The energy dependence of the single-transverse-spin asymmetry, A_N, and the cross section for neutron production at very forward angles were measured in the PHENIX experiment at RHIC for polarized p+p collisions at sqrt(s)=200 GeV. The neutrons were observed in forward detectors covering an angular range of up to 2.2 mrad. We report results for neutrons with momentum fraction of x_F=0.45 to 1.0. The energy dependence of the measured cross sections were consistent with x_F scaling, compared to measurements by an ISR experiment which measured neutron production in unpolarized p+p collisions at sqrt(s)=30.6--62.7 GeV. The cross sections for large x_F neutron production for p+p collisions, as well as those in e+p collisions measured at HERA, are described by a pion exchange mechanism. The observed forward neutron asymmetries were large, reaching A_N=-0.08+/-0.02 for x_F=0.8; the measured backward asymmetries, for negative x_F, were consistent with zero. The observed asymmetry for forward neutron production is discussed within the pion exchange framework, with interference between the spin-flip amplitude due to the pion exchange and nonflip amplitudes from all Reggeon exchanges. Within the pion exchange description, the measured neutron asymmetry is sensitive to the contribution of other Reggeon exchanges even for small amplitudes.
The cross section results for forward neutron production in $p$+$p$ collisions at $\sqrt{s}$ = 200 GeV are shown. Two different forms, exponential and Gaussian, were used for the $p_T$ distribution. The integrated $p_T$ region for each bin is 0 < $p_T$ < 0.11$x_F$ GeV/$c$.
The $x_F$ dependence of $A_N$ for neutron production in the ZDC trigger sample.
The $x_F$ dependence of $A_N$ for neutron production for the ZDC$\otimes$BBC trigger sample.
Measurements of neutral current cross sections for deep inelastic scattering in e+p collisions at HERA with a longitudinally polarised positron beam are presented. The single-differential cross-sections d(sigma)/dQ2, d(sigma)/dx and d(sigma)/dy and the reduced cross-section were measured in the kinematic region Q2 > 185 GeV2 and y < 0.9, where Q2 is the four-momentum transfer squared, x the Bjorken scaling variable, and y the inelasticity of the interaction. The measurements were performed separately for positively and negatively polarised positron beams. The measurements are based on an integrated luminosity of 135.5 pb-1 collected with the ZEUS detector in 2006 and 2007 at a centre-of-mass energy of 318 GeV. The structure functions F3 and F3(gamma)Z were determined by combining the e+p results presented in this paper with previously published e-p neutral current results. The asymmetry parameter A+ is used to demonstrate the parity violation predicted in electroweak interactions. The measurements are well described by the predictions of the Standard Model.
The single-differential cross section DSIG/DQ**2 (Y<0.9,Y(1-x)**2>0.004), corrected to the electroweak Born level, for zero polarisation, Pe=0.
The single-differential cross section DSIG/DQ**2 (Y<0.9,Y(1-x)**2>0.004), corrected to the electroweak Born level, for positive (Pe=+0.32) and negative (Pe=-0.36) polarisations.
The single-differential cross section DSIG/DX (Y<0.9,Y(1-x)**2>0.004) at Q^2=185 GeV^2, corrected to the electroweak Born level, for zero (Pe=0), positive (Pe=+0.32) and negative (Pe=-0.36) polarisations.
We report $J/\psi$ spectra for transverse momenta $p_T$> 5 GeV/$c$ at mid-rapidity in p+p and Au+Au collisions at sqrt(s_{NN}) = 200 GeV.The inclusive $J/\psi$ spectrum and the extracted $B$-hadron feed-down are compared to models incorporating different production mechanisms. We observe significant suppression of the $J/\psi$ yields for $p_T$> 5 GeV/$c$ in 0-30% Au+Au collisions relative to the p+p yield scaled by the number of binary nucleon-nucleon collisions in Au+Au collisions. In 30-60% collisions, no such suppression is observed.The level of suppression is consistently less than that of high-$p_T$ $\pi^{\pm}$ and low-$p_T$ $J/\psi$.
(Color online.) The invariant $J/\psi$ cross section versus $p_{T}$ in p+p collisions at $\sqrt{s}$ = 200 GeV. The vertical bars and boxes depict the statistical and systematic uncertainties, respectively. Also shown are results published by STAR [15] and PHENIX [20]. The curves show theoretical calculations described in the text.
(Color online.) The fraction of $B \rightarrow J/\psi$ over the inclusive $J/\psi$ yield in $p+p$ collisions. The FONLL+CEM model calculation is also shown.
$J/\psi$ $p_{T}$ distributions in Au+Au collisions with different centralities at $\sqrt{s_{NN}}$ = 200 GeV. For clarity, the data and curves have been scaled as indicated in the legends. The PHENIX results are reported in [6]. The curves are model fits described in the text.
The PHENIX experiment has measured the production of neutral pions in Au+Au collisions at sqrt(s_NN)=200 GeV. The new data offer a fourfold increase in recorded luminosity, providing higher precision and a larger reach in transverse momentum, p_T, to 20 GeV/c. The production ratio of eta/pi^0 is 0.46+/-0.01(stat)+/-0.05(syst), constant with p_T and collision centrality. The observed ratio is consistent with earlier measurements, as well as with the p+p and d+Au values. The production of pi^0 is suppressed by a factor of 5, as in earlier findings. However, with the improved statistical precision a small but significant rise of the nuclear modification factor, R_AA, vs p_T, with a slope of 0.0106+/-^(0.0034)_(0.0029)[GeV/c]^-1, is discernible in central collisions. A phenomenological extraction of the average fractional parton energy loss shows a decrease with increasing p_T. To study the path length dependence of suppression, the pi^0 yield was measured at different angles with respect to the event plane; a strong azimuthal dependence of the pi^0 R_AA is observed. The data are compared to theoretical models of parton energy loss as a function of the path length, L, in the medium. Models based on pQCD are insufficient to describe the data, while a hybrid model utilizing pQCD for the hard interactions and AdS/CFT for the soft interactions is consistent with the data.
Invariant yields of neutral pions, all centralities
Invariant yields of neutral pions, all centralities
$\Eta/ \pi^0 ratios
The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d+Au and p+p collisions at sqrt(s_NN)=200 GeV at the Relativistic Heavy Ion Collider, in the transverse-momentum range 0.85 < pT < 8.5 GeV/c. In central d+Au collisions, the nuclear modification factor R_dA at 1.5 < pT < 5 GeV/c displays evidence of enhancement of these electrons, relative to those produced in p+p collisions, and shows that the mass-dependent Cronin enhancement observed at RHIC extends to the heavy-D-meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-flavor mesons could contribute to the observed differences between the pi0 and heavy-flavor-electron nuclear modification factor R_AA.
Heavy flavor electron yield, Run-8 $p$ + $p$, $d$+Au collisions. Electrons from heavy flavor decays, separated by centrality. The lines represent a fit to the previous $p+p$ result [23], scaled by $N_{coll}$. The inset shows the ratio of photonic background electrons determined by the converter and cocktail methods for Minimum Bias $d$+Au collisions, with error bars (boxes) that represent the statistical uncertainty on the converter data (systematic uncertainty on the photonic-electron cocktail).
Heavy flavor electron yield, $d$+Au $\implies$ CHARGED X. Electrons from heavy flavor decays, separated by centrality. The lines represent a fit to the previous $p+p$ result [23], scaled by $N_{coll}$. The inset shows the ratio of photonic background electrons determined by the converter and cocktail methods for Minimum Bias $d$+Au collisions, with error bars (boxes) that represent the statistical uncertainty on the converter data (systematic uncertainty on the photonic-electron cocktail).
Heavy flavor electron $R_{dA}$ 0-100% d+Au collisions. The nuclear modification factors $R_{dA}$ and $R_{AA}$ for minimum bias $d$+Au and Au+Au collisions, for the $\pi^{0}$ and $e^{\pm}_{HF}$. The two boxes on the right side of the plot represent the global uncertainties in the $d$+Au (left) and Au+Au (right) values of $N_{coll}$ . An additional common global scaling uncertainty of 9.7% on $R_{dA}$ and $R_{AA}$ from the $p+p$ reference data is omitted for clarity.
Direct photons have been measured in sqrt(s_NN)=200 GeV d+Au collisions at midrapidity. A wide p_T range is covered by measurements of nearly-real virtual photons (1<p_T<6 GeV/c) and real photons (5<p_T<16 GeV/c). The invariant yield of the direct photons in d+Au collisions over the scaled p+p cross section is consistent with unity. Theoretical calculations assuming standard cold nuclear matter effects describe the data well for the entire p_T range. This indicates that the large enhancement of direct photons observed in Au+Au collisions for 1.0<p_T<2.5 GeV/c is due to a source other than the initial-state nuclear effects.
Direct photon fraction. The direct-photon fractions from the virtual-photon analysis as a function of $p_{T}$ in $p+p$ (MB) [1] collisions. The values in the table are equal to this mean value. The statistical and systematic uncertainties are shown by the bars and bands, respectively. The curves show expectations from a NLO pQCD calculation [17, 18] with different cutoff mass scales: (solid) $\mu$ = 0.5 $p_{T}$ , (dash) $\mu$ = 1.0 $p_{T}$ , and (dash-dot) $\mu$ = 2.0 $p_{T}$.
Direct photon fraction. The direct-photon fractions from the virtual-photon analysis as a function of $p_{T}$ in $d$+Au (MB) [1] collisions. The values in the table are equal to this mean value. The statistical and systematic uncertainties are shown by the bars and bands, respectively. The curves show expectations from a NLO pQCD calculation [17, 18] with different cutoff mass scales: (solid) $\mu$ = 0.5 $p_{T}$ , (dash) $\mu$ = 1.0 $p_{T}$ , and (dash-dot) $\mu$ = 2.0 $p_{T}$.
Direct photon cross section. (a) The invariant cross sections of the direct photon in $p+p$ [3, 4] and $d$+Au collisions. The $p+p$ fit result with the empirical parameterization described in the text is shown as well as NLO pQCD calculations, and the scaled $p+p$ fit is compared with the $d$+Au data. The closed and open symbols show the results from the virtual photon and $\pi_{0}$-tagging methods, respectively. The asterisk symbols show the result from the statistical subtraction method for $d$+Au data, overlapping with the virtual photon result in 3 < $p_{T}$ < 5 GeV/c. The values in the table are equal to this mean value. The bars and bands represent the point-to-point (ptp.) and $p_{T}$-correlated (cor.) uncertainties, respectively. (b) The $p+p$ data over the fit. The uncertainties of the fit due to both point-to-point (ptp.) and pT -correlated uncertainties of the data are summed quadratically, and the sum is shown as dotted lines. The NLO pQCD calculations divided by the fit are also shown.
Spectra of identified charged hadrons are measured in pp collisions at the LHC for sqrt(s) = 0.9, 2.76, and 7 TeV. Charged pions, kaons, and protons in the transverse-momentum range pt approximately 0.1-1.7 GeV and for rapidities abs(y) < 1 are identified via their energy loss in the CMS silicon tracker. The average pt increases rapidly with the mass of the hadron and the event charged-particle multiplicity, independently of the center-of-mass energy. The fully corrected pt spectra and integrated yields are compared to various tunes of the PYTHIA6 and PYTHIA8 event generators.
Measured transverse momentum distributions of identified charged hadrons (PI+, K+ and P) and at a centre-of-mass energy of 900 GeV.
Measured transverse momentum distributions of identified charged hadrons (PI-, K- and PBAR) and at a centre-of-mass energy of 900 GeV.
Measured transverse momentum distributions of identified charged hadrons (PI+, K+ and P) and at a centre-of-mass energy of 2760 GeV.
Inclusive e\pmp single and double differential cross sections for neutral and charged current deep inelastic scattering processes are measured with the H1 detector at HERA. The data were taken at a centre-of-mass energy of \surds = 319GeV with a total integrated luminosity of 333.7 pb-1 shared between two lepton beam charges and two longitudinal lepton polarisation modes. The differential cross sections are measured in the range of negative fourmomentum transfer squared, Q2, between 60 and 50 000GeV2, and Bjorken x between 0.0008 and 0.65. The measurements are combined with earlier published unpolarised H1 data to improve statistical precision and used to determine the structure function xF_3^gammaZ. A measurement of the neutral current parity violating structure function F_2^gammaZ is presented for the first time. The polarisation dependence of the charged current total cross section is also measured. The new measurements are well described by a next-to-leading order QCD fit based on all published H1 inclusive cross section data which are used to extract the parton distribution functions of the proton.
The Neutral Current Reduced Cross Section for E- P interactions with a beam polarisation of -25.8 % for Q^2 values of 120, 150, 200, 250 and 300 GeV^2.
The Neutral Current Reduced Cross Section for E- P interactions with a beam polarisation of -25.8 % for Q^2 values of 400, 500, 650, 800 and 1000 GeV^2.
The Neutral Current Reduced Cross Section for E- P interactions with a beam polarisation of -25.8 % for Q^2 values of 1200, 1500, 2000, 3000 and 5000 GeV^2.
The charged-particle production ratios $\bar{p}/p$, $K^-/K^+$, $\pi^-/\pi^+$, $(p + \bar{p})/(\pi^+ + \pi^-)$, $(K^+ + K^-)/(\pi^+ + \pi^-)$ and $(p + \bar{p})/(K^+ + K^-)$ are measured with the LHCb detector using $0.3 {\rm nb^{-1}}$ of $pp$ collisions delivered by the LHC at $\sqrt{s} = 0.9$ TeV and $1.8 {\rm nb^{-1}}$ at $\sqrt{s} = 7$ TeV. The measurements are performed as a function of transverse momentum $p_{\rm T}$ and pseudorapidity $\eta$. The production ratios are compared to the predictions of several Monte Carlo generator settings, none of which are able to describe adequately all observables. The ratio $\bar{p}/p$ is also considered as a function of rapidity loss, $\Delta y \equiv y_{\rm beam} - y$, and is used to constrain models of baryon transport.
The measured ratio of prompt antiproton to proton production at 900 GeV.
The measured ratio of prompt antiproton to proton production at 7000 GeV.
The measured ratio of prompt negative to positive kaon production at 900 GeV.
The production of isolated high-energy photons accompanied by jets has been measured in deep inelastic ep scattering with the ZEUS detector at HERA, using an integrated luminosity of 326 pb^{-1}. Measurements were made for exchanged photon virtualities, Q^2, in the range 10 to 350 GeV^2. The photons were measured in the transverse-energy and pseudorapidity ranges 4 < ET^gamma < 15 GeV and -0.7 < eta^gamma < 0.9, and the jets were measured in the transverse-energy and pseudorapidity ranges 2.5 < ET^jet <35 GeV and -1.5 < eta^jet < 1.8. Differential cross sections are presented as functions of these quantities. Perturbative QCD predictions give a reasonable description of the shape of the measured cross sections over most of the kinematic range, but the absolute normalisation is typically in disagreement by 20-30%.
The measured differential cross section as a function of Q**2.
The measured differential cross section as a function of X.
The measured differential cross section as a function of the transverse energy of the photon.
Forum