122726191
Observing ultra high energy cosmic rays with the High Resolution Fly’s Eye Detector
The High Resolution Fly’s Eye Detector (HiRes) detects and measures properties of ultra high energy, E>1018 eV, cosmic rays. HiRes exploits what is known as the “Air Fluorescence” technique which uses the atmosphere as a calorimeter. A brief description of this technique and how it is used by the HiRes detector will be given in this paper. The HiRes detector has been operational with two detector sites separated by 12.6 km since spring 1999. The two separated “eyes” enable the HiRes detector to obtain stereoscopic observations of the air showers. We also have a data set obtained with the first of the 2 sites from 2.5 years of observations in monocular mode. Preliminary results from both the monocular and stereo analysis will be described.The High Resolution Fly’s Eye Detector (HiRes) detects and measures properties of ultra high energy, E>1018 eV, cosmic rays. HiRes exploits what is known as the “Air Fluorescence” technique which uses the atmosphere as a calorimeter. A brief description of this technique and how it is used by the HiRes detector will be given in this paper. The HiRes detector has been operational with two detector sites separated by 12.6 km since spring 1999. The two separated “eyes” enable the HiRes detector to obtain stereoscopic observations of the air showers. We also have a data set obtained with the first of the 2 sites from 2.5 years of observations in monocular mode. Preliminary results from both the monocular and stereo analysis will be described.
124185401
Status of the High Altitude Water Cherenkov (HAWC) gamma ray observatory
73632090
Stereo Spectrum of UHECR showers at the HiRes Detector
We present a measurement of the energy spectrum of UHECR showers. This measurement uses the two HiRes detector sites separated by 12.6 km to perform stereoscopic observations of UHECR air showers. The technique of stereoscopic reconstruction of the shower geometry and longitudinal profile is described. The resolution of reconstructed shower parameters using these techniques has been estimated using a detector simulation. Using the independently measured shower profiles from each detector site the energy resolution has also been measured. The detector aperture has been estimated by using the detector simulation. The energy distribution and resultant energy spectrum will be shown.
122726191
Observing ultra high energy cosmic rays with the High Resolution Fly’s Eye Detector
The High Resolution Fly’s Eye Detector (HiRes) detects and measures properties of ultra high energy, E>1018 eV, cosmic rays. HiRes exploits what is known as the “Air Fluorescence” technique which uses the atmosphere as a calorimeter. A brief description of this technique and how it is used by the HiRes detector will be given in this paper. The HiRes detector has been operational with two detector sites separated by 12.6 km since spring 1999. The two separated “eyes” enable the HiRes detector to obtain stereoscopic observations of the air showers. We also have a data set obtained with the first of the 2 sites from 2.5 years of observations in monocular mode. Preliminary results from both the monocular and stereo analysis will be described.The High Resolution Fly’s Eye Detector (HiRes) detects and measures properties of ultra high energy, E>1018 eV, cosmic rays. HiRes exploits what is known as the “Air Fluorescence” technique which uses the atmosphere as a calorimeter. A brief description of this technique and how it is used by the HiRes detector will be given in this paper. The HiRes detector has been operational with two detector sites separated by 12.6 km since spring 1999. The two separated “eyes” enable the HiRes detector to obtain stereoscopic observations of the air showers. We also have a data set obtained with the first of the 2 sites from 2.5 years of observations in monocular mode. Preliminary results from both the monocular and stereo analysis will be described.
26918473
Geometry and optics calibration for air fluorescence detectors using star light
Abstract The high resolution Fly’s Eye (HiRes) detector in Dugway, Utah, is an air fluorescence detector designed for the measurement of the energy and arrival direction of cosmic ray particles with energy E >10 18 eV. HiRes monitors the night sky for fluorescence light from air shower cascades induced by cosmic ray primaries. The light is collected by mirrors and projected onto arrays of photomultiplier tubes that provide an image of the air shower. HiRes is an astronomical instrument, and the accuracy of the mirror pointing and understanding of the optical properties of the mirror–camera units is crucial. We present a method to cross-check and monitor the mirror pointing by using star light. A star crossing the field of view of a photomultiplier tube causes a temporary increase in the total light detected by the tube. Using UV bright stars, we analyze the pointing accuracy of the HiRes 2 detector, and evaluate the shape of a point-like object as a function of distance to the mirror axis.
120505412
PHOTOCATHODES IN ACCELERATOR APPLICATIONS
PHOTOCATHODES IN ACCELERATOR APPLICATIONS* J. S. Fraser, R. L. Sheffield, E. Gray, P. M.Giles, R. W. Springer and A. Loebs, MS-H825 Los Alamos National Laboratory, Alamos, NM 87545 Abstract Some electron accelerator applications require bursts of short ulses at high microscopic repetition rates and high pea E brightness. A illuminated by a mode-locked laser, is well suited to filling this need. The intrinsic brightness of a photoemitter beam is high; experiments are under way at Los Alamos to study the brightness of short bunches with hi h s ace charge after acceleration. A laser-illuminated E s,S t photoemitter is located in the first rf cavity of an injector linac. Diagnostics include pep er-pot emittance analyzer, a magnetic spectrometer, an 2 a streak camera. Introduction Electron accelerator applications that require a beam of high peak brightness as well a high pulse-repetition rate put severe demands on the electron source and injector. The conventional solution to this problem is to use a pulsed thermionic emitter of low peak brightness followed by a bunching, or phase compression, system that increases the peak current by a large factor. Ideally, the FJ eak brightness should increase in proportion to the unching factor; in however, the result always falls short of the ideal. An additional shortcoming; in the conventional buncher is that a repetition rate in excess of a few tens of megahertz is beyond the state of the art electronically swrtching a thermionic triode electron gun. There have been several reports of diode and triode guns operated in an rf cavity to produce electron pulses of width somewhat less than one-quarter of the rf period.1-3 The ultimate upper limit to this technique for triode guns may be the power dissi ation in the grid. In current app F lcations of rf-driven free-electron lasers, trains of over 300-A, 16-ps-wide (5nC charge) pulses are being used.4 Recent success 5 with the production of high peak currents from a laser-illuminated photocathode shows that high repetition rates in peak-brightness electron beams may be possible. At the Los Alamos National Laboratory, a program is under way to develop a high peak brightness, average current photoelectron injector. The Los Alamos Photoinjector Program 1985, the achievement of hi!h peak currents from a Cs,Sb uhotocathode was reported. It has been shown that thg laser-driven photocathode produces an intrinsically bright beam.‘j It remains to be demonstrated that short bunches can be accelerated to relativistic energies without loss of brightness. It is evident from simulation studies70f the acceleration of short bunches in an rf cavity that dense s lp ace charge the external rf field lead to a degradation o beam quality and, therefore, to a loss of brightness. Although pulses of only a few picoseconds can be produced in a photocathode, it now seems advisable to generate pulses that initially are about 100 ps long and thin, after acceleration to about 10 MeV, bunch them magnetically.8 Acceleration of the longer bunches is best done in a low-frequency linac at subharmonic of the main linac frequency.g Nevertheless, there is a strong incentive to accelerate the bunches as rapidly as possible, a condition that can be met only with high-frequency rf fields.‘O A study of the envelope equation Ref. 11 reveals that, for continuous beams, the dominance of space charge over emittance is adiabatically damped as Y-“~. A *Work performed under the auspices of U.S. Department of Energy and supported by the U.S. Army Strategic Defense Command. paper in these proceedinps’2 shows that for bunched beams, the damping dependence on energy is much stronger, namely y- . Therefore. the reauirement of maximum acceleratin gradient (hence a hiih frequency) to minimize the in if uence of space charge must be balanced against a conflicting need to accept long pulses (hence a low frequency to reduce the emittance growth associated with rf fields). The conceptual design of a subharmonic injector linac with an rf gun electron source has been described earlier.g The initial rf gun experiments, however, are being carried out at a high frequency because powerful klystron was available for use at 1300 MHz. A schematic diagram of the Los Alamos injector experiment is shown in Fig. 1. OtlnRTz SCHkCN -j Fig. 1. Plan view of the photoinjectorexperiment. Photocathode Design In recent years, photocathodes for sources have been made from wafers of B olarized electron aAs.13*14 Curre?! densities as high 180 A/cm2 have been reported. Photoemitters of Cs,Sb are less demanding o system cleanliness15 than are those of GaAs. An additional advantage of a positive electron affinity semiconductor like Cs,Sb lies in rapid emissio? of Jhe photoelectrons. l6 By contrast, the intrinsic emission-time uncertainty of GaAs has been measured in the range from 71 ps for active layers between 50 nm and 2 pm in thickness.16 A cesium antimonide (Cs Sb) photocathode was chosen for its ease of preparation within the vacuum environment linac and for its relative tolerance vacuum conditions in the injector linac.15 A photoinjector linac must be bakeable in its entirety to about 200°C ;nd be capable of maintaining a preferably lo-‘Otorr. If a Cs, b hotocathode LS damaged ,rrre below . lo- torr, in use, the damage can be erased y heating to 4OO”C, then a new one prepared in situ. The spectral response17 of Cs Sb extends from a quantum energy of 1.8 eV (A = B90 nm) to energies greater than 3.8 eV (A < 320 nm). Therefore, a Cs,Sb F hotocathode can be used with Nd:YAG laser doubled (A = 532 nm) or tripled (A = 355 nm). ?&%;;‘lG laser can readilv be mode-locked to deliver trains of 60-ps pulses at a microscopic repetition rate in a range from 120 MHz. Rf Gun Cavity Design The highest cavity is limited l!l ossible acceleration rate in rf .gu+n y the sparking breakdown characterlstlc of the cavity. A typical rf cavity, optimized for maximum effective shunt im edance ZT2, will have a ratio of peak surface electric fie acceleration gradientlo of about 6. A lower ratio, a larger maximum 1705 CH2387.9:87!000(- $ I .oO Q IEEE
118694674
Weak radiative B decays in the standard model and beyond
A discussion of the inclusive decays B → Xsγ and B → Xse+e− is given (Xs is a strange hadron), along with possible exclusive decay results from application of the Isgur‐Wise symmetry. The leading logarithmic strong interaction corrections are included. Decay rates for B → Xsγ include those predictions from the minimal standard model, the standard model with two Higgs doublets, and the minimal supersymmetric model. Decay rates for B → Xse+e− are reviewed in the standard model and the two Higgs doublet model.
85525002
The Theory of Parity Violation in Few-Nucleon Systems
Abstract We review recent progress in the theoretical description of hadronic parity violation in few-nucleon systems. After introducing the different methods that have been used to study parity-violating observables we discuss the available calculations for reactions with up to five nucleons. Particular emphasis is put on effective field theory calculations where they exist, but earlier and complementary approaches are also presented. We hope this review will serve as a guide for those who wish to know what calculations are available and what further calculations need to be completed before we can claim to have a comprehensive picture of parity violation in few nucleon systems.
120537010
Hyperons and Hypernuclei
119190019
An effective-field-theory analysis of low-energy parity-violation in nucleon–nucleon scattering
Abstract We analyze parity-violating nucleon–nucleon scattering at energies E m π 2 / M using the effective field theory appropriate for this regime. The minimal Lagrangian for short-range parity-violating NN interactions is written in an operator basis that encodes the five partial-wave transitions that dominate at these energies. We calculate the leading-order relationships between parity-violating NN asymmetries and the coefficients in the Lagrangian and also discuss the size of sub-leading corrections. We conclude with a discussion of further observables needed to completely determine the leading-order Lagrangian.
119971093
Effective hamiltonian for weak radiative B-meson decay☆
Abstract The inclusive rate for decay of a B-meson to a hard photon and strange hadronic final states (i.e., B→γXs with X s = K ∗ , etc.), is likely to be dominated by short-distance physics which gives rise to an effective hamiltonian that is a magnetic-moment-type operator. Strong interaction corrections to this hamiltonian are computed in the leading logarithmic approximation.