High-energy Data Research Articles

What are multiplicity distributions telling us about the QCD phase diagram?

Canonical partition functions Z n are very valuable tools for studying the QCD phase diagram at a finite temperature and density; they can be calculated from both high-energy heavy-ion collision experimental data and lattice QCD calculations. They help us to understand the features of experimental data from a theoretical point of view. We show that if we construct a whole Z n ( T ) , then we can obtain information on grand partition functions Z ( T , μ / T ) for any μ , where μ is the chemical potential. This means that if we obtain information at a fixed value of μ and T , we can obtain Z ( T , μ / T ) at other values of μ / T by extrapolation. In actual experimental measurements and lattice QCD simulations, a truncation on Z n is inevitably imposed, i.e., we can only obtain data for a limited number of Z n ( | n | ≤ N max ) . We discuss the consequence of this limitation, and show that the present RHIC data suggest that we are near the QCD phase transition at low energies.

Radiogenic and muon-induced backgrounds in the LUX dark matter detector

The Large Underground Xenon (LUX) dark matter experiment aims to detect rare low-energy interactions from Weakly Interacting Massive Particles (WIMPs). The radiogenic backgrounds in the LUX detector have been measured and compared with Monte Carlo simulation. Measurements of LUX high-energy data have provided direct constraints on all background sources contributing to the background model. The expected background rate from the background model for the 85.3day WIMP search run is (2.6±0.2stat±0.4sys)×10-3 events keVee-1kg-1day-1 in a 118kg fiducial volume. The observed background rate is (3.6±0.4stat)×10-3 events keVee-1kg-1day-1, consistent with model projections. The expectation for the radiogenic background in a subsequent one-year run is presented.

Unifying “soft” and “hard” diffractive exclusive vector meson production and deeply virtual Compton scattering

A Pomeron model applicable to both "`soft" and "hard" processes is suggested and tested against the high-energy data from virtual photon-induced reactions. The Pomeron is universal, containing two terms, a "soft" and a "hard" one, whose relative weight varies with $\widetilde {Q^2}=Q^2+M_V^2$, where $Q^2$ is the virtuality of the incoming photon and $M_V$ is the mass of the produced vector particle. With a small number of adjustable parameters, the model fits all available data on vector meson production and deeply virtual Compton scattering from HERA. Furthermore, we attempt to apply the model to hadron-induced reactions, by using high-energy data from proton-proton scattering.

Constraining the violation of the equivalence principle with IceCube atmospheric neutrino data

The recent high-statistics high-energy atmospheric neutrino data collected by IceCube open a new window to probe new physics scenarios that are suppressed in lower energy neutrino experiments. In this paper we analyze the IceCube atmospheric neutrino data to constrain the Violation of Equivalence Principle (VEP) in the framework of three neutrinos with non-universal gravitational couplings. In this scenario the effect of VEP on neutrino oscillation probabilities can be parametrized by two parameters $\Delta \gamma_{21}\equiv \gamma_2-\gamma_1$ and $\Delta\gamma_{31}\equiv \gamma_3-\gamma_1$, where $\gamma_i$'s denote the coupling of neutrino mass eigenstates to gravitational field. By analyzing the latest muon-tracks data sets of IceCube-40 and IceCube-79, besides providing the 2D allowed regions in $(\phi\Delta\gamma_{21},\phi\Delta\gamma_{31})$ plane, we obtain the upper limits $|\phi\Delta\gamma_{21}| < 9.1\times 10^{-27}$ (at 90\% C.L.) which improves the previous limit by $\sim4$ orders of magnitude and $|\phi\Delta\gamma_{31}| \lesssim 6\times 10^{-27}$ (at 90\% C.L.) which improves the current limit by $\sim1$ order of magnitude. Also we discuss in detail and analytically the effect of VEP on neutrino oscillation probabilities.

GPUs for real-time processing in HEP trigger systems

We describe a pilot project for the use of Graphics Processing Units (GPUs) for online triggering applications in High Energy Physics (HEP) experiments. Two major trends can be identified in the development of trigger and DAQ systems for HEP experiments: the massive use of general-purpose commodity systems such as commercial multicore PC farms for data acquisition, and the reduction of trigger levels implemented in hardware, towards a pure software selection system (trigger-less). The very innovative approach presented here aims at exploiting the parallel computing power of commercial GPUs to perform fast computations in software both at low- and high-level trigger stages. General-purpose computing on GPUs is emerging as a new paradigm in several fields of science, although so far applications have been tailored to the specific strengths of such devices as accelerator in offline computation. With the steady reduction of GPU latencies, and the increase in link and memory throughputs, the use of such devices for real-time applications in high-energy physics data acquisition and trigger systems is becoming very attractive. We discuss in details the use of online parallel computing on GPUs for synchronous low-level trigger with fixed latency. In particular we show preliminary results on a first test in the NA62 experiment at CERN. The use of GPUs in high-level triggers is also considered, the ATLAS experiment (and in particular the muon trigger) at CERN will be taken as a study case of possible applications.

Accurate binding energies of hydrogen, halogen, and dihydrogen bonded complexes and cation enhanced binding strengths

Interaction energy (Eint) values of a variety of hydrogen, halogen, and dihydrogen bonded complexes in the weak, medium, and strong regimes have been computed using W1BD, MP2, M06L density functional theory, and hybrid methods MP4//MP2, MP4//M06L, and CCSD(T)//MP2. W1BD level Eint and CCSD(T) results reported in the literature show very good agreement (mean absolute deviation = 0.19 kcal/mol). MP2 underestimates Eint while M06L shows accurate behavior for all except halogen and charge‐assisted hydrogen bonds. MP4//MP2, MP4//M06L, and CCSD(T)//MP2 yield Eint very close to those obtained from W1BD. The high accuracy energy data at MP4/MP2 is used to study the effect of a cation (Li+, NH4+) on the Eint. The cation enhances electron donation from the donor to noncovalent bonding region leading to substantial enhancement in Eint (∼141–566% for Li+ and ∼105–539% for NH4+) and promotes a noncovalent bond in the weak regime to medium regime and that in the medium regime to strong regime. © 2014 Wiley Periodicals, Inc.

Spallation cross sections for natFe and natCu targets for 120 GeV/c protons and pions

Spallation cross sections from thin natural copper and iron targets bombarded by a mixed 120 GeV/c proton/pion beam were measured in an activation experiment at CERN. The beam intensity was monitored by a calibrated ionization chamber and the activity of several spallation products was measured (14 for copper and 16 for iron) by \ensuremath{\gamma} spectrometry, allowing the absolute cross section of the mixed hadron beam to be derived. Monte Carlo simulations with the FLUKA code provided the ratio between the proton- and pion-induced reaction cross sections for a given spallation product, allowing us to extrapolate the individual cross sections for the proton- and the pion-induced reactions. Where possible the values were compared with literature data and showed to be generally in agreement with the highest energy data available.

FERMI-LAT DETECTION OF TWO HIGH GALACTIC LATITUDE GAMMA-RAY SOURCES, FERMI J1049.7+0435 AND J1103.2+1145

The Second Fermi LAT source catalog (Nolan et al. 2012) includes as many as 1,873 sources, but initial attempts to identify counterparts at other wavelengths resulted in 575 sources remaining unidentified. The 2FGL catalog is based on the first 24 months of LAT observation since its launch in 2008, but the LAT has now accumulated more than 5 years of high-energy gamma-ray data almost flawlessly, presenting the possibility of finding new sources which were too faint to be detected in the first two years of data or showed flaring activity after the catalog was created. In this paper we report on two new gamma-ray sources serendipitously discovered in the constellation Leo and discuss possible counterparts based on radio observations.

Light ion production in 175 MeV quasi mono-energetic neutron induced reactions on carbon, oxygen, and silicon

Double-differential cross sections of light ions (p, d, t, 3 He, and α) from carbon, oxygen, and silicon induced by 175 MeV quasi mono-energetic neutrons were measured using the Medley setup at the The Svedberg Laboratory (TSL) in order to benchmark evaluated nuclear data and nuclear reaction models. The Medley is a conventional spectrometer system which consists of eight counter telescopes. Each telescope is composed of two silicon surface barrier detectors as the ΔE detectors and a CsI(Tl) scintillator as the E detector for particle identification. The telescopes are placed at angles from 20° to 160° in steps of 20°. The measured double-differential production cross sections of light ions for oxygen and silicon are compared with PHITS calculations using the following nuclear reaction options: the high-energy nuclear data library (JENDL/HE-2007), the quantum molecular dynamics (QMD) model, the modified quantum molecular dynamics (MQMD) model, and the intra-nuclear cascade (INC) model based on the Bertini Model.

Bio-Mimic Optimization Strategies in Wireless Sensor Networks: A Survey

For the past 20 years, many authors have focused their investigations on wireless sensor networks. Various issues related to wireless sensor networks such as energy minimization (optimization), compression schemes, self-organizing network algorithms, routing protocols, quality of service management, security, energy harvesting, etc., have been extensively explored. The three most important issues among these are energy efficiency, quality of service and security management. To get the best possible results in one or more of these issues in wireless sensor networks optimization is necessary. Furthermore, in number of applications (e.g., body area sensor networks, vehicular ad hoc networks) these issues might conflict and require a trade-off amongst them. Due to the high energy consumption and data processing requirements, the use of classical algorithms has historically been disregarded. In this context contemporary researchers started using bio-mimetic strategy-based optimization techniques in the field of wireless sensor networks. These techniques are diverse and involve many different optimization algorithms. As far as we know, most existing works tend to focus only on optimization of one specific issue of the three mentioned above. It is high time that these individual efforts are put into perspective and a more holistic view is taken. In this paper we take a step in that direction by presenting a survey of the literature in the area of wireless sensor network optimization concentrating especially on the three most widely used bio-mimetic algorithms, namely, particle swarm optimization, ant colony optimization and genetic algorithm. In addition, to stimulate new research and development interests in this field, open research issues, challenges and future research directions are highlighted.

Inter-molecular correlations in liquid Se2Br2

The structure of molecular liquid Se2Br2 was analyzed by means of reverse Monte Carlo structural modeling, using a calculation based on high-energy x-ray diffraction data. It was found that, between the optical isomers of L and D types, the number of L–D neighboring molecular pairs increases, while that of the L–L and D–D pairs decreases with increasing temperature. From this temperature dependence and from the relaxation mode analysis of quasi-elastic neutron scattering spectra, it is reasonable to assume that the presence of L–D pairs relates to genuine inter-molecular interactions while the L–L and D–D pairs appear due to geometrical packing of the gauche-shaped molecules.

Fermi-LAT gamma-ray signal from Earth limb, systematic detector effects and their implications for the 130 GeV gamma-ray excess

We look for possible spectral features and systematic effects in Fermi-LAT publicly available high-energy gamma-ray data by studying photons from the Galactic centre, nearby galaxy clusters, nearby brightest galaxies, AGNs, unassociated sources, hydrogen clouds and Earth Limb. Apart from already known 130 GeV gamma-ray excesses from the first two sources, we find no new statistically significant signal from others. Much of our effort goes to studying Earth Limb photons. In the energy range 30 GeV to 200 GeV the Earth Limb gamma-ray spectrum follows power-law with spectral index 2.87\pm 0.04 at 95 % CL, in a good agreement with the PAMELA measurement of cosmic ray proton spectral index between 2.82-2.85, confirming the physical origin of the Limb gamma-rays. In small subsets of Earth Limb data with small photon incidence angle it is possible to obtain spectral features at different energies, including at 130 GeV, but determination of background, thus their significances, has large uncertainties in those cases. We observe systematic 2\sigma level differences in the Earth Limb spectra of gamma-rays with small and large incidence angles. The behaviour of those spectral features as well as background indicates that they are likely statistical fluctuations.

Computational particle physics for event generators and data analysis

High-energy physics data analysis relies heavily on the comparison between experimental and simulated data as stressed lately by the Higgs search at LHC and the recent identification of a Higgs-like new boson. The first link in the full simulation chain is the event generation both for background and for expected signals. Nowadays event generators are based on the automatic computation of matrix element or amplitude for each process of interest.Moreover, recent analysis techniques based on the matrix element likelihood method assign probabilities for every event to belong to any of a given set of possible processes. This method originally used for the top mass measurement, although computing intensive, has shown its efficiency at LHC to extract the new boson signal from the background.Serving both needs, the automatic calculation of matrix element is therefore more than ever of prime importance for particle physics. Initiated in the 80's, the techniques have matured for the lowest order calculations (tree-level), but become complex and CPU time consuming when higher order calculations involving loop diagrams are necessary like for QCD processes at LHC. New calculation techniques for next-to-leading order (NLO) have surfaced making possible the generation of processes with many final state particles (up to 6). If NLO calculations are in many cases under control, although not yet fully automatic, even higher precision calculations involving processes at 2-loops or more remain a big challenge.After a short introduction to particle physics and to the related theoretical framework, we will review some of the computing techniques that have been developed to make these calculations automatic. The main available packages and some of the most important applications for simulation and data analysis, in particular at LHC will also be summarized (see CCP2012 slides [1]).

Evidence for local monoclinic structure, polarization rotation, and morphotropic phase transitions in(1−x)BiFeO3-xBaTiO3solid solutions: A high-energy synchrotron x-ray powder diffraction study

We have presented evidence for composition-driven rhombohedral-to-cubic and cubic-to-tetragonal morphotropic phase transitions in (1 \ensuremath{-} $x$)BiFeO${}_{3}$-$x$BaTiO${}_{3}$ (BF-$x$BT) solid solutions at $x$ \ensuremath{\approx} 0.35 and 0.85, respectively. It is shown that these transitions lead to the appearance of two peaks in the composition variation of dielectric constant, similar to that in well-known piezoelectric ceramics. The existing controversies about the true structure of the so-called cubic phase of BF-$x$BT are resolved using high-energy synchrotron x-ray powder diffraction data. It is shown that the ferroelectric cubic phase of BF-$x$BT has got locally monoclinic structure of ${M}_{A}$ type in the $Cm$ space group whose polarization vector rotates on its mirror plane on increasing the concentration of BaTiO${}_{3}$ ($x$). The ferroelectric-to-paraelectric phase transition in pseudocubic monoclinic phase is shown to be of tricritical nature.

Exploring ντ−νs mixing with cascade events in DeepCore

The atmospheric neutrino data collected by the IceCube experiment and its low-energy extension DeepCore provide a unique opportunity to probe the neutrino sector of the Standard Model. In the low energy range the experiment have observed neutrino oscillations, and the high energy data are especially sensitive to signatures of new physics in the neutrino sector. In this context, we previously demonstrated the unmatched potential of the experiment to reveal the existence of light sterile neutrinos. The studies are routinely performed in the simplest 3+1 model concentrating on disappearance of muon neutrinos of TeV energy as a result of their mixing with a sterile neutrino. We here extend this analysis to include cascade events that are secondary electromagnetic and hadronic showers produced by neutrinos of all flavors. We find that it is possible to probe the complete parameter space of 3+1 model, including the poorly constrained mixing of the sterile neutrino to tau neutrinos. We show that ντ−νs mixing results into a unique signature in the data that will allow IceCube to obtain constraints well below the current upper limits.

AstrophysicalSfactor of3He(α,γ)7Be

Background: The ${}^{3}$He${(\ensuremath{\alpha},\ensuremath{\gamma})}^{7}$Be reaction is important for the neutrino production in the sun's core and the production of ${}^{7}$Li during big bang nucleosynthesis. The reaction mechanism is characterized by a strong direct capture component and nearby broad unbound resonance levels.Purpose: Recent experiments have opened up a new energy window into the reaction mechanism and it becomes more and more evident that, in order to understand the shape of the $S$ factor, theoretical calculations need to take into account possible resonance contributions from higher energies as well.Method: In the present work, a relatively wide energy window was investigated, ${E}_{c.m.}=300$--1460 keV, by detecting the prompt $\ensuremath{\gamma}$ rays from the reaction. An extensive $R$-matrix analysis was performed, utilizing all modern literature capture data, as well as elastic scattering data, which are important in constraining some $R$-matrix parameters.Results: The new experimental data agree very well with the modern literature data. The final result from the $R$-matrix fit gives a zero-energy $S$ factor of $S(0)=0.554(20)$ keV b. A table with the newly calculated reaction rate is given.Conclusions: The simultaneous $R$-matrix analysis of the ${}^{3}$He${(\ensuremath{\alpha},\ensuremath{\gamma})}^{7}$Be and ${}^{3}$He${(\ensuremath{\alpha},\ensuremath{\alpha})}^{3}$He channels yielded a reliable fit, consistent with all the included experimental data sets. In order to further constrain the reaction rate within the $R$-matrix framework, additional high-energy capture data, $\ensuremath{\gamma}$-ray angular distributions, and the inclusion of other relevant reaction channels are necessary.

Competitive I2 Sorption by Cu-BTC from Humid Gas Streams

Competitive sorption of molecular iodine gas from a mixed stream containing iodine and water vapor is identified and characterized for the hydrophilic Cu-BTC metal–organic framework. By combining simulation (Grand Canonical Monte Carlo and molecular dynamics simulations) with crystallography (high-energy synchrotron-based powder X-ray diffraction data and pair distribution function analyses), we show that I2 substantially adsorbs, in preference to water vapor, into two principal areas. First, it adsorbs in the smallest cage close to the copper paddle wheel. Second, it adsorbs within the main pore with close interactions with the benzene tricarboxylate organic linker. Analysis suggests that I2 forms an effective hydrophobic barrier to minimize water sorption. The finding is relevant to mixed gas streams in nuclear energy industrial processes and accident remediation. This also represents the highest reported I2 sorption by a metal–organic framework (175 wt % I2 or 3 I/Cu).

Can the “standard” unitarized Regge models describe the TOTEM data?

The standard Regge poles are considered as inputs for two unitarization methods: eikonal and U-matrix. It is shown that only models with three input pomerons and two input odderons can describe the high-energy data on pp and elastic scattering including the new data from Tevatron and LHC. However, it seems that both the considered models (eikonal and U-matrix) require a further modification (e.g., to explore nonlinear reggeon trajectories and/or nonexponential vertex functions) for a more satisfactory description of the data at 19.0 GeV TeV and GeV2.

Manganese 3×3 and3×3-R30∘structures and structural phase transition onw-GaN(0001¯) studied by scanning tunneling microscopy and first-principles theory

Manganese deposited on the N-polar face of wurtzite gallium nitride [GaN (000$\overline{1}$)] results in two unique surface reconstructions, depending on the deposition temperature. At lower temperature (less than 105${\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}$C), it is found that a metastable $3\ifmmode\times\else\texttimes\fi{}3$ structure forms. Mild annealing of this Mn $3\ifmmode\times\else\texttimes\fi{}3$ structure leads to an irreversible phase transition to a different, much more stable $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}R{30}^{\ensuremath{\circ}}$ structure which can withstand high-temperature annealing. Scanning tunneling microscopy (STM) and reflection high-energy electron diffraction data are compared with results from first-principles theoretical calculations. Theory finds a lowest-energy model for the $3\ifmmode\times\else\texttimes\fi{}3$ structure consisting of Mn trimers bonded to the Ga adlayer atoms but not with N atoms. The lowest-energy model for the more stable $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}R{30}^{\ensuremath{\circ}}$ structure involves Mn atoms substituting for Ga within the Ga adlayer and thus bonding with N atoms. Tersoff-Hamman simulations of the resulting lowest-energy structural models are found to be in very good agreement with the experimental STM images.

Noise Reduction in Material Decomposition for Low-Dose Dual-Energy Cone-Beam CT.

Dual-energy cone-beam CT (DE-CBCT) is an emerging technology with potential application in diagnostic imaging and image-guided interventions. This paper reports DE-CBCT feasibility and investigates decomposition algorithms for maximizing low-dose performance for reconstruction-based DE decomposition. A framework of binary decision theory is used to examine the accuracy of DE decompositions obtained from analytical reconstructions of differentially filtered low-energy (LE) and high-energy (HE) data and from penalized likelihood (PL) reconstructions with differential regularization using quadratic and total variation penalties. Accurate DE-CBCT decomposition benefits from consideration of all system noise components. Filtered backprojection (FBP) reconstruction-based decomposition was investigated with differential filtering of LE and HE data. Penalized likelihood reconstruction-based decomposition with differential regularization was hypothesized to further improve low-dose performance, especially when coupled with regularization through a total variation edge preserving penalty that encourages piecewise smooth images. Performance of decomposition was assessed in terms of a binary hypothesis framework of sensitivity, specificity, and accuracy. Studies involved experiments on a DE-CBCT testbench, phantoms of variable material type and concentration, and cadavers (knee arthrography). Studies support the overall feasibility of accurate, low-dose DE-CBCT at concentration down to 5 mg/ml (iodine), dose ~3-6 mGy, and accuracy of material classification ~90%. Reconstruction-based decomposition with quadratic PL performed comparably to FBP. PL with a total variation penalty provided edge preservation and piecewise smooth images that aided DE classification and achieved improved performance over FBP and quadratic PL, reaching accuracy of ~0.98 for 2 mg/mL iodine at 3.2 mGy, compared to approx. 0.9 for FBP and quadratic PL. Accurate material decomposition with DE-CBCT is feasible at low dose and benefits from a rigorous assessment of noise mechanisms among various reconstruction-based techniques. The work points to the potential for non-linear iterative reconstruction methods for high-quality decomposition at low material concentration and dose.