$\Lambda$ resonances studied in $K^-p\rightarrow \Sigma^0\pi^0$ in a chiral quark model

A chiral quark-model approach is extended to the study of the $\bar{K}N$ scattering at low energies. The process of $K^-p\rightarrow \Sigma^0\pi^0$ at $P_K\lesssim 800$ MeV/c (i.e. the center mass energy $W\lesssim 1.7$ GeV) is investigated. The $\Lambda(1405)S_{01}$ dominates the reactions over the energy region considered here. Around $P_K\simeq 400$ MeV/c, the $\Lambda(1520)D_{03}$ is responsible for a strong resonant peak in the cross section. Our analysis suggests that there exist configuration mixings within the $\Lambda(1405)S_{01}$ and $\Lambda(1670)S_{01}$ as admixtures of the $[\textbf{70},^2\textbf{1},1/2]$ and $[\textbf{70},^2\textbf{8},1/2]$ configurations. The $\Lambda(1405)S_{01}$ is dominated by $[\textbf{70},^2\textbf{1},1/2]$, and $\Lambda(1670)S_{01}$ by $[\textbf{70},^2\textbf{8},1/2]$. The non-resonant background contributions, i.e. $u$-channel and $t$-channel, also play important roles in the explanation of the angular distributions due to amplitude interferences.     

$J^{P}$ Assignments of $\Lambda_c^{+}$ Baryons

The ＂good＂ diquark is employed to study A＋ baryons within a mass loaded flux tube model. The study indicates that all A＋ baryons candidates in the 2008 review by the Particle Data Group （PDG） are well described in the mass loaded flux model. The quantum numbers JP of these A＋ candidates are assigned. If Ac（2765）＋ is an orbitally excited A＋, it is likely the JP=3/2＋one. If ∧c（2765）＋ is an orbitally excited ∑c, there ought to be another JP=3/2＋∧c＋with mass ≈2770 MeV. In the model, there exists no JP=1/2＋∧c＋（≈2700）predicted in existing literature. Ac （2940）＋ is very possible the orbitally excited baryon with     

$\mathcal{PT}$-Symmetric Quantum Electrodynamics—$\mathcal{PT}$QED

The construction of PT\mathcal{PT}-symmetric quantum electrodynamics is reviewed. In particular, the massless version of the theory in 1+1 dimensions (the Schwinger model) is solved. Difficulties with unitarity of the S-matrix are discussed.     

Photoproduction of the $\Theta^+$ and its vector and axial-vector structure

We present recent investigations on the vector and axial-vector transitions of the baryon antidecuplet within the framework of the self-consistent SU（3） chiral quark-soliton model, taking into account the 1/No rotational and linear mscorrections. The main contribution to the electric-like transition form factor comes from the wave-function corrections. This is a consequence of the generalized Ademollo-Gatto theorem. It is also found that in general the leading-order contributions are almost canceled by the rotational 1/No corrections. The results are summarized as follows： the vector and tensor K＇NO coupling constants, gK＊N= 0.74--0.87 and fk＊N =0.53--1.16, respectively, and F→KN = 0.71 MeV, based on the result of the KN coupling constant gKne =0.83. We also show the differential cross sections and beam asymmetries, based on the present results. We also discuss the connection of present results with the original work by Diakonov, Petrov, and Polyakov.     

$\ensuremath{\mathcal{P}}$$\ensuremath{\mathcal{T}}$ Symmetry vs. Hermiticity

The relation between the P\ensuremath{\mathcal{P}} T\ensuremath{\mathcal{T}} symmetry and Hermiticity is discussed. In the finite-dimensional linear space, any Hermitian matrix is a special case of P\ensuremath{\mathcal{P}} T\ensuremath{\mathcal{T}}-symmetric matrices. Explicit results in 2×2 are shown. The early belief that the P\ensuremath{\mathcal{P}} T\ensuremath{\mathcal{T}}-symmetric quantum mechanics is a generalization of the conventional Hermitian quantum mechanics is confirmed.     

Vitali $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{l} $$ Anatol’evich Zverev (On his 80th birthday)

Chronicle

Vitali $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ Anatol’evich Zverev (On his 80th birthday)     

Investigation of the anomaly in $\eta$-photoproduction off the neutron

Quasi-free photoproduction of wmesons off the neutron and off the proton has been studied using a deuterium target and bremsstrahlung photons produced by MAMI-C with incident energies up to 1.5 GeV. The wmesons were detected in coincidence with the recoil nucleons thus a fully exclusive measurement was performed. Preliminary results show a bump-like structure in the excitation function for the neutron close to W ≈ 1675 MeV which is not seen for the proton. Considering the experimental resolution and using a Breit-Wigner fit the width of this structure was approximated below 50 MeV.     

$\mathfrak{D}$ -Differentiation in Hilbert Space and the Structure of Quantum Mechanics

An appropriate kind of curved Hilbert space is developed in such a manner that it admits operators of - and -differentiation, which are the analogues of the familiar covariant and D-differentiation available in a manifold. These tools are then employed to shed light on the space-time structure of Quantum Mechanics, from the points of view of the Feynman ‘path integral’ and of canonical quantisation. (The latter contains, as a special case, quantisation in arbitrary curvilinear coordinates when space is flat.) The influence of curvature is emphasised throughout, with an illustration provided by the Aharonov-Bohm effect.     

Hund’s rule magnetism in C $\mathsf{_{60}}$ ions?

We investigate the occurrence of Hunds rule magnetism in C molecular ions, by computing the ground-state spin for all charge states n from -3 to +5. The two competing interactions, electron-vibration (e-v, including Jahn Teller, favoring low spin) and electron-electron (e-e, including Hund-rule exchange, favoring high spin), are accounted for based on previously computed ab initio coupling parameters. Treating the ion coordinates as classical, we first calculate and classify the static Jahn-Teller distorted states for all n, inclusive of both e-v and e-e effects. We then correct the adiabatic result by including the zero-point energy lowering associated with softening of vibrations at the adiabatic Jahn-Teller minima. Our overall result is that while, like in previous investigations, low-spin states prevail in negative ions, Hunds rule high spin dominates all positive C₆₀ ⁿ⁺ ions. This suggests also that Hund-rule magnetism could arise in fullerene cation-based solid state compounds, particularly those involving C₆₀ ²⁺.Received: 17 April 2003, Published online: 22 September 2003PACS: 36.40.Cg Electronic and magnetic properties of clusters - 61.48.+c Fullerenes and fullerene-related materials (structure) - 71.20.Tx Fullerenes and related materials; intercalation compounds (electronic structure) - 75.75.+a Magnetic properties of nanostructures     

Do we understand the single-spin asymmetry for $\pi^0$ inclusive production in pp collisions?

The cross section data for inclusive production in pp collisions is considered in a rather broad kinematic region in energy , Feynman variable x _F and transverse momentum p _T. The analysis of these data is done in the perturbative QCD framework at the next-to-leading order. We find that they cannot be correctly described in the entire kinematic domain and this leads us to conclude that the single-spin asymmetry, A _N for this process, observed several years ago at FNAL by the experiment E704 and the recent result obtained at BNL-RHIC by STAR, are two different phenomena.Received: 10 March 2004, Revised: 19 May 2004, Published online: 14 July 2004preprint CPT-2003/P.4581(UMR 6207 is Unité Mixte de Recherche du CNRS and of Universités Aix-Marseille I and Aix-Marseille II and of Université du Sud Toulon-Var, Laboratoire affilié á la FRUMAM)     

In memory of Vladimir Mikha $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{l}$$ lovich Kudryashov (December 11, 1930–February 26, 2003)

Chronicle

In memory of Vladimir Mikha $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ lovich Kudryashov (December 11, 1930–February 26, 2003)     

In memory of Alekse $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{l} $$ Sergeevich Nikiforov (March 28, 1927–October 1, 2002)

Chronicle

In memory of Alekse $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ Sergeevich Nikiforov (March 28, 1927–October 1, 2002)     

Deuteron and antideuteron measurements in Au + Au collisions at $\sqrt{s_{NN}}=200~\mbox{GeV}$ at RHIC-PHENIX

In Run-7 of RHIC operations PHENIX has recorded over 5.4 billion minimum bias events, facilitating a detailed study of deuteron and antideuteron production as a function of centrality and up to transverse momentum of p _T =5 GeV/c. We present transverse momentum p _T and transverse mass m _T spectra, mean transverse momentum 〈p _T 〉, source parameters, particle ratios, and nuclear modification factor R _CP . Deuteron and antideuteron spectra are compared to those of other identified particles and to hydrodynamical predictions.     

Superconductivity in the doped “pseudo-ladder” compound CaCu$_\mathsf{2}$O$_\mathsf{3}$

An effective anisotropic t-J model for the pseudo-ladder compound CaCu₂O₃ is proposed based on recent experimental studies and band structure calculations. Superconducting pairing mediated by the exchange interaction in the model is investigated as a function of doping away from the antiferromagnetic insulating state. It is shown that strong anisotropy in the electronic spectrum suppresses superconducting temperature in comparison with conventional copper-oxide superconductors with square lattices.     

Two photon exchange contributions to elastic $\vec{e}+p\rightarrow e+\vec{p}$ process in the non-local field formalism

We compute the two photon exchange contributions to elastic scattering of polarized electrons from target protons. We use a non-local field theory formalism for this calculation. The formalism maintains gauge invariance and provides a systematic procedure for making this calculation. The results depend on one unknown parameter, . We compute the two photon exchange correction to the ratio of electric to magnetic form factors extracted using polarization transfer experiments. The correction is found to be small if . However, for larger values of , the correction can be quite significant. The correction to the polarization transfer results goes in the right direction to explain their difference with the ratio measured by the Rosenbluth separation method. We find that the difference between the two experimental results can be explained for a wide range of values of the parameter . We also find that the corrections due to two photon exchange depend on the photon longitudinal polarization ε. Hence, we predict an ε dependence of the form factor ratio extracted using the polarization transfer technique. Finally, we obtain a limit on by requiring that the non-linearity in ε dependence of the unpolarized reduced cross section is within experimental errors.     

Study of Nucleon resonances in a chiral quark model via $\eta$ productions

In this report we investigate Wmeson productions on the proton via electromagnetic and hadron probes in a chiral quark model approach. The observables, such as, differential cross section and beam asymmetry for the two productions are calculated and compared with the experiment. The five known resonances S11（1535）,S11（1650）, P13（1720）, D13（1520）, and F15（1680） are found to be dominant in the reaction mechanisms in both channels. Significant contribution ＂missing resonances, no evidence is found within πp→ηn are also presented. from a new S11 resonances are deduced. For the so-called the investigated reactions. The partial wave amplitudes for     

Extending $\mathcal{P}\mathcal{T}$ Symmetry from Heisenberg Algebra to E2 Algebra

The E2 algebra has three elements, J, u, and v, which satisfy the commutation relations [u,J]=iv, [v,J]=−iu, [u,v]=0. We can construct the Hamiltonian H=J ²+gu, where g is a real parameter, from these elements. This Hamiltonian is Hermitian and consequently it has real eigenvalues. However, we can also construct the PT\mathcal{P}\mathcal{T}-symmetric and non-Hermitian Hamiltonian H=J ²+igu, where again g is real. As in the case of PT\mathcal{P}\mathcal{T}-symmetric Hamiltonians constructed from the elements x and p of the Heisenberg algebra, there are two regions in parameter space for this PT\mathcal{P}\mathcal{T}-symmetric Hamiltonian, a region of unbroken PT\mathcal{P}\mathcal{T} symmetry in which all the eigenvalues are real and a region of broken PT\mathcal{P}\mathcal{T} symmetry in which some of the eigenvalues are complex. The two regions are separated by a critical value of g.     

Study of direct photon plus jet production in CMS experiment at $\sqrt{s}$ = 14 TeV

We present simulation results of γ+jet analysis using CMS (compact muon solenoid) object-oriented software at the large hadron collider (LHC) center of mass energy = 14 TeV. The study of direct photon production helps in validating the perturbative quantum chromodynamics (pQCD) and providing information on the gluon distribution in the nucleons. Direct photon processes also constitute a major background to several other standard model (SM) processes and signals of new physics. Thus these processes need to be understood precisely in the new energy regime. In this work, we have done a detailed study of the GEANT4 simulated γ+jet events generated with Pythia, and the related background processes. Isolation cuts have been optimized for direct photon which improves the signal over background ratio by ∼25% as compared to previous studies done in CMS. The inclusion of a large Δφ cut between the photon and the leading jet at 40° in the analysis leads to a further increase of ∼15% in S/B, thus giving an overall gain of ∼42% in S/B ratio.