The neutron total cross section measurements on protons and nuclei in the energy range of 28–54 GEV

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THE NEUTRON TOTAL CROSS SECTION MEASUREMENTS ON PROTONS AND NUCLEI IN THE ENERGY RANGE OF 28-54 GEV A BABAEV, E BRACHMAN, G ELISEEV, A ERMILOV, Yu GALAKTIONOV Yu KAMISHKOV, V LUBIMOV, N LUGETSKY, V NAGOVITZIN, V NOZIK, V SHEVCHENKO, E SHUMILOV, 0 ZELDOVICH and T ZVETKOVA Institute for Theoretical and Expenmental

N BALAMATOV,

B GORYACHEV,

Physrcs, Moscow, USSR

E LEIKIN, A SIROTKIN, V TITOV and V TURIN

Moscow State Unzverszty, Moscow, USSR Recewed

The results of the total cross sectlon measurements Pb m the energy range of 28-54 CeV are reported

1 May 1974

of neutrons

The results of the neutron-proton and neutron-nuclew total cross-sections measurements are reported The experiment has been carried out at the Serphukov 70 GeV synchrotron for three intervals of the neutron energies correspondmg to the internal proton beam energy of 35,50 and 70 GeV The conventional transmlsslon technique was used I e the intensity of the beam passing through the target without an interaction was measured There are some pecuhantles of the neutron total cross section measurements 1) Neutrons undergo no Coulomb scattering This makes it possible to reach very low level of corrections coming from the particles scattered m the target 2) The absence of Coulomb scattermg allows to make use of a statlstlcally optimal target length (“thck” targets of l-2 interaction lengths), through which good enough statlstlcal accuracy at relatively low beam intensity 1s achieved 3) When working with “thick” targets there are some advantages m abandoning pure hydrogen or deutermm as the target material For n-p and n-d total cross section measurements the targets were made of hqmd compounds contammg hydrogen The compounds used were C7H1, and C6H6 for n-p, and D20 and Hz0 for n-d measurements The effective hydrogen density m such targets 1s almost the same as m a liquid hydrogen target and additional beam absoprtlon m carbon (or oxygen) can be easily compensated by mcreasmg the intensity of the mcommg beam On the other

on protons,

deuterons

and nuclei C, 0, Al, Cu, Sn,

hand with the complex targets one can get rid of systematic uncertamtles m the amount of hydrogen and deutermm, while It IS normally dlffcult to estimate accurately the density of liquid hydrogen 4) Some addltlonal comphcatlons arise due to the neutron beam being non-monochromatic These comphcatlons are, however, not very essential as soon as the energy dependence of the total cross sections 1s rather weak and the energy resolution of total absorption technique turns out to be sufficient m order not to introduce any additional errors m the total cross section The beam lay-out 1s shown m fig 1 The neutron beam taken under 0” to the machme orbit was formed and cleared by a system of colhmators and magnets with a comcal defining colhmator Lead converters (7 5 cm) brought the y-contammatlon to a neghglble level The contammatlon of Kf m the beam was also small The corrections m the total cross sections due to Ki contamination have been less than 0 05% and were onutted The beam was monitored by two independent counter telescopes MO1 and MO2 with a 1 cm iron converter placed m front of each of It Special precautions were taken to achieve the monitors hnearlty and stablhty The targets were put m and out of the beam with the maximum rate - every machme cycle - to make the influence of apparatus mstablhtles as low as possible 501

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Fig 1 a) The lay-out of the experlmental set-up (out of scale), Be mternal Be target, Pb lead y-converter, Kl, K2 KS Kq colhmators, Ml, M2, M3 cleanmg magnets, MOl, MO2 the beam monitor telewopes, T target assembly, A ant]-comcldence counters, F iron converter, S comcldence counter, KA the calorimeter b) The schemdtlc lay-out of the calorimeter, F external converter, S comcldence counter, C scmtdlator plates, Fe non plates

The detection system consisted of a total absorption spectrometer (calorimeter) m comcldence with a counter S In front of the counter S an iron converter F was put, and only the particles interacted m this converter were counted by the system The contammatlon of partrcles scattered m the target and counted by calornneter can be measured by putting the converters of different shape The correctlons due to this effect were not big even for heavy nuclei (20% for lead, 0 1% for hydrogen and deutenum) because the only particles scattered m the target with the momentum transfer less than 5 X 10m4 (GeV/c)-2 were confused with neutrons passing through the target without mteraction All data were read into the on-lme computer where the prehmmary analysis and checks were performed and data stored on magnetic tapes Special measurements were made to study possible sources of systematic errors The measured cross sections were found to be mdependent on the target length (when the length was varied from 0 5 to 3 mteraction lengths, the total cross section was constant wlthm some tenth of a percent) The data were taken at different beam lntensltles and m the final analysis the measured cross section values were extrapolated to zero intensity The neutron energy spectrum as well as the energy resolution of the calorimeter were studied to determine the mean values of energies for measured cross sections (see fig 2) 502

Systematic errors due to admixture of other particles (but neutrons) m the beam, chemical impurities m target materials etc , were less than 0 1% altogether Rg 3 shows the results of the total cross section measurements The total cross section of neutrons on

E GeV Fig 2 The shape of the neutron energy spectra taken for total cross sectlons measurements at three energies of Internal proton beam (35,50 and 70 GeV) The mean values of neutron energies (m GeV) for each case are mdlcated above the curves

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I

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’

nd . This Exp nd o [2]

76-

pdo P P

75-

gn

p]

f

b) np

l

This Exp

I

I

I

I

I

I

10

20

30

40

50

60

E GeV

Fig 3 The results of the total cross sectlons measurements of neutrons on protons (a) and deuterons (b), a\ well as on different nuclei (c -h) The dotted hnes Indicate system&c errors of ref [3 ]

protons (fig 3a), on deuterons (fig 3b) and on nuclei C, 0, Al, Cu, Sn and Pb (fig 3c-3h) are shown All systematic errors as well as statIstica ones are included mto the error bars For comparison m fig 3 the data of references [l ,2] taken at energies below 30 GeV and the proton-proton total cross section data of ref [3] are shown One can see that our values of the neutron-proton total cross sections are quite close to the proton-proton total cross sections From our np and nd cross sections, usmg pp and pd data of ref [3] one can calculated the Glauber correction twice 01 =%p

+ uPP - ‘ndp

Theoretical calculations of refs [4,7] differ only m details by taking mto account melastx screening effects For our energy range, the theory gives

O2 =Onp ’ Opp - Opd>

and again only from our data assuming onp = opp 03 =

If one neglects the weak energy dependence of o m ref [4], by averaging the values over three different energies, one gets 01 =32+03mb, 03=32?02mb

I 1

t

20,p - o,,d

02=36+05mb,

I 1

I

I

I

100

10 A

of atomic number A a IS the slope parameter m hnear fit of the totdl cross sectlons Fig 4 The value cz/utot as a function

energy dependence (utot = (I - 01 I?) The sohd lme represents the theoretlcal expectations (see the text)

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o*=34mb, with an error 0 1-O 2 mb (melastlc screening effect 0 5 mb [4] ) Bearing m mmd an uncertamty normally arising when comparmg two different experiments, one should consider the measured values of to be m agreement with the expectations of the theory if the melastic rescattermg 1s taken mto account Neutron-nuclei cross sectlons keep falling down when energy increases as one can see from fig 3b-3h There are also some mdlcatlons that the n-p total cross section has tendency to decrease at the studied energy range In fig 4 the energy dependence of the total n-p and n-nuclei cross sectlons as a function of atomrc number A is shown The solid lme m this figure represents the numerlcal evaluations of the energy dependence of the n-nuclei total cross sectlons which are made by using modified Glauber theory formulae given m ref [6] and melastlc screenmg effects taken mto account as m refs [4,5] A more detailed descrlptlons of the calculations will be given elsewhere From fig 4 one can conclude that the theory is m agreement with the expenmental data if one assumes some energy dependence of the nucleon-nucleon total cross sections over the studled energy interval

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LETTERS

2 September

1974

We wish to thank Dr Yu V Gorodkov for his partlclpatlon at the mltlal stage of the experunent We are indebted to Dr A Kaldalov and Dr L Kondratyuk for their attention and support while performing theoretlcal evaluations of the total cross sections We would like to thank Prof Yu D Prokoshkm and Prof K A Ter-Martlrosyan for then constant interest to the experiment and useful dlscusslons of the results of the experiment We appreciate the interest to the expenment of Prof I V Chuv~lo and Prof R M Salyaev

References [ 11 1 Engler et al, Phys Lett 31B (1970) 669,32B (1970) 716 [2] L W Jones et al , Phys Letters 36B (1971) 509 [3] Yu P Gorm et al, Yadern FIZ 14 (1971) 998 [4] A B Kaldalov, L A Kondratyuk, Nucl Phys B56 (1973) 904 [5] V A Karmanov and L A Kondratyuk, Plsma JETP 18 (1973) 451 [6] V Franco,Phys Lett 24 (1970) 1452 [7] V Annovich, Phys Lett 42B (1972) 224