ESTIMATION OF HADRON FORMATION LENGTH IN HIGH p⊥ PROCESSES IN PROTONNUCLEUS COLLISIONS AT 70 GeV

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ESTIMATION OF HADRON FORMATION LENGTH IN HIGH p ⊥ PROCESSES IN PROTONNUCLEUS

COLLISIONS AT 70 GeV

V. Abramov, B. Baldin, A. Buzulutskov, V. Glebov, A. Dyshkant, V.

Evdokimov, A. Krinitsin, V. Kryshkin, N. Kulman, V. Podstavkov, et al.

To cite this version:

V. Abramov, B. Baldin, A. Buzulutskov, V. Glebov, A. Dyshkant, et al.. ESTIMATION OF HADRON FORMATION LENGTH IN HIGH p ⊥ PROCESSES IN PROTONNUCLEUS COLLISIONS AT 70 GeV. Journal de Physique Colloques, 1982, 43 (C3), pp.C3-152-C3-154. �10.1051/jphyscol:1982334�.

�jpa-00221887�

JOURNAL DE PHYSIQUE

CoZZoque C3, supple'ment au n o 12, Tome 43, de'cembre 1982 page C3-152

E S T I M A T I O N OF HADRON FORMATION LENGTH I N H I G H p, PROCESSES I N PROTON- NUCLEUS C O L L I S I O N S A T 70 GeV

V.V. Abramov, B. Yu. B a l d i n , A.F. Buzulutskov, V. Yu. Glebov, A . S . Dyshkant, V.N. Evdokimov, A.N. K r i n i t s i n , V . I . Kryshkin, N. Yu. Kulman, V.M. Podstavkov, R.M. Sulyaev, L.K. Turchanovich, Yu. N. Vrazhnov and V.V. Zmushko

I n s t i t u t e for High Energy Physics, Serpukhov, Moscow D i s t r i c t , U. S . S. R.

In accordance with modern ideas particles with high transverse momenta (p,) are produced in hadron-hadron collisions via hard scat-

tering of fast partons at large angles " ' . Then the scattered par- ton fragments into hadrons producing a particle jet along the direc- tion of the parton momentum. Parton fragmentation (hadronization) is usually described in terms of a fragmentation function, however the mechanism of the process is not yet understood. The fragmentation is

supposed to be connected with interaction at large distances and confinement. Experiments with nuclear targets may be useful in solu- tion of the problem.

The present experiment was carried out for a systematic study of the A-dependence of hadron production @t, KL, p and 5) ^inclusive

cross section at p, in the range from 1 to 4.65 GeV/c at 70

The measurements were

on C, Al, Cu, Sn and Pb targets.

The experiment was carried out with a focusing double-arm spec&

rometer (PODS)

The spectrometer PODS has two identical arms used in this experiment as two independent spectrometers located at the angle of 160 m a d with respect to the incident proton beam. For the production of relativistic particles, this laboratory angle cor- responds to 90

in c.m. for pp-collisions. The data from two arms were summed, which strongly reduced influence of the beam angle un- certainty on the final results.

RESULTS

The invariant cross section of charged hadron production off nuclei were measured. The A-dependence of this process is often described by power a in equation:

The value of a grows with pl from less than a unity up to a value substantially more than unity for pl > 3 GeV/c. Similar behaviour

has been observed in other experiments /3-7/. But in contrast to

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982334

V.V. Abramov et al.

Fia. 1

Fig. 2:

Hadron formation length

versus

Dependence of ratio

versus A.

Fig.

3: Constituent quark

f omation Length

versus

C3- 1 5 4 JOURNAL DE PHYSIQUE

other experiments the power a has proved to be dependent on the choice of the pair of nuclei, i.e. the power low (1) is not valid, This can be seen directly in Fig. 1 where the value

is shown versus A . For the low (1) there would be in Fig. 1 a straight line with a slope proportional to

But in fact the power a decreases with A that can naturally be connected with absorption of formed hadrons inside a nucleus.

ESTIMATION OF HADRON FORMkTION LENGTH

The results of this experiment can be understood in the frame- work of parton model which takes into account single and double scrafi terings of partons inside the nucleus. It is also assumed in the mo- del that after passing a distance

fast parton starts to interact inelastically with nucleons with a finite cross section

in, So the estimated formation length In Pig. 2 Lh= L f

h.N in) L f is shown versus momentum is a function of parameter

in the case o in.

when o in

o in, i.e. when parton directly transforms into had- hN rons. The dashed line in Fig. 2 is the prediction made by N.N.Niko- laev

In Pig. 2 one can see that L h does not tend to 0 when the momentum approaches

That can be understood in the model of constituent quarks /9/. It is assumed in the model that at first stage of hadronization constituent quarks are formed at a distance

Lq, and hadrons are formed at much larger distance outside the nuc- leus. The formation length of constituent quark L q

Lf

2:) ^is

shown in Fig. 3. In this case

2;

40~:). ^Lq is approximately pro- portional to momentum as was expected theoretically

L f = &

and

CI =

1.10 & 0.04 GeV 2 .

1. Feynman

Field R.D., Fox G., Phys. Rev. 2 (1978) 3320.

2. Abramov V.V. et ale, Preprint IHEP 81-46, Serpukhov, 1981.

3. htreasyan D, et al., Phys, Rev, 9 (1979) 764.

4. Becker U. et al., Phys. Rev, Lett. 37 (1976) 1371.

5. Garbutt et al.,

Lett. (1977) 355.

6. Abramov V.V. et al., Yadernaya Fizika 2 (1 980) 660.

7. Abramov V,V. et al., Yadernaya Pizika 34 (1 981 1 1271.

8. Nikolaev N.N., Uspekhi Fizicheskikh Nauk 134 ⁽¹ 981

369.

9. Anisovich V. V. , ^{Nyiri J.,} Preprint KFKI-1 981 -56, Budapest,

1981,