116914560
Physicists make the most of antimatter.
121760874
Some Hadron Calorimeter Properties Relevant to Storage Rings
At wide angles in a storage ring environment, a substantial part of the energy seen by a hadron calorimeter can be in the form of very low momentum particles such as jet fragments or resonance cascade decay products. Data are presented on the deviations from Gaussian resolution and linear response for such low momentum particles. The differing responses to incident e-, μ-, π+-, K+-, p and at momenta below 10 GeV/c are also compared. In addition, we discuss the significance of angle effects for a 4π calorimeter, and the problems of combining data from calorimeters with different physical characteristics. Experimental data are presented on the difference in hadron response between a fine grain ("electromagnetic") lead calorimeter and a coarser ("hadron") iron calorimeter, and on the dependence of the response on the energy sharing between the two calorimeters.
117258763
A study of nucleon isobar production in proton-proton collisions
SummaryThe momentum spectra of protons scattered inelastically in proton-proton collisions were obtained in an external beam at NIMROD, using incident-proton momenta of 2.85, 4.55, 6.06 and 7.88 GeV/c, and various scattering angles in the range 22 to 144 mrad. The isobars of mass 1236, 1518 and 1688 MeV are clearly seen. There is evidence also in the spectra at small angles for the production of the 1410 MeV isobar at a mass of (1410±15) MeV and width (125±20) MeV. It is shown that the observed peak cannot be explained by the Deck effect. The differential cross-sections for the production of these isobars are presented in terms of the usual variabless andt, and are compared with absorption and Regge-pole model predictions. Fits to the data with various empirical functions of these variables are also investigated. The behaviour of the total cross-section for the 1236 MeV isobar is found to exhibit energy-dependence consistent with one-pion exchange, whereas the 1410 MeV and 1688 MeV isobar total cross-sections are found to be energy-independent. Also the total cross-section for the 1518 MeV isobar is found to exhibit energy-dependence in this energy range.RiassuntoSi sono ottenuti gli spettri delle quantità di moto dei protoni diffusi anelasticamente nelle collisioni protone-protone ottenute in un raggio esterno di NIMROD, usando quantità di moto del protone incidente di 2.85, 4.55, 6.06 e 7.88 GeV/c, e vari angoli di scattering da 22 a 144 mrad. Si vedono chiaramente gli isobari di massa 1236, 1518 e 1688 MeV. Si hanno anche prove negli spettri a piccoli angoli della produzione dell’isobaro da 1410 MeV di massa (1410±15) MeV e ampiezza (125±20) MeV. Si dimostra che il picco osservato non può essere spiegato con l’effetto Deck. Si presentano le sezioni d’urto differenziali per la produzione di questi isobari in funzioni delle usuali variabilis et, e si confrontano con le previsioni del modello dei poli di Regge e del modello di assorbimento. Si studiano anche le approssimazioni ai dati con varie funzioni empiriche di queste variabili. Si trova che il comportamento della sezione d’urto totale per l’isobaro da 1236 MeV presenta una dipendenza dall’energia che concorda con lo scambio di un pione, mentre le sezioni d’urto degli isobari da 1410 MeV e 1688 MeV risultano indipendenti dall’energia. Si trova che anche la sezione d’urto totale presenta una dipendenza dall’energia in questo intervallo di energie.РеэумеПолучаются импульсные спектры протонов, неупруго рассеянных в протон-протонных соударениях во внещнем пучке в HИMPOД, испольэуя импульсы падаюших протонов 2.85, 4.55, 6.06 и 7.88 ГЭB/c, и раэличные углы рассеяния в области от 22 до 144 миллирадиан. Четко видны иэобары с массами 1236, 1518 и 1688 MЭB. Также имеется подтверждение в спектрах при малых углах для рождения иэобары 1410 MЭB с массой (1410±15) MЭB и щириной (125±20) MЭB. Покаэывается, что наблюденный пик не может быть общяснен с помошью Эффекта Дека. Представлены дифференциальные поперечные сечения для рождения Этих иэобар в терминах обычных переменныхs иt, которые сравниваются с предскаэаниями моделей поглошения и полюсов Редже. Также исследуются подгонки для Этих данных с помошью раэличных Эмпирических функций Этих переменных. Найдено, что поведение полного поперечного сечения для иэобары 1236 MЭB обнаруживает Энергетическую эависимость, согласуюшуюся с одно-пионным обменом, в то зе время получено, что полные поперечные сечения иэобар 1410 MЭB и 1688 MЭB не эависят от Энергии. Также найдено, что полное поперечное сечение для иэобары 1518 MЭB обнаруживает эависимость от Энергии в Этой области Энергий.
120152123
Particle physics at the turn of the century
Aspects of particle physics are reviewed from an experimental viewpoint. The elementary constituents of the Universe are described, as are the fundamental forces through which they interact. Recent results are emphasized and there is some speculation about the future. No attempt has been made to give a complete bibliography, but a few references to recent reviews and original articles are given. A glossary of acronyms is included.
123687310
Antiproton--proton annihilation into charged pion and kaon pairs
Events of the type anti pp $Yields$ K$sup -$K$sup +$, $pi$$sup - $$pi$$sup +$ were studied at 0.79 to 2.43 GeV/c. Differential cross sections and Legendre coefficient ratios are shown. Resonances found as a result of model fitting showing spin--parity assignment versus mass squared are also shown. (JFP)
123678522
Options for machines and experiments in the future
The highest energy particle accelerators in operation and under construction are described briefly, together with a selection of detectors. Extrapolations of existing techniques both for accelerators and for detectors appear to be adequate for the next upward step in energy, but beyond this new techniques will probably have to be developed. Some predictions are given.
11311944
Precise calibration of LIGO test mass actuators using photon radiation pressure
Precise calibration of kilometer-scale interferometric gravitational wave detectors is crucial for source localization and waveform reconstruction. A technique that uses the radiation pressure of a power-modulated auxiliary laser to induce calibrated displacements of one of the ~10 kg arm cavity mirrors, a so-called photon calibrator, has been demonstrated previously and has recently been implemented on the LIGO detectors. In this paper, we discuss the inherent precision and accuracy of the LIGO photon calibrators and several improvements that have been developed to reduce the estimated voice coil actuator calibration uncertainties to less than 2% (1σ). These improvements include accounting for rotation-induced apparent length variations caused by interferometer and photon calibrator beam centering offsets, absolute laser power measurement using temperature-controlled InGaAs photodetectors mounted on integrating spheres and calibrated by NIST, minimizing errors induced by localized elastic deformation of the mirror surface by using a two-beam configuration with the photon calibrator beams symmetrically displaced about the center of the optic and simultaneously actuating the test mass with voice coil actuators and the photon calibrator to minimize fluctuations caused by the changing interferometer response. The photon calibrator is able to operate in the most sensitive interferometer configuration, and is expected to become a primary calibration method for future gravitational wave searches.
36815013
Prospects of gravitational wave data mining and exploration via evolutionary computing
Techniques of evolutionary computing have proven useful for a diverse array of fields in science and engineering. Because of the expected low signal to noise ratio of LIGO data and incomplete knowledge of gravitational waveforms, evolutionary computing is an excellent candidate for LIGO data analysis studies. Using the evolutionary computing methods of genetic algorithms and genetic programming, we have developed, as a proof of principle, search algorithms that are effective at finding sine-gaussian signals hidden in noise while maintaining a small false alarm rate. Because we used realistic LIGO noise as a training ground, the algorithms we have evolved should be well suited to detecting signals in actual LIGO data, as well as in simulated noise. These algorithms have continuously improved during the five days of their evolution and are expected to improve further the more they are evolved. The top performing algorithms from generation 100 and 199 were benchmarked using gaussian white noise to illustrate their performance and the improvement over 100 generations.
44041464
Inferring core-collapse supernova physics with gravitational waves
Stellar collapse and the subsequent development of a core-collapse supernova explosion emit bursts of gravitational waves (GWs) that might be detected by the advanced generation of laser interferometer gravitational-wave observatories such as Advanced LIGO, Advanced Virgo, and LCGT. GW bursts from core-collapse supernovae encode information on the intricate multidimensional dynamics at work at the core of a dying massive star and may provide direct evidence for the yet uncertain mechanism driving supernovae in massive stars. Recent multidimensional simulations of core-collapse supernovae exploding via the neutrino, magnetorotational, and acoustic explosion mechanisms have predicted GW signals which have distinct structure in both the time and frequency domains. Motivated by this, we describe a promising method for determining the most likely explosion mechanism underlying a hypothetical GW signal, based on principal component analysis and Bayesian model selection. Using simulated Advanced LIGO noise and assuming a single detector and linear waveform polarization for simplicity, we demonstrate that our method can distinguish magnetorotational explosions throughout the Milky Way (D≲10  kpc) and explosions driven by the neutrino and acoustic mechanisms to D≲2  kpc. Furthermore, we show that we can differentiate between models for rotating accretion-induced collapse of massive white dwarfs and models of rotating iron core collapse with high reliability out to several kpc.
14925786
Benefits of artificially generated gravity gradients for interferometric gravitational-wave detectors
We present an approach to experimentally evaluate gravity gradient noise, a potentially limiting noise source in advanced interferometric gravitational-wave detectors. In addition, the method can be used to provide sub-percent calibration in phase and amplitude. Knowledge of calibration to such certainties shall enhance the scientific output of the instruments in the case of an eventual detection of gravitational waves. The method relies on a rotating symmetrical two-body mass, a dynamic gravity field generator (DFG). The placement of the DFG in the proximity of one of the interferometer's suspended test masses generates a change in the local gravitational field detectable with current interferometric gravitational-wave detectors.
118446989
Stacking gravitational wave signals from soft gamma repeater bursts
Soft gamma repeaters (SGRs) have unique properties that make them intriguing targets for gravitational wave (GW) searches. They are nearby, their burst emission mechanism may involve neutron star crust fractures and excitation of quasinormal modes, and they burst repeatedly and sometimes spectacularly. A recent LIGO search for transient GW from these sources placed upper limits on a set of almost 200 individual SGR bursts. These limits were within the theoretically predicted range of some models. We present a new search strategy which builds upon the method used there by “stacking” potential GW signals from multiple SGR bursts. We assume that variation in the time difference between burst electromagnetic emission and burst GW emission is small relative to the GW signal duration, and we time-align GW excess power time-frequency tilings containing individual burst triggers to their corresponding electromagnetic emissions. Using Monte Carlo simulations, we confirm that gains in GW energy sensitivity of N^(1/2) are possible, where N is the number of stacked SGR bursts. Estimated sensitivities for a mock search for gravitational waves from the 2006 March 29 storm from SGR 1900+14 are also presented, for two GW emission models, “fluence-weighted” and “flat” (unweighted).