Results are presented on the production of single charged particles with transverse momentum in the range of 0.8-4.5 GeV/c in π^±p, K^-p, and pp collisions at 200 GeV/c and on correlations between the trigger particle and particles with opposite azimuthal angle

Abrams, R.

Ashford, V.

Bromberg, C.

Delzenero, R.

Dzierba, A.

Erhan, S.

Fox, G.

Goldberg, H.

Gomez, R.

Haggerty, H.

Juhala, R.

Kropac, W.

Lorenz, E.

Malamud, E.

Margulies, S.

McLeod, D.

Medinnis, M.

Mori, S.

Pine, J.

Rohlf, J.

Schlein, P.

Solomon, J.

Stampke, S.

Stanek, R.

Yung, K.

Caltech Authors - Main

VOLUME 43, NUMBER 8 PHYSICAL REVIEW LETTERS 20 AUGUST 1979 
Production and Correlations of Charged Particles with High P, in 200-Ge VIc 
1r±p, K-p, and pp Collisions 
C. Bromberg, (a) G. Fox, R. Gomez, J. Pine, S. Stampke, and K. Yung 
California Institute of Technology, Pasadena, California 91125 
and 
S. Erhan, E. Lorenz ,{b) M. Medinnis, J. Rohlf, (c) and P. Schlein 
University of California, Los Angeles, California 90024 
and 
V. Ashford,<dl H. Haggerty, R. Juhala,<el E. Malamud, and S. Mori 
Fermi National Accelerator Laboratory, Batavia, Illinois 60510 
and 
R. Abrams, R. Delzenero, H. Goldberg, S. Margulies, D. McLeod, J. Solomon, and R. Stanek 
University of Illinois at Chicago Circle, Chicago, Illinois 60680 
and 
A. Dzierba and W. Kropac<fl 
Indiana University, Bloomington, Indiana 47401 
(Received 19 April 1979) 
Results are presented on the production of single charged particles with transverse mo-
mentum in the range of 0.8-4.5 GeV/c in 1r"'p, K-p, andpp collisions at 200 GeV/c and on 
correlations between the trigger particle and particles with opposite azimuthal angle. 
High-transverse-momentum (P t) production of 
hadrons is thought to proceed through hard con-
stituent scattering. Earlier results1 on collective 
high-Pt phenomena (i.e., "jets") were obtained by 
us using a large-aperture calorimeter-triggered 
multiparticle spectrometer at the Fermi National 
Accelerator Laboratory. In this Letter, we pre-
sent production cross sections for single charged 
particles with 0.8<Pt<4.5 GeV/c and at 90° in the 
c.m. system, produced in 200-GeV/c rr-p, rr+p, 
and pp collisions. The ratios of the cross section 
for the reaction pp- h"' +X to that for rr-p-h"' +X 
and of that for rr+ p-h"' +X to that for rr· p-h"' +X 
are presented for different combinations of sec-
ondary hadron charges. Also, positive-to-nega-
tive charge ratios of Cerenkov-identified secon-
dary particles, as well as correlations between 
the charge of associated "away- side" particles 
(those on the opposite side in azimuth from the 
trigger particle) and the trigger-particle species, 
are given. 
Details of the spectrometer and of the single-
particle trigger used for the data presented here 
are found in Ref. 1. We note here that, in order 
to understand the properties of the trigger bias, 
data were recorded for several different calorim-
eter bias settings, corresponding to Pt lower lim-
its as low as 1.75 GeV/c and as high as 3.0 GeV/c. 
In general, a particle with Pt below the trigger 
threshold can trigger the calorimeter in any of 
three ways: (a) The observed energy loss in the 
calorimeter is an upward fluctuation; (b) the mag-
netic deflection can increase a particle's labora-
tory angle and hence its apparent Pt; or (c) an ad-
ditional particle deposits energy in the same calo-
rimeter cell. (a) and (b) are adequately account-
ed for in a Monte Carlo acceptance calculation, 
while (c) can be corrected for by observing any 
accompanying charged particles in the spectrom-
eter. Accompanying neutral particles are less 
frequent and can be estimated. Further details 
on these points will be reported elsewhere,2 al-
though we comment that in the ratios the effects 
of systematic errors arising from the trigger 
bias tend to cancel. Specifically, systematic er-
. rors contribute less than± 10% to the total error 
and are usually small compared to the statistical 
errors. The error bars on the ratios include the 
estimated systematic errors. 
The 22-cell Cerenkov counter Cu described 
in Ref. 1, was used to identify secondary parti-
cles wherever possible. For 70% of the data, C1 
was filled with air (K threshold"" 21 GeV/c) and 
the remainder of the time filled with a 2:1 helium-
air mixture (K threshold"" 32 GeV/c). At- 0.1 
rad in the laboratory (90° in the c.m. system), 
© 1979 The American Physical Society 561 
VoLUME 43, NuMBER 8 PHYSICAL REVIEW LETTERS 20 AuGusT 1979 
(a) (c) 
j 1.2 t + t • + 1 1030 1.0 
• 
• Thisexpt. 0.8 
~ "Chicago-1031 Princeton .2 (b) ~ II£> 'E ~ + ] a:: 
+ 1.5 ----............. 
rnb,tth. • '0 '0 1032 
"f,i j w • 1.0 ', 
1033 + ----Donaldson et ol (-n-0) 'l'\ 
0.5 
2 3 4 1 2 3 4 
Transverse momentum ( GeV /c) 
FIG. 1. (a) Inclusive invariant cross sections vs Pt for pp.:..... charged particle+ X. Chicago-Princeton points are 
from Ref. 3. (b) Ratio of cross section in (a) to that for 7!'-p-charged particle +X. Dashed curve is from Ref. 4. 
(c) Ratio of'll'+p to 1!'-P single-charged-particle cross sections. 
1r 's could be separated from a mixed K -P. sample 
withP, upto3.2 GeV/c; p's (and alsop's) could 
be separated from a mixed n -K sample with P, 
greater than 2.1 GeV/c. Since particleswith/3 =1 
produced an average of eight photoelectrons in 
air, pulse-height information could be used to 
identify 1r 's with P, > 2.1 GeV/c in these data; with 
helium-air corrections of up to 10-15% were nec-
essary for 1r background in the K -P sample. 
Figure 1(a) shows our measurement of the in-
clusive charged-particle cross section for pp col-
lisions. The results agree with the correspond-
ing data from Antreasyan et al.3 Figure 1(b) 
shows our ratio of the pp cross section to the cor-
responding 1r p charged-particle cross section. 
This ratio is almost identical to the (pp -n°)/ 
(n·p-n°) ratio of Donaldsonet al.4 Moreover, 
our ratio of n+p;n·p, which is seen in Fig. 1(c) 
to be Pt independent at a value near unity, also 
agrees with the Donaldson et al. results for 7T 0 
production. The falloff of our pp/1T" p ratio in 
Fig. 1(b) shows that there is a crossover of 1Tp 
and pp single-particle cross sections near P t 
""'3 GeV/c. 
The ratios of the single-particle cross-section 
components of pp interactions to 1T- p interactions 
are shown in Fig. 2(a) for like-sign trigger parti-
cles and in Fig. 2(b) for unlike-sign trigger par-
ticles; the same ratios for rr+ p and 7T- p interac-
tions are shown in Figs. 2(c) and 2(d). The curves 
show fits to the data of the function (1 - x J.)n, 
where X J. =P/Pt max. The presence of baryons in 
562 
the final state may complicate the interpretation 
of these results. However, since, as discussed 
below, the final-state baryon components in rr· p 
0.5 
0 
& 
2.0 
1.5 
0.5 
(a)t 
2.0 
-(1-x l" 1 
(c) 
(b) 
1.1 
9~-/+ 
1.3 't 
234 1234 
Transverse Momentum (GeV/c) 
FIG. 2. Ratios of single-particle cross sections for 
indicated initial state and trigger-particle charge. Solid 
curves are fits of (1-xJ.ln to the data with PJ. >1 GeV /c; 
the exponents, n, are shown; they have an uncertainty 
of±0.3 in (a) and (b), and ±0.4 in (c) and (d). (a) (pp 
-h+ +J()/(rr"p-h++X) and (pp-h" +X)/(rr-p-h" +X!; 
(b) (pp-h++X)/(rr·p-h"+J() and (pp-h"+J()/('Il'"p 
-h+ +}(); (c), (d) same as (a), (b) except for 'll'+p and 7!'-P 
initial states. 
VOLUME 43, NUMBER 8 PHYSICAL REVIEW LETTERS 20 AUGUST 1979 
5 (a) CP !:; pp- +/- (b)o l • pp- p/(7r++k+) 
l>l• ~p.,imool! ~ pp- +/- v CP • 71"-p- p/( 71"+ + k+) 7r+p-+/- 0 
t 
• 71"-P- iil(7r-+n 
4 71"-p-+/-
t+ tt 
0.5 k-p-+/-
t 
• • + + • • • / / • • • 3 0 • +--- ------
~ 7r CS. • p/p 
1-
<! 
• (p+k+Jt(p+n 0:: 
2 
.;. .., (7r++k+lt(7r-+n t cs • 11"+111"-
71"+ \ 
.J t 
FF T ~ f t • 71"- + • JI 
(d) 
(c) 
0~--~---7~--~--~---L--~----L----L--~L-L----L--~----L----L~ 
0 2 3 4 2 3 4 2 3 4 
TRANSVERSE MOMENTUM ( GeV /c) 
FIG. 3. (a) Trigger-particle charge-production ratio vs trigger-particle P t for pp, 1r±p, and K·p reactions. Open 
symbols are from Ref. 3. FF and CS curves are from Refs. 5 and 8. (b) Charge ratios of indicated identified trig-
ger particles for pp reactions. FF and CS curves are for (pp-rr+ +X)/(pp-rr· +X). (c) Same as (b) except for rr·p 
reactions. (d) Proton/meson production ratios for indicated reactions. 
and rr + p interactions are consistent with being 
nearly identical, the ratios displayed in Figs. 
2(c) and 2(d) are essentially the ratios for rr +K 
production only. These latter ratios are seen to 
vary very slowly if at all with Pt. · 
Figure 3{a) shows the +/- trigger charge ratio 
for pp, 7T ~p, and I1 p interactions versus Pt. The 
pp results agree well with those of CP.3 Despite 
differences in the initial-state quark content, rr+p 
is seen to have the same behavior as pp, and I1 p 
is similar torr· p. Both the rr+ p and rr· p results 
are seen to be correctly predicted by the early 
quantum chromodynamics (QCD) approximation 
of Field and Feynman5 (FF), although a quark-fu-
sion6 constituent-intercliange7 model (CIM) par-
ametrization by Chase and stirlingB (CS) is seen 
to disagree completely with the 7T+p result. The 
CIM term alone in CS fits neither rr+p nor 7T·p. 
The results for the identifie'd trigger particles 
are shown in Figs. 3(b)-3(d). The proton-beam 
data are seen to agree with the analogous results 
from Cp3 and with the FF and CS predictions for 
pp -'IT +X. We note that the ratio (p +K+)/('p +K") 
is much larger than the rr+ /'IT" ratio for the pro-
ton-beam data, whereas for the rr· beam, the two 
ratios are comparable. This is presumably be-
cause protons contain none of the valence quarks 
necessary to form p or K in the denominator of 
the first ratio. The PIP ratio for the 'IT- beam is 
seen to be close to unity, as compared with the 
larger p(p ratio of 6 or more for the proton 
beam.3 This presumably also results from the 
valence-quark content of the initial state. Final-
ly, Fig. 3(d) shows the proton/meson production 
ratios for the three reactions. None of the ratios 
appears to depend appreciably on Pt. The ratio 
for the lower-statistics 7T+p data (not shown) 
agrees with the 'IT- p data. 
We turn now to the charge correlations between 
"away-side" hadrons and the type of trigger par-
ticle.9 We define R 4 {h) as the away-side positive-
to-negative charge-production ratio for all 
charged particles with c.m. production angle 45° 
< e < 90° and lying in a ± 45° azimuthal wedge op-
posite the trigger particle; a is the incident beam 
particle and h is the trigger particle. In Fig. 4 
we plot Ra(7T) and Raf)( +P) for two different re-
gions of X 8 =- P.L away • P .1. trig /p .1. trig. We note that 
there is a dependence on x 8 and, furthermore, 
that Ra appears to depend only on the charge of 
the trigger particle and not on its type, in agree-
ment with QCD predictions.10 
In a simple quark fragmentation model, a neg-
ative trigger in a rr· p collision increases the 
likelihood that the away quark came from a pro-
ton, while a positive trigger suggests that the 
away quark came from the 'IT-. Thus, we expect 
Rrr-(h+)<Rrr-(h"), as observed. Further, since a 
563 
VoLUME 43, NuMBER 8 PHYSICAL REVIEW LETTERS 20 AuGUST 1979 
3 
a) 
2 
0 0 < Xe< 0.1 
"' • Xe > 0.4 a:: 
~ e 9 • + ¢ 
0 
b) 
2 + 
c. ~ a:: ¢ 
o~----~------~----~~----~~ 
7T+ 7T (kp)+ 
TRIGGER TYPE 
FIG. 4. The away-side charge production ratio for all 
away-side charged particles in the li- q; acceptance re-
gion described in the text, for the indicated trigger-par-
ticle types: (a) for rr"-beam, (b) for proton-beam parti-
cle. 
minus trigger can come either from the d quark 
in the incident proton or the d or ii quarks in 
the 1T-, the denominator inRrr(}z") will be en-
hanced somewhat and we expectRrr.(h")<Rp(h+), 
which is also seen. Thus the general pattern of 
the x 6 > 0.4 data in Fig. 4 agrees with the qualita-
tive predictions of the simple parton model, al-
though the differences between Rp(Jz") and Rp(Jz+) 
are larger than expected. A possible explanation 
is that all the residual valence quarks (those that 
do not directly participate in the hard scatter) in-
fluence the charge correlations on the far side. 
In other words, we are probably seeing contami-
nation from the forward jet.11 Whereas x6 > 0.4 
should be large enough to eliminate contamination 
from the large-x 11 component of the forward jet, 
it is not large enough to eliminate the low-x 11 
component. A detailed understanding of the quan-
titative features of the correlation data will have 
to await experiments at higher P 0 so that the 
contamination from the forward jet can be re-
duced. 
We are grateful for the assistance given us by 
the staffs of the Accelerator Division, the Meson 
Department, and the Research Services Depart-
ment at Fermilab. We thank B. Cambridge, 
R. Field, and A. Pagnamenta for useful discus-
sions. This work was supported in part by the 
U. S. National Science Foundation, the U. S. De-
564 
partment of Energy, and the University of Illinois 
Research Board. 
(alPresent address: Michigan State University, East 
Lansing, Mich. 48824. 
(blVisitor from the Max-Planck-Institut fiir Physik 
und Astrophysik, Munich. 
(clPresent address: California Institute of Technology, 
Pasadena, Cal. 91103. 
(d>Present address: Brookhaven National Laboratory, 
Upton, N.Y. 11973. 
(elPresent address: McDonnell-Douglas Corporation, 
St. Louis, Mo. 63121. 
H>Present address: Hughes Aircraft Corporation, 
Los Angeles, Cal. 90024. 
1c. Bromberg et al., Phys. Rev. Lett. 38, 1447 (1977); 
and Nucl. Phys. B134, 189 (1978), and !~Proceedings 
of the Eighth International SymPosium on Multi particle 
Dynamics, Kaysersberg, France, 1977, edited by 
R. Arnold, J. B. Gerber, and P. Schiibelin (Centre Na-
tional de la Recherche Scientifique, Strasbourg, France, 
1977), p. B89, and Phys. Rev. Lett. 42, 1202 (1979): 
2See also M. Medinnis Ph.D. thesisUniversity of Cali-
fornia at Los Angeles (unpublished); R. Stanek Ph.D. 
thesis, University of niinois, Chicago Circle (unpub-
lished). 
3D. Antreasyan etal., Phys. Rev. Lett. 38, 112, 115 
(1977), and Phys. Rev. D 19, 764 (1979), denoted by CP. 
4G. Donaldson et al., Phys. Rev. Lett. 36, 1110 (1976). 
5 -R. D. Field and R. P. Feynman, Phys. Rev. D 15, 
2590 (1977). -
6P. V. Landshoff and J. C. Polkinghorne, Phys. Rev. 
D 10, 891 (1974). 
7R. Blankenbecler, S. J. Brodsky, and J. Gunion, 
Phys. Rev. D 12, 3469 (1975). 
8M. K. Chas;-and W. J. Stirling, Nucl. Phys. B133, 
157 (1978). --
9Similar data from pp collisions in different kinematic 
regions are available from CERN [K. H. Hansen, in 
Proceedings of the Nineteenth International Conference 
on High Energy Physics, Tokyo, Japan, August 1978, 
edited by S. Homma, M. Kawaguchi, and H. Miyazawa 
(Physical Society of Japan, Tokyo, 1979), p. 177] and 
Fermilab [R. J. Fisk etal., Phys. Rev. Lett.40, 984 
(1978)]. -
10R. P. Feynman, R. D. Field, and G. C. Fox, Phys. 
Rev. D 18, 3320 (1978). 
11Theoretical descriptions of our correlation data 
should take into account our li selection on the away 
side; the contribution of away-side quarks may be en-
hanced with respect to that of gluons because particles 
are selected in the forward hemisphere; this may help 
explain the large value of Rp(h "). See M. K. Chase, 
Phys. Lett. 79B, 114 (1978). 


Production and Correlations of Charged Particles with High P_t in 200-Ge V/c π^±p, K^-p, and pp Collisions

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Production and Correlations of Charged Particles with High P_t in 200-Ge V/c π^±p, K^-p, and pp Collisions

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