The current progress of the ALICE Ring Imaging Cherenkov Detector

Recently, the last two modules (out of seven) of the ALICE High Momentum Particle Identification detector (HMPID) were assembled and tested. The full detector, after a pre-commissioning phase, has been installed in the experimental area, inside the ALICE solenoid, at the end of September 2006. In this paper we review the status of the ALICE/HMPID project and we present a summary of the series production of the CsI photo-cathodes. We describe the key features of the production procedure which ensures high quality photo-cathodes as well as the results of the quality assessment performed by means of a specially developed 2D scanner system able to produce a detailed map of the CsI photo-current over the entire photo-cathode surface. Finally we present our recent R&D efforts toward the development of a novel generation of imaging Cherenkov detectors with the aim to identify, in heavy ions collisions, hadrons up to 30 GeV/c.Comment: Presented at the Imaging-2006 Conference, Stockholm, Sweden, June 200

Aging of large area CsI photocathodes for the ALICE HMPID prototypes

The ALICE HMPID RICH detector is equipped with CsI photocathodes in a MWPC for the detection of Cherenkov photons. The long term operational experience with large area CsI photocathodes will be described. The RICH prototypes have shown a very high stability of operation and performance, at a gain of 10 \5 and with rates up to 2x10 \4 cm-2 s-1. When exposure to air has been avoided, no degradation of the CsI quantum efficiency has been observed on photocathodes periodically exposed to test-beams over 7 years, corresponding to local integrated charge densities of ~ 1 mC cm-2. The results of limited exposures to oxygen and humidity will also be presented

The Integrated HV, LV and Liquid Radiator Control System for the HMPID in the ALICE Experiment at LHC

The complexity and the underground location of the new generation experiments (ALICE, ATLAS, CMS and LHCb) at the CERN Large Hadron Collider (LHC) requires a reliable and user friendly control system to operate such large detectors remotely. Control system experts at CERN are deeply involved in developing the JCOP (Joint Controls Project) 'Framework', a software running in the PVSSII SCADA1 (Supervisory Control And Data Acquisition) system, that will provide a homogeneous and ready to use tool for the control system developers of the LHC experiments. The High Momentum Particle Identification Detector (HMPID), one of the ALICE2 sub-detectors, is being equipped with a Detector Control System (DCS) developed within the JCOP Framework. In this paper the basic features and the first results of the DCS prototype are presented

Study of the Quantum Efficiency of CsI Photocathodes Exposed to Oxygen and Water Vapour

The operation of CsI photocathodes in gaseous detectors requires special attention to the purity of the applied gas mixtures.We have studied the influence of oxygen and water vapour contaminations on the performance of CsI photocathodes for theALICE HMPID RICH prototype. Measurements were done through comparison of Cherenkov rings obtained from beamtests. Increased levels of oxygen and water vapour did not show any effect on the performance. The results of this studyfound a direct application in the way of storing CsI photocathodes over long periods nad in particular in the shipment of theHMPID prototype from CERN to the STAR experiment at BNL. (Abstract only available,full text to follow

A threshold imaging Cerenkov detector with CsI photocathodes

A Threshold Imaging Cherenkov (TIC) detector, in conjunction with a tracking device and a time-of-flight system, has been developed to allow pion, kaon and proton identification in the 3--8 GeV/$c$ range of momenta. The system allows spatial identification of the photons of particles above the Cherenkov threshold and their correlation to a particular track. The TIC detector uses a MWPC detector with a CsI coated photocathode for photon conversion. The results obtained in ultrarelativistic lead--lead collisions at the CERN SPS accelerator are presented

Two-kaon correlations in central Pb + Pb collisions at 158 A GeV/c

Two-particle interferometry of positive kaons is studied in Pb + Pb collisions at mean transverse momenta $\approx 0.25$ and 0.91 GeV/c. A three-dimensional analysis was applied to the lower $p_T$ data, while a two-dimensional analysis was used for the higher $p_T$ data. We find that the source size parameters are consistent with the $m_T$ scaling curve observed in pion correlation measurements in the same collisions, and that the duration time of kaon emission is consistent with zero within the experimental sensitivity.Comment: 4 pages incl. 1 table and 3 fig's; RevTeX; accepted for publication in PR

Strange Meson Enhancement in PbPb Collisions

The NA44 Collaboration has measured yields and differential distributions of K+, K-, pi+, pi- in transverse kinetic energy and rapidity, around the center-of-mass rapidity in 158 A GeV/c Pb+Pb collisions at the CERN SPS. A considerable enhancement of K+ production per pi is observed, as compared to p+p collisions at this energy. To illustrate the importance of secondary hadron rescattering as an enhancement mechanism, we compare strangeness production at the SPS and AGS with predictions of the transport model RQMD.Comment: 11 pages, including 4 figures, LATE

VHMPID: a new detector for the ALICE experiment at LHC

This article presents the basic idea of VHMPID, an upgrade detector for the ALICE experiment at LHC, CERN. The main goal of this detector is to extend the particle identification capabilities of ALICE to give more insight into the evolution of the hot and dense matter created in Pb-Pb collisions. Starting from the physics motivations and working principles the challenges and current status of development is detailed.Comment: 4 pages, 6 figures. To be published in EPJ Web of Conference

Two-Proton Correlations near Midrapidity in p+Pb and S+Pb Collisions at the CERN SPS

Correlations of two protons emitted near midrapidity in p+Pb collisions at 450 GeV/c and S+Pb collisions at 200A GeV/c are presented, as measured by the NA44 Experiment. The correlation effect, which arises as a result of final state interactions and Fermi-Dirac statistics, is related to the space-time characteristics of proton emission. The measured source sizes are smaller than the size of the target lead nucleus but larger than the sizes of the projectiles. A dependence on the collision centrality is observed; the source size increases with decreasing impact parameter. Proton source sizes near midrapidity appear to be smaller than those of pions in the same interactions. Quantitative agreement with the results of RQMD (v1.08) simulations is found for p+Pb collisions. For S+Pb collisions the measured correlation effect is somewhat weaker than that predicted by the model simulations, implying either a larger source size or larger contribution of protons from long-lived particle decays.Comment: 10 pages (LaTeX) text, 4 (EPS) figures; accepted for publication in Phys. Lett.

Effective Rheology of Bubbles Moving in a Capillary Tube

We calculate the average volumetric flux versus pressure drop of bubbles moving in a single capillary tube with varying diameter, finding a square-root relation from mapping the flow equations onto that of a driven overdamped pendulum. The calculation is based on a derivation of the equation of motion of a bubble train from considering the capillary forces and the entropy production associated with the viscous flow. We also calculate the configurational probability of the positions of the bubbles.Comment: 4 pages, 1 figur