References - Bogoliubov Laboratory of Theoretical Physics - JINR

Intensity profile (arb. units)
1
0.8
0.6
0.4
0.2
0
0.7
0.6
0.5
0.4
0.3
0.2
-6 -4 -2 0 2 4 6
Polarization profile
0.1
-6 -4 -2 0 2 4
Polarization vs I/Imax
0.7
0.6
0.5
0.4
0.3
0.2
χ 2 / ndf 8.687 / 9
Prob 0.4666
Pmax 0.6208 ± 0.01836
R 0.1108 ± 0.03984
0.1
0 0.2 0.4 0.6 0.8 1
(a) (b)
Figure 3: (a) Intensity (upper plot) and polarization (bottom plot) vs target position (arb. units),
measured in one of the RHIC stores for 100 GeV beam; gaussian fits are shown. (b) Polarization vs
intensity normalized to the intensity at beam center (I/Imax); fit of Eq. (6) to the data points is shown,
with extracted parameters Pmax and R.
4 Local Polarimeters
Local polarimeters employed by PHENIX and STAR also make a vital contribution to
the measurements and monitoring of the beam polarizations at RHIC. They are sensitive
to beam transverse polarizations. Their main role is to set up and to monitor the spin
direction at collision. For the physics measurements with longitudinally polarized beams
they are to confirm the absence of the polarization in transverse plane. In addition, they
also proved to be a precise tool to monitor beam polarization bunch by bunch and versus
time.
PHENIX local polarimetry is based on the analyzing power of the very forward neutron
production discovered in the first polarized proton RHIC run of 2001-2002 [9]. Forward
neutrons in PHENIX are measured by Zero-Degree Calorimeters (ZDC) with position
sensitive Shower-Max Detectors which cover ±2.8 mrad of the forward and backward
directions [10]. The analyzing power increases nearly linearity with center of mass energy
of colliding beams in the fixed ZDC geometry, which may indicate on pT scaling of AN
(Fig. 4a, [11]), taking into account the xF scaling of the forward neutron production cross
section ( [11]).
STAR local polarimetry is based on the sizable analyzing power of forward hadron
production, first measured at √ s