Measurement of the W boson production charge asymmetry at CDF

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1 Measurement of the boson production charge asmmetr at CDF Eva Halkiadakis Rutgers Universit Booung Han, Arie Bodek, Yeonsei Chung, Kevin McFarland Universit of Rochester For the CDF collaboration APS Meeting, April , St. Louis, MO

2 Phsics Motivation Parton distribution functions (PDFs describe quark and gluon content of the proton. PDFs are essential input to perturbative calculations of signal and background processes at hadron colliders. How can we gain insights into proton PDFs at the Tevatron? Measure charge asmmetr The measurement provides information on d(x/u(x of the proton April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 2

3 Charge Asmmetr at the Tevatron u quark carries higher fraction of proton momentum - + anti-proton direction proton direction April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 3

4 PDFs of the proton d# d# + + / d / d A( u( x1 d( x2 u( x1 d( x2 d# + d# + = / d / d " d( x1 u( x2 d( x1 u( x2 xf(x,q 2 d u u d log(x [ Measurement of the charge asmmetr constrains PDF s of the proton. April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 4

5 Lepton Charge Asmmetr Traditionall we measure lepton charge asmmetr leptonic deca involves ν P z ν is unmeasured lepton charge asmmetr is a convolution of both the charge asmmetr and V-A deca structure ( turn over at high η charge asmmetr does not have this effect, so we probe high CDF RunII: PRD 71, (2005 A( A (" = l = Least constrained at high η d" + d" + / d / d d" + d" / d / d + # d ( l / d" # d ( l / d" + # d ( l / d" + d ( l / d" April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 5

6 eν event selection Electron selection Isolated EM calorimeter energ Transverse Energ E T > 25 (20 GeV in central (forward detector Neutrino selection Determined from missing transverse energ missing E T > 25 GeV η ~538K events in central and ~177K in forward April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 6

7 April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 7 Analsis Technique I Measure ± rapidit Use mass constraint solve eqn. answer : Develop the weight factor Iterate the method to remove input bias ( ( P P E E M l l + " + = (,, (cos (,, (cos (,, (cos 2 2 * * 1 1,2 1,2 * 1,2 1,2 p P p P p P F T T T ± ± ± ± ± ± ± + = " " " " # $ $ % & + ' = z z P E P E ln 2 1 z l z z P P P + = can t measure 2 1, z P z P Probabilit of angular distribution Differential cross section

8 Analsis Technique II The production probabilit from angular distribution [cosθ * : in Collins-Soper frame ( rest frame] q < p > +q < p > q < p > +q < p > P ± (cos" *,, p T = (1 m cos" * 2 +Q(, p T (1± cos" * 2 q < p > +q < p > q < p > +q < p > ratio of two angular distributions at each rapidit April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 8

9 Electron Charge Identification Charge identification is crucial for this measurement. Measure charge fake rate using Z e + e - data sample. f mis = N same sign N opposite sign + N same sign April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 9

10 Backgrounds Measure jet backgrounds directl in data use extra energ isolation around electron to separate, and fit shape to background fraction use jet sample to predict measured from this background Z e + e - background from simulation April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 10

11 Sstematic Uncertainties 1. Trigger and electron ID efficiencies 2. Hadronic recoil energ scale 3. Calorimeter energ scale and resolution 4. PDF uncertaint 5. Uncertainties on QCD and Z e + e - background estimates 6. Uncertaint on charge fake rate Sstematics <1.5 % for > 2.0 April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 11

12 CDF Preliminar Result (1fb -1 Positive and negative agree, so fold Compare to NLO Prediction NLO error PDFs (CTEQ April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 12

13 CDF Preliminar Result (1fb -1 Compare to CTEQ6M (NLO and MRST2006 (NNLO PDFs and their uncertainties NNLO Prediction: C. Anastasiou et al., Phs. Rev. D69, (2004 MRST 2006 PDFs: A. D. Martin et al., hep-ph/ , Eur. Phs. J., C28, 455 (2003 CTEQ6M PDFs: J. Pumplin et al., hep-ph/ April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 13

14 First direct measurement of charge asmmetr despite additional complication of multiple solutions, it works appears that it will have impact on d/u of proton Conclusions Looking forward to working with PDF fitting groups to incorporate Thesis of B.Y. Han and method documented in B.Y.Han et al., arxiv:hep-ph/ April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 14

15 Backup April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 15

16 Sstematic Uncertainties April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 16

17 Acceptance correction April 12, 2008 Charge Asmmetr at CDF, E. Halkiadakis 17