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Register a new userNuclear dependence of light neutral meson production in p-A collisions at 400 GeV with NA60
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The NA60 experiment has studied low-mass muon pair production in proton-nucleus collisions with a system of Be, Cu, In, W, Pb and U targets, using a 400 GeV proton beam at the CERN SPS. The transverse momentum spectra of the $rho/omega$ and $phi$ mesons are measured in the full $p_mathrm{T}$ range accessible, from $p_mathrm{T} = 0$ up to 2 GeV/$c$. The nuclear dependence of the production cross sections of the $eta$, $omega$ and $phi$ mesons has been found to be consistent with the power law $sigma_mathrm{pA} propto mathrm{A}^alpha$, with the $alpha$ parameter increasing as a function of $p_mathrm{T}$ for all the particles, and an approximate hierarchy $alpha_eta approx alpha_phi > alpha_omega$. The cross section ratios $sigma_eta/sigma_omega$, $sigma_rho/sigma_omega$ and $sigma_phi/sigma_omega$ have been studied as a function of the size A of the production target, and an increase of the $eta$ and $phi$ yields relative to the $omega$ is observed from p-Be to p-U collisions.
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The NA60 experiment has studied low-mass muon pair production in proton-nucleus collisions with a system of Be, Cu, In, W, Pb and U targets using a 400 GeV/$c$ proton beam at the CERN SPS. The mass spectrum is well described by the superposition of the two-body and Dalitz decays of the light neutral mesons $eta$, $rho$, $omega$, $eta$ and $phi$. A new high-precision measurement of the electromagnetic transition form factors of the $eta$ and $omega$ mesons is presented, complemented with a measurement of the temperature parameter of the $rho$ meson in cold nuclear matter. The $pt$ spectra for the $omega$ and $phi$ mesons are extracted in the full $pt$ range accessible, up to $pt = 2$ GeV/$c$. The nuclear dependence of the production cross sections for the $eta$, $omega$ and $phi$ mesons has been investigated in terms of the power law $sigma_mathrm{pA} propto mathrm{A}^alpha$, and the $alpha$ parameter was studied as a function of $pt$.
The NA60 experiment has studied low-mass muon pairs production in proton-nucleus collisions at 400 GeV/$c$ at the CERN SPS. The mass spectrum is well described by the superposition of the two-body and Dalitz decays of the light neutral mesons $eta$, $rho$, $omega$, $eta$ and $phi$. The large collected statistics allows to isolate the contributions due to the Dalitz decays of the $eta$ and $omega$ mesons, from which the electromagnetic transition form factors of the two mesons have been extracted. The found values agree with the previous available measurements, improving their uncertainty thanks to the higher statistics. The results thus confirm the discrepancy with the prediction of the Vector Meson Dominance model in the case of the electromagnetic form factor of the $omega$ meson.
Results are presented from data recorded in 2009 by the PHENIX experiment at the Relativistic Heavy Ion Collider for the double-longitudinal spin asymmetry, $A_{LL}$, for $pi^0$ and $eta$ production in $sqrt{s} = 200$ GeV polarized $p$$+$$p$ collisions. Comparison of the $pi^0$ results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, $Delta G$, in the proton in the probed Bjorken $x$ range. The effect of adding the new 2009 pz data to a recent global analysis of polarized scattering data is also shown, resulting in a best fit value $Delta G^{[0.05,0.2]}_{mbox{DSSV}} = 0.06^{+0.11}_{-0.15}$ in the range $0.05<x<0.2$, with the uncertainty at $Delta chi^2 = 9$ when considering only statistical experimental uncertainties. Shifting the PHENIX data points by their systematic uncertainty leads to a variation of the best-fit value of $Delta G^{[0.05,0.2]}_{mbox{DSSV}}$ between $0.02$ and $0.12$, demonstrating the need for full treatment of the experimental systematic uncertainties in future global analyses.
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low mass vector meson, $omega$, $rho$, and $phi$, production through the dimuon decay channel at forward rapidity ($1.2<|y|<2.2$) in $p$$+$$p$ collisions at $sqrt{s}=200$ GeV. The differential cross sections for these mesons are measured as a function of both $p_T$ and rapidity. We also report the integrated differential cross sections over $1<p_T<7$ GeV/$c$ and $1.2<|y|<2.2$: $dsigma/dy(omega+rhorightarrowmumu) = 80 pm 6 mbox{(stat)} pm 12 mbox{(syst)}$ nb and $dsigma/dy(phirightarrowmumu) = 27 pm 3 mbox{(stat)} pm 4 mbox{(syst)}$ nb. These results are compared with midrapidity measurements and calculations.
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the invariant differential cross section for production of K^0_S , omega, eta prime, and phi mesons in p + p collisions at = 200 GeV. Measurements omega and phi production in different decay channels give consistent results. New results for the phi are in agreement with previously published data and extend the measured pT coverage. The spectral shapes of all hadron transverse momentum distributions measured by PHENIX are well described by a Tsallis distribution functional form with only two parameters, n and T, determining the high-pT and characterizing the low-pT regions of the spectra, respectively. The values of these parameters are very similar for all analyzed meson spectra, but with a lower parameter T extracted for protons. The integrated invariant cross sections calculated from the fitted distributions are found to be consistent with existing measurements and with statistical model predictions.
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