The inclusive production of charged hadrons in the collisions of quasi-real photons e+e- -> e+e- +X has been measured using the OPAL detector at LEP. The data were taken at e+e- centre-of-mass energies from 183 to 209 GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the hadrons are compared to theoretical calculations of up to next-to-leading order (NLO) in the strong coupling constant alpha{s}. The data are also compared to a measurement by the L3 Collaboration, in which a large deviation from the NLO predictions is observed.
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We present the first direct measurements of charged-particle multiplicity distributions for pp collisions at ISR energies. The measurements are performed by means of a streamer chamber detector with large solid-angle coverage and excellent multitrack efficiency. Particle densities are observed to rise in the central region as s increases. The multiplicity distributions in this region deviate from a Poisson Law, thus giving evidence for correlations. These correlations are of the same type as those obtained from clustering of the collision products. The mean charged multiplicity over the full rapidity range increases faster than log s . Our data do not support an early onset of KNO multiplicity scaling.
We present the directed flow ($v_1$) measured in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 62.4 GeV in the mid-pseudorapidity region $|\eta|<1.3$ and in the forward pseudorapidity region $2.5 < |\eta| < 4.0$. The results are obtained using the three-particle cumulant method, the event plane method with mixed harmonics, and for the first time at the Relativistic Heavy Ion Collider (RHIC), the standard method with the event plane reconstructed from spectator neutrons. Results from all three methods are in good agreement. Over the pseudorapidity range studied, charged particle directed flow is in the direction opposite to that of fragmentation neutrons.
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.
The charged-particle fractional momentum distribution within jets, D(z), has been measured in dijet events from 1.8-TeV p¯p collisions in the Collider Detector at Fermilab. As expected from scale breaking in quantum chromodynamics, the fragmentation function D(z) falls more steeply as dijet invariant mass increases from 60 to 200 GeV/c2. The average fraction of the jet momentum carried by charged particles is 0.65±0.02(stat)±0.08(syst).
Transverse momentum distributions and yields for $\pi^{\pm}$, $K^{\pm}$, $p$ and $\bar{p}$ in $p+p$ collisions at $\sqrt{s}$=200 and 62.4 GeV at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). These data provide important baseline spectra for comparisons with identified particle spectra in heavy ion collisions at RHIC. We present the inverse slope parameter $T_{\rm inv}$, mean transverse momentum $<p_T>$ and yield per unit rapidity $dN/dy$ at each energy, and compare them to other measurements at different $\sqrt{s}$ in $p+p$ and $p+\bar{p}$ collisions. We also present the scaling properties such as $m_T$ scaling, $x_T$ scaling on the $p_T$ spectra between different energies. To discuss the mechanism of the particle production in $p+p$ collisions, the measured spectra are compared to next-to-leading-order or next-to-leading-logarithmic perturbative quantum chromodynamics calculations.
We present results from a harmonic decomposition of two-particle azimuthal correlations measured with the STAR detector in Au+Au collisions for energies ranging from $\sqrt{s_{NN}}=7.7$ GeV to 200 GeV. The third harmonic $v_3^2\{2\}=\langle \cos3(\phi_1-\phi_2)\rangle$, where $\phi_1-\phi_2$ is the angular difference in azimuth, is studied as a function of the pseudorapidity difference between particle pairs $\Delta\eta = \eta_1-\eta_2$. Non-zero {\vthree} is directly related to the previously observed large-$\Delta\eta$ narrow-$\Delta\phi$ ridge correlations and has been shown in models to be sensitive to the existence of a low viscosity Quark Gluon Plasma (QGP) phase. For sufficiently central collisions, $v_3^2\{2\}$ persist down to an energy of 7.7 GeV suggesting that QGP may be created even in these low energy collisions. In peripheral collisions at these low energies however, $v_3^2\{2\}$ is consistent with zero. When scaled by pseudorapidity density of charged particle multiplicity per participating nucleon pair, $v_3^2\{2\}$ for central collisions shows a minimum near {\snn}$=20$ GeV.
The two-jet differential cross section d3σ(p¯p→jet 1+jet 2+X)/dEtdη1dη2, averaged over -0.6≤η1≤0.6, at √s =1.8 TeV, has been measured in the Collider Detector at Fermilab. The predictions of leading-order quantum chromodynamics for most choices of structure functions show agreement with the data.
We have made a precise measurement of the central inclusive jet cross section at sqrt(s) = 1.8 TeV. The measurement is based on an integrated luminosity of 92 pb-1 collected at the Fermilab Tevatron pbar-p Collider with the D-Zero detector. The cross section, reported as a function of jet transverse energy (ET >= 60 GeV) in the pseudorapidity interval |eta| <= 0.5, is in good agreement with predictions from next-to-leading order quantum chromodynamics.
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