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HARD HADRON PHENOMENOLOGY
D. Scott
To cite this version:
D. Scott. HARD HADRON PHENOMENOLOGY. Journal de Physique Colloques, 1982, 43 (C3),
pp.C3-155-C3-157. �10.1051/jphyscol:1982335�. �jpa-00221888�
JOURNAL DE P H Y S I Q U E
CoZZoque
C3,suppl6ment au n o
12,Tome
43,dgcembre
1982page
C3-155HARD HADRON PHENOMENOLOGY
D.M. Scott
University of Cambridge, Department of Applied Mathematics and Theoretical Physics, S i l v e r Street, Cambridge, CB3 9EW, U.K.
1. D i r e c t photons.
-
High pT d i r e c t photon production can be understood i n terms of O(as) Q C D . ~ A c a l c u l a t i o n 2 u s i n g xG(x) = 3 ( 1 - ~ ) ~ i s compared t o ISR d a t a 3 i n f i g 1. The dominant mechanism a t high p ~ i s gq + yq: t h e t r i g g e r photon i s unaccompanied, and i t u s u a l l y r e c o i l s a g a i n s t a u-quark. A t v e r y high p ~ bremsstrahlung mechanisms, e . g. qq -t qqy, may be important4, g i v i n g photonsaccompanied by a hadron j e t . There i s a h i n t of t h i s i n t h e data5: a t p ~ = 12 GeV
YA/Yu = T ~ / K E ,
(U)A = (un)accompanied, and s u r e l y Tg/TE i s n o t small.The
K "
2.4 f a c t o r i n Drell-Yan i s w e l l known.' The corresponding n e x t o r d e rc o r r e c t i o n t o gq + Yq h a s n o t been c a l c u l a t e d . An e s t i m a t e u s i n g s o f t gluons gives6 Ky = 1 + 5Tas/6, allowing a s o f t e r G ( x ) . The measured c r o s s s e c t i o n 7 f o r T+N -t YX a t /s = 19.4 GeV i s a f a c t o r - 1 0 h i g h e r t h a n t h e O(Cts) c a l c u l a t i o n 8 (which uses qq + yg t o o ) . Enhancements from
Ky
and from i n t r i n s i c kT smearing may be i m p o r t a n t , a s i nQCD
e x p l a n a t i o n s 9 of e a r l y Fermilab d a t a l o .Sack-to-back y'y a l l o w s f u r t h e r F D t e s t s , ''1 l2 The mechanism gg -t y'y through a quark box can be comparable t o qq -f
yy.
2. TN +
~+!J-x. -
Using quark d i s t r i b u t i o n s from D Y ' ~ , we can c a l c u l a t e t h e p ~ d i s t r i b u t i o n o f high mass p a i r s . The r e s u l t i s f a r below t h e data13. Smearing w i t h <Kg> = 1 Gev2 and u s i n g a high p ~ f a c t o r K t 2K
g i v e s agreement: s e e f i g . 2.K'
h a s been c a l c u l a t e d e x a c t l y : l5 f i g . 3. A s o f t gluon estimate16 g i v e sK'
= 1+
2raS/3 = K. Multigluon e f f e c t s may be important1'.3. High
-
A t y p i c a l p r o c e s s mY +y * ~
a t high p ~ is shown i n f i g . 4.I t i s normalised by fR. Nothing goes i n t h e d i r e c t i o n of t h e i n c i d e n t T . A sample r e s u l t 2 1 is shown i n f i g . 5.
4. ~ l u l t i g l u o n s .
-
The W ' s pT d i s t r i b u t i o n i npp
can be c a l c u l a t e d 2 3 u s i n g multigluon emission. The r e s u l t i n g s i n g l e l e p t o n spectrum from W -t %V i s compared t o t h a t from DY (p! = 0) i n f i g . 6. Multigluons a l s o provide e x t r a hadronic t r a n s v e r s e energy i n Z O e v e n t s . 2 35.
GAG JET.'^ -
This i s a new Monte-Carlo, not based on QCD. I t can d e s c r i b e momentum and t h r e e j e t d i s t r i b u t i o n s i n e+e- a n n i h i l a t i o n .6 . pp e l a s t i c s c a t t e r i n g . A s t h e r e a r e t o o many diagrams i n QCD f o r pp + a t high t , i t has been suggesteda5 t h a t we should r e v e r t t o a Drell-Yan-West
$8
type a n a l y s i s . Energy, a n g l e and s p i n dependence can be d e s c r i b e d . The c r o s s i n g p r o p e r t i e s of t h e amplitude, however, may n o t be c o r r e c t .
Acknowledgements.
-
I thank F. Halzen f o r moral and t h eUX
SERC f o r f i n a n c i a l s u p p o r t .Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982335
JOURNAL DE PHYSIQUE
4.1
tm < 8.5 GeV
P, ( G ~ v ) Fig.
1.-
P, ( G e V )
Fig.2. Solid line has
K = K ' = 2 . 4 . ,and
- smearing .
w.
K 'for non singlet
.rrN + ~ + ) J - Xm. High Swjst mechanism for pL = 200, m
= 5.5 GeV.
n N + p p X, at high pT.
PT (GeV)
+ -
Fig.5.
x N + v p X, pL =150 GeV Fig.6. +e+x,&
=540 GeV, 8 = 90'
D.M. S c o t t
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