W.W. Jacobs

Production of η' mesons in the pp→ppη' reaction at 3.67 GeV/c

Abstract The ratio of the total exclusive production cross sections for η and η mesons has been measured in the pp reaction at p beam =3.67xa0GeV/ c . The observed η ′ / η ratio is (0.83±0.11 +0.23 −0.18 )×10 −2 from which the exclusive η ′ meson production cross section is determined to be (1.12±0.15 +0.42 −0.31 )xa0μb. Differential cross section distributions have been measured. Their shape is consistent with isotropic η ′ meson production.

The STAR endcap electromagnetic calorimeter

The STAR endcap electromagnetic calorimeter will provide full azimuthal coverage for high-pT photons, electrons and electromagnetically decaying mesons over the pseudorapidity range 1.086⩽η⩽2.00. It includes a scintillating-strip shower-maximum detector to provide π0/γ discrimination and preshower and postshower layers to aid in distinguishing between electrons and charged hadrons. The triggering capabilities and coverage it offers are crucial for much of the spin physics program to be carried out in polarized proton–proton collisions.

K- meson production in the proton proton reaction at 3.67-GeV/c

Abstract The total cross section of the reaction pp→ppK+K− has been determined for proton–proton reactions with p beam =3.67 GeV /c . This represents the first cross section measurement of the pp→ppK−K+ channel near threshold, and is equivalent to the inclusive pp→ppK−X cross section at this beam momentum. The cross section determined at this beam momentum is about a factor 20 lower than that for inclusive pp→ppK+X meson production at the same CM energy above the corresponding threshold. This large difference in the K+ and K− meson inclusive production cross sections in proton-proton reactions is in strong contrast to cross sections measured in sub-threshold heavy ion collisions, which are similar in magnitude at the same energy per nucleon below the respective thresholds.

12C(6Li, d)16O at E(Li) = 90 MeV

Abstract The 12 C( 6 Li, d) 16 O reaction has been studied at E( 6 Li ) = 90.2 MeV with a magnetic spectrometer. Spectra up to E x ≈ 30 MeV in 16 O have been obtained and decay line widths, Γ c.m. , have been extracted for broad levels. Known α-cluster states ( J π = 2 + , E x = 6.9 MeV; J π = 4 + , E x = 10.35 MeV) are preferentially populated exhibit sharply forward peaked angular distributions in contrast with ( 6 Li, d) data obtained at lower bombarding energies. These features are well reproduced by reaction calculations assuming direct alpha-particle transfer provided one utilizes realistic optical model, target, and projectile wave functions. Alpha spectroscopic factors and reduced alpha widths have been extracted for levels E x J π = 1 − levels of astrophysical interest. The results are compared with other recent measurements and theoretical calculations. There is generally at least qualitative agreement (within × 2) between the various experiments and theories. The analysis indicates a non-negligible alpha width for the J π = 1 − level at E x = 7.1 MeV in 16 O (which determines the 12 C → 16 O stellar helium burning rate) with 0.3 θ α 2 (7.1 MeV)/ θ α 2 (9.6MeV) θ α 2 (7.1 MeV)/ θ α 2 (6.9 MeV)

Formation of the

Analyzing DISTO data of pp → pΛK+ at Tp = 2.50 and 2.85GeV to populate a previously reported X(2265) -resonance with Mx = 2267 MeV/c2 and Γx = 118 MeV at 2.85GeV, we found that the yield of X(2265) at 2.50GeV is much less than that at 2.85GeV (less than 10%), though it is expected from a kinematical consideration to be produced as much as 33% of that at 2.85GeV. The small population of X(2265) at 2.50GeV is consistent with the very weak production of Γ(1405) at the same incident energy toward its production threshold, thus indicating that Γ(1405) plays an important role as a doorway state for the formation of X(2265).

S=-1

We have analyzed data of the DISTO experiment on the exclusive pp → Ku2009+u2009 Λp process at Tpu2009=u20092.85xa0GeV to search for a Ku2009−u2009pp xa0(u2009≡u2009X) nuclear bound state to be formed in the pp → Ku2009+u2009u2009+u2009X reaction. The deviation spectra of the Ku2009+u2009 missing-mass ΔM (Ku2009+u2009) and Λp invariant-mass M(Λp) with selection of large-angle proton emission revealed a structure with MXu2009=u20092265 ±2xa0MeV/c2 and ΓXu2009=u2009118 ±8xa0MeV.

resonance X(2265) in the reaction

Abstract A magnetic spectrometer system has been constructed for the study of reactions with multiple charged particles in the final state, induced by polarized proton beams of few GeV energy. The system is based on a large-gap dipole magnet, with a liquid hydrogen target and scintillating fiber tracking detectors embedded inside the magnet. Multiwire proportional chambers, plastic scintillator hodoscopes, and threshold Cherenkov detectors placed outside the magnet provide additional tracking, triggering and particle identification capabilities. The system has been applied to study exclusive hyperon as well as pseudoscalar and vector meson production reactions at bombarding energies below 3xa0GeV. Additionally, it has been used to monitor the proton beam polarization at Laboratoire National Saturne. The components and performance of the system are reported.

pp -> X + K^+

Abstract Measurements of broad-range momentum spectra for (p, π − ) reactions near threshold on a number of target nuclei with 13⩽A⩽92 have revealed a striking and systematic selectivity for one or a few low-lying states In the residual nuclei. We propose that the dominant transitions lead to high-spin stretched (or nearly stretched) two-particle one-hole states (with respect to the target-nucleus ground-state configurations), as favored by a two-nucleon pion production mechanism. Experiments which might confirm this explanation and possible future applications of the (p, π − ) selectivity are discussed.

at 2.50 and 2.85 GeV

The data from the DISTO Collaboration on the exclusive pp ! pK + production acquired at T p = 2:85 GeV have been re-analysed in order to search for a deeply bound K pp( X) state, to be formed in the binary process pp! K + X. The preliminary spectra of the MK+ missingmass and of the Mp invariant-mass show, for large transverse-momenta of protons and kaons, a distinct broad peak with a mass MX = 2265 2 MeV=c 2 and a width X = 118 8 MeV=c 2 .

First exclusive measurements of the K − pp state populated in the pp → K + Λp reaction at 2.85 GeV

4(DISTO Collaboration) * The first exclusive measurements of the spin transfer parameter DN N in the reaction fJp -t p[{+Ahas been performed at Saturne with the polarized beam and with the DISTO spectrometer. The results suggest an OBE mechanism dominated by kaon exchange.