First Determination of Generalized Polarizabilities of the Proton by a Virtual Compton Scattering Experiment

Roche, J.; Lhuillier, D.; Bartsch, P.; Baumann, D.; Berthot, J.; Bertin, P.Y.; Breton, Vincent; Boeglin, W.; Böhm, R.; d’Hose, N.; Derber, S.; Degrande, N.; Ding, M.; Distler, M. O.; Ducret, J.E.; Ewald, I.; Fonvieille, H.; Friedrich, J.; Guichon, P.A.M.; Holvoet, H.; Hyde‐Wright, C. E.; Jennewein, P.; Kahrau, M.; Kerhoas, S.; Krygier, K. W.; Lannoy, B.; Liesenfeld, A.; Marchand, Claude; Marchand, D.; Marroncle, J.; Martino, J.; Merkel, H.; Merle, P.; Meyer, G. De; Mougey, J.; Müller, U.; Neuhausen, R.; Pospischil, Th.; Qúeḿener, G.; Ravel, O.; Roblin, Y.; Rohe, D.; Rosner, G.; Ryckbosch, D.; Schmieden, H.; Tamas, G.; Tytgat, M.; Vanderhaeghen, Marc; Hoorebeke, Luc Van; Vyver, R. Van de; Wiele, J. Van de; Vernin, P.; Wagner, Andreas; Walcher, Th.; Weiss, M. S.

doi:10.1103/physrevlett.85.708

Cited by 73 publications

(73 citation statements)

References 18 publications

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“…Our points connect smoothly to existing data, except to the (two independent) former measurements at Q 2 = 0.33 GeV 2 [4,6] which lie above the general trend. Somewhat in the spirit of our bin masking, which constrains the cross section to follow a well-defined q ′ cm -behavior, several fits were performed by the authors of the first VCS experiment [4] on their data at Q 2 = 0.33 GeV 2 , assuming different q ′ cm -evolutions of the cross section [23]. All the fits of [23], including the DR one, lead to an enhanced value for P LL − P T T /ǫ [and hence α E1 (Q 2 )], thus leaving the discrepancy unexplained for the electric GP.…”

Section: Lex and Dr Fitssupporting

confidence: 88%

“…1 accomodates well the experimental data for α E1 (Q 2 ), which behave almost like a pure dipole. The baryon chiral pertur- , MAMI [4,6] and JLab [12]. Open and filled circles correspond to DR analyses; open and filled squares correspond to LEX analyses.…”

Section: Lex and Dr Fitsmentioning

confidence: 99%

“…VCS on the proton, γ * p → γp, has been investigated at different laboratories (MAMI [4][5][6][7][8], MIT-Bates [9,10], JLab [11,12]) and photon virtualities Q 2 between 0.06 GeV 2 and 1.76 GeV 2 . A picture of the Q 2 -dependence of the scalar GPs of the proton, i.e., the electric and magnetic GPs α E1 (Q 2 ) and β M1 (Q 2 ), has slowly emerged from the measurements.…”

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confidence: 99%

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New Insight in the Q2 Dependence of Proton Generalized Polarizabilities

Beričič¹,

Correa²,

Benali³

et al. 2019

Phys. Rev. Lett.

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Virtual Compton scattering on the proton has been investigated at three yet unexplored values of the four-momentum transfer Q 2 : 0.10, 0.20 and 0.45 GeV 2 , at the Mainz Microtron. Fits performed using either the low-energy theorem or dispersion relations allowed the extraction of the structure functions PLL − PT T /ǫ and PLT , as well as the electric and magnetic generalized polarizabilities αE1(Q 2 ) and βM1(Q 2 ). These new results show a smooth and rapid fall-off of αE1(Q 2 ), in contrast to previous measurements at Q 2 = 0.33 GeV 2 , and provide for the first time a precise mapping of βM1(Q 2 ) in the low-Q 2 region.

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Section: Lex and Dr Fitssupporting

confidence: 88%

Section: Lex and Dr Fitsmentioning

confidence: 99%

mentioning

confidence: 99%

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New Insight in the Q2 Dependence of Proton Generalized Polarizabilities

Beričič¹,

Correa²,

Benali³

et al. 2019

Phys. Rev. Lett.

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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%

“…The effect of such systematic errors is thus greatly reduced by adopting this renormalization procedure. Every VCS experiment having low-q ′ cm data utilized them to test the absolute normalization of the cross section, and to renormalize it if needed [7,[74][75][76][77][78]83]. By this method, the overall normalization uncertainty was reduced to, e.g., ± 1% in the MAMI-I experiment [57,74] and in the MAMI-VI experiment [83].…”

Section: Systematic Errorsmentioning

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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Introduction to Chiral Perturbation Theory

Scherer

Advances in Nuclear Physics

446

642

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First Determination of Generalized Polarizabilities of the Proton by a Virtual Compton Scattering Experiment

Cited by 73 publications

References 18 publications

New Insight in the Q2 Dependence of Proton Generalized Polarizabilities

New Insight in the Q2 Dependence of Proton Generalized Polarizabilities

Virtual Compton scattering and nucleon generalized polarizabilities

Introduction to Chiral Perturbation Theory

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