# 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)**

- Fit to data with photon Et > 25 GeV
(gif) (Postscript)
- Fit to data with photon Et > 25 GeV, with estimated b contribution overlaid.
(gif) (Postscript)
- Photon + tagged jet invariant mass. The LO prediction is
normalised to the number of events in data.(gif)(Postscript)
- Missing Et. The LO prediction is
normalised to the number of events in data.(gif)(Postscript)
- Tagged jet Et. The LO prediction is
normalised to the number of events in data.(gif)(Postscript)
- Systematic error table for photon + b and photon + c cross-sections (gif)

** Plots/ Tables (QCD)**

- Fits to data for the following photon Et bins:
- Fits to data with b contribution overlaid for the following photon Et bins:
- Photon + b cross-section. The data are compared to LO (CTEQ5L)
predictions. (gif)
(Postscript)
- Photon + c cross-section The data are compared to LO (CTEQ5L)
predictions. (gif)
(Postscript)
- Ratio of photon + c to photon + b cross-section The data are compared to LO (CTEQ5L)
predictions. (gif)
(Postscript)
- Systematic error table for photon + b cross-section. (gif)
- Systematic error table for photon + c cross-section (gif)
- Systematic error table for photon + c/ photon + b cross-section ratio (gif)

## 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 **

- Systematic errors + final result of exotics photon + b and photon + c cross-sections (gif)
- Systematic errors + final result of QCD photon + b cross-section (gif)
- Systematic errors + final result of QCD photon + c cross-section (gif)
- Plot of QCD photon + b cross-section (gif)
- Plot of QCD photon + c cross-section (gif)

## Contacts

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