High-p_T pi^0 suppression in Au+Au collisions at sqrt(s_NN) = 200 GeV

Neutral pions with p_T = 1 - 8 GeV/c have been measured for 9 different centrality classes in Au+Au collisions at sqrt(s_NN) = 200 GeV by the PHENIX experiment at RHIC. The pi^0 multiplicity in central reactions is significantly below the binary collision scaled yields from both peripheral Au+Au and pp reactions. The observed suppression sets in for the 50-70% centrality class and increases with p_T and centrality. For the most central bin, the deficit amounts to a factor ~2.5 at p_T ~ 2 GeV/c gradually increasing to a factor ~6 at p_T ~ 8 GeV/c.Comment: 4 pages, 4 figures. Talk given at Quark Matter 2002 (QM 2002), Nantes, Bretagne, France, 18-24 Jul 2002. Minor corrections in tex

Unintegrated parton distributions and pion production in pppp collisions at SPS and RHIC energies

Inclusive cross sections for pion production in $pp$ collisions are calculated for the first time fully based on unintegrated gluon, quark and antiquark distributions (uPDF). We use recently developed Kwieci\'nski uPDF's and different phenomenological fragmentation functions (FF) from the literature. In addition to the $gg \to g$ diagram we include also $g q \to q$ and $q g \to q$ diagrams for inclusive parton production. The cross section for pions is obtained then by convoluting the inclusive parton distributions and FFs. Applications for SPS and RHIC are shown.Comment: 4 pages, 3 figures, a talk presented at the Quark Matter 2005 conference, Budapest, August 200

Summary of Results on Hard Probes

Results on observables related to hard scattering processes as presented at this conference are reviewed. This includes in particular measurements related to jet quenching, a phenomenon which has been predicted as a signature for the hot and dense early phase of strongly interacting matter.Comment: Summary talk at Quark Matter 2002, Nantes, Proceedings to be published in Nucl. Phys. A, 10 pages, 6 figures, (one figure added in this version

Centrality-dependence of Particle Production at RHIC and the Combinational Approach

The newly proposed combinational approach, called the grand combinational model (GCM), as would be described in detail in the text, is still under our careful scrutiny. By applying it, we have attempted to analyze here the characteristics of both the transverse momentum($p_{\rm{T}}$)-, and centrality-dependence of production of the main varieties of the secondaries measured in $AuAu$ collisions at BNL-RHIC at both $\sqrt{s_{\rm{NN}}}=130$ GeV and $\sqrt{s_{\rm{NN}}}=200$ GeV by PHENIX Collaboration. Besides, with the help of it, we have also investigated the nature of centrality-dependence of the average transverse momenta of the various major categories of particles in $AuAu$ collisions at RHIC. The model seems to survive quite smoothly the acid tests of the latest PHENIX data, as it accommodates data modestly well on these twin aspects. The study reveals a kind of universality of nature of the hadronic secondaries and also of the basic particle and nuclear interactions at high energies. However, in the end, we precisely point out both the strengths and limitations of the specific model under consideration here.Comment: 13 pages, 17 figures, accepted for publication in EPJ

High pT pi0 Production and Angular Correlations in 158 AGeV p+A and Pb+Pb Collisions

Recent results of the WA98 experiment with p and Pb induced reactions at 158 AGeV are presented. Azimuthal gamma-gamma correlations at high pT 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 pT of the photons and the size of the system. In Pb+Pb collisions 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.Comment: 4 pages, 2 figures, Talk presented at Quark Matter 2002, Nantes, France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A

High pTp_T Measurements from PHENIX

We present recent high transverse momentum measurements by the PHENIX experiment for Au+Au and p+p collisions at $\sqrt{s_{NN}} = 200$ GeV at the Relativistic Heavy Ion Collider (RHIC). We show particle spectra for neutral pions and charged hadrons, define and show the nuclear modification factor, and discuss particle composition. By means of the nuclear modification factor, we observe a suppression factor of 5-6 for neutral pions and 3-4 for charged hadrons in central collisions at high $p_T$. We find that the ratio of $\pi^0$ to $(h^++h^-)/2$ remains nearly constant at $\sim 0.5$ for $p_T = 2-9$ GeV/c. Finally we present strong evidence for the observation of jets in Au+Au collisions.Comment: 10 pages, 11 figures, Talk presented at Quark Matter 2002, Nantes, France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A

Light Scalar Mesons from Phi to Psi

The following topics are considered. 1) Confinement, chiral dynamics, and light scalar mesons. 2) Chiral shielding of the $\sigma(600)$. 3) The $\phi$ meson radiative decays about nature of light scalar resonances. 4) The $J/\psi$ decays about nature of light scalar resonances. 5) The $a_0(980)\to\gamma\gamma$ and $f_0(980)\to\gamma\gamma$ decays about nature of light scalar resonances. 6) New round in $\gamma\gamma\to\pi^+\pi^-$, the Belle data. Arguments in favor of the four-quark model of the $a_0(980)$ and $f_0(980)$ mesons are given.Comment: 7 pages, 7 figures. Talk presented by N.N. Achasov at the International Workshop "e+e- Collisions from Phi to Psi", February 27--March 2, 2006, BINP, Novosibirsk, Russian Federatio

Search for the onset of baryon anomaly at RHIC-PHENIX

The baryon production mechanism at the intermediate $p_T$ (2 - 5 GeV/$c$) at RHIC is still not well understood. The beam energy scan data in Cu+Cu and Au+Au systems at RHIC may provide us a further insight on the origin of the baryon anomaly and its evolution as a function of $\sqrt{s_{NN}}$. In 2005 RHIC physics program, the PHENIX experiment accumulated the first intensive low beam energy data in Cu+Cu collisions. We present the preliminary results of identified charged hadron spectra in Cu+Cu at $\sqrt{s_{NN}}$ = 22.5 and 62.4 GeV using the PHENIX detector. The centrality and beam energy dependences of (anti)proton to pion ratios and the nuclear modification factors for charged pions and (anti)protons are presented.Comment: 5 pages, 9 figures, proceedings for Hot Quarks 2006 workshop, Villasimius, Sardinia, Italy, May 15 - 20, 2006. Proceedings of the conference will be published in The European Physical Journal

The gaseous pixel device

The Gaseous Pixel Chamber is a new device developed during the last year within the LAA project at CERN. Basically we print electrodes onto a flexible Kapton foil with standard printed circuit technology used in the CERN workshops. We have found a design which allows us to operate the foil as a particle detector working in the gaseous limited streamer mode. This work has been previously reported. We are well satisfied with the operational characteristics that this device has reached so far (efficiency, ease to build and to operate). However, the demands imposed on any detector device at future hadron colliders are very stringent. There are still many possible improvements needed to meet the technical challenge for a device to work at the LHC,SSC or Eloisatron hadron collider (such as time response, space resolution, energy proportionality). Therefore we propose an R&D programme for studying the aspects that are relevant for application of this kind of detector within a hadron collider environment

Partial widths a_0(980)\to\gamma\gamma, f_0(980)\to\gamma\gamma and q\bar q-classification of the lightest scalar mesons

We calculate partial widths for the decays a_0(980)\to\gamma\gamma and f_0(980)\to\gamma\gamma under the assumption that a_0(980) and f_0(980) are members of the basic 1^3P_0 q\bar q nonet. The results are in a reasonable agreement with data thus giving an argument for a q\bar q origin of these mesons. We also calculate the \gamma\gamma partial widths for the other scalar mesons, members of the 2^3P_0 q\bar q nonet.Comment: 9 pages, LaTeX, 5 EPS figures, epsfig.st