2,117 Matching Results

Search Results

Advanced search parameters have been applied.

Type Ia Supernova Spectral Line Ratios as LuminosityIndicators

Description: Type Ia supernovae have played a crucial role in thediscovery of the dark energy, via the measurement of their light curvesand the determination of the peak brightness via fitting templates to theobserved lightcurve shape. Two spectroscopic indicators are also known tobe well correlated with peak luminosity. Since the spectroscopicluminosity indicators are obtained directly from observed spectra, theywill have different systematic errors than do measurements usingphotometry. Additionally, these spectroscopic indicators may be usefulfor studies of effects of evolution or age of the SNe~;Ia progenitorpopulation. We present several new variants of such spectroscopicindicators which are easy to automate and which minimize the effects ofnoise. We show that these spectroscopic indicators can be measured byproposed JDEM missions such as snap and JEDI.
Date: December 7, 2005
Creator: Bongard, Sebastien; Baron, E.; Smadja, G.; Branch, David & Hauschildt, Peter H.
Partner: UNT Libraries Government Documents Department

Rad-hard Luminosity Monitoring for the LHC

Description: Luminosity measurements at the high luminosity points of the LHC are very challenging due to the extremely high radiation levels in the order of 180 MGy/yr. They have designed an ionization chamber that uses a flowing inorganic gas mixture and a combination of metals and ceramics. With such a choice, an additional challenge is achieving the necessary speed to be able to resolve bunch-by-bunch luminosity data. They present the design, analysis and experimental results of the early demonstration tests of this device.
Date: June 24, 2007
Creator: Beche, J.F.; Byrd, J.M.; Chow, K.; Denes, P.; Ghiorso, W.; Matis,H.S. et al.
Partner: UNT Libraries Government Documents Department

The readout of the LHC beam luminosity monitor: Accurate shower energy measurements at a 40 MHz repetition rate

Description: The LHC beam luminosity monitor is based on the following principle. The neutrals that originate in LHC at every PP interaction create showers in the absorbers placed in front of the cryogenic separation dipoles. The shower energy, as it can be measured by suitable detectors in the absorbers is proportional to the number of neutral particles and, therefore, to the luminosity. This principle lends itself to a luminosity measurement on a bunch-by-bunch basis. However, detector and front-end electronics must comply with extremely stringent requirements. To make the bunch-by-bunch measurement feasible, their speed of operation must match the 40 MHz bunch repetition rate of LHC. Besides, in the actual operation the detector must stand extremely high radiation doses. The front-end electronics, to survive, must be located at some distance from the region of high radiation field, which means that a properly terminated, low-noise, cable connection is needed between detector and front-end electronics. After briefly reviewing the solutions that have been adopted for the detector and the front-end electronics and the results that have been obtained so far in tests on the beam, the latest version of the instrument in describe in detail. It will be shown how a clever detector design, a suitable front-end conception based on the use of a ''cold resistance'' cable termination and a careful low-noise design, along with the use of an effective deconvolution algorithm, make the luminosity measurement possible on a bunch-by-bunch basis at the LHC bunch repetition rates.
Date: May 10, 2003
Creator: Manfredi, P.F.; Ratti, L.; Speziali, V.; Traversi, G.; Manghisoni, M.; Re, V. et al.
Partner: UNT Libraries Government Documents Department

Parameters of an E+ E- collider in the VLHC tunnels

Description: The authors have discussed the option of building an e{sup +}e{sup -} collider in the tunnels of the VLHC in a number of notes [1,2,3,4,5]. Continued study of this option has shown that the operating range of the machine can be extended somewhat from previous papers and this note presents the most recent progress on the luminosity and high energy operation of this machine. They have assumed that this machine would be used to justify the construction of a tunnel which would eventually house the VLHC collider, and perhaps ultimately an ep collider.
Date: December 5, 2002
Creator: al., T. Sen et
Partner: UNT Libraries Government Documents Department

Aperture limitations for 2nd generation Nb3Sn LHC IR quadrupoles

Description: One of the straightforward ways towards the higher luminosity in the LHC is a replacement of the present 70-mm NbTi quadrupoles with Nb{sub 3}Sn quadrupoles which would provide the same field gradient but in a larger aperture. Conceptual designs of such quadrupoles with 90 mm aperture have been developed and studied. This paper discusses the possibilities and limitations of increasing the aperture of Nb{sub 3}Sn low-beta quadrupoles for a LHC luminosity upgrade up to 110 mm.
Date: June 2, 2003
Creator: Zlobin, Alexander V.; Kashikhin, Vadim V. & Strait, James B.
Partner: UNT Libraries Government Documents Department

Recent results and prospects for high pT physics at D-Zero

Description: The author presents recent results from the D0 experiment using {approx} 50 pb{sup -1} of data recorded at the center of mass energy of 1.96 TeV at the Fermilab Tevatron. In addition, the author summarizes prospects for high p{sub T} physics at the Tevatron as a function of integrated luminosity.
Date: September 11, 2003
Creator: Gerber, Cecilia Elena
Partner: UNT Libraries Government Documents Department

BEAM INDUCED PRESSURE RISE IN RHIC.

Description: Beam induced pressure rise in RHIC warm sections is one of the machine luminosity limits. The RHIC electron cloud and the beam transition pressure rise are discussed. Countermeasures and studies for RHIC pressure rise and RHIC upgrade are reported.
Date: May 16, 2005
Creator: ZHANG, S. Y.; ALESSI, J.; BAI, M. & AL., ET
Partner: UNT Libraries Government Documents Department

Diversity of Decline-Rate-Corrected Type 1a Supernova Rise times:One Mode or Two?

Description: B-band light-curve rise times for eight unusually well-observed nearby Type Ia supernova (SNe) are fitted by a newly developed template-building algorithm, using light-curve functions that are smooth, flexible, and free of potential bias from externally derived templates and other prior assumptions. From the available literature, photometric BVRI data collected over many months, including the earliest points, are reconciled, combined, and fitted to a unique time of explosion for each SN. On average, after they are corrected for light-curve decline rate, three SNe rise in 18.81 {+-} 0.36 days, while five SNe rise in 16.64 {+-} 0.21 days. If all eight SNe are sampled from a single parent population (a hypothesis not favored by statistical tests), the rms intrinsic scatter of the decline-rate-corrected SN rise time is 0.96{sub -0.25}{sup +0.52} days--a first measurement of this dispersion. The corresponding global mean rise time is 17.44 {+-} 0.39 days, where the uncertainty is dominated by intrinsic variance. This value is {approx}2 days shorter than two published averages that nominally are twice as precise, though also based on small samples. When comparing high-z to low-z SN luminosities for determining cosmological parameters, bias can be introduced by use of a light-curve template with an unrealistic rise time. If the period over which light curves are sampled depends on z in a manner typical of current search and measurement strategies, a two-day discrepancy in template rise time can bias the luminosity comparison by {approx}0.03 magnitudes.
Date: May 1, 2007
Creator: Strovink, Mark
Partner: UNT Libraries Government Documents Department

The rest-frame K-band luminosity function of galaxies in clusters to z = 1.3

Description: We derive the rest-frame K-band luminosity function for galaxies in 32 clusters at 0.6 < z < 1.3 using deep 3.6 {micro}m and 4.5 {micro}m imaging from the Spitzer Space Telescope InfraRed Array Camera (IRAC). The luminosity functions approximate the stellar mass function of the cluster galaxies. Their dependence on redshift indicates that massive cluster galaxies (to the characteristic luminosity M*{sub K}) are fully assembled at least at z {approx} 1.3 and that little significant accretion takes place at later times. The existence of massive, highly evolved galaxies at these epochs is likely to represent a significant challenge to theories of hierarchical structure formation where such objects are formed by the late accretion of spheroidal systems at z < 1.
Date: March 20, 2007
Creator: De Propris, R; Stanford, S A; Eisenhardt, P R; Holden, B P & Rosati, P
Partner: UNT Libraries Government Documents Department

Star-Formation in Low Radio Luminosity AGN from the Sloan Digital Sky Survey

Description: We investigate faint radio emission from low- to high-luminosity Active Galactic Nuclei (AGN) selected from the Sloan Digital Sky Survey (SDSS). Their radio properties are inferred by coadding large ensembles of radio image cut-outs from the FIRST survey, as almost all of the sources are individually undetected. We correlate the median radio flux densities against a range of other sample properties, including median values for redshift, [O III] luminosity, emission line ratios, and the strength of the 4000{angstrom} break. We detect a strong trend for sources that are actively undergoing star-formation to have excess radio emission beyond the {approx} 10{sup 28} ergs s{sup -1} Hz{sup -1} level found for sources without any discernible star-formation. Furthermore, this additional radio emission correlates well with the strength of the 4000{angstrom} break in the optical spectrum, and may be used to assess the age of the star-forming component. We examine two subsamples, one containing the systems with emission line ratios most like star-forming systems, and one with the sources that have characteristic AGN ratios. This division also separates the mechanism responsible for the radio emission (star-formation vs. AGN). For both cases we find a strong, almost identical, correlation between [O III] and radio luminosity, with the AGN sample extending toward lower, and the star-formation sample toward higher luminosities. A clearer separation between the two subsamples is seen as function of the central velocity dispersion {sigma} of the host galaxy. For systems at similar redshifts and values of {sigma}, the star-formation subsample is brighter than the AGN in the radio by an order of magnitude. This underlines the notion that the radio emission in star-forming systems can dominate the emission associated with the AGN.
Date: April 18, 2007
Creator: de Vries, W H; Hodge, J A; Becker, R H; White, R L & Helfand, D J
Partner: UNT Libraries Government Documents Department

BEAM PIPE DESORPTION RATE IN RHIC.

Description: In the past, an increase of beam intensity in RHIC has caused several decades of pressure rises in the warm sections during operation. This has been a major factor limiting the RHIC luminosity. About 430 meters of NEG coated beam pipes have been installed in the warm sections to ameliorate this problem. Beam ion induced desorption is one possible cause of pressure rises. A series beam studies in RHIC has been dedicated to estimate the desorption rate of various beam pipes (regular and NEG coated) at various warm sections. Correctors were used to generate local beam losses and consequently local pressure rises. The experimental results are presented and analyzed in this paper.
Date: June 23, 2006
Creator: HUANG, H.; FISCHER, W.; HE, P.; HSEUH, H.C.; IRISO, U.; PTITSYN, V. et al.
Partner: UNT Libraries Government Documents Department

Will at least one of the Higgs bosons of the next-to-minimal supersymmetric extension of the standard model be observable at LEP2 or the LHC?

Description: We demonstrate that there are regions of parameter space in the next-to-minimal (i.e. two-Higgs-doublet, one-Higgs-singlet superfield) supersymmetric extension of the SM for which none of the Higgs bosons are observable either at LEP2 with $\sqrt{s}=192 GeV$ and an integrated luminosity of $L=1000inverse pb$ or at the LHC with $L=600 inverse fb$.
Date: June 24, 1996
Creator: Gunion, John F.; Haber, Howard E. & Moroi, Takeo
Partner: UNT Libraries Government Documents Department

Study of the beam-beam limit in e{sup +}e{sup -} circular colliders

Description: Beam-beam effects limit the luminosity of circular colliders. Once the bunch population exceeds a threshold, the luminosity increases at a slower rate. This phenomenon is called the beam-beam limit. Onset of the beam-beam limit has been analyzed with various simulation methods based on the weak-strong and strong-strong models. We have observed that an incoherent phenomenon is mainly concerned in the beam-beam limit. The simulation have shown that equilibrium distributions of the two colliding beams are distorted from Gaussians when the luminosity is limited. The beam-beam limit is estimated to be (xi) {approx} 0.1 for a B factory with damping time of several thousand turns.
Date: April 2, 2004
Creator: Ohmi, K.; Tawada, M.; Cai, Y.; Kamada, S.; Oide, K. & Qiang, J.
Partner: UNT Libraries Government Documents Department

Jet algorithms at D0

Description: The D0 experiment at the Fermilab Tevatron proton-antiproton collider ({radical}s = 1.8 TeV) accumulated a large sample of high energy jet production data during Run 1 (1992-1996). Since March 2001, D0 has engaged in continuous data collection with an upgraded detector equipped for the higher energy ({radical}s = 1.96 TeV) and luminosity conditions of the Run 2 Tevatron. We summarize here pivotal measurements of Run 1 and consider their comparison to theoretical predictions and to other experiments. These factors elucidate D0's jet clustering algorithm strategy for Run 2 jet measurements. Preliminary measurements of jets from the Run 2 D0 experiment are also presented.
Date: January 2, 2003
Creator: Gallas, Elizabeth
Partner: UNT Libraries Government Documents Department

NEXT GENERATION IR MAGNETS FOR HADRON COLLIDERS.

Description: Brookhaven National Laboratory (BNL) is developing ''React & Wind'' designs and technology for building long high field accelerator magnets. This paper presents the R&D program for interaction region (IR) magnets made with ''Rutherford'' cable for the luminosity upgrade of the Large Hadron Collider (LHC). This paper will introduce a few new end design concepts that make the bend radius of the cable in the end independent of the coil aperture. These designs are suitable for building magnets with ''React & Wind'' technology.
Date: August 4, 2002
Creator: GUPTA,R.; ANERELLA,M.; COZZOLINO,J.; ESCALLIER,J.; GANETIS,G.; HARRISON,M. et al.
Partner: UNT Libraries Government Documents Department

Beam physics at Tevatron complex

Description: The challenge of achieving the Tevatron Run II luminosity goal of 3 {center_dot} 10{sup 32} cm{sup -2} s{sup -1} requires high level of engineering and machine operation, good and reliable diagnostics, and clear understanding of the underlying accelerator physics. Recent history demonstrated steady increase of the Tevatron luminosity, which was supported by each of the three listed above items. This report reviews major developments in the accelerator physics, which contributed in the Run II luminosity growth. Present limitations of the luminosity and projections of further luminosity growth are also discussed.
Date: May 28, 2003
Creator: Lebedev, Valeri A.
Partner: UNT Libraries Government Documents Department

Colliding Crystalline Beams

Description: The understanding of crystalline beams has advanced to the point where one can now, with reasonable confidence, undertake an analysis of the luminosity of colliding crystalline beams. Such a study is reported here. It is necessary to observe the criteria, previously stated, for the creation and stability of crystalline beams. This requires, firstly, the proper design of a lattice. Secondly, a crystal must be formed, and this can usually be done at various densities. Thirdly, the crystals in a colliding-beam machine are brought into collision. We study all of these processes using the molecular dynamics (MD) method. The work parallels what was done previously, but the new part is to study the crystal-crystal interaction in collision. We initially study the zero-temperature situation. If the beam-beam force (or equivalent tune shift) is too large then over-lapping crystals can not be created (rather two spatially separated crystals are formed). However, if the beam-beam force is less than but comparable to that of the space-charge forces between the particles, we find that overlapping crystals can be formed and the beam-beam tune shift can be of the order of unity. Operating at low but non-zero temperature can increase the luminosity by several orders of magnitude over that of a usual collider. The construction of an appropriate lattice, and the development of adequately strong coding, although theoretically achievable, is a challenge in practice.
Date: June 1, 1998
Creator: Wei, Jie & Sessler, A.M.
Partner: UNT Libraries Government Documents Department

MACHO observations of Type II cepheids and RV Tauri Stars in the LMC

Description: We report the of the existence of RV Tauri stars in the Large Magellanic Cloud (LMC). This class of variable star has hitherto been unidentified in the Magellanic Clouds. In light and color curve behavior the RV Tauri stars appear to be an extension of the Type II Cepheids to longer periods. A single period-luminosity-color relationship is seen to describe both the Type II Cepheids and the RV Tauri stars in the LMC.
Date: July 1, 1996
Creator: Alcock, C.; Pollard, K.A. & Alisman, R.A.
Partner: UNT Libraries Government Documents Department

Online calculation of the Tevatron collider luminosity using accelerator instrumentation

Description: The luminosity of a collision region may be calculated if one understands the lattice parameters and measures the beam intensities, the transverse and longitudinal emittances, and the individual proton and antiproton beam trajectories (space and time) through the collision region. This paper explores an attempt to make this calculation using beam instrumentation during Run 1b of the Tevatron. The instrumentation used is briefly described. The calculations and their uncertainties are compared to luminosities calculated independently by the Collider Experiments (CDF and D0).
Date: July 1, 1997
Creator: Hahn, A.A.
Partner: UNT Libraries Government Documents Department