Sensitivity to PDFs at the Tevatron.

1. Sensitivity to PDFs at the Tevatron. Mathieu Agelou CEA – Saclay Low x workshop, Sinaia, Romania Mathieu Agelou – LowX’05

2. Outline • The Tevatron and the detectors (CDF and DØ) • Top results : • tt cross-section • Single top • Z+jets events • W charge asymmetry Mathieu Agelou – LowX’05

3. collider Two experiments : DØ , CDF Run II since mars 2001 Chicago Accumulator Debuncher Booster proton Linac antiproton Main Injector Recycler DØ CDF Booster p CDF p Tevatron TeVatron Main Injector & Recycler circumference 6km DØ Acceleration complex of Fermilab Mathieu Agelou – LowX’05

4. DØ and CDF detectors h = 0 • 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 h = 1 z f • 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  Mathieu Agelou – LowX’05

5. Luminosity Numerous runs above 1032cm-2s-1 Peak luminosity Efficiency of data taking for the 2 experiments > 85% 1032 cm-2s-1 Integrated luminosity 4.1031 cm-2s-1 Jun 05 Jan 04 Jan 02 Analysis presented here : L up to 350 pb-1 Mathieu Agelou – LowX’05

6. top 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 (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-section in all channels : good cross-checks, different systematics. Mathieu Agelou – LowX’05

7. Pair production dilepton channel : l = e , m - small BR (~6%) - small backgrounds (WW, Z->tt) - 2 high PT leptons (>15 GeV) - 2 jets (>20 GeV) - > 15 GeV L = 230 p-1 hep-ex/0504058 semileptonic channel : l = e , m - larger BR (~30%) - Backgrounds (W+jets, multijets) - 1 high PT leptons (>20 GeV) - ≥ 3 jets (>15 GeV) - > 20 GeV L = 318 p-1 Mathieu Agelou – LowX’05

8. Pair production • Hadronic channel : • Large BR : ~45% • Huge multijet background • 6 jets (>15 GeV) Nobs = 220 Nbck = 186 Small sensitivity Difficult analysis Good agreement with NLO predictions Mathieu Agelou – LowX’05

9. b 0 8 8 b 1 9 8 ¾ p = ¾ p = s t : : Single top production • Electroweak interaction : • Top is produced singly in the final -> ’’single’’ top |Vtb| 2 main processes at the TeVatron |Vtb| a 3rd mode exists but will be visible only at LHC : • Theoritical cross section ~0.4 x cross section • Very difficult to observe because of the smaller multiplicity than • tests of standard model • Direct measurment of |Vtb| • V-A coupling • top polarisation • Window to new phenomena • New vector bosons • Anormalous couplings • RPV SUSY • Background to Higgs • searches : • same final state as WH Mathieu Agelou – LowX’05

10. Probing 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 DIS Proton structure e+e- -> jets FSR only Drell-Yan ISR only http://www.hep.vanderbilt.edu/~wjohns/fcp05/recent/Zack%20Sullivan-ZSFCP05.pdf Mathieu Agelou – LowX’05

11. Single top search 1) Basic event selection 2) Multivariate techniques exp/obs 3) Limit extraction ss< 4.5/6.4 pb st < 5.8/5.0 pb Mathieu Agelou – LowX’05

12. Z+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-sections Z + b / Z + jet so that some uncertainties cancel out Phys.Rev.Lett.94:161801,2005 Good agreement with NLO predictions using CTEQ6 (Campbell et.al PRD 074021 (2004) ) : 0.018  0.004 Mathieu Agelou – LowX’05

13. + ¡ + ¡ ( ) = ( ) = ( ) = ( ) = d d d d W W d d d d ¡ ¡ ¾ y ¾ y ( ) ¾ e ´ ¾ e ´ W W ( ) A A e e y ´ = W = + ¡ ( ) = ( ) = d + d d ¡ d ( ) = ( ) = W W e d d d d + + ¾ y ¾ y ¾ e ´ ¾ e ´ W W e e W 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 Input for ratio of u and d PDF Mathieu Agelou – LowX’05

14. CDF electron analysis 77930 selected W  en events Main background : QCD dijet (<2%) Corrected for charge misidentification rate, Background subtracted Gain in sensitivity if split in different ET bins Mathieu Agelou – LowX’05

15. Conclusion • 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 !! Mathieu Agelou – LowX’05