Measurement of Aerosols at the Pierre Auger Observatory

The air fluorescence detectors (FDs) of the Pierre Auger Observatory are vital for the determination of the air shower energy scale. To compensate for variations in atmospheric conditions that affect the energy measurement, the Observatory operates an array of monitoring instruments to record hourly atmospheric conditions across the detector site, an area exceeding 3,000 square km. This paper presents results from four instruments used to characterize the aerosol component of the atmosphere: the Central Laser Facility (CLF), which provides the FDs with calibrated laser shots; the scanning backscatter lidars, which operate at three FD sites; the Aerosol Phase Function monitors (APFs), which measure the aerosol scattering cross section at two FD locations; and the Horizontal Attenuation Monitor (HAM), which measures the wavelength dependence of aerosol attenuation.Comment: Contribution to the 30th International Cosmic Ray Conference, Merida Mexico, July 2007; 4 pages, 4 figure

The Fast Read-out System for the MAPMTs of COMPASS RICH-1

A fast readout system for the upgrade of the COMPASS RICH detector has been developed and successfully used for data taking in 2006 and 2007. The new readout system for the multi-anode PMTs in the central part of the photon detector of the RICH is based on the high-sensitivity MAD4 preamplifier-discriminator and the dead-time free F1-TDC chip characterized by high-resolution. The readout electronics has been designed taking into account the high photon flux in the central part of the detector and the requirement to run at high trigger rates of up to 100 kHz with negligible dead-time. The system is designed as a very compact setup and is mounted directly behind the multi-anode photomultipliers. The data are digitized on the frontend boards and transferred via optical links to the readout system. The read-out electronics system is described in detail together with its measured performances.Comment: Proceeding of RICH2007 Conference, Trieste, Oct. 2007. v2: minor change

Fast Photon Detection for Particle Identification with COMPASS RICH-1

Particle identification at high rates is an important challenge for many current and future high-energy physics experiments. The upgrade of the COMPASS RICH-1 detector requires a new technique for Cherenkov photon detection at count rates of several $10^6$ per channel in the central detector region, and a read-out system allowing for trigger rates of up to 100 kHz. To cope with these requirements, the photon detectors in the central region have been replaced with the detection system described in this paper. In the peripheral regions, the existing multi-wire proportional chambers with CsI photocathode are now read out via a new system employing APV pre-amplifiers and flash ADC chips. The new detection system consists of multi-anode photomultiplier tubes (MAPMT) and fast read-out electronics based on the MAD4 discriminator and the F1-TDC chip. The RICH-1 is in operation in its upgraded version for the 2006 CERN SPS run. We present the photon detection design, constructive aspects and the first Cherenkov light in the detector.Comment: Proceedings of the Imaging 2006 conference, Stockholm, Sweden, 27-30 June 2006, 5 pages, 6 figures, to appear in NIM A; corrected typo in caption of Fig.

Fast photon detection for the COMPASS RICH detector

The COMPASS experiment at the SPS accelerator at CERN uses a large scale Ring Imaging CHerenkov detector (RICH) to identify pions, kaons and protons in a wide momentum range. For the data taking in 2006, the COMPASS RICH has been upgraded in the central photon detection area (25% of the surface) with a new technology to detect Cherenkov photons at very high count rates of several 10^6 per second and channel and a new dead-time free read-out system, which allows trigger rates up to 100 kHz. The Cherenkov photons are detected by an array of 576 visible and ultra-violet sensitive multi-anode photomultipliers with 16 channels each. The upgraded detector showed an excellent performance during the 2006 data taking.Comment: Proceeding of the IPRD06 conference (Siena, Okt. 06

Interplay among transversity induced asymmetries in hadron leptoproduction

In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the difference of the azimuthal angles of the two hadrons. The similarity of transversity induced single and di-hadron asymmetries is discussed. A new analysis of the data allows to establish quantitative relationships among them, providing for the first time strong experimental indication that the underlying fragmentation mechanisms are all driven by a common physical process.Comment: 6 figure

Interplay among transversity induced asymmetries in hadron leptoproduction

In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the difference of the azimuthal angles of the two hadrons. The similarity of transversity induced single and di-hadron asymmetries is discussed. A new analysis of the data allows to establish quantitative relationships among them, providing for the first time strong experimental indication that the underlying fragmentation mechanisms are all driven by a common physical process.Comment: 6 figure

Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high pTp_T

We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$\it c$ to 4 GeV/$\it c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$\it c$ or 200 GeV/$\it c$ impinging on polarised $\mathrm{{}^6LiD}$ or $\mathrm{NH_3}$ targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation $\Delta G$ inside the nucleon in the range of the nucleon momentum fraction carried by gluons $0.05 < x_g < 0.2$