Role of 8Be → 2 α intermediate nuclei in the fragmentation of 16O relativistic nuclei in nuclear track emulsions

In searches along a track in the chamber irradiated at the Laboratory of High Energies at the Joint Institute for Nuclear Research (JINR, Dubna) with oxygen ions accelerated to a momentum of 4.5 GeV/c per nucleon, 215 events containing two or more doubly charged fragments of the primary nucleus were found. Emission angles in the track-emulsion plane were measured in these events. Their distribution is consistent with that which alpha particles are expected to have in an oxygen nucleus prior to its interaction with a track-emulsion nucleus. Events of the ¹⁶O ?? 2⁸Be ?? 4?? type were discovered for the first time. They are treated as events of the coherent electromagnetic dissociation of an oxygen nucleus. Among all events, about 14% of the ⁸Be ?? 2?? decays proceed through the ground state of spin-parity 0⁺; an approximately the same fraction of such decays proceed through the first excited state of spin-parity 2⁺.     

Singularities in the energy distribution of a single lepton in the search for dark matter particles at the international linear Collider/Compact linear Collider: Source for measuring their masses

The measuring of model-independent singularities in the energy distribution of a single lepton in the cascade process e ⁺ e ^? ?? D ⁺ D ^? ?? DDW ⁺ W ^? ?? DD(q q?)??? will allow one to reliably determine the mass of a candidate for dark matter D and its charged partners D ^± in future experiments at the International Linear Collider/Compact Linear Collider (ILC/CLIC).     

Photoproduction of π + p pairs on nuclei

The photoproduction of pion-nucleon pairs on nuclei was analyzed. The contributions of both nucleonic and isobar configurations in the ground state of nuclei were taken into account. The cross section for the photoproduction of pion-proton pairs in the reactions ¹⁶O(??, ?? ⁺ p)¹⁵C and ¹²C(??, ?? ⁺ p)¹¹Be were calculated.     

���Ѧ� Interaction Leading to N* and ��* Resonances

We have performed a calculation for the three-body ????? system by using the fixed center approximation to Faddeev equations, taking the interaction between ?? and ??, ?? and ??, and ?? and ?? from the chiral unitary approach. We find several peaks in the modulus squared of the three-body scattering amplitude, indicating the existence of resonances, which can be associated to known I?=?1/2, 3/2 and J ^P ?=?1/2⁺, 3/2⁺ and 5/2⁺ baryon states.     

Measurement of the cross section for the e + e ? → ωπ0 → π0π0γ process in the energy range of 1.1–1.9 GeV

The cross section for the e ⁺ e ^? ?? ???⁰ ?? ??⁰??⁰?? process has been measured in the energy range of 1.1?C1.9 GeV. The measurement has been made with the Spherical Neutral Detector at the VEPP-2000 e ⁺ e ^? collider. The data in the energy range of 1.1?C1.4 GeV are in agreement with the earlier measurements with the SND and CMD-2 detectors. The cross section has also been measured above 1.4 GeV.     

The effect of air impurities on pure neon luminescence

The luminescence decay curves of the 2p ₁ level of the NeI atom (the transition 3p??[1/2]₀?3s??[1/2] ₁ ^° , ?? = 585.2 nm) and the B ²?? _u ⁺ level of the N ₂ ⁺ molecule (the transition B ²?? _u ⁺ (?? = 0)?X ²?? _g ⁺ (??? = 0), ?? = 391.4 nm) in pure and air-containing neon are measured. The gas was excited by electron beam pulses (E _e = 150 keV, ?? = 5 ns, I _max = 500 A). It is shown that the molecular gases contained in air strongly quench the long-lived component of neon luminescence exciting due to dissociative recombination of Ne ₂ ⁺ molecular ions. The relative light yield at a wavelength of 585.2 nm as a function of the partial pressure of air in neon is determined to be ?? = (1+ 2??p)^?1, where p is the air pressure in Torr.     

AnomalousZ�� effects in the WW channel at NLC

We consider the virtual signals of aZ?? of very general type in the processe ⁺ e ^???W ⁺ W ^? at a future linear collider (NLC). We show that possible deviations from the SM predictions in this channel are related to similar deviations in the purely leptonic one in a way that is only characteristic of thisZ?? model, and not in general of possible competitor models with anomalous gauge couplings.     

Production of π0ρ0 pair in electron-positron annihilation in the Nambu-Jona-Lasinio model

The process e ⁺ e ^? ?? ??⁰??⁰ is described in the framework of the expanded NJL model in the energy region from 0.9 to 1.5 GeV. The contribution of intermediate state with vector mesons ??(782), ??(1020), and ???(1420), where ??? is the first radial excitation of ?? meson, was taken into account. Results obtained are in satisfactory agreement with experimental data.     

Annihilation semileptonic decays of <Emphasis Type="Italic">B</Emphasis> mesons and the model dependence on the choice of the distribution amplitude

The rare semileptonic B-meson decay B → ??⁺?^? is considered. The partial decay rate integrated over the 1–8 GeV² interval of the dilepton invariant mass squared is computed with a 10% systematic uncertainty arising from the model dependence of the distribution amplitude. The purely perturbative contribution to the decay probability amounts to ? ～ 10^?12, which suggests that the LHC experiments could observe the B → ??⁺?^? decay in a few years of data taking.     

Study of K−p→K1(890)n at 13 GeV

The results of a wire chamber spectrometer experiment studying $\text{K}$¹ (890) production in the reaction K^?p→ K^?π⁺n at 13 GeV are presented. Strong forward structure is observed for |t|< m²_π in the s-channel density matrix elements and differential cross section. These features are similar to those observed in π^?p→?⁰n data and are characteristics of π exchange. In contrast in the intermediate, |t| ～ 0.2 GeV², and large momentum transfer regions $\text{K}$¹ (890) production is demonstrated by the natural parity ??A₂ exchange contribution.     

Measurement and analysis of the π+π+ system produced at small momentum transfer in the reaction π+p→π+π+n at 12.5 GeV

From a wire chamber experiment 45 452 events were obtained from the reaction π⁺p→π⁺π⁺n. The I=2 phase shifts were determined in the π⁺π⁺ mass region 0.3–1.5 GeV. An amplitude analysis was performed. The results are compared with some theoretical predictions.     

Calculations of the level of primary radiation defects (displacements per atom) taking into account surface sputtering

The results of analytical estimates and computer simulations of the primary radiation damage level in the number of displacements per atom (dpa) in solids are presented and compared, taking into account the material sputtering under ion bombardment. Calculations were performed for the bombardment of carbon-based materials by Ar⁺, Ne⁺, and N⁺ ions with energies of 2?C30 keV, when considerable ion-induced changes in the material??s structure are observed. A comparison shows the close fit of the analytical and computer calculations.     

Reactions induced in (CF3I) n clusters by femtosecond UV laser pulses

The excitation and ionization of CF₃I molecules and their clusters by femtosecond UV laser pulses is studied. It is concluded that the types of excitation of free CF₃I molecules and their clusters by femtosecond UV laser pulses are different. The composition and kinetic energy of ion products observed upon the ionization of (CF₃I) _n clusters by femtosecond pulses are found to differ considerably from those obtained upon ionization by nanosecond pulses. It is shown that the molecular I ₂ ⁺ ion is produced in reactions induced in (CF₃I) _n clusters by UV radiation. Using the pump-probe method, we found the two channels of producing I ₂ ⁺ ions with characteristic times ??₁ ?? 1 ps and ??₂ ?? 7 ps. A model of the reactions under study proposed in the paper is consistent with our experimental results.     

Developments at the SLOWRI facility at RIKEN: precision optical spectroscopy of 7,9,10,11Be+ ions

Precision optical spectroscopy of radioactive Be isotopes produced in projectile fragmentation has been performed for the first time at the prototype SLOWRI facility of RIKEN RI-Beam Factory. The ground state hyperfine constants of ⁷Be⁺ and ¹¹Be⁺ were determined with relative accuracies of 6 × 10^?7 and 3 × 10^?8, respectively, by laser-microwave double resonance spectroscopy of laser-cooled ions in a trap. The optical transition energies from the ground S-state to the excited P-state of Be isotope ions were also measured to determine the nuclear charge radii from the isotope shifts. Development of the universal slow RI-beam facility??SLOWRI??based on the rf-carpet ion guide technique is progressing at RIKEN RI-beam factory. An additional capability of providing parasitic slow RI-beams from the projectile fragment separator BigRIPS is also discussed.     

Isotope-selective ionization utilizing molecular alignment and non-resonant multiphoton ionization

We demonstrate laser nitrogen isotope separation, which is based on field-free alignment and angular-dependent ionization of ¹⁴N₂ and ¹⁵N₂ isotopologues. A linearly polarized short laser pulse (???~?795?nm, ?????~?60?fs) creates rotational wave packets in the isotopologues, which periodically revive with different revival times as a result of different moments of inertia. Another linearly polarized short laser pulse (???~?795?nm, ?????~?60?fs) ionizes one of the isotopologues selectively as a result of their different angular distributions. In the present experiments, the ion yield ratio R [=I(¹⁵N₂ ⁺)/I(¹⁴N₂ ⁺)] can be changed in the range from 0.85 to 1.22, depending on the time delay between the two laser pulses.     

Measuring of mass and spin of dark matter particles at ILC

In many models stability of dark matter particles D (with mass M _D ) is ensured by a new conserved quantum number which we call the D-parity. We consider models which also contain charged D-odd particle D ^± (with mass M _±). We study the process e ⁺ e ^? ?? D ⁺ D ^? followed by decay of D ^± to D and gauge bosons W (either on-shell or off-shell). Measuring the end points of the energy distribution of W??s would determine M _D and M ^±. However, the hadron mode of W decay would lead to low precision in this measurement. while the information from the lepton mode looks incomplete. I show that it is sufficient to measure the energy distribution of a single lepton (for definiteness ??) in the process e ⁺ e ^? ?? ?? + 2jets + large missing E _T . The well identified singularities in this distribution allow for determination of M _D and M _± with a high precision. After that, measuring the corresponding cross section will allow one to determine the spin of D particles.     

Inclusive production in K+d reactions at 4.6 GeV/c

The investigations presented here are based on the data from a K⁺d experiment at 4.6 GeV/c performed with the 2 m bubble chamber at CERN. The topological K⁺d cross sections are determined. The integrated (semi-) inclusive single-particle cross sections for the production of π^?, K⁰ and Λ as well as (semi-)inclusive x- and p_T² distributions are measured and discussed.     

Analysis of the Λb → Λ?+?? transition in the SM4 using form factors from full QCD

Using the responsible form factors calculated via full QCD, we analyze the ?? _b ?? ???⁺?^? transition in the standard model containing fourth-generation quarks (SM4). We discuss the effects of the presence of the t?? fourth-family quark on related observables like branching ratio, forward-backward asymmetry, baryon polarization as well as double-lepton polarization asymmetries. We also compare our results with those obtained in the SM as well as with predictions of the SM4 but using form factors calculated within heavy-quark effective theory. The obtained results on the branching ratio indicate that the ? transition is more probable in full QCD comparing to the heavy-quark effective theory. It is also shown that the results on all considered observables in the SM4 deviate considerably from the SM predictions when m _t?? ?? 400 GeV.     

Observation of possible production and decay of short-living heavy neutral particles in the SKAT neutrino experiment

In the SKAT bubble chamber neutrino experiment production of a short-living neutral particle with mass (1.4?m?2.5) GeV/c² and lifetime τ≈6×10^?12 s has been detected. The event may be interpreted as production and decay of the heavy lepton M⁰→μ^?+e⁺+ν_e with mass (1.4?m_M⁰?2.1) GeV/c². It might also be the production of a charmed particle D⁰→e⁺+τ^?+ν_e (D⁰→e⁺+π^?+ν_e) with mass 1.4?m_D⁰?2.5) GeV/c² in a non-diagonal neutral current. The probability to interpret the event as other possible processes is very low.     

Measurement of the reactions K+d → K+d and K+d → p+pn and an investigation of elastic K+-nucleon scattering at 4.6 GeV/c

The coherent elastic reaction K⁺d → K⁺d and the break-up reaction K⁺d → K⁺pn are studied in a K⁺d experiment at 4.6 GeV/c which the CERN 2 m bubble chamber. Partial and differential cross sections are given and the slopes of the differential cross sections are determined. The results for the reaction K⁺d → K⁺p(n_s), where n_s denotes the spectator neutron, are compared with those of the reaction K⁺p → K⁺p on free protons. Combining our data with existing data on the reactions K⁺d → K⁰pp and K⁺p → K⁺p, parameters of the elastic K⁺-nucleon scattering at 4.6 GeV/c are determined in the framework of the Glauber model. The D-wave of the deuteron and spin-flip effects are taken into account.