J/psi production from proton-proton collisions at square root of s=200 GeV

J/psi production has been measured in proton-proton collisions at square root of s=200 GeV over a wide rapidity and transverse momentum range by the PHENIX experiment at the Relativistic Heavy Ion Collider. 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 4.0+/-0.6(stat)+/-0.6(syst)+/-0.4(abs) mu b. The mean transverse momentum is 1.80+/-0.23(stat)+/-0.16(syst) GeV/c.     

Absence of suppression in particle production at large transverse momentum in sqrt[s(NN)]=200 GeV d+Au collisions

Transverse momentum spectra of charged hadrons with p(T)<8 GeV/c and neutral pions with p(T)<10 GeV/c have been measured at midrapidity by the PHENIX experiment at BNL RHIC in d+Au collisions at sqrt[s(NN)]=200 GeV. The measured yields are compared to those in p+p collisions at the same sqrt[s(NN)] scaled up by the number of underlying nucleon-nucleon collisions in d+Au. The yield ratio does not show the suppression observed in central Au+Au collisions at RHIC. Instead, there is a small enhancement in the yield of high momentum particles.     

Suppressed pi(0) production at large transverse momentum in central Au+Au collisions at sqrt[s(NN)]=200 GeV

Transverse momentum spectra of neutral pions in the range 1相似文献   

Centrality dependence of charm production from a measurement of single electrons in Au+Au collisions at sqrt[s(NN)]=200 GeV

The PHENIX experiment has measured midrapidity transverse momentum spectra (0.4相似文献   

Organic reactions at high pressure. Asymmetric induction in the diels-alder reaction of p-benzoquinone with chiral 2,4-pentadienoic acid derivatives

Asymmetric induction in the high pressure (15 kbar, 1.5 GPa) Diels-Alder reaction of $\text{p}$-benzoquinone with chiral 2,4-pentadienoic acid derivatives is evaluated. The reactions afford 4a,5,8,8a-tetrahydro-1,4-naphthalenediones in up to 50% enantiomeric excess.     

Measurement of the slope of the π0-electromagnetic form factor

Using a magnetic spectrometer, we have studied 30 000 π⁰ → e⁺e^?γ events coming from K_π2⁺ decays in flight. We find a positive value for the slope of the neutral-pion electromagnetic form factor: a = +0.10 ± 0.03 (or a = +0.05 ± 0.03 without radiative corrections). This value is higher than the predictions of vector meson models.     

Observation of the π0 → e+e− decay

We have observed for the first time the very rare π⁰ → e⁺e^? decay. The tagged π⁰'s come from K⁺ → π⁺π⁰ decays in flight. We find the branching ratio to be (2.23_?1.1^+2.4) × 10^?7 (90% C.L.). This value is well above the QED unitary limit and comes in rough agreement with a second-order electromagnetic process mediated by vector mesons.     

Centrality dependence of charged particle multiplicity in Au-Au collisions at square root of (s)NN = 130 GeV

We present results for the charged-particle multiplicity distribution at midrapidity in Au-Au collisions at square root of [s(NN)] = 130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find dN(ch)/d eta(vertical line eta = 0) = 622+/-1(stat)+/-41(syst). The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.     

Measurement of the positive muon anomalous magnetic moment to 0.7 ppm

A higher precision measurement of the anomalous g value, a(mu)=(g-2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron, based on data collected in the year 2000. The result a(mu(+))=11 659 204(7)(5)x10(-10) (0.7 ppm) is in good agreement with previous measurements and has an error about one-half that of the combined previous data. The present world average experimental value is a(mu)(expt)=11 659 203(8)x10(-10) (0.7 ppm).