Three-dimensional (3D) velocity map imaging: from technique to application

The velocity map imaging (VMI) technique was first introduced by Eppink and Parker in 1997, as an improvement to the original ion imaging method by Houston and Chandler in 1987. The method has gained huge popularity over the past two decades and has become a standard tool for measuring high-resolution translational energy and angular distributions of ions and electrons. VMI has evolved gradually from 2D momentum measurements to 3D measurements with various implementations and configurations. The most recent advancement has brought unprecedented 3D performance to the technique in terms of resolutions (both spatial and temporal), multi-hit capability as well as acquisition speed while maintaining many attractive attributes afforded by conventional VMI such as being simple, cost-effective, visually appealing and versatile. In this tutorial we will discuss many technical aspects of the recent advancement and its application in probing correlated chemical dynamics.

Energy and angular distributions of the bottom quark in the electron–positron annihilation e+e−→ bW+t̄

The distributions of the bottom quark in the process [Formula: see text] are considered at the [Formula: see text] energy corresponding to the first construction stage of the Compact Linear Collider. The cross-sections of [Formula: see text], as functions of the [Formula: see text]-quark energy and angle with respect to the direction of the electron beam, are derived and calculated. The effects of physics beyond the Standard Model are included via the modified [Formula: see text] and [Formula: see text] couplings which naturally appear in effective field theories. In addition to the cross-sections, the energy and angular asymmetries are calculated. The dependence of these observables on the [Formula: see text] energy is calculated, and features of this dependence are investigated.

EXTENDED MSM METHOD TO ESTIMATE THE REACTIVITY OF A SUB-CRITICAL CORE DRIVEN BY AN ACCELERATOR BASED NEUTRON SOURCE

The Modified Source Multiplication method is used to determine an unknown reactivity level of a reactor from a known one if one has access to the detector counting for both levels when the reactor is fed by a constant neutron source like an Am-Be source. When available, an accelerator driven source, in continuous mode, can be useful as its intensity can be tunable and then adapted to the experimental conditions. However, in that case, the MSM technique must be extended to account for an external source whose intensity, energy and angular distributions can vary from one measurement to another. In this paper, this Modified Multi-Source Multiplication (MMSM) method is applied to measurements done during the FREYA project in the GUINEVERE facility, operated with the GENEPI-3C accelerator providing a mixture of (D,T) and (D,D) neutrons. The monitoring of these sources through the detection of the associated charged particles allows the calculation of the MMSM factors and the estimate of the reactivity values. The results are compared in different configurations with the reactivity obtained with an Am-Be source or in dynamic measurements performed with GENEPI-3C. Their excellent agreement shows the possibility of using such accelerator-based neutron sources for MSM measurements when they are correctly monitored. This is of great interest for deep sub-critical level characterization for which detector count rates per source neutrons might be low.

Understanding the MiniBooNE and the muon and electron g − 2 anomalies with a light Z′ and a second Higgs doublet

Two of the most widely studied extensions of the Standard Model (SM) are a) the addition of a new U(1) symmetry to its existing gauge groups, and b) the expansion of its scalar sector to incorporate a second Higgs doublet. We show that when combined, they allow us to understand the electron-like event excess seen in the MiniBooNE (MB) experiment as well as account for the observed anomalous values of the muon magnetic moment. A light Z′ associated with an additional U(1) coupled to baryons and to the dark sector, with flavor non-universal couplings to leptons, in conjunction with a second Higgs doublet is capable of explaining the MB excess. The Z′ obtains its mass from a dark singlet scalar, which mixes with the two Higgs doublets. Choosing benchmark parameter values, we show that $$ \mathrm{U}{(1)}_{B-3{L}_{\tau }} $$ U 1 B − 3 L τ , which is anomaly-free, and U(1)B, both provide (phenomenologically) equally good solutions to the excess. We also point out the other (anomaly-free) U(1) choices that may be possible upon fuller exploration of the parameter space. We obtain very good matches to the energy and angular distributions for neutrinos and anti-neutrinos in MB. The extended Higgs sector has two light CP-even scalars, h′ and H , and their masses and couplings are such that in principle, both contribute to help explain the MB excess as well as the present observed values of the muon and electron g − 2. We discuss the constraints on our model as well as future tests. Our work underlines the role that light scalars may play in understanding present-day low-energy anomalies. It also points to the possible existence of portals to the dark sector, i.e., a light gauge boson field (Z′) and a dark neutrino which mixes with the active neutrinos, as well as a dark sector light scalar which mixes with the extended Higgs sector.

Photodissociation of Iso-Propoxy (I-C3H7O) Radical at 248 Nm

<p>Photodissociation of the <i>i</i>-C₃H₇O radical is investigated using fast beam photofragment translational spectroscopy. Neutral <i>i</i>-C₃H₇O radicals are produced through the photodetachment of a fast beam of <i>i</i>-C₃H₇O^- anions and are subsequently dissociated using 248 nm (5.0 eV). The dominant product channels are CH₃ + CH₃CHO and OH + C₃H₆ with some contribution from H + C₃H₆O. CH₃ and H loss are attributed to dissociation on the ground electronic state of <i>i</i>-C₃H₇O, but in a nonstatistical manner because RRKM dissociation rates exceed the rate of energy randomization. Translational energy and angular distributions for OH loss are consistent with ground state dissociation, but the branching ratio for this channel is considerably higher than predicted from RRKM rate calculations. These results corroborate what has been observed previously in C₂H₅O dissociation at 5.2 eV that yields CH₃, H, and OH loss. Additionally, <i>i</i>-C₃H₇O undergoes three-body fragmentation to CH₃ + CH₃ + HCO and CH₃ + CH₄ + CO. These three-body channels are attributed to dissociation of <i>i</i>-C₃H₇O to CH₃ + CH₃CHO, followed by secondary dissociation of CH₃CHO on its ground electronic state.</p>

Photodissociation of Iso-Propoxy (I-C3H7O) Radical at 248 Nm

<p>Photodissociation of the <i>i</i>-C₃H₇O radical is investigated using fast beam photofragment translational spectroscopy. Neutral <i>i</i>-C₃H₇O radicals are produced through the photodetachment of a fast beam of <i>i</i>-C₃H₇O^- anions and are subsequently dissociated using 248 nm (5.0 eV). The dominant product channels are CH₃ + CH₃CHO and OH + C₃H₆ with some contribution from H + C₃H₆O. CH₃ and H loss are attributed to dissociation on the ground electronic state of <i>i</i>-C₃H₇O, but in a nonstatistical manner because RRKM dissociation rates exceed the rate of energy randomization. Translational energy and angular distributions for OH loss are consistent with ground state dissociation, but the branching ratio for this channel is considerably higher than predicted from RRKM rate calculations. These results corroborate what has been observed previously in C₂H₅O dissociation at 5.2 eV that yields CH₃, H, and OH loss. Additionally, <i>i</i>-C₃H₇O undergoes three-body fragmentation to CH₃ + CH₃ + HCO and CH₃ + CH₄ + CO. These three-body channels are attributed to dissociation of <i>i</i>-C₃H₇O to CH₃ + CH₃CHO, followed by secondary dissociation of CH₃CHO on its ground electronic state.</p>