Yu. V. Kharlov

Physics with the ALICE experiment

ALICE experiment at LHC collects data in pp collisions at 1497-1 = 0.9, 2.76, and 7 TeV and in PbPb collisions at 2.76 TeV. Highlights of the detector performance and an overview of experimental results measured with ALICE in pp and AA collisions are presented in this paper. Physics with protonproton collisions is focused on hadron spectroscopy at low and moderate pt. Measurements with lead-lead collisions are shown in comparison with those in pp collisions, and the properties of hot quark matter are discussed.

CASTOR: Centauro and strange object research in nucleus-nucleus collisions at the LHC☆

Abstract We present a phenomenological model which describes the formation of a Centauro fireball in the baryon-rich projectile fragmentation region in nucleus-nucleus interactions in the upper atmosphere and at the LHC, and its decay to non-strange baryons and Strangelets. Strangelets are assimilated to the “strongly penetrating component” frequently observed accompanying hadron-rich cosmic ray events. We describe the CASTOR subdetector for the ALICE experiment at the LHC. CASTOR will probe, in an event-by-event mode, the very forward, baryon-rich phase space 5.6 ≤ η ≤ 7.2 in 5.5 × A TeV central Pb + Pb collisions. It will look for events with pronounced imbalance between hadronic and photonic content and for deeply penetrating objects. We present results of simulations for the response of the CASTOR calorimeter to the passage of Strangelets.

A multicomputer data acquisition complex based on MISS and SUMMA electronics for the Hyperon-M experiment

A structure of the multicomputer data acquisition complex for the Hyperon-M experiment at the U-70 accelerator (Protvino, Russia) is described. This complex has been designed to collect and merge data from several particle detectors, the electronic systems of which are made either to the MISS or SUMMA standard. The MISS system is autonomously operated under control of a special ЛЭ-74 controller that collects information in its internal buffer storage during a beam spill. The data acquired are combined with the information from the SUMMA electronics and are copied to an external storage device (a hard disk of a computer) in intervals between spills. On the contrary, software control is needed for the SUMMA electronics to read data on each event. Software-and hardware-based methods are used to provide joint operation of the electronic systems made to diverse standards and guarantee that the streams of incoming data are correctly merged. The problems of net interactions between different parts of the multicomputer system and monitoring of this system are analyzed.

A data acquisition system of the “Hyperon-M” experiment on basis of the MISS electronics and controller with internal hardware buffering

The structure of the fast data acquisition system collecting data from multichannel particle detectors for experiments on an accelerator, which is based on MISS electronics, is described. A special feature of the architecture used is the ЛЭ-74 specialized controller that independently reads data from the detectors into the internal memory buffer on a real-time scale in the course of the beam spilling into the target. The stored information is rewritten from the internal buffer on the hard disk of the computer. The data are further transmitted via the local network in intervals between spills. This scheme allows one to avoid accessing slow peripherals in the course of the beam spill and, thus, to attain a speed that is only limited by the response speed of the used circuitry components. In tests conducted as part of the Hyperon-M experiment on the U-70 accelerator, an experimental data collection speed of up to 9 Mbyte/s was attained, which is comparable with the data transmission speed in existing local communication networks.

Formation and detection of centauro in Pb + Pb collisions at the LHC*

We present a phenomenological model describing the formation of a quark–gluon plasma (QGP) fireball in the very forward, baryon-rich rapidity region in nucleus–nucleus interactions, and its subsequent decay into baryons and possibly strangelets. The model explains the centauro events observed in cosmic rays and the long-penetrating component frequently accompanying them, and makes predictions for the LHC. We describe the CASTOR calorimeter, a subdetector to probe the very forward, baryon-rich rapidity region in Pb + Pb collisions at the LHC. The simulated response of the calorimeter to new effects is presented and its sensitivity is derived using a neural network technique.

Correcting the energy scale nonlinearity of the electromagnetic calorimeter by two-photon decays of a π0 meson

A method for correcting the nonlinearity of the electromagnetic calorimeter response is described. This method is based on minimizing the deviation of the measured mass of a neutral π0 meson decaying into two photons, depending on their energy. This method has been developed for the LGD2 electromagnetic calorimeter and used in the Hyperon-M experiment at the U-70 accelerator of the Institute for High Energy Physics. The proposed correction technique has made it possible to substantially reduce variations of the reconstructed π0 and η meson masses in accordance with their minimum energies.

Direct photon identification with artificial neural network in the photon spectrometer PHOS

A neural network method is developed to discriminate direct photons from the neutral pion background in the PHOS spectrometer of the ALICE experiment at the LHC collider. The neural net has been trained to distinguish different classes of events by analyzing the energy-profile tensor of a cluster in its eigen vector coordinate system. Monte-Carlo simulations show that this method diminishes by an order of magnitude the probability of � 0 -meson misidentification as a photon with respect to the direct photon identification efficiency in the energy range up to 120 GeV.

Methods of Coordinate Reconstruction in Gaseous Detectors with Cathode Readout

The methods for reconstructing the coordinates of charged particles in gaseous detectors with cathode readout are analyzed in detail. The spatial resolution is investigated using spatial-reconstruction procedures based on the known relations and the new formulas proposed in the paper. The use of this method is illustrated by processing the beam-test data of the charged-particle veto detector of the proton spectrometer for the ALICE experiment at the Large Hadron Collider (CERN). The spatial resolution of the detector based on the multiwire proportional chamber with cathode-pad readout (pad dimensions are 22 × 10.7 mm, the anode-wire pitch is 5.65 mm, and the anode–cathode gap is 5.5 mm), measured along and across the anode wires, is σx ≅ 0.14 cm and σy ≅ 0.15 cm, respectively.

A Charged-Particle Detector Based on Proportional Tubes with a Segmented Cathode and Cathode Readout

A charged-particle detector based on proportional tubes with cathode readout is described. The cathode is sectionalized into 2.2 × 2.2-cm pads. The detector was tested on high-energy particle beams. At an anode-to-cathode distance of 1.1 cm, the spatial resolution was 1.25 mm along the anode wire. A simulation model of the detector on the basis of the measured pad-response function was proposed, compared to the experimental data, and used to calculate the two-track resolution. The detector can be used in various experiments as a large-area multiparticle two-coordinate detector.

Measurement of neutral-meson masses in meson-nucleus interactions at a momentum of 7 GeV/c at the Hyperon-M setup

The π0, η, K0, ω, and f2(1270) masses were measured at the HYPERON-Msetup in meson-nucleus interactions at a momentum of 7 GeV/c by using six nuclear targets: Be, C, Al, Cu, Sn, and Pb. The experiment in question proved to be insensitive to the expected effects of a modification to the omega-meson mass in nuclear matter. As for the f2(1270) meson, its mass and width values averaged over all experimental data,