A new measurement of the structure functions PLL - PTT/ε and PLT in virtual Compton scattering at Q2 = 0.33 (GeV/c)2

Janssens, Peter; Doria, L.; Achenbach, P.; Gayoso, C. Ayerbe; Baumann, D.; Bernauer, J. C.; Bensafa, I. K.; Böhm, R.; Bosnar, D.; Burtin, E.; d’Hose, N.; Defaÿ, X.; Ding, M.; Distler, M. O.; Fonvieille, H.; Friedrich, J.; Laveissière, G.; Makek, M.; Marroncle, J.; Merkel, H.; Müller, U.; Nungesser, L.; Pasquini, B.; Pochodzalla, J.; Postavaru, Octavian; Potokar, M.; Ryckbosch, D.; Majos, S. Sánchez; Schlimme, B. S.; Seimetz, M.; Širca, S.; Tamas, G.; Vyver, R. Van de; Hoorebeke, Luc Van; Overloop, A. Van; Walcher, Th.; Weinriefer, M.

doi:10.1140/epja/i2008-10609-3

Cited by 28 publications

(41 citation statements)

References 28 publications

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“…11, where panel (a) shows the electric polarizability and panel (b) the magnetic one. The theoretical uncertainty of our calculation is sufficiently large to agree with all the data, including the new [14] and old [10,11] MAMI data that tend to disagree among themselves. We can see that the DR curve agrees with the new MAMI data very well, while missing the older data, especially for α E1 .…”

Section: Discussionsupporting

confidence: 52%

“…7, 8, 9 and 10, we show our Bχ PT results (red solid line, with cyan band indicating the uncertainty estimate), compared with the fixed-t DR calculation (blue bands), and experimental data where available. In this calculation we used the Bradford et al [64] parametrization of nucleon form [8,9]; green open diamond, MIT-Bates (LEX) [8,9]; purple solid square, MAMI (DR) [14]; purple open square, MAMI (LEX) [14]; red solid triangle, MAMI1 (LEX) [10]; red solid inverted triangle, MAMI1 (DR) [12]; red open triangle, MAMI2 (LEX) [11]. Some of the data points are shifted to the right in order to enhance their visibility; namely, .…”

Section: Results For Vcs Observablesmentioning

confidence: 99%

“…The non-Born VCS amplitude, carrying the information about the "inelastic" structure of the nucleon, is the unknown piece that one is trying to access in the ep bremsstrahlung. Over the past two decades the experimental studies clearly demonstrated the feasibility of an accurate extraction of proton GPs from ep bremsstrahlung [8][9][10][11][12][13][14]. This experimental progress has been echoed by theory advances.…”

Section: Introductionmentioning

confidence: 99%

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Generalized polarizabilities of the nucleon in baryon chiral perturbation theory

2017

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The nucleon generalized polarizabilities (GPs), probed in virtual Compton scattering (VCS), describe the spatial distribution of the polarization density in a nucleon. They are accessed experimentally via the process of electronproton bremsstrahlung (ep → epγ ) at electron-beam facilities, such as MIT-Bates, CEBAF (Jefferson Lab), and MAMI (Mainz). We present the calculation of the nucleon GPs and VCS observables at next-to-leading order in baryon chiral perturbation theory (Bχ PT), and confront the results with the empirical information. At this order our results are predictions, in the sense that all the parameters are well known from elsewhere. Within the relatively large uncertainties of our calculation we find good agreement with the experimental observations of VCS and the empirical extractions of the GPs. We find large discrepancies with previous chiral calculations -all done in heavy-baryon χ PT (HBχ PT) -and discuss the differences between Bχ PT and HBχ PT responsible for these discrepancies.

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Section: Discussionsupporting

confidence: 52%

Section: Results For Vcs Observablesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Generalized polarizabilities of the nucleon in baryon chiral perturbation theory

2017

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“…The exclusive reaction is then identified using the missing mass squared of the undetected photon. Complementary information can be found in previous reviews [4][5][6][7][8][9]; details on apparatus and physics analyses can be found in the Thesis works [55][56][57][60][61][62][63][64][65][66][67][68][69][70][71][72][73] and the experimental publications [7,11,[74][75][76][77][78][79][80][81][82][83].…”

Section: Methodsmentioning

confidence: 99%

Virtual Compton scattering and nucleon generalized polarizabilities

Fonvieille

Pasquini

Sparveris

2020

Progress in Particle and Nuclear Physics

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This review gives an update on virtual Compton scattering (VCS) off the nucleon, γ * N → N γ, in the low-energy regime. We recall the theoretical formalism related to the generalized polarizabilities (GPs) and model predictions for these observables. We present the GP extraction methods that are used in the experiments: the approach based on the low-energy theorem for VCS and the formalism of Dispersion Relations. We then review the experimental results, with a focus on the progress brought by recent experimental data on proton GPs, and we conclude by some perspectives in the field of VCS at low energy. Theoretical frameworkThis section reviews the formalism related to the nucleon GPs. We first outline some basic properties of polarizabilities and their generalization to finite Q 2 (Sect. 3.1). Then the main ingredients of the low-energy theorem in VCS are summarized in Sect. 3.2. A synthetic overview of model predictions for GPs is given in Sect. 3.3, and the DR formalism is presented in more details in Sect. 3.4. We then move closer to experimental aspects with Sects. 3.5 to 3.7. From real to virtual Compton scatteringThe polarizabilities of a composite object are fundamental characteristics of the system, just as its mass or shape. Among all the known properties of the nucleon, polarizabilities have the unique status of characterizing the nucleon dynamical response to an external electromagnetic (EM) field, describing how easy the charge and magnetization distributions inside the nucleon are distorted by the EM field. Real Compton scattering (RCS) experiments, performed since more than 50 years, have accumulated an 1 Note that this is up to a rotation of the leptonic plane by the azimuthal angle ϕ ′ e lab of the scattered electron. If specified, ϕ ′ e lab is then a sixth independent variable. 2 Other sets of variables are sometimes used, such as (k lab , k ′ lab , θ ′ e lab ) or (Q 2 , √ s, ǫ) for the leptonic vertex, and t instead of cos θ cm . 3 We also findQ = Q2 , andq 0cm defined in the Appendix. 4 This is for instance the case for all experimental values of Q 2 in Sect. 4. 2 qcm √ Q 2 q 0

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“…The scattered electron direction defines φ = 0. The H(e, e p)γ reaction was measured below the pion threshold in several experiments [1,[6][7][8] and in the region of the (1232) resonance [9,10].…”

Section: A Kinematicsmentioning

confidence: 99%

Virtual Compton scattering and neutral pion electroproduction in the resonance region up to the deep inelastic region at backward angles

Laveissière¹,

Degrande²,

Jaminion³

et al. 2009

Phys. Rev. C

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We have made the first measurements of the virtual Compton scattering (VCS) process via the H(e, e p)γ exclusive reaction in the nucleon resonance region, at backward angles. Results are presented for the W -dependence at fixed Q 2 = 1 GeV 2 and for the Q 2 dependence at fixed W near 1.5 GeV. The VCS data show resonant structures in the first and second resonance regions. The observed Q 2 dependence is smooth. The measured ratio of H(e, e p)γ to H(e, e p)π 0 cross sections emphasizes the different sensitivity of these two reactions to the various nucleon resonances. Finally, when compared to real Compton scattering (RCS) at high energy and large angles, our VCS data at the highest W (1.8-1.9 GeV) show a striking Q 2 independence, which may suggest a transition to a perturbative scattering mechanism at the quark level.

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A new measurement of the structure functions PLL - PTT/ε and PLT in virtual Compton scattering at Q2 = 0.33 (GeV/c)2

Cited by 28 publications

References 28 publications

Generalized polarizabilities of the nucleon in baryon chiral perturbation theory

Generalized polarizabilities of the nucleon in baryon chiral perturbation theory

Virtual Compton scattering and nucleon generalized polarizabilities

Virtual Compton scattering and neutral pion electroproduction in the resonance region up to the deep inelastic region at backward angles

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