Inclusive Asymmetries
(a retrospective view of V. L. Solovianov's work)
Mikhail N. Ukhanov
Institute for High Energy Physics,
Protvino, Moscow region, Russia
Abstract. In this talk I would like to present a retrospective view of the work done by Vladimir
L. Solovianov. He began his work in sixties in Dubna. And it happened to be that he participated
in many experiments, which were in the main stream of the experimental program over the
decades. In the last years he initiated several projects, which were again at the edge of the
investigation of the spin puzzle in the High Energy Physics domain.
SEVERAL FACTS OF HIS LIFE
He did his diploma project in the Dubna Joint Institute for Nuclear Research. After
graduation from the Moscow State University in 1964 he began his career in the
Institute for High Energy Physics in Protvino. In 1975 he defended his PhD in High
Energy Physics devoted to the studies of the energy dependence of p-p elastic
scattering cross section at 35-55 GeV. In the beginning of 80-s a new big accelerator
facility was started next to the existing U-70 ring. Solovianov became the spokesman
of NEPTUN - one of the experimental programs at UNK. The NEPTUN experiment
goal was the investigation of the polarization phenomena in interaction of the primary
UNK beam with internal polarized target. In 2001 together with Professor A.D. Krisch
from the University of Michigan he began the SPIN@U-70 project aimed at studies of
elastic scattering of the high intensity extracted 70 GeV proton beam with polarized
proton target.
SEVERAL EXPERIMENTS OF HIS LIFE
In his first experiment the asymmetry of TU+ production in polarized proton beam
interaction with hydrogen target at 612 MeV was measured at Dubna [1]. Part of these
studies comprised his diploma project and resulted in several publications. In Protvino
he entered a group, which conducted a series of experiments with polarized target
aimed at investigation of elastic scattering of various particle species on the polarized
protons in the energy range from 35 GeV to 55 GeV [2]. Then he began studies of
elastic scattering at the CERN SPS accelerator at 150 GeV [3]. A very significant part
of his activities was devoted to the measurements of inclusive asymmetry in rip
interactions at 40 GeV [4]. In the mid nineties he took part in the commissioning and
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
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running of the FNAL E704 experiment where many interesting results were obtained
[5].
FIGURE 1. Apparatus to study the elastic scattering on polarized
target at IHEP U-70 accelerator in Protvino
ELASTIC SCATTERING AT U-70
Setup Layout
This setup [6] was created to study the polarization effects in the elastic scattering
of positive and negative particles of various species on a polarized proton target at the
U-70 accelerator in IHEP, Protvino, see fig. 1. A propanediol target was embedded in
the magnetic field provided by two superconducting Helmholz coils. The field
direction was horizontal. The coil design allowed detection of the recoil protons in the
horizontal plane. The setup could do the measurements of both the spin rotation
parameter in the horizontal plane and the polarization parameter in the vertical plane.
The beam line design provided the beams of positive and negative particles with
only a small change in the position of the first five magnetic elements and installation
of a magnetic shield near the U-70 ring. The particle fluxes per burst were 3M for
negative sign and 1M for positive. Beam contents were determined by a set of
threshold Cherenkov counters. For the negative beam the percentage was 97.9/1.8/0.3
for TiVKVanti-proton. For the positive one it was 94/5/1 for p/7i+/K+.
Polarization and Spin Rotation Parameter Measurements
The polarization parameter P has been measured at 40 GeV for n~p-, K p-, p(bar)
p-interactions [7]. The event reconstruction uses information from the scintillation
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counters in order to determine the kinematics of each event. For quasi-elastic
scattering on bound nucleons the Fermi momentum of the target particle results in
different kinematics where, in particular, the coplanarity of the incident and outgoing
momenta and the exact angular correlation between the outgoing particle are no longer
verified. This feature is used to eliminate a large fraction of the background events.
The anticoincidence counters around the target provide a good rejection of reactions
with more than two charged particles in final state. The normalization of successive
runs with opposite target polarization was made using three different monitors:
-Counting of the incident particles.
-Counting events in the plane containing the target polarization.
-Counting the quasi-elastic events outside the elastic peak.
The latter monitor gave the most stable result. All three monitors gave the results,
which were consistent within errors.
Subtraction of the background under the "elastic peak" uses the data obtained with
a carbon target. The normalization of the carbon data to the polarized data was done in
the region outside the "elastic peak" of angular correlation distribution.
A total of 1.5M events were recorded for further analyses. During the exposition
two matrices were used to select the events for recording. One, called PHI-matrix,
required only two particles in the final state, which should satisfy the coplanarity
constraint. Another one put constraint on the scattering angle - the THETA-matrix.
The events, without the THETA trigger, come mostly from the quasi-elastic scattering
on the bound protons. They were used for the background subtraction. After the final
selection about 40K double scattering events retained with incident n and only 786
with K".
The method of data reduction and analyses in measurement of the spin rotation
parameter are essentially the same as for polarization measurement [8].
The results of polarization and spin rotation parameters are presented on fig 2 and 3
respectively. Measured P value in np elastic scattering extends up to \t\ = 1.8
(GeV/c)2. The characteristic dip is observed at the same value \t\ = 0.6 (GeV/c)2 as at
lower energies. The polarization in Kp at 40 GeV is consistent with zero up to \t\ ~ 0.5
(GeV/c)2. Data for p(bar)-p scattering exhibits an important structure. In particular,
large polarization at \t\ > 0.6 (GeV/c)2 shows an important contribution of the single
helicity flip amplitude.
The final selection of the spin rotation parameter measurements retains about 20K
events. The magnitude of R shows no significant variation with energy from 3.8 to 45
GeV. The t-dependence is weak and similar to those obtained in earlier experiments at
6 and 16 GeV.
50
nP
K'p
FIGURE 2. Transfer momentum distribution of
the polarization parameter in a) rip, b) K'p, c)
p(bar)-p interactions at 40 GeV. Lines are
prediction of various models see[7] for references,
FIGURE 3. Results for R in rip elastic scattering
at 40 GeV/c. The models prediction are represented
by dashed and dot-dashed lines respectively see [8]
for references. The solid line represents the
function R = -cos 9P,
POLARIZATION MEASUREMENT AT 150 GEV
This experiment was done at the CERN SPS accelerator in 1978 [3]. The setup
layout is shown on fig. 4. The polarization parameter was measured in the elastic pp
scattering at 150 GeV. The transfer momentum covers range from 0.2 < | t \ < 3
(GeV/c) . The measured elastic cross section spans 5 orders of magnitude going down
to -10 nb/(GeV/c)2 at | f | =3 (GeV/c)2.
The incoming beam reached the Polarized Target (PT) through a hole in the yoke of
the target magnet. The target consisted of 15 cm long 2 cm diameter propanediol
sample kept at 0.55 K in 2.5T magnetic field. The average polarization was 90%. A
carbon target was used for -20% of time to measure the background distribution from
scattering on bound protons. It consists of 10 graphite discs 5 mm thick equally spaced
in a copper container of the same size as the PT.
In order to have a good background rejection one needs precise measurements and
redundancy in determination of the kinematics of reaction. The scattered proton was
detected by counter and forward hodoscopes located at 49 meters. The trajectory, bent
by two magnets by 13 mrad, was measured by four sets of multi wire proportional
chambers (MWPC) with a precision of ±0.07 mrad.
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F5_!
RF3______F2F1
1.5
20
2,5
-t (GeV2)
FIGURE 4. Layout of the apparatus
used to measure the polarization
parameter at 150 GeV. The target region
is shown in lager scale at the bottom.
FIGURE 5. The polarization P(t) , calculated
from the separately fitted functions dN+/dt and dN~
/dtj is shown (solid line) together with the
experimental points.
The recoil proton was detected by the counters Tl and T2 located alongside the
target cryostat, and after 3.8 m by two scintillation hodoscopes. Also the time of flight
to the hodoscopes was measured. The recoil proton momentum was measured by six
MWPCs: two of them inside the magnet and four outside the filed region.
The relative errors in momentum determination were 1% in the forward arm, 2%
for low t and (2%p) for -t > 0.8 (GeV/c)2 in the backward arm.
The data analysis were done in three steps: I) at least one track required in both
arms; II) the tracks must originate from a vertex, with a vertex resolution of 1 mm; III)
after adjustment of the beam parameters, the kinematical 4C-fit should give the
positive result for the elastic scattering hypothesis. The selection criteria required the
vertex to be within 1 cm from the target axis and a 6% cut on the chi-square
kinematical fit probability.
From the shape of the chi-square distribution the signal to background ratio was
found to be between 3% at low t values up to 10% at high t. Further checks on
coplanarity, angular and momentum correlation supported this conclusion.
52
The polarization parameter dependence versus transfer momentum is shown on fig.
5. The solid curve represents the polarization calculated from independent fit of the
measured differential cross sections for two target polarizations.
The polarization parameter evidently becomes negative at around \t\ = I (GeV/c)2
and it tends to change the sign in the region where dip is observed in the differential
cross section. The t dependence is similar to the data obtained at 150 GeV in Fermilab
jet-target experiment, where recoil proton polarization was measured with a
polarimeter. At large r-values the polarization is definitely positive despite the errors,
agrees with the trend, observed in the Fermilab experiment at 300 GeV.
POLARIZATION IN 7TP-» TT N AT 40 GEV
The experiment was carried out at U-70 accelerator [4, 9]. The beam line design
was essentially the same as it was for the elastic scattering measurements [6]. In this
reaction the final state particles are all neutral. The gamma-quanta from 71° are
detected by the electromagnetic calorimeter (ECAL). The veto system suppresses
production of the charged particles in the ECAL aperture and gamma-quanta outside
it. The main part of the veto is made of the interlaced layers of lead-scintillator, which
are viewed by photomultipliers (PM). The hermeticity of the veto system is one of the
main issues. The overall suppression factor due to the veto system was about 10"5 from
the initial beam intensity.
FIGURE 6. Results for P in n'p elastic
scattering at 40 GeV/c. Model predictions
are also shown.
-95 •-
The neutrons were detected by two blocks, placed symmetrically relative to the
beam axis. Each block had acceptance of 30 degree in azimuth and 0.15 < \t\ < 1.3
(Gev/c)2. Each block consisted of 40 cells (5H x 8V). The cells were made of a
scintillator 10x10x50 cm3 viewed by a PM. The neutron detection efficiency was
about 30-35% for neutrons with energy greater than 200 MeV. All cells were
calibrated in the muon beam.
The ECAL was calibrated in the electron beams with energy from 10 to 40 GeV.
The energy resolution was 15%/V# +3% FWHM. Coordinate resolution for the single
gamma was 3 mm. The separation of two showers, required to reconstruct the energy
with efficiency about 90%, was 35 mm.
53
The scintillation hodoscope was mechanically attached to the ECAL platform. It
was used to monitor the beam position stability and provided the survey data for the
ECAL position relative to the beam hodoscopes.
In 1983 an upgrade was done to the electromagnetic calorimeter. As a result the
effective mass resolution was improved and available r-range was extended until \t\ =3
(GeV/c)2. The result of the polarization measurement in the charge exchange reaction
at 40 GeV is presented on the fig. 6. For the first time oscillation of the polarization
asymmetry was observed. At the transfer momentum \t\ < 0.4 (GeV/c)2 the
asymmetry is about 4-6% and positive. At the \t\ value ~0.25 a minimum is seen with
the confidence level of 99%.
SINGLE SPIN ASYMMETRY IN INCLUSIVE d> PRODUCTION
AT 200 GEVINPP INTERACTIONS
The well known state of the art polarized proton and polarized anti-proton beams
facility was designed at Fermilab and commissioned in E704 experiment [5]. The
design made use of the parity violating decay of the Lambda hyperons, which
provided the polarized beams. The polarization of the beam is determined by tagging
the beam particles trajectories. The tagged beam polarization values, which range from
0.65 to -0.65, are divided into three parts with average polarization of +0.45, -0.45
and 0. These values were confirmed by two independent measurements using
reactions of known analyzing power. A set of spin-rotating magnet changed the
direction of polarization from the transverse-horizontal to the vertical direction at the
experimental target and reversed the sign 4 or 5 times per hour. The whole setup
consisted of many detectors like proportional chambers, Cherenkov counters,
hodoscopes and calorimeters. Photons from the decay of neutral mesons produced in
100 cm hydrogen target were detected in the Central Electromagnetic Calorimeters
CEMC-1 and CEMC2, located symmetrically to the left and to the right of the beam
axis at 10 m from the target. The photon-pair background under the 71° peak, due to
uncorrelated pairs and 7i°s produced outside the target region, varied form 15% to
20%. The effective mass resolution varied from ±9 MeV/c2 at xF=0.1 to ±30 MeV/c2
at xF=0.7. The asymmetry in the mass region outside the 71° peak from 250 MeV to
450 MeV was found to be consistent with zero within statistical errors of less then 3%
over the entire range of XF.
In principle, each of the two CEMC detectors can be used to determine the
asymmetries either with the two oppositely polarized parts of the beam or with beam
polarization reversal by the spin-rotating magnets. The observed consistency among
the different ways to calculate the asymmetry provides a check of instrumental errors.
The calculated "false asymmetry" for events tagged with an average zero beam
polarization was found to be less then 1% for PT up to 3 GeV/c and less 3% for higher
PT values. The relative systematic error proportional to An is about 10% and mainly
due to the uncertainty in the beam polarization and a small contribution from
uncorrelated photon pairs and neutral mesons produced outside the target volume.
54
1
1
1
1
t>
1.4 O
1
1
lo.io
FIGURE 7. a) Plot of the asymmetry parameter An
as a function of XF averaged over pT b) The "false
asymmetry calculated for events with beam
polarization of zero. Only the statistical errors are
shown.
0.05
o
^-jhfci.
0.05
(b)
i
0
.2
' i. '
'i
A
.6
i
XF
.
The results on asymmetry measurements versus XF is shown on the fig. 7. The
growth of asymmetry when 71° momentum gets close to the polarized incident proton
momentum allude to the valence quark responsibility.
RAMPEX EXPERIMENT
The experiment is aimed at measurement of the single spin inclusive asymmetries
in Tip f interactions at 40 GeV and pp f interactions at 70 GeV for various final state
particles [12]. The experiment uses beam line #14 at U-70 accelerator in IHEP,
Protvino.
Incident beam particles strike the polarized proton propanediol target. The
secondary particles are detected in the setup, which consist of the charged particle
spectrometer and two calorimeters. The charged particle spectrometer has a traditional
composition: five sets of proportional chambers, analyzing magnet and two multichannel threshold Cherenkov counters for particle identification.
FIGURE 8. Layout of the RAMPEX Experiment
55
The central axis of the setup is rotated by 10 degrees relative to the beam direction
which corresponds to 90 degrees in the center of mass system. The trigger system has
two sources - the electromagnetic and hadron calorimeters. In both calorimeters the
trigger signal comes from fast analog sum of signals of the calorimeter cells weighted
to be proportional to the transverse energy deposition in the calorimeter. The
spectrometer acceptance allows detection of the final state particles produced with
transverse momentum more than 3 GeV/c and -0.3 < XF < +0.6.
The whole apparatus was commissioned in 2000. Accumulated data is being
analyzed and the apparatus tuning has been performed in the series of tune-up runs.
SPIN@U70 SPECTROMETER
The SPIN@U-70 experiment was approved by the IHEP (Protvino) PAC in 2001.
The main goal of the experiment is the measurement of spin effects in the elastic
scattering of 70 GeV protons with a polarized proton target in the domain of extremely
high transverse momentum of the recoil proton.
Movable recoil arm of the spectrometer consist of (starting from the interaction
point) a pair of focusing quadrupole magnet (Ql, Q2), swiping dipole magnet (Ml),
another pair of quadrupoles (Q3, Q4) and bending magnet (M2). The momentum of
the recoil proton is measured in the spectrometer magnet (M3), which bends the
particle by 12 degrees upward.
FIGURE 9. Layout of the SPIN @ U70
Spectrometer.
M3
Since elastic production cross section at transverse momentum squared of 12
(GeV/c)2 is about 0.3 pb one needs high intensity beam to reach such values. The
experimental setup utilizes the beam line #8 of the U-70 accelerator in IHEP, Protvino.
The high intensity proton beam comes from the U-70 ring using the bent crystal slow
extraction technique
The beam parameters were measured in the tune up run in April 2002. During the
run the design values of the beam size and the stability of the beam position at the
interaction point were achieved. The recoil arm magnets setting were also tuned
56
during this run using the polyethylene target equivalent and simplified detector set by
detection of elastic events at low transverse momentum. More detailed report on
the.results of this run was given at the Prague Spin and Symmetry Symposium in July
2002 and in report given by Luppov V.G. on this conference [11].
ACKNOWLEDGMENTS
I would like to thank the organizing committee for the hospitality and support they
provided me during my stay at BNL. I am also grateful to the IHEP directorate who
encouraged and supported my trip to this conference.
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