Photon + heavy flavour production at CDF

We measure the photon + b and photon + c cross-sections. We present cross-sections both as a function of photon Et, in order to test QCD predictions at different energy scales, and for all photons with an Et exceeding 25 GeV to gain maximal statistical sensitivity to deviations that could signal new physics production. Results are compared to and found to be consistent with Pythia LO predictions. We find no evidence so far of new physics production.

The results below are preliminary and use 66.7 pb-1 of data. Results were blessed on 10/07/03 and 11/07/03 for the exotics and QCD analyses respectively. More details can be obtained by referring to CDF note CDF6538.


Method

We obtain a sample of photon + heavy flavour in data by requiring events to contain a central photon of Et>25 GeV, and a jet tagged by SECVTX. We fit the secondary vertex mass distribution of the tagged jets to determine the number of events containing b, c and uds quarks in our data. In order to determine fake photon background contributions, we use the estimated number of take photons from CPR detector information and multiply this by the fractions of b, c and uds events fitted from a representative background sample. We obtain the number of real photons +b, and real photons +c, by subtracting the background contribution from our original fit. By dividing these numbers by the selection, tagging and trigger efficiencies, and the integrated luminosity, we determine the production cross-sections.

Plots illustrating method

(Note: colour shading in some postscript plots may only be visible when viewed with gs, not gv.)
  • Templates for secondary vertex mass. (gif) (Postscript)
  • Fit to background (jet50 data). This plot is the "template prediction" corresponding to the fit result (this is not the same as the weighted sum of template distributions, as template statistical uncertainties are taken into account). (gif) (Postscript)

    Results

    Using 66.7 pb-1 of data, we determine for events with photons of Et > 25 GeV (exotics analysis):
    
    sigma(b + gamma) = 40.6  +/- 19.5 (stat.)  +7.4 -7.8   (sys.) pb
    sigma(c + gamma) = 486.2 +/- 152.9 (stat.) +86.5 -90.9 (sys.) pb
    
    
    Here are the final results for the QCD analysis for the photon + b and photon + c cross-sections , and for the cross-section ratio . The errors are the combined statistical and systematic.

    Plots/ Tables (Exotics)

    Plots/ Tables (QCD)


    Cross-check

    We repeated the analysis but assumed the composition of real photon tagged events from Monte Carlo. The overall normalisation of this measurement is sensitive to photon + heavy quark content, and can cross check our method to extract b and c directly from data.

    Plots/ Tables

    Contacts

    For more information, please contact Ronan McNulty or Tara Shears.