Rho0 production and possible modification in Au+Au and p+p collisions at S(NN)**1/2 = 200-GeV

The STAR collaboration
Phys.Rev.Lett. 92 (2004) 092301, 2004.

We report results on rho(770)^0 -> pi+pi- production at midrapidity in p+p and peripheral Au+Au collisions at sqrt(s_NN) = 200 GeV. This is the first direct measurement of rho(770)^0 -> pi+pi- in heavy-ion collisions. The measured rho^0 peak in the invariant mass distribution is shifted by ~40 MeV/c^2 in minimum bias p+p interactions and ~70 MeV/c^2 in peripheral Au+Au collisions. The rho^0 mass shift is dependent on transverse momentum and multiplicity. The modification of the rho^0 meson mass, width, and shape due to phase space and dynamical effects are discussed.

  • Figure 1


    The raw $\pi^{+} \pi^{-}$ invariant mass distributions after subtraction of the like-sign reference distribution for minimum bias p+p (top) and...

  • Figure 1 inserted plot


    The raw $\pi^{+} \pi^{-}$ invariant mass (solid line) and the like-sign reference distributions (open circles) for peripheral Au+Au collisions.

  • Figure 2


    The $\rho^{0}$ mass as a function of $p_{T}$ for minimum bias $p$+$p$ (filled circles), high multiplicity $p$+$p$ (open triangles), and...

  • Figure 3


    The $p_{T}$ distributions at $|y|<0.5$ for minimum bias $p$+$p$ and peripheral Au+Au collisions. See text for an explanation of the...

  • Figure 4


    $\rho^{0}/\pi$ ratios as a function of c.m. system energy. The ratios are from measurements in $e^{+} e^{−}$ collisions at $10.45$...

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