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Submitted on 1 Jan 1973
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OBSERVATION OF INCREASING CHARGED MULTIPLICITY AS A FUNCTION OF
TRANSVERSE MOMENTUM IN 28.5 GeV/c pp INTERACTIONS (P 454)
P. Schübelin
To cite this version:
P. Schübelin. OBSERVATION OF INCREASING CHARGED MULTIPLICITY AS A FUNCTION OF TRANSVERSE MOMENTUM IN 28.5 GeV/c pp INTERACTIONS (P 454). Journal de Physique Colloques, 1973, 34 (C1), pp.C1-401-C1-403. �10.1051/jphyscol:1973154�. �jpa-00215234�
CHARGED MULTIPLICITY AND TRANSVERSE MOMENTUM
OBSERVATION OF INCREASING CHARGED MULTIPLICITY AS A FUNCTION OF TRANSVERSE MOMENTUM IN 28.5 GeV/c pp INTERACTIONS (P 454)
P . SCH~~BELIN B.N.L.
Systematic studies of multiparticle final states in PP collisions around 30 GeV/c have been carried out in bubble chambers [I]. They have covered extensively the large cross-section peripheral interactions but have had no access to rare events, e.g. large momen- tum transfer collisions. They have suffered from technical shortcomings in identifying the final state protons. The simplest features of the data, i.e. sin- gle particle inclusive distributions and two-body correlations can be understood in terms of the produc- tion and decay characteristics of the excited nucleon system (nova model) [2 I. The data appear insensitive to detailed features of the dynamics. A study of col- lisions imparting higher transverse momentum to the incident proton may be more sensitive to the dynamics since in that case one is probing a more central re- gion of the proton. With this motivation we have ini- tiated a study of such central collisions with a no- vel instrument, the Multiparticle Argo Spectrometer System 13 1 (MASS), at the AGS.
We report here the dependence of the mean charged multiplicity NCH on the transverse momentum pl -
of the forward proton in the reaction
for five intervals of missing mass MM. To measure this dependence, we have used two of the three spec- trometers constituting the ensemble of MASS. The High Momentum Spectrometer (HMS) was used to trigger upon, identify, and momentum analyze the forward proton. In three floor positions, scattering angles in the labo- ratory frame between 14 mrad and 100 mrad and momenta between 10 GeV/c and 28.5 GeV/c were covered. The an- gular and momentum resolutions were * .2 mrad and
+ .3 % at 20 GeV/c respectively and the solid angle acceptance was 33 mr horizontally by 10 mr vertical- ly. The vertex spectrometer [4 ] (VS) was used to mea- sure the charged multiplicity. It consisted of nine digitized cylindrical wire spark chambers operating in a ten kilogauss magnetic field and surrounding an
eight inch long hydrogen target. The chambers subten- ded a solid angle such that 89 % of all charged par- ticles were detected. Track identification in the VS was performed with the automatic track recognition code Pitrack [5]. A subset of the data was scanned by physicists to determine the biases. Approximately 6 % of all tracks were not recognized by Pitrack.
The charged multiplicity distribution for three in- tenrals of pL in the MM interval 2.0 to 3.0 GeV are displayed in Fig. 1. Losses of charged particles have
I # EVENTS - Pl= 1.90 GeV/C
-
Fig. 1.- The corrected charged multiplicity distribu- tions in the MM interval 2.0 - 3.0 GeV for three values of transverse momentum to the forward proton.
been calculated using charge consenration on an event by avent basis. The losses of two particles of oppo- site charge were determined from the known losses of two particles of equal charge.
It is apparent from the data that the multiplicity distribution for high pl differs from the other two
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1973154
d i s t r i b u t i o n s r e s u l t i n g i n a h i g h e r mean charged mul- r e c o n s t r u c t i o n inefficiencies. F~~ d e t a i l e d informa- t i p l i c i t y . Since t h e average m i s s i n g mass v a l u e d i f - t i o n on each data p o i n t , see ~ ~1. b l ~
f e r e d by a small amount f o r d i f f e r e n t pl i n t e r v a l s ,
T.bl< I
a s m a l l c o r r e c t i o n 6Nm h a s been a p p l i e d (Table I ) .
~
li..~.~ in c a
The c o r r e c t i o n was based on t h e o b s e r v a t i o n o f a li-
- 2.0 0.499'0.14) 0.03 2.4 0 . 3 9 0.07 2.93tO.OT
n e a r r e l a t i o n s h i p between NCH and MM f o r f i x e d pL - - ,,, 1.05(0.12l 0.02 2.62 0.32 0.07 1.01 t 0.05
- 1 1.98(0.10) -0.01 2.66 -- -- 2.66 t 0.61
w i t h a s l o p e of .75 GeV . ,,, ,, < 3.0 0.46(0.15) 0.04 1.28 0.45 0.10 3.83 t0.05
I n F i g . 2 we show t h e v a r i a t i o n of t h e mean charged Ei- 2.6 0.98(0.14) 0.01 1.20 0.42 0.10 3.72 t0.01
1.90(0.15) -0.02 3.83 0.47 0.22 4.50 t0.21
m u l t i p l i c i t y NCH w i t h pA f o r f i v e i n t e r v a l s o f MM.
While t h e d a t a show l i t t l e v a r i a t i o n of NCH w i t h p, up t o 1 GeV/c, a r a p i d r i s e of - NCH can be s e e n f o r v a l u e s of p, > 1 GeV/c . I t i s p o s s i b l e t h a t t h e
lowest MM i n t e r v a l does n o t d i s p l a y t h i s behavior
.-MM=1.70GeV O-MM=2.60 GeV r-MM =3.60 GeV
o- MM = 4.50 GeV
.
-MM = 5.20 GeVF i g . 2.- The v a r i a t i o n of t h e a v e r a g e charged m u l t i - p l i c i t y RCH w i t h pl f o r f i v e i n t e r v a l s o f m i s s i n g mass MM.
because of i n s u f f i c i e n t a v a i l a b l e energy. The e r r o r s i n F i g . 2 do n o t i n c l u d e a n o v e r a l l s y s t e m a t i c e r r o r . We have i n v e s t i g a t e d t h e s y s t e m a t i c e r r o r on NCH - by comparing s u b s e t s of o u r d a t a a t low pl w i t h bubble chamber i n f o r m a t i o n . Our NCH - i s s y s t e m a t i c a l l y h i - gher by - 5 % compared t o t h e mean charged m u l t i p l i - c i t y i n bubble chamber d a t a 161. We a t t r i b u t e t h i s d i f f e r e n c e t o u n d e t e c t e d secondary i n t e r a c t i o n s i n t h e hydrogen t a r g e t , gamma conversion c l o s e t o t h e v e r t e x e t c . The d a t a have n o t been c o r r e c t e d f o r t h i s
s y s t e m a t i c e r r o r .
We have a l s o looked a t t h e c o r r e c t i o n s a s a func- t i o n o f p, . Charge c o r r e c t i o n s a r e t h e same w i t h i n e r r o r s f o r a l l i n t e r v a l s of p, . I n o t h e r words, t h e u n c o r r e c t e d d a t a show t h e same behavior o f - gCH
v e r s u s pl a s t h e c o r r e c t e d ones b u t t h e NCH va- l u e s a r e lower by about 17 % due t o s o l i d a n g l e l o s -
The d a t a i n F i g . 2 s u g g e s t t h a t some new phenomenon may be o c c u r i n g i n PP c o l l i s i o n s when one of t h e f i n a l s t a t e p r o t o n s emerges w i t h a pL > 1 GeV/c ; t h i s phenomenon m a n i f e s t s i t s e l f i n a n i n c r e a s i n g mul.
t i p l i c i t y f o r a f i x e d MM - . I n o r d e r t o g a i n f u r t h e r
i n s i g h t i n t o p o s s i b l e mechanisms we have examined two more p r o p e r t i e s of t h e d a t a : (1) t h e two-body e f f e c - t i v e mass d i s t r i b u t i o n s of t h e n e g a t i v e p a r t i c l e i n t h e VS - assuming i t i s a n - w i t h t h e HMS t r i g g e r proton and (2) t h e f r a c t i o n of t h e p a r t i c l e s i n t h e VS t h a t a r e on t h e s i d e of t h e beam o p p o s i t e t o t h e HMS p r o t o n . For ==2.6 GeV and TA=1.9 GeV/c , we f i n d t h a t t h e e f f e c t i v e mass d i s t r i b u t i o n has a n ave- r a g e v a l u e of 3 . 8 GeV and t h a t only 13 % of t h e masse a r e s m a l l e r t h a n 1.8 GeV. T h i s r e s u l t i s c o n s i s t e n t w i t h a c a l c u l a t i o n based on t h e assumption t h a t only t h e t a r g e t p r o t o n i s e x c i t e d i n t h e c o l l i s i o n and subsequently decays a c c o r d i n g t o phase space i n t o f i v bodies 171. For t h e f r a c t i o n of t h e p a r t i c l e s o p p o s i t t h e HMS p r o t o n we g e t 83 % ; t h e t a r g e t e x c i t a t i o n c a l c u l a t i o n [7 ] y i e l d s 86 %.
The p r e d i c t i o n of t h e m u l t i p e r i p h e r a l model i s i n marked c o n t r a s t t o t h e d a t a ; f o r a f i x e d MM t h i s model [8 ] g i v e s a n ?i which d e c r e a s e s a s Ln (a+b pL) 2
121. Assuming t h a t t h e e v e n t s we a r e d e t e c t i n g involv only t a r g e t f r a g m e n t a t i o n , t h e observed e f f e c t i s a l s unexpected i n t h e framework o f a nova model, which g i v e s - N N MM w i t h no dependence on p i . I t i s wort
n o t i n g however t h a t t h e c r o s s - s e c t i o n [Y] f o r obser-
5.0 < M (5.5 Ei - 5.2
0.39(0.06) -0.01 4.67 0.75 0.24 5.46 tO.11
0.66(0.05) -0.02 4.37 0.82 0.33 5.52 t0.03
0.79(0.01) 0.08 4.18 0.66 0.36 5.58i0.08
L.ZO(0.08) -0.01 6.98 0.82 0.36 6.16 t O.W
p : *v.r.g. <.,"Sv.r.r Cornrnlum of the t o w a r d procon I" C.Y/c; <hC h.ll-"idth L* %" p.r."ih..ls
- m : ~ v e r e g e mieeinp mass in C ~ V in the r m g e a t m i s a i n ~ -a. as mdicrred.
6%: correction the .ver.ge multlpll~ity due 10 the adjustment $ f t o chc nominal value.
Fo : charged r n l ~ i ~ ~ i ~ i t ~ detemlned by r1mC1 and sorrecrrd by d h .
bl, : carrccrim of charged multipliclry u s m g charge conserv.rion.
liiZ : correction of rh.rged lu~ripliciry for losses O F ~o pnrrtsles with opposite charge.
NCB : Pln.1 mean charged mulrlplleiry. m d srarlsrlcal and random syllmltlc error.
CHARGED MULTIPLICITY AND TRANSVERSE MOMENTUM C1-403
pl
-
2 GeV/c we are observing events that occur with- 5 -3
a frequency 10 of events at pI=O GeV/c and 10 of events at pL=l GeV/c . It is conceivable, for example, that beam proton fragmentation or double- nova excitation occuring at pl=l.O -1.5 GeV/c (and hence having a much larger cross-section) could con- tribute to an HMS proton with pL=2 GeV/c through a rare decay configuration. It seems clear that the calculation of such a contribution would be very sen- sitive to details of the nova model. If, as indicated by data at NAL energies [lo], one needs a combination of multiperipheral and diffraction dissociation (nova) models then it may be possible to obtain our effect
if the cross-sections for the two mechanisms have different pl dependencies.
In the limiting fragmentation picture [I1 1, the proton is an extended object of limited rigidity, and an increase of N with p- , is expected and has been conjectured [I21 to be (assuming there is enough available energy)
where is the average transverse momentum in hackon-hadron collisions [13 I.
A bremsstrahlung mechanism [14] of pion production would also favor increasing N - ; how such pictures alone would give constant W for pA<l GeV/c is not obvious.
In conclusion, we have observed a sharp increase of iCH in PP collisions at 28.5 GeV/c when pL to the trigger proton is larger than 1 GeV/c. There is an indication from the data that one is observing mainly target fragmentation, at least for MM<3 GeV - .
The observed dependence of NCH with pl is not predicted by existing models. Whether one is seeing evidence of some new phenomenon associated with close collisions, e.g. proton substructure, is a matter of speculation ; what does seem clear is that this is an important new area of investigation.
REFERENCES
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RAMANAUSKAS (A.), SCHUBELIN (P.), THORNDIKE [13] Making the usual assumption for no's one can (A. ) , TURKOT (F .) and VON LINDERN (L .) , Expe- write Eq. (2) for gCH as
rimental Meson Spectroscopy ed. BALTAY (C.) and ROSENFELD (A.) , Columbia University Press,
N .Y . (1970) 581. - 2 p~
A complete description of MASS to be submitted NCH = 7 (PI) hence
for publication.
[ 4 ] FICENEC (J.R.), STRINGFELLOW (B.c.), COLLINS -
(G.B.), RAMANAUSKAS (A.), SCHUBELIN (P.) ,
TURKOT (F .), submitted to Nuclear Instruments d N ~ ~ - L 3
( ) = T (pl) = .6 GeV/c
and Methods, May 1973. d P ~
[5 1 GILBERT (D.R.) , SCHREINER (W .N .) , TROWER (W .P.)
and S C ~ B E L I N (P.), to be submitted to Nuclear -
Instruments and Methods.
[6] The bubble chamber mean charged multiplicity for a crude evaluation of (>jl - from the data of
= 2.6 GeV is lower by 4.7 % and for Fig. 2 for pl > 1 GeV/c yields 0.7 GeV/c .
MM = 3.6 GeV by 6.8 %.
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171 Private communication from SLANSKY (R.). - 164 (1967) 1822 ;
STODOLSKY (L.), Phys. Rev. Letters 8 (1972)
60.
