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

2 Story of Discoveries

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

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

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 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 qq bar of the same flavour, this gives another factor ~ 1/20. Thirdly Drell-Yang is a s channel only process, while qq bar 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 grainRe-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). 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 Muon Trigger - Level 1 Efficiency of Level 1 Muon Trigger as function of Threshold Ingredients: Muon Reconstruction and Isolation

Napoli Doct. School 9 JULY Muon Trigger - Level2

Napoli Doct. School 9 JULY Randal Sundrum Models

Napoli Doct. School 9 JULY Z’ Models

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

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

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

Napoli Doct. School 9 JULY High Mass Muon Pairs - Selection Requires 2 muon tracks of opposite sign. 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 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 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 Z 0 peak, the Drell-Yan background has a characteristic AFB of about 0.6 and provides a useful starting point.

Napoli Doct. School 9 JULY The sign of cos  * 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.

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

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

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

Napoli Doct. School 9 JULY Evolution of the Asymmetry

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

Napoli Doct. School 9 JULY Asymmetry for various models

Napoli Doct. School 9 JULY Capability to distinguish among Models

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

Napoli Doct. School 9 JULY RS Graviton reach