The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC) reports measurements of azimuthal dihadron correlations near midrapidity in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV. These measurements complement recent analyses by experiments at the Large Hadron Collider (LHC) involving central $p$$+$Pb collisions at $\sqrt{s_{_{NN}}}$=5.02 TeV, which have indicated strong anisotropic long-range correlations in angular distributions of hadron pairs. The origin of these anisotropies is currently unknown. Various competing explanations include parton saturation and hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies in $d$$+$Au collisions compared to those seen in $p$$+$Pb collisions at the LHC. The larger extracted $v_2$ values in $d$$+$Au collisions at RHIC are consistent with expectations from hydrodynamic calculations owing to the larger expected initial-state eccentricity compared with that from $p$$+$Pb collisions. When both are divided by an estimate of the initial-state eccentricity the scaled anisotropies follow a common trend with multiplicity that may extend to heavy ion data at RHIC and the LHC, where the anisotropies are widely thought to arise from hydrodynamic flow.
In an experiment performed at the CERN Intersecting Storage Rings (ISR), 11 e + e − pairs of high invariant mass value (> 2.5 GeV/c 2 ) have been observed. Of these events, 9 can be interpreted as arising from the reaction p + p → J (3.1) + anything. the cross-section for this reaction is estimated and compared with the result obtained at lower centre-of-mass energies.
The production of electrons with very high transverse momentum has been studied in the UA2 experiment at the CERN\(\bar pp\) collider (\(\sqrt s\)=540 GeV). From a sample of events containing an electron candidate withpT>15 GeV/c, we extract a clear signal resulting from the production of the charged intermediate vector bosonW±, which subsequently decays into an electron and a neutrino. We study theW production and decay properties. Further-more, we refine our results on the production and decay of the neutral vector bosonZ0. Finally, we compare the experimental results to the predictions of the standard model of the unified electro-weak theory.
We report new measurements of inclusive direct photon production at high transverse momenta (pT) for π− and p interactions on Be at 500 GeV/c. The yields as a function of pT and rapidity (y) are in good agreement with expectations from next-to-leading-log QCD calculations employing recently extracted quark and gluon structure functions.
Data were taken at the energy 2 E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the ϱ , ω and φ production by e + e − annilations. Assuming a π + π − π 0 π 0 production by the quasi two-body process e + e − → ϱ → ωπ 0 we give the correspondi ng cross section σ (e + e − → π + π − π 0 π 0 ) = (1.1 ± 0.5) 10 −32 cm 2 . Since no events with 3 and 4 charged pions have been observed σ (e + e − → π + π − π 0 π − ) ⩽ 1.5 × 10 −33 cm 2 .
The distribution of the transverse energy in jets has been measured in p p collisions at s =1.8 TeV TeV using the DØ detector at Fermilab. This measurement of the jet shape is made as a function of jet transverse energy in both the central and forward rapidity regions. Jets are shown to narrow both with increasing transverse energy and with increasing rapidity. Next-to-leading order partonic QCD calculations are compared to the data. Although the calculations qualitatively describe the data, they are shown to be very dependent on renormalization scale, parton clustering algorithm, and jet direction definition and they fail to describe the data in all regions consistently.
We have studied the production of J/ψ and ψ(2S) charmonium mesons in 515 GeV/c π−Be collisions in the Feynman-x range 0.1<xF<0.8. J/ψ mesons were detected via their decay into μ+μ−, and ψ(2S) mesons were studied in both the μ+μ− and J/ψπ+π− decay modes. J/ψ differential cross sections have been measured as functions of xF,pT2, and the cosine of the Gottfried-Jackson decay angle. We measure an inclusive J/ψ cross section of B(J/ψ→μ+μ−)σ(π−Be→J/ψ+X)/A= [9.3±0.1(stat)±1.1(syst)] nb/nucleon for J/ψ xF≳0.1. Our results are compared with those from other experiments performed at lower beam energies. We also measure the differential ψ(2S) cross section as a function of both xF and pT2, and a ψ(2S) inclusive cross section of B(ψ(2S)→J/ψπ+π−)σ(π−Be→ψ(2S)+X)/A=[7. 4±1.5(stat)±1.2(syst)] nb/nucleon for ψ(2S) xF≳0.1. The fraction of the inclusive J/ψ yield due to ψ(2S) meson decays is 0.083±0.017(stat) ±0.013(syst), and the observed ratio of ψ(2S) decay rates is B(ψ(2S)→J/ψπ+π−)/B(ψ(2S)→μ+μ−) =30.2±7.2(stat)±6.8(syst). We have searched for production of ‘‘hidden’’ charm resonances decaying into either J/ψπ±,ψ(2S)π±, or J/ψπ+π− systems, and report an upper limit of 3.1 nb/nucleon for the product of branching ratio and cross section for the recently reported enhancement at a J/ψπ+π− mass of 3.836 GeV/c2. © 1996 The American Physical Society.
The inclusive cross sections times leptonic branching ratios for W and Z boson production in PbarP collisions at Sqrt(s)=1.8 TeV were measured using the D0 detector at the Fermilab Tevatron collider: Sigma_W*B(W->e, nu) = 2.36 +/- 0.07 +/- 0.13 nb, Sigma_W*B(W->mu,nu) = 2.09 +/- 0.23 +/- 0.11 nb, Sigma_Z*B(Z-> e, e) = 0.218 +/- 0.011 +/- 0.012 nb, Sigma_Z*B(Z->mu,mu) = 0.178 +/- 0.030 +/- 0.009 nb. The first error is the combined statistical and systematic uncertainty, and the second reflects the uncertainty in the luminosity. For the combined electron and muon analyses we find: [Sigma_W*B(W->l,nu)]/[Sigma_Z*B(Z->l,l)] = 10.90 +/- 0.49. Assuming Standard Model couplings, this result is used to determine the width of the W boson: Gamma(W) = 2.044 +/- 0.093 GeV.
The Fermilab E866/NuSea Collaboration has measured the Drell-Yan dimuon cross sections in 800 GeV/$c$ $pp$ and $pd$ collisions. This represents the first measurement of the Drell-Yan cross section in $pp$ collisions over a broad kinematic region and the most extensive study to date of the Drell-Yan cross section in $pd$ collisions. The results indicate that recent global parton distribution fits provide a good description of the light antiquark sea in the nucleon over the Bjorken-$x$ range $0.03 \lesssim x < 0.15$, but overestimate the valence quark distributions as $x \to 1$.
We present a measurement of the cross section for the reaction e + e − → e + e − π + π − π + π − at SPEAR. This channel is found to be large and dominated by the process γγ → ϱ 0 ϱ 0 → π + π − π + π − . The cross section, which is small just above the four-pion threshold, exhibits a large enhancement near the ϱ 0 ϱ 0 threshold.
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