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DRELL-YAN

q. e  , .  / Z. e + , +. q. DRELL-YAN. Story of Discoveries. Story of Discoveries. 1983. Lederman 1978. Drell Yan. q. e  , .  / Z. p T  > 6 GeV |  | < 2.5. e + , +. q. Inversion of e + e   qq at LEP. LHC 1 fb -1. Z pole. Total cross section pdf

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DRELL-YAN

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  1. q e, /Z e+, + q DRELL-YAN Napoli Doct. School 9 JULY 07

  2. Story of Discoveries Napoli Doct. School 9 JULY 07

  3. Story of Discoveries 1983 Lederman 1978 Napoli Doct. School 9 JULY 07

  4. Drell Yan q e, /Z pT > 6 GeV || < 2.5 e+, + q Inversion of e+e qq at LEP LHC 1 fb-1 Z pole • Total cross section • pdf • parton lumi • search for Z, extra dim. , ... • Much higher mass reach as • compared to Tevatron Napoli Doct. School 9 JULY 07

  5. Comparison with jet-jet cross section At m = 1 TeV jet jet cross section is 1 pb/GeV (||<1) and Drell-Yang (||<2.5) is 10-5 pb/GeV. Do we understand this qualitatively ? First we pay a ratio (_em/_s)2 for the coupling to the photon (Z) vs the coupling to gluon. Secondly Drell Yang can happen only via qqbar of the same flavour, this gives another factor ~ 1/20. Thirdly Drell-Yang is a s channel only process, while qqbar has also a very important t-channel contribution. Fourtly in s channel jet jet one has 6x3 final states + gluon gluon Napoli Doct. School 9 JULY 07

  6. Generalties Di-lepton final state usually easy to trigger and to identify. Trigger and identification efficiency depend on the lepton energy. Typically one can trigger on single lepton > 20 GeV. Napoli Doct. School 9 JULY 07

  7. Electrons Electron showers deposit their energy in several crystals in the ECAL. Approximately 94% of the incident energy of a single electron or photon is contained in 3×3 crystals, and 97% in 5×5 crystals. Summing the energy measured in such fixed arrays gives the best performance for unconverted photons, or for electrons in the test beam. The presence in CMS of material in front of the calorimeter results in bremsstrahlung and photon conversions. Because of the strong magnetic field the energy reaching the calorimeter is spread in . The spread energy is clustered by building a cluster of clusters, a “supercluster,” which is extended in . Energy and position are obtained from the PH and shape of the cluster. A number of corrections have to be applied. Calibration is very important: uniformity and energy scale. Once crystals are intercalibrated the energy scale is set by the Z peak into e+e- Napoli Doct. School 9 JULY 07

  8. Electron Triggers - Level 1 Leve1 Trigger: from calorimeter. Ingredients : Energy and Isolation. Napoli Doct. School 9 JULY 07

  9. Electron Triggers - Level 2 • Re-clustering and re-definition of energy with finer grain • Search for a pixel hit in coincidence with the electron trajectory (typically search region in r-phi very small due to constraint on the beam spot). Pixel Matching Track matched with pixel Napoli Doct. School 9 JULY 07

  10. Muon Trigger - Level 1 Ingredients: Muon Reconstruction and Isolation Efficiency of Level 1 Muon Trigger as function of Threshold Napoli Doct. School 9 JULY 07

  11. Muon Trigger - Level2 Napoli Doct. School 9 JULY 07

  12. Randal Sundrum Models Napoli Doct. School 9 JULY 07

  13. Z’ Models Napoli Doct. School 9 JULY 07

  14. High Mass Electrons Pairs -leakege An important characteristic of the signal events is that the very energetic final state electrons may have a significant energy leakage beyond the ECAL. The energy deposit in the CMS hadronic calorimeter (HCAL) cell behind the ECAL cluster is included in the measurement, event by event. This procedure leads to an improvement of the energy determination, as shown by the study of single electron and photon calibration files at fixed energy. Napoli Doct. School 9 JULY 07

  15. High Mass electron pairs- Saturation For very energetic electrons and photons, saturation occurs in the ECAL single crystal electronics because of the limited dynamical range of the Multi-Gain-Pre-Amplifier. From 2004 test beam data analysis, the saturation threshold has been established to be at 1.7 TeV in the barrel crystals and 3.0 TeV for the endcaps. The Method uses the crystal near the saturated one , sampling a fraction of the shower. The correct estimate of energy deposit with a resolution of around 7%. In addition, dedicated corrections, depending both on the electron energy and %, are performed for remaining losses. Napoli Doct. School 9 JULY 07

  16. High mass electron pairs - Selection Events with electrons trigger. At least 2 Super Clusters energy > 100GeV. H/E<0.1 against isolated hadrons Econe /Esc < 0.02 (Cone R 0.5) Napoli Doct. School 9 JULY 07

  17. Hign mass electron pairs- results Napoli Doct. School 9 JULY 07

  18. High energy electrons Discovery luminosity Z’ RS Graviton Napoli Doct. School 9 JULY 07

  19. High Mass Muon Pairs - Selection • Requires 2 muon tracks of opposite sign. • For each track examine the variation of the fit including/excluding all muon chambers but from 1st station and all muon chambers hits that looks contaminated by em showers. Take fit with best 2 Napoli Doct. School 9 JULY 07

  20. Distinguishing among different Z’ models The forward-backward asymmetry, AFB, of the leptonic decay products provides information on parity-violating couplings, on and off resonance For CM energies well above the Z0 peak, the Drell-Yan background has a characteristic AFB of about 0.6 and provides a useful starting point. Napoli Doct. School 9 JULY 07

  21. In proton-proton interactions, the quark direction is ambiguous experimentally since a quark can originate with equal probability from either proton, and the sign of cos * is not directly measurable. We follow infer the sign of cos * by assuming that the longitudinal motion of the dimuon system is in the direction of the proton contributing the annihilating quark, since a quark in a proton typically carries a larger momentum fraction x than does an anti-quark. We refer to the inference of the wrong sign of cos * as “mistagging” the sign. If not accounted for, the mistagged events, particularly at low y, reduce (“dilute”) the apparent value of AFB. Some authors deal with this problem by removing events below a chosen y threshold, or by examining AFB in bins of y. An approached is described which assigns the probability of a mistag on an event-by-event basis, thus using all events in a given sample. The knowledge of the mistagging probability depends on the Parton Distribution . The sign of cos* Napoli Doct. School 9 JULY 07

  22. How good is this approximization ? MC Truth Sign Inferred All events, no acceptance Watch the y scale Napoli Doct. School 9 JULY 07

  23. Miss tag probability All events Miss tagged events Ratio DEPEND ON PDFs Napoli Doct. School 9 JULY 07

  24. Effect of the acceptance Before Acceptance AFTER Acceptance Napoli Doct. School 9 JULY 07

  25. Evolution of the Asymmetry Napoli Doct. School 9 JULY 07

  26. First 500 Events (4 fb-1) Napoli Doct. School 9 JULY 07

  27. Asymmetry for various models Napoli Doct. School 9 JULY 07

  28. Capability to distinguish among Models Napoli Doct. School 9 JULY 07

  29. Comparison among mu and e channels Napoli Doct. School 9 JULY 07

  30. RS Graviton reach Napoli Doct. School 9 JULY 07

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