The NA60 experiment studies muon pair production at the CERN SPS. In this letter we report on a precision measurement of J/psi in In-In collisions. We have studied the J/psi centrality distribution, and we have compared it with the one expected if absorption in cold nuclear matter were the only active suppression mechanism. For collisions involving more than ~80 participant nucleons, we find that an extra suppression is present. This result is in qualitative agreement with previous Pb-Pb measurements by the NA50 experiment, but no theoretical explanation is presently able to coherently describe both results.
The single spin asymmetry for inclusive direct-photon production has been measured using a polarized proton beam of 200 GeV/c with an unpolarized proton target at −0.15 < xf < 0.15 and 2.5 < pt < 3.1 GeV/c at Fermilab. The data on the cross section for pp → γX at 2.5 < pt < 3.8 GeV/c are also provided. The measurement was done using lead-glass calorimeters and photon detectors which surrounded the fiducial area of the calorimeters. Background rejection has been done using these surrounding photon detectors. The cross section obtained is consistent with the results of previous measurements assuming a nuclear dependence of A 1.0 . The single spin asymmetry, A N , for the direct-photon production is consistent with zero within experimental uncertainty.
The inclusive production of omega and phi mesons is studied in the backward region of the interaction of 12 GeV protons with polyethylene, carbon, and copper targets. The mesons are measured in e^+ e^- decay channels. The production cross sections of the mesons are presented as functions of rapidity y and transverse momentum p_T. The nuclear mass number dependences (A dependences) are found to be A^{0.710 +/- 0.021(stat) +/- 0.037(syst)} for omega mesons and A^{0.937 +/- 0.049(stat) +/- 0.018(syst)} for phi mesons in the region of 0.9 < y < 1.7 and p_T < 0.75 GeV/c.
Results from the HELIOS External Spectrometer on kaon production in 200 GeV/ A S + W and p + W collisions are presented. The K π ratios are compared with results from a lower beam energy and are found to be remarkably similar. Evidence for secondary production of K + by meson-baryon rescattering is reviewed. Our results at y = 1.0–1.5 are compared with neutral strange particle results at midrapidity.
We report on the production ofe± μ∓ pairs in 450 GeV/c pBe collisions at the CERN SPS. Theeμ signal, which has average missing energy of 21 GeV, is shown to be consistent with expectations from charm decay, and implies a σ ×B for\(c\bar c\) production in p-nucleon collisions of 0.63 ± 0.35μb. Alternatively, using an estimate of charm production from other experiments, the data imply a 95% confidence level upper limit of 1.16μb on any new physics process which producese±μ∓.
Multiplicity distributions of charged particles produced in the pseudorapidity range 0.9 < η lab < 5.5 were measured in oxygen-nucleus collisions for Al, Ag, and W target nuclei at incident energies of 60 and 200 GeV per nucleon. The multiplicity differential cross sections and the pseudorapidity distributions as a function of transverse energy are presented for the various target nuclei. The correlation between charged multiplicity and transverse energy is studied as a function of transverse energy. Data are compared with predictions of the IRIS and FRITIOF generators.
We present measurements of the rapidity and transverse-momentum distributions of the protons emitted in S+W, O+W, andp+W reactions at 200 GeV/A around the target rapidity (y=1). The rapidity density rises linearly with the transverse energy for all three systems, but the slope forp+W is much steeper than for O+W and S+W. The rapidity density forp+W is much higher than predicted by summing single nucleonnucleon collisions without any nuclear effects, indicating substantial rescattering of the produced particles. The predictions of the VENUS 3 model, including rescattering, show reasonable agreement with the data for all three systems. We do not have evidence for a strong collective flow of the outgoing particles.
The HELIOS experiment has measured inclusivep⊥ spectra of negative particles in the rapidity region 1.0<y<1.9. The general shape of thep⊥ spectra in p +W, O+W and S+W is similar, but cannot be described by a single exponential. Compared to p+p collisions, an excess is observed for low and highp⊥. This effect increases with the projectile mass. Except for very lowE⊥, the average transverse momentum <p⊥> is found to be approximately constant up to the highest accessible values ofE⊥.
We have measured the inclusive cross-section as a function of missing energy, due to the production of neutrinos or new weakly interacting neutral particles in 450 GeV/c proton-nucleus collisions, using calorimetric measurements of visible event energy. Upper limits are placed on the production of new particles as a function of their energy. These upper limits are typically an order
J/psi production has been measured in proton-proton collisions at sqrt(s)= 200 GeV over a wide rapidity and transverse momentum range by the PHENIX experiment at RHIC. Distributions of the rapidity and transverse momentum, along with measurements of the mean transverse momentum and total production cross section are presented and compared to available theoretical calculations. The total J/psi cross section is 3.99 +/- 0.61(stat) +/- 0.58(sys) +/- 0.40(abs) micro barns. The mean transverse momentum is 1.80 +/- 0.23(stat) +/- 0.16(sys) GeV/c.
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