High Energy Physics Index

High Energy Physics Index
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Total Pages: 638
Release: 1992
Genre: Particles (Nuclear physics)
ISBN:

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Direct Electron Pair Production In. Pi. −p Interactions at 16 GeV/c and a Model for Direct Lepton and Photon Production at Low P/sub T.

Direct Electron Pair Production In. Pi. −p Interactions at 16 GeV/c and a Model for Direct Lepton and Photon Production at Low P/sub T.
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Total Pages:
Release: 1981
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ISBN:

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The production of prompt electron-positron pairs in 16 GeV/c .pi.−p collisions has been measured using the LASS spectrometer at SLAC. An excess of events is observed above the estimated contributions of direct and Dalitz decay of known resonances in the kinematic range defined by 0.1 less than or equal to x less than or equal to 0.45, 0 less than or equal to P/sub T/ less than or equal to 0.8 GeV/c and 0.2 less than or equal to M(ee−) less than or equal to 0.7 GeV/c2. The excess signal decreases slowly with increasing M, but exhibits very steep x and P/sub T/2 dependence. The contribution of this signal to the e+e−/.pi./sup +/.pi.− and .gamma./.pi. ratios is discussed. Detailed comparisons are made between e/sup +/e− distributions and the corresponding low mass .mu./sup +/.mu.− distributions, and a simple production mechanism is proposed which describes the 16 GeV/c data well. The implications for direct photon production are presented, and it is shown that the model provides simultaneously a good description of the experimental data on the (e/.pi.) and (.mu./.pi.) ratios for p/sub T/

Direct Electron Pair Production In. Pi. −p Interactions at 16 GeV

Direct Electron Pair Production In. Pi. −p Interactions at 16 GeV
Author:
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Total Pages:
Release: 1981
Genre:
ISBN:

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The production of prompt electron-positron pairs in 16 GeV/c .pi.−p collisions has been measured using the LASS spectrometer at SLAC. An excess of events is observed above the estimated contributions of direct and Dalitz decay of known resonances in the kinematic range defined by 0.1 less than or equal to x less than or equal to 0.45, 0 less than or equal to P/sub T/ less than or equal to 0.8 GeV/c and 0.2 less than or equal to M(ee−) less than or equal to 0.7 GeV/c2. The excess signal decreases slowly with increasing M, but exhibits very steep x and P/sub T/2 dependence. The contribution of this signal to the ee−/.pi./sup +/.pi.− and .gamma./.pi. ratios is discussed. Detailed comparisons are made between e/sup +/e− distributions and the corresponding low mass .mu./sup +/.mu.− distributions, and a simple production mechanism is proposed which describes the 16 GeV/c data well. The implications for direct photon production are presented, and it is shown that the model provides simultaneously a good description of the experimental data on the (e/.pi.) and (.mu./.pi.) ratios for p/sub T/

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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ISBN:

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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.