CERN Accelerating science

Article
Title	Recent results from the WA98-experiment
Author(s)	Büsching, H (CERN)
Collaboration	WA98 Collaboration
Publication	2002
In:	AIP Conf. Proc. 610 (2002) 502-506
In:	International conference on nuclear physics, Berkeley, CA, USA, 30 Jul - 3 Aug 2001, pp.502-506
DOI	10.1063/1.1469979
Subject category	Nuclear Physics
Accelerator/Facility, Experiment	CERN SPS ; WA98
Abstract	Recent results of the WA98 experiment with p and Pb induced reactions at 158 AGeV are presented. The invariant yield of direct photons in central Pb+Pb collisions is shown as a function of transverse momentum. A significant direct photon signal is seen at P/sub T/>1.5 GeV/c. The results constitute the first observation of direct photons in ultrarelativistic heavy-ion collisions. Azimuthal gamma - gamma correlations at high P/sub T/ were studied in search for a signal of jet like structures. A clear indication for back-to-back correlations can be seen in p+A with a strong dependence on the P/sub T/ of the photons and the size of the system. In Pb+Pb in plane elliptic flow has been observed. Results on transverse mass spectra of neutral pions measured at central rapidity are presented for impact parameter selected Pb+Pb collisions. In going from peripheral to medium central collisions there is a nuclear enhancement increasing with transverse mass similar to the Cronin effect, while for very central collisions this enhancement appears to be weaker than expected. (27 refs).

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