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Sensitivity to PDFs at the Tevatron.Sensitivity to PDFs at the Tevatron.

Mathieu AgelouCEA – Saclay

Low x workshop, Sinaia, Romania

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OutlineOutline

• The Tevatron and the detectors (CDF and DØ)

• Top results : – tt cross-section– Single top

• Z+jets events

• W charge asymmetry

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Acceleration complex of FermilabAcceleration complex of Fermilab

DØ

CDFTeVatron

GeVs 1960circumference 6km

Main Injector

Recycler

Accumulator

DebuncherLinac

Booster

proton

antiproton

• collider • Two experiments : DØ , CDF• Run II since mars 2001

pp

Main Injector & Recycler

TevatronBooster

p p

Chicago

CDF DØ

TeVs 96.1@

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DØ and CDF detectorsDØ and CDF detectors• Silicium tracker, || < 3 Fiber tracker, |tck| < 1.6• Solenoidal magnet 2 T• Calorimeter : U-LAr EM ~ 15%/E, HAD ~ 80%/E• Muons (scint. + drift chambers) || < 2 & toroidal magnet 1.8T

• Silicium tracker, || < 2, R < 30 cm Drift chambers |tck| < 1• Calorimeter : scint. tiles + Pb/Fe (EM/HAD) EM ~ 13.5%/E, HAD ~ 80%/E• Time-of-Flight• Solenoidal magnet 1.4 T• Muons : || < 1.5, 80% in

= 1= 0

z

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LuminosityLuminosity

4.1031 cm-2s-1

Jan

02

Jan

04

1032 cm-2s-1

Numerous runs above 1032cm-

2s-1

Analysis presented here : L up to 350 pb-1

Efficiency of data taking forthe 2 experiments > 85%

Integrated luminosity

Peak luminosity

Jun

05

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top quark production at the Tevatrontop quark production at the Tevatron

• 2 production processes :– Via the strong interaction– Via the electroweak interaction

• Strong interaction : pair production

85% annihilation 15% gluon fusion

qq

(reverse at LHC)

World only top sample : - measurement of its mass (Jiri’s talk) - studies of its properties :

- W helicity- Rare decays

Important to measure the cross-sectionin all channels : good cross-checks, different systematics.

TeVspbtt 96.1@77.6

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Pair productionPair production

dilepton channel : l = e , - small BR (~6%) - small backgrounds (WW, Z->) - 2 high PT leptons (>15 GeV)

- 2 jets (>20 GeV) - > 15 GeV

TE

semileptonic channel : l = e , - larger BR (~30%) - Backgrounds (W+jets, multijets) - 1 high PT leptons (>20 GeV)

- ≥ 3 jets (>15 GeV) - > 20 GeVTE

L = 318 p-1

L = 230 p-1

pbsyststattt )(9.0)(9.09.7

pblumisysttt )(6.0)(1.16.8 2.37.2

hep-ex/0504058

CDF

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Pair productionPair production• Hadronic channel :

– Large BR : ~45%– Huge multijet background– 6 jets (>15 GeV)

pblumisyststattt )(5.0)()(7.7 7.48.3

4.33.3

Nobs = 220Nbck = 186

Small sensitivityDifficult analysis

Good agreement withNLO predictions

CDF

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Single top productionSingle top production

• Electroweak interaction :– Top is produced singly in the final -> ’’single’’ top

¾t = 1:98pb

2 main processes at the TeVatron

• Theoritical cross section ~0.4 x cross section

• Very difficult to observe because of the smaller multiplicity than

tt

a 3rd mode exists but will be visible only at LHC :

• Window to new phenomena - New vector bosons- Anormalous couplings- RPV SUSY

• tests of standard model– Direct measurment of |Vtb|

– V-A coupling– top polarisation

¾s = 0:88pb

|Vtb||Vtb|

• Background to Higgssearches : same final state as WH

tt

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Probing pQCD with single topProbing pQCD with single top

• Recently, theorists (esp. Z.Sullivan) think the single top process as a tool to understand perturbative QCD.

• “single top is a new Drell-Yan and DIS process”

• s-channel : ISR and FSR color independent• t-channel : DDIS, 2 different scales

http://www.hep.vanderbilt.edu/~wjohns/fcp05/recent/Zack%20Sullivan-ZSFCP05.pdf

Drell-YanISR only

e+e- -> jetsFSR only

DISProton structure

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Single top searchSingle top search

2) Multivariate techniques

1) Basic event selection

3) Limit extractionss < 4.5/6.4 pb< 4.5/6.4 pbt t < 5.8/5.0 pb< 5.8/5.0 pb

ss < 4.5/6.4 pb< 4.5/6.4 pbt t < 5.8/5.0 pb< 5.8/5.0 pb

exp/obs

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Z+b / Z+jet cross-sections ratioZ+b / Z+jet cross-sections ratio

• Measurement of Z+b jets cross section :– Important background for Higgs searches in the ZH process.– Give insight on b PDF

Z + 1 b

We measure ratios of cross-sectionsZ + b / Z + jet so that some uncertaintiescancel out

)()(004.0023.0)(

)( 002.0003.0 syststat

jZ

bZ

Good agreement with NLO predictions using CTEQ6(Campbell et.al PRD 074021 (2004) ) : 0.018 0.004

Phys.Rev.Lett.94:161801,2005

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W charge asymmetryW charge asymmetry

• At the Tevatron, W are produced mainly via u and d quark :– ud̅ W+

– du̅ W-

• In average, u quarks in protons (u̅ in p̅) carry higher momentum fraction than d (d̅ in p̅) quarks. This leads to a boost of :– the W+ in the proton direction– the W- in the antiproton direction

• Asymmetry is defined like this :

• Since we do not measure the pz of the neutrino, we use the pseudorapidity of the charged lepton :

Forward-backward charge asymmetry

A(´e) = d¾(e+ )=d´e ¡ d¾(e¡ )=d´ed¾(e+ )=d´e+d¾(e¡ )=d´e

A(yW ) = d¾(W + )=dyW ¡ d¾(W ¡ )=dyWd¾(W + )=dyW +d¾(W ¡ )=dyW

Input for ratio of u and d PDF

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CDF electron analysisCDF electron analysis

77930 selected W e eventsMain background : QCD dijet (<2%)

Gain in sensitivity if split in different ET bins

CDF

Corrected for charge misidentification rate,Background subtracted

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ConclusionConclusion

• Various measurements at the Tevatron can probe/constraint the PDFs

• Top pair cross-sections in agreement with NLO expectations

• Single top : once discovered, tool to probe pQCD, b PDF

• Ratio Z+b / Z+jet : first test of b PDF -> good agreement

• W charge asymmetry : input for ratio of u and d quark PDF

• The first 1 fb-1 of Run II data has been delivered !

STAY TUNED for new results !!