References - Bogoliubov Laboratory of Theoretical Physics - JINR

2 H-Jet Polarimeter
The polarized hydrogen jet target polarimeter locates at one of the collision points in the
RHIC accelerator and measures polarization of one of the two RHIC beams at a time.
In 2008 the the H-Jet polarimeter was tested running both beams separated vertically,
and both incident on the jet. In 2009 RHIC run it allowed the H-Jet to simultaneously
monitor the polarization of both beams on store by store basis.
H-Jet polarimeter consists mainly of three parts: atomic beam source, scattering chamber
and Breit-Rabi polarimeter (BRP). Atomic beam source produces polarized atomic
hydrogen jet with velocity 1560 ± 20 m/c [2] which crosses RHIC proton beam in scattering
chamber perpendicularly. The FWHM of the jet in the center of scattering chamber
is ∼ 6.5 mm. The total atomic beam intensity in the scattering chamber was measured
to be (12.4 ± 0.2) · 1016 atoms/cm2 [3]. Along the RHIC beam axis the target thickness
is (1.3 ± 0.2) · 1012 atoms/cm2 [2]. BRP measured the atomic hydrogen polarization. It
is monitored during the run and showed a stable polarization of Ptarget =0.924 after
correction for ∼ 3% molecular hydrogen contamination, which diluted jet polarization [2].
Recoil protons from elastic pp scattering are detected using an array of silicon detectors
located on the left and right of the beam at a distance ∼80 cm (Fig. 1a)). The elastically
scattered protons are identified with small background contamination (∼ 4%) using the
kinematical correlation between recoil proton kinetic energy and time of flight, and kinetic
energy and scattering angle (or silicon detector strip number in Fig. 1a)). Then asymmetry
between scattering on the left and on the right are measured relative to beam polarization
direction or target polarization direction. Since beam polarization direction alternates
every bunch (separated by 106 ns) or pair of bunches, and target polarization flips every
∼ 10 min, we simultaneously collect data for all beam-target spin configurations: N L ↑ ,
N L ↓ , N R ↑ and N L ↓ , where subscript denotes the beam or target polarization direction, and
superscript relates to left or right detector, defined relative to beam direction. Using so
called square-root formula:
� �
ɛ =
N L ↑ · N R ↓ −
�
N L ↑ · N R ↓ +
N R ↑ · N L ↓
�
N R ↑ · N L ↓
, (1)
we cancel effects from left-right detector acceptance asymmetry and spin up-down beam
luminosity asymmetry, when measuring raw asymmetry relative to beam polarization,
ɛbeam, or relative to target polarization ɛtarget.
Beam polarization Pbeam is then defined from the measured asymmetries ɛbeam and
ɛtarget and known target polarization Ptarget:
Pbeam = − ɛbeam
ɛtarget
· Ptarget. (2)
The details of H-Jet setup and Data Acquisition system are described elsewhere [4].
The asymmetry measurements were performed for the recoil proton kinetic energy
range TR =1− 4 MeV (corresponding to a momentum transfer 0.002 < −t