Measurements, with the BRAHMS detector, of the antiproton to proton ratio at central and forward rapidities are presented for Au+Au reactions at sqrt{s_{NN}}=130 GeV, and for three different collision centralities. For collisions in the 0-40% centrality range we find $N(\bar{{\rm p}})/N({\rm p}) = 0.64 +- 0.04 (stat.) +- 0.06 (syst.) at y ~0, 0.66 +- 0.03 +- 0.06 at y ~ 0.7, and 0.41 +- 0.04 +- 0.06 at y ~ 2. The ratios are found to be nearly independent of collision centrality and transverse momentum. The measurements demonstrate that the antiproton and proton rapidity densities vary differently with rapidity, and indicate that a net-baryon free midrapidity plateau (Bjorken limit) is not reached at this RHIC energy.
$\overline{\mathrm{p}}/\mathrm{p}$ versus $\mathrm{Centrality}$ for $\overline{\mathrm{p}}$, $\mathrm{p}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=130\,\mathrm{Ge\!V}$
$\overline{\mathrm{p}}/\mathrm{p}$ versus $p_{\mathrm{T}}$ for $\overline{\mathrm{p}}$, $\mathrm{p}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=130\,\mathrm{Ge\!V}$
$\overline{\mathrm{p}}/\mathrm{p}$ versus $p_{\mathrm{T}}$ for $\overline{\mathrm{p}}$, $\mathrm{p}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=130\,\mathrm{Ge\!V}$
We present ratios of the numbers of charged antiparticles to particles (pions, kaons and protons) in Au + Au collisions at $\sqrt{s_{NN}}=200$ GeV as a function of rapidity in the range $y$=0-3. While the particle ratios at midrapidity are approaching unity, the $K^-/K^+$ and $\bar{p}/p$ ratios decrease significantly at forward rapidities. An interpretation of the results within the statistical model indicates a reduction of the baryon chemical potential from $\mu_B \approx 130$MeV at $y$=3 to $\mu_B \approx 25$MeV at $y$=0.
$\mathrm{\pi}^{-}/\mathrm{\pi}^{+}$ versus $p_{\mathrm{T}}$ for $\mathrm{\pi}^{+}$, $\mathrm{\pi}^{-}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$
$\mathrm{K}^{-}/\mathrm{K}^{+}$ versus $p_{\mathrm{T}}$ for $\mathrm{K}^{-}$, $\mathrm{K}^{+}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$
$\overline{\mathrm{p}}/\mathrm{p}$ versus $p_{\mathrm{T}}$ for $\overline{\mathrm{p}}$, $\mathrm{p}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$
Yields for J/psi production in Cu+Cu collisions at sqrt (s_NN)= 200 GeV have been measured by the PHENIX experiment over the rapidity range |y| < 2.2 at transverse momenta from 0 to beyond 5 GeV/c. The invariant yield is obtained as a function of rapidity, transverse momentum and collision centrality, and compared with results in p+p and Au+Au collisions at the same energy. The Cu+Cu data provide greatly improved precision over existing Au+Au data for J/psi production in collisions with small to intermediate numbers of participants, providing a key constraint that is needed for disentangling cold and hot nuclear matter effects.
J/PSI yield versus transverse momentum PT, at mid rapidity : -0.35<y<0.35, for a centrality range of 0-20%.
J/psi-->e+e- invariant yield in Cu+Cu collisions as a function of p_T at mid-rapidity for the 0-20 centrality range. The statistical and systematic uncertainties vary point-to-point and are listed for each measured value. An additional global systematic uncertainty is provided in each column heading, which applies to all data points per column.
J/PSI yield versus transverse momentum PT, at mid rapidity : -0.35<y<0.35, for a centrality range of 20-40%.
We present spectra of charged pions and protons in 0-10% central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at mid-rapidity ($y=0$) and forward pseudorapidity ($\eta=2.2$) measured with the BRAHMS experiment at RHIC. The spectra are compared to spectra from p+p collisions at the same energy scaled by the number of binary collisions. The resulting nuclear modification factors for central Au+Au collisions at both $y=0$ and $\eta=2.2$ exhibit suppression for charged pions but not for (anti-)protons at intermediate $p_T$. The $\bar{p}/\pi^-$ ratios have been measured up to $p_T\sim 3$ GeV/$c$ at the two rapidities and the results indicate that a significant fraction of the charged hadrons produced at intermediate $p_T$ range are (anti-)protons at both mid-rapidity and $\eta = 2.2$.
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\overline{\mathrm{p}}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\mathrm{\pi}^{-}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\mathrm{p}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$
We report on a study of the transverse momentum dependence of nuclear modification factors $R_{dAu}$ for charged hadrons produced in deuteron + gold collisions at $\sqrt{s_{NN}=\unit[200]{GeV}$, as a function of collision centrality and of the pseudorapidity ($\eta = 0,1,2.2,3.2 $) of the produced hadrons. We find significant and systematic decrease of $R_{dAu}$ with increasing rapidity. The midrapidity enhancement and the forward rapidity suppression are more pronounced in central collisions relative to peripheral collisions. These results are relevant to the study of the possible onset of gluon saturation at RHIC energies.
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\frac{h^{+}+h^{-}}{2}$,$\frac{h^{+}+h^{-}}{2}$ in $\mathrm{p}\mathrm{p}$,$\mathrm{d}-\mathrm{Au}$ at $\sqrt{s}=200\,\mathrm{Ge\!V}$ near $\eta=0$
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\frac{h^{+}+h^{-}}{2}$,$\frac{h^{+}+h^{-}}{2}$ in $\mathrm{p}\mathrm{p}$,$\mathrm{d}-\mathrm{Au}$ at $\sqrt{s}=200\,\mathrm{Ge\!V}$ near $\eta=1$
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\mathrm{h}^{-}$,$\mathrm{h}^{-}$ in $\mathrm{p}\mathrm{p}$,$\mathrm{d}-\mathrm{Au}$ at $\sqrt{s}=200\,\mathrm{Ge\!V}$ near $\eta=2.2$
Transverse momentum spectra and rapidity densities, dN/dy, of protons, anti-protons, and net--protons (p-pbar) from central (0-5%) Au+Au collisions at sqrt(sNN) = 200 GeV were measured with the BRAHMS experiment within the rapidity range 0 < y < 3. The proton and anti-proton dN/dy decrease from mid-rapidity to y=3. The net-proton yield is roughly constant for y<1 at dN/dy~7, and increases to dN/dy~12 at y~3. The data show that collisions at this energy exhibit a high degree of transparency and that the linear scaling of rapidity loss with rapidity observed at lower energies is broken. The energy loss per participant nucleon is estimated to be 73 +- 6 GeV.
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\mathrm{p}$,$\overline{\mathrm{p}}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$ . NaN values means no observation.
$\frac{\mathrm{d}N}{\mathrm{d}y}$ versus $y$ for $\mathrm{p}$,$\overline{\mathrm{p}}$,$\mathrm{p}-\overline{\mathrm{p}}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$ . The correction for the $\Lambda$ contribution is not straight forward since BRAHMS does not measure the $\Lambda$s and PHENIX and STAR only measures the $\Lambda$s at mid-rapidity! If one assumes that the mid-rapidity estimated in the paper of $$R=\frac{\Lambda-\bar{\Lambda}}{\mathrm{p}-\bar{\mathrm{p}}} = \frac{\Lambda}{\mathrm{p}} = \frac{\bar{\Lambda}}{\bar{\mathrm{p}}} = 0.93\pm 0.11(\mathrm{stat})\pm 0.25(\mathrm{syst}) $$ and the BRAHMS "acceptance factor" of $A=0.53\pm 0.05$ which includes both that only 64% decays to protons and that some are rejected by the requirement of the track to point back to the IP. The corrected $\mathrm{p}$ ($\bar{\mathrm{p}}$ or net-$\mathrm{p}$) is then : $$\left.\frac{\mathrm{d}N}{\mathrm{d}y}\right|_{\mathrm{corrected}} = \frac{\mathrm{d}N}{\mathrm{d}y}(1/(1+RA))= \frac{\mathrm{d}N}{\mathrm{d}y}\left(0.67\pm 0.05(\mathrm{stat})\pm 0.11(\mathrm{syst})\right)$$ Which can be used at all rapidities if one believes that R is constant. The fact that net-$\mathrm{K}=\mathrm{K}^{+}-\mathrm{K}^{-}$ follows net-$\mathrm{p}$ (see fx. talk by Djamel Ouerdane at QM04), seems to indicate that the net-$\Lambda$ follow the net-$\mathrm{p}$ trend and the correction is reasonable.
We have measured rapidity densities dN/dy of pions and kaons over a broad rapidity range (-0.1 < y < 3.5) for central Au+Au collisions at sqrt(snn) = 200 GeV. These data have significant implications for the chemistry and dynamics of the dense system that is initially created in the collisions. The full phase-space yields are 1660 +/- 15 +/- 133 (pi+), 1683 +/- 16 +/- 135 (pi-), 286 +/- 5 +/- 23 (K+) and 242 +/- 4 +/- 19 (K-). The systematics of the strange to non--strange meson ratios are found to track the variation of the baryo-chemical potential with rapidity and energy. Landau--Carruthers hydrodynamic is found to describe the bulk transport of the pions in the longitudinal direction.
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\mathrm{\pi}^{+}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$ near $y=-0.1-0.0$ for $0-5$% central
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\mathrm{\pi}^{+}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$ near $y=0.0-0.1$ for $0-5$% central
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\mathrm{\pi}^{+}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$ near $y=0.4-0.6$ for $0-5$% central
Particle production of identified charged hadrons, $\pi^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ in Au+Au collisions at $\sqrt(snn) =$ 200 GeV has been studied as a function of transverse momentum and collision centrality at $y=0$ and $y\sim1$ by the BRAHMS experiment at RHIC. Significant collective transverse flow at kinetic freeze-out has been observed in the collisions. The magnitude of the flow rises with the collision centrality. Proton and kaon yields relative to the pion production increase strongly as the transverse momentum increases and also increase with centrality. Particle yields per participant nucleon show a weak dependence on the centrality for all particle species. Hadron production remains relatively constant within one unit around midrapidity in Au+Au collisions at $\sqrt(snn) =$ 200 GeV.
$\frac{1}{2\pi p_{\mathrm{T}}}\frac{\mathrm{d}^2N}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y}$ versus $p_{\mathrm{T}}$ for $\mathrm{\pi}^{+}$,$\mathrm{\pi}^{-}$,$\mathrm{K}^{+}$,$\mathrm{K}^{-}$,$\mathrm{p}$,$\overline{\mathrm{p}}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$
$\langle p_{\mathrm{T}}\rangle$ versus $N_{\mathrm{part}}$ for $\mathrm{\pi}^{+}$,$\mathrm{\pi}^{-}$,$\mathrm{K}^{+}$,$\mathrm{K}^{-}$,$\mathrm{p}$,$\overline{\mathrm{p}}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$
$\beta_{\mathrm{S}}$,$T$,$\chi^2$,$\nu$ versus $\mathrm{Centrality}$ for $\mathrm{h}^{+}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$
We present charged particle densities as a function of pseudorapidity and collision centrality for the 197Au+197Au reaction at Sqrt{s_NN}=200 GeV. For the 5% most central events we obtain dN_ch/deta(eta=0) = 625 +/- 55 and N_ch(-4.7<= eta <= 4.7) = 4630+-370, i.e. 14% and 21% increases, respectively, relative to Sqrt{s_NN}=130 GeV collisions. Charged-particle production per pair of participant nucleons is found to increase from peripheral to central collisions around mid-rapidity. These results constrain current models of particle production at the highest RHIC energy.
$\mathrm{d}N/\mathrm{d}\eta$ versus $\eta$ for $x^{\pm}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$ for $0-5$% central, $5-10$% central, $10-20$% central, $20-30$% central, $30-40$% central, $40-50$% central
$\mathrm{d}N/\mathrm{d}\eta$ versus $\eta$ for $x^{\pm}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$ for $0-5$% central, $5-10$% central, $10-20$% central, $20-30$% central, $30-40$% central, $40-50$% central
$\mathrm{d}N/\mathrm{d}\eta$ versus $\eta$ for $x^{\pm}$ in $\mathrm{Au}-\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=200\,\mathrm{Ge\!V}$ for $0-5$% central, $5-10$% central, $20-30$% central, $40-50$% central
We present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0-5%, 5-10%, 10-20%, and 20-30% most central events) in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV at the LHC. The measurement is performed using the full coverage of the ALICE detectors, $-5.0 < \eta < 5.5$, and employing a special analysis technique based on collisions arising from LHC "satellite" bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles ($N_{\rm ch} = 17165 \pm 772$ for the 0-5% most central collisions). From the measured ${\rm d}N_{\rm ch}/{\rm d}\eta$ distribution we derive the rapidity density distribution, ${\rm d}N_{\rm ch}/{\rm d}y$, under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models.
$\rm dN_{ch}/d\eta$ versus $\eta$ for different centralities. Errors are systematic as statistical errors are negligible.
Total number of produced charged particles extrapolated to beam rapidity as a function of the number of participating nucleons in the collision. Statistical errors are negligible. The first(sys) error is the correlated systematic error and the second is that which is uncorrelated to the other points.
$\rm dN_{ch}/d\eta$ per participant pair versus the number of participating nucleons in the collision for different eta ranges. Errors are systematic as statistical errors are negligible.
Forum