Constraints on PDF uncertainties from CDF

DIS 2006, Tsukuba

22.04.2006

Cigdem Issever

for the

CDF Collaboration

University of Oxford

DIS 2006 22.04.06 C. Issever 2

Outline

• Introduction

• Tevatron & CDF detector

• EWK Results (95% of the talk)

• Jet results (see talk “Inclusive jet production at the Tevatron (CDF)” of Olga Norniella in (HFS-5))

• Conclusion

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Main Injector(new)

Tevatron

DØCDF

Chicago

p source

Booster

Tevatronproton-antiproton collisionss = 1.96 TeV (Run I 1.8 TeV) 36 bunches: 396 ns crossing timePeak luminosity is now ~ 1032 cm-2 s-1

Ultimately 4 – 9 fb-1 by 2009

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CDF Recorded Data

Jet results with 1.0 fb-1

1.6 fb-1 delivered1.2 fb-1 recorded

EWK results

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CDF RUN II Detector

Si Detector

COT Tracker

EM Cal Had Cal

MuonUpgraded for RUN II• New silicon tracking• New drift chamber• Increased muon coveraged• New TOF• New plug calorimeters

PLUG

Silicon DetectorCDF Data taking effi 80% - 85%.

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EWK Physics – Input to PDFs

Motivation

• Test SM (precise measurements)

• Constraints on PDFs

• Search for physics beyond SM

• Important input to LHC

Outlook

• W forward cross section, 223/pb

• Z →ττ and μμ cross Section, 330/pb

• W charge asymmetry, 170/pb

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ET>25GeV

W/Z Gauge Bosons Identification

• At hadronic collider W and Z bosons hadronic decays are overwhelmed by QCD background.

identification through leptonic decays

We Z

W± signature: Isolated Isolated Energetic Lepton + EEnergetic Lepton + ETT

Z Signature: Two Isolated Energetic Two Isolated Energetic Leptons (opposite charge)Leptons (opposite charge)

PT>20GeV

PT>20GeV

ET>20GeV Position of μ consistent with extrapolated track

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W cross section in the forward region

Extension into forward region:1.2 < |η| < 2.8 using calorimeter seeded tracking

Complementary to central

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W cross section in the forward region

48165 ~4.8%

LA

NN bkgobs

0.07

Systematics on A = 0.2567:

Axε

2%

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W cross section in the forward region

223pb-1

σ = 2.796 +/-0.013(stat) + 0.095 – 0.090 (syst) +/- 0.168 (lum.)nb.

NNLO σ(pp→W) @ 1.96 TeV, Stirling, van Neerven = 2.687 +- 0.054(Th)

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Central-to-Forward W vis. cross section ratio

(visible)=TOT*A where A is the kin. and geo accept.

• Strategy: assign sys uncertainties but PDF, NLO/NNLO effect to vis

• In this way:

•Most of the luminosity uncertainty cancels in the ratio

•All other uncertainties are uncorrelated

•Accuracy can be used to constrain PDFs

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• vis(central) =664.2±11.7 pb (Ete>25, ETn>25, |ele|<1)

• vis(forward) =718±21 pb (Ete>20, ET>25, 1.2<|ele|<2.8)

• vis(central)/vis(forward) =0.925±0.033• 1% assigned as luminosity syst. (slightly overestimate)

• NLO ratios (taking into account correlations between central and forward):

• CTEQ= 0.9243±0.037

• MRST01E= 0.94137±0.011

• Most uncertainties will go down with more data useful to constrain PDFs

Central-to-Forward W vis. cross section ratio

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Z → μμ cross section (|η| < 1) using 337 pb-1

σ=261.2 ± 2.7 (stat) + 5.8 - 6.9 (sys) ± 15.1 (lum) pb

66 116

337pb-1

NNLO @ 1.96 TeV Stirling, van Neerven σ(pp→Z)=251.3+-0.5(Th)

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Z →τe τh cross section using 349 pb-1

• 316 signal events• 60 % τ identification efficiency and 5% acceptance• Most systematics are data driven will be reduced with more stat.

σ=265+-20(stat)+-21(syst)+-15(lumi) pb

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Cross section summary

new

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W Charge Asymmetry

W- W+

yWprotonantiproton

u

d

dyWddyWd

dyWddyWdA

WW

WW

/)(/)(

/)(/)(

W+u de+

proton anti-proton

Asymmetry in W production complicated by unknown pz use lepton asymmetry:

which convolves W production with V-A decay.

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W Charge Asymmetry Run II 170pb-1

A as function of ET provides better probe of x dependence.

Statistic allowed two bins.

Will be included into next generation of PDFs.

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W Charge Asymmetry – new method

Lepton asymmetry has turn over at high |η| due to V-A

W charge asymmetry does not have this effect, so we don’t

purely probe high yW

• Determination of yW with W mass constrain gives 2 possible solutions.• Evaluate weight factor F1,2 for each y1,2 solution.• Parameterize F1,2 with

1. the angular distribution of (1+-cosΘ*)2

2. with W cross section, σ(yW), but this depends on asymmetry• Iterative procedure!!

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W charge asymmetry – new method

Iterative procedure

• Smaller statistical errors• Greater sensitivity• No additional systematics due to new method

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Jet

Midpoint jet cross section

Good agreement with NLO

More details see talk of Olga Norniella in (HFS-5): Jets 1

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Results with KT: Data/NLO; 1fbResults with KT: Data/NLO; 1fb-1-1

Measurements in the forward region will allow to reduce the PDFs uncertainties

IR and CL safeNo splitting or merging

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Conclusions

New cross section measurements from CDF• W → eν in forward region (1.2 < |η| < 2.8) using 223 pb-1

• Central-to-forward W vis cross section ratio• Z → μμ using 337 pb-1

• Z → τe τh using 349pb-1

• Inclusive Jets with Mitpoint using 1.04 fb-1

• Inclusive Jet s with Kt algorithm using 0.96 fb-1

Excellent base for next set of analyses• dσ/dy for W → eν

• dσ/dpt for Z → μμ

• Tau widely used in SM measurements and SUSY, Higgs

New generation of W&Z measurements(R, W Charge Asymmetry, … )

on the way !!

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Backup Slides

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W forward cross section

Electron: Et > 20GeV1.2 < |η|<2.8

Neutrino: MEt > 25 GeV

Vertex: |z0| < 60 cm

Electron ID: Had/Em<0.05Isolation<0.1

 Δ(XPES,XTrk) < 3 cm

 Δ(YPES,YTrk) < 3 cm

E/P < 2.0

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Z → μμ cross section (|η| < 1)

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Z →τe τh cross section

CDF strategy for hadronic tau reconstruction:

1. Charge tracks define signal and isolation cone (shrinking cone vs. E)

isolation: require no tracks in isolation cone

2. Hadronic calorimeter cluster (to suppress e background)

3. π0 required in isolation cone (identified by shower maximum detector)

• taus difficult to reconstruct at hadron colliders• Z→ττ exploits event topology to suppress backgrounds (QCD&W+jet)

Z→ττ event selection:• τ→e: electron + isolated track (ET>10 GeV)• τ→h: PT(seed) > 6 GeV & PT(signal)>15 GeV• remove backgrounds by event topology cuts

= 30o

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Z→ττ cross section

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Z→ττ cross section -- Systematics

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W Asymmetry – new method

Leading order W production

from Bo Young Han

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I. The angular distribution of ( )2 from W production

ratio of two angular distributions at each rapidity

*1 cos

* * 2 * 2(cos , , ) (1 cos ) ( , )(1 cos )W WW t W tP y p Q y p

– in Collin-Soper frame

– The W production Probability from angular distribution

*cos

q P q P q P q P

q P q P q P q P

q P q P q P q P

from Bo Young Han

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II. Weight must also depend on W+- cross-section.

– But cross-sections depend on W asymmetry! This method must be iterated.

III. Iteration procedure

*1,2 1,2 1,2

1,2 * *1 1 1 2 2 2

(cos , , ) ( )

(cos , , ) ( ) (cos , , ) ( )

Wt

W Wt t

P y p yF

P y p y P y p y

measuringasymmetry

the closest asymmetry to data

assumedsample

F1 min( )2new assumed

sampleFn

reconstructionInputdata

YesNo

if no,

from Bo Young Han

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Sensitivity Study , 400pb-1 MC data

generated by Pythia

Selecting W events high PT electron : ET > 25 GeV Missing ET > 25 GeV

Used CTEQ6M errors PDF 40 sets for PDF uncertainty

Comparison of statistical uncertainty between lepton and W boson asymmetry

Our method has statistical sensitivity to probe PDFs

W e

from Bo Young Han

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Systematic Uncertainty

Weight Factors depend on Q(yW, Pt

W) and σ(yW)

1. Ratio of two angular distributions, Q(yW, Pt

W)– PDF dependence

2. W cross section, σ(yW)– PDF dependence

from Bo Young Han

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Systematic Uncertainty (cont.)The uncertainties from the

energy measurement– Energy scale – Energy resolution (not

yet)

3. Electron ET scale– ±0.1%(1σ) : |η| < 1.1– ±0.15%(1σ) : |η| > 1.1

4. Missing ET scale– W boson Recoil energy

tuning

from Bo Young Han