arXiv subjects

A. Gillitzer

Publications and source records attributed to A. Gillitzer.

30 records · Page 2Linked to original sources

arXiv2008

Two-Pion Production in Proton-Proton Collisions with Polarized Beam

The two-pion production reaction $\vec{p}p\to ppπ^+π^-$ was measured with a polarized proton beam at $T_p \approx$ 750 and 800 MeV using the short version of the COSY-TOF spectrometer. The implementation of a delayed pulse technique for Quirl and central calorimeter provided positive $π^+$ identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle measurements. Thus all four-momenta of the emerging particles could be determined with 1-4 overconstraints. Total and differential cross sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous data and theoretical calculations. In contrast to predictions we find significant analyzing power values up to $A_y$ = 0.3.

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arXiv2007

Single π^- production in np collisions for excess energies up to 90 MeV

The quasifree reaction $np\to pp\pim$ was studied in a kinematically complete experiment by bombarding a liquid hydrogen target with a deuteron beam of momentum 1.85 GeV/c and analyzing the data along the lines of the spectator model. In addition to the three charged ejectiles the spectator proton was also detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was identified by its momentum and flight direction thus yielding access to the Fermi motion of the bound neutron and to the effective neutron 4-momentum vector $\mathbb{P}_n$ which differed from event to event. A range of almost 90 MeV excess energy above threshold was covered. Energy dependent angular distributions, invariant mass spectra as well as fully covered Dalitz plots were deduced. Sizeable $pp$ FSI effects were found as were contributions of $p$ and $d$ partial waves. The behavior of the elementary cross section $σ_{01}$ close to threshold is discussed in view of new cross section data. In comparison with existing literature data the results provide a sensitive test of the spectator model.

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arXiv2007

Improved study of a possible Theta+ production in the pp -> p K0 sigma+ reaction with the COSY-TOF spectrometer

The pp -> p K0 Sigma+ reaction was investigated with the TOF spectrometer at COSY at 3.059 GeV/c incident beam momentum. The main objective was to clarify whether or not a narrow exotic S = +1 resnance, the Theta+ pentaquark, is populated at 1.53 GeV/c2 in the K0 p subsystem with a data sample of much higher statistical significance compared to the previously reported data in this channel. An analysis of these data does not confirm the existence of the Theta+ pentaquark. This is expressed as an upper limit for the cross section sigma (pp -> p K0 Sigma+) < 0.15 microbarn at the 95 percent confidence level.

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arXiv2007

Comparison of Isoscalar Vector Meson Production Cross Sections in Proton-Proton Collisions

The reaction $ pp\to pp\bf ω$ was investigated with the TOF spectrometer, which is an external experiment at the accelerator COSY (Forschungszentrum Jülich, Germany). Total as well as differential cross sections were determined at an excess energy of $93 MeV$ ($p_{beam}=2950 MeV/c$). Using the total cross section of $(9.0\pm 0.7 \pm1.1) μb$ for the reaction $ pp\to ppω$ determined here and existing data for the reaction $pp\to pp\bf ϕ$, the ratio $\mathcal{R}_{ϕ/ω}=σ_ϕ/σ_ω$ turns out to be significantly larger than expected by the Okubo-Zweig-Iizuka (OZI) rule. The uncertainty of this ratio is considerably smaller than in previous determinations. The differential distributions show that the $ω$ production is still dominated by S-wave production at this excess energy, however higher partial waves clearly contribute. A comparison of the measured angular distributions for $ω$ production to published distributions for $ϕ$ production at $83 MeV$ shows that the data are consistent with an identical production mechanism for both vector mesons.

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arXiv2006

Single-Pion Production in pp Collisions at =.95 GeV/c (I)

The single-pion production reactions $pp\to dπ^+$, $pp\to npπ^+$ and $pp\to ppπ^0$ were measured at a beam momentum of 0.95 GeV/c ($T_p \approx$ 400 MeV) using the short version of the COSY-TOF spectrometer. The implementation of a central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements. Thus all pion production channels were recorded with 1-4 overconstraints. The total and differential cross sections obtained are compared to previous data and theoretical calculations. Main emphasis is put on the discussion of the $ppπ^0$ channel, where we obtain angular distributions different from previous experimental results, however, partly in good agreement with recent phenomenological and theoretical predictions. In particular we observe very large anisotropies for the $π^0$ angular distributions in the kinematical region of small relative proton momenta revealing there a dominance of proton spinflip transitions associated with $π^0$ $s$- and $d$-partial waves and emphasizing the important role of $π^0$ d-waves.

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arXiv2004

Production of phi Mesons in Au+Au Collisions at 11.7 A GeV/c

We report on a measurement of phi-meson production in Au+Au collisions at a beam momentum of 11.7 A GeV/c by Experiment E917 at the AGS. The measurement covers the midrapidity region 1.2 < y < 1.6. Transverse-mass spectra and the rapidity distribution are presented as functions of centrality characterized by the number of participant projectile nucleons. The yield of phi's per participant projectile nucleon increases strongly in central collisions in a manner similar to that observed for kaons.

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arXiv2004

Precision spectroscopy of pionic 1s states of Sn nuclei and evidence for partial restoration of chiral symmetry in the nuclear medium

Deeply bound 1s states of $π^-$ in $^{115,119,123}$Sn were preferentially observed using the Sn($d$,$^3$He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were precisely determined, and were used to deduce the isovector parameter of the s-wave pion-nucleus potential to be $b_1 =-0.115\pm 0.007 ~m_π^{-1}$. The observed enhancement of $|b_1|$ over the free $πN$ value ($b_1^{\rm free}/b_1 = 0.78 \pm 0.05$) indicates a reduction of the chiral order parameter, $f^{*}_π (ρ)^2/f_π^2 \approx 0.64$, at the normal nuclear density, $ρ= ρ_0$.

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arXiv2004

Evidence for a narrow resonance at 1530 MeV/c2 in the K0 p - system of the reaction pp --> Sigma+ K0 p from the COSY-TOF experiment

The hadronic reaction pp --> Sigma+ K0 p was measured exclusively at a beam momentum of 2.95 GeV/c using the TOF detector at the COSY storage ring. A narrow peak was observed in the invariant mass spectrum of the K0 p subsystem at 1530 +- 5 MeV/c2 with a significance of 4 - 6 standard deviations, depending on background assumptions. The upper limit of 18 +- 4 MeV/c2 (FWHM) for its width is given by the experimental resolution. The corresponding total cross section is estimated to be about 0.4 +- 0.1(stat) +- 0.1(syst) microbarn. Since a resonance in this subsystem must have strangeness S = + 1 we claim it to be the Theta+ state for which very recently evidence was found in various experiments.

hep-ex↗

arXiv2003

Hadron Physics at COSY

The workshop 'Hadron Physics at COSY' held from July 7th to July 10th 2003 in Bad Honnef brought together experimentalists and theoreticians from various fields of hadron physics to identify the key physics questions, which can be addressed with (un-) polarized proton and deuteron induced reactions at COSY. Topics discussed include charge symmetry breaking, elastic and inelastic nucleon-nucleon and nucleon-deuteron interactions, hadrons in the medium, mesonic bound states, meson and baryon resonances, and the hyperon-nucleon system. In addition prospects of the planned GSI facility were discussed. These Miniproceedings contain besides short summaries of the presentations the most relevant references for the field.

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arXiv2001

Baryon Rapidity Loss in Relativistic Au+Au Collisions

An excitation function of proton rapidity distributions for different centralities is reported from AGS Experiment E917 for Au+Au collisions at 6, 8, and 10.8 GeV/nucleon. The rapidity distributions from peripheral collisions have a valley at midrapidity which smoothly change to distributions that peak at midrapidity for central collisions. The mean rapidity loss increases with increasing beam energy, whereas the fraction of protons consistent with isotropic emission from a thermal source at midrapidity decreases with increasing beam energy.

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arXiv2001

Antilambda production in Au+Au collisions at 11.7 A GeV/c

We present results from Experiment E917 for antilambda and antiproton production in Au+Au collisions at 11.7 A GeV. We have measured invariant spectra and yields for both species in central and peripheral collisions. We find that the antilambda/antiproton ratio near mid-rapidity increases from 0.26+0.19-0.15 in peripheral collisions to 3.6+4.7-1.8 in central collisions, a value that is substantially larger than current theoretical estimates.

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arXiv1998

Formation of $η$-mesic Nuclei Using the Recoilless (d,$^3$He) Reaction

We propose to use the recoilless (d,$^3$He) reaction to produce $η$-mesic nuclei. This reaction has been used to observe deeply bound pionic states and proven to be powerful recently. We calculate $η$-mesic bound states in the nucleus using an optical potential and their formation cross section with the Green function method. Then, we carefully check the experimental feasibility. We find that $η$-mesic nuclei can be observed experimentally using the (d,$^3$He) reaction. We also mention the possibility to study the formation of $ω$-mesic nuclei.

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