Techniques and Concepts of High-Energy Physics IV

593 Pages·1988·26.404 MB·English

by  I. Hinchliffe (auth.), Thomas Ferbel (eds.)

Techniques and Concepts
of High-Energy
Physics IV
NA TO ASI Series
Advanced Science Institutes Series
A series presenting the results of activities sponsored by the NATO Science Committee,
which aims at the dissemination of advanced scientific and technological knowledge,
with a view to strengthening links between scientific communities.
The series is published by an international board of publishers in conjunction with the
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A Life Sciences Plenum Publishing Corporation
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and Physical Sciences Dordrecht, Boston, and Lancaster
D Behavioral and Social Sciences Martinus Nijhoff Publishers
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Materials Sciences
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H Cell Biology Paris, and Tokyo
Recent Volumes in this Series
Volume 159-Lattice Gauge Theory '86
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Volume 160-Super Field Theories
edited by H. C. Lee, V. Elias, G. Kunstatter, R. B. Mann,
and K. S. Viswanathan
Volume 161-Quantum Measurement and Chaos
edited by E. R. Pike and Sarben Sarkar
Volume 162-<.!uantum Uncertainties: Recent and Future Experiments
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edited by William M. Honig, David W. Kraft, and Emilio Panarella
Volume 163-Thin Film Growth Techniques for Low-Dimensional Structures
edited by R. F. C. Farrow, S. S. P. Parkin, P. J. Dobson,
J. H. Neave, and A. S. Arrott
Volume 164-Techniques and Concepts of High-Energy Physics IV
edited by Thomas Ferbel
Volume 165-Relativistic Channeling
edited by R. Carrigan and J. Ellison
Series B: Physics
Techniques and Concepts
of High-Energy
Physics IV
Edited by
Thomas Ferbel
University of Rochester
Rochester, New York
Plenum Press
New York and London
Published in cooperation with NATO Scientific Affairs Division
Proceedings of a NATO Advaneed Study Institute on
Techniques and Coneepts of High-Energy Physies,
held June 19-30, 1986,
in St. Croix, U.S. Virgin Islands
Library of Congress Cataloging in Publieation Data
NATO Advaneed Study Institute on Teehniques and Coneepts of High-Energy
Physies (4th: 1986: Christiansted, V. 1.)
TeChniques and concepts of high-energy physics IV I edited by Thomas
Ferbel.
p. em.-(NATO ASI series. Series B, Physies; v. 164)
"Proeeedings of NATO Advaneed Study Institute on Teehniques and Con
eepts of High-Energy Physies, held June 19-30, 1986, in St. Croix, U.S. Virgin
Islands"-T.p. verso.
"Published in eooperation with NATO Seientifie Affairs Division."
Ineludes bibliographieal referenees and index.
ISBN 978-1-4684-5403-1 ISBN 978-1-4684-5401-7 (eBook)
DOI 10.1007/978-1-4684-5401-7
1. Partieles (Nuelear physies)-Congresses. I. Ferbel, Thomas. 11. North
Atlantie Treaty Organization. Seientifie Affairs Division. 111. Title. IV. Series.
QC793.N38 1986
539.7/21-de19 87-21293
CIP
© 1987 Plenum Press, New York
Softcover reprint of the hardcover 1s t edition 1987
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PREFACE
The fourth Advanced Study Institute (ASI) on Techniques and
Concepts of High Energy Physics was held once again at the Hotel on
the Cay, in the scenic harbor of Christiansted, St. Croix, U.S. Virgin
Islands. The ASI brought together a total of 67 participants, from 17
different countries. It was a great success, due to the dedication of
the inspiring lecturers, the exceptional student body, and, of course,
the beautiful setting.
The primary support for the meeting was again provided by the
Scientific Affairs Division of NATO. The ASI was cosponsored by the
U.S. Department of Energy, by Fermilab, by the National Science
Foundation, and by the University of Rochester. A special contri
bution from the Oliver S. and Jennie R. Donaldson Charitable Trust
provided an important degree of flexibility, as well as· support for
worthy students from developing nations.
As in the case of the previous ASI's, the'scientific program was
designed for advanced graduate students and recent PhD recipients in
experimental particle physics. The present volume of lectures should
complement the material published in the first three ASI's, and prove
to be of value to a wider audience of physicists.
It is a pleasure to acknowledge the encouragement and support
that I have continued to receive from colleagues and friends in
organizing this meeting. I am indebted to the members of my Advisory
Committee for their infinite patience and excellent advice. I am
grateful to my distinguished lecturers for participating in the ASI.
I thank John Bythel of the West Indies Lab for providing us with a
description of the geology and marine life of St. Croix, and Albert
Lang for talking him into it. I thank Melissa Franklin for organizing
the student presentations. I also wish to thank Earle Fowler, Bernard
Hildebrand and Bill Wallenmeyer for support from the Department of
Energy, and David Berley for the assistance from the National Science
Foundation. I thank Leon Lederman for providing me with access to the
talents of Angela Gonzales at Fermilab. At Rochester, I am indebted
to Judy Mack, Sal Spinnichia, and especially Connie Jones, for organi
zational assistance and typing. I owe thanks to Shirley and Ray
Boudreau and to Hurchell Greenaway, the managers of the facilities at
the Hotel on the Cay, for their and their staffs' hospitality. I wish
to acknowledge the generosity of Chris Lirakis and of Mrs. Marjorie
Atwood of the Donaldson Trust. Finally, I thank Dr. Craig Sinclair of
NATO for his continuing cooperation and confidence.
T. Ferbel
Rochester, New York
May 1987
v
CONTENTS
Old Physics, New Physics and Colliders .••••••••••• 1
I. Hinchliffe
An Introduction to String Theory • • • . • • • • • • • • • • • 59
D. Gross
Experimental Puzzles Beyond the Standard Model • • • • • • . • 105
A. Savoy-Navarro
Physics at the CERN pp Collider and Status of the
Electroweak Theory • • • • • • • • • • • • 205
L. DiLella
Weak Decays of Heavy Quarks. • • • • • . • • • • • • • • • • • 275
D. Hitlin
HERA: Physics, Machine and Experiments •••••••••••• 375
G. Wolf
Principles and Construction of Linear Col1iders. • • • • • • • 451
J. Rees
Vertex Detectors 475
C. Damerell
Participants • • • • • • • . • • • • • • • • • • • . • • • • • 587
Lecturers and Advisory Committee • . . • • • . . • • • . . • . 589
Index. • • • • • • . . • . • • • • • • • • . • • • • • • • • . 591
vii
OLD PHYSICS, NEW PHYSICS AND COLLIDERS
I. Hinchliffe
Lawrence Berkeley Laboratory
University of California
Berkeley, California 94720
Introduction
In these lectures, I shall discuss some topics in the standard model of strong and
electroweak interactions and shall then point out some problems in this model and
indicate how these problems are attacked in some theoretical models. I shall begin
with a discussion of radiative corrections in the Glashow-Weinberg-Salam model,!
stressing how these corrections may be measured at LEP and the SLC. I shall then
discuss some features of QCD which are relevant to hadron colliders. This discussion
will complement the lectures of Luigi DiLella,2 who has shown impressive evidence
from the CERN SppS collider for the correctness of QCD. In my discussion of the
unsolved problems of the standard model I shall not discuss supersymmetric theories
since their· theoretical aspects and phenomenological consequences are discussed by
other lecturers at this schoo1.3 I shall however, discuss some aspects of models in
which quarks and leptons are composite particles.
1. Testing the Weinberg-Salam model.
The Lagrangian describing the weak and electromagnetic interactions of the quarks
and leptons is given by!
.c = -! P.. FIW - ! G GIW
4IW G 41W
+ i'fLi'Y"'D,.."pLi (1.1)
+ JJ.a(~+~) - .A(~+~)2
+ + +
.A"klL,k~eR,k .Auk!qL,k~+UR,1 .AdklqL,k~dR,1
where
and
are the field strength tensors for the three gauge bosons of SU(2)L (W:) and U(I) (BJ.L),
which have coupling constants 92 and 91. The indices on the fermion fields are gen
eration indices which take values in the range (1,2,3).
The left-handed fermions appear in SU(2)L doublets
~iL: lL = ~(1 -'s) ( : ), qL = ~(1 -'s) ( ~ )
which have U(I) charges -1, and 1/3. The right-handed fermions appear as SU(2)L
singlets
1 1 1
~iR : eR = -(1 + Is)e, UR = -(1 + 15)u, dR = -(1 + 15)d
2 2 2
with U(I) charges -2, 4/3 and -2/3, respectively. This pattern is, of course, repli
cated for the second and thirq generations which contain the 11 and T leptons and
the strange, charm, top and bottom quarks. The Higgs doublet cP has U(I) charge
-1. The covariant derivatives DJ.L are given by
DJ.L = (8J.L -i9 T'W: -i91~BJ.L).
2
Here y is the U(I) charge of the representation on which DJ.L acts. For an SU(2)
doublet T4 = T4/2, where T4 is a Pauli matrix, while for an SU(2) singlet, T = o.
This Lagrangian contains seventeen parameters. There are two gauge coupling
constants 92 and 91 describing the interactions of the SU(2) and U(I) gauge theo
ries. Two parameters 11 and >. determine the Higgs mass and the interactions of the
Higgs field with itself. The remaining parameters are the quark and lepton Yukawa
couplings >'i. Let us examine the spectrum of physical states in the model.
For 112 > 0 the ground state of the theory is given when the Higgs field cp has a
non-zero vacuum expectation value (VEV):
(1.2)
with v = (112/>.)1/2. This non-zero VEV results in a mass for three of the four gauge
bosons. The charged gauge bosons of SU(2)L have mass
(1.3)
There is a massless neutral gauge boson, the photon,
AJ.L = sinOwW; - sinOwBJ.L
and a massive boson
+
with mass M~ = V2(9~ 9~)/4. Here the weak mixing angle Ow is given by
tan Ow = 91. (1.4)
92
2
Table 1: Couplings of physical particles in the Weinberg-Salam model (uni
tary gauge). I is a fermion of charge Qf and weak isospin Ts (= + 1 for u,
c, t quarks and neutrinos, -1 otherwise).
g2 -
WI! 20
Wl'h"(l -15)1
Zf! 2 sm. ew e cos ew Z"fJ"(Vf -+ af/5)1
Vf = Ts - 4Qsin2 Ow
Af = T3
HWW y2Mw HW:W;
HZZ
HI!
The electric charge of the electron is given by e = 92 sin Ow. The non-zero value of 11
results in lepton masses
(1.5)
The quark masses are more complicated since weak interactions allow transitions
+
between different generations, i.e., S -t U W-. The Yukawa interactions of the up
quarks can be chosen to be diagonal, i.e.,
The masses of the charge 2/3 quarks are then given by
11
mu; = .Au; 0' (1.6)
The down quark mass matrix contains seven parameters which are the masses of
the d, s and b quarks and the four angles of the Kobayashi-Maskawa mixing matrix.
The final parameter is the Higgs mass mH = ~ tnw /92' The theory has a large
number of parameters but is able to describe a wealth of experimental data. The
most important parameters are v, 91 and 92 which control the strength of weak and
electromagnetic interactions. Most experimental tests of the model do not depend
upon quark or lepton masses (or alternatively, on the quark and lepton Yukawa
couplings) so that experimental success is more remarkable.
The W and Z bosons couple to quarks, leptons and the remaining physical Higgs
boson H with interactions shown in Table 1.
I have so far discussed the model at the tree level, i.e., to lowest order in the
coupling constants 91 and 92. Before discussing tests of the theory, it is worth noting
the approximate size of the radiative corrections which can be expected. These cor
=
rections will depend upon the fine coupling constant a e2/(471"). In addition, tests
will be made over a large range of momenta. Momentum transfers can be very small
(for example, in Thompson scattering) or very high (for example, the production of a
Z or W boson). The gauge interactions produce effects which depend logarithmically
3
on these scales. Hence an order of magnitude estimate of radiative corrections will
give aI7l'Idg(Ma./m~). This is of order 5%. Some experiments are already sensitive
to corrections of this size; experiments at the ZO resonance performed at LEp4 or
the SLC5 will be more sensitive so it is important to discuss radiative corrections in
some detail.
I will begin with the radiative corrections in Quantum Electrodynamics. Consider
the scattering of two charged partitles of mass M, at momentum transfer Q. To lowest
order in a, this scattering is described by the exchange of a single photon (Fig. 1a).
If the theory contains a particle of mass me, the effect of this particle can appear at
next order in perturbation theory via the graph of Fig. lb. The relevant Feynman
diagram is the one-loop correction to the photon self energy shown in Fig. 2. This
graph is given by
(1.7)
This integral is divergent; we can regulate it by performing the loop integral in n
dimensions, i.e. by making the replacement6
(a) (b)
Figure 1: (a) Feynman diagram showing a contribution to the scattering
of two charged particles in QED; (b) A higher order contribu
tion.
f
1
Figure 2: A contribution to the photon self energy at one loop due to a
charged fermion of mass me.
4