Elementary Particle Physics Experiments Research Articles

Indirectly cooled secondary-particle production target at J-PARC Hadron Experimental Facility

The Hadron Experimental Facility at the Japan Proton Accelerator Research Complex is used for various nuclear and elementary particle physics experiments that use secondary particle beams. The secondary-particle production target is a key element for the generation of particles such as kaons and pions. To increase beam power, a new target was developed and installed. The target, which is made of gold and indirectly cooled with water, was designed so that the maximum stresses do not exceed the allowable stresses determined based on the pressure vessel standard. 95 kW is considered to be the maximum power of the primary proton beam for a 5.2-s beam duration. The new target was stably operated up to a power of 65 kW. In addition, beam position estimation based on multipoint temperature measurements of the target was demonstrated.

Role of native and impurity defects in optical absorption and luminescence of Li2MoO4 scintillation crystals

The Li2MoO4 crystals have been considered as perspective cryogenic scintillation materials to be used in elementary particle physics experiments related to dark matter search and properties of neutrino. Since the crystals may be used as cryogenic scintillators, the native vacancies, uncontrolled impurities and other defects play the key role in worsening of their scintillation characteristics. The paper presents complex experimental and computational studies of the electronic structure and optical properties of Li2MoO4 crystals. The studies are aimed to explain peculiarities of the optical (luminescence) properties of Li2MoO4 using the electronic structure results obtained for a wide range of point defects and their combinations. For investigations, several samples of Li2MoO4 with different defectiveness were grown using Czohralski method and characterized by SEM and ICP-OES technique. Luminescence emission spectra of the samples under X-ray and laser excitations, optical and IR absorption spectra, TSL characteristics of the samples were recorded and analyzed. Ability to incorporate some gases was examined by measuring absorption spectra after one-year storage of the samples at ambient conditions. The electronic structures of several kinds of point defects (natural vacancies, iso- and aliovalent cationic and anionic substitutions, interstitial ions and molecular groups) in Li2MoO4 were calculated using the DFT-based plane-wave pseudopotential method. Geometries of lattice relaxations around defects, partial densities of states and energies of defect formation were calculated and analyzed together with experimental results. Performed analysis allowed making several conclusions regarding the origin of spectral components of intrinsic and defect-related luminescence, formation of defect-related bands in the optical and IR absorption spectra, dependence of TSL characteristics on sample defectiveness. It was found that isovalent cationic substitutions on lithium positions are presented in substantial concentrations in the Li2MoO4 samples and such defects form shallow traps which can affect scintillation characteristics in cryogenic experiments. Substantial effect of gases inclusions on the optical characteristics of crystals can be related to the peculiarity of the crystal lattice structure - the presence of empty "channels", which can incorporate molecular objects like H2O, -CH3 or -OH.

Particle production reactions in laser-boosted lepton collisions

The need for ever higher energies in lepton colliders gives rise to the investigation of new accelerator schemes for elementary particle physics experiments. One perceivable way to increase the collision energy would be to combine conventional lepton acceleration with strong laser fields, making use of the momentum boost a charged particle experiences inside a plane electromagnetic wave. As an example for a process taking place in such a laser-boosted collision, Higgs boson creation is studied in detail. We further discuss other possible particle production processes that could be implemented in such a collider scheme and specify the required technical demands.

A pulse shape discrimination method with csi using the ratio of areas for identifying neutrons and gamma rays

Identification of gamma rays and neutrons is a fundamental technique used in elementary particle physics experiments, such as the search for dark matter, double beta decay, etc. The pulse shape discrimination (PSD) methods with liquid and crystal scintillators, a well-known technology, have been under development for several decades. The PSD methods with crystal scintillators are known to be less stable and less effective than PSD methods with liquid crystals. Here, an improved PSD technique with a CsI crystal scintillator based on the well-known PSD methods with liquid scintillators is introduced. In this study, we found the possibility that the proposed PSD with a CsI crystal scintillator provides a performance to discriminate gamma rays and neutrons equivalent to that of a PSD with a liquid scintillator.

Fast High Resolution Position-Sensitive Gaseous Detectors

The present review describes a new coordinate detectors based on gas micro-pattern technology, which are applied in experiments in elementary particle physics and with SR beams. The microstrip gas chambers (MSGC) on substrates with electronic conductivity are presented in the paper. Such detectors are shown to have spatial resolution better than 100 micron and to be able to effectively operate at particle rates up to 106 s-1mm-2, that at least by two orders of magnitude higher than rate capability of multiwire proportional chambers. Essential part of the review is devoted to studies of the cascades of gas electron multipliers (GEM). In particular, the dependence of gas amplification and conditions of a discharge occurrence on the number of GEMs in cascade, on the distribution of potentials between GEMs in cascade and on gas mixture in the presence of hadron flux are discussed. Gas micro-pattern technology is widely used for the development of coordinate detectors. In the present review we describe as an example the detectors with triple GEM cascades for the tagging system of the KEDR experiment at the VEPP-4M collider

OPTIMIZATION OF TAU IDENTIFICATION IN ATLAS EXPERIMENT USING MULTIVARIATE TOOLS

Elementary particle physics experiments, which search for very rare processes, require the efficient analysis and selection algorithms able to separate a signal from the overwhelming background. Four learning machine algorithms have been applied to identify τ leptons in the ATLAS experiment: projective likelihood estimator (LL), Probability Density Estimator with Range Searches (PDE-RS), Neural Network, and the Support Vector Machine (SVM). All four methods have similar performance, which is significantly better than the baseline cut analysis. This indicates that the achieved background rejection is close to the maximal achievable performance.

Implementation of the SVM algorithm for high energy physics data analysis

Elementary particle physics experiments, searching for very rare processes require the efficientanalysis and selection algorithms able to separate signal from the overwhelming background. Inthe last ten years a number of powerful kernel-based learning machines, like Support VectorMachines (SVM), have been developed. SVM approach to signal and background separation isbased on building a separating hyperplane defined by the support vectors. The margin betweenthem and the hyperplane is maximized. The extensions to a non-linear separation are performed bymapping the input vectors into a high dimensional space, in which data can be linearly separated.The use of kernel functions allows us to perform computations in a high dimension feature spacewithout explicitly knowing a mapping function.We have implemented an SVM algorithm and integrated it with the CERN ROOT package,which is currently a standard analysis tool used by elementary particle physicists. We also used theimplemented SVM package to identify hadronic decays of τ leptons in the ATLAS experiment atLHC accelerator. The performance of the method is compared to the likelihood estimator, whichdoes not take into account correlations between variables. The use of SVM significantly reducesthe number of background events.

Epitaxial silicon detectors for particle tracking—Radiation tolerance at extreme hadron fluences

Diodes processed on n-type epitaxial silicon with a thickness of 25, 50 and 75 μm had been irradiated with reactor neutrons and high-energy protons (24 GeV/ c) up to integrated fluences of Φ eq=10 16 cm −2. Systematic experiments on radiation-induced damage effects revealed the following results: in contrast to standard and oxygen-enriched float zone (FZ) silicon devices no space charge sign inversion was observed after irradiation. It is shown that the radiation-generated concentration of deep acceptors, dominating the behavior of n-type FZ diodes, is compensated by creation of shallow donors. Thus a positive space charge is maintained throughout the irradiation up to the highest fluence and even during prolonged elevated-temperature annealing cycles. Defect analysis studies using thermally stimulated current measurements attribute the effect to a damage-induced shallow donor at E C−0.23 eV. It is argued that, as in the case of thermal donors, oxygen dimers, out diffusing from the Cz substrate during the diode processing, are responsible precursers. Results from extensive annealing experiments at elevated temperatures are verified by comparison with prolonged room-temperature annealing. These results showed that in contrast to FZ detectors, which always have to be cooled, room-temperature storage during beam off periods of future elementary particle physics experiments would even be beneficial for n-type epi-silicon detectors. A dedicated experiment at CERN-PS had successfully proven this expectation. It was verified, that in such a scenario the depletion voltage for the epi-detector could always be kept at a moderate level throughout the full S-LHC operation (foreseen upgrade of the large hadron collider). Practically no difference with respect to FZ-silicon devices was found in the damage-induced bulk generation current. The charge trapping measured with 90Sr electrons (mip's) is also almost identical to what was expected. A charge collection efficiency of 60% (2500 e) in 50 μm n-type epi-diodes after 24 GeV/ c proton irradiation with Φ eq=6.2×10 15 cm −2 was reported recently, independent of the operating temperature down to −20 °C.

Future semiconductor detectors using advanced microelectronics with post-processing, hybridization and packaging technology

Several challenges for tracking with semiconductor detectors in the high rate environment of future elementary particle physics experiments are discussed, such as reduction of spurious hits and ambiguities and identification of short-lived ‘messenger’ particles inside jets. To meet these requirements, the instrumentation increasingly calls on progress in microelectronics. Advanced silicon integration technology for 3D packaging now offers post-processing of CMOS such as wafer thinning to 50 μm and through-wafer vias of <10 μm. These technologies might be applied to create new tracking detectors which can handle vertexing under the difficult rate conditions. The sensor layers can be only ∼50 μm thick with low-noise performance and better radiation hardness by using small volume pixels. Multi-layer sensors with integrated coincidence signal processing could discriminate real tracks from various sources of background. Even in a ∼400 μm thick 3D assembly, the vectors of tracks can be determined in ∼10° bins and this multi-voxel device is called ‘vector detector’. The measured vectors can be used to associate the main tracks to their vertices in the interaction region at high luminosity colliders and to establish an on-line, first-level trigger signature.

Facts of life with $\gamma_5$

The increasing precision of many experiments in elementary particle physics leads to continuing interest in perturbative higher order calculations in the electroweak Standard Model or extensions of it. Such calculations are of increasing complexity because more loops and/or more legs are considered. Correspondingly efficient computational methods are mandatory for many calculations. One problem which affects the feasibility of higher order calculations is the problem with gamma(5) in dimensional regularization. Since the subject thirty years after its invention is still controversial I advocate here some ideas which seem not to be common knowledge but might shed some new light on the problem. I present arguments in favor of utilizing an anticommuting gamma(5) and a simple 4-dimensional treatment of the hard anomalies.

The Physical Review: The First Hundred Years. A Selection of Seminal Papers and Commentaries

Contents: 1. The Physical Review: Then and Now. 2. Hundred Years of The Physical Review 3. The Early Years 1893-1930 4. Atomic Physics 5. Nuclear Physics. 6. Statistical Physics, Integrable, and Chaotic Systems. 7. Gravity Physics and Cosmology. 8. Cosmic Radiation: Discoveries Reported in The Physical Review 9. Condensed Matter. 10. Plasma Physics. 11. Elementary Particle Physics Experiments. 12. A Century of Particle Theory. 13. Science and Technology. 14. Quantum Mechanics: Does the Wave Function Provide a Complete Description of Physical Reality?

Cryogenic detectors for experiments in elementary particle physics

The development of cryogenic detectors is largely motivated by the need for very good energy resolution in a number of particle physics experiments, and by the need to detect very small energy depositions. Good energy resolution can be obtained by utilizing the smallness of the superconducting energy gap or detecting the phonons which are produced by particle interactions. These detection schemes require low temperatures, where in addition the thermal fluctuations are small compared to the minute energies expected to be deposited in some experiments. Moreover, cryogenic detectors permit the tailoring of the target or absorber materials to match the particle physics goals. The basic physics behind the detection of excitations induced by particle interactions in bulk single crystal materials is reviewed, and recent results on the efficient detection of these excitations with series arrays of superconducting tunnel junctions are presented. Progress towards the implementation of particle physics experiments, such as the detection of low energy solar neutrinos, search for dark matter particles, search for neutrinoless double beta-decay and precision observation of a 17 keV neutrino in beta-decay, using cryogenic detectors is reviewed.

Effects of ionising radiation on the noise properties of electron devices and monolithic circuits

Experiments in elementary particle physics with accelerators of the collider type employ detectors very close to the beam pipe, so that the front-end preamplifiers associated with these detectors are subject to the field of ionising radiation present in the interaction region of the accelerator. The front-end preamplifiers have, accordingly, to be designed with a sufficient degree of radiation tolerance. The present paper aims at discussing some experimental observations concerning the degradation of the noise behaviour of active devices and monolithic preamplifiers after exposure to ionising radiation. Such an experimental analysis led to the design of radiation-tolerant, low noise circuits that will be employed in the Aleph experiment at LEP.

A large, high-speed memory buffer for high energy physics data

Abstract Many high-data-rate experiments in elementary particle physics suffer large dead-times due to the slow speeds with which the on-line computer can read in data from each event. To eliminate this bottle-neck, we have designed, constructed, and made extensive use in a physics experiment of a 4 megabyte memory buffer which employs ordinary dynamic RAM memory chips and which accepts all of our event data generated during a beam spill at Fermilab at a rate of 14 Mbyte per second.

The silicon micropattern detector: A dream?

The present use of silicon microstrip detectors in elementary particle physics experiments is described and future needs are evaluated. Possibilities and problems to be encountered in the development of a true two-dimensional detector with intelligent data collection are discussed. This paper serves as an introduction to various other contributions to the conference proceedings, either dealing with futuristic device designs or with cautious steps on the road of technology development.