The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.
Projections of the correlation function C.
Projections of the correlation function C.
Projections of the correlation function C.
Electroproduction of exclusive $\phi$ vector mesons has been studied with the CLAS detector in the kinematical range $1.6\leq Q^2\leq 3.8$ GeV$^{2}$, $0.0\leq t^{\prime}\leq 3.6$ GeV$^{2}$, and $2.0\leq W\leq 3.0$ GeV. The scaling exponent for the total cross section as $1/(Q^2+M_{\phi}^2)^n$ was determined to be $n=2.49\pm 0.33$. The slope of the four-momentum transfer $t'$ distribution is $b_{\phi}=0.98 \pm 0.17$ GeV$^{-2}$. The data are consistent with the assumption of s-channel helicity conservation (SCHC). Under this assumption, we determine the ratio of longitudinal to transverse cross sections to be $R=0.86 \pm 0.24$. A 2-gluon exchange model is able to reproduce the main features of the data.
Axis error includes +- 18.6/18.6 contribution.
Axis error includes +- 18.6/18.6 contribution.
Axis error includes +- 18.6/18.6 contribution.
Results on charged pion and kaon production in central Pb+Pb collisions at 20A and 30A GeV are presented and compared to data at lower and higher energies. A rapid change of the energy dependence is observed around 30A GeV for the yields of pions and kaons as well as for the shape of the transverse mass spectra. The change is compatible with the prediction that the threshold for production of a state of deconfined matter at the early stage of the collisions is located at low SPS energies.
Transverse mass spectra for pion production in the central rapidity region for collisions at 20 GeV per nucleon.
Transverse mass spectra for pion production in the central rapidity region for collisions at 30 GeV per nucleon.
Transverse mass spectra for kaon production in the central rapidity region for collisions at 20 GeV per nucleon.
Photoproduction of the cascade resonances has been investigated in the reactions $\gamma p \to K^+ K^+ (X)$ and $\gamma p \to K^+ K^+ \pi^- (X)$. The mass split of the $\Xi$ doublet is measured to be $5.4\pm 1.8$ MeV/c$^2$, consistent with existing measurements. The differential (total) cross sections for the $\Xi^{-}$ have been determined for photon beam energies from 2.75 to 3.85 (4.75) GeV, and are consistent with a possible production mechanism of $Y^*\to K^+\Xi^-$ through a $t$-channel process. The reaction $\gamma p \to K^+ K^+ \pi^-[\Xi^0]$ has also been investigated in search of excited cascade resonances. No significant signal of excited cascade states other than the $\Xi^-(1530)$ is observed. The cross section results of the $\Xi^-(1530)$ have also been obtained for photon beam energies from 3.35 to 4.75 GeV.
Differential cross section for XI- production as a function of the invariant mass of the XI- with either of the K+ mesons for incident photon energy 2.79 Gev.
Differential cross section for XI- production as a function of the invariant mass of the XI- with either of the K+ mesons for incident photon energy 2.89 Gev.
Differential cross section for XI- production as a function of the invariant mass of the XI- with either of the K+ mesons for incident photon energy 2.99 Gev.
We present the first measurement of the Q^2-dependence of the neutron spin structure function g_2^n at five kinematic points covering 0.57 (GeV/c)^2 <= Q^2 <= 1.34 (GeV/c)^2 at x~0.2. Though the naive quark-parton model predicts g_2=0, non-zero values for g_2 occur in more realistic models of the nucleon which include quark-gluon correlations, finite quark masses or orbital angular momentum. When scattering from a non-interacting quark, $g_2^n$ can be predicted using next-to-leading order fits to world data for g_1^n. Deviations from this prediction provide an opportunity to examine QCD dynamics in nucleon structure. Our results show a positive deviation from this prediction at lower Q^2, indicating that contributions such as quark-gluon interactions may be important. Precision data obtained for g_1^n are consistent with next-to-leading order fits to world data.
Measured values of G1N ang G2N.
The first measurement of the p n -> d omega total cross section has been achieved at mean excess energies of Q = 28 and 57 MeV by using a deuterium cluster-jet target. The momentum of the fast deuteron was measured in the ANKE spectrometer at COSY-Juelich and that of the slow spectator proton p(sp) from the p d -> p(sp) d omega reaction in a silicon telescope placed close to the target. The cross sections lie above those measured for p p -> p p omega but seem to be below theoretical predictions.
Total cross sections after the P N --> DEUT OMEGA reaction just above threshold.
Measurements at 19 beam kinetic energies between 1795 and 2235 MeV are reported for the pp elastic scattering spin correlation parameter A00nn=ANN=CNN. The c.m. angular range is typically 60–100°. The measurements were performed at Saturne II with a vertically polarized beam and target (transverse to the beam direction and scattering plane), a magnetic spectrometer and a recoil detector, both instrumented with multiwire proportional chambers, and beam polarimeters. These results are compared to previous data from Saturne II and elsewhere.
Measured values of CNN at EKIN 1795 Mev.. Fractional systematic uncertainty in the absolute beam and target polarization is +-0.110.
Measured values of CNN at EKIN 1845 Mev.. Fractional systematic uncertainty in the absolute beam and target polarization is +-0.073.
Measured values of CNN at EKIN 1935 Mev.. Fractional systematic uncertainty in the absolute beam and target polarization is +-0.095.
A polarized proton beam extracted from SATURNE II was scattered on an unpolarized CH 2 target. The angular distribution of the beam analyzing power A oono was measured at large angles from 1.98 to 2.8 GeV and at 0.80 GeV nominal beam kinetic energy. The same observable was determined at the fixed mean laboratory angle of 13.9° in the same energy range. Both measurements are by-products of an experiment measuring the spin correlation parameter A oon .
Analysing power measurements at a fixed laboratory angle of 13.9 degrees.
No description provided.
No description provided.
The quasifree p+n→d+η reaction cross section has been measured at the threshold using 1295 MeV protons in the CELSIUS storage ring and an internal cluster-jet deuterium target. The kinematics is chosen such that the target proton can be assumed to be a spectator. The Fermi momentum of the target neutron is used to extract the energy dependence of the cross section by reconstructing the kinematics on an event-by-event basis. The data cover excess energies from threshold to 10 MeV in the center of mass of the final dη system. Approaching the threshold the cross section is enhanced compared to what is expected from phase space. This behavior is typical for a strong final-state interaction.
Cross section as a function of the C.M. excess energy.
The 1H(e,e′K+)Λ reaction was studied as a function of the squared four-momentum transfer, Q2, and the virtual photon polarization, ɛ. For each of four Q2 settings, 0.52, 0.75, 1.00, and 2.00 (GeV/c)2, the longitudinal and transverse virtual photon cross sections were extracted in measurements at three virtual photon polarizations. The Q2 dependence of the σL/σT ratio differs significantly from current theoretical predictions. This, combined with the precision of the measurement, implies a need for revision of existing calculations.
The systematic and statistical errors are added in quadrature. OMEGA is the solid angle of K+ in CMS.
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