tests of the standard model at the tevatron

Mark Adams Mark Adams UICUIC Trends in HEP Yalta Crimea Conference Sept. 2006Trends in HEP Yalta Crimea Conference Sept. 2006

Tests of the Standard Tests of the Standard Model at the TevatronModel at the Tevatron

Mark AdamsMark Adams

University of Illinois at ChicagoUniversity of Illinois at Chicago

Representing the D0 and CDF Representing the D0 and CDF CollaborationsCollaborations

Trends in HEP Yalta Crimea Conference

Mark AdamsMark Adams UICUIC Trends in HEP Yalta Crimea Conference Sept. 2006Trends in HEP Yalta Crimea Conference Sept. 2006

Tevatron Tests of the Standard ModelTevatron Tests of the Standard Model

Standard ModelStandard ModelElectroweak Electroweak

Measurements Measurements W, Z W, Z DibosonDiboson

Top Top selection, methodsselection, methodsPropertiesPropertiescross section cross section single topsingle top

Higgs searchHiggs search

Focus on top,W,Z and the missing

Properties depend on each other through higher order corrections

Higgs


Tevatron LuminosityTevatron Luminosity

Run I Lumi 1000 pb-

1period

Mar. 2001 – July 2006

4-8 fb-1 expected by end of 2009

1 fb-1

Typical data samples in Typical data samples in this talk this talk

~350, ~950 pb~350, ~950 pb-1-1

2 fb2 fb-1 -1 soonsoon

4-8 fb4-8 fb-1 -1 by 2009by 2009

Important analysis tools Important analysis tools

Lepton triggering and IDLepton triggering and ID

b-taggingb-tagging

jet resolutionjet resolution

MET (e.g. calibrated with MET (e.g. calibrated with dijet data)dijet data)


Bosons and DibosonsBosons and DibosonsEfficient lepton triggers and selectionEfficient lepton triggers and selection

Electron, muon, MET calibrations keyElectron, muon, MET calibrations key

e+,+

Backgrounds Backgrounds QCD and DY QCD and DY very smallvery small

Must model Must model data & data & calibrate calibrate energy scale energy scale to obtain to obtain widthswidths

Extract W mass Extract W mass from edge of from edge of distributiondistribution

W(e)Z(ee)

Z peak from LEP


W massW massExtract W mass from fit of Jacobian Extract W mass from fit of Jacobian

edge edge mmTT

2 2 = 2p= 2pTTllppTT

(1-cos(1-cos))Radiative Corrections – introduce Radiative Corrections – introduce

weak dependence on mweak dependence on mtt, M, MHH, m, mXX

Systematic errors is the whole Systematic errors is the whole gamegame

RII will eventually improve resultsRII will eventually improve resultsLEP 80.392+-0.039 GeVLEP 80.392+-0.039 GeVTev R1 80.452+-0.059 GeVTev R1 80.452+-0.059 GeV

W W

t

bW W

W

HW W

X

X

mW ~

mt2

mW ~ ln(mH) ew Physics

edge


W WidthW Width

R= R=

Extract Extract WW assuming SM ( assuming SM ( and and W-lW-l),LEP for Z BR),LEP for Z BR

R=10.84+-0.15 +-0.14R=10.84+-0.15 +-0.14

WW=2.092+-0.042 CDF=2.092+-0.042 CDF

D0D0R=10.82+-0.16 +-R=10.82+-0.16 +-

0.25+0.13(pdf)0.25+0.13(pdf)

W *BR(W-l)

Z *BR(Z-ll)


Inclusive W, Z Cross SectionsInclusive W, Z Cross Sections

Systematic errors 2%Luminosity 6%NNLO theory 2-3%

Central lepton triggersLepton ID and trigger efficiency criticalSmall backgrounds (QCD, DY) subtracted

70-350 pb-1 samplesNNLO Hamberg, van Neervan, Matsura 191; Anastasiou, 2004

W Z


Diboson ProductionDiboson Production

Sensitive to SM trilinear Sensitive to SM trilinear vector boson coupling – vector boson coupling – depends on qdepends on q22

Cross section and Cross section and kinematics also kinematics also sensitive to anomalous sensitive to anomalous couplingscouplings

trilinear boson vertex

procesprocesss

Cross Cross

SectionSection

(WW)(WW) 12.4 pb12.4 pb

(WZ) (WZ) 3.7 pb3.7 pb

(ZZ)(ZZ) 1.4 pb1.4 pb

WWWW llll

WW+WZWW+WZ lljjjj

WZWZ llllll

ZZ not ready yetZZ not ready yet


Inclusive WZ SM Production D0Inclusive WZ SM Production D0

WZ Candidate Mass versus Missing ET

three leptons plus MET


WZ to lWZ to lll Evidence from D0 ll Evidence from D0

12 trilepton events observed in 760-860 pb-1

Expect 7.5 1.2 signal and 3.6 0.2 background

3.3 effect

(WZ) = 3.98 pb

NLO prediction is 3.7 pb

+1.91-1.53


W, Z and Diboson cross W, Z and Diboson cross sectionssections

Triple Vertex Coupling has been measured

Cross sections for W,Z, W, Z and WW(ll) and WZ(lll) are found to agree with SM

ZZ is next challenge


Top – what do we know?Top – what do we know?

Last of particle of 3 families structureMassiveCharge +2/3t -> WbSpinShort lifetime

m/m <2% (combined)-4/3 excluded at 95%C.L.

(D0)

ct<52.5m at 95%C.L.(CDF)

~100%

Not directly


Top event selectionTop event selection

Decay modes Decay modes define topologies:define topologies:

dileptondilepton

lepton+jetlepton+jet

all hadronicall hadronic


Top Mass – Combined TevatronTop Mass – Combined Tevatron

Mass lower than Mass lower than previous years previous years (shift from 175)(shift from 175)

Dominated by l+j Dominated by l+j weights CDF 62% and weights CDF 62% and D0 19% (different D0 19% (different lumi)lumi)

RunII in-situ RunII in-situ JESJES from W-qq’ in l+jfrom W-qq’ in l+j


Top Mass CDF and D0 Top Mass CDF and D0 All channels shownAll channels shownNew promise - CDF New promise - CDF

average b decay average b decay length independent of length independent of JESJES

Some possible channel Some possible channel dependence –watch in dependence –watch in futurefuture

ChannelChannel Mass (GeV)Mass (GeV)

dileptondilepton 167 167 4.3 4.3

l+jl+j 171.3 171.3 2.2 2.2

All jetAll jet 173.4 173.4 4.3 4.3


Top Lifetime MeasurementTop Lifetime MeasurementTop quark decays before Top quark decays before

hadronizinghadronizing

CDF measures lifetime CDF measures lifetime upper limit in e and upper limit in e and channels. channels.

Compare track impact Compare track impact param from Z decays to param from Z decays to top events to extract ctop events to extract c

c<52.5mm at 95%C.L.

Modeled Observed in Z Observed in top


Top quark lifetime limitTop quark lifetime limit

ttbar events selection: ttbar events selection: electron/muon, >= 3 electron/muon, >= 3 jets containing a jets containing a secondary vertex secondary vertex tagged jet; large tagged jet; large missing energy. missing energy.

Search for long-lived Search for long-lived toptop

Electron/muon tracks Electron/muon tracks from Z determine the from Z determine the detector resolution, : detector resolution, :

cτcτ < 52.5 μm @ 95% < 52.5 μm @ 95% CLCL


Top Quark ChargeTop Quark Charge

Can’t measure charge directly Can’t measure charge directly but can rule out exotic.but can rule out exotic.

Selection: 2 isolated leptons, Selection: 2 isolated leptons, large MET, >3 jets, large MET, >3 jets,

2 b-tagged jets2 b-tagged jets

Measure charge of top under Measure charge of top under two charge assumptionstwo charge assumptions: : +2e/3+2e/3 and and -4e/3-4e/3

4e/3 charge 4e/3 charge excluded to 94% excluded to 94% C.L.C.L.

Pt-weighted charge of lepton and b-jet


tt Resonances CDFtt Resonances CDFCan ttbar come from a resonance? Stringent limits.


W-Boson Helicity W-Boson Helicity Fractions in Top-Quark Fractions in Top-Quark DecaysDecaysUse fully reconstructed top events. Top decays before hadronizing – decays keep helicity infocos* uses angle between top and lepton in the W rest framefraction of longitudinally (f0) and right-handed (f+) polarized fraction of longitudinally (f0) and right-handed (f+) polarized

W bosons W bosons f0= 0.61 ± 0.12 ± 0.06 with f+ fixed to zero,f0= 0.61 ± 0.12 ± 0.06 with f+ fixed to zero,f+= -0.06 ± 0.06 ± 0.03f+= -0.06 ± 0.06 ± 0.03 with f0 fixed to the SM expectation of with f0 fixed to the SM expectation of

0.70. 0.70. f+ < 0.11 at 95% CLf+ < 0.11 at 95% CL

D0 f+= 0.00 ± 0.13 ± 0.07D0 f+= 0.00 ± 0.13 ± 0.07D0 determines f+ < 0.25 at 95% CLD0 determines f+ < 0.25 at 95% CLCDF 955pbCDF 955pb--

11

Right Handed W excluded at 10% level

http://www-cdf.fnal.gov/physics/new/top/2006/tprop/whelicity_cts/blessed_695/fits_all.eps

http://www-cdf.fnal.gov/physics/new/top/2006/tprop/whelicity_cts/blessed_695/cts_data_fr_fit.eps


Single Top Production via Weak Single Top Production via Weak InteractionInteraction

Test of SM – does single top production exist?Test of SM – does single top production exist?o Cross Section proportional to |VCross Section proportional to |Vtbtb||2

o Test of CKM matrix unitarity: VTest of CKM matrix unitarity: Vutut2+V+Vctct

2+V+Vbtbt2

=1 =1 Sensitive to 4th generationSame channel as WH - Wbb

s-channel 0.88 pbt-channel 1.98 pb


Single Top selection - D0Single Top selection - D0

D0 analysis (370pbD0 analysis (370pb-1-1))

CDF analysis (695pbCDF analysis (695pb-1-1) described by N. Giokaris) described by N. Giokaris

Isolated lepton (e or )pT> 15 GeV; |e|<1.1 or ||< 2.0

Missing ET> 15 GeV

Between 2-4 jets ET>15GeV; ||<3.4

1 jet E> 25 GeV1 or more b-tags

t-channelt-channel 15.015.0

s-channels-channel 9.59.5

expected expected backgrounbackgroundd

452452

datadata 443443

1 b-tag1 b-tag

>1 b-tag>1 b-tag367367

7676


Sample of discriminant inputsSample of discriminant inputs

Discriminants built to Discriminants built to distinguish s or t channel from distinguish s or t channel from

backgrounds tt and W+jbackgrounds tt and W+j

Ql*leading-jet


Likelihood Discriminant Results Likelihood Discriminant Results

(t) < 4.4pb(t) < 4.4pb(s) < 5.0pb (s) < 5.0pb

Data sets – separate electron/muon and 1 b-tag/ >1 b-tag (4 sets)With 4 signal-background pairs:, s-channel/W+jets, s-channel/ttbar, t-channel/W+jets and t-channel/ttbar)16 LD – combined fit to 4 2D distributionse.g. Likelihood Discriminants for s-channel/t-channel vs ttb/ W+jets

Approaching SM predictionsApproaching SM predictionsUpdated results expected soon from Updated results expected soon from

both experimentsboth experiments


SM Higgs Production and SM Higgs Production and DecaysDecays

Dominant Decaysbb for MH < 135 GeVWW* for MH > 135 GeV

Search strategy: MH <135 GeV: associated production WH and ZH with Hbb decay Backgrounds: Wbb, Zbb, top, WZ,QCD + leptonic WWW* & WW*

MH >135 GeV: gg H production with decay to WW*

Backgrounds: WW, DY, W/ZZ, tt, tW, + leptonic with WWW*

Production

mH (GeV/c2)

Decays

pb


LEP EWWG fit LEP EWWG fit Constraints on the Constraints on the

Higgs massHiggs mass

LEP1 and SLD indirect LEP1 and SLD indirect measurements measurements

LEP2 and Tevatron LEP2 and Tevatron

114 GeV limit;114 GeV limit; m mWW; m; mtoptop

Light Higgs PreferredLight Higgs Preferred

85 GeV 85 GeV

upper limit of 166 GeVupper limit of 166 GeV

+39-28


SM HiggsSM Higgs

Standard Model Standard Model Simplest Higgs mechanism Simplest Higgs mechanism possible (doublet field -> 1 possible (doublet field -> 1 physical Higgs particle)physical Higgs particle)

Higgs is a singleHiggs is a single neutral neutral scalar particlescalar particle

Interacts with all SM Interacts with all SM particles but couples more particles but couples more strongly with more strongly with more massive particlesmassive particles

SM tested precisely but mass of Higgs unknown. Mass is related to other measureables via loops

LEP Direct limit: MH > 114 GeV at 95%New CDF/D0 top mass (171.4 2.1 GeV) New LEP W mass (80.392 0.029 GeV)

• MH = 85 +39 -28 GeV• MH < 166 GeV at 95 % CL

Low mass Higgs is preferred

LEP EWWG

http://www-cdf.fnal.gov/physics/new/top/summaryplots/s06_mt_mw_contours.gif


SM Heavy Higgs: SM Heavy Higgs: H H WW* WW* l lll

2 high Pt leptons and missing Et

spin 0 Higgs – WW - leptons prefers same directionNo Higgs mass peak!CDF and DØ published on 0.3-0.4 fb-1

4th generation?

CDF

H


WW production

W + jet/ production:

H WW* llD0 Update

Major backgrounds

Updated DØ analysis: L ~ 950 pb-1 in H WW* ee and e L ~ 930 pb-1 in H WW*

Selection Strategy:• Presection: lepton ID, trigger, opposite charge leptons• Remove QCD and Zl+l-: ET > 20 GeV

• Higgs Mass Dependent Cuts: Invariant Mass (Ml+l-); Min. Transverse Mass Sum of lepton pT

l and ET (pT

l + ET)

• Anti tt(bar) cut: HT = PTjet < 100 GeV

• Spin correlation in WW pair: (l,l) < 2.0


SM only a factor 4 away

We exclude 4th generation models, for which mH=150-185

GeV

Results for HWW*

Expected/Observed # of events for mH = 160 GeV (L ~ 950 pb-1):

If mH= 160 GeV, ~ 2 higgs in our sample!

WW slides G. Benardi


WHWWW* (360-380 pb-1)2 like-sign leptons (one from H and one from W)Important in intermediate mass region 125-145 GeVBackgrounds: WW, WZ, sign flips and QCD fake leptons

Events after preselection


Final Selection for WWW*Topological Likelihood discriminant, built on 3 variables per channel


Exclusion limit for WWW*Events after Topological Likelihood discriminant

Effect on global combination significant in the intermediate region (125-145 GeV)


CDF and D0 may reach exclusion for a 115 GeV Higgs with 3 fb-1 of data!

Combined Higgs boson Search at DØ

With high statistics (1 fb-1)Data/SM = ~ 5 at 160 GeV

Low statistics (0.3 fb-1)cross-section factors Data/SM: ~ 15 at 115 GeV~ 9 at 160 GeV

WH -WWW

ZH -bbZH -llbb


Combined Tevatron SM Combined Tevatron SM HiggsHiggs

mH Limit/SM(GeV)

Observed

115 10.4

130 10.6

160 3.9

180 5.8

Quickly approaching sensitivity required to exclude the Higgs at the Tevatron


Expected Improvements at DØ and CDF

D0New b-tagging tool based on Neural Net - improves

efficiency 33% at 0.5% fake rateJet Energy Resolution (recalibration+track jet

algorithm: add momentum from out of cone trks) 20% improvement

Calibrate b jet with ZbbDØ Upgrade

L1Cal Trigger - Efficiency improvement for (ZHnnbb, hbb)

L0 silicon tracking improves b-tagCDFIncrease acceptance forward: muons and improved tracking and b-tagging Add additional channels:

in the WH and WW analyses tau-leptons have not been used. Improve jet resolution

Neural Networks, better optimization


Tevatron SM Higgs SearchTevatron SM Higgs SearchProspects updated in 2003 in the low Higgs

mass regionW(Z) H l(,ll) bb optimization of analysisSensitivity in the mass region above LEP limit

(114 GeV ) begins at ~2 fb-

1

With 8 fb-1 exclusion 115-135 GeV & 145-180 GeV,

3-sigma discovery/evidence at 115

– 130 GeV

Tevatron8 fb-1

LEP

Exclu

ded

Ldt (fb-1)

Using knowledge from recent data (use D0 300 pb-1; add improvements at both experiments) extrapolate exclusion limit:

At 115 GeV need ~3 fb-1

At 160 GeV need ~5 fb-1

95% CL exclusion for mH= 115-185 GeV with 8 fb-1


ConclusionsConclusionsStandard Model is being tests at the percent levelStandard Model is being tests at the percent level

W, Z and diboson cross sections match SMW, Z and diboson cross sections match SMTop quark Top quark

Properties, mass, cross sections as expectedProperties, mass, cross sections as expectedSingle Top sensitivity reaching observational Single Top sensitivity reaching observational levellevel

BBs s oscillations observedoscillations observedSM Higgs – Combining channels and experiments SM Higgs – Combining channels and experiments

demonstrates exclusion possible up to 185 GeV demonstrates exclusion possible up to 185 GeV mass by 2009.mass by 2009.


Backup SlidesBackup Slides


Preselection: Trigger, ID, leptons of opposite charge: pTl1 = 15 GeV; pT

l2 = 10 GeV

e e e ee e

Missing Transverse Energy > 20 GeV Cut (to suppress Z/Missing Transverse Energy > 20 GeV Cut (to suppress Z/* * l l++ll-- background) background)

e ee e e e

H WW* ee / e/ (950-930 pb-1)


HHWW* : final selectionWW* : final selection

MH=160GeV (x10)

Final selections

e ee

lepton-lepton

tests of the standard model at the tevatron

Documents

z decays

widthsextract w mass

lepw massextract w mass

z dibosontop selection

jtop mass cdf

brzllinclusive w

lumi1000 pb

cdf collaborationstrends