will be found at high pT.• Theoretical uncertainties: p.d.f.’s & higher order corrections

L = 30 fb-1

• Variables:

Wγ: (mWγ , |ηγ*| ) and (pTγ,

θ* )WZ: (mWZ , |ηZ*| ) and (pTZ,

θ* )

sensitive to high-energy behaviour: mWV, pT

V

sensitive to angular information: |ηV*|, θ*

• SM: vanishing helicity at low |η|Non-standard TGC: partially eliminates `zero radiation’

Using max-Likelihood fit to mWV |ηV*|