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At least 253 records · Page 14Linked to original sources
arXiv2011

Reference heavy flavour cross sections in pp collisions at sqrt(s) = 2.76 TeV, using a pQCD-driven sqrt(s)-scaling of ALICE measurements at sqrt(s) = 7 TeV

We provide a reference in proton-proton collisions at the energy of the Pb-Pb 2010 run at the LHC, sqrt(s) = 2.76 TeV, for the pt-differential production cross section of D0, D+, and D*+ mesons in |y| < 0.5, of electrons from heavy flavour decays in |y| < 0.9, and of muons from heavy flavour decays in 2.5 < y < 4. The reference is obtained by applying a pQCD-driven scaling (based on the FONLL calculation) to ALICE preliminary data at sqrt(s) = 7 TeV. In order to validate the procedure, we scale the D meson cross section to sqrt(s) = 1.96 TeV and compare to the corresponding measurements from the CDF experiment.

hep-ph↗
arXiv2011

Experimental Status of Vud from Neutron Decay

The matrix element Vud of the CKM matrix can be determined by two independent measurements on neutron decay: the neutron lifetime tau and the ratio of coupling constants lambda, which is most precisely determined by measurements of the beta asymmetry angular correlation coefficient A. We present recent progress on the determination of these values and derive a world average of Vud = 0.9743 (2)RC (8)tau (12)lambda.

nucl-ex↗
arXiv2011

Selected highlights from the study of mesons

We provide a brief review of recent progress in the study of mesons using QCD's Dyson-Schwinger equations. Along the way we touch on aspects of confinement and dynamical chiral symmetry breaking but in the main focus upon: exact results for pseudoscalar mesons, including aspects of the eta-eta' problem; a realisation that the so-called vacuum condensates are actually an intrinsic, localised property of hadrons; an essentially nonperturbative procedure for constructing a symmetry-preserving Bethe-Salpeter kernel, which has enabled a demonstration that dressed-quarks possess momentum-dependent anomalous chromo- and electromagnetic moments that are large at infrared momenta, and resolution of a longstanding problem in understanding the mass-splitting between rho- and a1-mesons such that they are now readily seen to be parity partners in the meson spectrum; features of electromagnetic form factors connected with charged and neutral pions; and computation and explanation of valence-quark distribution functions in pseudoscalar mesons. We argue that in solving QCD, a constructive feedback between theory and extant and forthcoming experiments will enable constraints to be placed on the infrared behaviour of QCD's beta-function, the nonperturbative quantity at the core of hadron physics.

nucl-th↗
arXiv2011

Search for Narrow Nucleon Resonance in $γp\to ηp$

Results of a partial wave analysis of new high-statistics data on $γp\to pη$ from MAMI are presented. A fit using known broad resonances and only standard background amplitudes can not describe the relatively narrow peaking structure in the cross section in the mass region of 1660-1750 MeV which follows a minimum. An improved description of the data can be reached by either assuming the existence of a narrow resonance at a mass of about 1700 MeV with small photo-coupling or by a threshold effect. In the latter case the observed structure is explained by a strong (resonant or non-resonant) $γp\toωp$ coupling in the $S_{11}$ partial wave. When the beam asymmetry data, published by part of the GRAAL collaboration, are included in the fit, the solution with a narrow $P_{11}$ state is slightly preferred. In that fit, mass and width of the hypothetical resonance are determined to $M\sim$1694 MeV and $Γ\sim 40$ MeV, respectively, and the photo-coupling to $\sqrt{{\rm Br}_{ηN}} A_{1/2}^p \sim 2.6\cdot 10^{-3}$ GeV$^{-1/2}$. High precision measurements of the target asymmetry and $F$-observable are mandatory to establish the possible existence of such a narrow state and to provide the necessary information to define which partial wave is responsible for the structure observed in the data.

hep-ph↗
arXiv2011

BESIII: "charming" physics at an e$^+$e$^-$ collider machine

Despite the successes of the standard model, the non-perturbative dynamics of the strong interaction are not fully understood yet. Charmonium spectroscopy serves as an ideal tool to shed light on the dynamics of the strong interaction such as quark confinement and the generation of hadron masses. The BESIII collaboration studies extensively the strong interaction and various aspects that could shed light on physics beyond the standard model via copious e$^+$e$^-$ collisions at the BESIII/BEPCII facility in Beijing, China, in the charmonium mass regime. We present a few of the recent results with the emphasis on charmonium spectroscopy studies using 106$\times10^6$ $ψ^\prime$ events.

hep-ex↗
arXiv2011

Notes on New Narrow N*

We briefly discuss the most recent evidences for narrow nucleon excitation with mass around 1680 MeV. The data show that the N* should have much stronger photocoupling to the neutron than to the proton. That makes it a good candidate for the anti-decuplet member.

nucl-th↗
arXiv2011

Pionic Supergiant Radiohalos as Integral Record of Pion Emission During Nuclear Fission

In this paper we presented a short review of radioactive halos as from the perspective of their interpretation as integral record in time of different kind of known or unknown radioactivities. A special attention is paid for the unified interpretation of the supergiant halos (SGH), discovered by Grady, Walker and Laemlein, as integral record of pion emission during fission.

nucl-th↗
arXiv2011

Exploring the nucleon structure through GPDs and TDAs in hard exclusive processes

Generalized Parton Distributions (GPDs) offer a new way to access the quark and gluon nucleon structure. We review recent progress in this domain, emphasizing the need to supplement the experimental study of deeply virtual Compton scattering by its crossed version, timelike Compton scattering. We also describe the extension of the GPD concept to three quark operators and the relevance of their nucleon to meson matrix elements, namely the transition distribution amplitudes (TDAs) which factorize in backward meson electroproduction and related processes. We discuss the main properties of the TDAs. \

hep-ph↗
arXiv2011

Small-${\it x}$ and Forward Measurements at STAR

Measurements of azimuthal differences between forward di-pions are sensitive to the low-${\it x}$ gluon content of the proton and provide the best opportunity to probe for gluon saturation in nuclei. Previously reported analyses have shown that the gluon saturation regime may have been reached at STAR by looking at forward di-pions in d+Au collisions. Further insight into the uncorrelated pedestal below the near-side and away-side peaks in azimuthal correlations may be provided by differentiating between d+Au and p+Au collisions, by tagging on intact neutrons in the deuteron beam in d+Au collisions. Comparisons to recent theories indicate that multi-parton interactions play a more significant role in d+Au collisions than p+Au collisions and offer a unique opportunity to study correlations between leading partons inside nucleons. The general features found for the peaks in forward di-pion azimuthal correlations in d+Au collisions are also present in p+Au collisions.

nucl-ex↗
arXiv2011

On Generation of Photons Carrying Orbital Angular Momentum in the Helical Undulator

We analyze properties of electromagnetic radiation in helical undulators with a particular emphasis on orbital angular momentum of the radiated photons. We demonstrate that all harmonics higher than the first one radiated in a helical undulator carry an angular momentum. We discuss some possible applications of this phenomenon and the ways of effective generation of these photons in a helical undulator. We call for review of results of experiments performed where the higher harmonics radiated in a helical undulator might be involved.

physics.acc-ph↗
arXiv2013

Kinematics of a cascade decay for the precision measurement of $^{29}{\rm Si}$ binding energy

Comparison of a Penning trap and a flat-crystal spectrometer experiments gives a direct test of $E=mc^2$. The result is $1-Δmc^2/E =(-1.4 \pm 4.4) \times 10^{-7}$ for $^{29}{\rm Si}$ and $^{33}{\rm S}$. The dominant uncertainty is on the $γ$-ray measurement in neutron capture reactions, and the secondary $γ$-ray has the uncertainty 4.0 eV for $^{29}{\rm Si}$. We calculated the Doppler effect of the secondary $γ$-ray as $-646.9 \cos θ$ eV from the relativistic energy momentum relation of the $^{28}{\rm Si}(n,γ)^{29}{\rm Si}$ reaction. This corresponds to the full wave of half maximum of 431.3 eV. The error 4.0 eV comes mainly from the Bragg angle measurement between the centroids of the linewidths which means that only the most probable part of the whole data has been considered. It is necessary to confirm the assumption of the isotropy for the object to measure. We discussed a coincidence measurement as one of the methods to overcome the assumption.

nucl-th↗
arXiv2011

The MAJORANA Experiment

The MAJORANA collaboration is actively pursuing research and development aimed at a tonne-scale 76Ge neutrinoless double-beta decay) experiment. The current, primary focus is the construction of the MAJORANA DEMONSTRATOR experiment, an R&D effort that will field approximately 40kg of germanium detectors with mixed enrichment levels. This article provides a status update on the construction of the DEMONSTRATOR.

nucl-ex↗
arXiv2011

Chiral Magnetic Effect and evolution of electromagnetic field

The energy dependence of observable two particle correlator in search for the local strong parity violation in Au+Au collisions is estimated within a simple phenomenological model. The model reproduces available RHIC data but at LHC predicts that the Chiral Magnetic effect (CME) will be about 20 times weaker than at RHIC, contrary to the first LHC measurements. In the lower energy range this effect should vanish sharply at energy somewhere above the top SPS one with agreement with the preliminary results of the Beam Energy Scan program. To elucidate CME background effects a transport HSD model including magnetic field evolution is put forward and electromagnetic dynamics at the RHIC energy is investigated. It is observed that the electromagnetic field included into the hadronic model does not influence on observables due to mutual compensation of effects of electric and magnetic fields.

nucl-th↗
arXiv2011

Electromagnetic Calorimeter for HADES

We propose to build the Electromagnetic calorimeter for the HADES di-lepton spectrometer. It will enable to measure the data on neutral meson production from nucleus-nucleus collisions, which are essential for interpretation of dilepton data, but are unknown in the energy range of planned experiments (2-10 GeV per nucleon). The calorimeter will improve the electron-hadron separation, and will be used for detection of photons from strange resonances in elementary and HI reactions. Detailed description of the detector layout, the support structure, the electronic readout and its performance studied via Monte Carlo simulations and series of dedicated test experiments is presented. The device will cover the total area of about 8 m^2 at polar angles between 12 and 45 degrees with almost full azimuthal coverage. The photon and electron energy resolution achieved in test experiments amounts to 5-6%/sqrt(E[GeV]) which is sufficient for the eta meson reconstruction with S/B ratio of 0.4% in Ni+Ni collisions at 8 AGeV. A purity of the identified leptons after the hadron rejection, resulting from simulations based on the test measurements, is better than 80% at momenta above 500 MeV/c, where time-of-flight cannot be used.

nucl-ex↗
arXiv2011

Simulation of Reactors for Antineutrino Experiments Using DRAGON

From the discovery of the neutrino to the precision neutrino oscillation measurements in KamLAND, nuclear reactors have proven to be an important source of antineutrinos. As their power and our knowledge of neutrino physics has increased, more sensitive measurements have become possible. The next generation of reactor antineutrino experiments require more detailed simulations of the reactor core. Many of the reactor simulation codes are proprietary which makes detailed studies difficult. Here we present the results of the open source DRAGON code and compare it to other industry standards for reactor modeling. We use published data from the Takahama reactor to determine the quality of the simulations. The propagation of the uncertainty to the antineutrino flux is also discussed.

nucl-ex↗
arXiv2011

Central Meson Production in ALICE

The ALICE experiment at the Large Hadron Collider (LHC) at CERN consists of a central barrel, a muon spectrometer and of additional detectors for trigger and event classification purposes. The low transverse momentum threshold of the central barrel gives ALICE a unique opportunity to study the low mass sector of central production at the LHC. First analysis results of meson production in double gap events in proton-proton collisions at $\sqrt{s}$ = 7 TeV and in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV are presented.

hep-ex↗
arXiv2011

Transverse momentum spectra of identified charged hadrons with the ALICE detector in Pb--Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV

The measurement of identified charged-hadron production at mid-rapidity ($|y| < 0.5$) performed with the ALICE experiment is presented for Pb--Pb collisions at $\sqrt{s_{\rm NN}} = \rm .76 TeV$. The transverse momentum spectra of $π^{\pm}$, $K^{\pm}$, $p$ and $\bar{p}$ are measured from 100 MeV/c up to 3 GeV/c for pions, from 200 MeV/c up to 2 GeV/c for kaons and from 300 MeV/c up to 3 GeV/c for protons and antiprotons using the \emph{dE/dx} and the \emph{time-of-flight} particle-identification techniques. Preliminary results on charged hadron production yields and particle ratios are reported as a function of $p_{T}$ and collision centrality. Finally, the results are discussed in terms of hydrodynamics-inspired models and compared with published RHIC data in Au--Au collisions at $\sqrt{s_{\rm NN}} = \rm 200 GeV$ and predictions for the LHC.

nucl-ex↗