Pion Polarizability, Radiative Transitions, and Quark Gluon Plasma Signatures

Abstract

Can one expect gamma rays rates from the QGP to be higher than from the hot hadronic gas phase? Xiong, Shuryak, Brown (XSB) calculate photon production from a hot hadronic gas via the reaction $π^- + ρ^0 \rightarrow π^- + γ$. They assume that this reaction proceeds through the a$_1$(1260). They also use their estimated a$_1$ radiative width to calculate the pion polarizability; following a connection noted previously by Holstein. However, for a$_1$(1260) $\rightarrow πγ$, the experimental radiative width is more than two times less than the value 1.4 MeV estimated and used by XSB. We describe how the gamma production reaction can be studied in Fermilab E781 (via the inverse reaction, with detailed balance) via the Primakoff reaction $π^- + γ\rightarrow π^- + ρ^0$. Such a study can provide the data base for evaluations of the utility of gamma production experiments in QGP searches. One can experimentally check the a$_1$ dominance assumption of XSB. A remeasurement of the a$_1(1260)$ radiative width and of the pion polarizability in Fermilab E781 will also allow us to reevaluate the consistency of their expected relationship.