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Deuterons in Photoproduction at HERA: Summer Project Report

This report by Erik Strahler from University of Wisconsin in 2004 outlines a study on deuteron and anti-deuteron production in photoproduction at HERA. The report covers topics such as cuts, mean particle curves, sigmas, and results obtained. The study aimed to analyze deuteron production mechanisms through inclusive photoproduction samples and data analysis techniques. Initial cuts were applied to the data, and mean particle curves were plotted to identify deuteron signals. Results indicated possible deuteron excess in the 2000 data compared to 1998 data, with good agreement in anti-deuteron measurements. Conclusion suggests further work for accurate deuteron cross-section determination.

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Deuterons in Photoproduction at HERA: Summer Project Report

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  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 • 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.

  3. 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

  4. 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

  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. 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 …

  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. 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

  9. 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

  10. 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…

  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 = 0.0017 is about twice that measured by H1. This could be due to lack of full background studies. • Further work is called for!

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