10 Matching Results

Results open in a new window/tab.

The 4Ms Chandra Deep Field-South Number Counts Apportioned By Source Class: Pervasive Active Galactic Nuclei and the Ascent of Normal Galaxies (open access)

The 4Ms Chandra Deep Field-South Number Counts Apportioned By Source Class: Pervasive Active Galactic Nuclei and the Ascent of Normal Galaxies

This article presents cumulative and differential number-count measurements for the recently completed 4 Ms Chandra Deep Field-South survey.
Date: April 9, 2012
Creator: Lehmer, Bret; Xue, Yongquan; Brandt, William Nielsen; Alexander, David M.; Bauer, Franz E.; Brusa, Marcella et al.
System: The UNT Digital Library
Acceptance of Classified Excess Components for Disposal at Area 5 (open access)

Acceptance of Classified Excess Components for Disposal at Area 5

This slide-show discusses weapons dismantlement and disposal, issues related to classified waste and their solutions.
Date: April 9, 2012
Creator: Poling, Jeanne & Saad, Max
System: The UNT Digital Library
B+ and D(S)+ Decay Constants from Belle and BaBar (open access)

B+ and D(S)+ Decay Constants from Belle and BaBar

The Belle and Babar experiments have measured the branching fractions for B{sup +} {yields} {tau}{sup +}{nu} and D{sub s}{sup +} {yields} {mu}{sup +}{nu} decays. From these measurements one can extract the B{sup +} and D{sub s}{sup +} decay constants, which can be compared to lattice QCD calculations. For the D{sub s}{sup +} decay constant, there is currently a 2.1 {sigma} difference between the calculated value and the measured value.
Date: April 9, 2012
Creator: Schwartz, A.J. & U., /Cincinnati
System: The UNT Digital Library
Future Synchrotron Light Sources Based on Ultimate Storage Rings (open access)

Future Synchrotron Light Sources Based on Ultimate Storage Rings

The main purpose of this talk is to describe how far one might push the state of the art in storage ring design. The talk will start with an overview of the latest developments and advances in the design of synchrotron light sources based on the concept of an 'ultimate' storage ring. The review will establish how bright a ring based light source might be, where the frontier of technological challenges are, and what the limits of accelerator physics are. Emphasis will be given to possible improvements in accelerator design and developments in technology toward the goal of achieving an ultimate storage ring. An ultimate storage ring (USR), defined as an electron ring-based light source having an emittance in both transverse planes at the diffraction limit for the range of X-ray wavelengths of interest for a scientific community, would provide very high brightness photons having high transverse coherence that would extend the capabilities of X-ray imaging and probe techniques beyond today's performance. It would be a cost-effective, high-coherence 4th generation light source, competitive with one based on energy recovery linac (ERL) technology, serving a large number of users studying material, chemical, and biological sciences. Furthermore, because of the experience accumulated …
Date: April 9, 2012
Creator: Cai, Yunhai
System: The UNT Digital Library
High Energy Electron Signals from Dark Matter Annihilation in the Sun (open access)

High Energy Electron Signals from Dark Matter Annihilation in the Sun

In this paper we discuss two mechanisms by which high energy electrons resulting from dark matter annihilations in or near the Sun can arrive at the Earth. Specifically, electrons can escape the sun if DM annihilates into long-lived states, or if dark matter scatters inelastically, which would leave a halo of dark matter outside of the sun. Such a localized source of electrons may affect the spectra observed by experiments with narrower fields of view oriented towards the sun, such as ATIC, differently from those with larger fields of view such as Fermi. We suggest a simple test of these possibilities with existing Fermi data that is more sensitive than limits from final state radiation. If observed, such a signal will constitute an unequivocal signature of dark matter.
Date: April 9, 2012
Creator: Schuster, Philip; Toro, Natalia; Weiner, Neal & Yavin, Itay
System: The UNT Digital Library
Lepton-Flavor-Violating Tau Decays at BaBar (open access)

Lepton-Flavor-Violating Tau Decays at BaBar

We present the most recent searches for lepton-flavor-violating (LFV) {tau} decays in BABAR. We find no evidence of {tau} decaying to three charged leptons or to a charged lepton and a neutral meson (K{sub S}{sup 0}, {rho}, {phi}, K*{sup 0}, {bar K}*{sup 0}), and set upper limits on the corresponding branching fractions (BF) between 1.8 and 19 x 10{sup -8} at 90% confidence level (CL).
Date: April 9, 2012
Creator: Marchiori, G. & /Paris, LPTHE
System: The UNT Digital Library
Model-Independent Results for the Decay B \to L Nu(L) Gamma at BaBar (open access)

Model-Independent Results for the Decay B \to L Nu(L) Gamma at BaBar

We present a search for the radiative leptonic decays B{sub +} {yields} e{sup +} {nu}{sub e}{gamma} and B{sup +} {yields} {mu}{sup +}{nu}{sub {mu}}{gamma} using data collected by the BABAR detector at the PEP-II B factory. We fully reconstruct the hadronic decay of one of the B mesons in {Upsilon}(4S) {yields} B{sup +}B{sup -} and then search for evidence of the signal decay within the rest of the event. This method provides clean kinematic information on the signal's missing energy and high momentum photon and lepton, and allows for a model-independent analysis of this decay. Using a data sample of 465 million B-meson pairs, we obtain sensitivity to branching fractions of the same order as predicted by the Standard Model. We report a model-independent branching fraction upper limit of {Beta}(B{sup +} {yields} {ell}{sup +}{nu}{sub {ell}}{gamma}) < 15.6 x 10{sup -6} ({ell} = e or {mu}) at the 90% confidence level.
Date: April 9, 2012
Creator: Lindemann, D. M.
System: The UNT Digital Library
Quarkonium Physics at a Fixed-Target Experiment Using the LHC Beams (open access)

Quarkonium Physics at a Fixed-Target Experiment Using the LHC Beams

We outline the many quarkonium-physics opportunities offered by a multi-purpose fixed-target experiment using the p and Pb LHC beams extracted by a bent crystal. This provides an integrated luminosity of 0.5 fb{sup -1} per year on a typical 1cm-long target. Such an extraction mode does not alter the performance of the collider experiments at the LHC. With such a high luminosity, one can analyse quarkonium production in great details in pp, pd and pA collisions at {radical}s{sub NN} {approx_equal} 115 GeV and at {radical}s{sub NN} {approx_equal} 72 GeV in PbA collisions. In a typical pp (pA) run, the obtained quarkonium yields per unit of rapidity are 2-3 orders of magnitude larger than those expected at RHIC and about respectively 10 (70) times larger than for ALICE. In PbA, they are comparable. By instrumenting the target-rapidity region, the large negative-x{sub F} domain can be accessed for the first time, greatly extending previous measurements by Hera-B and E866. Such analyses should help resolving the quarkonium-production controversies and clear the way for gluon PDF extraction via quarkonium studies. The nuclear target-species versatility provides a unique opportunity to study nuclear matter and the features of the hot and dense matter formed in PbA collisions. …
Date: April 9, 2012
Creator: Lansberg, J. P.; Brodsky, S.J.; Fleuret, F. & Hadjidakis, C.
System: The UNT Digital Library
Studies of Charmonium-Like States at BaBar (open access)

Studies of Charmonium-Like States at BaBar

Several charmonium-like states above D{bar D} threshold have been discovered at the Belle and BABAR B-factories. Some of these states are produced via Initial State Radiation (e.g. Y(4260) and Y(4350)), and some are observed in B-meson decays (e.g. X(3872), and Y(3940)). The Belle observations of the enhancements in the {Psi}(2S){pi}{sup -} and {chi}{sub cl}{pi}{sup -}, i.e. the Z(4430){sup -}, Z{sub 1}(4050){sup -}, and Z{sub 2}(4250){sup -}, have generated a great deal of interest, because such states must have minimum quark content (c{bar c}d{bar u}), i.e. these are four-quark states. The BABAR Collaboration does not confirm the existence of the Z(4430){sup -}.
Date: April 9, 2012
Creator: Mokhtar, Arafat Gabareen
System: The UNT Digital Library
Toward fully self-consistent simulation of the interaction of E-Clouds and beams with WARP-POSINST (open access)

Toward fully self-consistent simulation of the interaction of E-Clouds and beams with WARP-POSINST

To predict the evolution of electron clouds and their effect on the beam, the high energy physics community has relied so far on the complementary use of 'buildup' and 'single/multi-bunch instability' reduced descriptions. The former describes the evolution of electron clouds at a given location in the ring, or 'station', under the influence of prescribed beams and external fields [1], while the latter (sometimes also referred as the 'quasi-static' approximation [2]) follows the interaction between the beams and the electron clouds around the accelerator with prescribed initial distributions of electrons, assumed to be concentrated at a number of discrete 'stations' around the ring. Examples of single bunch instability codes include HEADTAIL [3], QuickPIC [4, 5], and PEHTS [6]. By contrast, a fully self-consistent approach, in which both the electron cloud and beam distributions evolve simultaneously under their mutual influence without any restriction on their relative motion, is required for modeling the interaction of high-intensity beams with electron clouds for heavy-ion beam-driven fusion and warm-dense matter science. This community has relied on the use of Particle-In-Cell (PIC) methods through the development and use of the WARP-POSINST code suite [1, 7, 8]. The development of novel numerical techniques (including adaptive mesh refinement, …
Date: April 9, 2012
Creator: Lawrence Livermore National Laboratory
System: The UNT Digital Library