Proton Timelike Form Factors Near Threshold via Antiproton-Nucleus Electromagnetic Annihilation

In the reaction of the antiproton-deuteron electromagnetic annihilation pbar + d --> e+e-n the value of the invariant mass M of the (e+e-) pair can be near or below the (pbar p) mass even for enough high momentum of incident antiproton. This allows to access the proton electromagnetic form factors in the time-like region of q^2 near the (pbar p) threshold. We estimate the cross section dsigma(pbar + d --> e+e-n)/dM for an antiproton beam momentum of 1.5 GeV/c. We find that near the (pbar p) threshold this cross section is about 1 pb/MeV. The case of heavy nuclei target is also discussed. Elements of experimental feasibility are presented for the process pbar + d --> e+e-n in the context of the Panda project. We conclude that this process has a chance to be measurable at Panda.Comment: 12 pages, 5 figures, Contribution to the proceedings of the 29-th International Workshop on Nuclear Theory, June 21-25, 2010, Rila Mountains, Bulgari

VCS-E93050 Experimental Offsets Determination for DA1 and DA2 datasets ADDENDUM

This note is an addendum to my previous memo on offsets (of dec.2001 - PCCF RI 0127). It reports how the study was conducted further, and contains improved offsets for DA1 and DA2 analysis

Sljedeće mjerenje virtualnog Comptonovog raspršenja u MAMI

A new ep → epγ experiment is foreseen at MAMI in order to study the Q2 - dependence of the structure functions PLL − PT T /ǫ and PLT and the generalized polarizabilities αE(Q2 ) and βM(Q2 ) of the proton.Predviđamo novo mjerenje ep → epγ u MAMI radi proučavanja Q2 -ovisnosti strukturnih funkcija PLL − PT T /ǫ i PLT te poopćenih polarizabilnosti αE(Q2 ) i βM(Q2 ) protona

VCS-E93050 Polarizability data at Q^2= 1 and 2 GeV^2. Practical use of radiative corrections to measured cross sections d5σ (ep \ to epγ)

February 2000. // Revised april 2007This short note summarizes how in practice one applies radiative corrections to the measured cross sections d^5σ (ep\ to epγ) for DA-1 and DA-2 data of VCS-E93050 (polarizabilities). It does not intend to explain what radiative corrections are. For this I refer to specialized litterature (see References)

Generalized spin polarizabilities of the nucleon in Heavy Baryon Chiral Perturbation Theory at order O(p4){\mathcal O}(p^4)

We present the first heavy baryon chiral perturbation theory calculation at ${\mathcal O}(p^4)$ for the spin-dependent amplitudes for virtual Compton scattering off the nucleon, and extract the ${\cal O}(p^4)$ order results for the generalized spin polarizabilities of the nucleon.Comment: 4 pages, 2 figs, minor corrections to text, version to appear in Phys. Rev. Let

Virtualno Comptonovo raspršenje na niskim energijama i poopćene polarizivosti nukleona

Virtual Compton scattering (VCS) γ ∗p → γp at low CM energy gives access to the generalized polarizabilities of the nucleon. These observables generalize the concept of electromagnetic polarizabilities to the case of a virtual photon. Dedicated VCS experiments have been performed at MAMI, Jefferson Lab and MIT-Bates. The experimental status is reviewed, including methods of analysis and physical results. The measurement of absolute (ep → epγ) cross sections allows the extraction of the two unpolarized VCS structure functions PLL − PTT/ǫ and PLT, which are combinations of the generalized polarizabilities of the proton. Future prospects in the field of VCS at low energy are also presented.Virtualno Comptonovo raspršenje (VCR) γ ∗p → γp na niskim energijama u CMS pruža mogućnost određivanja poopćenih polarizivosti nukleona. Te opservable poopćuju pojam elektromagnetske polarizivosti za slučaj virtualnih fotona. Usmjerena mjerenja VCR načinjena su u MAMI, Jefferson Labu i u MIT-Batesu. Dajemo pregled mjerenja, te metoda analize podataka i ishode. Mjerenja apsolutnih udarnih presjeka reakcije (ep→epγ) dozvoljava izvođenje dviju strukturnih funkcija VCR bez polarizacije PLL − PTT/ǫ i PLT, koje su kombinacije poopćenih polarizivosti protona. Predstavljaju se izgledi budućih istraživanja VCR a niskim energijama