High Transverse Momentum Phenomena Involving $pi$ and Eta Mesons

High Transverse Momentum Phenomena Involving $pi$ and Eta Mesons
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Release: 1975
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The inclusive production of $pi$ and eta mesons at theta/sub cm/ = 90$sup 0$ was measured for proton-proton collisions at five center-of-mass energies between 23.5 and 62.4 GeV. The momentum correlation of charged particles emitted together with a large transverse momentum $pi$ was also studied using two magnetic spectrometers each centered at theta/sub cm/ = 90$sup 0$. (auth).

Photon and Neutral Pi 0 Production in (197)Au + (197)Au Collisions at Sqrt S(NN)

Photon and Neutral Pi 0 Production in (197)Au + (197)Au Collisions at Sqrt S(NN)
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Total Pages: 96
Release: 2002
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Inclusive transverse momentum spectra of photons and [pi]°s at mid-rapidity are studied as a function of collision centrality for 197Au+ 197Au collisions at √s{sub NN} = 130 GeV. Photon pair conversions have been reconstructed from charged tracks measured by the main Time Project Chamber of the STAR experiment at the RHIC heavy ion facility. The transverse momentum resolution of photons with this method is estimated to be [Delta]p{sub t}/p{sub t} = 2% at 0.125 GeV/c and 5% at 2.5 GeV/c. Photon spectra were measured up to a transverse momentum of 2.4 GeV/c between ± 0.5 units of rapidity. The dominant photon production mechanism, the [pi]° → [gamma][gamma] decay, was measured between 0.25-2.5 GeV/c and ± 1 units of rapidity. Spectra are reported for the top 11%, 11-34% and 34-85% centrality classes. It was observed that in mid-central and central collisions the relative contribution of the [pi]° → [gamma][gamma] decay to the inclusive photon spectrum decreases above a transverse momentum of 1.65 GeV/c. In central collisions the magnitude of the decrease from p{sub t} = 1.65 GeV/c to 2.4 GeV/c is 20%. It is unlikely that contributions from other [pi]° decay channels and other particle decays fully explain this decrease. The centrality dependence on the shapes of the [pi]° spectra was analyzed with Boltmann and Bose-Einstein functions. In the transverse momentum windows of the spectra, the extracted temperatures are near 0.295 GeV. These temperatures are substantially higher than those extracted from [pi]{sup {+-}} spectra in a lower range of transverse momentum. This is an indication that the shapes of the pion spectra deviate from purely exponential shapes.