a r X i v :h e p -e x /0511036v 2 16 N o v 2005
SINGLE SPIN ASYMMETRY OF CHARGED HADRON PRODUCTION
BY 40GEV/C POLARIZED PROTONS V.V.Abramov
P B ·cosφ
N ↑?N ↓
39+1?3%,and the polarization direction is changed each18min during30s.The beam intensity and the position are measured by the ionization chambers and the scintillation hodoscopes.
Figure1:Schematic of experimental layout FODS-2.
The measurements were carried out with the FODS-2,spectrometer(Fig.1).It consists of an analyzing magnet,the drift chambers,the Cherenkov radiation spectrometer (SCOCH)for the particle identi?cation(π±,K±,p andˉp),the scintillation counters,and the hadron calorimeters to trigger on the high energy hadrons.Inside the magnet there is also a beam dump made of tungsten and copper.There are two arms which can be rotated around the target center situated in front of the magnet to change the secondary particle angle.
There are two threshold Cherenkov counters using air at the atmospheric pressure inserted in the magnet which are used for further improvement of particle identi?cation. 3Measurements
The measurements of A N in the range?0.15≤x F≤0.2and0.5≤p T≤4GeV/c are carried out with the symmetrical arm positions at angles of±160mrad(mean c.m.angle θcm=±86o).The results for the two arms and the di?erent values of the magnetic?eld B in the spectrometer are averaged,which partially cancels systematical uncertainties connected with the variation of the beam position in the vertical direction,the intensity monitor and the apparatus drift.Another set of measurements is carried out with the arms,rotated by70mrad(the left arm is atθcm=48o with0.05≤x F≤0.7and 0.5≤p T≤2.5GeV/c,and the right arm is atθcm=105o with?0.25≤x F≤?0.05and 0.7≤p T≤3GeV/c).Both polarities of magnetic?eld B in the spectrometer magnet are used for data taking to reduce systematic uncertainties.In addition,two values of the magnetic?eld(B and B/2)are used to extend the momentum range of the data.
The reconstructed trajectory of a particle downstream the spectrometer magnet and beam coordinates from the beam hodoscopes are used to determine its momentum,production angles and vertex Z-coordinate.After all cuts are applied,the remaining events are identi?ed in the SCOCH and threshold cherenkov counters.The integrated beam?ux is measured by the ionization chamber and is used to calculate normalized particle rates (N↑and N↓)for two signs of the beam polarization.The beam coordinates,measured by the X and Y hodoscope planes,are used to estimate the mean beam position(X B and Y B)during a spill,separately for“UP”and“Down”polarization signs.It was found that the mean beam coordinates,averaged over a group of runs with similar conditions,can di?er for“UP”and“Down”beam polarizations up to±0.5mm.Since the normalized rates N↑and N↓depend on the beam position,the false asymmetry can be added to the analyzing power A N.Cuts on beam coordinates are imposed to level the X B and Y B for “UP”and“Down”polarization sign with4μm accuracy to avoid the false asymmetry. The other sources of systematic uncertainties,remaining after the above cuts are applied, contribute up to4%to the systematic error?,which is estimated from run to run A N variation.The?is added in the quadrature to the statistical error at each data point. 5Single spin asymmetries
The dependence of A N on transverse momentum(p T)forπ±,K±,p andˉp production
on C and Cu targets and at two c.m.angles(≈48o and≈85o)are shown in Figs.
The signi?cant value of A N is seen inπ+,π?,K+and proton production atθcm≈48o
, GeV/c Figure2:A N dependence on p T for p↑+C(Cu)→π++X.
, GeV/c Figure3:A N dependence on p T for p↑+C(Cu)→π?+X.
on both targets.The A N atθcm≈85o is approximately two times smaller inπ+and K+production and reveals a breakdown at p T≈2.5GeV/c in its p T dependence,which could indicate a transition to the predicted pQCD regime.The A N for K?andˉp production is consistent with zero for both targets and all c.m.angles,as expected due to small sea quark polarization.The proton data atθcm≈48o reveal an oscillation of A N
with minimum at1.3GeV/c and maximum near2.2GeV/c.The SSA atθcm≈105o
, GeV/c Figure4:A N dependence on p T for p↑+C(Cu)→K++X.
, GeV/c Figure5:A N dependence on p T for p↑+C(Cu)→K?+X.
p T , GeV/c
Figure6:A N dependence on p T for p↑+C(Cu)→p+X.
, GeV/c Figure7:A N dependence on p T for p↑+C(Cu)→ˉp+X.
are shown in Figs.8and9forπ+andπ?,respectively.For all charged hadrons the SSA is close to zero atθcm near105o.No signi?cant A-dependence is observed in the above data.
Comparison of FODS-2results with the data,measured at22GeV/cand at200 GeV/c,is shown in Figs.8-9as a function of a scaling variable X S=(X R+X F)/2?X0, where X0=0.075N Q+2N Q M Q(1+cosθcm)/
to zero.No signi?cant A-dependence is observed for the SSA.The SSA for K?andˉp are consistent with zero,as expected due to the small sea quark polarization.The scaling behavior of SSA is seen forθcm≤50o and p T≥0.6GeV/c.The SSA is close to zero for θcm≈105o.
We are grateful to the IHEP sta?for their assistance with setting up the experiment and the IHEP directorate for their support.
, GeV/c Figure8:A N vs p T at104.4o.
, GeV/c Figure9:A N vs p T at104.4o.
S Figure10:A N vs X S forπ+pro-duction at22,40,and200GeV.
S Figure11:A N vs X S forπ?pro-duction at22,40,and200GeV.
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