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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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Drell yan

q

e,

/Z

e+, +

q

DRELL-YAN

Napoli Doct. School 9 JULY 07


Story of discoveries

Story of Discoveries

Napoli Doct. School 9 JULY 07


Story of discoveries1

Story of Discoveries

1983

Lederman 1978

Napoli Doct. School 9 JULY 07


Drell yan

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


Comparison with jet jet cross section

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


Generalties

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


Electrons

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


Electron triggers level 1

Electron Triggers - Level 1

Leve1 Trigger: from calorimeter. Ingredients : Energy and Isolation.

Napoli Doct. School 9 JULY 07


Electron triggers level 2

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


Muon trigger level 1

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


Muon trigger level2

Muon Trigger - Level2

Napoli Doct. School 9 JULY 07


Randal sundrum models

Randal Sundrum Models

Napoli Doct. School 9 JULY 07


Z models

Z’ Models

Napoli Doct. School 9 JULY 07


High mass electrons pairs leakege

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


High mass electron pairs saturation

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


High mass electron pairs selection

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


Hign mass electron pairs results

Hign mass electron pairs- results

Napoli Doct. School 9 JULY 07


High energy electrons discovery luminosity

High energy electrons Discovery luminosity

Z’

RS Graviton

Napoli Doct. School 9 JULY 07


High mass muon pairs selection

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


Distinguishing among different z models

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


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 .

The sign of cos*

Napoli Doct. School 9 JULY 07


How good is this approximization

How good is this approximization ?

MC Truth

Sign Inferred

All events, no acceptance

Watch the y scale

Napoli Doct. School 9 JULY 07


Miss tag probability

Miss tag probability

All events

Miss tagged events

Ratio

DEPEND ON PDFs

Napoli Doct. School 9 JULY 07


Effect of the acceptance

Effect of the acceptance

Before Acceptance

AFTER Acceptance

Napoli Doct. School 9 JULY 07


Evolution of the asymmetry

Evolution of the Asymmetry

Napoli Doct. School 9 JULY 07


First 500 events 4 fb 1

First 500 Events (4 fb-1)

Napoli Doct. School 9 JULY 07


Asymmetry for various models

Asymmetry for various models

Napoli Doct. School 9 JULY 07


Capability to distinguish among models

Capability to distinguish among Models

Napoli Doct. School 9 JULY 07


Comparison among mu and e channels

Comparison among mu and e channels

Napoli Doct. School 9 JULY 07


Rs graviton reach

RS Graviton reach

Napoli Doct. School 9 JULY 07


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