Time Of Flight System Research Articles

Study of QGP signatures with the ϕ → K + K – signal in Pb-Pb ALICE events

The phi->K+K- decay channel in Pb-Pb collisions at LHC is studied through a full simulation of the ALICE detector. The study focuses on possible signatures in this channel of quark-gluon plasma (QGP) formation. On a basis of 10^6 collisions at high centrality some proposed QGP signatures are clearly visible both in K+K- invariant mass and transverse mass distributions. The high significance of this observation appears to reside heavily on the use of the TOF (Time Of Flight) system of ALICE in addition to its central tracking detectors.

Study of QGP signatures with the ϕ → K + K – signal in Pb-Pb ALICE events

The ϕ → K+K– decay channel in Pb-Pb collisions at LHC is studied through a full simulation of the ALICE detector. The study focuses on possible signatures in this channel of quark-gluon plasma (QGP) formation. On a basis of 106 collisions at high centrality some proposed QGP signatures are clearly visible both in K + K– invariant mass and transverse mass distributions. The high significance of this observation appears to reside heavily on the use of the TOF (Time Of Flight) system of ALICE in addition to its central tracking detectors.

The large-area time-of-flight upgrade for STAR

The STAR experiment at RHIC concentrates on the tracking of charged hadrons via ionization in gas- and silicon-based detectors, and the detection of electrons and photons via calorimetry, in a wide and azimuthally complete acceptance that’s unique at RHIC. STAR’s ability to directly identify the species of the tracked charged hadrons is however limited to “low” hadron momenta. Approximately 30% of the charged particles in the event at higher momenta cannot be directly identified, which hampers the physics reach of STAR in a number of key areas. To address this blind spot, STAR aims to surround the entire cylindrical surface of the tracking detectors with a large-area (∼50m2) time-of-flight (TOF) system based on the relatively new technology called the multi-gap resistive plate chamber (MRPC). Prototype TOF systems based on this technology were operated in STAR throughout the last two RHIC running periods. The design and operation of STAR’s MRPCs, the performance of the two prototype systems, and an overview of the design of the planned large-area system, will be discussed.

Optimization of momentum imaging systems using electric and magnetic fields

Time-of-flight (TOF) momentum imaging systems utilize the x, y, t information from charged particles striking a position-sensitive detector to infer the x, y, and z components of the particles’ initial momenta. This measurement capability can lead to the complete experimental determination of multi-ionization/fragmentation dynamics. In the case of electron detection, the addition of a magnetic field leads to a significantly increased operational energy range. This study shows that the TOF system has to be carefully designed in order to optimize the magnetic confinement effect. Expressions for the optimal dimensions of a single electric field TOF system are derived and factors contributing to the resolution are discussed, along with their application to an existing imaging system.

The Space Experiment PAMELA

We present in this paper a status report of the space experiment PAMELA. PAMELA is a satellite-borne experiment which primarily aims to measure the antiproton and positron spectra in the cosmic radiation over a large energy range (from 80 MeV up to 190 GeV for antiprotons and from 50 MeV up to 270 GeV for positrons) and to search for antinuclei with a sensitivity of the order of 10 −8 in the antihelium/helium ratio. In addition, it will measure the light nuclear component of cosmic rays and investigate phenomena connected with Solar and Earth physics. The apparatus will be installed onboard the polar orbiting Resurs DK1 satellite, which will be launched into space by a Soyuz TM2 rocket in 2004 from Baikonur cosmodrome in Kazakhstan, for a 3 year long mission. PAMELA consists of: a time of flight system, a transition radiation detector, a magnetic spectrometer, an anticoincidence detector, an electromagnetic imaging calorimeter, a shower tail catcher scintillator and a neutron detector.

The mesh PM for the AMS Time Of Flight, comparison between simulation and measurements

A simulation of fine mesh photomultipliers (PM) has been performed in order to understand their behavior in a magnetic field, in view of their use in the Time Of Flight system of the AMS-02 experiment, which is a cosmic ray spectrometer to be operated in space after 2006. The model on which the phototube simulation is based is described and a comparison with the experimental data are given. The simulation results can account for the apparent fine mesh low gain and bad single photoelectron resolution. The time response of a fine mesh in a magnetic field has been investigated with the use of the Monte Carlo, which also turned out to be a useful tool in understanding the change of PM gain as a function of the angle between the magnetic field and the PM axis. All the Monte Carlo results agree quite well with the data taken.

The Time Of Flight (TOF) system of the ALICE experiment

The double-stack Multigap Resistive Plate Chamber (MRPC) is the detector chosen for the large Time-Of-Flight system of the ALICE experiment at CERN LHC. The TOF barrel has to cover an area of 160 m2 and has to be highly segmented (160.000 readout pads of 2.5×3.5 cm2) in order to keep the occupancy at the 15% level. In this article recent results on several prototype MRPCs are presented, with particular emphasis on the study of the uniformity of these devices.

Laser-based calibration for the HARP time of flight system

A precise calibration and monitoring system has been developed for the HARP experiment scintillator-based time of flight system. An Nd-YAG laser with passive Q-switch and active/passive mode-locking and a custom-made laser light injection system based on a bundle of IR monomode optical fibers were used. The laser pulse timing was provided by a novel ultrafast InGaAs MSM photodiode, with 30 ps risetime. Experience over a several month data taking period in 2001 and 2002 shows that drifts in timing down to about 70 ps can be traced.

A single Time-of-Flight tray based on multigap resistive plate chambers for the STAR experiment at RHIC

The STAR experiment at RHIC plans to implement a 60m2 Time-of-Flight (TOF) system. The Multigap Resistive Plate Chamber (MRPC) is a suitable candidate for the STAR TOF system due to its time resolution of order of 60ps with efficiencies in excess of 97%. We obtained this result with modules composed of 6 gas gaps of 220μm and pad area of 20cm2. In this paper, we report on the performance of this MRPC module and present the current status of the construction and installation into STAR of a prototype tray.

The AMS-02 Time of Flight system

The Time-of-Flight (TOF) system of the AMS detector gives the fast trigger to the read out electronics and measures velocity, direction and charge of the crossing particles. The first version of the detector (called AMS-01) has flown in 1998 aboard of the shuttle Discovery for a 10 days test mission, and collected about 10 8 events. The new version (called AMS-02) will be installed on the International Space Station and will operate for at least three years, collecting roughly 10 10 Cosmic Ray (CR) particles. The TOF system of AMS-01 successfully operated during the test mission, obtaining a time resolution of 120 ps for protons and better for other CR ions. The TOF system of AMS-02 will be different due to the strong fringing magnetic field and weight constraints.

The CDF-II time-of-flight detector

A Time-of-Flight (TOF) detector, based on plastic scintillator and fine-mesh photomultiplier tubes, has been added to the CDF-II experiment. Since August 2001, the TOF system has been fully instrumented and integrated into the CDF-II data acquisition system. The TOF system will provide particle identification of low momentum charged pions, kaons and protons in pp̄ collisions. With a design resolution goal of about 100ps, separation between charged kaons and pions is expected at the 2 sigma level for momenta below 1.6GeV/c, which enhances CDF's b-flavor tagging capabilities. We describe the design of the TOF detector and discuss its on-line and off-line calibration. Some performance benchmarks using proton–antiproton collision data are presented.

A detailed Monte Carlo simulation for the Belle TOF system

We have developed a detailed Monte Carlo simulation program for the Belle time-of-flight (TOF) system. Based on GEANT simulation, it takes account of all physics processes in the TOF scintillation counters and readout electronics. The simulation reproduces very well the performance of the Belle TOF system, including the dE/dx response, the time walk effect, the time resolution, and the hit efficiency due to beam background. In this report, we will describe the Belle TOF simulation program in detail.

High voltage generator for the power supply of photomultipliers in the time of flight system of Alpha Magnetic Spectrometer-2 experiment

In this report, the behaviour of the first prototype high voltage generator (HVG) that might be used in the time of flight (TOF) system for the AMS-2 experiment is described. The system receives a positive continuous voltage about 100–120 V as input, and it provides a programmable negative continuous voltage from −1600 to −2400 V as output, versus a total load of 50 MΩ. The most important aspect is the absence of a transformer which usually is used in the step-up DC–DC converters. In the TOF system of alpha magnetic spectrometer (AMS)-2 experiment there is a big magnetic field, higher than 2 kG, that does not allow to use a transformer, therefore this prompted us to use the Cockroft–Walton system. The power consumption is about 300 mW and the peak-to-peak high frequency ripple is lower than 0.3% of the output high voltage. We also estimated the reliability of the HVG and we obtained a failure probability lower than 0.5% after three years of continuous functioning. Besides, in this report, much importance was given to the calculation of a simple model of the system to estimate the stability margins.

The PAMELA experiment in space

We provide in this paper a status report of the space experiment PAMELA. PAMELA aims primarily to measure the flux of antiparticles, namely antiprotons and positrons, in cosmic rays with unprecedented statistics over a large energy range. In addition, it will measure the light nuclear components of cosmic rays, investigate phenomena connected to Solar and Earth physics and it will search for cosmic ray antinuclei with sensitivity better than 10 −7 in the He /He ratio. PAMELA consists of a magnet spectrometer, a transition radiation detector, an imaging calorimeter, a time of flight system and an anticoincidence detector. The apparatus will be installed on board of the Russian satellite of the Resurs type in a polar orbit at about 680 km of altitude. The launch is foreseen for late 2002/early 2003.

Time-of-flight mass spectrometry (concepts, achievements, and prospects)

A brief account is given of the history of dynamic mass spectrometers from the time of their advent. The reasons for their relatively slow development in the 1930s–1940s of the last century are discussed. The general principle underlying the operation of all dynamic mass spectrometers, the difference between the velocities of motion of ions differing in mass but having the same energy, is pointed out. In accordance with its title, the review considers in more detail the history of development of time-of-flight (TOF) mass spectrometers and stresses their two major advantages over the static (magnetic) instruments, namely, the unlimited mass range and the possibility of obtaining extremely rapidly mass spectra over a broad ion mass range. This accounts for the fast progress in their performance and broad application in the period of 1960s–1980s, when investigation of heavy, thermally unstable organic molecules was started and efficient methods of producing their ions were developed. A serious limitation on the resolution of TOF instruments was largely removed after the formulation of the reflectron principle of TOF mass-spectrometer design. The problem of a further increase of the resolution of TOF systems is discussed. The illustrations of TOF reflectron applications are presented, and a possibility of analyzing molecules and clusters with masses of up to millions of daltons is pointed out. These merits have resulted in a sharp increase of production and a broadening of application potential of TOF mass spectrometers compared to the magnetic setups, particularly in the field of biophysics, biochemistry, and organic chemistry. In conclusion the broad horizons opened by the TOF magnetic-resonance mass spectrometers (MRMS) in the area of high-precision mass spectrometric measurements are pointed out.

TOF system at MALT – Measurement of 129I

At Micro-Analysis Laboratory Tandem (MALT), the University of Tokyo, we have developed a new Accelerator mass spectrometry (AMS) technique with a time-of-flight (TOF) detection system for the measurement of 129I. By measuring not only the TOF but also the energy of the ions, we were successful in the discrimination of 129I from the isotope 127I and another ion with almost the same velocity. The measurement is performed with a reproducibility of 9%. The sensitivity of the system is at a ratio of 10 −14.

Combined time-of-flight and Doppler ultrasonic tracking system for better performance in robot tracking

An integrated ultrasonic robot tracking system that combines both a time-of-flight (TOF) and a Doppler tracking system is introduced. As TOF and Doppler tracking systems both have advantages and limitations, better accuracy and resolution can be achieved in three-dimensional dynamic robot tracking by combining the two systems. In the paper, the working principles, structure and experimental results for the TOF, Doppler and the combined tracking system are described in detail.

Medium Energy Neutral Atom (MENA) Imager for the Image Mission

The Medium Energy Neutral Atom (MENA) imager was developed in response to the Imaging from the Magnetopause to the Aurora for Global Exploration (IMAGE) requirement to produce images of energetic neutral atoms (ENAs) in the energy range from 1 to 30 keV. These images will be used to infer characteristics of magnetospheric ion distributions. The MENA imager is a slit camera that images incident ENAs in the polar angle (based on a conventional spherical coordinate system defined by the spacecraft spin axis) and utilizes the spacecraft spin to image in azimuth. The speed of incident ENAs is determined by measuring the time-of-flight (TOF) from the entrance aperture to the detector. A carbon foil in the entrance aperture yields secondary electrons, which are imaged using a position-sensitive Start detector segment. This provides both the one- dimensional (1D) position at which the ENA passed through the aperture and a Start time for the TOF system. Impact of the incident ENA on the 1D position-sensitive Stop detector segment provides both a Stop-timing signal and the location that the ENA impacts the detector. The ENA incident polar angle is derived from the measured Stop and Start positions. Species identification (H vs. O) is based on variation in secondary electron yield with mass for a fixed ENA speed. The MENA imager is designed to produce images with 8 4 angular resolution over a field of view 140 360, over an energy range from 1 keV to 30 keV. Thus, the MENA imager is well suited to conduct measurements relevant to the Earth's ring current, plasma sheet, and (at times) magnetosheath and cusp.

Construction of a time-of-flight measurement system to study the low energy positronium production

Abstract To investigates the low energy positronium (Ps) production in terms of target temperatures and materials, surface condition and so on, we adopt the time-of-flight (TOF) method and perform extensive Monte Carlo simulation to design an apparatus. Under reasonable assumptions in the simulation with respect to an initial energy distribution of Ps, we examine how cleanly ortho-positronium (oPs) is observed without being subject to large backgrounds of 2γ decay from e+e− annihilation. The simulation finds that the contribution of 2γ events is suppressed by 10−6 smaller than the generated Ps by using the 2.5-cm thick W and 4.6-cm Pb collimators with slit gap of 1 mm. We inject slow positron beams on the W target installed in the TOF system and move the position of the target. Then we expect the position resolution of 1.5 mm resulting the accuracy of determining the oPs velocity 20%, corresponding to 1.1×106 cm/s for thermal Ps with 30 meV.

Time-of-flight PET

Time-of-Flight (TOF) positron emission tomographs (PET) were developed during the 1980s and early 1990s. Initial investigations into the potential improvements in signal-to-noise ratios if TOF information was utilized were published in 1980. By 1982, two groups (Washington University and Commissariat á l'Energie Atomique-Laboratorie d'Electronique et de L'Informatique [CEA-LETI]) were designing and building the first TOF tomographs. A third group at the University of Texas also designed and built a TOF system. These systems were optimized for high count-rate imaging of short-lived radiotracers for applications such as cardiac blood flow. The first system put into operation for patient scans was the Super PETT I built at Washington University by Michel Ter-Pogossian and his colleagues. The Washington University group went on to design two additional versions of TOF systems and the CEA-LETI group developed two basic tomograph designs. As Bismuth Germanate (BGO)-based scanners were refined, it became clear that the TOF systems could not provide the same high spatial resolution as offered by the newer systems. The use of the fast scintillators required for TOF systems also resulted in lower intrinsic sensitivity that was only partially compensated for by the effective gain in sensitivity offered by TOF image reconstruction techniques. Further development of TOF systems was suspended in the early 1990s. With the development of new scintillators that provide more light output and are denser than those available in the 1980s and considerably faster than BGO, there is new interest in the application of TOF techniques for future tomograph designs.