Cross Sections For Final States Research Articles

Single-particle structure of neutron-rich Sr isotopes via H2(Sr94,95,96, p) reactions

Background: The region around neutron number N=60 in the neutron-rich Sr and Zr nuclei is one of the most dramatic examples of a ground-state shape transition from (near) spherical below N=60 to strongly deformed shapes in the heavier isotopes. Purpose: The single-particle structure of Sr95-97 approaching the ground-state shape transition at Sr98 has been investigated via single-neutron transfer reactions using the (d,p) reaction in inverse kinematics. These reactions selectively populate states with a large overlap of the projectile ground state coupled to a neutron in a single-particle orbital. Method: Radioactive Sr94,95,96 nuclei with energies of 5.5 AMeV were used to bombard a CD2, where D denotes H2, target. Recoiling light charged particles and γ rays were detected using a quasi-4π silicon strip detector array and a 12-element Ge array. The excitation energy of states populated was reconstructed employing the missing mass method combined with γ-ray tagging and differential cross sections for final states were extracted. Results: A reaction model analysis of the angular distributions allowed for firm spin assignments to be made for the low-lying 352, 556, and 681 keV excited states in Sr95 and a constraint has been placed on the spin of the higher-lying 1666 keV state. Angular distributions have been extracted for ten states populated in the H2(Sr95,p)Sr96 reaction, and constraints have been provided for the spins and parities of several final states. Additionally, the 0, 167, and 522 keV states in Sr97 were populated through the H2(Sr96,p) reaction. Spectroscopic factors for all three reactions were extracted. Conclusions: Results are compared to shell-model calculations in several model spaces and the structure of low-lying states in Sr94 and Sr95 is well described. The spectroscopic strength of the 0+ and 2+ states in Sr96 is significantly more fragmented than predicted. The spectroscopic factors for the H2(Sr96,p)Sr97 reaction suggest that the two lowest-lying excited states have significant overlap with the weakly deformed ground state of Sr96, but the ground state of Sr97 has a different structure.

Probing QCD with Photons and Jets at the ATLAS detector

This contribution gives an overview of the recent measurements of the differential cross sections for final states involving photons and/or jets at the centre-of-mass energies of 8 and 13 TeV, published by the ATLAS Collaboration. The results are compared with several next-to-leading order calculations and with the latest predictions of various Monte Carlo generators. New measurements of transverse energy-energy correlations and their associated asymmetries in multi-jet events at 8 TeV are also presented. Both measurements are used to extract the strong coupling constant and test the renormalization group equation.

Composite scalars at CERN LEP: Constraining technicolor theories

CERN LEP I and LEP II data can be used to constrain technicolor models with light, neutral pseudo-- Nambu-Goldstone bosons ${P}^{a}.$ We use published limits on branching ratios and cross sections for final states with photons, large missing energy, jet pairs, or $b\overline{b}$ pairs to constrain the anomalous ${P}^{a}{Z}^{0}{Z}^{0},$ ${P}^{a}{Z}^{0}\ensuremath{\gamma},$ and ${P}^{a}\ensuremath{\gamma}\ensuremath{\gamma}$ couplings. From these results, we derive bounds on the size of the technicolor gauge group and the number of technifermion doublets in models such as low-scale technicolor.

Study of neutral-current four-fermion and ZZ production in e +e − collisions at [formula omitted] 183 GeV

A study of neutral-current four-fermion processes is performed using a data sample corresponding to 55.3 pb −1 of integrated luminosity collected by the L3 detector at LEP at an average centre-of-mass energy of 183 GeV. The neutral-current four-fermion cross sections for final states with a pair of charged leptons plus jets and with four charged leptons are measured to be consistent with the Standard Model predictions. Events with fermion pair masses close to the Z boson mass are selected in all observable final states and the ZZ production cross section is measured to be σ ZZ =0.30 +0.22 +0.07 −0.16 −0.03 pb, in agreement with the Standard Model expectation. No evidence for the existence of anomalous triple gauge boson ZZZ and ZZ γ couplings is found and limits on these couplings are set.

Threshold two-pion photo- and electroproduction: More neutrals than expected

We present an exploratory study of two-pion photo- and electroproduction off the nucleon in the threshold region. To calculate the pertinent amplitudes, we make use of heavy baryon chiral perturbation theory. We show that due to finite chiral loops the production cross section for final states with two neutral pions is considerably enhanced. The experimental implications are briefly discussed.

Collisionally aided coherent emission at an optical frequency.

With the development of high-power laser sources, it has become possible to study a new class of collisional-radiative reactions. Theoretical and experimental studies of such collisionally-aided reactions, which require the action of a collision and an external radiation field simultaneously, were aimed initially at calculating or measuring the overall initial to final state cross-sections /1/- Subsequently, it became appreciated that such reactions can also produce coherence among degenerate magnetic sublevels, and that a study of the final state magnetic polarization yields additional information concerning the collisional interaction /2/. In a parallel development /3/, a series of experiments was carried out in which a collisionally-aided excitation of a coherence between the non-degenerate 3P1/2 and 3P3/2 states of Na was generated.

Electron capture to Rydberg states: C4+in collisions with H2

The problem of extracting selective information on the distribution of final-state (nl) population following high-energy electron capture is addressed. As a prototype reaction, the authors study the quasihydrogenic system C4+(1s2)+T going to C3+(1s2nl)+T(?) at energies 2<or=E<or=5 MeV, where T=H2 or He. Theoretically, two multiple scattering approaches (IA and CDW) are generalised to include capture to high-lying states (nl arbitrary), and experimentally the EUV emission spectra subsequent to the capture process are examined. The experimentally deduced cross sections for final states 3<or=n<or=10 and l=0, 1, 2 are then compared with theory. The data satisfy the n-3 law and the experimental trends are equally well reproduced by the IA or CDW calculations. In contrast, the first and second Born cross sections are found to be inadequate to represent the data. This in turn gives further evidence of the inadequacy of the latter theories and provides a measure of the importance of multiple scattering effects in capture processes. To the authors' knowledge, these results represent the first quantitative comparison between theory and experiment in this high-energy regime and at this level of discrimination.

KN π final states in K +p interactions at 7.3 GeV/ c

Data are presented on the production of the KN π final states in K +p interactions at 7.3 GeV/ c. The energy dependence of the KN π final state cross sections, the effective-mass distributions, and the spectra of c.m. longitudinal momenta are given, and features of these data are compared with predictions of the generalized Veneziano (GV) model. Furthermore, we present the momentum transfer and decay angular distributions for K ∗ (890), K ∗ (1420) and Δ (1236) production within the KN π final states and discuss these quasi-two-body reactions in terms of the GV model.

Study of [formula omitted] annihilation at 2.5 GeV/ c with production of two kaons in final state

Cross sections for final states and resonance production are given and compared to a statistical model proposed by Lamb. Transverse and longitudinal momenta are studied and the Goldhaber effect is tested. Baryon exchange mechanisms appear.

Cross sections of final states produced in [formula omitted]N interactions at 3 GeV/c

Cross sections of final states produced in K−n interactions at 3 GeV/c are presented. The results, obtained in a 7 events/ub bubble chamber exposure with deuterium, are compared with results from an earlier K−p exposure at the same incident K− momentum.

Study of multi-body final states in K+p reactions at an incident momentum of 5 GeV/c

Abstract Results are given on the comparison of the predictions of the multiperipheral model of Chan, Loskiewicz and allison with the experimental data obtained from a study of the interactions of 5 GeV/c K+ mesons with protons. Comparisons have been made in the three-, four-, five- and six-body final states containing a proton, kaon and pions. With the addition of resonance production to the model, adequate predictions of experimental distributions are obtained. An attempt is made to describe the energy variation of the three- and four-body final-state cross sections.

D,αReactions onC12,N14, andO16Induced by 24-MeV Deuterons

Alpha-particle energy spectra from $d,\ensuremath{\alpha}$ reactions on ${\mathrm{C}}^{12}$, ${\mathrm{N}}^{14}$, and ${\mathrm{O}}^{16}$ have been obtained using 24-MeV deuterons. The development of a high-resolution semiconductor $\frac{\mathrm{EdE}}{\mathrm{dx}}$ counter telescope made possible the observation of alpha-particle groups arising from the formation of final states of higher excitation than previously studied by these reactions. Angular distributions corresponding to resolvable final states are presented. Marked variation in the relative cross sections of final states was observed in the energy spectra. In an effort to explain the nature of this preferential population, these final states are correlated, where possible, with their expected configurations. A distorted-wave Born-approximation analysis was made for several of the transitions; the outstanding characteristic of this analysis was the strong preference for $L=2$ transitions over $L=0$ transitions.