Dubna "Delta-Sigma" Experiment: Results Of
Treatment And Analysis Of Statistics
Accumulated In 2001 Data Taking Run On
Energy Dependence QfA0L(np)
V.I. Sharov1, N.G. Anischenko1, V.G. Antonenko2, S.AAverichev1, L.S.
Azhgirey3, V.D. Bartenev1, N.A. Bazhanov4, A.A. Belyaev5, N.A.
Blinov1, N.S. Borisov3, S.B. Borzakov6, Yu.T. Borzunov1, Yu.P.
Bushuev1, L.P. Chernenko6, E.V. Chernykh1, V.F. Chumakov1, S.A.
Dolgii1, A.N. Fedorov3, V. V. Fimushkin1, M. Finger3'7, M. Finger Jr.3,
L.B. Golovanov1, G.M. Gurevich8, A. Janata9, A.D. Kirillov1, V.G
Kolomiets3, E.V. Komogorov1, A.D. Kovalenko1, A.I. Kovalev4, V.A.
Krasnov1, P. Krstonoshich3, E.S. Kuzmin3, V.P. Ladygin1, A.B. Lazarev3,
F. Lehar10, A. de Lesquen10, M.Yu. Liburg1, A.N. Livanov1, A.A.
Lukhanin5, P.K. Maniakov1, V.N. Matafonov3, E.A. Matyushevsky1, V.D.
Moroz1, A.A. Morozov1, A.B. Neganov3, GP. Nikolaevsky1, A.A.
Nomofilov1, Tz. Panteleev6'11, Yu.K. Pilipenko1,1.L. Pisarev3, Yu.A.
Plis3, Yu.P. Polunin2, A.N. Prokofiev4, V.Yu. Prytkov1, P.A. Rukoyatkin1,
V.A. Schedrov4, O.N. Schevelev3, S.N. Shilov3, R.A. Shindin, Yu.A.
Shishov1, V.B. Shutov1, M. Slunecka3, V. Sluneckova3, A.Yu. Starikov1,
GD. Stoletov3, L.N. Strunov1, A.L. Svetov1, Yu.A. Usov3, T. Vasiliev1,
V.I. Volkov1, E.I. Vorobiev1,1.P. Yudin12,1.V. Zaitsev1, A.A. Zhdanov4,
V.N. Zhmyrov3
1
Joint Institute for Nuclear Research, Laboratory of High Energies, 141980 Dubna, Russia
2
Russian Scientific Center "Kurchatov Institute", 123182Moscow, Russia
Joint Institute for Nuclear Research, Dzhelepov Laboratory of Nuclear Problems, 141980 Dubna,
Russia
4
Peterburg Nuclear Physics Institute, High Energy Physics Division, 188350 Gatchina, Russia
5
Kharkov Institute of Physics and Technology, 310108 Kharkov, Ukraine
6
Joint Institute for Nuclear Research, Frank Laboratory of Neutron Physics, 141980 Dubna, Russia
7
Charles University, Faculty of Mathematics and Physics, VHolesovickach 2, 180 OOPraha 8, Czech
Republic
8
Russian Academy of Sciences, Institute for Nuclear Research, 117312 Moscow, Russia
9
Nuclear Research Institute, 25068 Rez, Czech Republic
10
DAPNIA, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France
11
Bulgarian Academy of Sciences, Institute for Nuclear Research and Nuclear Energy, Tsarigradsko
shaussee boulevard 72, 1784 Sofia, Bulgaria
12
Joint Institute for Nuclear Research, Laboratory of Particle Physics, 141980 Dubna, Russia
3
CP675, Spin 2002:15th Int'l. Spin Physics Symposium and Workshop on Polarized Electron
Sources and Polarimeters, edited by Y. L Makdisi, A. U. Luccio, and W. W. MacKay
© 2003 American Institute of Physics 0-7354-0136-5/03/$20.00
563
Abstract. New results on energy dependence of the Aa^np) over a GeV energy region are
presented. Measurements of the np spin-dependent total cross section difference A<Ji(np) were
carried out at the Synchrophasotron of the Laboratory of High Energies of the Joint Institute for
Nuclear Research in Dubna. A quasi-monochromatic neutron beam was produced by break-up of
accelerated and extracted polarized deuterons. The neutrons were transmitted through a large
proton polarized target. The values of AaL were measured as a difference between the np total
cross sections for parallel and antiparallel beam and target polarizations, both oriented along the
beam momentum. In 2001 data taking run the Aa^np) value were measured at 1.4, 1.7, 1.9 and
2.0 GeV. A fast decrease of AaL(np) with increasing energy above 1.1 GeV, as it was first seen
from our previous data, was confirmed. The obtained results are also compared with model
predictions and with the phase shift analysis fits. The investigations are carrying out under a
program of the "DELTA-SIGMA experiment" project. The aims of these studies are to obtain
the values of imaginary and real parts of the spin-dependent forward n/?-scattering amplitudes
over the energy range of 1.2-3.7 GeV for the first time.
INTRODUCTION
This contribution presents new results for the spin-dependent neutron-proton total
cross section difference Aoi(np) obtained in 2001 with a quasi-monochromatic
polarized neutron beam and a polarized proton target (PPT). The values of AoL(np)
were measured at neutron beam kinetic energies of 1.4, 1.7, 1.9 and 2.0 GeV. The
obtained results are presented together with our previous results and compared with
the dynamic model predictions and with the phase shift analysis fits.
Two spin-dependent observables A<JL and Aor are defined as a difference in the
NN total cross sections for antiparallel and parallel beam and target polarizations,
oriented longitudinally L and transverse T to the beam direction. The NN total cross
section differences AOL and Aor together with the spin-independent total cross
section aotot are linearly related to three non-vanishing imaginary parts of the NN
forward scattering amplitudes via optical theorems. The A<JL,T data allow a direct
determination of the imaginary parts of the spin dependent NN forward scattering
amplitudes and check predictions of available dynamic models of strong interactions
and provide an important contribution to a database of phase-shift analyses (PSA). It is
also possible to deduce the AOL,T nucleon-nucleon isosinglet (1=0) parts using the
measured np quantities and the existing/?/? (isitriplet/=7) results.
A large amount of results for np elastic scattering and transmission experiments at
energies up to 1.1 GeV was accumulated by the end of the 80-th. This data set allowed
one the direct determination of the spin dependent np forward scattering amplitudes
and to perform phase-shift analysis fits for np interactions up to this energy boundary.
The possibility to extend measurements of the np spin-dependent observables to
higher energies exists now at the Dubna Synchrophasotron (JINR LHE) only.
The measurements of energy dependences of differences of np total cross sections
A<JL and Aor for parallel and antiparallel particle spins oriented longitudinally (L) or
transverse (T) were proposed [1,2] at the beginning of the 90-th and started [3-7] in
Dubna. To implement the proposed AOL,T(^P) experimental program, a large
Argonne-Saclay polarized proton target (PPT) was reconstructed in Dubna [8,9], and a
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new polarized neutron beam line with suitable parameters [10,11] was constructed and
tested . A set of necessary neutron detectors with corresponding electronics, rather
modern data acquisition system and other needed equipment were also prepared, tuned
and tested. Two successful data taking runs were carried out in 1995 and 1997. The
energy dependence of Aoifap) was measured at 1.19, 1.59, 1.79, 2.2, 2.49, and 3.66
GeV [3-7]. The results of these runs are also presented.
In the last few years the measurements of spin-correlation parameters Aookk(np) and
Aoom(np) from np^np elastic charge exchange at 0°(Lab.) were also prepared in frame
of the "Delta-Sigma experiment" project. These spin-correlation np observables can be
simultaneously (and independently) with the A<jL,r(np) measurements. A magnetic
spectrometer with multiwire proportional chambers for detection of protons from
np-^np elastic charge exchange at 0°(Lab.) was installed and tested at the polarized
neutron beam line. The data set of np polarization observables to be obtained will
allow to extract the values of imaginary and real parts of spin dependent forward np
scattering amplitudes first over this energy range.
DETERMINATION OF THE AaL^np) OBSERVABLES
In this paper, we use NN formalism and the notations for elastic nucleon-nucleon
scattering observables from [12].
The general expression of the total cross section for a polarized nucleon beam
transmitted through a polarized proton target, with arbitrary directions of beam and
target polarizations is
<r« = <TO« + 0i«(4» PT) + °2tot(PB> Wr> *),
(1)
where PB and PT are the beam and target polarizations, and k is a unit vector in the
beam momentum direction. The term afoot is the total cross section for unpolarized
particles, and the <Jitot, &2tot are the spin-dependent contributions which connect with
the measurable observables A<JT and A<JL by :
- A<7r = 2<7ltof = [<7(TT) - <7(4/T)] I(PBPT\
- &<TL = 2(<7ltt + <72tof) = [<O - <rC)]/(/iPr).
(2)
(3)
The values of aotot, Aor and Aoi are linearly connected with the imaginary parts
of the three independent forward scattering invariant amplitudes a + b, c and d via
optical theorems :
(4)
(5)
(6)
where K is the CM momentum of the incident nucleon. Relations (5) and (6) allow
one to extract the imaginary parts of the spin-dependent invariant amplitudes c(0) and
d(0) at an angle of 0° from the measured values of A<JT and ActUsing the measured values of Aa(np) and the existing Aa(pp) data at the same
energy, one can deduce AOL,T(!=O) as
A<7 Ar (/= 0) = 2A<TLT(np) - &<TL,T(pp).
(7)
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EXPERIMENTAL SET-UP
A quasi-monochromatic neutron beam was produced by break-up of accelerated
and extracted polarized deuterons. Both polarized deuteron and polarized free neutron
beam lines [10,11], the two polarimeters, the neutron production target BT,
collimators C1-C4, the spin rotation magnet SRM, the polarized proton target PPT
[8,9], neutron beam monitors Ml, M2, transmission detectors T1-T3 and the apparatus
for monitoring the neutron beam profiles NP are shown in Fig.l. The associated
electronics and the data acquisition system are also described in [3-7].
FIGURE 1. Layout of the Set-up in the Experimental Hall.
Deuterons were extracted at energies of 1.4, 1.7, 1.9 and 2.0 GeV for the AoL(np)
measurements. The beam momentapd were known with a relative accuracy of ~ ±1 %.
The intensity of the primary polarized deuteron beam was ~ 2 • 109d/cycle. It was
continuously monitored using two calibrated ionization chambers placed in the focal
points F3 and F4 of the deuteron beam line before the neutron production target BT.
Different characteristics of the accelerated and extracted deuteron beam and the status
of the used beam lines were in part available on the Laboratory Ethernet (cycle by
cycle).
The beam of free quasi-monochromatic polarized neutrons was obtained by breakup of vector polarized deuterons at 0° in BT. Neglecting the BT thickness, the
laboratory momentum of neutrons pn = p/2 with a momentum spread of FWHM ~5%.
The BT contained 20 cm Be with a cross section of 8 x 8 cm2. During the data
acquisition, the position and X,Y-profiles of the neutron beam were continuously
monitored by a neutron profilometer NP with multiwire proportional chambers closely
placed downstream the last transmission detector.
The value and direction of neutron beam polarization PB(ri) after deuteron breakup at 0° and for pn = p/2 are the same as the vector polarization PB(d) of the incident
deuteron beam. During the run, the polarization PB(d) and hence the neutron beam
polarization PB(ri) were reversed every cycle, as requested.
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The prepared neutron beam has the vertical orientation of PB(n) as the accelerated
and extracted deuteron beam. For a purpose of the Aoi(np) measurements, we have to
turn the neutron spins from the vertical to the longitudinal direction. This was done by
a spin-rotating magnet SRM in the neutron beam line. The SRM magnetic field was
continuously monitored by a Hall probe.
The value of PB(d) was continuously monitored by relative polarimeter during the
data acquisition. The deuteron beam, considered as a beam of quasi-free protons and
neutrons, collided with a C//2 target, and quasifree protons, scattered at 14° lab., were
detected in coincidence with the protons detected by recoil arms. The weighted
average value of deuteron beam polarization was 0.528 ± 0.004(stat) ± O.OOS(syst).
The frozen-spin polarized proton target, reconstructed to a movable device [8,9],
was used. The target material was pentanol CsHif). The pentanol beads were loaded
into the thin wall teflon container 200 mm long and 30 mm in diameter placed inside
the dilution refrigerator. The number of hydrogen atoms per cm2 for the target was
nH=(9-138 ±0.10) 1023/cm2. The PT measurements were carried out using a computercontrolled NMR system. The average value of proton polarization was 0.6 with
uncertainty of ±5 %.
RESULTS AND DISCUSSION
The measured -Aoi(np) values are presented in Fig.2. The errors are statistical
only. The results from refs.[3-7] together with the existing Aoi(np) data (see for
example [13]), obtained with free polarized neutrons at lower energies, are also shown
in Fig.2. We can see that the new results are smoothly connected with the lower
energy data and confirm a fast decrease to zero within a 1.2-2.0 GeV energy region,
observed previously [3-7].
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FIGURE 2. Energy dependence of the -AaL(np) observable obtained with free neutron polarized
beams.
567
The solid curves show the last energy-dependent GW/VPI-PSA [14] fits (SAID
FX98 and SP99 solutions) of this observable over the interval from 0.1 to 1.3 GeV.
Above 1.1 GeV (SATURNE II), the np database is insufficient and a high energy part
of the Aoi(np) predictions [14] still disagrees with the measured data.
Below 2.0 GeV, a usual meson exchange theory of NN scattering [15] gives the
Aoi(np) energy dependence as shown by the dotted curve in Fig.2. It can be seen that
this model provides a qualitative description only.
ACKNOWLEDGEMENTS
The authors thank the JINR, JINR LHE and LNP Directorates for their support of
these investigations.
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