Charmed Particle Photoproduction and a Search for .The charmed quark, the fourth heaviest quark,

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  • Charmed Particle Photoproduction and a Search for Magnetic Monopoles

    Michael Koratzinos

    Imperial College

    London

    A thesis submitted to the University of London

    for the degree of Doctor of Philosophy.

    January 1991

  • Abstract

    A sea rch f o r M a g n e tic M o n o p o le s : A large superconductive detector for cosmic magnetic monopoles has been designed, tested and has collected data for a year. It incorporates three coils, one of which has a novel configuration that maximises the sensitive volume but responds with a non-unique signal to a monopole.

    The effective area of the detector is 0.18m2 and the effective observation time 6600 hours. One event has been seen that is consistent with a monopole passage and cannot be attributed to an extraneous cause. This event was registered in the coil with the poorer signal discrimination. The monopole flux implied from this single event (equal to 7.2x 10~ 12cm ~ 2s ~ 1s r ~ l) is three orders of magnitude higher than the Parker Bound.

    M e a su re m e n t o f ch a rm e d p a r t ic le p h o to p ro d u c tio n : An investigation of charmed particle photoproduction is presented. Data are taken from NA14/2, a high energy photo- production experiment at CERN, that has collected 17 million triggers during the period 1985-86 at a mean photon energy of 95GeV. High statistics charmed signals have been extracted, with the high resolution silicon vertex detector that was incorporated into the NA14 spectrometer playing an important role.

    The channels investigated are D -*-Kn and D + - * K n n . The results presented are from 4.3 million triggers directly processed through a 3081/E emulator farm. The values measured for the contributions to the charmed photoproduction cross section over the energy range 40160 GeV are:

  • Introduction

    This thesis covers two independent topics in the field of High Energy Physics, spanning over six

    years of work in the field. These two topics are presented in chronological order: Part 1 deals with a

    Monopole Detector experiment situated at the Blackett Laboratory, Imperial College, London, over

    the period 1983-85. Part 2 refers to a Photoproduction experiment named NA14/2 situated at CERN,

    the European Centre for Particle Physics, in Geneva, that has collected data in the period 1985-86.

    A search for magnetic monopoles

    The publication of a candidate monopole event by an experiment at Stanford in 1982 stimulated

    intense experimental and theoretical activity in the field of magnetic monopoles. Grand Unification

    theories had already suggested that massive magnetic monopoles ( mass of & lQ 16G e V ) were created in

    the very early stages of the universe, but astronomical observations limited their present flux to very

    low, almost undetectable, values.

    A number of groups around the world were set to repeat the original Stanford experiment with

    much larger sensitive areas, and the Imperial College group was one of them. This part of the thesis

    describes the design, testing, data collection and analysis for the Imperial College monopole detector.

    A review of monopole theory is also included.

    A measurement of charmed particle photoproduction

    The charmed quark, the fourth heaviest quark, has been known for some time now (it was dis

    covered in 1974). However, the physics of charmed particles is far from fully exploited to date.

    NA14/2 is one of the experiments set to exploit charm physics. It is a fixed target experiment situated

    in the North Area of CERN utilising a photon beam for the charmed particle creation. The photon

    vii

  • beam is derived from the proton beam of the Super Proton Synchrotron (SPS) an underground

    accelerator of 8km circumference at CERN. Charm photoproduction has the advantage of being

    quite simple in the framework of QCD and therefore it allows QCD predictions to be tested with

    experimental data.

    In this part of the thesis we discuss the analysis leading to a measurement of total charm particle

    photoproduction cross section. The theory of charm photoproduction is also presented together with

    a detailed description of the experiment (in both hardware and software levels).

    Authors contribution

    This thesis covers a wide range of topics, containing the contributions of numerous people.

    Whenever possible, these contributions are acknowledged by referencing the original publication. The

    specific contribution of the author in this work includes: The formalization of the superconducting

    monopole detector theory; some work in the data acquisition system and the signal analysis of the

    Imperial College monopole detector; the Monte Carlo simulation for the above detector; the 3081/E

    emulator project of NA14/2; the tagging simulation; and, finally, the analysis leading to the measure

    ment of the charmed particle photoproduction cross section.

    vin

  • Contents

    Abstract .......................................................................................................................................................... vi

    Introduction ............................................................................................................................................... viiA search for magnetic monopoles .................................................................................................. viiA measurement of charmed particle photoproduction................................................................. vii

    Part 1: A S e a r c h f o r M a g n e t i c M o n o p o i e s ................................................. 2

    1 MAGNETIC MONOPOLES - INTRODUCTION . . ............................................................... 31.1 On the monopole nature ..................................................................................................... 3

    1.1.1 Monopoles and Grand Unified T heories............................................................... 31.2 Cosmology ............................................................................................................................ 5

    1.2.1 The Kibble process .................................................................................................. 51.2.2 Thermal monopole production............................................................................... 8

    1.3 Monopole abundance........................................................................................................... 81.3.1 Cosmic monopole abundance.................................................................................. 81.3.2 Monopole capture by astronomical ob jects.............................. 9

    1.4 Monopole velocities........................................................................................................... 101.5 Flux lim its............................................................................................................................ 11

    1.5.1 Mass contribution lim its......................................................................................... 121.5.2 Monopoles and astrophysical magnetic field s...................................................... 131.5.3 Monopole nucleon decay catalysis........................................................................ 16

    1.6 Motivation for monopole search...................................................................................... 182 MONOPOLE DETECTORS....................................................................................................... 19

    2.1 Inductive detectors.............................................................................................................. 202.2 Superconducting detectors ................................................................................................ 22

    3 THEORY OF THE SUPERCONDUCTING DETECTOR................................................. 263.1 Single superconducting lo o p .............................................................................................. 263.2 The astatic asymmetric pair ............................................................................................... 293.3 The window frame configuration .................................................................................... 31

    4 THE IMPERIAL COLLEGE MONOPOLE DETECTOR................................................... 344.1 General outlook.................................................................................................................. 344.2 Cryostat .............................................................................................................................. 364.3 Magnetic and radio frequency (RF) shielding................................................................. 37

    4.3.1 mu-metal shields ..................................................................................................... 374.3.2 Superconducting shield ........................................................................................... 394.3.3 RF shielding ........................................................................................................... 39

    4.4 Detector framework........................................................................................................... 394.5 Detector coils ..................................................................................................................... 414.6 SQ U ID s.............................................................................................................................. 414.7 Calibrati