Table Of ContentAbsolute polarimetry at RHIC
H. Okada1, , I. Alekseev†, A. Bravar2, , G. Bunce ,‡, S. Dhawan§,
∗ ∗∗ ∗∗
K.O. Eyser3,¶, R. Gill , W. Haeberli , H. Huang , O. Jinnouchi4,‡,
∗∗ k ∗∗
Y. Makdisi , I. Nakagawa††, A. Nass5, , N. Saito6, , E. Stephenson‡‡,
∗∗ ∗∗ ∗
D. Sviridia†, T. Wise , J. Wood and A. Zelenski
8 k ∗∗ ∗∗
0
0 KyotoUniversity,Sakyo-ku,Kyoto606-8502,Japan
∗
2 †InstituteforTheoreticalandExperimentalPhysics(ITEP),117259Moscow,Russia
BrookhavenNationalLaboratory,Upton,NY11973,USA
n ∗∗
a ‡RIKENBNLResearchCenter,Upton,NY11973,USA
J §YaleUniversity,NewHaven,CT06520,USA
9 ¶UniversityofCalifornia,Riverside,CA92521,USA
kUniversityofWisconsin,Madison,WI53706,USA
] ††RIKEN,Wako,JAPAN
x ‡‡IndianaUniversityCyclotronFacility,Bloomington,IN47408,USA
e
-
l
c Abstract. Precise and absolute beam polarization measurements are critical for the RHIC spin
u physicsprogram.Because all experimentalspin-dependentresults are normalizedby beam polar-
n
ization,thenormalizationuncertaintycontributesdirectlytofinalphysicsuncertainties.We aimed
[ toperformthebeampolarizationmeasurementtoanaccuracyofD Pbeam/Pbeam<5%.
2 The absolute polarimeter consists of Polarized Atomic Hydrogen Gas Jet Targetand left-right
v pairs of silicon strip detectors and was installed in the RHIC-ring in 2004. This system features
9 proton-protonelasticscatteringintheCoulombnuclearinterference(CNI)region.Precisemeasure-
8 mentsoftheanalyzingpowerA ofthisprocesshasallowedustoachieveD P /P =4.2%in
N beam beam
3 2005forthefirstlongspin-physicsrun.
1
In this report, we describe the entire set up and performanceof the system. The procedure of
.
2 beampolarizationmeasurementandanalysisresultsfrom2004 2005aredescribed.Physicstopics
1 ofA intheCNIregion(four-momentumtransfersquared0.00−1< t<0.032(GeV/c)2)arealso
N
7 discussed.Wepointoutthecurrentissuesandexpectedoptimumac−curacyin2006andthefuture.
0
: Keywords: Elasticscattering,spin,coulombnuclearinterference
v PACS: 13.88.+e,13.85.Dz,29.27.Pj,29.27.Hj
i
X
r Introduction
a
The RHIC spin physics program has been a unique opportunity and important com-
ponent of the overall RHIC physics program. Essential to this spin program are the
polarized proton beams to investigate spin-dependent structure in the nucleon. Several
types of spin-dependent asymmetries in high energy proton-proton (pp) collisions pro-
1 Presentaddress:BrookhavenNationalLaboratory,Upton,NY11973,USA
2 Presentaddress:UniversityofGeneva,1205Geneva,Switzerland
3 Presentaddress:DeutschesElektronenSynchrotron,22607Hamburg,Germany
4 Presentaddress:KEK,Tukuba,Japan
5 Presentaddress:UniversityofErlangen,91058Erlangen,Germany
6 Presentaddress:KEK,Tukuba,Japan
vide detailed studies of the structure of the proton at a new level of accuracy. Because
all experimental results are normalized by beam polarization, P , the normalization
beam
uncertainty contributes directly to final physics uncertainties. Therefore accurate and
absolutepolarization measurements are crucial. P is obtained from raw asymmetry,
beam
e , for the transversely polarized proton beam divided by analyzing power, A , of a
beam N
certain interactionasshowninEquation1.
e
beam
P = (1)
beam
A
N
We aimed to achieve an accuracy of D P /P < 5% at any beam energy from
beam beam
injection (24 GeV/c) to flat-top (100 GeV/c and 250 GeV/c in the near future). Ideal
interactionsforpolarimetryshouldsatisfythefollowingconditions:
1. well-knownormeasureableand non-zero analyzingpower,
2. high event rate interaction (large cross-section and/or thicker target) to save data
takingtime,
3. similarkinematicsfordifferent beammomentaforcommondetectorset up.
The elastic scattering of the polarized proton beam off a nuclear target A (p A
↑
→
pA) in the Coulomb nuclear interference (CNI) region is an ideal process. We choose
proton and carbon for A. A is a function of four-momentum transfer squared, t.
N
We are looking at very small t in the order of 10 3 (GeV/c) 2. We have two ty−pes
− −
−
of polarimeters to meet above requirements. One is the RHIC pC-polarimeter, which
satisfies item 2 and 3. This polarimeter serves as a semi-on-line beam polarization
monitor during the RHIC-run period to tune up the beam acceleration. The RHIC
pC polarimeter also provides fill-by-fill offline P results to experimental groups.
beam
However,its accuracy islimited(D P /P >20%)mainlydueto a difficultyof t
beam beam
−
range measurement in pC elastic scattering. This difficulty is connected to the need to
caliblateeach year.Theotherpolarimeter,thePolarizedAtomicHydrogenJetTarget
Polarimeter (H-Jet polarimeter in short) serves as an absolute calibration of the RHIC
pCpolarimeter.TheH-Jet polarimetersatisfies item1 and 3. In thisreport, we focus on
theH-jet polarimeter.Details oftheRHIC pCpolarimeterare discussedin[1].
The pp elastic scattering process is 2-body exclusive scattering with identical parti-
cles. A for the target polarization and the beam polarization should be same as shown
N
inEquation2. e e
target beam
A = = , (2)
N
−P P
target beam
e israwasymmetryfortheppelasticscatteringforthetransverselypolarizedproton
target
targetandP isawellcalibratedpolarizedprotontarget,whichwewilldiscusslater.
target
Therefore we can change the role of which is polarized between the target proton and
thebeam proton.Thenthebeam polarizationismeasured as:
e
beam
P = P . (3)
beam targete
−
target
ThebeautyoftheH-Jetpolarimeteristhatwecancancelthecommonfactorsofsystem-
aticuncertaintyofe and e .By accumulatingenoughstatistics,D P /P
target beam beam beam
D P /P is realizable. AlthoughA does notappear explicitlyin Equation 3, pr≈e-
target target N
cisemeasurementsofA areveryimportanttoconfirmthattheH-Jetpolarimeterworks
N
properlyat anytime.
In addition to polarimetry, precise measurements of A in the CNI region are im-
N
portant to understand the reaction mechanism completely. The pp elastic scattering is
describedinspin-flipand non-fliptransitionamplitudes.Each amplitudeisasumofthe
electro magneticandhadronicforces as functionsof√sand t.A isexpressedas,
N
−
Im[f em(s,t)f had (s,t)+f had(s,t)f em(s,t)]
A SF NF ∗ SF NF . (4)
N ≈− f em(s,t)+f had(s,t) 2
| NF NF |
The electro magnetic part of amplitudes (f em(s,t) and f em(s,t)) are precisely under-
NF SF
stood by quantum electrodynamics (QED). The hadronic part of the non-flip amplitude
(f had(s,t)),whichisrelatedtotheunpolarizeddifferentialcross-sectionandtotalcross-
NF
section via the optical theorem at t = 0, is also understood very well. The first term
of Equation 4 is calculable and ha−s a peak around t 0.003 (GeV/c)2 [2] which is
− ≃
generated byproton’sanomalousmagneticmoment.
However,thesecondterm,whichincludesf had(s,t),isnotwell-known.Thehadronic
SF
reaction in the CNI region is described by non-perturbative quantum chromodynamics
(QCD) and a precise prediction is not available. The presence of f had(s,t) should
SF
introduce a deviation in magnitude from the first term and, consequently, there is no
precisepredictionofA .AninitialmeasurementofA intheCNIregionwasperformed
N N
by the E704 experiment at 200 GeV/c [3]. However, precision of data was insufficient
forpolarimetry.
In the followingsections,we will introducethe H-Jet target system,experimental set
up and analysis procedures and then we will report on A results from RUN4. We will
N
also report on P from RUN5 which was the first long spin-physics run. Finally, we
beam
willdiscusscurrent issuesand expectedoptimumprecisionin 2006and thefuture.
H-Jet-target system
The system was installed in the RHIC-ring tunnel for the first time in March 2004.
The commissioningwas successfully done. Assembly sequence of the systemhad been
completed within 15 months [4, 5]. The H-Jet-target system is 3.5 m in height and
approximately 3000 kg in weight. The target is a free atomic beam, comes from the
top in Figure 1, and crosses the RHIC proton beams perpendicularly. In this report, we
define the negative y-axis as the atomic beam direction and the positive z-axis is the
RHIC proton beam direction. The velocity of the atomic beam is 1560 20 m/s [4]
±
and negligible with respect to the RHIC beam. The H-Jet-target system is placed on
rails along the x-axis. The entire system can be moved along the x-axis by 10 mm,
±
in order to adjust the target center to the RHIC beam center. As Figure 1 displays, the
systemconsistsofmainly3 partsincludingninevacuumchambersandninedifferential
vacuumstages:
1. AtomicBeam Source, ABS: 1stto5th chambers.Polarize theatomichydrogen.
2. Scattering chamber: 6th chamber. Collisions between the target-proton and the
beam-proton occur here. The recoil spectrometers are mounted on both sides of
flanges.
3. Breit-Rabi Polarimeter, BRP: 7th to 9th chamber. Measure nuclear polarization,
P .
±
+ -
H = p + e H2dissociator
|1> |2> |3> |4> Hyperfine state
Sextupolemagnets system ABS
separating
focusing
RF transitions
(SFT, WFT)
Nuclear polarization
Holding Scattering
P+ OR P-
field magnet chamber
Sextupolemagnets system BRP
nd
separating 2 RF
transitions
focusing
for
calibration
Ion gauge beam detector
FIGURE1. H-Jetsystemoverview.
The polarization cycle was (+/0/ )=(500/50/500) seconds and Figure 2 displays a
−
sampleofthemeasuredP inthe2004commissioningrun[6]. H-Jet-target systemwas
stable over the experimen±tal period. The mean values for nuclear polarization of the
atoms: P =0.958 0.001.
| ±| ±
1
r.
a
ol
p
0.98
0.96
0.94
l P+ m -(P-)
0.92
0 5 10 15 20
time (h)
FIGURE2. NuclearpolarizationmeasuredbyBRPin2004.
The BRP measures the atomic hydrogen polarization, therefore we need to account
for the effect on the polarization from background hydrogen molecules. Actually, there
werestillsomemolecularhydrogeninthescatteringchamberandthemeasurementwas
H /H 0.015[4].Thismeansthatthedilutionisabout3%intermsofhydrogenatoms.
2
∼
Assumingthemolecularhydrogenisunpolarized,theeffectivetargetpolarizationinthe
2004commissioningrunwas P =0.924 0.018.
target
±
6000
u.)16000
5000 nt (a.14000
u12000
.u.) 4000 nt Co10000
(a 3000 6.5 mm Eve 8000
e FWHM = 6.9 mm
at 2000 6000
r 4000
1000
2000
2.5 mm
0 00 10 20 30 40 50 60 70 80 90 10·0103
0 5 10 15 Position Gage
position (mm)
FIGURE3. Left:Atomicbeamprofilemeasurementsbythecompressiontubemethod.Right:Atomic
beamprofilemeasurementsbyRHIC-beamandtherecoilspectrometer.
Next,wedescribetheprofileandthedensityofatomicbeambriefly.Theatomicbeam
profilewas measured witha2mmdiametercompressiontube.Theresultsare displayed
in left side of Figure 3. At the center of the scattering chamber, the FWHM of the
atomic beam is 6.5mm and agrees with the design value. Furthermore, we measured
the target profile by fixing the RHIC beam (s 1 mm) position and moving the
∼
entire H-Jet-target system in 1.5 mm steps. The right side of Figure 3 displays event
counts detected by recoil spectrometer versus position. Comparing left and right plots
of Figure 3, the two independent measurements agree very well. The target profile
measurementusingRHIC-beamisimportanttofindthebestcollisionpointandestimate
the unpolarized background fraction. The total atomic beam intensity in the scattering
chamberwasmeasuredtobe(12.4 0.2) 1016atoms/s[6].Takingthemeasuredatomic
± ·
beamintensity,velocityandprofile,thearealtargetthicknessalongRHICbeamaxis(the
z-axis)wascalculated to be(1.3 0.2) 1012atoms/cm2 [4].
± ·
Recoil spectrometer
The left side of Figure 4 displays a schematic layout of the experimental set up to
detectppelasticscatteringevents.Recoilprotonsweredetectedusinganarrayofsilicon
detectorslocatedtotheleftandrightofthebeamatadistanceD 80cm.Threepairsof
≃
silicondetectorscoveredanazimuthalangleof15 centeredonthehorizontalmid-plane.
◦
Detectors were 70.4 50 mm2 in size, with a 4.4 mm read out pitch for a total of 16
×
channelsperdetector.Wecoverrecoilprotonsofkineticenergyof0.6 T 17.0MeV.
R
The recoil angle, q , is obtained by the detector channel number in ≤ 5.5≤mrad steps.
R
≃
ThisangularresolutioniscomparabletotheH-Jet-target size.
The silicon detectors were 400 m m thick. Recoil protons with kinetic energies,T ,
R
∼
up to 7 MeV are fully absorbed. The energy calibration of the silicon detectors was
performed using two a sources 241Am, 5.486 MeV (and 148Gd, 3.183 MeV for three
out of six detectors). Resolution of T in the fully absorbed region is D T = 0.6 MeV.
R R
More energetic protons punched through the detectors, depositing only a fraction of
their energy. Therefore T for punch-through protons needs to be corrected using the
R
detector thickness and tables for energy loss in silicon [7]. The 4-momentum transfer
s)100
n
F (
o
T 80
Left side
recoil detector
60
40
proton 20
target
RHIC
proton beam 0
Right side
recoil detector 0 2 4 6 8 10 12 14 16 18 20
T (MeV)
R
FIGURE4. Left:Sketchofleft-rightpairofsilicondetectors.Right:ThecorrelationbetweenTOF and
the incident energy,T , in one of the silicon detectors. Two solid lines correspondsto 8 nsec shifted
R
±
withrespecttotheexpectedTOFvalueforgivenT fromEquation5.
R
squared is given by t =2M T . The time-of-flight, TOF, is measured with respect to
p R
−
the bunch crossing timed by the accelerator RF clock. The estimated TOF resolution is
D TOF 3nsecandaresultoftheintrinsictimeresolutionofthedetectors( 2nsec)and
thelen≃gthoftheRHICbeambunches(s 1.5nsec).Detailsoftherecoil≤spectrometer
≃
andanalysisforRUN4 are discussedin[8].
Elastic event selection
In the pp elastic scattering process, both the forward-scattered particle and the recoil
particle are protons and no other particles are produced in the process. The elastic
process can be identified by detecting the recoil particle only, by identifying the recoil
particle as a proton throughout the relation of TOF and T , and by observing that the
R
missing mass of the forward scattered system is the proton mass. Recoil protons were
identifiedusingthenon-relativisticrelation
1
T = M (D/TOF)2. (5)
R p
2
The right plot of Figure 4 displays T and TOF correlation from one detector for 16
R
channels.WecanseerecoilprotonsclearlyaroundtheexpectedTOFvalueforT .Inthis
R
figure,theenergyforpunch-througheventshavebeencorrected[8,9].Theeventswhich
are vertically distributed around 5.5 MeV are from the calibration a source (241Am).
(The punch-through correction causes another vertical distribution around 7.5 MeV.)
Events less than 3 MeV and less than 30 nsec are prompt particles, which are possibly
pions from beam-related interactions upstream. Events were selected in a TOF interval
of 8 nsec around the expected TOF value for recoil protons of a given T as shown in
R
±
twolinesinthefigure.
Onthebasisofthemeasuredq andT ,themassoftheundetectedforwardscattered
R R
system(themissingmassM ) can bereconstructed,
X
M 2 =M 2 2 (M +E )T sinq 2M T (E2 M2) , (6)
X p − (cid:16) p 1 R− Rq p R 1− p (cid:17)
event count (a.u.)11124680000000000000 Signal-channels
12000
10000
8000 Side-channels
6000
4000
2000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
channel#
FIGURE5. EventdistributionofacertainT intervalasfunctionofchannelnumber.
R
whereE istheenergy oftheincidentbeamproton.For pp elasticscattering,eventsare
1
identifiedonthebasisoftheq -T relation
R R
E M
T =2M sin2q 1− p, (7)
R p R
E +M
1 p
which is obtained applying M = M in Equation 6. The difference for E = 24 GeV
X p 1
and E =100 GeV, the two beam energies reported here, is 3 mrad at T =17 MeV
1 R
∼
andsmallershiftatlowerenergiesFigure5displaystheeventdistributionofacertainT
R
interval as function of channel number. For each T bin pp elastic events were selected
R
intheproperdetectorstripscentered around theexpectedq angle.
R
The channel for diffractive dissociation opens at MX > Mp+Mp = 1.08 GeV/c2.
The kinematical boundary for MX = Mp+Mp is given by Equation 6 and is out of
the acceptance for E = 24 GeV. For E = 100 GeV, the kinematical boundary for
1 1
the MX = Mp+Mp is inside the acceptance for TR > 8 MeV. But the contamination
isestimatedtobelessthan 0.5%from M spectra.
X
The selected event yield is sorted by T bins. We collected 4.3 M events in fourteen
R
T bins at 100 GeV/c and 0.8 M events in nine T bins at 24 GeV/c in the region
R R
0.001 t 0.035 (GeV/c)2 (0.5 T 17 MeV) using the "clock-wise" beam.
R
≤− ≤ ≤ ≤
Furthermore,theselectedeventyieldineachT binissortedbyspinstates(beam,target,
R
up-down) and the detector side (left-right). Finally, we calculate raw asymmetries of
targetorbeam polarizationusingthesquare-root formula:
NL NR NR NL
q q
e = ↑ · ↓ − ↑ · ↓ , (8)
NL NR+ NR NL
q q
· ·
↑ ↓ ↑ ↓
where if we sort by H-Jet-target (beam) polarization, we have e (e ). This
target beam
expressioncancels luminosityand acceptances asymmetries.
A measurements from RUN4
N
A dataare obtainedas follows:
N
e 1
target
A = , (9)
N
− P 1 R
T BG
−
whereR isthebackgroundlevelsforeachT bin.Thebackgroundsconsistedof(a)a
BG R
particles from the calibration sources, (b) beam scraping, and (c) beam scattering from
theunpolarizedresidual target gas.The dominantcomponentwas (c), dueto unfocused
molecular hydrogen, and was accounted for as a dilution of the target polarization.
Therefore, R isestimatedtobe0.02 0.03from(a) and (b)[9].
BG
∼
Figure 6 displaystheresultsfor A at 100 GeV/c(open circles)and 24 GeV/c(black
N
filledcircles)in2004.Theuncertaintiesshownarestatistical.Thelowerbandsrepresent
the total systematicuncertainties. The thick and thin solid lines are the QED prediction
withnospin-dependenthadroniccontribution(f had)andcorrespondstothefirsttermin
SF
Equation4 at thesebeam momenta.
N
A0.07 24 GeV/c
100 GeV/c
0.06
f had=0, 24 GeV/c
SF
0.05 f had=0, 100 GeV/c
SF
0.04
0.03
0.02
0.01
0
10-3 10-2
-t (GeV/c)2
FIGURE 6. A data at 24 GeV/c and 100 GeV/c. The uncertainties shown are statistical and lower
N
bandsrepresentthesystematicones.ThickandthinsolidlinesaretheQEDpredictionwithoutf had.
SF
Sources ofsystematicuncertaintiescomefromT bin-dependentandoverallnormal-
R
ization:(1)theuncertainty onthetarget polarizationgivingan overallD P /P =
target target
2.0% normalization uncertainty; (2) the left-right detector acceptance asymmetry; (3)
event selection criteria; and (4) background contribution from (a) and (b). The major
componentwas (2)at the lowestand highest T bins from detectoredges. We also have
R
arelativelylargeacceptance asymmetryatthepunched-throughenergy region.
For the A measurements, we averaged beam spin up-down states to obtain unpolar-
N
ized beam. The difference of absolute value of beam polarization between spin-up and
spin-downstates was confirmed to be small by acquiring the results from the RHIC-pC
polarimeter. Therefore the residual components beam polarization has no effect on this
result.
The A data at 24 GeV/c (√s = 6.8 GeV) and 100 GeV/c (√s = 13.7 GeV) are
N
consistentintheregionof t <10 2.However,theseA resultsatdifferent√senergies
− N
indicatea√sdependence−off had(s,t).TheA dataat√s=6.8GeVarenot consistent
SF N
with the solid line (c 2/ndf=35.5/9) and this discrepancy implies the presence of a
hadronic spin-flip contribution, f had(s,t) [10]. On the other hand, the A data at √s=
SF N
13.7GeV are consistentwiththeQED prediction(c 2/ndf=13.4/14)[9].
The theoretical efforts to determine f had(s,t)including its √s dependence are ongo-
SF
ing.Usingexperimentalresults(A inppelasticscatteringat√s=13.7GeVandinpC
N
elasticscatteringat√s=6.4GeV[11]and13.7GeV[12])asinputparameters,predic-
tion for A at √s = 6.8 GeV was given in recent work [13]. The prediction suggested
N
a significant √s dependence of f had(s,t), and agreed with our data within 1-s uncer-
SF
tainty. More comparisons between theoretical prediction and further experimental data
atdifferent beammomentaare required tounderstandf had(s,t).
SF
P results from RUN5
beam
In2005,oneofthetwoRHICbeamswascenteredontheH-Jet-targetforseveraldays
to accumulate enough statistics for a precise measurement of the beam polarization.
We displaced the "unused" beam approximately 10 mm horizontally and vertically
from the H-Jet-target center. Both beams were measured repeatedly over the course
of a few weeks. Detailed experimental set up and analysis for RUN5 are discussed
in [14]. We accumulated 5.3 M events for the "clock-wise" beam and 4.2 M events for
the "counter-clock-wise" beam. e and e for both beams were calculated using
target beam
Equation 8. We confirmed that A = e /P from both beams were consistent
N target target
−
with A of 2004 results. For polarimetry use, we use data in the peak asymmetry
N
region of 1 T 4 MeV to eliminate acceptance asymmetry and prompt events.
R
≤ ≤
Then, P is obtained using Equation 3. The total systematicuncertainty in 2005 was
beam
D Psys. /P =2.9%.Thedominanttwocomponentswere:
target target
• backgroundsfromresidual gasand displaced(notused)beam (2.2%),
• uncertaintyonthetarget polarizationgivingan overallD Ptarget/Ptarget =2.0%.
Studies of backgrounds were carried out by varying the measured background contri-
butions near the elastic pp signal. The strip distributionsshow a uniformly spread yield
over the non-signal strips. (An example at a certain T interval is shown in Figure 5.)
R
By increasing the number of strips used for the elastic peak, the background contri-
bution can be increased in a controlled way. Figures 7 and 8 explain this study of the
"clock-wise" beam and the "counter-clock-wise" beam. The right parts of these figures
summarizetheasymmetryratiosfordifferentnumberofstripsforthesignalregion,go-
ing from one to eight. The original asymmetries were calculated with two strips. The
open circle and open diamondsymbolson the left refer to four and eight strips, thereby
doublingandquadruplingthebackgroundcontributions.Asymmetryratioofthe"clock-
wise" beam seems to drop slightly, and that of the "counter-clock-wise" beam rises,
but the variations are smaller than the statistical uncertainties. Therefore, these differ-
ences do not necessarily point to a polarization dependence of inelastic events. Also,
no clear asymmetry has been seen in background events. Absolute beam polariza-
tionsofthe "clock-wise"and the"counter-clock-wise" beams at 100 GeV/c in 2005 are
49.3% 1.5%(stat.) 1.4%(sys.)and 44.3% 1.3%(stat.) 1.3%(sys.). We achieved
accurat±ebeam polariz±ationmeasurementD P ±/P =4.2±%.
beam beam
Future prospect
Finally,thecurrent issuesandexpected optimumprecisionin2006and thefutureare
discussed here briefly. More data are collected in RUN6, 8.2 M events for the "clock-
wise"beamand10.7Meventsforthe"counter-clock-wise"beamat100GeV/c.Theex-
pected statistical uncertainty is approximately 1 %. More detailed study of background
contribution to systematic contribution is ongoing. An improvement to reduce the un-
certainty for the unpolarized fraction of the H-Jet-target is required for a breakthrough
toanewlevelofaccuracy.
0.05 o
˛mmetry 0.04 etry rati0.56
asy ymm0.55
0.03 as
0.54
0.02
0.53
0.01
0.52
0 1 2 3 4 5 6 1 2 3 4 5 8
T (MeV) signal strip width
R
FIGURE 7. Background study for the "clock-wise" beam of RUN5. Left: Filled circle refers to two
stripsforthe originalasymmetry.Opencircle andopendiamondsymbolsreferto fourandeightstrips.
Uppergroupise andlowergroupise .Right:Asymmetryratioasafunctionofsignalstripwidth.
target beam
˛mmetry 00..0045 etry ratio00..5521
y m
as0.03 asym 0.5
0.49
0.02
0.48
0.01
0.47
0 1 2 3 4 5 6 1 2 3 4 5 8
T (MeV) signal strip width
R
FIGURE8. SameasFigure7forthe"counter-clock-wise"beamofRUN5.
A data at different beam energies are an important physics topic. In RUN6, we
N
also took 31 GeV/c data with better statistics than RUN4 24 GeV/c. These data will
contributeto acomprehensiveunderstandingoff had(s,t).
SF
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