1. 06/30/05 Mathieu Agelou – LowX’05 1 Sensitivity to PDFs at the Tevatron. Mathieu Agelou CEA – Saclay Low x workshop, Sinaia, Romania

2. 06/30/05 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

3. 06/30/05 Mathieu Agelou – LowX’05 3 Acceleration complex of Fermilab DØ CDF TeVatron circumference 6km Main Injector Recycler Accumulator Debuncher Linac Booster proton antiproton collider Two experiments : DØ, CDF Run II since mars 2001 Main Injector & Recycler Tevatron Booster pp p Chicago CDF DØ

4. 06/30/05 Mathieu Agelou – LowX’05 4 DØ 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 

5. 06/30/05 Mathieu Agelou – LowX’05 5 Luminosity 4.10 31 cm -2 s -1 Jan 02 Jan 04 10 32 cm -2 s -1 Numerous runs above 10 32 cm -2 s -1 Analysis presented here : L up to 350 pb -1 Efficiency of data taking for the 2 experiments > 85% Integrated luminosity Peak luminosity Jun 05

6. 06/30/05 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.

7. 06/30/05 Mathieu Agelou – LowX’05 7 Pair production dilepton channel : l = e,   - small BR (~6%) - small backgrounds (WW, Z->  ) - 2 high P T leptons (>15 GeV) - 2 jets (>20 GeV) - > 15 GeV semileptonic channel : l = e,   - larger BR (~30%) - Backgrounds (W+jets, multijets) - 1 high P T leptons (>20 GeV) - ≥ 3 jets (>15 GeV) - > 20 GeV L = 318 p -1 L = 230 p -1 hep-ex/0504058

8. 06/30/05 Mathieu Agelou – LowX’05 8 Pair production Hadronic channel : –Large BR : ~45% –Huge multijet background –6 jets (>15 GeV) N obs = 220 N bck = 186 Small sensitivity Difficult analysis Good agreement with NLO predictions

9. 06/30/05 Mathieu Agelou – LowX’05 9 Single top production Electroweak interaction : –Top is produced singly in the final -> ’’single’’ top ¾ t = 1 : 98 p b 2 main processes at the TeVatron Theoritical cross section ~0.4 x cross section Very difficult to observe because of the smaller multiplicity than a 3 rd 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 |V tb | – V-A coupling – top polarisation ¾ s = 0 : 88 p b |V tb | Background to Higgs searches : same final state as WH

10. 06/30/05 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 http://www.hep.vanderbilt.edu/~wjohns/fcp05/recent/Zack%20Sullivan-ZSFCP05.pdf Drell-Yan ISR only e + e - -> jets FSR only DIS Proton structure

11. 06/30/05 Mathieu Agelou – LowX’05 11 Single top search 2) Multivariate techniques 1) Basic event selection 3) Limit extraction  s < 4.5/6.4 pb  t < 5.8/5.0 pb  s < 4.5/6.4 pb  t < 5.8/5.0 pb exp/obs

12. 06/30/05 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 Good agreement with NLO predictions using CTEQ6 (Campbell et.al PRD 074021 (2004) ) : 0.018  0.004 Phys.Rev.Lett.94:161801,2005

13. 06/30/05 Mathieu Agelou – LowX’05 13 W charge asymmetry At the Tevatron, W are produced mainly via u and d quark : –ud̅  W + –du ̅  W - In average, u quarks in protons (u ̅ in p ̅ ) carry higher momentum fraction than d (d ̅ in p ̅ ) 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 p z of the neutrino, we use the pseudorapidity of the charged lepton : Forward-backward charge asymmetry A ( ´ e ) = d ¾ ( e + )= d ´ e ¡ d ¾ ( e ¡ )= d ´ e d ¾ ( e + )= d ´ e + d ¾ ( e ¡ )= d ´ e A ( y W ) = d ¾ ( W + )= d y W ¡ d ¾ ( W ¡ )= d y W d ¾ ( W + )= d y W + d ¾ ( W ¡ )= d y W Input for ratio of u and d PDF

14. 06/30/05 Mathieu Agelou – LowX’05 14 CDF electron analysis 77930 selected W  e events Main background : QCD dijet (<2%) Gain in sensitivity if split in different E T bins Corrected for charge misidentification rate, Background subtracted

15. 06/30/05 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 !!