Measurement of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>Production in the Nuclear Medium by<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml

Starostin, A.; Staudenmaier, H. M.; Allgower, C.; Bekrenev, V.; Berger, Edmond L.; Briscoe, W. J.; Clajus, M.; Comfort, J. R.; Craig, K.; Grosnick, D.; Isenhower, D.; Knecht, N. S.; Koetke, D. D.; Koulbardis, A.; Kozlenko, N.; Kruglov, S. P.; Kycia, T. F.; Lolos, G. J.; Lopatin, I.; Manley, D. M.; Manweiler, B.; Marušić, A.; McDonald, S.; Nefkens, B. M. K.; Olmsted, J.; Papandreou, Z.; Peaslee, D. C.; Peterson, R.J.; Phaisangittisakul, N.; Prakhov, S.; Pulver, M.; Ramirez, A. F.; Sadler, M. E.; Shafi, A.; Šlaus, I.; Spinka, H.; Stanislaus, S.; Supek, I.; Tippens, W. B.

doi:10.1103/physrevlett.85.5539

Cited by 70 publications

(42 citation statements)

References 17 publications

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“…This effect was interpreted as a signature for an in-medium modification of the ππ interaction in the I=J=0 channel. A similar effect was found by a pion-induced experiment of the Crystal Ball collaboration [13] where a nuclear-mass dependence of the π • π • -mass distribution was observed. For the interpretation of the previously described pioninduced measurements two issues have to be addressed.…”

supporting

confidence: 63%

In-Medium Modifications of theππInteraction in Photon-Induced Reactions

et al. 2002

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Differential cross sections of the reactions (γ, π • π • ) and (γ, π • π +/− ) have been measured for several nuclei ( 1 H, 12 C, and nat Pb) at an incident-photon energy of Eγ =400-460 MeV at the taggedphoton facility at MAMI-B using the TAPS spectrometer. A significant nuclear-mass dependence of the ππ invariant-mass distribution is found in the π • π • channel. This dependence is not observed in the π • π +/− channel and is consistent with an in-medium modification of the ππ interaction in the I=J=0 channel. The data are compared to π-induced measurements and to calculations within a chiral-unitary approach.One of the challenges in nuclear physics is to study the properties of hadrons and the modification of these properties when the hadron is embedded in a nuclear manybody system. Although much has been learned about the properties of hadrons in free space, there is a lack of information for particles in a dense environment. In this Letter, an experiment is described which has measured correlated pion pairs photoproduced on nuclei in the scalar-isoscalar J=I=0 channel, also known as the σ mode. In Ref.[1] the σ meson is identified as the f 0 (400-1200). The large natural width in free space of Γ=400-500 MeV [2] makes it doubtful that this particle is a mesonic state, and has initiated many discussions on its nature. An in-medium study of the I=J=0 channel could provide a better insight into the nature of the σ meson.Within some theoretical approaches of quantum chromodynamics (QCD) [3,4,5], the σ is treated as a pure qq state (J P =0 + ) and regarded as the chiral partner of the pion (J P =0 − ). Chiral symmetry is spontaneously broken in the QCD vacuum, resulting in a mass difference between the pion and the σ. For large baryon densities, it is predicted that chiral symmetry is partially restored, leading to a degeneracy in mass of the pion and the σ. Since the pion approximates a Goldstone boson, the pion mass is not expected to change dramatically with increasing nuclear density ρ. Hence, these models predict a significant drop in the mass of the σ. A measurement of the inmedium σ→ ππ mass distribution might be essential for the understanding of the mechanism of chiral-symmetry breaking.Alternatively, the in-medium σ mode can be considered to be a resonant state of two pions [6,7,8,9]. In vacuum, the ππ system is mildly attractive. However, in the nuclear medium the ππ interaction strength could increase, thereby changing width and pole position of the resonant state. Experimental data on the density dependence of pion-pair interactions in the nuclear medium can provide evidence for this phenomenon.The first measurement of the in-medium ππ mass was obtained by a pion-induced experiment by the CHAOS collaboration [10,11,12]. A rising accumulation of strength at low π + π − mass was observed with increasing nuclear mass whereas such an enhancement was not seen in the π + π + -mass distributions. This effect was interpreted as a signature for an in-medium modification of the ππ interaction in the I=J=0 chann...

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supporting

confidence: 63%

In-Medium Modifications of theππInteraction in Photon-Induced Reactions

et al. 2002

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“…In a recent work [12] we obtained the pionic piece of the scalar susceptibility by taking the derivative with respect to the quark mass (in practice to the pion mass) of the pion scalar density 2 , which is a component of the condensate of the medium. We showed that the medium effects affecting the scalar susceptibility are precisely the same that the ones governing the reshaping of the strength in the low invariant mass region in two-pion production experiments [13][14][15]. One purpose of the present paper is to provide a unified description of two quantities, i.e., the effect of the nuclear scalar field and of the pion loops in a way compatible with saturation properties of nuclear matter.…”

Section: Introductionmentioning

confidence: 99%

QCD susceptibilities and nuclear matter saturation in a chiral theory: Inclusion of pion loops

Chanfray

Ericson

2007

Phys. Rev. C

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We derive the equation of state of symmetric nuclear matter in a relativistic theory with σ and ω exchange. We take a chiral version of this model which insures all the chiral constraints. Going beyond the mean field approach we introduce the effects of the pion loops. For the parameters of the model, in order to fix those linked to pion exchange, we exploit the most recent information on the short-range part of the spin-isospin interaction. For those linked to the scalar meson exchange we make use of an analysis of lattice results on the nucleon mass evolution with the quark mass. With these inputs we are able reach a correct description of the saturation properties. From the equation of state of symmetric nuclear matter we also derive the density dependence of the quark condensate and of the QCD susceptibilities.

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“…First effects have been observed by the CHAOS collaboration in pion-induced reactions [2] and later by the CB@BNL collaboration [3]. Both experiments observed an in-medium modification of the ππ interaction in the I = J = 0 channel.…”

Section: Introductionmentioning

confidence: 83%

Double Pion Photoproduction off nuclei - search for the in-medium modification of theσ-meson

Maghrbi

2012

EPJ Web of Conferences

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Abstract. The photoproduction of π 0 π 0 and π 0 π +/− pairs has been investigated in view of the of in-medium modifications the σ-meson. The measurements have been done at the Mainz MAMI accelerator, using the Glasgow photon tagging spectrometer and a 4π electromagnetic calorimeter, consisting of the Crystal Ball and TAPS detectors . The measurements covered different nuclear targets ( 2 H, 7 Li, 12 C, 40 Ca, and nat Pb) and the statistical quality of the data was improved compared to the previous experiments. The energy and mass dependence of the invariant mass distributions suggests that Final State Interactions play a very important role, but some of the observed effects can also be related to a possible in-medium modification of the σ-meson.

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Measurement ofπ0π0Production in the Nuclear Medium byπ

Cited by 70 publications

References 17 publications

In-Medium Modifications of theππInteraction in Photon-Induced Reactions

In-Medium Modifications of theππInteraction in Photon-Induced Reactions

QCD susceptibilities and nuclear matter saturation in a chiral theory: Inclusion of pion loops

Double Pion Photoproduction off nuclei - search for the in-medium modification of theσ-meson

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