M. Stancari

A gas analyzer for the internal polarized target of the HERMES experiment

A gas analyzer has been developed for the internal polarized target of the HERMES experiment at DESY in order to determine the relative amount of atomic and molecular hydrogen or deuterium in a gas sample. The precise quantitative knowledge of this ratio is crucial because the nucleons in atoms and molecules contribute differently to the average nuclear polarization of the target gas. A new calibration technique used to derive the relative sensitivity to atoms and molecules is presented. As an example, it is shown how the gas analyzer is used within the HERMES environment to divide the molecules in the gas sample into an unpolarized and a potentially polarized fraction.

Precision measurements of the total and partial widths of the ψ (2 S) charmonium meson with a new complementary-scan technique in over(p, ̄) p annihilations

We present new precision measurements of the {Psi}(2S) total and partial widths from excitation curves obtained in antiproton-proton annihilations by Fermilab experiment E835 at the Antiproton Accumulator in the year 2000. A new technique of complementary scans was developed to study narrow resonances with stochastically cooled antiproton beams. It relies on precise revolution-frequency and orbit-length measurements, while making the analysis of the excitation curve almost independent of machine lattice parameters. For the {Psi}(2S) meson, by studying the processes {bar p}p {yields} e{sup +}e{sup -} and {bar p}p {yields} J/{Psi} + X {yields} e{sup +}e{sup -} + X, we measure the width {Gamma} = 290 {+-} 25(sta) {+-} 4(sys) keV and the combination of partial widths {Gamma}{sub e{sup +}e{sup -}}{Gamma}{sub {bar p}p}/{Gamma} = 579 {+-} 38(sta) {+-} 36(sys) meV, which represent the most precise measurements to date.

Measurement of the resonance parameters of the χ1(13P1) and χ2(13P2) states of charmonium formed in antiproton–proton annihilations

The authors have studied the {sup 3}P{sub J} ({chi}{sub e}) states of charmonium in formation by antiproton-proton annihilations in experiment E835 at the Fermilab Antiproton Source. The authors report new measurements of the mass, width, and B({chi}{sub cJ} {yields} {bar p}p) x {Lambda}({chi}{sub eJ} {yields} J/{psi} + anything) for the {chi}{sub c1} and {chi}{sub c2} by means of the inclusive reaction {bar p}p {yields} {chi}{sub cJ} {yields} J/{psi} + anything {yields} (e{sup +}e{sup -}) + anything. Using the subsample of events where {chi}{sub cJ} {yields} {gamma} + J/{psi} {yields} {gamma} + (e{sup +}e{sup -}) is fully reconstructed, we derive B({chi}{sub cJ} {yields} {bar p}p) x {Lambda}({chi}{sub cJ} {yields} J/{psi} + {gamma}). They summarize the results of the E760 (updated) and E835 measurements of mass, width and B({chi}{sub cJ} {yields} {bar p}p){Lambda}({chi}{sub cJ} {yields} J/{psi} + {gamma}) (J = 0,1,2) and discuss the significance of these measurements.

The storage cell of the polarized H/D internal gas target of the HERMES experiment at HERA

The storage cell of the internal, longitudinally polarized, atomic gas target of the HERMES experiment is presented. The polarized atoms of hydrogen or deuterium are accumulated in an open-ended thin walled storage cell through which the circulating electron or positron beam of the HERA accelerator passes. The target areal density is 10 14 atoms=cm 2 ; two orders of magnitude larger than without the cell. The construction details of the cell are described and the cell’s performance during HERMES run of 1997–2000 is discussed. r 2002 Published by Elsevier Science B.V.

Studies of Beam Formation and Rest Gas Attenuation in Atomic Beam Sources

At the SpinLab test stand (University of Ferrara), the elastic scattering cross section for molecular hydrogen has been determined for relative velocities in the range 1500–3000 m/s from the measured attenuation of a beam traversing a chamber of rest gas. This cross section is a fundamental input for simulations of gas flows in an atomic beam source with the Direct Simulation Monte Carlo method. Both the predicted beam intensity and width of the beams velocity distribution are sensitive to the cross section value, and agreement with the measured values is demonstrated for the first time. The simulations also predict properties of the expansion that are difficult to access experimentally, namely a peaking factor of 1.45±0.05 that is essentially independent of input flow in the range 25–250 sccm, and an increase in the beam divergence at the skimmer exit for higher input flows.

Test Bench Studies and Simulations of Atomic Beam Sources

Two new test bench studies have deepened the understanding of polarized gas targets and the atomic beam sources (ABS) that fill them. The attenuation coefficient for beam loss due to rest gas scattering has been measured over a range of beam velocities. The total scattering cross sections can be extracted from these measurements for the first time.Low conductance injection tubes have the potential to increase the thickness of storage cell targets. Injection tubes with internal fins were characterized, and the beam loss at the tube exit was larger than expected. Beam simulations agree with the measured intensity loss only when the atoms’ trajectories have a non‐zero azimuthal velocity component.

The Polarized Target for Spin Filtering Studies at COSY and AD

The setup of the polarized target for the spin filtering studies at COSY and AD will be shown together with the planned measurements. The target fulfills all the requirements coming from the experiment.