New results and perspectives on R AA measurements below 20 GeV CM-energy at fixed target machines Zoltán FODOR, András LÁSZLÓ, György VESZTERGOMBI for the NA49 Collaboration Poster for QM06, Shanghai

ABSTRACT Measurements of high p t pion, kaon and proton production play a central role in the understanding of AA, pA and pp interactions. The cleanest signature for jet-quenching is provided by the measurement of the nuclear modification factor R AA. Latest NA49 results at 158 GeV on R CP comparing central to peripheral collisions indicate a picture which is qualitatively similar to the RHIC at a somewhat weaker scale. In order to better understand the picture one needs high p t pp, and pA data to be able to disentangle the Cronin- and jet-quenching effects. High statistic high precision pp data on charged pion production was published by the NA49 collaboration up to pt of 2.2 GeV/c. By accepting reduced accuracy the p t range can be increased at least by 0.5 GeV/c. As in the case of RHIC experiments one can compare the pp and AA particle yields in exactly the same detector which will minimize the systematic effects.. The present pp statistics is surely not enough to go above 3 GeV/c in p t. It will be shown how far one can go in the near future using the upgraded NA49 detector at 17.3 GeV CM-energy. NA49-future proposal, Study of Hadron Production in Hadron-Nucleus and Nucleus-Nucleus Collisions at the CERN SPS, CERN-SPSC SPSC-P-330 Assuming the existence of an effect of transverse spectra modification at 17.3 GeV, one is wondering: is there a threshold energy somewhere at lower value? In the long- run the FAIR accelerator is planned to provide at the CBM-detector proton/sec beam intensity upto 90 GeV energy. This unprecendented luminosity provides a unique possibility to extend the p t range into practically unknown territory. The perspectives of these extreme luminosities will be discussed.

C. Alt et al., Nucl.Phys. A 774, 473 (2006), arXiv: nucl-ex/ T. Schuster et al., submitted to J. Phys. G, arXiv: nucl-ex/

One of the most striking features observed at BNL-RHIC is the suppression of high p t production in central A+A collisions relative to peripheral A+A collisions. This is generally interpreted as a sign of parton energy loss in hot and dense hadronic matter created at the early stage of nucleus-nucleus collisions. This interpretation implies that the suppression should disappear at low energies where the energy is not enough for creation of the deconfined state of matter. Numerous results on energy dependence of hadron yields and spectra indicate that the onset of deconfinement is located at the low SPS energies (see e.g. previous NA49 experimental results and theoretical calculations on the critical point). Existing central and peripherial PbPb collision data from the NA49 experiment allows to measure the R CP ratio upto about 3.5 GeV/c. No substantial suppression is seen in this range, but the interpretation of this result is hindered by the poorly known interference with the Cronin-effect. Motivation for jet-quenching search in PbPb at SPS

p+p p+Pb

Reference pp ad pPb data from the NA49 experiment In parallel with the PbPb programme, reference data were collected also for pp and pPb interactions in the NA49 experiment, which allows to measure identified p t spectra upto 2.6 GeV/c at 17.3 GeV/nucleon energy. One can find in the same p t range identified pp and dAu spectra from the PHENIX experiment at 200 GeV/nucleon energy. Comparing R pPb/pp and R dAu/pp for identified pion spectra, one observes about a factor of 3 and a factor of 2 increase, respectively at the different energies between 0.5 and 2.5 GeV/c. In view of the fact that there was not correction for the centrality of the recorded data, they seem to be in the same range. There is a more significant difference between the R PbPb/pp and R AuAu/pp spectra which indicates a broad peaking in RHIC data at 1.5 GeV/c but one can only guess a “saturation” in lower energy SPS data above 2 GeV/c to be confirmed in future experiments if larger statistics will be available.

One expects that ratios relative to pPb and dAu yields can provide “Cronin-free”comparisons. One observes a remarkable similarity of the ratios R AA and R CP. More data are required to identify whether the SPS data remains below 1 for binary scaling. The present results indicate however that there is some „quenching” even at 17.3 GeV.

The NA49-future experiment at the CERN SPS The NA49-future experiment is proposed to study nucleus-nucleus collisions to find evidence for the critical point of strongly interacting matter, to measure proton-proton, proton-nucleus interactions for reference and for a deeper understanding of the high p t penomena and to collect reference data for T2K and cosmic-ray experiments. Larger acceptance and DAQ rate increase are planned.

Innovative new detector to cover larger phase-space

80-90 GeV

Motivation for new measurements below = 20 GeV Practically no high or medium P t data between E inc = 24 and 200 GeV Mysterious transition around GeV: convex versus concave spectra Emergence of Cronin-effect in pA interactions is completely unknown energy dependence centrality dependence particle type dependence particle correlations Production of Upsilon (9.5 GeV) particles near the threshold.

One needs the NA49-future experiment capable to increase the P t range upto 4 GeV/c

Benchmark NA49 pp at E = 158 GeV 30 events/spill Events Energy > 3 GeV/c > 4 GeV/c > 5 GeV/c Estimates with the assumption proton/sec 10 9 interaction/sec 1 day= Suppression day= day= day= Suppression For symmetric nuclei max energy 90/2 assumed CBM Perspectives

“Straight” tracks from main vertex 1-dim Hough – transform:  - histogram  N(  i ) in  bins M(  i ) = N(  i ) + N(  i+1 ) in 2  bins Correct for bin boundary crossing: High P t PHYSICS: High transverse momentum means high 3-momentum

Silicon tracker in FAIR-CBM experiment Special trigger for high intensity 1O 9 interaction/sec in pp,pA reactions SIMULATION: 4 hybrid(pixel) + 5 strip = 9 silicon planes “Mosaic” front-end structure (  ) regions in M(i,j,k) buffers. Exhaustive search for all tracks in (p min,p max ) corridors. TEST RESULT: 1000-fold PILEUP in pC interactions Corridor-width optimized for tracks p > 6 GeV/c and pt > 3 GeV/c Algorithm efficiency: 100 %, with some multiple solutions picking up some random points, giving practically the same track-parameters Highly parallel algorithm is well adapted for processor clusters. Development work is in progress in the frame of FUTURE-DAQ project part of the EU FP6 contract n HadronPhysics -

E N D