1. Deuterons in Photoproduction at HERA
Erik Strahler, University of Wisconsin
2004 Summer Project Report
August 5, 2004
Outline:
Introduction
Cuts
dE/dx
Mean Particle Curves
Sigmas
Results
Conclusion

2. Introduction Inclusive Photoproduction sample
part of 2000 data (about 1/3)
~15.4 pb-1
Search for a deuteron (anti-deuteron) signal
Form of signal tells us about whether deuterons are produced by direct hadronization, or whether by a ‘gluing together’ process afterwards.

3. Cuts Online: Offline: Ntrkvtx r 5 PT r 150 MeV -1.75 < h < 1.75
Reject real electrons
probability > 90% AND
energy > 5 GeV AND
yel < 0.8
|Zvtx| < 30 cm
165 < Wjb < 252 GeV (from ZUFOS)
r 5 primary vertex tracks
> 40 CTD hits (stereo + axial)
> 5 hit superlayers

4. dE/dx dE/dx plotted against track momentum Clear bands corresponding
to p, K, p, and d
Create preliminary curves to roughly separate the particle bands

5. Mean Particle Curves Want to fit a curve to each particle band
Split dE/dx vs. p into 15 momentum slices
Plot dE/dx in each bin, and fit gaussians.
Large peak belongs to p (K are buried). Smaller peak in is protons.
In log scale you can see the small deuteron contribution.

6. Mean Particle Curves …
Plot Gaussian fit means vs. center of momentum bins
Fit with parameterization of the Bethe-Bloch formula
dE/dx = C0 / p2 +C1
deuteron statistics are not high enough for real particle identification
proton statistics are quite good, so we’ll use them to get the cut

7. # of sigmas cut Vary number of sigmas away from mean particle curve
y axis shows total number of tracks above mean curve minus number lying between mean curve and sigma curve n.
A place with little change between adjacent sigma curves is thus ideal for a cut

8. Final Cuts Above method used to determine upper cuts.
Start with 3 s curve and vary by trial and error to get a rough cut for the lower edge of proton band
Make universal cut of dE/dx > 1.8 mips to eliminate p, K background.

9. Results Deuterons: 1998: d/p = 0.023 p/total = 0.0057 1998+2000:
Possible deuteron excess in 2000 data
Circled area: remnants from the proton band that escaped the cut. A larger remnant could explain the 2000 excess.

10. Results… Antideuterons: 1998: dbar/pbar = 0.0017 pbar/total = 0.0055:
pbar/total =
Good agreement
Once again, uncut proton contamination.

11. Conclusion Only first step towards deuteron cross-section
Need to consider whether background is present, and how to remove
Measured value of dbar/pbar = is about twice that measured by H1. This could be due to lack of full background studies.
Further work is called for!