Photon Photon Collisions: Proceedings of the Fifth International Workshop on Photon Photon Collisions held at the Rheinisch Westfälische Technische Hochschule Aachen, April 13–16,1983

422 Pages·1983·5.272 MB·English

by  R. D. Field (auth.), Ch. Berger (eds.)

Lecture setoN
in scisyhP
detidE by .H Araki, ,otoyK J. Ehlers, ,nehcnOM K. ,ppeH Ziirich
.R ,nhahneppiK ,nehcnitM .H A. Weidenmiiller, grebledieH
dna J. Zittartz, K6ln
191
notohP notohP Collisions
Proceedings of the Fifth International Workshop
on Photon Photon Collisions
held at the Rheinisch-Westftilische Technische
Hochschule Aachen, April 13-16,1983
Edited by Ch. Berger
Springer-Verlag
Berlin grebledieH New York oykoT 3891
Editor
Ch. regreB
I. Physikalisches lnstitut red
Rheinisch-WestMischen Technischen Hochschule Aachen
SommerfeldstraBe, D-5100 Aachen 1
ISBN O-19621-045-3 galreV-regnirpS nilreB Heidelberg New YorkTokyo
ISBN O-19621-783-0 galreV-regnirpS New York Heidelberg nilreB Tokyo
This krow is subject to copyright, All rights are ,devreser whether the whole ro part of the material
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Preface
ehT fifth International Workshop on Photon Photon Collisions saw held at Aachen
from 31 to 61 April 1983. Continuing a tradition started only two years oga at the
Paris Conference ew had, besides the plenary talks, experimental and theoretical
parallel sessions. These discussion sessions proved to eb a remarkable success.
'Two Photon Physics' plays na important role in testing quantum chromodynamics,
our candidate theory of strong interactions. A large amount of wen data sah been
presented at the workshop dna many bothersome theoretical problems are won more
thoroughly understood. I hope that this continuous experimental dna theoretical
effort leads to a deeper understanding of the underlying strong interaction dy-
namics.
ehT Aachen Conference saw financially supported by the namreG Federal Government
and by the State of Nordrhein Westfalen. ehT administrational, technical, and fi-
nancial support by the Technische Hochschule Aachen dna especially the I. Physika-
lisches Institut is gratefully acknowledged. I have also to thank the srebmem of
the International Advisory Committee for their work in preparing the conference.
Last but not least, I want to express ym gratitude to the speakers for their
excellent talks.
.hC Berger
July 30, 1983
International Advisory eettimmoC
.A Barbiellini, ,NREC Switzerland
.hC Berger, Aachen, ynamreG
S.J. Brodsky, ,CALS ASU
.E Gabathuler, ,NREC Switzerland
.P Kessler, Paris, France
.P Landshoff, Cambridge, England
.K LUbelsmeyer, Aachen, ynamreG
J.C. Sense, ,FEHKIN Netherlands
.P S~ding, ,YSED ynamreG
R.J. ,reyemedeW Bonn, ynamreG
STNETNOC
Session I (Chairman: K. LUbelsmeyer, Aachen)
R.D. Field: Photon Production in Hadron-Hadron Collisions .. ..................... I
Session II (Chairman: U. Timm, )YSED
J.E. Olsson: Resonance Production in ~ Reactions ............................... 45
F.M. Renard: Resonance Production in ~y Collisions .............................. 74
Session III (Chairman: P. Kessler, Paris)
R. Petronzio: Status of DCQ ..................................................... 101
N. Wermes: Jet Production and High TP Phenomena in Photon-Photon Reactions ...... 911
Session IV (Chairman: P. S~ding, )YSED
W.J. Stirling: Hard Hadronic Final States in owT Photon Processes ............... 241
.H Kolanoski: Hadronic Final States in Soft Photon-Photon Scattering ............ 571
Session V (Chairman: .W Bardeen, Fermilab)
.W Wagner: Total Cross Sections and Photon Structure Functions .................. 206
.M Pohl: DEQ Processes in owT Photon Reactions .................................. 234
Session VI (Chairman: A. Donnachie, Manchester)
D.W. Duke: A Theoretical Review of the Photon Structure Function ................ 152
J.H. Field: yy and e~ Collisions at Future High Energy Colliders ................ 270
Session VII (Chairman: R.J. Wedemeyer, Bonn)
.H Spitzer: Summary of the Experimental Discussion Session ...................... 318
D.M. Scott: Summary of Theory Parallel Sessions ................................. 358
Session VIII (Chairman: S.J. Brodsky, CALS
W.R. Frazer: Two-Photon Physics, 1983: Summary .................................. 377
Experimental Session (Abstracts) ................................................ 397
Theoretical Session (Abstracts) ................................................. 408
List of Participants ............................................................ 415
Photon-Photon Production in Hadron-Hadron Collisions *t
R. .D Field
Particle Theory Group, Department of Physics,
University of Florida, Gainesville, FL 32611
May 1983
ABSTRACT
Quantum Chromodynamic (QCD) estimates are made for the large transverse
momentum production of single and double photons in pp, ,p--p and ~p
collisions. In addition to the pure QED annihilation term q~ ÷ yy, it is
found that the QCD induced gluon-gluon subprocess gg ÷ ,yy is an important
source of double photons. Photon Bremsstrahlung contributions are also
examined.
*Invited talk presented at the 5th International Workshop on Photon-Photon
Collisions, 13-16 April 1983, Aachen, Germany.
tWork supported by the U.S. Department of Energy under contract No. DE-AS-05-
81-ER40008.
Usually at a topical conference on a specific subject at least one
speaker is asked to discuss related topics. Here I will examine the subject
of photon-photon production at this workshop on photon-photon collisions.
Fig. 1(a) shows the dominate Born constituent subprocess, yy÷qq, for the
+ - + -
reaction e e ÷e e +hadrons. The inverse process, qq+yy, shown in Fig. l(b)
results in photon-photon production in hadron-hadron collisions. The QED
annihilation term, qq÷yy, together with the 0CD induced gluon-gluon
subprocess, gg÷yy, are the major sources of double photons at large PT and
produce quite spectacular events in which a large PT proton on one side is
balanced by another photon on the "away-side" with roughly the same transverse
momentum. I present here estimates made by E. Berger, E. Braaten, and myself
I on single and double photons in ~p, pp, and p--p collisions 2. Although
the rates for the production of two photons is small, experimental study of
the systematics of these processes will provide valuable information on the
size of the strong interaction coupling constant, ~s(0), and on the charge of
the quark 3. Also, knowledge of the gluon distributions within hadrons and
of the effective transverse momentum of partons in the hadrons can be gained.
Let us begin our examination of photon-photon production by considering
the production of single and double photons in ~ p collisions. Except for
couplings and color factors the differential cross section for q~÷yy is
identical to that for qq÷yg. The ratio is given by
^ ^
do/dt(q~÷yy) 3 ( em 2
eq, (i)
^ ^ = -- )
do/dt(qq÷yg) 4 ~s
where eq is the quark charge. If we are naive and assume that single and
double photons are produced solely by these annihilation subprocesses and
further consider only valance quarks then we arrive at several interesting
)a( Photon- Photon Collisions"
~
e +
e +
>
q
>
-e
e-
(b) Photon- Photon Production"
\ >
m P / ,~" >
J >
P
>
Fig. .i (a) Born term for the production of quark jets from the collision of
+ - +
two photons in the reaction e e ÷e e qq. (b) Born term for the production of
two photons by quark-antiquark annihilation in hadron-hadron collisions.
predictions. For ~-p collisions we arrive at
a
Edo/d3p(~-p÷Ty+X) 3 aem~ 2 i (~),
(2a)
Edo/d3p(-p÷y+X) = ~ e.---~-. u iff
s s
where I have only included the subprocesses yy+u--u and~u÷yg. Similarly the
subprocesses yy÷d--d and dd÷Tg yield
Edo/d3p(~+p÷yy+X) 3 aem~ 2 1 )m_~_~(
(2b)
Edo/d3p(+p÷y+X) = ~ -a s " ed = ~-"1 s
for ~+p collisions. The added approximation that there are twice as many u
quarks than d quarks within the proton gives
Edo/d3p(~+p÷y+X) 1 fed2 1
(3a)
Ed~/d3p(~-p÷y+X) = ~ u'--e" iff '~-
and
Ed~/d3p(~+p÷yy+X) 1
(3b)
Ed~/d3p(-p÷yy+X) 2 ( u )2 I
Our naive reasoning leads to a ~ beam that is 32 times more efficient at
producing double photons and 8 times more efficient at producing single
+
photons than a ~ beam. Furthermore, we see from (2) that, in this
approximation, the double to single photon ratio provides a direct measure of
the strong interaction coupling constant, as, and that one expects this ratio
+
to be about 0.01 for ~-p collisions and 4 times smaller for ~ p collisions
(with a ~ 0.25). This would mean that for ~-p collisions one would expect
s
that, on the average, one out of every i00 large PT photon triggers are
balanced on the "away-side" by a photon of roughly the same PT" If there were
Ratios
0.1
3 5 ( 1 ~
I I I I I I
Ok 4.0 5.0 6.0 7.0 80 9.0 I0.0
TP )VeG(
Fig. .2 Beam ratios dna double ot single photon ratios ni p~ collisions ta
W=27.4 VeG dna el=90°: (~+/=-)p÷yl+x (solid dots); (~+/~-)p÷yiY2+X (solid
squares); ~-p÷(YIY2/YI)+X pu( pointing triangles); ~+p÷(YiY2/Yl)+X (down
pointing triangles). Also shown era eht naive estimates fo )2( dna :)3(
3 2
l (ed/eu)2 (dashed line); ~ 3 (=em/% ~e) (dot-dashed line); ~ (~em/~s)ed
(dotted line).