The process e+e- --> p anti-p gamma is studied using 469 fb-1 of integrated luminosity collected with the BABAR detector at the PEP-II collider, at an e+e- center-of-mass energy of 10.6 GeV. From the analysis of the p anti-p invariant mass spectrum, the energy dependence of the cross section for e+e- --> p anti-p is measured from threshold to 4.5 GeV. The energy dependence of the ratio of electric and magnetic form factors, |G_E/G_M|, and the asymmetry in the proton angular distribution are measured for p anti-p masses below 3 GeV. We also measure the branching fractions for the decays J/psi --> p anti-p and psi(2S) --> p anti p.
Measurement of the cross section as a function of the invariant mass of the PBAR-P system and the effective form factor for the reaction E+ E- --> PBAR P. The contributions from J/PSI and PSI(25) decaying to PBAR-P have been subtracted. The form factor error is the combined statistical and systematic.
The reaction gamma + p -> K+ + Sigma + pi was used to determine the invariant mass distributions or "line shapes" of the Sigma+ pi-, Sigma- pi+ and Sigma0 pi0 final states, from threshold at 1328 MeV/c^2 through the mass range of the Lambda(1405) and the Lambda(1520). The measurements were made with the CLAS system at Jefferson Lab using tagged real photons, for center-of-mass energies 1.95 < W < 2.85 GeV. The three mass distributions differ strongly in the vicinity of the I=0 \Lambda(1405), indicating the presence of substantial I=1 strength in the reaction. Background contributions to the data from the Sigma0(1385) and from K^* Sigma production were studied and shown to have negligible influence. To separate the isospin amplitudes, Breit-Wigner model fits were made that included channel-coupling distortions due to the NKbar threshold. A best fit to all the data was obtained after including a phenomenological I=1, J^P = 1/2^- amplitude with a centroid at 1394\pm20 MeV/c^2 and a second I=1 amplitude at 1413\pm10 MeV/c^2. The centroid of the I=0 Lambda(1405) strength was found at the Sigma pi threshold, with the observed shape determined largely by channel-coupling, leading to an apparent overall peak near 1405 MeV/c^2.
Invariant mass distributions of the three SIGMA-PI combinations for centre-of-mass energies, W, from 1.95 to 2.05 GeV corresponding to incident photon energies from 1.56 to 1.77 GeV.
Invariant mass distributions of the three SIGMA-PI combinations for centre-of-mass energies, W, from 2.05 to 2.15 GeV corresponding to incident photon energies from 1.77 to 1.99 GeV.
Invariant mass distributions of the three SIGMA-PI combinations for centre-of-mass energies, W, from 2.15 to 2.25 GeV corresponding to incident photon energies from 1.99 to 2.23 GeV.
We report measurements of the third harmonic coefficient of the azimuthal anisotropy, v_3, known as triangular flow. The analysis is for charged particles in Au+Au collisions at sqrtsNN = 200 GeV, based on data from the STAR experiment at the Relativistic Heavy Ion Collider. Two-particle correlations as a function of their pseudorapidity separation are fit with narrow and wide Gaussians. Measurements of triangular flow are extracted from the wide Gaussian, from two-particle cumulants with a pseudorapidity gap, and also from event plane analysis methods with a large pseudorapidity gap between the particles and the event plane. These results are reported as a function of transverse momentum and centrality. A large dependence on the pseudorapidity gap is found. Results are compared with other experiments and model calculations.
Gaussian Width (W) as a function of transverse momentum for most central (0-5%) and mid-central (30-40%) Au+Au collision at sqrt(snn)=200 GEV.
Amplitude (A) as a function of transverse momentum for most central (0-5%) and mid-central (30-40%) Au+Au collision at sqrt(snn)=200 GEV.
Gaussian Width (W) as a function of centrality for Like Sign (LS) and Charge Independent (CI) particles for Au+Au collision at sqrt(snn)=200 GEV.
Measurements of the elliptic flow, $v_{2}$, of identified hadrons ($\pi^{\pm}$, $K^{\pm}$, $K_{s}^{0}$, $p$, $\bar{p}$, $\phi$, $\Lambda$, $\bar{\Lambda}$, $\Xi^{-}$, $\bar{\Xi}^{+}$, $\Omega^{-}$, $\bar{\Omega}^{+}$) in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV are presented. The measurements were done at mid-rapidity using the Time Projection Chamber and the Time-of-Flight detectors of the STAR experiment during the Beam Energy Scan program at RHIC. A significant difference in the $v_{2}$ values for particles and the corresponding anti-particles was observed at all transverse momenta for the first time. The difference increases with decreasing center-of-mass energy, $\sqrt{s_{NN}}$ (or increasing baryon chemical potential, $\mu_{B}$) and is larger for the baryons as compared to the mesons. This implies that particles and anti-particles are no longer consistent with the universal number-of-constituent quark (NCQ) scaling of $v_{2}$ that was observed at $\sqrt{s_{NN}}=$ 200 GeV. However, for the group of particles NCQ scaling at $(m_{T}-m_{0})/n_{q}>$ 0.4 GeV/$c^{2}$ is not violated within $\pm$10%. The $v_{2}$ values for $\phi$ mesons at 7.7 and 11.5 GeV are approximately two standard deviations from the trend defined by the other hadrons at the highest measured $p_{T}$ values.
The elliptic flow,v_2, as a function of the transverse momentum,p_T, from 0–80% central Au+Au collisions for various particle species and energies.
The elliptic flow,v_2, as a function of the transverse momentum,p_T, from 0–80% central Au+Au collisions for various particle species and energies.
The elliptic flow,v_2, as a function of the transverse momentum,p_T, from 0–80% central Au+Au collisions for various particle species and energies.
Elliptic flow ($v_{2}$) values for identified particles at mid-rapidity in Au+Au collisions, measured by the STAR experiment in the Beam Energy Scan at RHIC at $\sqrt{s_{NN}}=$ 7.7--62.4 GeV, are presented. A beam-energy dependent difference of the values of $v_{2}$ between particles and corresponding anti-particles was observed. The difference increases with decreasing beam energy and is larger for baryons compared to mesons. This implies that, at lower energies, particles and anti-particles are not consistent with the universal number-of-constituent-quark (NCQ) scaling of $v_{2}$ that was observed at $\sqrt{s_{NN}}=$ 200 GeV.
The elliptic flow $v_{2}$ of protons and anti-protons as a function of the transverse momentum, $p_{T}$, for 0–80$\%$ central Au+Au collisions. The lower panels show the difference in $v_{2}(p_{T})$ between the particles and anti-particles. The solid curves are fits with a horizontal line. The shaded areas depict the magnitude of the systematic errors.
The elliptic flow $v_{2}$ of protons and anti-protons as a function of the transverse momentum, $p_{T}$, for 0–80$\%$ central Au+Au collisions. The lower panels show the difference in $v_{2}(p_{T})$ between the particles and anti-particles. The solid curves are fits with a horizontal line. The shaded areas depict the magnitude of the systematic errors.
The elliptic flow $v_{2}$ of protons and anti-protons as a function of the transverse momentum, $p_{T}$, for 0–80$\%$ central Au+Au collisions. The lower panels show the difference in $v_{2}(p_{T})$ between the particles and anti-particles. The solid curves are fits with a horizontal line. The shaded areas depict the magnitude of the systematic errors.
We present a study of the average transverse momentum ($p_t$) fluctuations and $p_t$ correlations for charged particles produced in Cu+Cu collisions at midrapidity for $\sqrt{s_{NN}} =$ 62.4 and 200 GeV. These results are compared with those published for Au+Au collisions at the same energies, to explore the system size dependence. In addition to the collision energy and system size dependence, the $p_t$ correlation results have been studied as functions of the collision centralities, the ranges in $p_t$, the pseudorapidity $\eta$, and the azimuthal angle $\phi$. The square root of the measured $p_t$ correlations when scaled by mean $p_t$ is found to be independent of both colliding beam energy and system size studied. Transport-based model calculations are found to have a better quantitative agreement with the measurements compared to models which incorporate only jetlike correlations.
Event-by-event $\langle p_{t}\rangle$ distributions for data and mixed events in central Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 and 62.4 GeV.
Comparison of dynamical $\langle p_{t}\rangle$ fluctuations in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV as a function of the number of participanting nucleons.
Comparison of dynamical $\langle p_{t}\rangle$ fluctuations in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV as a function of the number of participanting nucleons.
This Letter reports a measurement of the cross section for producing pairs of central prompt isolated photons in proton-antiproton collisions at a total energy of 1.96 TeV using data corresponding to 9.5/fb integrated luminosity collected with the CDF II detector at the Fermilab Tevatron. The measured differential cross section is compared to three calculations derived from the theory of strong interactions. These include a prediction based on a leading order matrix element calculation merged with parton shower, a next-to-leading order, and a next-to-next-to-leading order calculation. The first and last calculations reproduce most aspects of the data, thus showing the importance of higher-order contributions for understanding the theory of strong interaction and improving measurements of the Higgs boson and searches for new phenomena in diphoton final states.
The measured differential cross sections for $M_{\gamma\gamma}$ , together with the predictions from the Sherpa and NNLO Monte Carlos.
The measured differential cross sections for $M_{\gamma\gamma}$ when $P_T > M_{\gamma\gamma}$ , together with the predictions from the Sherpa and NNLO Monte Carlos.
The measured differential cross sections for $M_{\gamma\gamma}$ when $P_T < M_{\gamma\gamma}$ , together with the predictions from the Sherpa and NNLO Monte Carlos.
The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the photon is an excellent approximation to the initial p_T of the jet and the ratio z_T=p_T^h/p_T^\gamma is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. I_ AA, the ratio of jet fragment yield in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high z_T. The fragment yield at low z_T is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles.
Direct photon-hadron pair per-trigger yields vs Delta-phi (Au+Au and p+p)
Integrated per-trigger yields and I_AA vs xi
Integrated per-trigger yields and I_AA vs xi
The measurement of J/{psi} azimuthal anisotropy is presented as a function of transverse momentum for different centralities in Au+Au collisions at {sqrt{s_{NN}}} = 200 GeV. The measured J/{psi} elliptic flow is consistent with zero within errors for transverse momentum between 2 and 10 GeV/c. Our measurement suggests that J/{psi} with relatively large transverse momentum are not dominantly produced by coalescence from thermalized charm quarks, when comparing to model calculations.
J/Psi azimuthal anisotropy v2 vs pT measured via the dielectron channel in 0-10%, 10-40%, and 40-80% central Au+Au collisions at 200 GeV. The brackets represent systematic errors. The boxes show the estimated maximum possible range of v2 if the nonflow influence is corrected. The mean pT in each bin for v2 calculation is drawn, but is shifted a little for some centralities so that all points can be seen clearly.
J/Psi azimuthal anisotropy v2 vs pT measured via the dielectron channel in 0-80% central Au+Au collisions at 200 GeV. The brackets represent systematic errors. The boxes show the estimated maximum possible range of v2 if the nonflow influence is corrected.
Jet-medium interactions are studied via a multi-hadron correlation technique (called "2+1"), where a pair of back-to-back hadron triggers with large transverse momentum is used as a proxy for a di-jet. This work extends the previous analysis for nearly-symmetric trigger pairs with the highest momentum threshold of trigger hadron of 5 GeV/$c$ with the new calorimeter-based triggers with energy thresholds of up to 10 GeV and above. The distributions of associated hadrons are studied in terms of correlation shapes and per-trigger yields on each trigger side. In contrast with di-hadron correlation results with single triggers, the associated hadron distributions for back-to-back triggers from central Au+Au data at $\sqrt{s_{NN}}$=200 GeV show no strong modifications compared to d+Au data at the same energy. An imbalance in the total transverse momentum between hadrons attributed to the near-side and away-side of jet-like peaks is observed. The relative imbalance in the Au+Au measurement with respect to d+Au reference is found to increase with the asymmetry of the trigger pair, consistent with expectation from medium-induced energy loss effects. In addition, this relative total transverse momentum imbalance is found to decrease for softer associated hadrons. Such evolution indicates the energy missing at higher associated momenta is converted into softer hadrons.
Projections of 2-D correlation functions on $\Delta \phi$ (a) (with $|\Delta \eta|$ < 1.0) and $\Delta \eta$ (b) (with $|\Delta \phi|$ < 0.7) for the hadrons associated with their respective triggers (T1 for near-side, T2 for away–side) are shown for d+Au (circles) and central 0-20% Au+Au (squares).
Projections of 2-D correlation functions on $\Delta \phi$ (a) (with $|\Delta \eta|$ < 1.0) and $\Delta \eta$ (b) (with $|\Delta \phi|$ < 0.7) for the hadrons associated with their respective triggers (T1 for near-side, T2 for away–side) are shown for d+Au (circles) and central 0-20% Au+Au (squares).
Projections of 2-D correlation functions on $\Delta \phi$ (a) (with $|\Delta \eta|$ < 1.0) and $\Delta \eta$ (b) (with $|\Delta \phi|$ < 0.7) for the hadrons associated with their respective triggers (T1 for near-side, T2 for away–side) are shown for d+Au (circles) and central 0-20% Au+Au (squares).
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