Using Drell Yan to Probe the Underlying Event in Run 2 at CDF

 

  Deepak Kar, Rick Field 

University of Florida

 

Abstract:

We study the event topology in Drell-Yan lepton-pair production in proton-antiproton collisions at 1.96 TeV in Run 2 at CDF. We use the direction of the lepton-pair on a event by event basis to define three regions of \eta-\phi space; toward, away and transverse. The "transverse" region is very sensitive to the "underlying event". The data are corrected to the particle level and are then compared with the PYTHIA Tune AW. The properties of the "underlying event" are examined as a function of the lepton-pair transverse momentum. The data are also compared with a previous analysis on the behavior of the "underlying event" in high transverse momentum jet production. The goal is to improve our understanding and modeling of the high energy collider events.

 

Analysis Strategy:

  • High PT Electron and Muon Data, yielding ~65,000 electron and muon (oppositely charged) pairs each, passing all selection cuts, corresponding to about 2.7 fb-1 of data.
  • Charged Particles with pT > 0.5 GeV/c and letal <1.
  • Using events with the lepton pair invariant mass in the Z region:  70 GeV/c2 < M(ll) < 110 GeV/c2.
  • Error bars coming both from statistical and systematic (due to lepton selection and charged particle selection) uncertainties - however it is dominated by statistical uncertainty.

 

Blessed Plots:

Variables Describing Underlying Event

Transverse Region (Compared with leading jet results)

  

TransMAX, MIN  and DIF Regions (Compared with leading jet results)

 
Toward Region Transverse+Toward Region Away Region (Compared with leading jet results) All Three Regions

Number of charged particles

pnchg.eps 

(pnchgJ.eps)

maxminnchg.eps 

(maxminnchgJ.eps)

difnch.eps 

(difnchgJ.eps)

 

tnchg.eps

nchg1.eps

nchg2.eps

anchg.eps

(anchgJ.eps)

nchg3.eps

Scalar PT sum of charged particles

pcptsum.eps 

(pcptsumJ.eps)

maxmincptsum.eps 

(maxmincptsumJ.eps)

difcptsum.eps 

(difcptsumJ.eps)

tcptsum.eps

cptsum1.eps

cptsum2.eps

acptsum.eps

(acptsumJ.eps)

cptsum3.eps
Average PT of charged particles
(Require at least 1 charged particle)

pcptave.eps 

(pcptaveJ.eps)

tcptave.eps cptave2.eps acptave.eps cptave3.eps
Maximum PT of charged particle
(Require at least 1 charged particle)

pcptmax.eps

(pcptmaxJ.eps)

tcptmax.eps cptmax2.eps acptmax.eps cptmax3.eps

Correlation Plots

Charged pT Average Against Charged Multiplicity

Charged pT Average Against Charged Multiplicity (Z pT < 10 GeV/c)

Lepton Pair pT Average Against Charged Multiplicity

 

 

ptnchg.eps ptnchg10.eps zptnchg.eps

 

Additional Links:

  • For a detailed discussion on how we divide the central region into transverse, toward and away region, please check Rick Fields public page.

 

Contact:

Deepak Kar (dkar@phys.ufl.edu)