Astrophysical <Emphasis Type="Italic">S</Emphasis> factor for the radiative-capture reaction <Emphasis Type="Italic">p</Emphasis><Superscript>6</Superscript>Li → <Superscript>7</Superscript>Beγ

A new measurement of differential cross sections for elastic p ⁶Li scattering in the energy range 0.35–1.2 MeV was performed. A partial-wave analysis of the data obtained in this way was carried out, and potentials simulating the p ⁶Li interaction were constructed. Various experiments devoted to studying elastic p ⁶Li scattering over the broad energy range of 0.5–50 MeV were analyzed on the basis of the optical model. By using the potentials obtained from the partial-wave analysis, the possibility of describing the astrophysical S factor for radiative proton capture on ⁶Li at low energies was considered within the potential cluster model involving forbidden states.     

Astrophysical <Emphasis Type="Italic">S</Emphasis>-factor of the <Emphasis Type="Italic">p</Emphasis><Superscript>7</Superscript>Li → <Superscript>8</Superscript>Beγ capture at low energies

The interaction potentials describing some phases of elastic p ⁷Li scattering for energies up to 0.8 MeV and the ground bound P ₀ state of the ⁸Be nucleus in the p ⁷Li cluster channel are obtained. The astrophysical S-factor of the p ⁷Li → ⁸Beγ radiative capture is considered for the potential cluster model.     

Astrophysical <Emphasis Type="Italic">S</Emphasis>-factor of the <Emphasis Type="Italic">p</Emphasis><Superscript>9</Superscript>Be → <Superscript>10</Superscript>Bγ radiative capture

The S-factor of the p ⁹Be → ¹⁰Bγ radiative capture is considered at astrophysical energies in the potential cluster model where orbital states are classified by the Young schemes.     

Eight resonances and a half for the reaction <Emphasis Type="Italic">γ</Emphasis> + <Emphasis Type="Italic">p</Emphasis>→<Emphasis Type="Italic">η</Emphasis> + <Emphasis Type="Italic">p</Emphasis>

On the basis of the dynamical model for meson photoproduction on nucleons, it is shown that only eight broad resonances (of width in excess of 120 MeV), of which two belong to the class of missing resonances, are required for reproducing experimental data from the threshold for the reaction γp → ηp to the photon energy of 3 GeV.     

Nuclear asymptotic normalization coefficients for <Superscript>14</Superscript>N → <Superscript>13</Superscript>C + <Emphasis Type="Italic">p</Emphasis> configurations and astrophysical <Emphasis Type="Italic">S</Emphasis> factor for radiative proton capture

Empirical values of the asymptotic normalization coefficient for proton bound states in the ¹⁴N nucleus for the first five levels were obtained from an analysis of the experimental differential cross sections known from our measurements and from the literature for the reaction ¹³C(³He, d)¹⁴N in the projectile-energy range between about 15 and 40 MeV. The values obtained in this way were used to calculate the astrophysical S factors for the reaction ¹³C(p, γ)¹⁴N in the case of the population of the first five levels of the 14N nucleus. The calculations were based on the R-matrix approach. The calculated values are in good agreement with the experimental astrophysical S factor at energies below 1 MeV.     

Process <Emphasis Type="Italic">γ</Emphasis>*<Emphasis Type="Italic">γ</Emphasis> → <Emphasis Type="Italic">σ</Emphasis> at large virtuality of <Emphasis Type="Italic">γ</Emphasis>*

The process γ*γ → σ is investigated in the framework of the SU(2)×SU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of γ* in the Euclidean kinematic domain. The asymptotic behavior of this form factor resembles the asymptotic behavior of the γ*γ → π form factor.     

Astrophysical S-factor of some (<Emphasis Type="Italic">p</Emphasis>, <Emphasis Type="Italic">γ</Emphasis>) Reactions

We have studied the important astrophysical S-factor for 36 known p-nuclei with (p, γ) reactions at low energy in the mass region A\(\approx \) 74–196. This is done by folding the density-dependent M3Y (DDM3Y) interaction with spherical relativistic mean field (RMF) densities. The densities are obtained from different parameter sets such as G1, G2, NL1, NL2, NL3*, NL-SH, DD-ME1, DD-ME2 and DD-PC1. The independence of the S-factor on different densities is discussed and compared with experimental data and with NON-SMOKER calculations whenever available.     

On mass corrections to the decay <Emphasis Type="Italic">P</Emphasis> → <Emphasis Type="Italic">l</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">l</Emphasis><Superscript>−</Superscript>

The Mellin-Barnes representation is used to improve the theoretical estimate of mass corrections to the width of a light pseudoscalar meson decay into a lepton pair, P → l ⁺ l ⁻. The full resummation of the terms ln(m _l ²/Λ²)(m _l ²/Λ²) ⁿ and (m _l ²/Λ²) ⁿ to the decay amplitude is performed, where m _l is the lepton mass and Λ ≈ m _ρ is the characteristic scale of the P → γ*γ* form factor. The total effect of the mass corrections for the e ⁺ e ⁻ channel is negligible and, for the μ⁺μ⁻channel, its order is of a few percent. The text was submitted by the authors in English.     

Spin structure of the “Forward” nucleon charge-exchange reaction <Emphasis Type="Italic">n</Emphasis> + <Emphasis Type="Italic">p</Emphasis> → <Emphasis Type="Italic">p</Emphasis> + <Emphasis Type="Italic">n</Emphasis> and the deuteron charge-exchange breakup

The structure of the nucleon charge-exchange process n + p → p + n is investigated basing on the isotopic invariance of the nucleon-nucleon scattering. Using the operator of permutation of the spin projections of the neutron and proton, the connection between the spin matrices, describing the amplitude of the nucleon charge-exchange process at zero angle and the amplitude of the elastic scattering of the neutron on the proton in the “backward” direction, has been considered. Due to the optical theorem, the spin-independent part of the differential cross section of the process n + p → p + n at zero angle for unpolarized particles is expressed through the difference of total cross sections of unpolarized proton-proton and neutron-proton scattering. Meantime, the spin-dependent part of this cross section is proportional to the differential cross section of the deuteron charge-exchange breakup d + p → (pp) + n at zero angle at the deuteron momentum k _d = 2 k _n (k _n is the initial neutron momentum). Analysis shows that, assuming the real part of the spin-independent term of the “forward” amplitude of the process n + p → p + n to be smaller or of the same order as compared with the imaginary part, in the wide range of neutron laboratory momenta k _n > 700 MeV/c the main contribution into the differential cross section of the process n + p → p + n at zero angle is provided namely by the spin-dependent term.     

Deviation from the standard model in the decay <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">νγ</Emphasis>

A precise investigation of radiative pion decay (π⁺ → e⁺νγ) in a pion beam from the meson factory of the Paul Scherrer Institute (Switzerland) was performed by the PIBETA Collaboration with the aid of the PIBETA detector. This resulted in finding 41 601 events of radiative pion decay in three kinematical regions. The absolute values of the branching ratio for radiative pion decay were determined in each of these regions. To a precision approximately four times higher than that known previously, the ratio of the axial-vector to the vector form factor was found to be γ ≡ F _A /F _V = 0.443 (15), the latter being fixed at F _V = 0.0259. The number of events found in the kinematical region specified by photon energies of E_γ > 55.6 MeV, positron energies of E _e > 20.0 MeV, and angles of θ_{γ, e} > 40° between the momenta of the corresponding particles (B region) was 5233. In region B, the measured branching ratio for radiative pion decay, R_π→evγ(expt) = 11.6(3) × 10^?8, proved to be smaller by eight standard deviations than that which follows from the Standard Model, R_π→evγ (theor) = 14.34(1) × 10^?8.     

General formulas for invariant functions describing generalized <Emphasis Type="Italic">γN</Emphasis> → <Emphasis Type="Italic">γN</Emphasis> reactions within the method of effective Lagrangians

The crossed channels of generalized γN → γN reactions are considered. The coefficients in the transformation from independent helicity amplitudes to invariant functions are calculated. Explicit expressions for the invariant functions are derived with allowance for the contribution from the Born diagrams in the s, u, and t channels and the diagrams for six resonances in the s and u channels. It is shown that the calculated invariant functions satisfy the crossing-symmetry requirements.     

Investigation of the process <Emphasis Type="Italic">J/ψ</Emphasis> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> with the KEDR detector

The product of the electron width of the J/ψ meson and the probability for its decay to an electron-positron pair was measured by using data from the KEDR experiment at the VEPP-4M electron-positron collider. The result was Γ _ee × Γ _ee /Γ = 0.3392 ± 0.0068(stat.) ± 0.0063(syst.) keV.     

The quest for <Emphasis Type="Italic">μ</Emphasis> → <Emphasis Type="Italic">e</Emphasis><Emphasis Type="Italic">γ</Emphasis>: present and future

The quest for μ → eγ is one of the most important endeavors to search for New Physics beyond the Standard Model. In this talk I will review the current status of the experimental searches by the MEG Collaboration at PSI. I will also present a study of the experimental limiting factors that will define the ultimate performances, and hence the sensitivity, in the search for μ → eγ with continuous muon beams of extremely high rate (one or even two orders of magnitude larger than the present beams), whose construction is under consideration for the next decade.     

Astrophysical <Emphasis Type="Italic">S</Emphasis>-factor of T(<Superscript>4</Superscript>He, γ)<Superscript>7</Superscript>Li reaction at <Emphasis Type="Italic">E</Emphasis><Subscript>cm</Subscript> = 15.7 keV

The astrophysical S-factor of the reaction T(⁴He, γ)⁷Li is measured for the first time at the center of mass energy E _cm = 15.7 keV, lower than the energy range of the Standard Big Bang Nucleosynthesis (SBBN) model. The experiment is performed on a Hall pulsed accelerator (TPU, Tomsk). An acceleration pulse length of 10 μs allows one to suppress the background of cosmic radiation and the ambient medium by five orders of magnitude. A beam intensity of ~ 5 × 10^{14 4}He⁺ ions per pulse allows one to measure an extremely low reaction yield. The yield of γ-quanta with the energies E _γ ⁰ = 2483.7 keV and E _γ ¹ = 2006.1 keV is registered by NaI(Tl) detectors with the efficiency ε = 0.331 ± 0.026. A method for direct measurement of the background from the chain of reactions T(⁴He, ⁴He)T→T(T, 2n)X→(n, γ) and/or (n, n′γ) which ends by neutron activation of materials surrounding the target is proposed and implemented in this study. The value of the astrophysical S-factor of the reaction T(⁴He, γ)⁷Li S _αt (E _cm = 15.7 keV) = 0.091 ± 0.032 keV b provides the choice from the set of experimental data for the astrophysical S _αt -factor in favor of experimental data [4] with S _αt (E _cm = 0) = 0.1067 ± 0.0064 keV b.     

ALICE-PHOS: acceptance and efficiency correction factors <Emphasis Type="Italic">p</Emphasis>−<Emphasis Type="Italic">p</Emphasis>→<Emphasis Type="Italic">π</Emphasis><Superscript>0</Superscript>+<Emphasis Type="Italic">X</Emphasis> at 10 TeV

In ultra-relativistic Heavy-Ion Collisions (HIC), the properties of the quark gluon plasma (QGP) can be explored, in particular, via measurements of neutral pions. The π ⁰ is an important probe for both proton and heavy ion physics. In the former case, π ⁰ production provides an important mean of testing pQCD as well as useful data to constrain current and future theoretical models. In the latter case, π ⁰ measurements will serve as a baseline for exploring the nature of the HIC hard scattering. In the ALICE experiment, π ⁰ mesons are identified as they decay into two photons (π ⁰→γ γ) using the high-resolution photon spectrometer (PHOS). PHOS will measure π ⁰ transverse momentum over a wide range, from hundreds of MeV/c to several tens of GeV/c. An estimation of π ⁰ production cross-section in proton–proton collisions is calculated in a next-to-leading order (NLO) approximation and first presented. The π ⁰ geometrical acceptance and the identification efficiency along with the analysis on the invariant mass are the two important correction factors for obtaining a realistic π ⁰ spectrum discussed in this paper.