Invariant-mass dependence of two-pion inclusive correlation functions

We study high-energy two-particle inclusive correlations as a function of the invariant mass $M$ of the pair. Using data from 205-GeV/c $\mathrm{pp}$ interactions, we compare the correlation functions $C\left(M\right)\mathrm{}$ for (+-) and (--) pairs of produced pions. Strong positive correlations are observed in both distributions in the form of a broad threshold enhancement at small $M$. The decrease of $C\left(M\right)\mathrm{}$ as $M$ increases is interpreted in the Mueller-Regge framework. From the $M$ dependence of $C^{+-}$ we extract an effective-trajectory intercept of roughly $\alpha \mathrm{}\left(0\right)\mathrm{}\simeq 0.5\pm 0.1$, consistent with the ($\rho ,f$) pair. For the exotic (--) system, we find a low intercept, $\alpha \mathrm{}\left(0\right)\mathrm{}\simeq -0.5\mathrm{}$. A $\rho$ signal is observed above background in $C^{+-}\mathrm{}\left(M\right)\mathrm{}$. Near threshold, effects suggestive of Bose symmetry are seen but are not conclusive. In an exclusive picture, we relate most of the correlation in the threshold region to resonances involving three or more pions. We also examine the joint correlations in $M$ and the azimuthal angle $\phi$.