Spectator Process Research Articles

Multiple Auger decay following ionization-excitation of Ne i

The photoionization-excitation spectrum of Ne i, in which an electron in the $1s$ shell is ionized and the $2p$ orbital electron simultaneously excited to the $np$ orbital, is investigated in detail for complex satellite states ${\mathrm{Ne}}^{+}$ $1{s}^{\text{--}1}2{p}^{\text{--}1}{(}^{1,3}P)np$ $(n=3,4,5,6,7)$. Then, the multiple Auger decay process is studied using the multistep method, including cascade, knock-out, and shake-off mechanisms, based on perturbation theory for the satellite states ${\mathrm{Ne}}^{+}$ $1{s}^{\text{--}1}2{p}^{\text{--}1}({}^{1,3}\mathrm{P})np$ $(n=3,4)$ with two holes. The major single Auger decay can be described as a spectator process that valence electrons remain in the original orbitals. For double Auger decay, direct and cascade processes are considered, in which the direct mechanism is dominated by the spectator process, while the cascade mechanism is mainly from the participator process. For triple Auger decay, the important contribution is from the process consisting of direct double Auger and the subsequent single Auger electron emissions. The calculated ion yields of ${\mathrm{Ne}}^{2+}$, ${\mathrm{Ne}}^{3+}$, and ${\mathrm{Ne}}^{4+}$ for multiple Auger process of satellite states ${\mathrm{Ne}}^{+}$ $1{s}^{\text{--}1}2{p}^{\text{--}1}{(}^{1,3}P)np$ $(n=3,4)$ are consistent with experimental values [Hikosaka et al., Phys. Rev. A 97, 023405 (2018)].

Observation of D+(s)K- and evidence for D+(s)pi- final states in neutral B decays.

We report the first observation of a B meson decay that is not accessible by a direct spectator process. The channel B(0)-->D(+)(s)K- is found in a sample of 85 x 10(6) BB; events, collected with the Belle detector at KEKB, with a branching fraction B(B(0)-->D(+)(s)K-)=(4.6(+1.2)(-1.1)+/-1.3) x 10(-5). We also obtain evidence for the B0-->D(+)(s)pi(-) decay with branching fraction B(B0-->D(+)(s)pi(-))=(2.4(+1.0)(-0.8)+/-0.7) x 10(-5). This value may be used to extract a model-dependent value of |V(ub)|.

Leading nucleons from peripheral processes in lepton deep inelastic scattering and the nucleon structure

The experimental information on nucleon production in lepton deep inelastic scattering (DIS) is rather scarce. Recently there is a growing interest in understanding the mechanism of the production of baryons in DIS, stimulated by recent results on leading protons and neutrons from electron-proton scattering at HERA. I review on different peripheral mechanisms of nucleon (proton or neutron) production in lepton DIS and discuss their role in understanding the spectra of nucleons for both fixed target and collider experiments. In DIS ep → e′Xh, the QCD hardness scale gradually diminishes from the hard scale, Q 2, in the virtual photon (current) fragmentation region to the soft, hadronic, scale in the proton (target) fragmentation region. This suggests a similarity of the inclusive spectra of leading protons and neutrons, h = p, n, in high energy hadron-proton collisions and in lepton DIS at small Bjorken-χ. The semi-inclusive cross section for production of slow protons in charged-current deep inelastic (anti)neutrino scattering on protons and neutrons is discussed. The standard hadronization models based upon the color neutralization mechanism appear to underestimate the rate of slow proton production on hydrogen. The presence of the virtual mesons (pions) in the nucleon leads to an additional mechanism for proton production, referred to as spectator process. The results of the calculations are compared with the CERN bubble chamber (BEBC) data. I discuss the structure of deep-inelastic events induced by the pione-xchange at HERA kinematics. Most of the event characteristics do not provide a possibility to distinguish the ordinary DIS fragmentation events from those induced by the pion-exchange mechanism. The only exception is the energy distribution of outgoing neutrons. The pion cloud model predicts energy distribution of neutrons which differs significantly from the standard hadronization models which can in principle be verified experimentally. A detailed analysis of semi-exclusive diffractive processes in ep DIS at HERA, with the diffractive final states in the forward direction is presented. The contributions of the subleading f 0; ω,a 2, ρ reggeons and the pion exchanges to the diffractive structure function with the forward proton or neutron are estimated. It is found that the ( a 2, ρ) reggeons are entirely responsible for the forward neutron production at χ IP < 10 −3. The π N production in the forward region is estimated using the Deck mechanism. The significance of this reaction for the processes measured at HERA is discussed. In the DIS production of leading protons DIS off neutral pions must be supplemented by a contribution from isoscalar reggeon ( f0) exchange extrapolated down to moderate values of χ L . I comment on the χ and Q 2 dependence of leading proton production as a probe of a universal pattern of the χ, Q 2 evolution of the nucleon and meson (reggeon) structure functions at small χ.

Slow proton production in semi-inclusive deep inelastic scattering and the pion cloud in the nucleon

The semi-inclusive cross section for producing slow protons in charged current deep inelastic (anti-) neutrino scattering on protons and neutrons is calculated as a function of the Bjorken $x$ and the proton momentum. The standard hadronization models based upon the colour neutralization mechanism appear to underestimate the rate of slow proton production on hydrogen. The presence of the virtual mesons (pions) in the nucleon leads to an additional mechanism for proton production, referred to as spectator process. It is found that at low proton momenta both mechanisms compete, whereas the spectator mechanism dominates at very small momenta, while the color neutralization mechanism dominates at momenta larger than 1-2 \, GeV$/c$. The results of the calculations are compared with the CERN bubble chamber (BEBC) data. The spectator model predicts a sharp increase of the semi-inclusive cross section at small $x$ due to the sea quarks in virtual mesons.

Vibrationally resolved states in the HS fragment studied by means of electron-excited Auger spectroscopy.

An autoionization spectrum of the ${\mathrm{H}}_{2}$S molecule has been identified from the comparison between the Auger electrons recorded by means of high-resolution electron-beam and monochromatic Al K\ensuremath{\alpha} exciting sources. Due to the high energy resolution the measured kinetic energies can be used for a precise assignment. Our results support a model of a fast dissociation of the core-excited ${\mathrm{H}}_{2}$${\mathrm{S}}^{\mathrm{*}}$ (2p${)}^{\mathrm{\ensuremath{-}}1}$(6${\mathit{a}}_{1}$${)}^{1}$ and (2p${)}^{\mathrm{\ensuremath{-}}1}$(3${\mathit{b}}_{2}$${)}^{1}$ states into core-excited ${\mathrm{HS}}^{\mathrm{*}}$ (2p${)}^{\mathrm{\ensuremath{-}}1}$(2\ensuremath{\pi}${)}^{4}$ followed by autoionization decay into the ${\mathrm{HS}}^{+}$ radical. Vibrational structures are resolved and assigned to the $^{3}\mathrm{\ensuremath{\Sigma}}^{\mathrm{\ensuremath{-}}}$ and $^{1}\mathrm{\ensuremath{\Delta}}$ final states in the ${\mathrm{HS}}^{+}$ radical. No participator Auger process in ${\mathrm{H}}_{2}$${\mathrm{S}}^{\mathrm{*}}$ could be identified. However, contributions from the spectator process in ${\mathrm{H}}_{2}$${\mathrm{S}}^{\mathrm{*}}$ might be present.

Charmed-meson nonleptonic decays andSU(3) symmetry

Based on the analysis ofSU(3) symmetry property, we propose that the Cabibbo-favoured nonleptonic decays of charmed mesons should be treated in two different cases: i) octet-octet final states and ii) octet-singlet final states. In case i) the spectator process gives correct predictions, but in case ii) the decay mechanism is different. We give a theoretical lower limit of BR(D s + →ωπ+) which cannot go through spectator process. This channel, as well as D s + →ωe+ ν are recommended to search for in experiments.

Rockaby and the Art of Inadvertent Interpretation

Eclipsed among the millions of critical words that have been lavished on Samuel Beckett is an uncomfortable and frequently avoided question: on what level can spectators be expected to understand his theater? Some critics have tried to address this issue by pointing out parallels between the dilemmas of Beckett's characters and those of his audiences, with limited success, but I want to shift the field of inquiry by discussing affinities between the actor's process of creating characters in rehearsal and the spectator's process of apprehending plays in performance. I focus predominantly on Rockaby, because Billie Whitelaw's extraordinary performance is well documented and also because there is an important article by Charles Lyons about the process of perceiving this play. Lyons's essay, which has application to Beckett 's other works as well, is to my knowledge unique in its detail concerning perception, yet strangely it does not mention Whitelaw at all despite the fact that her kind of acting figures hugely in the process described.

Reinterpretation of theH2(d,pp)nnreaction at 80 MeV

Leeman et al. measured $^{2}\mathrm{H}(d,pp)\mathrm{nn}$ cross sections at 80 MeV. They interpreted their results in terms of double spectator processes and had limited success in fitting their spectra. We obtain good fits to all their reported data by assuming final-state interactions between both final $n\ensuremath{-}p$ pairs and ignoring the double spectator process.NUCLEAR REACTIONS $^{2}\mathrm{H}(d,pp)\mathrm{nn}$, $E=80$ MeV; calculated $\ensuremath{\sigma}({E}_{1},{E}_{2},{\ensuremath{\theta}}_{1},{\ensuremath{\theta}}_{2})$ assuming $n\ensuremath{-}p$ final-state interactions. Improved fits over original interpretation assuming double spectator process.

Importance of the short-range correlation in proton-nucleus backward scattering

We study inclusive spectra of backward emitted protons for proton- or (other elementary particles) -nucleus reactions. With a simple quasifree model, we observe that the spectator process dominates for the backward emission. With this reaction mechanism the high-momentum part of the inclusive proton spectra can be explained by the short-range nucleon-nucleon correlation.

D+dfour-body breakup reaction at 80 MeV

The $d+d$ four-body breakup reaction has been studied in a geometry chosen to emphasize the double spectator process. Data were obtained at a bombarding energy of 80 MeV for the coincident detection of both emitted protons at several equal angle pairs. Comparison with simple plane wave Born approximation calculations suggests that, in addition to the double spectator process, another process, more strongly localized in phase space, is important. It is suggested that such a process is the double spin-flip excitation of both deuterons to the singlet state.[NUCLEAR REACTIONS $d+d\ensuremath{\rightarrow}2p+2n$, ${E}_{0}=80$ MeV; measured $\frac{{d}^{4}\ensuremath{\sigma}}{d{\ensuremath{\Omega}}_{{p}_{1}}d{\ensuremath{\Omega}}_{{p}_{2}}d{E}_{{p}_{1}}d{E}_{{p}_{2}}}({\ensuremath{\theta}}_{{p}_{1}},{\ensuremath{\theta}}_{{p}_{2}},{E}_{{p}_{1}},{E}_{{p}_{2}})$; coplanar geometry; PWBA analysis.]

Coincidence study of the reaction 2H(d, dp)n

Absolute coincidence cross sections were measured for the reaction 2H(d, dp)n at E d = 20.7 MeV. Strong peaks were observed centered at the minimum neutron laboratory energies. Their shapes were well fitted by PWBA calculations using both zero- and finite-range transition potentials, and by the PWBA modified by including the final p-n interaction. These calculations suggested the importance of both the simple spectator process and more complex mechanisms. DWBA calculations gave poorer fits. No conclusive evidence for unbound 3He levels was obtained.