The process $ep \to e^{\prime}p^{\prime}\pi^0$ has been measured at $Q^2$ = 6.4 and 7.7 \ufourmomts in Jefferson Lab's Hall C. Unpolarized differential cross sections are reported in the virtual photon-proton center of mass frame considering the process $\gamma^{\ast}p \to p^{\prime}\pi^0$. Various details relating to the background subtractions, radiative corrections and systematic errors are discussed. The usefulness of the data with regard to the measurement of the electromagnetic properties of the well known $\Delta(1232)$ resonance is covered in detail. Specifically considered are the electromagnetic and scalar-magnetic ratios $R_{EM}$ and $R_{SM}$ along with the magnetic transition form factor $G_M^{\ast}$. It is found that the rapid fall off of the $\Delta(1232)$ contribution continues into this region of momentum transfer and that other resonances
Differential cross sections at Q**2=6.564 GeV**2, EPSILON=0.4523, W=1.112 GeV and COS(THETA(*))=-0.9 for the small SOS spectrometer.
Differential cross sections at Q**2=6.564 GeV**2, EPSILON=0.4523, W=1.112 GeV and COS(THETA(*))=-0.7 for the small SOS spectrometer.
Differential cross sections at Q**2=6.564 GeV**2, EPSILON=0.4523, W=1.112 GeV and COS(THETA(*))=-0.5 for the small SOS spectrometer.
We present the multiplicity and pseudorapidity distributions of photons produced in Au+Au and Cu+Cu collisions at \sqrt{s_NN} = 62.4 and 200 GeV. The photons are measured in the region -3.7 < \eta < -2.3 using the photon multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of the collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for Au+Au and Cu+Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 +/- 0.1 and 1.2 +/- 0.1 for \sqrt{s_NN} = 62.4 GeV and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of \eta - ybeam, are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies.
Fig. 1. (Color online.) Top panel: Photon reconstruction efficiency $\left(\epsilon_{\gamma}\right)$ (solid symbols) and purity of photon sample $\left(f_{\mathrm{p}}\right)$ (open symbols) for PMD as a function of pseudorapidity $(\eta)$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=$ $200 \mathrm{GeV}$. Bottom panel: Comparison between estimated $\epsilon_{\gamma}$ and $f_{\mathrm{p}}$ for PMD as a function of $\eta$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=62.4 \mathrm{GeV}$ using HIJING and AMPT models. The error bars on the AMPT data are statistical and those for HIJING are within the symbol size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
Fig. 1. (Color online.) Top panel: Photon reconstruction efficiency $\left(\epsilon_{\gamma}\right)$ (solid symbols) and purity of photon sample $\left(f_{\mathrm{p}}\right)$ (open symbols) for PMD as a function of pseudorapidity $(\eta)$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=$ $200 \mathrm{GeV}$. Bottom panel: Comparison between estimated $\epsilon_{\gamma}$ and $f_{\mathrm{p}}$ for PMD as a function of $\eta$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=62.4 \mathrm{GeV}$ using HIJING and AMPT models. The error bars on the AMPT data are statistical and those for HIJING are within the symbol size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
Fig. 2. (Color online.) Event-by-event photon multiplicity distributions (solid circles) for $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=62.4$ and $200 \mathrm{GeV} .$ The distributions for top $0-5 \%$ central $\mathrm{Au}+$ Au collisions and top $0-10 \%$ central $\mathrm{Cu}+\mathrm{Cu}$ collisions are also shown (open circles). The photon multiplicity distributions for central collisions are observed to be Gaussian (solid line). Only statistical errors are shown. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
Forward-backward multiplicity correlation strengths have been measured for the first time with the STAR detector for Au+Au and $\textit{p+p}$ collisions at $\sqrt{s_{NN}}$ = 200 GeV. Strong short and long range correlations are seen in central (0-10%) Au+Au collisions. The magnitude of these correlations decrease with decreasing centrality until only short range correlations are observed in 40-50% Au+Au collisions. The results are in agreement with predictions from the Dual Parton and Color Glass Condensate models.
FB Correlation strength for Au+Au at different centralities and p+p reactions as a function of $\Delta\eta$.
Backward-forward dispersion, $D_{bf}^{2}$ and forward-forward dispersion $D_{bf}^{2}$ for Au+Au 0-10% centrality and p+p reactions as a function of $\Delta\eta$.
We present results on the system size dependence of high transverse momentum di-hadron correlations at $\sqrt{s_{NN}}$ = 200 GeV as measured by STAR at RHIC. Measurements in d+Au, Cu+Cu and Au+Au collisions reveal similar jet-like correlation yields at small angular separation ($\Delta\phi\sim0$, $\Delta\eta\sim0$) for all systems and centralities. Previous measurements have shown that the away-side yield is suppressed in heavy-ion collisions. We present measurements of the away-side suppression as a function of transverse momentum and centrality in Cu+Cu and Au+Au collisions. The suppression is found to be similar in Cu+Cu and Au+Au collisions at a similar number of participants. The results are compared to theoretical calculations based on the parton quenching model and the modified fragmentation model. The observed differences between data and theory indicate that the correlated yields presented here will provide important constraints on medium density profile and energy loss model parameters.
Di-hadron correlations in $\Delta\phi$ for small $|\Delta\eta|$ ($|\Delta\eta|<0.7$) and large ($0.7<|\Delta\eta|<1.7$), scaled to match small $|\Delta\eta|$ at large $\Delta\phi$.
Subtracted distributions for di-hadron correlations in $\Delta\phi$ for small $|\Delta\eta|$ ($|\Delta\eta|<0.7$) minus large ($0.7<|\Delta\eta|<1.7$), scaled to match small $|\Delta\eta|$ at large $\Delta\phi$.
Subtracted distributions for di-hadron correlations in $\Delta\eta$.
Differential cross sections for the reaction $\gamma p \to n \pi^+$ have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.725 to 2.875 GeV. Where available, the results obtained here compare well with previously published results for the reaction. Agreement with the SAID and MAID analyses is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been made up to 2.7 GeV. Resonance couplings have been extracted and compared to previous determinations. With the addition of these cross sections to the world data set, significant changes have occurred in the high-energy behavior of the SAID cross-section predictions and amplitudes.
Differential cross sections for incident photon energies 0.725, 0.775, 0.825and 0.875 GeV.
Differential cross sections for incident photon energies 0.925, 0.975, 1.025and 1.075 GeV.
Differential cross sections for incident photon energies 1.125, 1.175, 1.225and 1.275 GeV.
We report e+e- --> b anti-b cross section measurements by the BABAR experiment performed during an energy scan in the range of 10.54 to 11.20 GeV at the PEP-II e+e- collider. A total relative error of about 5% is reached in more than three hundred center-of-mass energy steps, separated by about 5 MeV. These measurements can be used to derive precise information on the parameters of the Y(10860) and Y(11020) resonances. In particular we show that their widths may be smaller than previously measured.
Measured values of R(b) from the detailed scan in SQRT(S),. where R(b) is the ratio between the number of observed E+ E- --> B BBAR(GAMMA) normalized to luminosity divided to the bare dimuon cross-section.
The differential cross-section for the process p(e,e'p)eta has been measured at Q2 ~ 5.7 and 7.0 (GeV/c)2 for centre-of-mass energies from threshold to 1.8 GeV, encompassing the S11(1535) resonance, which dominates the channel. This is the highest momentum transfer measurement of this exclusive process to date. The helicity-conserving transition amplitude A_1/2, for the production of the S11(1535) resonance, is extracted from the data. This quantity appears to begin scaling as 1/Q3, a predicted signal of the dominance of perturbative QCD, at Q2 ~ 5 (GeV/c)2.
Total cross section for the lower Q**2 data as a function of W. The errors are statistics and systematic added in quadrature.
Total cross section for the higher Q**2 data as a function of W. The errors are statistics and systematic added in quadrature.
Lower Q**2 extracted differential cross section at W = 1.500 GeV and cos(theta(eta) = -0.917, -0.750 and -0.583.
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.
A search for charmonium and other new states is performed in a study of exclusive initial-state-radiation production of D Dbar events from electron-positron annihilations at a center-of-mass energy of 10.58 GeV. The data sample corresponds to an integrated luminosity of 384 fb-1 and was recorded by the BABAR experiment at the PEP-II storage ring. The D Dbar mass spectrum shows clear evidence of the psi(3770) plus other structures near 3.9, 4.1, and 4.4 GeV/c^2. No evidence for Y(4260) -> D Dbar is observed, leading to an upper limit of B(Y(4260) -> D Dbar)/B(Y(4260) -> J/psi pi+ pi-) < 1.0 at 90 % confidence level.
Measured cross section for D0 DBAR0 and D+ D- production. Bins with no data are shown with a 'dash'.
Using the CLEO-c detector at the Cornell Electron Storage Ring, we have measured inclusive and exclusive cross sections for the production of D+, D0 and Ds+ mesons in e+e- annihilations at thirteen center-of-mass energies between 3.97 and 4.26 GeV. Exclusive cross sections are presented for final states consisting of two charm mesons (DD, D*D, D*D*, Ds+Ds-, Ds*+Ds-, and Ds*+Ds*-) and for processes in which the charm-meson pair is accompanied by a pion. No enhancement in any final state is observed at the energy of the Y(4260).
Exclusive cross section for two body neutral non-strange charm mesons.
Exclusive cross section for two body charged non-strange charm mesons.
Exclusive cross section for two body strange charm mesons.
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