We present a measurement of the cross section of the process $e^+e^-\to\pi^+pi^-\psi(2S)$ from threshold up to 8 GeV center-of-mass energy using events containing initial-state radiation, produced at the PEP-II $e^+e^-$ storage rings. The study is based on 298 fb$^{-1}$ of data recorded with the BaBar detector. A structure is observed in the cross-section not far above threshold, near 4.32 GeV. We also investigate the compatibility of this structure with the Y(4260) previously reported by this experiment.
The measured c.m. energy dependence of the cross section with statistical errors only.. Bins with no recorded data are shown as a 'dash'.
We present the centrality dependent measurement of multiplicity and pseudorapidity distributions of charged particles and photons in Au + Au collisions at sqrt{s_NN} = 62.4 GeV. The charged particles and photons are measured in the pseudorapidity region 2.9 < eta < 3.9 and 2.3 < eta < 3.7, respectively. We have studied the scaling of particle production with the number of participating nucleons and the number of binary collisions. The photon and charged particle production in the measured pseudorapidity range has been shown to be consistent with energy independent limiting fragmentation behavior. The photons are observed to follow a centrality independent limiting fragmentation behavior while for the charged particles it is centrality dependent. We have carried out a comparative study of the pseudorapidity distributions of positively charged hadrons, negatively charged hadrons, photons, pions, net protons in nucleus--nucleus collisions and pseudorapidity distributions from p+p collisions. From these comparisons we conclude that baryons in the inclusive charged particle distribution are responsible for the observed centrality dependence of limiting fragmentation. The mesons are found to follow an energy independent behavior of limiting fragmentation while the behavior of baryons seems to be energy dependent.
(Color Online) Variation of $N_{ch}$ normalized to the number of participating nucleon pair in the FTPC coverage $(2.9 \leq \eta \leq 3.9)$ and $N_{\gamma}$ normalized to the number of participating nucleon pair in the PMD acceptance $(2.3 \leq \eta \leq 3.7)$ as a function of $N_{part}$. The lower band shows the uncertainty in the ratio due to uncertainties in $N_{part}$ calculations.
(Color Online) Variation of $N_{ch}$ normalized to the number of participating nucleon pair in the FTPC coverage $(2.9 \leq \eta \leq 3.9)$ and $N_{\gamma}$ normalized to the number of participating nucleon pair in the PMD acceptance $(2.3 \leq \eta \leq 3.7)$ as a function of $N_{part}$. The lower band shows the uncertainty in the ratio due to uncertainties in $N_{part}$ calculations.
(Color Online) Variation of $N_{ch}$ normalized to the number of collisions in the FTPC coverage $(2.9 \leq \eta \leq 3.9)$ and $N_{\gamma}$ normalized to number of collisions, in the PMD coverage $(2.3 \leq \eta \leq 3.7)$ as a function of $N_{coll}$. The lower band shows the uncertainty in the ratio due to uncertainties in $N_{coll}$ calculations.
We present results for two-particle transverse momentum correlations, <dpt,i dpt,j>, as a function of event centrality for Au+Au collisions at sqrt(sNN) = 20, 62, 130, and 200 GeV at the Relativistic Heavy Ion Collider. We observe correlations decreasing with centrality that are similar at all four incident energies. The correlations multiplied by the multiplicity density increase with incident energy and the centrality dependence may show evidence of processes such as thermalization, minijet production, or the saturation of transverse flow. The square root of the correlations divided by the event-wise average transverse momentum per event shows little or no beam energy dependence and generally agrees with previous measurements at the Super Proton Synchrotron.
Average transverse momentum per event for Au+Au at $\sqrt{s_{NN}}$ = 20 GeV for the 5% most central collisions.
Average transverse momentum per event for Au+Au at $\sqrt{s_{NN}}$ = 62 GeV for the 5% most central collisions.
Average transverse momentum per event for Au+Au at $\sqrt{s_{NN}}$ = 130 GeV for the 5% most central collisions.
Measurements of the forward-angle differential cross section for elastic electron-proton scattering were made in the range of momentum transfer from Q2=2.9 to 31.3 (GeV/c)2 using an electron beam at the Stanford Linear Accelerator Center. The data span six orders of magnitude in cross section. Combinded statistical and systematic uncertainties in the cross section measurements ranged from 3.6% at low Q2 to 19% at high Q2. These data have been used to extract the proton magnetic form factor GMp(Q2) and Dirac form factor F1p(Q2) by using form factor scaling. The logarithmic falloff of Q4F1p expected from leading twist predictions of perturbative quantum chromodynamics is consistent with the new data at high Q2. Some nonperturbative and hybrid calculations also agree with our results.
No description provided.
Formfactor scaling assumes (Ge=Gm/mu).
We have performed absolute measurements of the differential cross section for elastic e−p scattering in the range of momentum transfer from Q2=2.9 to 31.3 (GeV/c)2. Combined statistical and systematic uncertainties in the cross-section measurements ranged from 3% at low Q2 to 19% at high Q2. These data have been used to extract the proton magnetic form factor GMp(Q2). The results show a smooth decrease of Q4GMp with momentum transfer above Q2=10 (GeV/c)2. These results are compared with recent predictions of perturbative QCD.
No description provided.
No description provided.
No description provided.