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Recent QCD results in  collisions at LEP

Recent QCD results in  collisions at LEP. Mikhail Shapkin IHEP Protvino Russia. For DELPHI and L3 collaborations. The LEP Accelerator e + e - collisions at s  91 GeV (LEP I), s = 161-207 GeV (LEP II)

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Recent QCD results in  collisions at LEP

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  1. Recent QCD results in  collisions at LEP Mikhail Shapkin IHEP Protvino Russia For DELPHI and L3 collaborations Rencontres de Moriond, March 18-25 2006

  2. The LEP Accelerator e+e- collisions at s 91 GeV (LEP I), s = 161-207 GeV (LEP II) Integrated luminosity ~150 pb-1 /experiment(LEP I) , ~700 pb-1 /experiment (LEP II) The dominant interactions at LEP II are two-photon processes LEP II is the best place to study two-photon physics (high energy, high cross section, low background) Rencontres de Moriond, March 18-25 2006

  3. Two-photon collisions Q2 = -q12= 2  E1 E1 (1 - cos1) P2 = -q22= 2  E2 E2 (1 - cos2) W 2 = ( i Ei )2 - ( i Pi )2   The final state can be: 1. Lepton pairs 2. A single resonant state 3. A non-resonant hadronic state Rencontres de Moriond, March 18-25 2006

  4. The two-photon events can be classified as: 1. Double-tagged events (Q2, P2 >> 0) Both scattered e aredetecded, Q2and P2 are well measured, W2 can be measured directly No unfolding. Cross section of  collisions  BFKL LO and NLO prediction 2. Single-tagged events (Q2>> P2~ 0) Only one scattered electron is detected, one photon is highly virtual and the other is quasi-real, Q2 is well measured. Photon structure function Electron structure function  Exclusive vector mesons 3.Non-tagged events (Q2~ P2~ 0) Both scattered e are lost in the beam pipe, both photons are quasi-real. Inclusive Charm and Beauty Single particle and Dijet Resonances Rencontres de Moriond, March 18-25 2006

  5. Typical selection criteria for non-tagged events Nch 4: Minimize +– bkg. 3 GeV < Wvis< 35 GeV ET(charged) > 3 GeV Ldt=617 pb-1 Nev  300k Background cont.  1% Rencontres de Moriond, March 18-25 2006

  6. Hadrons Muons DELPHI Preliminary DELPHI Preliminary QED 2 2 Y = ln(W2**/Q1Q2), Q1,Q2 are in the range [10-200] GeV2 2 2 Double tagged events EP-PH 2005-029 hhahhh Muons production is used for tuning the experimental cuts Rencontres de Moriond, March 18-25 2006

  7. Photon structure function F2 Phys. Lett. B622 (2005) 249-264 deeX(x,Q2) 22  =  [(1+(1-y)2)F2(x,Q2)-y2FL(x,Q2)], x = Q2/2(p·q), y = (q·p)/(k·p) dxdQ2 xQ4   Rencontres de Moriond, March 18-25 2006

  8. Photon structure function (cont.) Rencontres de Moriond, March 18-25 2006

  9. deeeX 22  =  [(1+(1-y)2)F2(z,Q2)-y2FL(z,Q2)], dzdQ2 zQ4 z = Q2/(2·p·q) = sin2(tag/2)/(E/Etag– cos2(tag/2)) e e e Electron structure function F2 DELPHI 2005-025 CONF 745 DELPHI Preliminary Advantage: z is determined from the scattered electron only. No need of hadronic mass measurement as in the case of x for photon structure function. Rencontres de Moriond, March 18-25 2006

  10. Electron structure function (cont.) DELPHI Preliminary Rencontres de Moriond, March 18-25 2006

  11. Exclusive reactions g g 00,g g +- ) Phys. Lett. B615 (2005) 19-30 non-tagged events (0 < Q2< 0.02 GeV2) + single-tagged events (0.2 GeV2 < Q2< 30 GeV2) 1.1 GeV < W < 3 GeV Phys. Rev. D 62 (2000) 073014. 00 n = 2.9  0.1+- n = 2.3  0.2 Rencontres de Moriond, March 18-25 2006

  12.  cross section g g 00cross section measured by PLUTO and L3 differ at low Q2.  g g* 00is well reproduced by GVDM-based parameterization for Q2 > 0.2GeV2.+-data are less satisfactorily described over the whole Q2 range.  The relativemagnitude of +-and00 production changes in the vicinity of Q21GeV2 different -pair productions mechanisms at low and high Q2. Rencontres de Moriond, March 18-25 2006

  13. Open charm and beauty production in two-photon collisions – (e+e–  e+e– bbX) = 14.93.33.4 pb DELPHI 2003-015 CONF 635 Untagged events D* tagging used for extracting the open charm cross section K-lepton charge correlation increase the purity of b and c events Muon and electron spectra global fit gives the open c and b cross section Rencontres de Moriond, March 18-25 2006

  14. Open charm and beauty production in two-photon collisions Phys. Lett. B619 (2005) 71-81 Muons Electrons (e+e–  e+e–bbX) = 12.62.42.3 pb (e+e–  e+e–bbX) = 13.02.42.3 pb Combined result: (e+e–  e+e–bbX) = 12.81.72.3 pb Rencontres de Moriond, March 18-25 2006

  15. Open charm and beauty production in two-photon collisions - (e+e- e+e-cc)  1000 pb ( 10%) - (e+e- e+e-bb)  13 pb ( 30%) DELPHI, prel. Rencontres de Moriond, March 18-25 2006

  16. Search of b Phys. Lett. B634 (2006) 340. Rencontres de Moriond, March 18-25 2006

  17. Prel. Inclusive single particle production L3: Phys. Lett. B554 (2003) 105. Rencontres de Moriond, March 18-25 2006

  18. Inclusive single particle production(cont.) Prel. Prel. Rencontres de Moriond, March 18-25 2006

  19. Di-jet production DELPHI 2005-007 CONF 727 Cross-section (pb/GeV) Preliminary LO NLO measured = 17.10.3 pb Expectations:for LO 20.20.1 pbfor NLO 17.80.1 pb -1 <  < 1, pt > 3 GeV Rencontres de Moriond, March 18-25 2006

  20. Summary • Double tagged events have been studied with virtualities of both photons between 10 and 200 GeV2 and for final state invariant mass above 2 GeV. The hadron production is in reasonable agreement with NLO BFKL prediction • The structure function of photon has been measured in the range 11<Q2<34 GeV2 and 0.006<x<0.556. The data are better reproduced by the higher order parton density function of GRV. LnQ2 evolution is confirmed. • The electron structure function has been measured and has been found to agree with the photon structure function. • Exclusive meson pair production has been measured. The QCD-based dee/dQ2 descriptionreproduceswell-data in the interval 0.2<Q2<30 GeV2.-pole description of the Q2 dependence is excluded in this Q2 interval. GVDM model describes well the 00 production for Q2>0.2 GeV2 and fails for +–. Rencontres de Moriond, March 18-25 2006

  21. Summary (cont.) • Open beauty production has been measured. DELPHI, L3 and OPAL cross sections agree with each other but are about 3 times larger than QCD prediction. • b has been searched for. No signal has been found yet. • Inclusive single particle production agrees within errors with the NLO QCD prediction. Systematic uncertainties due to background contamination in high Ptregion are important. • Di-jet production has been studied and found to be in good agreement with NLO QCD prediction. Rencontres de Moriond, March 18-25 2006

  22. Backup slides Rencontres de Moriond, March 18-25 2006

  23. Search of b (ALEPH) Phys. Lett. B530 (2002) 56. Rencontres de Moriond, March 18-25 2006

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