Diffractive Interaction and Scaling Violation inpp →π ⁰Interaction and GeV Excess in Galactic Diffuse Gamma‐Ray Spectrum of EGRET

Abstract

We present here a new calculation of the gamma-ray spectrum from pp ! 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 0 ! in the sub-to multiple 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 ! 0 cross sections and the Feynman scaling hypothesis. We show, in this work, that the diffractive process makes the gamma-ray spectrum harder than the incident proton spectrum by $0.05 in the power-law index and that the scaling violation produces 30%-80% more 0 than the scaling model for incident proton energies above 100 GeV. A combination of the two can explain about half of the GeV excess with the local cosmic proton ( power-law index $2.7). The excess can be fully explained if the proton spectral index in the Galactic ridge is a little harder ($0.2 in power-law index) than the local spectrum. Given also in the paper is that the diffractive process enhances e + over e À and the scaling violation gives 50%-100% higherp yield than without the violation, both in the multiple GeV range.

Parameterization of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes

“…This work is an extension of that by Kamae et al (2005), where up-to-date knowledge of the 0 yield in the p-p inelastic interaction has been used to predict the Galactic diffuse gammaray emission. The authors have found that past calculations (Stecker 1970(Stecker , 1973(Stecker , 1990Strong et al 1978;Stephens & Badhwar 1981;Dermer 1986aDermer , 1986bDermer , 2000Mori 1997) had left out the diffractive interaction and the Feynman scaling violation in the nondiffractive inelastic interaction.…”

“…The formulae are derived from the up-to-date p-p interaction model by Kamae et al (2005), which incorporates the logarithmically rising inelastic cross section, the diffraction dissociation process, and the Feynman scaling violation. To improve fidelity to experimental data in lower energies, two baryon resonance contributions have been added: one representing Á(1232) and the other representing multiple resonances around 1600 MeV/c À2 .…”

“…Another important finding by them is that most previous calculations have assumed an energyindependent p-p inelastic cross section of about 24 mbarn for T p 3 10 GeV, whereas recent experimental data have established a logarithmic increase with the incident proton energy. Updating these shortfalls has changed the prediction of the gamma-ray spectrum in the GeV band significantly: the gamma-ray power-law index is harder than that of the incident proton, and the GeV-TeV gammaray flux is significantly larger than that predicted on the constant cross section and Feynman scaling (Kamae et al 2005). The model by Kamae et al (2005) will hereafter be referred to as model A.…”

“…Updating these shortfalls has changed the prediction of the gamma-ray spectrum in the GeV band significantly: the gamma-ray power-law index is harder than that of the incident proton, and the GeV-TeV gammaray flux is significantly larger than that predicted on the constant cross section and Feynman scaling (Kamae et al 2005). The model by Kamae et al (2005) will hereafter be referred to as model A.…”

TeVγrays and neutrinos from photodisintegration of nuclei in Cygnus OB2

“…[97] and the inclusion of diffractive interactions and scaling violations in Ref. [98] (see the Appendix of Ref. [99] for a a comparison of different approaches).…”