120213557
Strong Interaction Effects in Weak Radiative $\bar{B}$ Meson Decay
Strong-interaction corrections to the effective hamiltonian for weak radiative B-meson decay (i.e., B → Xsγ, where Xs denotes a strange hadronic final state) are calculated using the leading logarithmic approximation. The inclusive rate for decays B → Xsγ, where the energy of the photon is large, is computed in the standard model with minimal particle content and in extensions of the minimal standard model with two Higgs doublets.
56337141
Parity-violating neutron spin rotation in hydrogen and deuterium
AbstractWe calculate the (parity-violating) spin-rotation angle of a polarized neutron beam through hydrogen and deuterium targets, using pionless effective field theory up to next-to-leading order. Our result is part of a program to obtain the five leading independent low-energy parameters that characterize hadronic parity violation from few-body observables in one systematic and consistent framework. The two spin-rotation angles provide independent constraints on these parameters. Our result for np spin rotation is $$\frac{1}
{\rho }\frac{{d\varphi _{PV}^{np} }}
{{dl}} = \left[ {4.5 \pm 0.5} \right] rad MeV^{ - \frac{1}
{2}} \left( {2g^{\left( {^3 S_1 - ^3 P_1 } \right)} + g^{\left( {^3 S_1 - ^3 P_1 } \right)} } \right) - \left[ {18.5 \pm 1.9} \right] rad MeV^{ - \frac{1}
{2}} \left( {g_{\left( {\Delta {\rm I} = 0} \right)}^{\left( {^1 S_0 - ^3 P_0 } \right)} - 2g_{\left( {\Delta {\rm I} = 2} \right)}^{\left( {^1 S_0 - ^3 P_0 } \right)} } \right)$$, while for nd spin rotation we obtain $$\frac{1}
{\rho }\frac{{d\varphi _{PV}^{nd} }}
{{dl}} = \left[ {8.0 \pm 0.8} \right] rad MeV^{ - \frac{1}
{2}} g^{\left( {^3 S_1 - ^1 P_1 } \right)} + \left[ {17.0 \pm 1.7} \right] rad MeV^{ - \frac{1}
{2}} g^{\left( {^3 S_1 - ^3 P_1 } \right)} + \left[ {2.3 \pm 0.5} \right] rad MeV^{ - \frac{1}
{2}} \left( {3g_{\left( {\Delta {\rm I} = 0} \right)}^{\left( {^1 S_0 - ^3 P_0 } \right)} - 2g_{\left( {\Delta {\rm I} = 1} \right)}^{\left( {^1 S_0 - ^3 P_0 } \right)} } \right)$$, where the g(X-Y), in units of $$MeV^{ - \frac{3}
{2}}$$, are the presently unknown parameters in the leading-order parity-violating Lagrangian. Using naıve dimensional analysis to estimate the typical size of the couplings, we expect the signal for standard target densities to be $$\left| {\frac{{d\varphi _{PV} }}
{{dl}}} \right| \approx \left[ {10^{ - 7} \ldots 10^{ - 6} } \right]\frac{{rad}}
{m}$$ for both hydrogen and deuterium targets. We find no indication that the nd observable is enhanced compared to the np one. All results are properly renormalized. An estimate of the numerical and systematic uncertainties of our calculations indicates excellent convergence. An appendix contains the relevant partial-wave projectors of the three-nucleon system.
120537010
Hyperons and Hypernuclei
1267166
Can fermions save large N dimensional reduction
This paper explores whether Eguchi-Kawai reduction for gauge theories with adjoint fermions is valid. The Eguchi-Kawai reduction relates gauge theories in different numbers of dimensions in the large N limit provided that certain conditions are met. In principle, this relation opens up the possibility of learning about the dynamics of 4D gauge theories through techniques only available in lower dimensions. Dimensional reduction can be understood as a special case of large N equivalence between theories related by an orbifold projection. In this work, we focus on the simplest case of dimensional reduction, relating a 4D gauge theory to a 3D gauge theory via an orbifold projection. A necessary condition for the large N equivalence between the 4D and 3D theories to hold is that certain discrete symmetries in the two theories must not be broken spontaneously. In pure 4D Yang-Mills theory, these symmetries break spontaneously as the size of one of the spacetime dimensions shrinks. An analysis of the effect of adjoint fermions on the relevant symmetries of the 4D theory shows that the fermions help stabilize the symmetries. We consider the same problem from the point of view of the lower dimensional 3D theory and find that, surprisingly, adjoint fermions are not generally enough to stabilize the necessary symmetries of the 3D theory. In fact, a rich phase diagram arises, with a complicated pattern of symmetry breaking. We discuss the possible causes and consequences of this finding.
119535257
Heavy baryon chiral perturbation theory and the weak nonleptonic p-wave decays of the baryon octet
Abstract Considerable confusion in the literature about heavy baryon chiral perturbation theory, its convergence properties, and appropriate calculational techniques, make it timely to discuss the nonleptonic p-wave decays of the octet of baryons. We present model independent results.
118865932
Weak Radiative B Meson Decay
Weak radiative B meson decays, → γX s have a B meson decaying to a hard photon (i.e., E γ ≳ 2 GeV) and strange hadronic final states X s . The prediction of the standard model (with minimal particle content) for the rate for this process is reviewed. Particular attention is paid to the role of strong interaction corrections, which have a significant impact on the rate.
110934427
Experience in construction and testing of plastic limited streamer chambers
The manufacture and testing of multicell limited streamer chambers for use in the hadron calorimeter of the OPAL detector and LEP (Large Electron Positron Collider) are described. All operations, from chamber cathode coating to the testing of completed subassemblies, have been performed under the same roof. With reasonable care and quality control, the established technology produced chambers several meters long with an overall success rate of about 90%. Treatment of the carbon coating with Breox B-35 was effective in eliminating uncertainties in the cathode performance. >
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
67767062
Measurement of the Flux of UHE Cosmic Rays by the HiRes Detectors Observing in both Monocular and Stereo- scopic Modes
The High Resolution Fly’s Eye Detector (HiRes) detects and measures properties of ultra high energy cosmic rays (UHECR). The HiRes detector exploits the air fluorescence technique that 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 the fall of 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 a total of 4.0 years of observations in monocular mode. Preliminary results from both the monocular and stereo analysis will be described.
124438200
Preliminary stereo results from the High Resolution Fly's Eye cosmic ray observatory
The High Resolution Fly's Eye Cosmic Ray Ob- servatory consists of two detector sites located on hilltops in the western desert of Utah. The two sites are separated by 12.6 km. Stereoscopic observations from the two sites en- able the location of air showers to be more accurately recon- structed by using triangulation. The improved geometrical reconstruction provides for a more precise measurement of both the energy of the primary cosmic ray particle and the depth of the shower maximum. Preliminary results from ap- proximately 1000 hours of stereo on-time 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.