Pentaquarks—status report

I discuss the recent experimental and theoretical developments following the discovery of the 8⁺ pentaquark, an exoticuudd \(\bar s\) baryon resonance observed in theKN channel by several experiments, and an exotic Ξ^*?? (ddss \(\bar u\)) reported by NA49 at CERN. I focus on the theoretical interpretation of the data, both in terms of quark and chiral degrees of freedom, on the predictions for related exotic states, and on several unresolved questions raised by the experimental data, such as why some experiments observe the pentaquarks and other don't, the apparently extremely narrow width of the Θ⁺ and the determination of its parity. I also describe the likely properties of the proposed heavy-quark pentaquarks, an anticharmed exotic baryon Θ _c uudd \(\bar c\) and Θ _b ⁺ (uudd \(\bar b\)) which are expected to be extremely narrow or even stable against strong decays. H1 recently reported observation of a possible Θ _c candidate inD ^*? p channel. Pentaquarks are also being searched for ine ⁺ e ^? annihilation and γγ collisions in the LEP data and atB-factories.     

Proj ect for m easuri ng th e n eutro n el ectromag n etic form factor i n th e r eactio n e+ e− → n$$ \bar n $$ at th e VEPP-2000 collid er

A project aimed at measuring the neutron electromagnetic form factor in the reaction e ⁺ e ^? → n \(\bar n\) with the SND detector at the VEPP-2000 e ⁺ e ^? collider is presented. The results obtained for the time resolution of the NaI(Tl) counter using flash-ADC are reported along with estimates of the efficiency of separation of neutron-antineutron events.     

$$\bar K$$ optical potential at finite temperatureoptical potential at finite temperature

The \(\bar K\) optical potential is microscopically calculated from the \(\bar K\)N effective interaction in nuclear matter at T=0 and finite temperature, with the aim to adapt our calculations to the experimental conditions in heavy-ion collisions. In the rank of densities (0-2_ρ0), the finite temperature \(\bar K\) optical potential shows a smoother behaviour compared to the T=0 case. The model has also been applied to the study of the ratio between K⁺ and K^? produced at GSI with T around 70 MeV. The results point at the necessity of introducing an attractive \(\bar K\) optical potential.     

Neutrino-astrophysics,nuclear physics,and particle physics at intense,pulsed, stopped-pion sources

Intense pulsed proton beams of ～ 1 GeV impinging on high-Z targets are intense sources of ν_μ from the (τ=26 ns) decay of π⁺, and \(\bar \nu _\mu \) and ν_e from the stopped μ⁺ decays. A pulse structure, narrow in time, allows the separation of reactions due to ν_μ from those from reactions involving \(\bar \nu _\mu\) and ν_e. The energy spectra are in the energy range of interest to nuclear astrophysics. A number of possible experiments relevant to solar neutrinos, supernovae collapse, weak interactions in nuclei, and intrinsic properties of neutrinos are discussed.     

Phenomenology of light- and strange-quark simultaneous production at high energies

This letter presents an extension of EPL116(2017)62001 to light- and strange-quark nonequilibrium chemical phase-space occupancy factors (γ_q,s). The resulting damped trigonometric functionalities relating γ_q,s to the nucleon-nucleon center-of-mass energies (\(\sqrt {{s_{NN}}} \)) looks very similar except different coefficients. The phenomenology of the resulting γ_q,s(\(\sqrt {{s_{NN}}} \)) describes a rapid decrease at \(\sqrt {{s_{NN}}} \) ? 7GeV followed by a faster increase up to ~20 GeV. Then, both γ_q,s become nonsensitive to \(\sqrt {{s_{NN}}} \). Although these differ from γ _s (\(\sqrt {{s_{NN}}} \))obtained at γ _q (\(\sqrt {{s_{NN}}} \))=1, various particle ratios including K⁺/π⁺, K^?/π^?, Λ/π^?, Λ?/π^?, Ξ⁺/π⁺, and Ω/π^?, can well be reproduced, as well. We conclude that γ_q,s(\(\sqrt {{s_{NN}}} \)) should be instead determined from fits of various particle yields and ratios but not merely from fits to the particle ratio K⁺/π⁺.     

Quark-hadron duality and production of charmonia and doubly charmed baryons in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> anninhilation

The cross sections for the production of charmonia and doubly charmed baryons in e ⁺ e ^? annihilation at an interaction energy of \(\sqrt s \) = 10.6 GeV are predicted under the assumption of quark—hadron duality. The method used is shown to remove some contradictions between experimental data and perturbative QCD.     

Dominant decays of scalar leptoquarks and scalar gluons in the minimal four-color symmetry model

Fermionic and weak decays of the scalar leptoquarks S = S ₁ ⁽⁺⁾ , S ₁ ^(?) , and S _m and the scalar gluons F = F ₁ and F ₂ predicted by the minimal model involving four-color symmetry and the Higgs mechanism of quark-and lepton-mass splitting are considered. The widths and the branching ratios are calculated for these decays, and the results are analyzed versus the couplings and masses of decaying particles. It is shown that, at relatively small mass splittings Δm within scalar doublets (Δm < m _W), the fermionic decays S ₁ ⁽⁺⁾ → tl _j ⁺ , S ₁ ^(?) → v _i \(\tilde b\), S _m → t \(\tilde \nu \) _j, F ₁ → t \(\tilde b\), and F ₂ → t \(\tilde t\), which are characterized by few-GeV widths for m _S, m _F < 1 TeV and decay branching ratios close to unity, are dominant, but that, for Δm > m _W, the weak decays S → S′W and F → F’W compete with the above fermionic decays. In the case of m _S < m _t, the processes S ₁ ⁽⁺⁾ → cl _j ⁺ , S ₁ ^(?) → v _i \(\tilde b\), S _m → bl _j ⁺ , and S _m → c \(\tilde \nu \) _j, whose total branching ratios are Br(S ₁ ⁽⁺⁾ → cl ⁺) ≈ Br(S ₁ ^(?) → v \(\tilde b\)) ≈ 1, Br(S _m → bl ⁺) ≈ 0.9, and Br(S _m → c \(\tilde \nu \)) ≈ 0.1, appear to be dominant decays of scalar leptoquarks. Searches for these decays at LHC and the Tevatron are of interest.     

Effects of four-fermion contact interactions in the Bhabha process at linear electron-positron colliders

For the case of longitudinally polarized primary beams, effects are investigated that are induced by four-fermion contact interactions in the process e⁺e^? → e⁺e^? occurring at linear electron-positron colliders of energy in the range \(\sqrt s = 0.5 - 1 TeV\). Model-independent constraints on the parameters of four-fermion contact interactions are obtained. It is shown that the sensitivity of the Bhabha process to the parameter Λ_LR is considerably higher than the sensitivity of the leptonic process e⁺e^? → μ⁺μ^?; at the same time, the sensitivities of these processes to the parameters Λ_RR and Λ_LL are commensurate.     

Charmonium 2007: New experimental results

The most important experimental results in charmonium physics in the energy region above the threshold for open-charm production that were obtained in recent years are surveyed. The first measurements of the exclusive cross sections for e ⁺ e ^? → D \(\bar D\), D \(\bar D\)*, and D* \(\bar D\)* processes are discussed along with the discovered decay ψ(4415) → \(\bar D_2^* \)(2460). The properties of charmonium-like states, including the group of states Y (4260), Y (4325), and Y (4660) with quantum numbers of J ^PC = 1^??; the X(3940) and X(4160) states discovered in the process of double charmonium production in e ⁺ e ^? annihilation; and the X(3872), Y(3940), and Z ^±(4430) states found in B-meson decays, are presented.     

On the structure of the von Neumann algebras generated by local functions of the free bose field

It is shown that the von Neumann algebra\(R_\mathfrak{B} \)(B) generated by any scalar local functionB(x) of the free fieldA ₀(x) is equal either to\(R_\mathfrak{B} \)(A ₀) or to\(R_\mathfrak{B} \)(:A ₀ ² :). The latter statement holds if the state space space\(\mathfrak{H}_B \) obtained from the vacuum state by repeated application ofB(x) is orthogonal to the one particle subspace. In the proof of these statements, space-time limiting techniques are used.     

CP violation at colliders

The prospects of experimental detection ofCP violation ate ⁺ e ^? and\(pp/p\bar p\) colliders are reviewed. After a general discussion on the quantities which can measureCP violation and on the implications of theCPT theorem, various possibilities of measuringCP violation arising outside the standard model are taken up.CP violation in leptonic processes, especially polarization effects ine ⁺ e ^?→l ⁺ l ^? are discussed next.CP violation in\(t\overline t \) andW ⁺ W ^? production and decay is also described.     

Ds+ → π+ π+ π− decay: The $$1^3 P_0 s\bar s$$ component in scalar-isoscalar mesons

We calculate the processes \(D_s^ + \to \pi ^ + s\bar s\) and D _s ⁺ → π⁺resonance, respectively, in the spectator and W-annihilation mechanisms. The data on the reaction D _s ⁺ → π⁺ρ⁰, which is due to the W-annihilation mechanism only, point to a negligibly small contribution of the W annihilation to the production of scalar-isoscalar resonances D _s ⁺ ?π⁺f₀. As to spectator mechanism, we evaluate the \(1^3 P_0 s\bar s\) component in the resonances f₀(980), f₀(1300), and f₀(1500) and broad state f₀(1200–1600) on the basis of data on the decay ratios D _s ⁺ ?π⁺f₀/(D _s ⁺ ?π⁺_θ). The data point to a large \(s\bar s\) component in the \(f_0 (980):40 \lesssim s\bar s \lesssim 70\% \). Nearly 30% of the \(1^3 P_0 s\bar s\) component flows to the mass region 1300–1500 MeV, being shared by f₀(1300), f₀(1500), and broad state f₀(1200–1600): the interference of these states results in a peak near 1400 MeV with the width around 200 MeV. Our calculations show that the yield of the radial-excitation state\(2^3 P_0 s\bar s\)is relatively suppressed, \({{\Gamma (D_s^ + \to \pi ^ + (2^3 P_0 s\bar s))} \mathord{\left/ {\vphantom {{\Gamma (D_s^ + \to \pi ^ + (2^3 P_0 s\bar s))} {\Gamma (D_s^ + \to \pi ^ + (1^3 P_0 s\bar s))}}} \right. \kern-\nulldelimiterspace} {\Gamma (D_s^ + \to \pi ^ + (1^3 P_0 s\bar s))}} \lesssim 0.05\).     

Die absolute Intensität der durch Elektronenstoß in einer dicken Wolfram-Antikathode erzeugtenL α -Strahlung

The number\(N_{L_\alpha }^{dir} \) (produced) ofL _α -photons produced by electron-bombardment in a thick target of tungsten per incident electron has been measured absolutely with the Ross-filter method and relatively with the crystal-spectrometer method in the energyregion up to the 3.6 times theL _III-ionization energy\(E_{L_{III} } \). The result can be presented in the following empirical form:\(N_{L_\alpha }^{dir} \) (produced)=4π·?·(U ₀?1) ⁿ with ?=0.52·10^?4±5% andn=1.44±0.02\((U_0 = E_0 /E_{L_{III} }< 3.6)\). Out of this the number\(n_{L_{III} } \) ofL _III-ionizations per electron which is slowed down to the energy\(E_{L_{III} } \) within the target, has been evaluated. The computation of\(n_{L_{III} } \) out of the elementary process by usingBethe's non-relativistic formulae for totalL _III-ionization cross sectionQ _L and energy loss-dE/ds is in full agreement with experiment in the region 2<U ₀<3.6, if the constants in\(Q_{L_{III} } \) are chosen as follows:\(B = 4E_{L_{III} } , b_{L_{III} } = 0.25 \cdot 5.89\). By comparison of this result for\(b_{L_{III} } \) with the corresponding value ofb _K in the totalK-ionization cross-sectionQ _K for copper (b _K=0.35·2.26) it is concluded that\(Q_{L_{III} } \) is considerably higher than predicted by theory. The necessary correction factors as e.g. loss ofL _III-ionizations by rediffusion of electrons and portion of indirectly producedL _α -radiation-radiation are determined for tungsten quantitatively.     

Neutron-antineutron oscillations in the trapping box

The problem of n-\(\bar n\) oscillations for ultracold neutrons confined within a trap is reexamined. It is shown that the growth of the \(\bar n\) component with time is to a decent accuracy given by \(P(\bar n) = \varepsilon _{n\bar n}^2 t_L t\), where \(\varepsilon _{n\bar n}\) is the mixing parameter and t _L ～ 1 s is the neutron propagation time between subsequent collisions with the trap walls. Possible corrections to this law and open questions are discussed.     

Influence of photon-neutrino processes on the cooling of a magnetar

The influence of a strongly magnetized dense plasma on the photon-neutrino processes γe ^± → e ^±ν\(\bar \nu \), γ → ν\(\bar \nu \), and γγ → ν\(\bar \nu \) is considered; invariant amplitudes of the γe ^± → e ^±ν\(\bar \nu \) and γγ → ν\(\bar \nu \) reactions are calculated. The contributions from these processes to the neutrino luminosity are calculated in the special case of a cold plasma. Under these conditions, the contribution from the process γ → ν\(\bar \nu \) to the neutrino emissivity is shown to be strongly suppressed compared to the contributions from the photoneutrino and photon conversion processes. Since the neutron star cooling curve can be modified through a change of the neutrino luminosity in a strong magnetic field, the magnetic field strength in the outer crust of the magnetar is assumed to be constrained.     

Pentaquark decay is suppressed by chirality conservation

It is shown that, if the pentaquark \(\Theta ^ + = uudd\bar s\) baryon can be represented by the local quark current η_Θ, its decay Θ⁺→nK⁺(pK⁰) is forbidden in the limit of chirality conservation. The Θ⁺ decay width Γ is proportional to \(\alpha _s^2 \left\langle {0\left| {\bar qq} \right|0} \right\rangle ^2\), where \(\left\langle {0\left| {\bar qq} \right|0} \right\rangle ,q = u,d,s\), is quark condensate, and, therefore, is strongly suppressed. The polarization operator of the pentaquark current is calculated using the operator product expansion. The Θ⁺ mass found by the QCD sum rules method is in reasonable agreement with experiment.     

Calculation of the fine structure of the triplet state $$\tilde a^3 A_2 $$ of the ozone molecule by the method of multiconfiguration self-consistent field

The zero-field splitting of the \(\tilde a^3 A_2 \) state of the O₃ molecule is interpreted on the basis of ab initio quantum-chemical calculations. The spin—orbit coupling with the ground X¹A₁ state is shown to make the main contribution to the zero-field splitting of the \(\tilde a^3 A_2 \) term (the state of the ³σπ type). The calculated parameters D and E agree well with experiment.     

Schrödinger equation in multiply connected spaces and phase optics

The magnetic vector potential\(\vec A\) in a field free spaceR ₀ cannot be removed by gauge transformations in general, ifR ₀ is multiply connected.Aharonov andBohm ¹ have noticed recently that\(\vec A\) therefore should have more physical meaning than only to give the magnetic field by differentiation. They could show that\(\vec A\) inR ₀ may influence the phase ofSchrödinger'sψ-function in an observable manner. We want to point out here that this influence can be expressed in a simple, general form: “A closed magnetic field line operates uponψ like ae Φ/?-phase-shifter placed on any area bounded by the field line.” Surface like phase shifters are familiar in phase optics. There exists a narrow relationship between electron scattering at magnetic fields and some special problems of phase optics. An electron phase contrast microscope is discussed.     

Analysis of th e $$Hb\bar b$$ coupling constant and CP-violation eff ects at th e futur e e+ e− collid er

The \(e^ + e^ - \to b\bar bv\bar v\) process, where υ is an electron, muon, or τ-lepton neutrino, is analyzed in detail for the general form of the coupling constant of a Higgs boson with b quarks, with the (m _b /v)(a+Iγ₅b) parameterization of the \(Hb\bar b\) interaction. This process is shown to be highly sensitive to this coupling constant. Experiments at the future with \(\sqrt s = 500 - GeV\) linear collider will provide limits of 2 and 20% for deviations of the parameters a and b, respectively, from their Standard Model values. Results concerning the \(e^ + e^ - \to b\bar bv\bar v\) process in combination with the independent measurements of the partial width \(\Gamma _{H \to b\bar b}\) can testify to the CP origin of the Higgs sector of the theory.     

Surface superconductivity and<Emphasis Type="Italic">H</Emphasis><Subscript><Emphasis Type="Italic">c3</Emphasis></Subscript> in UPt<Subscript>3</Subscript>

Ginzburg-Landau (GL) theory is used to study surface superconductivity for UPt₃ for various order parameter symmetries (OPS), andH _c3 is found for all principal directions of the surface normal\(\hat n\) and the field [1]. Assuming specular reflection, and allowing for reorientation of the antiferromagnetic symmetry breaking field in the models withE _1g ,E _2g ,E _1u , orE _2u symmetry, the experiments of Keller et al. [2] with\(\hat n = \hat a\) can be qualitatively explained for all OPS except possiblyA _1u ⊕B _1u . The implied GL parameters then predict qualitatively different and OPS dependent behavior for\(\hat n = \hat a^* \) and\(\hat n = \hat c\). Study ofH _c3 for these surfaces would give strong clues about the OPS of UPt₃.