M.M. Aggarwal, Z. Ahammed, A.L.S. Angelis, V. Antonenko, V. Arefiev, V. Astakhov, V. Avdeitchikov, T.C. Awes, P.V.K.S. Baba, S.K. Badyal, S. Bathe, B. Batiounia, C. Baumann, T. Bernier, K.B. Bhalla, V.S. Bhatia, C. Blume, D. Bucher, H. Büsching, L. Carlén, S. Chattopadhyay, M.P. Decowski, H. Delagrange, P. Donni, M.R. Dutta Majumdar, K. El Chenawi, A.K. Dubey, K. Enosawa, S. Fokin, V. Frolov, M.S. Ganti, S. Garpman, O. Gavrishchuk, F.J.M. Geurts, T.K. Ghosh, R. Glasow, B. Guskov, H. Å.Gustafsson, H. H.Gutbrod, I. Hrivnacova, M. Ippolitov, H. Kalechofsky, R. Kamermans, K. Karadjev, K. Karpio, B. W. Kolb, I. Kosarev, I. Koutcheryaev, A. Kugler, P. Kulinich, M. Kurata, A. Lebedev, H. Löhner, L. Luquin, D.P. Mahapatra, V. Manko, M. Martin, G. Mart́ınez, A. Maximov, Y. Miake, G.C. Mishra, B. Mohanty, M.-J. Mora, D. Morrison, T. Mukhanova, D. S. Mukhopadhyay, H. Naef, B. K. Nandi, S. K. Nayak, T. K. Nayak, A. Nianine, V. Nikitine, S. Nikolaev, P. Nilsson, S. Nishimura, P. Nomokonov, J. Nystrand, A. Oskarsson, I. Otterlund, S. Pavliouk, T. Peitzmann, D. Peressounko, V. Petracek, S.C. Phatak, W. Pinganaud, F. Plasil, M.L. Purschke, J. Rak, M. Rammler, R. Raniwala, S. Raniwala, N.K. Rao, F. Retiere, K. Reygers, G. Roland, L. Rosselet, I. Roufanov, C. Roy, J.M. Rubio, S.S. Sambyal, R. Santo, S. Sato, H. Schlagheck, H.-R. Schmidt, Y. Schutz, G. Shabratova, T.H. Shah, I. Sibiriak, T. Siemiarczuk, D. Silvermyr, B.C. Sinha, N. Slavine, K. Söderström, G. Sood, S.P. Sørensen, P. Stankus, G. Stefanek, P. Steinberg, E. Stenlund, M. Sumbera, T. Svensson, A. Tsvetkov, L. Tykarski, E.C.v.d. Pijll, N.v. Eijndhoven, G.J.v. Nieuwenhuizen, A. Vinogradov, Y.P. Viyogi, A. Vodopianov, S. Vörös, B. Wys louch, G.R. Young 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 (WA98 Collaboration) 21 University of Panjab, Chandigarh 160014, India 32 Variable Energy Cyclotron Centre, Calcutta 700064, India 43 University of Geneva, CH-1211 Geneva 4,Switzerland 54 RRC “Kurchatov Institute”, RU-123182 Moscow 65 Joint Institute for Nuclear Research, RU-141980 Dubna, Russia 76 Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6372, USA 87 University of Jammu, Jammu 180001, India 98 University of Münster, D-48149 Münster, Germany 109 SUBATECH, Ecole des Mines, Nantes, France 1110 University of Rajasthan, Jaipur 302004, Rajasthan, India 1211 University of Lund, SE-221 00 Lund, Sweden 1312 MIT Cambridge, MA 02139 1413 Institute of Physics, Bhubaneswar 751005, India 1514 University of Tsukuba, Ibaraki 305, Japan 1615 Universiteit Utrecht/NIKHEF, NL-3508 TA Utrecht, The Netherlands 1716 KVI, University of Groningen, NL-9747 AA Groningen, The Netherlands 1817 Gesellschaft für Schwerionenforschung (GSI), D-64220 Darmstadt, Germany 1918 Nuclear Physics Institute, CZ-250 68 Rez, Czech Rep. 2019 Institute for Nuclear Studies, 00-681 Warsaw, Poland 2120 University of Tennessee, Knoxville, Tennessee 37966, USA Deceased (Dated: May 17, 2021)

M.M. Aggarwal, Z. Ahammed, A.L.S. Angelis, V. Antonenko, V. Arefiev, V. Astakhov, V. Avdeitchikov, T.C. Awes, P.V.K.S. Baba, S.K. Badyal, S. Bathe, B. Batiounia, T. Bernier, K.B. Bhalla, V.S. Bhatia, C. Blume, D. Bucher, H. Büsching, L. Carlén, S. Chattopadhyay, M.P. Decowski, H. Delagrange, P. Donni, M.R. Dutta Majumdar, K. El Chenawi, A.K. Dubey, K. Enosawa, S. Fokin, V. Frolov, M.S. Ganti, S. Garpman, O. Gavrishchuk, F.J.M. Geurts, T.K. Ghosh, R. Glasow, B. Guskov, H. Å.Gustafsson, H. H.Gutbrod, I. Hrivnacova, M. Ippolitov, H. Kalechofsky, K. Karadjev, K. Karpio, B. W. Kolb, I. Kosarev, I. Koutcheryaev, A. Kugler, P. Kulinich, M. Kurata, A. Lebedev, H. Löhner, L. Luquin, D.P. Mahapatra, V. Manko, M. Martin, G. Mart́ınez, A. Maximov, Y. Miake, G.C. Mishra, B. Mohanty, M.-J. Mora, D. Morrison, T. Mukhanova, D. S. Mukhopadhyay, H. Naef, B. K. Nandi, S. K. Nayak, T. K. Nayak, A. Nianine, V. Nikitine, S. Nikolaev, P. Nilsson, S. Nishimura, P. Nomokonov, J. Nystrand, A. Oskarsson, I. Otterlund, T. Peitzmann, D. Peressounko, V. Petracek, W. Pinganaud, F. Plasil, M.L. Purschke, J. Rak, R. Raniwala, S. Raniwala, N.K. Rao, F. Retiere, K. Reygers, G. Roland, L. Rosselet, I. Roufanov, C. Roy, J.M. Rubio, S.S. Sambyal, R. Santo, S. Sato, H. Schlagheck, H.-R. Schmidt, Y. Schutz, G. Shabratova, T.H. Shah, I. Sibiriak, T. Siemiarczuk, D. Silvermyr, B.C. Sinha, N. Slavine, K. Söderström, G. Sood, S.P. Sørensen, P. Stankus, G. Stefanek, P. Steinberg, E. Stenlund, M. Sumbera, T. Svensson, A. Tsvetkov, L. Tykarski, E.C.v.d. Pijll, N.v. Eijndhoven, G.J.v. Nieuwenhuizen, A. Vinogradov, Y.P. Viyogi, A. Vodopianov, S. Vörös, B. Wys louch, G.R. Young (WA98 Collaboration) 1 University of Panjab, Chandigarh 160014, India 2 Variable Energy Cyclotron Centre, Calcutta 700064, India 3 University of Geneva, CH-1211 Geneva 4,Switzerland 4 RRC “Kurchatov Institute”, RU-123182 Moscow 5 Joint Institute for Nuclear Research, RU-141980 Dubna, Russia 6 Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6372, USA 7 University of Jammu, Jammu 180001, India 8 University of Münster, D-48149 Münster, Germany 9 SUBATECH, Ecole des Mines, Nantes, France 10 University of Rajasthan, Jaipur 302004, Rajasthan, India 11 University of Lund, SE-221 00 Lund, Sweden 12 MIT Cambridge, MA 02139 13 Institute of Physics, Bhubaneswar 751005, India 14 University of Tsukuba, Ibaraki 305, Japan 15 Universiteit Utrecht/NIKHEF, NL-3508 TA Utrecht, The Netherlands 16 KVI, University of Groningen, NL-9747 AA Groningen, The Netherlands 17 Gesellschaft für Schwerionenforschung (GSI), D-64220 Darmstadt, Germany 18 Nuclear Physics Institute, CZ-250 68 Rez, Czech Rep. 19 Institute for Nuclear Studies, 00-681 Warsaw, Poland and 20 University of Tennessee, Knoxville, Tennessee 37966, USA (Dated: February 14, 2014)

Measurements of direct photon production in p+Pb and p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$ are presented. Upper limits on the direct photon yield as a function of $p_\mathrm{T}$ are derived and compared to the results for Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 17.3$ GeV. The production of the $\eta$ meson, which is an important input to the direct photon signal extraction, has been determined in the $\eta \rightarrow 2\gamma$ channel for p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$.

M.M. Aggarwal, Z. Ahammed, A.L.S. Angelis, V. Antonenko, V. Arefiev , V. Astakhov , V. Avdeitchikov , T.C. Awes, P.V.K.S. Baba, S.K. Badyal, S. Bathe, B. Batiounia , T. Bernier, K.B. Bhalla, V.S. Bhatia, C. Blume, D. Bucher, H. Büsching, L. Carlen, S. Chattopadhyay, A.C. Das, M.P. Decowski, P. Donni, A.K. Dubey, M.R. Dutta Majumdar, K. Enosawa, S. Fokin, V. Frolov , M.S. Ganti, S. Garpman, O. Gavrishchuk , F.J.M. Geurts, R. Glasow, B. Guskov , H.A. Gustafsson, H.H. Gutbrod , I. Hrivnacova, M. Ippolitov, H. Kalechofsky, R. Kamermans, K. Karadjev, K. Karpio, B.W. Kolb, I. Kosarev , I. Koutcheryaev, A. Kugler, P. Kulinich, M. Kurata, A. Lebedev, H. Löhner , D.P. Mahapatra, V. Manko, M. Martin, Y. Miake, G.C. Mishra, B. Mohanty, D. Morrison, D.S. Mukhopadhyay, H. Naef, B.K. Nandi, S.K. Nayak, T.K. Nayak, A. Nianine, V. Nikitine , S. Nikolaev, S. Nishimura, P. Nomokov , J. Nystrand, A. Oskarsson, I. Otterlund, S.C. Phatak, S. Pavliouk , T. Peitzmann, V. Petracek, F. Plasil, M.L. Purschke, J. Rak, R. Raniwala, S. Raniwala, N.K. Rao, F. Retiere , K. Reygers, G. Roland, L. Rosselet, I. Roufanov , J.M. Rubio, S.S. Sambyal, R. Santo, S. Sato, H. Schlagheck, H.-R. Schmidt, Y. Schutz , G. Shabratova , I. Sibiriak, T. Siemiarczuk, B.C. Sinha, N. Slavine , K. Söderström, G. Sood, S.P. Sørensen, P. Stankus, G. Stefanek, P. Steinberg, E. Stenlund, M. Sumbera, T. Svensson, M.D. Trivedi, A. Tsvetkov, L. Tykarski, J. Urbahn, N.v. Eijndhoven, G.J.v. Nieuwenhuizen, A. Vinogradov, Y.P. Viyogi, A. Vodopianov , S. Vörös, B. Wyslouch, and G.R. Young

Several hadronic observables have been studied in central 158A GeV Pb+Pb collisions using data measured by the WA98 experiment at CERN: single π and K production, as well as twoand three-pion interferometry. The Wiedemann-Heinz hydrodynamical model has been fitted to the pion spectrum, giving an estimate of the temperature and transverse flow velocity. Bose-Einstein correlations between two identified π have been analysed as a function of kT , using two different parameterizations. The results indicate that the source does not have a strictly boost invariant expansion or spend time in a long-lived intermediate phase. A comparison between data and a hydrodynamical based simulation shows very good agreement for the radii parameters as a function of kT . The pion phase-space density at freeze-out has been measured and agrees well with the Tomás̆ik-Heinz model. A large pion chemical potential close to the condensation limit of mπ seems to be excluded. The threepion Bose-Einstein interferometry shows a substantial contribution of the genuine three-pion correlation, but not quite as large as expected for a fully chaotic and symmetric source.

The effect of the final state Coulomb interaction on particles produced in Pb+Pb collisions at 158 A GeV/c has been investigated in the WA98 experiment through the study of the pi-/pi+ and K-/K+ ratios measured as a function of transverse mass. While the ratio for kaons shows no significant transverse mass dependence, the pi-/pi+ ratio is enhanced at small transverse mass values with an enhancement that increases with centrality. A silicon pad detector located near the target is used to estimate the contribution of hyperon decays to the pi-/pi+ ratio. The comparison of results with predictions of the RQMD model in which the Coulomb interaction has been incorporated allows to place constraints on the time of the pion freeze-out.

The azimuthal distributions of photons and charged particles with respect to the event plane are investigated as a function of centrality in Pb + Pb collisions at 158 ·A GeV/c in the WA98 experiment at the CERN SPS. The anisotropy of the azimuthal distributions is characterized using a Fourier analysis. For both the photon and charged particle distributions the first two Fourier coefficients are observed to decrease with increasing centrality. The observed anisotropies of the photon distributions compare well with the expectations from the charged particle measurements for all centralities.

The azimuthal distributions of photons and charged particles with respect to the event plane are investigated as a function of centrality in Pb-208 + Pb-208 collisions at 158 (.) A GeV/c in the WA98 experiment at the CERN SPS. The anisotropy of the azimuthal distributions is characterized using a Fourier analysis. For both the photon and charged particle distributions the first two Fourier coefficients are observed to decrease with increasing centrality. The observed anisotropies of the photon distributions compare well with the expectations from the charged particle measurements for all centralities.

Directed and elliptic flow of inclusive photons near mid-rapidity in $158 $A GeV Pb+Pb collisions has been studied. The data have been obtained with the photon spectrometer LEDA of the WA98 experiment at the CERN SPS. The flow strength has been measured for various centralities as a function of $p_T$ and rapidity over $0.18 < p_T < 1.5 \mathrm{GeV}/c$ and $2.3 < y < 2.9$. The angular anisotropy has been studied relative to an event plane obtained in the target fragmentation region that shows the elliptic flow to be in-plane. The elliptic flow has also been studied using two-particle correlations and shown to give similar results. A small directed flow component is observed. Both the directed and elliptic flow strengths increase with $p_T$. The photon flow results are used to estimate the corresponding neutral pion flow.

Two-particle correlations of direct photons were measured in central 208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was extracted from the correlation strength and compared to theoretical calculations.

Results on the study of localized fluctuations in the multiplicity of charged particles and photons produced in 158A GeV/c Pb+Pb collisions are presented for varying centralities. The charged versus neutral particle multiplicity correlations in common phase space regions of varying azimuthal sizes are analyzed by two different methods. Various types of mixed events are constructed to probe fluctuations arising from different sources. The measured results are compared to those from simulations and from mixed events. The comparison indicates the presence of nonstatistical fluctuations in both the charged particle and photon multiplicities in limited azimuthal regions. However, no correlated charged-neutral fluctuations, a possible signature of formation of disoriented chiral condensates, are observed. An upper limit on the production of disoriented chiral condensates is set.

A measurement of direct photon production in Pb-208+Pb-208 collisions at 158 A GeV has been carried out in the CERN WA98 experiment. Invariant yield of direct photons was extracted as a function of transverse momentum in the interval 0.5 < P-T < 3.3 GeV/c for peripheral, and 0.5 < P-T < 4.0 GeV/c for central collisions. Direct photon yield was extracted on a statistical basis as the difference between the measured inclusive spectrum of photons, and the calculated spectrum of photons which result from all hadrons with significant radiative decay contributions. While no direct photon excess was observed for the peripheral event sample, a significant direct photon signal, compared to statistical and systematical errors, was seen in central collisions at P-T > 1.5 GeV/c. The result constitutes the first observation of direct photons in ultrarelativistic heavy-ion collisions.

Event-by-event fluctuations in the multiplicities of charged particles and photons, and the total transverse energy in 158A GeV Pb+Pb collisions are studied for a wide range of centralities. For narrow centrality bins the multiplicity and transverse energy distributions are found to be near perfect Gaussians. The effect of detector acceptance on the multiplicity fluctuations has been studied and demonstrated to follow statistical considerations. The centrality dependence of the charged particle multiplicity fluctuations in the measured data has been found to agree reasonably well with those obtained from a participant model. However, for photons the multiplicity fluctuations have been found to be lower compared to those obtained from a participant model. The multiplicity and transverse energy fluctuations have also been compared to those obtained from the VENUS event generator.

Scaled factorial moment analysis for the multiplicity distribu- tions of shower particles in the pseudorapidity phase space has been done. An evidence for the presence of dynamical uctuations has been shown for the non-peripheral interactions of28Si+Ag(Br) at 14.6 A GeV/c and 4.5 A GeV/c.The results have been compared with the values obtained from data sample calculated by cascade-evaporation model.

Results from the multiplicity distributions of inclusive photons and charged particles, scaling of particle multiplicities, event-by-event multiplicity fluctuations, and charged-neutral fluctuations in 158A GeV Pb+Pb collisions are presented and discussed. A scaling of charged particle multiplicity as N part 1.07±0.05 and photos as N part 1.12±0.03 have been observed, indicating violation of naive wounded nucleon model. The analysis of localized charged-neutral fluctuation indicates a model-independent demonstration of non-statistical fluctuations in both charged particles and photons in limited azimuthal regions. However, no correlated charged-neutral fluctuations are observed.

Results on transverse mass spectra of neutral pions measured at central rapidity are presented for impact parameter selected 158·A GeV Pb + Pb, and Pb + Nb collisions. The distributions cover the range 0.5 GeV/c ≤ mT − m0 ≤ 4 GeV/c . The change of the spectral shape with centrality is studied in detail. In going from peripheral to medium central collisions there is a nuclear enhancement increasing with transverse mass similar to the well known Cronin effect, while for very central collisions this enhancement appears to be weaker than expected. PACS. 25.75.Dw Particle and resonance production 2 M.M. Aggarwal et al.: Transverse mass distributions of neutral pions from Pb-induced reactions at 158·A GeV