SPIN@U-70: An Experiment to Measure
the Analyzing Power An in Very-high-/*/p-p
Elastic Scattering at 70 GeV*
V.G. Luppov1**, L.V. Alexeevala, V. A. Anferovlb, E.D. Courant1,
Ya.S. Derbenev1, G. Fidecaro10, M. Fidecaro10, F.Z. Khiarild,
S.V. Koutinla, A.D. Krisch1", M.A Leonovala, A.M.T. Lin1,
W. Lorenzon1, VS. Morozovla, D.C. Peasleele, C.C. Peters1,
R.S. Raymond1, D.W. Siverslf, J.A. Stewartlg, S.M. Varzar1",
V.K. Wong1, K. Yonehara1, D.G. Crabb2, Yu.M. Ado3, A.G Afonin3,
V.I. Belousov3, B.V. Chujko3, A.N. Davidenko3, N.A. Galyaev3,
V.I. Garkusha3, V.N. Grishin3, V.A. Kachanov3, Yu.V. Kharlov3,
V.I. Kotov3, A.V. Kusnetsov3, V.A. Medvedev3, Yu.M. Melnik3,
V.V. Mochalov3, A.I. Mysnik3, S.B. Nurushev3, A.F. Prudkoglyad3,
P.A. Semenov3, V.L. Solovianov31", V.P. Stepanov3, V.A. Teplyakov3,
S.M. Troshin3, A.G. Ufimtsev3, M.N. Ukhanov3, A.E. Yakutin3,
V.N. Zapolsky3, V.G. Zarucheisky3, N.S. Borisov4, V.V. Fimushkin4,
V.A. Nikitin4, P.V. Nomokonov4, LA. Rufanov4, Yu.K. Pilipenko4,
P.P.J. Delheij5, W.T.H. van Oers5, and A.N. Zelenski5h
1
2
University of Michigan, Ann Arbor, USA
University of Virginia, Charlottesville, USA
3
IHEP, Protvino, Russia
4
JINR, Dubna, Russia
5
TRIUMF, Vancouver, Canada
Abstract. The SPIN@U-70 experiment plans to measure the one-spin analyzing power An for
70 GeV proton-proton elastic scattering at large P± values of 1 to 12 (GeV/c)2. The Michigan
frozen NH3 polarized proton target (Solid PPT) should later be installed in the Channel 8
extracted beam-line of the 70 GeV U-70 accelerator in IHEP, Protvino. The forward-scattered
protons are detected by small scintillation counters placed at about 9 m from the PPT, while the
Supported by a U.S. Department of Energy Research Grant
E-mail: [email protected]
Spokesperson for SPIN@U-70 Collaboration, e-mail: [email protected]
Deceased
Also at: Moscow State University
Also at: IUCF
Also at: CERN
Also at: UCAPS/RI, King Fahd University
Also at: University of Maryland
Also at: Portland Physics Institute
Also at: DESY-Zeuthen
Also at: Brookhaven/INR-Moscow
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
538
recoil-scattered protons are detected by a 35-m-long focusing magnetic spectrometer, with a
12 degree vertical bend, placed at 30 degrees to the beam. A tune-up run for testing the beam
and the spectrometer, using a polyethylene target, was carried out in April 2002 at IHEP. The
layout and the results of the test run are presented.
The SPIN@U-70 experiment plans to use a high intensity 70 GeV unpolarized
extracted proton beam from the U-70 accelerator at IHEP-Protvino in Russia to
measure the analyzing power An in p + p^ —» p + p at large-P^2. We would scatter
the high intensity beam from a polarized proton target and measure the quantity,
A
_
mea _
where Amea is the measured asymmetry, PT is the target polarization, and JV(T) and
N(i) are the normalized elastic event rates with the spin up and spin down,
respectively.
Our main goal is to determine if the
unexpected large value of An,
• 24 GeV CERN
discovered in large-P/ proton-proton
• 28 GeV AGS
• 24 GeV AGS
elastic scattering at the AGS, persists to
-3
higher energy and larger P± [1,2]. At
24 GeV the one-spin analyzing power
An was found to be 20.4% ± 3.9% near
P_L of 7 (GeV/c)2, as shown in Fig. 1.
This large and unexpected spin effect
has been difficult to reconcile with
conventional
models
of
strong
interactions such as perturbative
Quantum Chromodynamics (PQCD).
The validity of PQCD is predicted to
improve with increasing energy and
-.1 increasing P± . This 70 GeV experiment
would increase the maximum P± by a
factor of about 1.7; it would also
increase the maximum energy for An
data at high-P^2 by a factor of about 2.5.
The experiment would use the
Michigan 1-watt-cooling-power solid
FIGURE 1. The analyzing power An is plotted
polarized proton target containing against P± for spin polarized proton-proton
radiation-doped frozen ammonia (NHs) elastic scattering at 24 and 28 GeV.
beads. This target [3] successfully
operated with an average polarizaton of 85% during a 3-month run at the AGS with an
average beam intensity of 1011 protons per sec; this allowed the precise large P±
measurements [1] ofAn shown in Fig. 1.
.1
539
The SPIN@U-70 spectrometer is shown in Fig. 2. The forward-scattered protons
are detected by small scintillation counters placed at about 9 m from the PPT, while
the recoil-scattered protons are detected by a 35-m-long focusing magnetic
spectrometer, with a 12 degree vertical bend, placed at 30 degrees to the beam.
Table 1 lists the angles and momenta for both the forward and recoil protons, as well
as the \B - dl of the recoil-spectrometer magnets for various P±. The dipole fields
for the spectrometer's angles were calculated from the recoil protons' kinematics. The
beam optics program TRANSPORT calculated the quadrupoles' gradients needed to
focus the recoil protons to fit through the spectrometer's apertures. Most focusing is
done by the vertically focusing Qi and the horizontally focusing Cfa; this gives the
spectrometer a larger vertical acceptance angle A^ ai (=A^ /a6 sin^ 2 ) than its
horizontal acceptance angle A8lab. For each P±, the horizontal angle 0R is correlated
with the elastic recoil momentum PR.
Q1,Q2,Q3,Q4 are quadrupoles
1U,M2,H3 are dipoles
RH1,RV1.EH2,RV2 for recoil proton angle
W1,W2,¥3,T4 for recoil proton momentum
S1,S2,S3 for recoil proton Ume-of—flight
FV1.FV2 for forward proton angle
8123,0123,11123 for beam Interaction monitors
RHj, RHj
RV3 RVi
30m
20m
10m
0
FIGURE 2. SPIN@U-70 spectrometer.
We estimated the event rates and errors in An for large-P^2 proton-proton elastic
scattering at U-70 using the Michigan solid PPT and the SPIN@U-70 recoil
spectrometer in U-70's Channel 8 extracted 70 GeV proton beam-line. Table 2 lists
the estimated event rate and error inAn for each P± point. We may run with a lower
beam intensity at P± = 1 (GeV/c)2 to reduce accidentals since the statistical precision
is around 0.03%. Note that a superconducting quadrupole magnet Qi is required in the
veiy-large P± region. The measurements of An should be rather precise, with an error
of less than 1%, forP/ up to 6.0 (GeV/c)2, and less than 5% atP/ = 12.0 (GeV/c)2.
In spring 2001, installation of SPIN@U-70 started in the Channel 8 extracted
beam-line of the 70 GeV U-70 accelerator in IHEP. The 35-m-long recoil
Spectrometer's MI, Nfe, and MS dipoles and Qi, Cfa, Qs, and Q4 quadrupole magnets,
their movable stands, electric and water systems were installed. On 5-10 November
2001, a beam tune-up run showed that the Channel-8 extracted beam at the PPT
540
TABLE 1. Angles and momenta of elastic protons and magnet strengths. Positive
corresponds to bending to the right for PPT, MI and M2 and bending up for M3. The recoil
angle after the PPT magnet is 0^; it differs from BR by « eBle/^T IPR .
Pi
BF
2
degrees
PF
GeV/c
degrees
PR
GeV/c
0.825°
1.176°
1.452°
1.690°
1.906°
2.107°
2.296°
2.477°
2.653°
2.824°
3.159°
69.5
68.9
68.4
67.8
67.2
66.6
66.0
65.4
64.8
64.2
62.9
61.44°
52.19°
46.22°
41.87°
38.48°
35.72°
33.41°
31.44°
29.72°
28.20°
25.61°
1.139
1.790
2.399
2.997
3.594
4.196
4.804
5.423
6.051
6.692
8.015
(GeV/c)
1
2
3
4
5
6
7
8
9
10
12
BR
BlSr
kG-m
4.42
4.46
4.50
4.54
4.57
4.61
-4.65
-4.69
-4.73
-4.77
-4.85
PR
degrees
54.94°
48.08°
43.17°
39.44°
36.46°
34.00°
34.91°
32.76°
30.89°
29.26°
26.48°
Djeff
M\
KL
kG-m
31.5
36.3
35.7
32.1
26.4
19.1
26.8
17.0
6.2
-5.7
-32.1
*&
kG-m
-15.8
-18.0
-17.6
-15.7
-12.9
-9.4
-13.1
-8.3
-3.0
2.8
15.7
Djeff
M3
m
kG-m
7.94
12.48
16.73
20.90
25.06
29.26
33.50
37.82
42.20
46.67
55.89
TABLE 2. Event rates and errors in An for p-p elastic scattering at U-70.
Pi
(GeV/c)
(GeV/c)
mr
1.0
2.0
3.0
4.0
5.0
6.0
0.06
0.09
0.25
0.35
0.45
0.56
159
177
194
210
225
240
4000
90
7.0
8.0
9.0
10.0
12.0
0.67
0.79
0.92
1.06
1.25
254
268
282
296
324
2
At
dtfdt
2
Events
per hour
Hours
Events
(N)
4.0
0.9
0.22
230000
8600
5500
1800
550
180
100
100
100
100
100
200
2.3 107
8.6 105
5.5 105
1.8 105
5.5 104
3.6 104
0.03%
0.1%
0.2%
0.3%
0.5%
0.6%
0.055
0.016
0.0047
0.0017
0.0003
56
20
7.3
3.2
0.73
200
300
400
600
800
1.1 104
6.0 103
2.9 103
1.9 103
5.8 102
1.1%
1.5%
nb
(GeV/c)2
19
[.ssV^T1
Super Q!
2.2%
2.7%
4.9%
location can be as small as 2.5x2.5 mm FWHM and can stay centered within 0.5 mm.
A typical beam intensity was 1 - 4 • 1011 protons/pulse. During the run a vertical
beam rastering system was successfully tested. During U-70's January-February 2002
shut-down, IHEP finished installing SPIN@U-70. On 11 March 2002, Michigan's
shipment of detectors and electronics, needed for the April 2002 run, arrived at
Moscow's SVO Airport. This shipment was then impounded by Russian Customs.
[Note added: In early November 2002 it was returned to Michigan.]
Although the shipment of equipment was impounded, a short 19-26 April 2002 test
run still occurred, using a polyethylene target. Some simple IHEP detectors and
electronics were prepared in only a few weeks and were successfully used for the run.
The resulting almost 100 to 1 signal to background rate in the 81-81.5 coincidence data,
541
shown in Fig. 3, indicates that the 35-m-long Elastic Recoil Spectrometer is quite
effective in discriminating against inelastic and other background events.
800
700
600
500
400
300
= 2.10
M3 = 0.32
200
FIGURE 3. Magnet Curve: The
Elastic Recoil Spectrometer event
rate (81-81.5 coincidences) is plotted
against the current in the 3-m-long
68-ton MI bending dipole magnet.
Note that the ratio of the signal to
background is almost 100 to 1 in the
elastic peak. The single detector data
rates are also shown along with the
coincidences between the closetogether S2 and S3 detectors.
100
MI current
Unfortunately, due to the problems with Russian Customs, the SPIN@U-70
experiment was recently suspended until the problems can be fully resolved.
1. D. G. Crabb et a/., Phys. Rev. Lett. 65, 3241 (1990).
2. P. R. Cameron et a/., Phys. Rev. Rap. Comm. D32, 3070 (1985);
D. C. Peaslee eta!., Phys. Rev. Lett. 51, 2359 (1983);
P. H. Hansen et a/., ibid 50, 802 (1983).
3. D. G. Crabb et a/., Phys. Rev. Lett. 64, 2627 (1990).
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