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A Study of Leading Neutrons i11 yp Collisions at HERA

by

Milos Brkic

A thesis submitted in conformity with the requirements

for the degree of Doctm· of Philosophy

Graduate Department of Physics

University of Toronto

Copyright© 1996 by Milos Brkic

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A Study of Leading Neutrons in yp Collisions at HERA

Ph. D. thesis I 996

by Milos Brkic

Graduate Department of Physics

University of Toronto

Abstract

High energy (£>·WO GeV) leading neutrons were obserYcd for the first time in electron-proton

(ep 1 co]isions. in the data co!lcctcd in 1993 with the ZEUS detector at the HERA collider. This

\Va~. done using the test Forwa:d Neutron Calorimeter I FNC). In this thesis. first. the ZEUS detec­

tor setup is described. including a detailed description of the FNC. its in-situ calibration and the

determination of its acceptanc1!.

At an cp collidcr photon-proton physics (photoproduction) can also be studied using the •ilmost

rea! ph<Hons emitted by the electron beam. \V!th the FNC. leading neutron physics \Vas studied

using the ZEUS photoproduction data sample. at an average yp center of mass energy of 180 GcV.

The ltr-a results arc presented here. including the inclusive neutron spectrum. The characteristics

of evcr:.ts containing such leading neutrons in photoproduction are discussed and compared to the

overall photoproduction sample. Tl1c One Pion Exchange model from hadron-hadron collisions

was found to be consistent with the presented data. The total photon-pion cross section was mea­

sured using the FNC to tag <!n almost real pion beam. It was found to be

cryrc (90 GeV) = 92 ± 5 (stat.)± 28 (syst.) µb.

The inclusive transverse momentum (pT) distributions of charged particles in photoproduction

are also presented for non-diffractive events, the diffractive events in two bins of the diffracting

mass, as well as for the non-diffractive leading neutron tagged events. The results are discussed

and compared to the previous photoproduction and hadron-hadron data.

ii

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.. Biting into a sweetfruir. 1i-e should remember H·irlz gnzt­

iwde those u-Jzo planted the tree. "

Vietnamese proverb

Acknowledgments ~

Fram the inexhaustible list of people I should thank. l ..:an only mention a ft'w. Thus1..· l may

not mention have in no \vay helped less. Throu!!hout my studies the help ..:ame at two levds. Both

should be acknowledged equally. Some of those I thank for helping immensely with the wnrk its.!lf

include:

• My supervisor and mentor John F. Martin whose patiern.:e. understanding, and ad\'ice was great­ly appreciated. With his numerous suggestions upon reading the drafts he made this thesis a bet­ter and more complete work. I also thank him for allowing mt: tht: freedom to find my own place within the ZEUS collage.

• Garry Levman to whom I am indebted for pointing me to Uc intt:resting suhjt:ct. as wdl as his uncountable advice.

• Doug Stairs for great cnmments in the time of nc:ed.

• All the members of the :-NC group. Special th.mks go to K;:ith Furutani for the eountkss hums in the rucksack and many a late night discussion and Sampa Bhadra for her constant enthusiasm and moral support.

• The CAL group, including: 'f atsu Tsurugai, Luis Hcrvas. Andres Kruse. Alan Caldwell. Steve Ritz, Uli Kotz and many others without whom the FNC would never have heen read out.

• Bill Frisken, Doug Hasell, Gavin Stairs. Tony Kiang. Helen Fawcett. Cathy Farrow and all the others who joined the efforts at the Markham calorimeter construction site.

• All the members of the ZEUS collaboration and especially - Robert Klanner, Bernd Lohr. and Peppe Iacobucci for their leadership and invaluable comments in my physics group.

• Yosilihisa Iga for his implementation of the FNC into MOZART.

• Johannes Mainusch and Cortney Sampson for the photoproduction acceptances as well as nu­merous fruitful discussions.

• Michal Kasprzak for doing a great job on the pT analysis and for all his help in that area.

• Dave Gilkinson and the ZARAH gurus for easing the pain of massive computing.

• Burkhard Burow for trying to make me a ZEUS hero.

The other group deserving recognition provided support on a more private level. To hcgin

with it numbers all the members of the Canadian group at DESY, who were like family away from

home during my stay in Hamburg, Germany. The "immediate family" deserves a special mention.

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