Beam-polarization asymmetries for the p(gamma-->, K+)Lambda and p(gamma-->, K+)Sigma(0) reactions for E(gamma)=1.5-2.4 GeV

Beam polarization asymmetries for the p(gamma-->,K+)Lambda and p(gamma-->,K+)Sigma(0) reactions are measured for the first time for E(gamma)=1.5-2.4 GeV and 0.6相似文献   

Structure in the K+-nucleon I = 0 total cross section below 1.1 GeV/c

Measurements have been carried out of total cross sections of positive kaons on hydrogen and deuterium to a statistical precision of better than ± 0.1 mb for most points in the range of laboratory momentum from 410 to 1065 MeV/c in intervals of approximately 50 MeV/c. A very broad elastic structure in the I = 0 state is inferred.     

Measurements of the cross section for e(+)e(-) --> hadrons at center-of-mass energies from 2 to 5 GeV

We report values of R = sigma(e(+)e(-)-->hadrons)/sigma(e(+)e(-)-->mu(+)mu(-)) for 85 center-of-mass energies between 2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider.     

On the magnitude of the Li + He → B + n reaction cross section at the Big-Bang temperature

The ⁸Li + ⁴He → ¹¹B + n reaction at Ecm<2 MeV$E_{\mathrm{cm}}<2\text{MeV}$ is a process of relevant astrophysical interest for which a remarkable experimental discrepancy between inclusive and exclusive cross-section measurements exists. In this Letter, a new inclusive neutron measurement at Ecm=1.05±0.16 MeV$E_{\mathrm{cm}}=1.05\pm 0.16\text{MeV}$ is given. The radioactive ⁸Li beam was delivered by the EXCYT facility. The cross section was determined by a low-background measurement of the time correlation between the ⁸Li projectile arrival to the target and the following neutron capture in a threshold-less 4π thermalization counter. This new data strengthens the reliability of the previous inclusive reaction cross-section data and altogether are consistent with a significant population of ¹¹B levels at high excitation energy.     

Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at square root of s = 200 GeV

We report a measurement of the longitudinal double-spin asymmetry A(LL) and the differential cross section for inclusive midrapidity jet production in polarized proton collisions at square root of s = 200 GeV. The cross section data cover transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order perturbative QCD evaluations. The A(LL) data cover 5 < pT < 17 GeV/c and disfavor at 98% C.L. maximal positive gluon polarization in the polarized nucleon.     

Differential cross-sections for pp → π−π+, K−K+ between 0.8 and 2.4 GeV/c

We present measurements from a spark chamber experiment of the differential cross-sections for $\text{p}$p → π^?π⁺, K^?K⁺ at 20 momenta in the range 0.8–2.4 GeV/c (c.m. energy 2.02 to 2.57 GeV). The c.m. angular range was $\text{?0.95 <}\text{cos}\text{θ}{}^1\text{< 0.95}$. There are about 2000π^?π⁺ events and about 300 K^?K⁺ events at each momentum.     

Search for the Theta+ pentaquark in the reaction gammad --> pK-K+n

A search for the Theta+ in the reaction gammad --> pK-K+n was completed using the CLAS detector at Jefferson Lab. A study of the same reaction, published earlier, reported the observation of a narrow Theta+ resonance. The present experiment, with more than 30 times the integrated luminosity of our earlier measurement, does not show any evidence for a narrow pentaquark resonance. The angle-integrated upper limit on Theta+ production in the mass range of 1.52-1.56 GeV/c2 for the gammad --> pK-Theta+ reaction is 0.3 nb (95% C.L.). This upper limit depends on assumptions made for the mass and angular distribution of Theta+ production. Using Lambda(1520) production as an empirical measure of rescattering in the deuteron, the cross section upper limit for the elementary gamman --> K-Theta+ reaction is estimated to be a factor of 10 higher, i.e., approximately 3 nb (95% C.L.).     

Induced long-range dipole-field-enhanced antihydrogen formation in the p + Ps(n = 2) --> e(-) + H(n < or = 2) reaction

We report high-precision calculations that correctly include the rearrangement channels by solving the modified Faddeev equations for energies between the Ps(n = 2) and H(n = 3) thresholds, which involve six and eight open channels. We find that 99% of the antihydrogen is formed in H(n = 2). Just above the Ps(n = 2) threshold the S, P, and D partial waves contribute nearly 1400pi(a(2)0) near the maximum. We find evidence that the induced long-range dipole potential is responsible for such a large H formation cross section. The possibility of utilizing this resonance to synthesize low-energy H is discussed.