New results and perspectives on RAA measurements

below 20 GeV CM-energy at fixed target machines

Zoltán FODOR, András LÁSZLÓ, György VESZTERGOMBI

for the NA49 Collaboration

Poster for QM06, Shanghai

ABSTRACTMeasurements of high pt pion, kaon and proton production play a central role in theunderstanding of AA, pA and pp interactions. The cleanest signature for jet-quenchingis provided by the measurement of the nuclear modification factor RAA.

Latest NA49 results at 158 GeV on RCP 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-Nucleusand Nucleus-Nucleus Collisions at the CERN SPS, CERN-SPSC-2006-034 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 1011 proton/secbeam intensity upto 90 GeV energy. This unprecendented luminosity provides a unique possibility to extend the pt 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/0510054

T. Schuster et al., submitted to J. Phys. G, arXiv: nucl-ex/0606005

One of the most striking features observed at BNL-RHIC is the suppression of high pt 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 energieswhere the energy is not enough for creation of the deconfined state of matter.

Numerous results on energy dependence of hadron yields and spectra indicate thatthe 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 RCP 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+p

p+Pb p+Pb

Reference pp ad pPb data from the NA49 experiment

In parallel with the PbPb programme, reference data were collected also for pp andpPb 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 pt range identified pp and dAu spectra from the PHENIX experiment at 200 GeV/nucleon energy.

Comparing RpPb/pp and RdAu/pp for identified pion spectra, one observes about a factor of 3 and a factor of 2 increase, respectively at the different energiesbetween 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 RPbPb/pp and RAuAu/pp spectrawhich 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 RAA and RCP.

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 findevidence 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 pt 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 GeVs

Practically no high or medium Pt data between Einc = 24 and 200 GeV

Mysterious transition around 80-90 GeV: convex versus concave spectra

Emergence of Cronin-effect in pA interactions is completely unknown

energy dependencecentrality dependenceparticle type dependenceparticle correlations

Production of Upsilon (9.5 GeV) particles near the threshold.

One needs the NA49-future experiment capable to increase the Pt 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

2 106 158 100 1 0.01Estimates with the assumption 1011 proton/sec 109 interaction/sec

1 day=1014 158 5 109 5 107 5 105

Suppression 10-1 10-2 10-3

1 day=1014 90 5 108 5 105 500

20 day=2 1015 90 1010 107 104

20 day=2 1015 45 107 10 0

Suppression 10-3 10-6 10-10

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 2bins

Correct for bin boundary crossing:

High Pt PHYSICS: High transverse momentum means high 3-momentum

Silicon tracker in FAIR-CBM experiment

Special trigger for high intensity 1O9 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 (pmin,pmax) 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. 506078. - HadronPhysics -

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