Strange Particle Correlation Studies with the STAR detector

1. C.Greiner, B. Müller Phys. Lett. B 219 (1989) 199 S. Pratt, F.Wang, Phys. Rev. Lett. (1999) 83 3138 RTO=6fm RTS=6fm RL=6 fm, l=1 - Perfect detector RTO=5.77fm RTS=5.67fm RL=5.61fm, l=0.811 - Mtm resolution s = 7 MeV/c RTO=5.47fmRTS=5.75fmRL=5.75fm, l=0.59 - Mtm resolution + Signal/Noise = 6 C(k) F. Antinori et al. Nucl. Phys. A661 (1999) 130c WA97 F. Antinori et al. Nucl. Phys A661 (1999) 130c WA97 Strange Particle Correlation Studies with the STAR detector Thomas J. Humanic and Helen Caines, Ohio State University, OH for the STAR Strangeness and HBT Physics Working Group and the STAR Collaboration K0s-K0s L-L Theory: Theory: ABSTRACT We present preliminary analysis of the K0s-K0s , L-Proton and L-L correlations as measured by the STAR detector at RHIC. We also discuss some of the unique physics questions and experimental challenges that are probed by these more unconventional correlation studies. • Advantages: • No coulomb repulsion problems • Less 2 track resolution problems • Few distortions from resonance decays – • Could use K+-K0s mixing as background to remove even these resonances • K0s is not a strangeness eigenstate - unique interference term that may provide additional space-time information The shape of the L-L correlation is harder to predict for a given freeze-out radius as the scattering length (a) and effective range (Reff) are not well known. The plot opposite shows predictions for a 6 fm source assuming different values of a and Reff S. Pratt L-p Shown here is a set of simulations showing how the STAR resolution will affect the K0sK0s measurement. Theory: Another possible interesting feature of the L-L correlation is the possibility of detecting the presence of a L-L resonance. Shown opposite is are predictions for the correlation assuming differing radii and widths of the assumed resonance. L-p correlations may be more sensitive to large source sizes than p-p correlations as the L-p system does not suffer from coulomb repulsion affects which mask large sources in charged particle correlations. Previous measurements: If, however, the resonance is quasi-bound (the H-di-baryon) the observed affect becomes harder to distinguish and it is unlikely that the H0 will be discovered this way (but you never know!) The line is not a fit to the data but an indication of the shape of the correlation function for a 6 fm source. Shown are p-p and L-p correlations for source sizes: 4 ( ), 6 (), 10 ( Ο ) fm. Note here k is used. k = | pL – pp| /2 as opposed to q = | pL – pp| Previous measurements: The line is not a fit to the data but an indication of the shape of the correlation function for a 2 fm source, assuming Fermi-Dirac statistics only For unlike particle correlations it is important to form the q (k) in terms of the relative momentum measured in the center-of-mass frame of the two particles. STAR results: We currently reconstruct ~1.3 K0s/event. Although the mass, and hence momentum resolution is not as good as for the L it is still perfectly reasonable for correlation studies. As shown above. One may also extract information about the time difference of the freeze-out of different particle species. By conserving the sign of the relative momentum vector one may be able to determine which particle was emitted first. If strange - non-strange baryon correlations can get sufficiently detailed (the few percent level) we may be able to resolve the question of whether strange particles are emitted simultaneously with non-strange baryons or not. STAR results: As can be seen in the plot below we are statistics limited and hence no firm comment can currently be made about the strength of the L-L correlation. Clearly, however, we have the coverage and an excellent momentum resolution for the L. (See STAR poster by Adam Kisiel on K-p correlations for more details) c2/ndf = 25.21/24 l = 0.7 ±0.5 R = 6.5 ± 2.3 STAR results: While the L-p correlation seems ideal due to the lack of merging etc. there is a problem in obtaining low-q pairs. The mean pt for L1 GeV/c while the high pt cut off for the proton is also  1 GeV/c, due to the need to identify the proton via dE/dx. Hence obtaining low q is not as simple as one might assume. We currently reconstruct ~0.4 L/event. Therefore it is predicted that ~ 10 Million events are needed to produce a reasonable correlation with the present reconstruction efficiencies A radius of 6.6 fm is obtained from a fit to the data. This is large compared to that obtained for charged kaons (~ 4fm). However again we feel that the fit is statistics limited, indicated by the large error on the L parameter. With the inclusion of the SVT in the next run, and the higher energy, it is expect that the yield will increase and hence the required number of events will decrease STAR Preliminary More statistics from the next run will allow to make a firm statement about the K0s radius.