The WA97 and NA57 experiments |
Nuclear modification factors |
|
|
|
|
Suppression of particles carrying a high transverse momentum in heavy ion collisions compared to nucleon-nucleon collisions is an important result from RHIC experiments. Comparisons between nuclear collisions and scaled nucleon-nucleon collisions are expressed by the nuclear modification factor RAA(pT). Similar effects are observed when peripheral nuclear collisions are compared to central collisions, expressed by the central-to-peripheral nuclear modification factor RCP(pT) .
The definition of RAA(pT) is given as NA57 has made measurements in the centrality range from 0 to 55% of the total inelastic cross section. Data are presented in centrality bins, with 40-55% being the most peripheral bin. Central-to-peripheral modification factors are presented here, using the four most central bins as the "central" bin, and the most peripheral bin as "peripheral". At the top SPS energy we observe a similar difference between mesons (K0) and baryons (Λ) as observed at RHIC energies. For low pT values we observe values close to participant scaling. At SPS energies there is a marked difference between Λ and , corresponding with the lower value of the /Λ yield ratio reported earlier.
Comparisons with STAR results from RHIC and WA98 results from SPS are shown in the figure below.
|
|
|
The figure below shows a comparison with predictions from X.N.Wang and the PQM model (private communication). The comparisons show that within these models, parton energy loss in the nuclear medium is necessary to describe the NA57 data. A full discussion on the NA57 nuclear modification factor results, including references to other work, can be found in our RCP paper. |
|
| |||
| Last updated 01/09/2006 by Håvard Helstrup |
and the definition of RCP(pT) is given as 
.
