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

Introduction Inclusive Photoproduction sample 1998 + 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.

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

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

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.

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

# 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

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.

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.

Results… Antideuterons: 1998: dbar/pbar = 0.0017 pbar/total = 0.0055 1998+2000: pbar/total = 0.0054 Good agreement Once again, uncut proton contamination.

Conclusion Only first step towards deuteron cross-section Need to consider whether background is present, and how to remove Measured value of dbar/pbar = 0.0017 is about twice that measured by H1. This could be due to lack of full background studies. Further work is called for!