The strong interaction shift and width of the ground state of pionic hydrogen

Abstract. The hadronic shift in pionic hydrogen has been redetermined to be 1s = 7.086 ± 0.007(stat) ± 0.006(sys) eV by X-ray spectroscopy of ground state transitions applying various energy calibration schemes. The experiment was performed at the high-intensity low-energy pion beam of the Paul Scherrer Institut by using the cyclotron trap and an ultimate-resolution Bragg spectrometer with bent crystals.

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“…The arrangement was similar to the one outlined in ref. [37] where the πBe line was used to determine the spectrometer response.…”

Section: Experimental Approachmentioning

confidence: 99%

Hadronic shift in pionic hydrogen

et al. 2014

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“…Consequently when formed the ground state atom has kinetic energies of typically about 1 eV but occasionally up to 100 eV. For recent experiments on energy distributions of ground state µp/πp atoms see Sigg et al (1996) and Schottmüller et al (1999). Note that at formation of the ground state atom the hyperfine states are statistically populated, i.e.…”

Section: A Muons In Pure Hydrogenmentioning

confidence: 99%

Induced pseudoscalar coupling of the proton weak interaction

2003

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The induced pseudoscalar coupling gp is the least well known of the weak coupling constants of the proton's charged-current interaction. Its size is dictated by chiral symmetry arguments, and its measurement represents an important test of quantum chromodynamics at low energies. During the past decade a large body of new data relevant to the coupling gp has been accumulated. This data includes measurements of radiative and non radiative muon capture on targets ranging from hydrogen and few-nucleon systems to complex nuclei. Herein the authors review the theoretical underpinnings of gp, the experimental studies of gp, and the procedures and uncertainties in extracting the coupling from data. Current puzzles are highlighted and future opportunities are discussed.

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“…However, they are not well established especially for those flavor neutral mesons that are characterized by very short life times making investigations of the meson-nucleon potential in the standard way via scattering experiments impossible. So far, based on the shift and width of the ground state of pionic hydrogen atoms [4], only the scattering length of the π 0 -nucleon potential is accurately determined with a precision of about 0.001 fm. The scattering length for the η-nucleon potential is determined more than two orders of magnitude less precisely, with phenomenological values quoted for the real part between ∼0.2 fm and ∼1 fm depending on the analysis method [5].…”

mentioning

confidence: 99%

Determination of theη′-Proton Scattering Length in Free Space

et al. 2014

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Taking advantage of both the high mass resolution of the COSY-11 detector and the high energy resolution of the low-emittance proton-beam of the Cooler Synchrotron COSY we determine the excitation function for the pp → ppη ′ reaction close-to-threshold. Combining these data with previous results we extract the scattering length for the η ′ -proton potential in free space to be Re(a pη ′ ) = 0 ± 0.43 fm and Im(a pη ′ ) = 0.37 In this letter we report the determination of the scattering length for the interaction of the η ′ meson with the proton based on the shape of the excitation function for the pp → ppη ′ reaction measured close to the kinematic threshold. Using the high mass resolution of the updated COSY-11 detector [1,2] and the low-emittance proton-beam of the Cooler Synchrotron COSY [3] the excitation function was determined down to excess energy Q = 0.76 MeV above threshold, with the precision ∆Q = 0.1 MeV improved by more than a factor of five with respect to previous measurements. The improved resolution enabled quantitative extraction of the η ′ proton scattering length in free space.The scattering lengths describing interaction potentials between mesons and nucleons are of fundamental importance in hadron physics. However, they are not well established especially for those flavor neutral mesons that are characterized by very short life times making investigations of the meson-nucleon potential in the standard way via scattering experiments impossible. So far, based on the shift and width of the ground state of pionic hydrogen atoms [4], only the scattering length of the π 0 -nucleon potential is accurately determined with a precision of about 0.001 fm. The scattering length for the η-nucleon potential is determined more than two orders of magnitude less precisely, with phenomenological values quoted for the real part between ∼0.2 fm and ∼1 fm depending on the analysis method [5]. Until now the η ′ -nucleon scattering length had been estimated only qualitatively [6].Measurements of the η-and η ′ -nucleon and nucleus systems are sensitive to dynamical chiral and axial U(1) symmetry breaking in low energy QCD. While pions and kaons are would-be Goldstone bosons associated with chiral symmetry, the isosinglet η and η ′ mesons are too massive by about 300-400 MeV for them to be pure Goldstone states. They receive extra mass from non-perturbative gluon dynamics associated with the QCD axial anomaly. This OZI violation is also expected to influence the η ′ -nucleon interaction [7]. Without the gluonic mass contribution the η ′ would be a strange quark state after η-η ′ mixing (and the η would be a light-quark state degenerate with the pion), mirroring the situation with isoscalar φ and ω vector mesons. To the extent that coupling to nucleons and nuclear matter is induced by light-quark components in the meson, any observed scattering length and mass shift in medium is induced by the QCD axial anomaly that generates part of the η ′ mass [8].In COSY-11 the η ′ meson was produced in p-p collisions of the COSY ...

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The strong interaction shift and width of the ground state of pionic hydrogen

Cited by 60 publications

References 38 publications

Hadronic shift in pionic hydrogen

Hadronic shift in pionic hydrogen

Induced pseudoscalar coupling of the proton weak interaction

Determination of theη′-Proton Scattering Length in Free Space

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