Pion-pion correlations at low relative momentum produced in p-p collisions at 27.5 GeV/c.

We have measured the momentum correlation of pion pairs produced in the collisions of 27.5 GeV/c protons in liquid hydrogen. By considering events for which all final state particles have been measured, we have succeeded in reducing backgrounds due to particle misidentification below 5% for ${\ensuremath{\pi}}^{+}$ and 1% for ${\ensuremath{\pi}}^{\ensuremath{-}}$. Our use of a precision magnetic spectrometer has provided an accurate determination of particle momenta and excellent acceptance for particle pairs with small relative momentum essential for correlations studies. A large data sample of fully reconstructed events (1 \ifmmode\times\else\texttimes\fi{} ${10}^{6}$) allows us to analyze the correlations for ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}$ pairs separately, and also as a function of the final state multiplicity. We find that the pion pair correlations scale 0.98 fm describes the data well. We do not find any indication of multiplicity dependence of the correlation scale for multiplicities from 6 to 14 final state particles.