Measurement of the Initial State Gluon Radiation using Drell-Yan Events at CDF

Hyon San Seo, Geum Bong Yu, Un-Ki Yang
Seoul National University

Willis Sakumoto
University of Rochester
last modification: 7/3/2018
  • Public Note (CDF11243): pdf

  • Abstract

    This is a measurement of the initial state gluon radiation (ISR) in proton-antiproton collisions at √s = 1.96 TeV. This analysis uses Drell-Yan (Z/γ* → ee,μμ) events in the CDF data sample, corresponding to an integrated luminosity of 9.4 fb-1. We find that the mean value of the transverse momentum distribution of the dilepton system is a good observable to measure the effect of the ISR. This observable has a good logarithmic dependence on the mass square of the dileptons, which is parameterized as a linear function of -7.61+2.15log(M2). The measurement of this observable provides a good way to estimate the effect of the ISR at very high mass region, and it can be used to control the size of the ISR effect in other physics processes.

    Plots

    A. Comparison of dilepton mass distribution and background contribution




    B. Dimuon <pT> distribution at reconstruction level for different mass region (backgrounds are subtracted)


    This is dimuon <pT> distribution at each mass bin and combined mass bin after background subtraction. Overall, dimuon <pT> distribution show good agreement.




    C. Dielectron <pT> distribution at reconstruction level for different mass region (backgrounds are subtracted)


    This is dielectron <pT> distribution at each mass bin and combined mass bin after background subtraction. Overall, dielectron <pT> distribution show good agreement.




    D. The measured <pT> as a function of <M>2


    The black line is data at reconstruction level and red line is data corrected to generator level. Left plot is muon channel and right plot is electron channel.




    E. Systematic uncertainty




    F. The mean of pT(Z/γ*) according to event scale(M2)


         
         

    The mean pT of Z/γ* shows logarithmic dependency on M2. The dimuon and dielectron channel show consistent result. The fit result with both channel is (-7.61±0.69)+(2.15∓0.08)×log(M2). Two fitting parameters are strongly anti-correlated(-99.95%). The fit result with only muon channel is (-7.78±0.92)+(2.18∓0.10)×log(M2). The fit result with only electron channel is (-7.58±1.04)+(2.15∓0.12)×log(M2).