electroweak physics at the tevatron aidan robson university of glasgow for the cdf and d0...

Electroweak Physics at the Tevatron

Aidan RobsonUniversity of Glasgow

for the CDF and D0 CollaborationsAspen, 13 February 2011

CDF Zee

(from Stirling, ICHEP04)

2004, using < 100 pb–1

2Electroweak Physics at the Tevatron

3

Jets

W/Z

HiggsSusy

quarktop

bottomquark

dibosons


4

Zg WZ ZZ WW/WZ -> lnjj

Motivation

High-statistics precision measurements

Diboson physics

Outlook


pT(Z) x3 G(W)

5

Tevatron

h = 1.0

h = 0.6

h = 2.0muonchambers

D0

h=2

h=3

0 1 2 3 m

2

1

0

tracker had cal

hadronic calEM cal had

calsolenoid

pre-radiator shower max

silicon

EM cal

h=1

CDF

Fibre tracker to |h|<1.8Calorimeter to |h|<4Muon system to |h|<2

Drift chamber to |h|<1Further tracking from SiCalorimeter to |h|<3Muon system to |h|<1.5


Electrons: good EM shower shape small hadronic energy isolated in calorimeter well-matching good track (except far forward)

Muons: MIP in calorimeter isolated hits in muon chamber well-matching good track

Z selection: 2 oppositely-charged electrons or muons invariant mass consistent with mZ

W selection: exactly one electron or muon energy imbalance in reconstructed event, associated with neutrino

6Electroweak Physics at the Tevatron

W and Z selection

7

pT(Z) ppT

pZantiproton proton

y1/2 ln E+pz

E–pz

CDF

[~angular variable]

pT(Z)300

d/d

p T

pT(Z)300

d/d

p T

pT(Z)300

d/d

p T0<|y|<1 1<|y|<2 2<|y|<3 distribution different for different y?

pT(Z)pT(Z)

pQCD reliable

resummation / parton shower with non-perturbative model

resummationrequired

multiple soft gluon radiation

300

Z Z

2

Z

2

Z

Z/g*

q

q

l+

l–

Electroweak Physics at the Tevatron 8

Earlier pT(Z)

PRL 100 102002 (2008)

Electron channel:

Compare 4 models: Resbos with default parameters Resbos with additional NLO–NNLO K-factor NNLO (Melnikov and Petriello) NNLO rescaled at to data at 30GeV/c

RESBOS event generator implements NLO QCD and CSS resummation


pT(Z)New measurement in muon channelPresented at the level of particles entering the detectorto avoid model-dependent corrections

However for comparison with previous measurement, correct to 4p and for mass window:

Phys. Lett. B 693 522

10

pT(Z)


At particle level:

Phys. Lett. B 693 522

f*h

11

aT : component of pT(ll) transverse to dilepton thrust axis.Less susceptible than pT(ll) to detector effects

Best variable:

€

φη* = tan(φacop /2)sin(θη

* ) – highly correlated with aT/mll

( measures scattering angle of leptons wrt beam, in rest frame of dilepton system)

€

θη*



f*h

eee

mm

arXiv:1010.0262


f*h

arXiv:1010.0262


Drell-Yan angular coefficients

LO term : determine Afb

LO term

cos2θ : higher order term

(θ, φ) terms

very small terms

Rest frame of dilepton system

Integrate over all cosθ ,

=0 =0

Integrate over all φ ,



A2=A0 at LO‘Lam-Tung’ relationTrue only for spin-1 gluons,strongly broken for scalar gluons



A4 sensitive to Weinberg angle

A4 using 2.1 fb-1 data = 0.1098 ± 0.0079

Translated to sin2θW in FEWZ : sin2θW = 0.2331±0.0008

Translated sin2θW in POWHEG : sin2θW = 0.2328±0.0008

CDF Run II Preliminary


W charge asymmetry

Al() = A(yW) (V–A) ~

d s (l+)/d – ds (l–)/d d(x)

ds (l+)/d + ds (l–)/d u(x)

AW(y) d s (W+)/dy – ds (W–)/dy

d s (W+)/dy + ds (W–)/dy

Run 1 measurement resulted in d quark increased by 30% at Q2=(20GeV)2

W±

p p

nl±

duu

uud


W charge asymmetry

19

mW

mW:D0: mW = 80402 ± 43 MeV/c2

CDF: mW = 80413 ± 48 MeV/c2

Tev: mW = 80420 ± 31 MeV/c2 (includes Run 1)

LEP: mW = 80376 ± 33 MeV/c2Heading to CDF 25MeV/c2 measurement

CDF DmZ (stat)

published (200/pb) 43 MeV

expected (2.3/fb) 13 MeV


20

GW

Tev error improves from 62 to 49 MeVElectroweak Physics at the Tevatron

GW predicted in Standard Model: GW

SM = 2091±2 MeV (PDG)


Dibosons

q

q’

W/Z/gW/Z

W/Z/g

Wg Zg WW tt WZ t ZZ H→ WW

22

Zg

photon ET (GeV)

even

ts

Zg

Z

g

non-SM

h 3, Z

Zg

|h3| < 0.037, |h4| < 0.0017 @95%CL (L=1.2TeV)

h3, Zgg

SM

non-SM

Z

g

Using (Z→ll)+gand (Z→ )nn +g

WZq

q’

W

Z/g

W

σ(pp → WZ) = (4.1 ± 0.7) pb

σ(pp → WZ) / σ(pp → Z) = (5.5 ± 0.9) x 10-4

23


WZ

arXiv:1006.0671

σ(pp → WZ) = (3.9 (stat+sys) ± 0.31 (lumi)) pb +1.01

–0.85


WZ

arXiv:1006.0671

€

−0.075 < λ Z < 0.093

−0.027 < Δκ Z < 0.080

for L=2TeV

26

ZZ seen in 4 lepton at 5.7σAll now observed!

ZZ4l

Wg Zg WW tt WZ t ZZ H→ WW

Z

Z

q

q’

σ(pp → ZZ ) = (1.7 +1.2

-0.7 (stat) ± 0.2 (syst)) pb

σ(pp → ZZ) / σ(pp → Z) = (2.3+1.5

-0.9 (stat) ± 0.3 (syst)) x 10-4


ZZllnn


WW/WZ lnjj

Similar final state to low-mass Higgs:

MuonsElectrons


WW/WZ lnjj

5.4

σ(WW+WZ ) = (18.1 ± 3.3(stat) ± 2.5(sys) )pb

5.2s significance


WW/WZ lnjjUse matrixelementtechniques

5.4

σ(WW+WZ ) = (16.5 +3.3

-3.0) pb

5.4s significance

31

Tevatron outlookEnd : Sep 2011(?)

Inte

grat

ed lu

min

osity

(pb–1

)

On tape: ~ 8.5 fb-1 per experimentResults shown today : 1-7 fb-1

now2002Electroweak Physics at the Tevatron

32

Outlook

♦ Completing strong electroweak physics programme

♦ Focusing on high-statistics Tevatron legacy measurements and diboson physics underpinning symmetry-breaking searches



WW/WZ lnjj

differences q.g jets

36

W+

W–

Z/gW+

W–

W+

W–

W+

W–

Z/g

W+

W–

W+

W–

W+

W–

W+

W–

W+

W–

W+

W–

HH

required to cancel high-energy behaviour

WW scattering


W/Z primitive objects

for non-collider physicists

38

H

g

gp

p


Higgs Physics at the Tevatron 39

PDFs

Tevatrony = 2 0 2

LHC

H

g

gp

p

spp→H = sgg→H fg/p(x1,Q=MH) fg/p(x2,Q=MH) + …

Higgs Physics at the Tevatron 40/54

Matrix element method Use LO matrix element (MCFM) to compute event probability

HWWlnlnWWlnlnZZllnnW+partonln+jetWgln+g

ET modellepton energy resn

px

py

pz

lep1

LO |M|2 :px

py

pz

lep2

Ex , Eyparton lepton fake rateg conversion rate

xobs:

(with true values y)

Compute likelihood ratio discriminator

R =Ps

Ps + SkbiPb

i

i

kb is relative fraction of expected background contrib.Ps computed for each mH

Fit templates (separately for high S/B and low S/B dilepton types)

Higgs Physics at the Tevatron 41/54

Neural network method

NNscore

0 1

var1

var2var n

Background Higgs

¨ Various versions. Current:¨ Apply preselection (eg ET to remove Drell-Yan)¨ Train on {all backgrounds / WW} against Higgs mH=110,120…160…200 { possibly separate ee,em, }mm

x10

¨ Pass signal/all backgrounds through net¨ Form templates

NN

0 1

Pass templates and data to fitter

ET

SET

mll

Elep1

Elep2

ETsigData

HWWWW

DYWgWZZZt t

fakes

ETjet1

DRleptons

Dfleptons

Df ET lep or jet

ETjet2

Njets

Most recent CDF“combined ME/NN” analysis also uses ME LRs as NN input variables

42

mtMatrix element-based top mass measurementLepton+jets with 4.8fb-1

NN for background discriminationLikelihood fit over variables sensitive to top massSimultaneous constraint of jet energy scale using W in lepton+jets

mt =172.8 ± 1.3total GeV(0.7stat 0.6JES 0.8sys)

More precise than CDF 2009!Expect 1GeV precision achievable

ET modellepton energy resn

px

py

pz

lep1

px

py

pz

jet1

Ex , Eyxobs:

(true values y)

etc.

Higgs Physics at the Tevatron


Single top

Single top observed 2009.

u

W

l

g

b

b

bt

W

d

nu

W

l

b

b

t W

d

n

t-channels-channel

t-ch

anne

l cro

ss s

ectio

n [p

b]

s-channel cross section [pb]


Limit settingbackgroundsuppression

signalseparation

Background

Higgs signal x 10

even

ts

XX = some observable

H1=SM+Higgs (of mass mH)H0=SM only

Construct test statistic Q = P(data|H1)/P(data|H0) –2lnQ = c2(data|H1) – c2(data|H0) , marginalized over nuisance params except s H

Find 95th percentile of resulting s H distribution – this is 95% CL upper limit.

When computed with collider data this is the “observed limit”

Repeat for pseudoexperiments drawn from expected distributions to build up expected outcomes

Median of expected outcomes is “expected limit”E

xpec

ted

outc

omes

95% CL Limit/SM

Median = expected limit

sH (pb)

95%

sH/sSM

95%

0 20 1 2

rescalePDF

45

Indirect constraintse+

e–

Z

H

Z b

bmH>114GeV mH<154GeV

estimated final precision


Tevatron projectionEnd : Sep 2011?

On tape: ~ 6 fb-1 per experimentResults shown today : 3-5 fb-1

Inte

grat

ed lu

min

osity

(fb–1

)

Aidan Robson Glasgow University 47/22

W charge asymmetry

unknown neutrino pZ is a smaller effect

for higher ET electrons

measurement divided into two ET regions

for given he, ET regions probe different yW and therefore different x

experimental challenges:alignment; charge misidentification

measurement relies on calorimeter-seeded silicon tracking

PRD 71 052002

First Run 2 charge asymmetry measurement: similar approach to Run 1

|he|

|he|


W charge asym. – new methodInstead: probe the W rapidity directly

MW constraint two kinematic solutions for pz of .nAmbiguity can be resolved statistically from knowncentre-of-mass * distribution for V-A decay®weight solutions according to (cos*, y, pT

W )d s /dy is an input; iterate to remove dependence.

Uncertainties: Charge mis-ID rate Energy scale and mismeasurement Background/trigger/electron ID

Relies on Si-only tracking

cos* cos*


W charge asym. – new method

Under improvement using better forward tracking and higher stats

W width Generator: LO MC matched with Resbos (QCD ISR) and Berends/Kleiss (QED FSR)

Fast simulation for templates: electron conversions + showering muon energy loss parametric model of recoil energy (QCD, underlying event + brem)

Tracking scale/resn

Calorimeter scale/resn

mmm (GeV)

mee (GeV)

Backgrounds

mT (GeV) mT (GeV)

D =G 21 MeV, 31 MeV

D =G 17 MeV, 26 MeV

D =G 32 MeV D =G 33 MeV

D =G 54 MeV (ele), 49 MeV (mu)

c2/dof=27.1/22

c2/dof=18/22

GW = 2032 ± 73 (stat+sys) MeV

(GWSM = 2091 ± 2 MeV)

PRL 100 071801 (2008)

€

R =σ ( pp → W )

σ ( pp → Z)⋅

Γ(Z)

Γ(Z → ll )⋅

Γ(W → l ν )

Γ(W )

Compare to CDF indirect measurement:

NNLO calc From LEP

SM value

GW (indirect) = 2092 ± 42 MeVJ Phys G 34 2457

World most precisesingle measurement

W width

electroweak physics at the tevatron aidan robson university of glasgow for the cdf and d0...

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