Development of a triple GEM UV-photon detector operated in pure CF4 for the PHENIX experiment

Results obtained with a triple GEM detector operated in pure CF4 with and without a reflective CsI photocathode are presented. The detector operates in a stable mode at gains up to 10^4. A deviation from exponential growth starts to develop when the total charge exceeds ~ 4 10^6 e leading to gain saturation when the total charge is ~ 2 10^7 e and making the structure relatively robust against discharges. No aging effects are observed in the GEM foils after a total accumulated charge of ~ 10 mC/cm^2 at the anode. The ion back-flow current to the reflective photocathode is comparable to the electron current to the anode. However, no significant degradation of the CsI photocathode is observed for a total ion back-flow charge of ~ 7 mC/cm^2.Comment: 14 pages, 11 figures, Submitted to NIM

Construction and Expected Performance of the Hadron Blind Detector for the PHENIX Experiment at RHIC

A new Hadron Blind Detector (HBD) for electron identification in high density hadron environment has been installed in the PHENIX detector at RHIC in the fall of 2006. The HBD will identify low momentum electron-positron pairs to reduce the combinatorial background in the $e^{+}e^{-}$ mass spectrum, mainly in the low-mass region below 1 GeV/c$^{2}$. The HBD is a windowless proximity-focusing Cherenkov detector with a radiator length of 50 cm, a CsI photocathode and three layers of Gas Electron Multipliers (GEM). The HBD uses pure CF$_{4}$ as a radiator and a detector gas. Construction details and the expected performance of the detector are described.Comment: QM2006 proceedings, 4 pages 3 figure

A Hadron Blind Detector for the PHENIX Experiment

A novel Hadron Blind Detector (HBD) has been developed for an upgrade of the PHENIX experiment at RHIC. The HBD will allow a precise measurement of electron-positron pairs from the decay of the light vector mesons and the low-mass pair continuum in heavy-ion collisions. The detector consists of a 50 cm long radiator filled with pure CF4 and directly coupled in a windowless configuration to a triple Gas Electron Multiplier (GEM) detector with a CsI photocathode evaporated on the top face of the first GEM foil.Comment: 4 pages, 3 figures, Quark Matter 2005 conference proceeding

Design, Construction, Operation and Performance of a Hadron Blind Detector for the PHENIX Experiment

A Hadron Blind Detector (HBD) has been developed, constructed and successfully operated within the PHENIX detector at RHIC. The HBD is a Cherenkov detector operated with pure CF4. It has a 50 cm long radiator directly coupled in a window- less configuration to a readout element consisting of a triple GEM stack, with a CsI photocathode evaporated on the top surface of the top GEM and pad readout at the bottom of the stack. This paper gives a comprehensive account of the construction, operation and in-beam performance of the detector.Comment: 51 pages, 39 Figures, submitted to Nuclear Instruments and Method

Semi-Hard Scattering Unraveled from Collective Dynamics by Two-Pion Azimuthal Correlations in 158 A GeV/c Pb + Au Collisions

Elliptic flow and two-particle azimuthal correlations of charged hadrons and high-$p_T$ pions ($p_T>$ 1 GeV/$c$) have been measured close to mid-rapidity in 158A GeV/$c$ Pb+Au collisions by the CERES experiment. Elliptic flow ($v_2$) rises linearly with $p_T$ to a value of about 10% at 2 GeV/$c$. Beyond $p_T\approx$ 1.5 GeV/$c$, the slope decreases considerably, possibly indicating a saturation of $v_2$ at high $p_T$. Two-pion azimuthal anisotropies for $p_T>$ 1.2 GeV/$c$ exceed the elliptic flow values by about 60% in mid-central collisions. These non-flow contributions are attributed to near-side and back-to-back jet-like correlations, the latter exhibiting centrality dependent broadening.Comment: Submitted to Phys. Rev. Letters, 4 pages, 5 figure

Low-mass e+e- pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4 (stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed pt.Comment: 17 pages, 4 figures, submitted to Phys.Lett.

Lambda production in 40 A GeV/c Pb-Au collisions

During the 1999 lead run, CERES has measured hadron and electron-pair production at 40 A GeV/c beam momentum with the spectrometer upgraded by the addition of a radial TPC. Here the analysis of lambda and antilambda will be presented.Comment: 8 pages, 8 figures. 6th International Conference on Strange Quarks in Matter, Frankfurt 200

Leptonic and charged kaon decay modes of the ϕ\phi meson measured in heavy-ion collisions at the CERN SPS

We report a measurement of $\phi$ meson production in central Pb+Au collisions at E$_{lab}$/A=158 GeV. For the first time in heavy-ion collisions, $\phi$ mesons were reconstructed in the same experiment both in the K$^+$K$^-$ and the dilepton decay channel. Near mid-rapidity, this yields rapidity densities, corrected for production at the same rapidity value, of 2.05 +- 0.14(stat) +- 0.25(syst) and 2.04 +- 0.49(stat)+-{0.32}(syst), respectively. The shape of the measured transverse momentum spectra is also in close agreement in both decay channels. The data rule out a possible enhancement of the $\phi$ yield in the leptonic over the hadronic channel by a factor larger than 1.6 at 95% CL.Comment: 11 pages, 4 figures,submitted to Phys. Rev. Let