Diffractive Interaction and Scaling Violation in pp-pizero Interaction and GeV Excess in Galactic Diffuse Gamma-Ray Spectrum of EGRET
The authors present here a new calculation of the gamma-ray spectrum from pp {yields} {pi}{sup 0} in the Galactic ridge environment. The calculation includes the diffractive p-p interaction and incorporates the Feynman scaling violation for the first time. Galactic diffuse gamma-rays come, predominantly, from {pi}{sup 0} {yields} {gamma}{gamma} in the sub-GeV to multi-GeV range. Hunter et al. found, however, an excess in the GeV range (GeV Excess) in the EGRET Galactic diffuse spectrum above the prediction based on experimental pp {yields} {pi}{sup 0} cross-sections and the Feynman scaling hypothesis. They show, in this work, that the diffractive process makes the gamma-ray spectrum harder than the incident proton spectrum by {approx} 0.05 in power-law index, and, that the scaling violation produces 30-80% more {pi}{sup 0} than the scaling model for incident proton energies above 100 GeV. Combination of the two can explain about a half of the GeV Excess with the local cosmic proton (power-law index {approx} 2.7). The excess can be fully explained if the proton spectral index in the Galactic ridge is a little harder ({approx} 0.2 in power-law index) than the local spectrum. Given also in the paper is that the diffractive process enhances e{sup +} over e{sup -} and the scaling violation gives 50-100% higher {bar p} yield than without the violation, both in the multi-GeV range.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 839986
- Report Number(s):
- SLAC-PUB-10819; TRN: US0503441
- Country of Publication:
- United States
- Language:
- English
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