Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of rho^0 and direct pi^+pi^- photoproduction in ultra-peripheral relativistic heavy ion collisions at sqrt(s_{NN})=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of sigma(AuAu) -> Au^*Au^*rho^0 = 530 pm 19 (stat.) pm 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The rho^0 transverse momentum spectrum (p_{T}^2) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus/ we find sigma_{inc}/sigma_{coh} = 0.29 pm 0.03 (stat.) pm 0.08 (syst.). The ratio of direct pi^+pi^- to rho^0 production is comparable to that observed in gamma p collisions at HERA, and appears to be independent of photon energy. Finally, the measured rho^0 spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.
ZDC spectra obtained with the minimum bias sample after the $\rho^{0}$ selection cuts are applied, and fit with three Gaussians. The east ZDC is shown on the left and the west ZDC is shown on the right. The ratio of numbers of candidates in the West ZDC of 1n:2n:3n is 1: 0.48 $\pm$ 0.03: 0.42 $\pm$ 0.03, while in the East ZDC, we find 1n:2n:3n is 1: 0.46 $\pm$ 0.03: 0.42 $\pm$ 0.03.
ZDC spectra obtained with the minimum bias sample after the $\rho^{0}$ selection cuts are applied, and fit with three Gaussians. The east ZDC is shown on the left and the west ZDC is shown on the right. The ratio of numbers of candidates in the West ZDC of 1n:2n:3n is 1: 0.48 $\pm$ 0.03: 0.42 $\pm$ 0.03, while in the East ZDC, we find 1n:2n:3n is 1: 0.46 $\pm$ 0.03: 0.42 $\pm$ 0.03.
The invariant mass distribution for the coherently produced $\rho^{0}$ candidates from the minimum bias sample with the cut on the $\rho^{0}$ transverse momentum $p_{T}$ < 150 MeV/c. The hatched area is the contribution from the combinatorial background. The solid line corresponds to Eq. 3 which encompasses the Breit-Wigner (dashed), the mass independent contribution from the direct $\pi^{+}\pi^{-}$ production (dash-dotted), and the interference term(dotted).
A three-dimensional (3D) correlation function obtained from mid-rapidity, low pT pion pairs in central Au+Au collisions at sqrt(s_NN)=200 GeV is studied. The extracted model-independent source function indicates a long range tail in the directions of the pion pair transverse momentum (out) and the beam (long). Model comparisons to these distensions indicate a proper breakup time \tau_0 ~ 9 fm/c and a mean proper emission duration \Delta\tau ~ 2 fm/c, leading to sizable emission time differences (<|\Delta \tau_LCM |> ~ 12 fm/c), partly due to resonance decays. They also suggest an outside-in 'burning' of the emission source reminiscent of many hydrodynamical models.
1D correlation function. Systematic errors are less than the statistical errors.
Experimental correlation moments $R^0(q)$ Data. Systematic errors are less than the statistical errors.
Experimental correlation moments $R^0(q)$ Fit. Systematic errors are less than the statistical errors.
We report PHENIX measurements of the correlation of a trigger hadron at intermediate transverse momentum (2.5<p_{T,trig}<4 GeV/c), with associated mesons or baryons at lower p_{T,assoc}, in Au+Au collisions at sqrt(s_NN) = 200 GeV. The jet correlations for both baryons and mesons show similar shape alterations as a function of centrality, characteristic of strong modification of the away-side jet. The ratio of jet-associated baryons to mesons for this jet increases with centrality and p_{T,assoc} and, in the most central collisions, reaches a value similar to that for inclusive measurements. This trend is incompatible with in-vacuum fragmentation, but could be due to jet-like contributions from correlated soft partons which recombine upon hadronization.
<p>Correlation functions for associated partner mesons for centrality selections of 20-40% and 70-90%.</p> <p><i>Note that only statistical uncertainties are available.</i></p>
<p>Correlation functions for associated partner baryons for centrality selections of 20-40% and 70-90%.</p> <p><i>Note that only statistical uncertainties are available.</i></p>
<p>Jet-pair distributions for associated mesons for $1 < p_{T,assoc} < 1.3\ \mathrm{GeV}/c$ and $1.6 < p_{T,assoc} < 2.0\ \mathrm{GeV}/c$. Results are for a hadron trigger $2.5 < p_T < 4.0\ \mathrm{GeV}/c$ and centrality selections of 0-20% and 20-40%.</p> <p><i>Note that only statistical uncertainties are available.</i></p>
We present a new measurement of the difference between the nucleon strange and antistrange quark distributions from dimuon events recorded by the NuTeV experiment at Fermilab. This analysis is the first to use a complete next to leading order QCD d escription of charm production from neutrino scattering. Dimuon events in neutrino deep inelastic scattering allow direct and independent study of the strange and antistrange content of the nucleon. We find a positive strange asymmetry with a significance of 1.6sigma . We also report a new measurement of the charm mass.
Neutrino forward dimuon cross sections for Y bins 0.32, 0.56 and 0.77 as a function of X for neutrino energy 88.
Neutrino forward dimuon cross sections for Y bins 0.32, 0.56 and 0.77 as a function of X for neutrino energy 174.
Neutrino forward dimuon cross sections for Y bins 0.32, 0.56 and 0.77 as a function of X for neutrino energy 247.
We present a measurement of the cross section for W-boson production in association with jets in pbarp collisions at sqrt(s)=1.96$ TeV. The analysis uses a data sample corresponding to an integrated luminosity of 320 pb^-1 collected with the CDF II detector. W bosons are identified in their electron decay channel and jets are reconstructed using a cone algorithm. For each W+>= n-jet sample ($n= 1 - 4$) we measure sigma(ppbar =>W+>=n$-jet)x BR(W => e nu) with respect to the transverse energy E_T of the n^th-highest E_T jet above 20 GeV, for a restricted W => e nu decay phase space. The cross sections, corrected for all detector effects, can be directly compared to particle level W+ jet(s) predictions. We present here comparisons to leading order and next-to-leading order predictions.
Measured ET differential cross section of the 1st jet in >= 1 JET plus W < E NU > events.
Measured ET differential cross section of the 2nd jet in >= 2 JET plus W < E NU > events.
Measured ET differential cross section of the 3rd jet in >= 3 JET plus W < E NU > events.
The production of isolated photons in deep-inelastic scattering $ep\to e \gamma X$ is measured with the H1 detector at HERA. The measurement is performed in the kinematic range of negative four-momentum transfer squared $4<Q^2<150 $~GeV$^2$ and a mass of the hadronic system $W_X>50$ GeV. The analysis is based on a total integrated luminosity of 227~pb$^{-1}$. The production cross section of isolatedphotons with a transverse energy in the range $3 < E_T^\gamma < 10$ GeV and pseudorapidity range $-1.2 < \eta^\gamma < 1.8$ is measured as a function of $E_T^\gamma$, $\eta^\gamma$ and $Q^2$. Isolated photon cross sections are also measured for events with no jets or at least one hadronic jet. The measurements are compared with predictions from Monte Carlo generators modelling the photon radiation from the quark and the electron lines, as well as with calculations at leading and next to leading order in the strong coupling. The predictions significantly underestimate the measured cross sections.
Measured inclusive isolated photon cross section.
Measured total cross section for isolated photons plus no-jets and 1-jet.
Differential cross section as a function of the photon ET.
Three- and four-jet production is measured in deep-inelastic $ep$ scattering at low $x$ and $Q^2$ with the H1 detector using an integrated luminosity of $44{.}2 {\rm pb}^{-1}$. Several phase space regions are selected for the three-jet analysis in order to study the underlying parton dynamics from global topologies to the more restrictive regions of forward jets close to the proton direction. The measurements of cross sections for events with at least three jets are compared to fixed order QCD predictions of ${\mathcal{O}}(\alpha_{\rm s}^2)$ and ${\mathcal{O}}(\alpha_{\rm s}^3) $ and with Monte Carlo simulation programs where higher order effects are approximated by parton showers. A good overall description is provided by the ${\mathcal{O}}(\alpha_{\rm s}^3) $ calculation. Too few events are predicted at the lowest $x \sim 10^{-4}$, especially for topologies with two forward jets. This hints to large contributions at low $x$ from initial state radiation of gluons close to the proton direction and unordered in transverse momentum. The Monte Carlo program in which gluon radiation is generated by the colour dipole model gives a good description of both the three- and the four-jet data in absolute normalisation and shape.
Differential cross section as a function of the minimum number of jet for events with at least 3-jets.
Differential cross section as a function of X for events with at least 3-jets.
Differential cross section for events with at least 3-jets as a function of the pseudorapidity of each jet.
All of the experimental data points presented in the original paper are correct and unchanged (including statistical and systematic uncertainties). However, herein we correct a comparison between the experimental data and a theoretical picture, because we discovered a mistake in the code used. All of the most probable sigma_breakup values differ by less than 0.4 mb from those originally presented. However, the one standard deviation uncertainties (that include contributions from both the statistical and systematic uncertainties on the experimental data points) are approximately 30-60% larger than originally reported. We give a table of the new comparison results and corrected versions of Figs. 8-11 of the original paper and we note that no correction is needed for results from the data-driven method in Fig. 13.
J/PSI invariant (1/(2PI*PT))*D2(N)/DPT/DYRAP versus rapidity in D+AU collisions, over 3 bins of rapidity.
J/PSI invariant (1/(2PI*PT))*D2(N)/DPT/DYRAP versus rapidity in D+AU collisions, over 5 bins of rapidity.
J/PSI invariant (1/(2PI*PT))*D2(N)/DPT/DYRAP versus PT at backward rapidity (-2.2<y<-1.2) in D+AU collisions.
We present the first measurement of the production cross section of a W boson with a single charm quark (c) in p-pbar collisions at sqrt(s)=1.96 TeV, using soft muon tagging of c jets. In a data sample of ~1.8 fb-1, recorded with the CDF II detector at the Fermilab Tevatron, we select events with W+1 or 2 jets. We use the charge correlation between the W and the muon from the semileptonic decay of a charm hadron to extract the Wc signal. We measure sigma_{Wc}(p_{Tc}>20 GeV/c, |\eta_c|<1.5)\times BR(W->\ell\nu) = 9.8+/-3.2 pb, in agreement with theoretical expectations.
The measured cross section for leptonic decay of the W.
We present a measurement of the muon neutrino-nucleon inclusive charged current cross-section, off an isoscalar target, in the neutrino energy range $2.5 \leq E_\nu \leq 40$ GeV. The significance of this measurement is its precision, $\pm 4$% in $2.5 \leq E_\nu \leq 10$ GeV, and $\pm 2.6$% in $10 \leq E_\nu \leq 40$ GeV regions, where significant uncertainties in previous experiments still exist, and its importance to the current and proposed long baseline neutrino oscillation experiments.
Inclusive muon-neutrino charged current cross section.
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