Search results for "Crystal Ball"
showing 10 items of 51 documents
Transmetabolism: the non‐conformist approach to biotechnology
2021
Research work of the author is funded by Agencia Estatal de Investigación (AEI), Ministerio de Ciencia e Innovación (grant SETH ref. RTI2018-095584-B-C41-42-43-44 co-financed by ERDF) and the European Union H2020 (BioRobooST project ID 210491758; MIPLACE project ref. PCI2019-111845-2, Programación Conjunta Internacional 2019, AEI).
Study of η and η′ Photoproduction at MAMI
2017
The reactions γp→ηp and γp→η′p are measured from their thresholds up to the center-of-mass energy W=1.96 GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections are obtained with unprecedented statistical accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section for η photoproduction at the energies in the vicinity of the η′ threshold, W=1896 MeV (Eγ=1447 MeV). Within the framework of a revised ηMAID isobar model, the cusp, in connection with a steep rise of the η′ total cross section from its threshold, can only be explained by a strong coupling of the poorly known N(1895)1/2− …
Compton scattering off pions and electromagnetic polarizabilities
2019
The electric ($\alpha_\pi$) and magnetic ($\beta_\pi$) Compton polarizabilities of both the charged and the neutral pion are of fundamental interest in the low-energy sector of quantum chromodynamics (QCD). Pion polarizabilities affect the shape of the $\gamma\pi\to\gamma\pi$ Compton scattering angular distribution at back scattering angles and $\gamma\gamma\to\pi\pi$ absolute cross sections. Theory derivations are given of the $\gamma\pi\to\gamma\pi$ Compton scattering differential cross section, dispersion relations, and sum rules in terms of the polarizabilities. We review experimental charged and neutral polarizability studies and theoretical predictions. The $\pi^0$ polarizabilities we…
First measurement of the polarization observable E and helicity-dependent cross sections in single π 0 photoproduction from quasi-free nucleons
2017
The double-polarization observable $E$ and the helicity-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ have been measured for the first time for single $\pi^{0}$ photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the $\pi^0$ meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the $\pi^{0}N$ final state. A comparison to data mea…
First measurement of helicity-dependent cross sections in π0η photoproduction from quasi-free nucleons
2018
The helicity-dependent cross sections for the photoproduction of $\pi^0\eta$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the $\sigma_{1/2}$ (photon and target spin antiparallel) and $\sigma_{3/2}$ (parallel spins) components to be measured for quasi-free production of $\pi^0\eta$ pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant pr…
Study of the partial wave structure of π0η photoproduction on protons
2013
Abstract Analysis of the partial wave structure of γ p → π 0 η p reaction is presented in the energy region from threshold up to the total center-of-mass energy W = 1.9 GeV . Angular distributions measured with the Crystal Ball/TAPS hermetic detector system at the Mainz Microtron MAMI are expanded in terms of spherical harmonics. The relation of the extracted moments to the partial wave structure of the reaction amplitude is discussed and compared with predictions from model calculations.
Meson Decays with Crystal Ball at MAMI
2012
The Crystal Ball at MAMI setup offers excellent possibilities to study decays of light mesons like η , η ′ , and ω . Here, recent results on η and ω decays are presented. Furthermore, future perspectives in this field at MAMI are described.
Coherent ψ(2S) photo-production in ultra-peripheral Pb Pb collisions at sNN=2.76 TeV
2015
We have performed the first measurement of the coherent ψ(2S) photo-production cross section in ultraperipheral Pb–Pb collisions at the LHC. This charmonium excited state is reconstructed via the ψ(2S) → l +l − and ψ(2S) → J/ψπ+π− decays, where the J/ψ decays into two leptons. The analysis is based on an event sample corresponding to an integrated luminosity of about 22 μb−1. The cross section for coherent ψ(2S) production in the rapidity interval −0.9 < y < 0.9 is dσcoh ψ(2S)/dy = 0.83±0.19 stat+syst mb. The ψ(2S) to J/ψ coherent cross section ratio is 0.34+0.08 −0.07(stat + syst). The obtained results are compared to predictions from theoretical models.
ηandη′Physics at MAMI
2014
The Crystal Ball/TAPS setup at MAMI is ideally suited to detect neutral and electromagnetic decays of the η and η′ mesons. In this contribution recent results on η and η′ decays from the Crystal Ball/TAPS experiment at MAMI are presented. These are the accurate measruement of η′ photoproduction cross-sections in the threshold region, the determination of the timelike electromagnetic transition form factors, and a test of low-energy QCD with the η → π 0 γγ decay. Finally, further perspectives are discussed.
Spin Physics with Photons — Technical Highlights and Spin-Offs
2016
The spin, as a fundamental property of a particle, has been a main object of investigation in particle and nuclear physics research in recent decades. For complete spin investigation, one requires a polarized target in addition to polarized beams and a recoil polarimeter. The advent of advanced beam and large acceptance detector technologies has driven the development of highly polarized, full angular acceptance targets. The Crystal Ball detector with its unique capability to cope with multi photon final states is used in Mainz at the A2 real photon facility in combination with a frozen spin polarized target. Technical highlights from the development of thin superconducting magnets to prov…