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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
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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.
Online: Ntrkvtx r 5 PTr 150 MeV -1.75 < h < 1.75 Offline: 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 Cuts
dE/dx plotted against track momentum Clear bands corresponding to p, K, p, and d Create preliminary curves to roughly separate the particle bands dE/dx
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.
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 Mean Particle Curves …
# 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
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. Final Cuts
Deuterons: 1998: d/p = 0.023 p/total = 0.0057 1998+2000: d/p = 0.034 p/total = 0.0055 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: dbar/pbar = 0.0017 pbar/total = 0.0054 Good agreement Once again, uncut proton contamination. Results…
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!