Deuterons in Photoproduction at HERA Erik Strahler University

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

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. E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 2

Cuts Online: Offline: • Ntrkvtx r 5 • PT r 150 Me. V • -1. 75 < h < 1. 75 • Reject real electrons probability > 90% AND energy > 5 Ge. V AND yel < 0. 8 • |Zvtx| < 30 cm • 165 < Wjb < 252 Ge. V (from ZUFOS) • r 5 primary vertex tracks • > 40 CTD hits (stereo + axial) • > 5 hit superlayers E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 3

d. E/dx plotted against track momentum Clear bands corresponding to p, K, p, and d Create preliminary curves to roughly separate the particle bands E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 4

Mean Particle Curves • Want to fit a curve to each particle band • Split d. E/dx vs. p into 15 momentum slices • Plot d. E/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. E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 5

Mean Particle Curves … • Plot Gaussian fit means vs. center of momentum bins • Fit with parameterization of the Bethe-Bloch formula d. E/dx = C 0 / p 2 +C 1 • deuteron statistics are not high enough for real particle identification • proton statistics are quite good, so we’ll use them to get the cut E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 6

# 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 E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 7

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 d. E/dx > 1. 8 mips to eliminate p, K background. E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 8

Results 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. E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 9

Results… Antideuterons: 1998: dbar/pbar = 0. 0017 pbar/total = 0. 0055 1998+2000: dbar/pbar = 0. 0017 pbar/total = 0. 0054 Once again, uncut proton contamination. Good agreement E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 10

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 H 1. This could be due to lack of full background studies. • Further work is called for! E. Strahler, U. Wisconsin, Deuterons in Photoproduction, Summer 2004 Report August 5, 2004 - 11