arXiv subjects

S. Paul

Publications and source records attributed to S. Paul.

At least 91 records · Page 5Linked to original sources

arXiv2011

Solid oxygen as converter for the production of ultra-cold neutrons

We have investigated solid oxygen as a converter material for the production of ultra-cold neutrons. In a first series of experiments the crystal preparation was examined. An optically semi-transparent solid $α$-oxygen crystal has been prepared. In a second series of experiments such a crystal prepared indentically as in the first series of experiments has been exposed to the cold neutron flux of the MEPHISTO beam line of the FRM II. Ultra-cold neutrons produced inside the oxygen crystal have been extracted and the count rates have been measured at different converter temperatures. The results of these measurements give a clear signal of the superthermal UCN production mechanism in $α$-oxygen. The mean free loss length of UCN inside the crystal at a temperature of 5\,K was determined to be in the order of $20\,\mathrm{cm}$.

nucl-ex↗

arXiv2011

Evolution of shocks and turbulence in the formation of galaxy clusters embedded in Megaparsec-scale filaments

Massive structures like cluster of galaxies, embedded in cosmic filaments, release enormous amount of energy through their interactions. These events are associated with production of Mpc-scale shocks and injection of considerable amount of turbulence, affecting the non-thermal energy budget of the ICM. In order to study this thoroughly, we performed a set of cosmological simulations using the hydrodynamical code Enzo. We studied the formation of clusters undergoing major mergers, the propagation of merger shocks and their interaction with the filamentary cosmic web. This interaction is shown to produce peripheral structures remarkably similar to giant radio relics observed, for example, in Abell 3376 and Abell 3667. We find a relatively long timescale (about 4 Gyr) for turbulence decay in the centre of major merging clusters. This timescale is substantially longer than typically assumed in the turbulent re-acceleration models, invoked for explaining the statistics of observed radio halos.

astro-ph.CO↗

arXiv2010

Evolution of shocks and turbulence in major cluster mergers

We performed a set of cosmological simulations of major mergers in galaxy clusters to study the evolution of merger shocks and the subsequent injection of turbulence in the post-shock region and in the intra-cluster medium (ICM). The computations were done with the grid-based, adaptive mesh refinement hydro code Enzo, using an especially designed refinement criteria for refining turbulent flows in the vicinity of shocks. A substantial amount of turbulence energy is injected in the ICM due to major merger. Our simulations show that the shock launched after a major merger develops an ellipsoidal shape and gets broken by the interaction with the filamentary cosmic web around the merging cluster. The size of the post-shock region along the direction of shock propagation is about 300 kpc h^-1, and the turbulent velocity dispersion in this region is larger than 100 km s^-1. Scaling analysis of the turbulence energy with the cluster mass within our cluster sample is consistent with M^(5/3), i.e. the scaling law for the thermal energy in the self-similar cluster model. This clearly indicates the close relation between virialization and injection of turbulence in the cluster evolution. We found that the ratio of the turbulent to total pressure in the cluster core within 2 Gyr after the major merger is larger than 10%, and it takes about 4 Gyr to get relaxed, which is substantially longer than typically assumed in the turbulent re-acceleration models, invoked to explain the statistics of observed radio halos. Striking similarities in the morphology and other physical parameters between our simulations and the "symmetrical radio relics" found at the periphery of the merging cluster A3376 are finally discussed. In particular, the interaction between the merger shock and the filaments surrounding the cluster could explain the presence of "notch-like" features at the edges of the double relics.

astro-ph.CO↗

arXiv2010

Production of Ultra-Cold-Neutrons in Solid α-Oxygen

Our recent neutron scattering measurements of phonons and magnons in solid α-oxygen have led us to a new understanding of the production mechanismen of ultra-cold-neutrons (UCN) in this super-thermal converter. The UCN production in solid α-oxygen is dominated by the excitation of phonons. The contribution of magnons to UCN production becomes only slightly important above E >10 meV and at E >4 meV. Solid α-oxygen is in comparison to solid deuterium less effcient in the down-scattering of thermal or cold neutrons into the UCN energy regime.

nucl-ex↗

arXiv2010

New Understanding of Ultra-Cold Neutron Production in Solid Deuterium

Our recent neutron scattering measurements of phonons and other quasi-particle excitations in solid deuterium (sD$_2$) and the extraction of the density of states for phonons and rotational transitions in sD2 have led us to a new understanding of the production of ultra-cold neutrons (UCN) in sD2. This new picture is somehow different to earlier published results for sD2. The cross section for UCN production in sD2 has been determined by using the density of states G1(E) in combination with the incoherent approximation and by a direct calibration of our measured neutron cross sections with the known cross section of the J=1 -> 0 rotational transition in deuterium. Both methods deliver new data on this cross section and agree quite well with direct measurements of this energy averaged UCN production cross section.

nucl-ex↗

arXiv2010

The PANDA GEM-based TPC Prototype

We report on the development of a GEM-based TPC prototype for the PANDA experiment. The design and requirements of this device will be illustrated, with particular emphasis on the properties of the recently tested GEM-detector, the characterization of the read-out electronics and the development of the tracking software that allows to evaluate the GEM-TPC data.

nucl-ex↗

arXiv2010

Period doubling route to chaos in Taylor-Green dynamo

We perform spectral simulations of dynamo for magnetic Prandtl number of one with Taylor-Green forcing. We observe dynamo transition through a supercritical pitchfork bifurcation. Beyond the transition, the numerical simulations reveal complex dynamo states with windows of constant, periodic, quasiperiodic, and chaotic magnetic field configurations. For some forcing amplitudes, multiple attractors were obtained for different initial conditions. We show that one of the chaotic windows follows the period-doubling route to chaos.

nlin.CD↗

arXiv2010

A Novel Generic Framework for Track Fitting in Complex Detector Systems

This paper presents a novel framework for track fitting which is usable in a wide range of experiments, independent of the specific event topology, detector setup, or magnetic field arrangement. This goal is achieved through a completely modular design. Fitting algorithms are implemented as interchangeable modules. At present, the framework contains a validated Kalman filter. Track parameterizations and the routines required to extrapolate the track parameters and their covariance matrices through the experiment are also implemented as interchangeable modules. Different track parameterizations and extrapolation routines can be used simultaneously for fitting of the same physical track. Representations of detector hits are the third modular ingredient to the framework. The hit dimensionality and orientation of planar tracking detectors are not restricted. Tracking information from detectors which do not measure the passage of particles in a fixed physical detector plane, e.g. drift chambers or TPCs, is used without any simplifications. The concept is implemented in a light-weight C++ library called GENFIT, which is available as free software.

hep-ex↗

arXiv2009

First Principles Analysis of Electron-Phonon Interaction in Graphene

The electron-phonon interaction in monolayer graphene is investigated by using density functional perturbation theory. The results indicate that the electron-phonon interaction strength is of comparable magnitude for all four in-plane phonon branches and must be considered simultaneously. Moreover, the calculated scattering rates suggest an acoustic phonon contribution that is much weaker than previously thought, revealing the role of optical phonons even at low energies. Accordingly it is predicted, in good agreement with a recent measurement, that the intrinsic mobility of graphene may be more than an order of magnitude larger than the high values reported in suspended samples.

cond-mat.mes-hall↗

arXiv2009

Neutron to Mirror-Neutron Oscillations in the Presence of Mirror Magnetic Fields

We performed ultracold neutron (UCN) storage measurements to search for additional losses due to neutron (n) to mirror-neutron (n') oscillations as a function of an applied magnetic field B. In the presence of a mirror magnetic field B', UCN losses would be maximal for B = B'. We did not observe any indication for nn' oscillations and placed a lower limit on the oscillation time of tau_{nn'} > 12.0 s at 95% C.L. for any B' between 0 and 12.5 uT.

nucl-ex↗

arXiv2009

Density of states in solid deuterium: Inelastic neutron scattering study

The dynamics of solid deuterium (sD2) is studied by means of inelastic scattering (coherent and incoherent) of thermal and cold neutrons at different temperatures and para-ortho ratios. In this paper, the results for the generalized density of states (GDOS) are presented and discussed. The measurements were performed at the thermal neutron time-of-flight (TOF) instrument IN4 at ILL Grenoble and at the cold neutron TOF instrument TOFTOF at FRM II Garching. The GDOS comprises besides the hcp phonon excitations of the sD2 the rotational transitions J = 0 ->1 and J = 1 -> 2. The intensities of these rotational excitations depend strongly on the ortho-D2 molecule concentration co in sD2. Above E = 10 meV there are still strong excitations, which very likely may originate from higher energy damped optical phonons and multi-phonon contributions. A method for separating the one- and multi-phononon contributions to the density of states willbe presented and discussed.

cond-mat.mtrl-sci↗

arXiv2009

First principles calculations of lattice thermal conductivity in mono- and bi-layer graphene

Using calculations from first principles we have investigated the lattice thermal conductivity of ideal mono- and bi-layer graphene sheets. Our results demonstrate that the intrinsic thermal conductivity of both mono- and bi-layer graphene is around 2200 W/mK at 300 K, a value close to the one observed theoretically and experimentally in graphite basal plane, and at higher temperatures it decreases with the expected 1/T dependence. The little variation between mono- and bi-layer thermal conductivity suggests that increasing the number of layers does not affect significantly the in-plane thermal properties of these systems.

cond-mat.mtrl-sci↗

arXiv2009

Pattern recognition and PID for COMPASS RICH-1

A package for pattern recognition and PID by COMPASS RICH-1 has been developed and used for the analysis of COMPASS data collected in the years 2002 to 2004, and 2006-2007 with the upgraded RICH-1 photon detectors. It has allowed the full characterization of the detector in the starting version and in the upgraded one, as well as the PID for physics results. We report about the package structure and algorithms, and the detector characterization and PID results.

physics.ins-det↗

arXiv2008

An Improved Neutron Electric Dipole Moment Experiment

A new measurement of the neutron EDM, using Ramsey's method of separated oscillatory fields, is in preparation at the new high intensity source of ultra-cold neutrons (UCN) at the Paul Scherrer Institute, Villigen, Switzerland (PSI). The existence of a non-zero nEDM would violate both parity and time reversal symmetry and, given the CPT theorem, might lead to a discovery of new CP violating mechanisms. Already the current upper limit for the nEDM (|d_n|<2.9E-26 e.cm) constrains some extensions of the Standard Model. The new experiment aims at a two orders of magnitude reduction of the experimental uncertainty, to be achieved mainly by (1) the higher UCN flux provided by the new PSI source, (2) better magnetic field control with improved magnetometry and (3) a double chamber configuration with opposite electric field directions. The first stage of the experiment will use an upgrade of the RAL/Sussex/ILL group's apparatus (which has produced the current best result) moved from Institut Laue-Langevin to PSI. The final accuracy will be achieved in a further step with a new spectrometer, presently in the design phase.

nucl-ex↗

arXiv2008

Integration of e^(x^n) and e^(-x^n) in forms of series, their applications in the field of differential equation; introducing generalized form of Skewness and Kurtosis; extension of starling's approximation

In this paper we tried a different approach to work out the integrals of e^(x^n) and e^(-x^n). Integration by parts shows a nice pattern which can be reduced to a form of series. We have shown both the indefinite and definite integrals of the functions mentioned along with some essential properties e.g. conditions of convergence of the series. Further more, we used the integrals in form of series to find out series solution of differential equations of the form x[(d^2 y)/(dx^2)]-(n-1)(dy/dx)-n^2 x^(2n-1)y-nx^n=0 and x[(d^2 y)/(dx^2)] -(n-1)(dy/dx)-n^2x^(2n-1)y+(n-1)=0, using some non standard method. We introduced modified Normal distribution incorporating some properties derived from the above integrals and defined a generalized version of Skewness and Kurtosis. Finally we extended Starling's approximation to limit [n to infinity ] (2n)! ~ 2n * \sqrt{(2π)} [(2n/e)]^(2n).

math.GM↗

arXiv2008

Methods and Models for Hadron Physics

A round table held during the Hadron07 Conference focusing on experimental observations of new hadronic states, on theoretical perspectives for their description, and on the role of hadronic spectroscopy in furthering our knowledge of the fundamental theory of strong interactions.

hep-ph↗

arXiv2008

Hyperspherical Partial Wave Theory with Two-term Error Correction

Hyperspherical Partial Wave Theory has been applied to calculate T-matrix elements and Single Differential Cross-Section (SDCS) results for electron-hydrogen ionization process within Temkin-Poet model potential. We considered three different values of step length to compute the radial part of final state wave function. Numerical outcomes show that T-matrix elements and SDCS values depend on the step length h. Here, we have presented T-matrix elements and the corresponding SDCS results for 0.0075 a.u., 0.009 a.u. and 0.01 a.u. values of h and for 27.2eV, 40.8ev and 54.4eV impact energies. With the help of the calculated data for three different step lengths, we have been able to evaluate a two-term error function depending on the step length h. Finally, two-term error corrected T-matrix elements and the corresponding SDCS values have been computed. We fitted our two-term error corrected SDCS results by a suitable curve and compared with the benchmark results of Jones et al. [Phys. Rev. A, 66, 032717 (2002)]. Our fitted curves agree very well with the calculated results of Jones et al. and two-term error corrected SDCS results somewhere agree with the benchmark results. Two-term error corrected SDCS results are significantly better than the calculated SDCS results of different step lengths.

quant-ph↗

arXiv2007

Observation of a resonance in the K$_s$p decay channel at a mass of 1765 MeV/c$^2$

We report on the observation of a K$_s$p resonance signal at a mass of 1765$\pm$5 MeV/c$^2$, with intrinsic width $Γ= 108\pm 22$ MeV/c$^2$, produced inclusively in $Σ^-$-nucleus interactions at 340 GeV/c in the hyperon beam experiment WA89 at CERN. The signal was observed in the kinematic region $x_F>0.7$, in this region its production cross section rises approximately linearly with $(1-x_F)$, reaching $BR(X\to K_S p)\cdot dσ/dx_F = (5.2\pm 2.3) μb $ per nucleon at $x_F=0.8$. The hard \xf spectrum suggests the presence of a strong leading particle effect in the production and hence the identification as a $Σ^{*+}$ state. No corresponding peaks were observed in the $K^- p$ and $Λπ^{\pm}$ mass spectra.

hep-ex↗