Showing papers on "Proton published in 2008"

Ab initio determination of light hadron masses.

Abstract: More than 99% of the mass of the visible universe is made up of protons and neutrons. Both particles are much heavier than their quark and gluon constituents, and the Standard Model of particle physics should explain this difference. We present a full ab initio calculation of the masses of protons, neutrons, and other light hadrons, using lattice quantum chromodynamics. Pion masses down to 190 mega-electron volts are used to extrapolate to the physical point, with lattice sizes of approximately four times the inverse pion mass. Three lattice spacings are used for a continuum extrapolation. Our results completely agree with experimental observations and represent a quantitative confirmation of this aspect of the Standard Model with fully controlled uncertainties.

Radiation pressure acceleration of thin foils with circularly polarized laser pulses

Abstract: A new regime is described for radiation pressure acceleration of a thin foil by an intense laser beam of above 1020 W cm−2. Highly monoenergetic proton beams extending to giga-electron-volt energies can be produced with very high efficiency using circularly polarized light. The proton beams have a very small divergence angle (<4°). This new method allows the construction of ultra-compact proton and ion accelerators with ultra-short particle bursts.

Generating high-current monoenergetic proton beams by a circularly polarized laser pulse in the phase-stable acceleration regime

Abstract: A new ion acceleration method, namely, phase-stable acceleration, using circularly-polarized laser pulses is proposed. When the initial target density n0 and thickness D satisfy aL �� n0=ncD=� L and D>l s with aL, � L, ls, and nc the normalized laser amplitude, the laser wavelength in vacuum, the plasma skin depth, and the critical density of the incident laser pulse, respectively, a quasiequilibrium for the electrons is established by the light pressure and the space charge electrostatic field at the interacting front of the laser pulse. The ions within the skin depth of the laser pulse are synchronously accelerated and bunched by the electrostatic field, and thereby a high-intensity monoenergetic proton beam can be generated. The proton dynamics is investigated analytically and the results are verified by one- and two- dimensional particle-in-cell simulations.

Probing Cold Dense Nuclear Matter

Abstract: The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars.

First Penning Trap Mass Measurements beyond the Proton Drip Line

Abstract: The masses of six neutron-deficient rare holmium and thulium isotopes close to the proton drip line were determined with the SHIPTRAP Penning trap mass spectrometer. For the first time the masses of the proton-unbound isotopes {sup 144,145}Ho and {sup 147,148}Tm were directly measured. The proton separation energies were derived from the measured mass values and compared to predictions from mass formulas. The new values of the proton separation energies are used to determine the location of the proton drip line for holmium and thulium more accurately.

Energy spectra of gamma-rays, electrons and neutrinos produced at interactions of relativistic protons with low energy radiation

Abstract: We derived simple analytical parametrizations for energy distributions of photons, electrons, and neutrinos produced in interactions of relativistic protons with an isotropic monochromatic radiation field. The results on photomeson processes are obtained using numerical simulations of proton-photon interactions based on the public available Monte Carlo code SOPHIA. For calculations of energy spectra of electrons and positrons from the pair-production (Bethe-Heitler) process we suggest a simple formalism based on the well-known differential cross section of the process in the rest frame of the proton. The analytical presentations of energy distributions of photons and leptons provide a simple but accurate approach for calculations of broadband energy spectra of gamma rays and neutrinos in cosmic proton accelerators located in radiation dominated environments.

Reduction of spectroscopic strength: Weakly-bound and strongly-bound single-particle states studied using one-nucleon knockout reactions

Abstract: Both one-proton and one-neutron knockout reactions were performed with fast beams of two asymmetric, neutron-deficient rare isotopes produced by projectile fragmentation. The reactions are used to probe the nucleon spectroscopic strengths at both the weakly and strongly bound nucleon Fermi surfaces. The one-proton knockout reactions Be-9(S-28, P-27)X and Be-9(Si-24, Al-23)X probe the weakly bound valence proton states and the one-neutron knockout reactions and Be-9(S-28, S-27)X and Be-9(Si-24, Si-23)X the strongly bound neutron states in the two systems. The spectroscopic strengths are extracted from the measured cross sections by comparisons with an eikonal reaction theory. The reduction of the experimentally deduced spectroscopic strengths, relative to the predictions of shell-model calculations, is of order 0.8-0.9 in the removal of weakly bound protons and 0.3-0.4 in the knockout of the strongly bound neutrons. These results support previous studies at the extremes of nuclear binding and provide further evidence that in asymmetric nuclear systems the nucleons of the deficient species, at the more-bound Fermi surface are more strongly correlated than those of the more weakly bound excess species.

Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe

Abstract: The Standard Model of particle physics assumes that the so-called fundamental constants are universal and unchanging. Absorption lines arising in molecular clouds along quasar sightlines offer a precise test for variations in the proton-to-electron mass ratio, μ, over cosmological time and distance scales. The inversion transitions of ammonia are particularly sensitive to μ as compared to molecular rotational transitions. Comparing the available ammonia spectra observed toward the quasar B0218+357 with new, high-quality rotational spectra, we present the first detailed measurement of μ with this technique, limiting relative deviations from the laboratory value to |Δμ/μ|

The Effects of a κ-Distribution in the Heliosheath on the Global Heliosphere and ENA Flux at 1 AU

Abstract: In this paper we investigate heliosheath energetic neutral atom (ENA) fluxes at keV energies, by assuming that the heliosheath proton distribution can be approximated using a κ-distribution. The choice of the κ-parameter derives from observational data of the solar wind (SW). Our work has direct applications to the upcoming IBEX mission, since we generate all-sky ENA maps within the IBEX energy range (10 eV-6 keV), as well as ENA energy spectra in several directions. We find that the use of κ, as opposed to a Maxwellian, gives rise to greatly increased ENA fluxes above 1 keV, while medium-energy fluxes are somewhat reduced. We show how IBEX data can be used to estimate the spectral slope of the proton distribution in the heliosheath, and that the use of κ reduces the differences between ENA maps at different energies. We also investigate the effect that introducing a κ-distribution has on the global interaction between the SW and the local interstellar medium (LISM), and find that there is generally an increase in energy transport from the heliosphere into the LISM, due to the modified profile of ENA energies. This results in a termination shock that moves out by 4 AU, a heliopause that moves in by 9 AU, and a bow shock 25 AU farther out, in the nose direction.

Spin-Dependent WIMP Limits from a Bubble Chamber

Abstract: Bubble chambers were the dominant technology used for particle detection in accelerator experiments for several decades, eventually falling into disuse with the advent of other techniques. We report here on a new application for these devices. We operated an ultraclean, room-temperature bubble chamber containing 1.5 kilograms of superheated CF3I, a target maximally sensitive to spin-dependent and -independent weakly interacting massive particle (WIMP) couplings. An extreme intrinsic insensitivity to the backgrounds that commonly limit direct searches for dark matter was measured in this device under operating conditions leading to the detection of low-energy nuclear recoils like those expected from WIMPs. Improved limits on the spin-dependent WIMP-proton scattering cross section were extracted during our experiments, excluding this type of coupling as a possible explanation for a recent claim of particle dark-matter detection.

Spatial Structure and Collisionless Electron Heating in Balmer-dominated Shocks

Abstract: Balmer-dominated shocks in supernova remnants (SNRs) produce strong hydrogen lines with a two-component profile composed of a narrow contribution from cold upstream hydrogen atoms and abroad contribution from hydrogen atoms that have undergone charge transfer reactions with hot protons. Observations of emission lines from edgewise shocks in SNRs can constrain the gas velocity and collisionless electron heating at the shock front. Downstream hydrogen atoms engage in charge transfer, excitation, and ionization reactions, defining an interaction region called the shock transition zone. The properties of hot hydrogen atoms produced by charge transfers (called broad neutrals) are critical for accurately calculating the structure and radiation from the shock transition zone. This paper is the third in a series describing the kinetic, fluid, and emission properties of Balmer-dominated shocks, and it is the first to properly treat the effect of broad neutral kinetics on the shock transition zone structure. We use our models to extract shock parameters from observations of Balmer-dominated SNRs. We find that the inferred shock velocities and electrontemperaturesarelower thanthoseof previouscalculations by 1500 km s � 1 . This effect is primarily due to the fact that excitation by proton collisions and charge transfer to excitedlevelsfavorthehigh-speedpartof theneutralhydrogenvelocitydistribution.Ourresultshaveastrongdependence on the ratio of the electron to proton temperatures, � � Te/Tp, which allows us to construct a relation � (vs) between the temperature ratio and the shock velocity.We compare our calculations to previous results byGhavamian and coworkers. Subject headingg shock waves — supernova remnants Online material: color figures

Nuclear enhancement of universal dynamics of high parton densities.

Abstract: We show that the enhancement of the saturation scale in large nuclei relative to the proton is significantly influenced by the effects of quantum evolution and the impact parameter dependence of dipole cross sections in high energy QCD. We demonstrate that there is a strong A dependence in diffractive deeply inelastic scattering and discuss its sensitivity to the measurement of the recoil nucleus.

The Solar Electron and Proton Telescope for the STEREO Mission

Abstract: The Solar Electron and Proton Telescope (SEPT), one of four instruments of the Solar Energetic Particle (SEP) suite for the IMPACT investigation, is designed to provide the three-dimensional distribution of energetic electrons and protons with good energy and time resolution. This knowledge is essential for characterizing the dynamic behaviour of CME associated and solar flare associated events. SEPT consists of two dual double-ended magnet/foil particle telescopes which cleanly separate and measure electrons in the energy range from 30–400 keV and protons from 60–7 000 keV. Anisotropy information on a non-spinning spacecraft is provided by the two separate telescopes: SEPT-E looking in the ecliptic plane along the Parker spiral magnetic field both towards and away from the Sun, and SEPT-NS looking vertical to the ecliptic plane towards North and South. The dual set-up refers to two adjacent sensor apertures for each of the four view directions: one for protons, one for electrons. The double-ended set-up refers to the detector stack with view cones in two opposite directions: one side (electron side) is covered by a thin foil, the other side (proton side) is surrounded by a magnet. The thin foil leaves the electron spectrum essentially unchanged but stops low energy protons. The magnet sweeps away electrons but lets ions pass. The total geometry factor for electrons and protons is 0.52 cm2 sr and 0.68 cm2 sr, respectively. This paper describes the design and calibration of SEPT as well as the scientific objectives that the instrument will address.

Implications of the cosmic ray spectrum for the mass composition at the highest energies

Abstract: The significant attenuation of the cosmic ray flux above ~5 × 1019 eV suggests that the observed high energy spectrum is shaped by the so-called GZK effect (GZK: Greisen–Zatsepin–Kuzmin). This interaction of ultra-high energy cosmic rays (UHECRs) with the ambient radiation fields also affects their composition. We review the effect of photodissociation interactions on different nuclear species and analyze the phenomenology of secondary-proton production as a function of energy. We show that, by itself, the UHECR spectrum does not constrain the composition of cosmic rays at their extragalactic sources. While the propagated composition (i.e., as observed at Earth) cannot contain significant amounts of intermediate mass nuclei (say between He and Si), whatever the source composition, and while it is vastly proton dominated when protons are able to reach energies above 1020 eV at the source, we show that the propagated composition can be dominated by Fe and sub-Fe nuclei at the highest energies, either if the sources are very strongly enriched in Fe nuclei (a rather improbable situation), or if the accelerated protons have a maximum energy of a few 1019 eV at the sources. We also show that in the latter cases, the expected flux above 3 × 1020 eV is very much reduced as compared to the case when protons dominate in this energy range, both at the sources and at Earth.

The all-particle spectrum of primary cosmic rays in the wide energy range from 10^14 eV to 10^17 eV observed with the Tibet-III air-shower array

Abstract: We present an updated all-particle energy spectrum of primary cosmic rays in a wide range from 10^14 eV to 10^17 eV using 5.5 times 10^7 events collected in the period from 2000 November through 2004 October by the Tibet-III air-shower array located at 4300 m above sea level (atmospheric depth of 606 g/cm^2). The size spectrum exhibits a sharp knee at a corresponding primary energy around 4 PeV. This work uses increased statistics and new simulation calculations for the analysis. We performed extensive Monte Carlo calculations and discuss the model dependences involved in the final result assuming interaction models of QGSJET01c and SIBYLL2.1 and primary composition models of heavy dominant (HD) and proton dominant (PD) ones. Pure proton and pure iron primary models are also examined as extreme cases. The detector simulation was also made to improve the accuracy of determining the size of the air showers and the energy of the primary particle. We confirmed that the all-particle energy spectra obtained under various plausible model parameters are not significantly different from each other as expected from the characteristics of the experiment at the high altitude, where the air showers of the primary energy around the knee reaches near maximum development and their features are dominated by electromagnetic components leading to the weak dependence on the interaction model or the primary mass. This is the highest-statistical and the best systematics-controlled measurement covering the widest energy range around the knee energy region.

A Thermoreversible and Proton-Induced Gel−Sol Phase Transition with Remarkable Fluorescence Variation

Abstract: We have synthesized a novel highly fluorescent organogel system that uses a functional molecule with aggregation-induced enhanced emission (AIEE) properties. This AIEE organo gelator is more advanced than previously reported fluorescent gelators because it is practically nonfluorescent in the molecular sol state but highly fluorescent in the gel state, with a 170-fold enhancement in fluorescence intensity. This “functional fluorescent gelator” molecule forms strongly fluorescent and self-assembled gels in both nonpolar and polar protic solvents, even at low concentrations on the order of 0.2 wt %. These self-assembled organogels undergo completely thermoreversible and proton-induced gel-to-sol phase transitions with concomitant fluorescence intensity modulations. Moreover, we have demonstrated selective spatial patterning using the gel-to-sol transition with this organogel system.

Forward Neutral-Pion Transverse Single-Spin Asymmetries in p + p Collisions at √s = 200 GeV

Abstract: We report precision measurements of the Feynman x (x(F)) dependence, and first measurements of the transverse momentum (p(T)) dependence, of transverse single-spin asymmetries for the production of pi(0) mesons from polarized proton collisions at s=200 GeV. The x(F) dependence of the results is in fair agreement with perturbative QCD model calculations that identify orbital motion of quarks and gluons within the proton as the origin of the spin effects. Results for the p(T) dependence at fixed x(F) are not consistent with these same perturbative QCD-based calculations.

Long-Range Proton Transfer in Aqueous Acid−Base Reactions†

Abstract: We study the mechanism of proton transfer (PT) in the aqueous acid−base reaction between the photoacid 8-hydroxy-1,3,6-pyrenetrisulfonic acid (HPTS) and acetate by probing the vibrational resonances of HPTS, acetate, and the hydrated proton with femtosecond mid-infrared laser pulses. We find that PT takes place in a distribution of hydrogen-bound reaction complexes that differ in the number of water molecules separating the acid and the base. The number of intervening water molecules ranges from 0 to 5, which, together with a strongly distance-dependent PT rate, explains the observed highly nonexponential reaction kinetics. The kinetic isotope effect for the reaction is determined to be 1.5, indicating that tunneling does not play a significant role in the transfer of the proton. Rather, the transfer mechanism is best described in terms of the adiabatic PT picture as it has been formulated by Hynes and co-workers [Staib, A.; Borgis, D.; Hynes, J. T. J. Chem. Phys. 1995, 102, 2487. Ando, K.; Hynes, J. T. J...

Comparative reliability of proton spectroscopy techniques designed to improve detection of J-coupled metabolites.

Abstract: Improved detection of J-coupled neurometabolites through the use of modified proton magnetic resonance spectroscopy (1H-MRS) techniques has recently been reported. TE-averaged point-resolved spectroscopy (PRESS) uses the J modulation effects by averaging FIDs with differing echo times to improve detection of glutamate, while standard PRESS detection of glutamate can be improved by using an appropriate single echo determined from J-modulation simulations. In the present study, the reliabilities of TE-averaged PRESS, standard PRESS with TE = 40 ms, and standard PRESS with TE = 30 ms in detecting metabolite levels in the cingulate gyrus of the human brain at 3T were compared in six subjects. TE-averaged PRESS measures showed a mean variability of 9% for N-acetyl aspartate, choline, and creatine, compared with < 4% for the 30- and 40-ms PRESS techniques. The coefficients of variation for glutamate were 10%, 7%, and 5% for TE-averaged, 30-ms, and 40-ms PRESS, respectively. PRESS with a TE of 40 ms also demonstrated improved reliability for GABA and glutamine concentrations. These results show that with the appropriate selection of echo time standard PRESS can be a reliable (1)H-MRS technique for the measurement of J-coupled neurometabolites in the human brain and, moreover, compares favorably with at least one J-edited technique.

The High Energy Telescope for STEREO

Abstract: The IMPACT investigation for the STEREO Mission includes a complement of Solar Energetic Particle instruments on each of the two STEREO spacecraft. Of these instruments, the High Energy Telescopes (HETs) provide the highest energy measurements. This paper describes the HETs in detail, including the scientific objectives, the sensors, the overall mechanical and electrical design, and the on-board software. The HETs are designed to measure the abundances and energy spectra of electrons, protons, He, and heavier nuclei up to Fe in interplanetary space. For protons and He that stop in the HET, the kinetic energy range corresponds to ∼13 to 40 MeV/n. Protons that do not stop in the telescope (referred to as penetrating protons) are measured up to ∼100 MeV/n, as are penetrating He. For stopping He, the individual isotopes 3He and 4He can be distinguished. Stopping electrons are measured in the energy range ∼0.7–6 MeV.

Shock acceleration of solar energetic protons : the first 10 minutes

Abstract: Proton acceleration at a parallel coronal shock is modeled with self-consistent Alfven wave excitation and shock transmission. 18 - 50 keV seed protons at 0.1% of plasma proton density are accelerated in 10 minutes to a power-law intensity spectrum rolling over at 300 MeV by a 2500km s-1 shock traveling outward from 3.5 solar radius, for typical coronal conditions and low ambient wave intensities. Interaction of high-energy protons of large pitch-angles with Alfven waves amplified by low-energy protons of small pitch angles is key to rapid acceleration. Shock acceleration is not significantly retarded by sunward streaming protons interacting with downstream waves. There is no significant second-order Fermi acceleration.

Proton transfer in a polar solvent from ring polymer reaction rate theory.

Abstract: We have used the ring polymer molecular dynamics method to study the Azzouz–Borgis model for proton transfer between phenol (AH) and trimethylamine (B) in liquid methyl chloride. When the A–H distance is used as the reaction coordinate, the ring polymer trajectories are found to exhibit multiple recrossings of the transition state dividing surface and to give a rate coefficient that is smaller than the quantum transition state theory value by an order of magnitude. This is to be expected on kinematic grounds for a heavy-light-heavy reaction when the light atom transfer coordinate is used as the reaction coordinate, and it clearly precludes the use of transition state theory with this reaction coordinate. As has been shown previously for this problem, a solvent polarization coordinate defined in terms of the expectation value of the proton transfer distance in the ground adiabatic quantum state provides a better reaction coordinate with less recrossing. These results are discussed in light of the wide body of earlier theoretical work on the Azzouz–Borgis model and the considerable range of previously reported values for its proton and deuteron transfer rate coefficients.

Investigation of Pygmy Dipole Resonances in the Tin Region

Abstract: The evolution of the low-energy electromagnetic dipole response with the neutron excess is investigated along the Sn isotopic chain within an approach incorporating Hartree-Fock-Bogoljubov (HFB) and multiphonon quasiparticle-phonon model (QPM) theory. General aspects of the relationship of nuclear skins and dipole sum rules are discussed. Neutron and proton transition densities serve to identify the pygmy dipole resonance (PDR) as a generic mode of excitation. The PDR is distinct from the GDR by its own characteristic pattern given by a mixture of isoscalar and isovector components. Results for the {sup 100}Sn-{sup 132}Sn isotopes and the several N=82 isotones are presented. In the heavy Sn isotopes the PDR excitations are closely related to the thickness of the neutron skin. Approaching {sup 100}Sn a gradual change from a neutron to a proton skin is found and the character of the PDR is changed correspondingly. A delicate balance between Coulomb and strong interaction effects is found. The fragmentation of the PDR strength in {sup 124}Sn is investigated by multiphonon calculations. Recent measurements of the dipole response in {sup 130,132}Sn are well reproduced.

Empirical transverse charge densities in the nucleon and the nucleon-to-delta transition.

Abstract: Using only the current empirical information on the nucleon electromagnetic form factors we map out the transverse charge density in proton and neutron as viewed from a light front moving towards a transversely polarized nucleon. These charge densities are characterized by a dipole pattern, in addition to the monopole field corresponding with the unpolarized density. Furthermore, we use the latest empirical information on the $N\ensuremath{\rightarrow}\ensuremath{\Delta}$ transition form factors to map out the transition charge density which induces the $N\ensuremath{\rightarrow}\ensuremath{\Delta}$ excitation. This transition charge density in a transversely polarized $N$ and $\ensuremath{\Delta}$ contains both monopole, dipole and quadrupole patterns, the latter corresponding with a deformation of the $N$ and $\ensuremath{\Delta}$ charge distribution.

Recent observation of short range nucleon correlations in nuclei and their implications for the structure of nuclei and neutron stars

Abstract: Novel processes probing the decay of nucleus after removal of a nucleon with momentum larger than Fermi momentum by hard probes nally proved unambiguously the evidence for long sought presence of short-range correlations (SRCs) in nuclei. In combination with the analysis of large Q 2 , A(e,e’)X processes at x > 1 they allow us to conclude that (i) practically all nucleons with momenta 300 MeV/c belong to SRCs, consisting mostly of two nucleons, ii) probability of such SRCs in medium and heavy nuclei is 25%, iii) a fast removal of such nucleon practically always leads to emission of correlated nucleon with approximately opposite momentum, iv) proton removal from twonucleon SRCs in 90% of cases is accompanied by a removal of a neutron and only in 10% by a removal of another proton. We explain that observed absolute probabilities and the isospin structure of two nucleon SRCs conrm the