arXiv subjects

A. Starostin

Publications and source records attributed to A. Starostin.

46 records · Page 3Linked to original sources

arXiv2009

Beam-Helicity Asymmetries in Double Pion Photoproduction off the Proton

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels $\vecγp\to π^{+}π^0n$, $\vecγp\to π^{0}π^0p$ and $\vecγp\to π^{+}π^{-}p$ . The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of $π^0$ mesons were detected in a $~4π$ electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction dynamics.

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arXiv2009

Measurement of $π^0 Λ$, $\bar{K}^0 n$, and $π^0 Σ^0$ production in $K^- p$ interactions for $p_{K^-}$ between 514 and 750 MeV/$c$

Differential cross sections and hyperon polarizations have been measured for $\bar{K}^0 n$, $π^0 Λ$, and $π^0 Σ^0$ production in $K^- p$ interactions at eight $K^-$ momenta between 514 and 750 MeV/$c$. The experiment detected the multiphoton final states with the Crystal Ball spectrometer using a $K^-$ beam from the Alternating Gradient Synchrotron of BNL. The results provide significantly greater precision than the existing data, allowing a detailed reexamination of the excited hyperon states in our energy range.

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arXiv2009

Measurement of the Slope Parameter $α$ for the $η\to 3π^0$ decay with the Crystal Ball detector at the Mainz Microtron (MAMI-C)

The dynamics of the $η\to 3π^0$ decay have been studied with the Crystal Ball multiphoton spectrometer and the TAPS calorimeter. Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz microtron MAMI-C and tagged by the Glasgow photon spectrometer were used for $η$-meson production. The analysis of $3 \times 10^6$ $γp \to ηp \to 3π^0 p \to 6γp$ events yields the value $α=-0.032\pm0.003$ for the $η\to 3π^0$ slope parameter, which agrees with the majority of recent experimental results and has the smallest uncertainty. The $π^0π^0$ invariant-mass spectrum was investigated for the occurrence of a cusplike structure in the vicinity of the $π^+π^-$ threshold. The observed effect is small and does not affect our measured value for the slope parameter.

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arXiv2009

Determination of the Dalitz plot parameter alpha for the decay eta->3pi^0 with the Crystal Ball at MAMI-B

A precise measurement of the Dalitz plot parameter, alpha, for the eta->3pi^0 decay is presented. The experiment was performed with the Crystal Ball and TAPS large acceptance photon detectors at the tagged photon beam facility of the MAMI-B electron accelerator in Mainz. High statistics of 1.8*10^6 eta->3pi^0 events were obtained, giving the result alpha = -0.032 +/- 0.002(stat) +/- 0.002(syst).

hep-ex↗

arXiv2008

The WASA Detector Facility at CELSIUS

The WASA 4pi multidetector system, aimed at investigating light meson production in light ion collisions and eta meson rare decays at the CELSIUS storage ring in Uppsala is presented. A detailed description of the design, together with the anticipated and achieved performance parameters are given.

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arXiv2007

Incoherent pion photoproduction on $^{12}$C

We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The $^{12}$C$(γ,π^{0})^{12}$C$^{*}_{4.4MeV}$ reaction has been studied with the Glasgow photon tagger at MAMI employing a new technique which uses the large solid angle Crystal Ball detector both as a $π^{0}$ spectrometer and to detect decay photons from the excited residual nucleus. The technique has potential applications to a broad range of future nuclear measurements with the Crystal Ball and similar detector systems elsewhere. The data are sensitive to the propagation of the $Δ$ in the nuclear medium and will give the first information on matter transition form factors from measurements with an electromagnetic probe. The incoherent cross sections are compared to two theoretical predictions including a $Δ$-hole model.

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arXiv2004

Measurement of Inverse Pion Photoproduction at Energies Spanning the N(1440) Resonance

Differential cross sections for the process pi^- p -> gamma n have been measured at Brookhaven National Laboratory's Alternating Gradient Synchrotron with the Crystal Ball multiphoton spectrometer. Measurements were made at 18 pion momenta from 238 to 748 MeV/c, corresponding to E_gamma for the inverse reaction from 285 to 769 MeV. The data have been used to evaluate the gamma n multipoles in the vicinity of the N(1440) resonance. We compare our data and multipoles to previous determinations. A new three-parameter SAID fit yields 36 +/- 7 (GeV)^-1/2 X 10^-3 for the A^n_1/2 amplitude of the P_11.

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arXiv2004

Does the Sigma(1580)3/2- resonance exist?

Precise new data for the reaction $K^- p \to π^0 Λ$ are presented in the c.m. energy range 1565 to 1600 MeV. Our analysis of these data sheds new light on claims for the $Σ(1580){3/2}^-$ resonance, which (if it exists with the specified quantum numbers) must be an exotic baryon because of its very low mass. Our results show no evidence for this state.

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arXiv2002

Meson production on complex nuclei by pi^- with the Crystal Ball detector

We report on preliminary results for the production of neutral mesons by 750 MeV/$c$ $π^-$ on complex nuclear targets (C, Al, Cu) and hydrogen. Our simultaneous measurement of $π^0$, $2π^0$, and $η$ final states allows an investigation of the nuclear final-state-interaction effects. The data show that nuclear absorption is mainly responsible for an observed change in the shape of the $2π^0$ invariant mass spectra. Our preliminary result for the $σ\to γγ$ branching ratio is BR$(σ\to γγ) < 3.6\times 10^{-3} \times ϕ$ at 90% C.L. on a carbon target, where $ϕ$ is the fraction of $2π^0$ produced via the $σ$ intermediate state.

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arXiv2002

In Search of the f0 (or "sigma") Meson: New data on pi0 pi0 Production by pi- and K- on Hydrogen

We present preliminary results on the cross sections and Dalitz-plot densities for the process pi- p -> pi0 pi0 n from threshold to p(pi)=750 MeV/c as well as for K- p -> pi0 pi0 Lambda and K- p -> pi0 pi0 Sigma0 at p(K)=520 to 750 MeV/c. We have found that sigma(tot)(pi- p -> pi0 pi0 n) ~= 2sigma(tot)(K- p -> pi0 pi0 Lambda). The pi0 pi0 n Dalitz plots are very nonuniform, expecially for the higher p(pi), with a high concentration of events on an "island" around m(pi n) ~= 1.2 GeV and Gamma ~= 0.1 GeV peaking at high pi0 pi0 invariant mass. This is indicative of the dominant role of the Delta0(1234)(3/2^+) resonance in the final state. The pi0 pi0 Lambda Dalitz plots are strikingly similar to the ones for pi0 pi0 n except that the island is concentrated at m(pi Lambda) ~= 1.38 GeV and has a narrower width, Gamma ~= 0.05 GeV. This indicates the dominant role of the Sigma0(1385)(3/2+) resonance. The similarity in the Dalitz plots and the proportionality of the total cross sections are an impressive testimony of the applicability of broken SU(3) flavor symmetry to reaction dynamics. We have measured sigma(tot)(K- p -> pi0 pi0 Lambda) ~= 6sigma(tot)(K- p -> pi0 pi0 Sigma0) and observed that the Dalitz plots for these processes are very different. The Dalitz plots for pi0 pi0 Sigma0 show some enhancement at low pi0 pi0 invariant mass, and there is good indication for the Lambda(1405) intermediate state but there is no island; at the highest p(K), there is some evidence for the Lambda(1520) intermediate state. The above features of pi0 pi0 production by pi- and K- can all be understood if f0 production is small.

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