Laboratori Nazionali di Frascati INFN PacificSpin2015 October 6 th - PowerPoint PPT Presentation

Silvia Pisano Laboratori Nazionali di Frascati INFN PacificSpin2015 – October 6 th , 2015.

The interactions of the nucleon The nucleon is sensitive to all the interactions known so far up 𝑟 𝑟 How the nucleon experiences a specific interactions is 𝑟 𝑟 encoded in a charge → it depends on the nature of the operator describing the interaction up down What is the spatial size of the nucleon? 𝑟 𝑟 And how its charges are distributed in its bulk? What is the orbital angular momentum of the nucleon constituents? 𝑇 𝑟 𝑀 𝑟 And how its description relates to the full-QCD description encoded in lattice-based calculations? 𝐾 𝑕 PacificSpin2015 – October 6 th , 2015.

GPDs & Deeply-Virtual Compton Scattering Generalized Parton Distributions → transverse spatial images of quarks and gluons as a function of their longitudinal momentum fraction. There are 4 chiral-even + 4 chiral-odd GPDs for any quark flavor 𝒚 𝒖 = 𝒒 − 𝒒′ 𝟑 𝒚 𝑪 𝝄 ≈ 𝟑 − 𝒚 𝑪 𝑰 𝒓 𝒚, 𝟏, 𝟏 = 𝒈 𝟐 𝒚 𝒓 𝒚, 𝟏, 𝟏 = 𝒉 𝟐 𝒚 𝑰 𝒓 𝒚, 𝟏, 𝟏 = 𝒊 𝟐 𝒚 𝑰 𝑼 (for 𝒚 > 0; antiquark for 𝒚 <0) PacificSpin2015 – October 6 th , 2015.

Sensitivity to GPDs in observables - Compton Form Factors Only (ξ, 𝑢) are experimentally accessible, not 𝑦 . GPDs will enter in the observables through The two parts will be accessible through observables sensitive to the imaginary (𝐵 𝑀𝑉 , 𝐵 𝑉𝑀 ) or the real part (𝐵 𝑀𝑀 , 𝐵 𝐶𝑓𝑏𝑛𝐷ℎ𝑏𝑠𝑕𝑓 ) of the amplitude. The following Compton Form Factors are introduced (experimentally observable): 1 𝐼 𝑟 𝑦, ξ, 𝑢 − 𝐼 𝑟 (−𝑦, ξ, 𝑢) 1 1 𝑆𝑓𝓘 𝑟 = 𝑓 2𝑟 𝑄 ξ−𝑦 − ξ+𝑦 𝑒𝑦 0 𝐽𝑛𝓘 𝑟 = 𝜌𝑓 2𝑟 𝐼 𝑟 ξ, ξ, 𝑢 − 𝐼 𝑟 (−ξ, ξ, 𝑢) 4 PacificSpin2015 – October 6 th , 2015.

Accessing GPDs through DVCS observables Different observables are sensitive to different combinations of Compton Form Factors and electromagnetic Form Factors: 1. Beam-Spin Asymmetry : + 𝑙𝐺 ∆𝜏 𝑀𝑉 ∝ sin 𝜒 𝐽𝑛 𝐺 1 𝓘 + ξ 𝐺 1 + 𝐺 2 𝓘 2 𝓕 𝑒𝜒 𝜏 = |𝐶𝐼| 2 + 𝐽 𝐶𝐼 ∙ 𝐸𝑊𝐷𝑇 2. Target-Spin Asymmetry : + |𝐸𝑊𝐷𝑇| 2 + ξ 𝐺 ∆𝜏 𝑉𝑀 ∝ sin 𝜒 𝐽𝑛 𝐺 1 𝓘 1 + 𝐺 2 𝓘 + 𝑙𝐺 2 𝓕 𝑒𝜒 Access to LINEAR combinations of GPDs (instead of bilinear) thanks to 3. Double-Spin Asymmetry : the presence of Bethe-Heitler 𝑦 𝐶 + ξ 𝐺 ∆𝜏 𝑀𝑀 ∝ (𝐵 + 𝐶cos 𝜒) 𝑆𝑓 𝐺 1 𝓘 1 + 𝐺 𝓘 + 2 𝓕 𝑒𝜒 2 Asymmetries identified as modulations in 𝜒 , the angle 4. Transverse Target-Spin Asymmetry : between the leptonic and the ∆𝜏 𝑉𝑈 ∝ sin 𝜒 𝐽𝑛 𝑙(𝐺 2 𝓘 − 𝐺 1 𝓕) + … 𝑒𝜒 5 hadronic plane PacificSpin2015 – October 6 th , 2015.

Thomas Jefferson National Accelerator Facility The CEBAF (Continuous Electron Beams Accelerator Facility) operates in the Thomas Jefferson National Accelerator Facility (Newport News, VA, USA). The Cebaf:  provides a continuous electron beam with a duty factor ~ 100%;  with a beam energy up to 6 GeV; 𝜏 𝐹 𝐹 ~10 −5 );  has a good energy resolution (  and the beam has a polarization ~ 85% 6 PacificSpin2015 – October 6 th , 2015.

The three experimental Halls@JLab The CEBAF provides longitudinally-polarized electrons to 3 experimental Halls, characterized Hall-A: High-resolution spectrometers ( 𝜺𝒒 𝒒 ~𝟐𝟏 −𝟓 ), by different and complementary characteristics. measurements with well- defined kinematics at very- high luminosity NIM A 522, 294 (2004) Hall-B: high luminosity, Large acceptance, Multi- particle final state measurements NIM A 503, 513 (2003) Hall C: High momentum spectromer and Short Orbit Spectrometer — well- controlled acceptance for precise cross section measurements PRC 78, 045202 (2008) PacificSpin2015 – October 6 th , 2015. 7

The 12-GeV upgrade High Resolution 4 experimental halls with a longitudinally-polarized electron Spectrometer beam of 𝐹 𝑓 − up to 12 GeV. (HRS) pair and specialized large installation experiments CLAS12: large acceptance, high luminosity Super High Momentum Spectrometer (SHMS) at high luminosity and forward angles SoLID RICH for CLAS12 PacificSpin2015 – October 6 th , 2015. 8

Experiments and phase-space coverage Different experiments (will) explore (-ed) different regions of the phase space … ranging from the gluon-dominated domain of HERA to the quark valence region of JLab Fixed-target experiments in the past: HERMES@Desy: 𝑓 ± beam ( 𝐹 𝑓 = 27𝐻𝑓𝑊 ) o Hall-A, CLAS@JLab: 𝑓 − beam ( 𝐹 𝑓 = 6𝐻𝑓𝑊 ) o Future experiments: Hall-A, CLAS12@JLab12: 𝑓 − beam ( 𝐹 𝑓 = o 12𝐻𝑓𝑊 ) COMPASSII@CERN: 𝜈 ± beam ( 𝐹 𝑓 = 160𝐻𝑓𝑊 ) o PacificSpin2015 – October 6 th , 2015.

DVCS on the proton in Hall-A (E00-110) Significan contribution from 𝓤 𝐸𝑊𝐷𝑇 2 ( 𝜒 - o independent) and 𝓤 𝑗𝑜𝑢 o Clear deviation from BH-only behaviour around 𝜒 = 180° o Helicity-dependent cross-section twist-2 dominated no 𝑅 2 dependence visible in the CFFs (evolution o effects negligible for the present 𝑅 2 lever arm) 𝑦 𝐶 = 0.37, 𝑅 2 = 2.36 𝐻𝑓𝑊 2 , −𝑢 = 0.32 𝐻𝑓𝑊 2 M. Defurne et. al., hep-ex :1504.05453 PacificSpin2015 – October 6 th , 2015.

DVCS on the proton in Hall-A (E00-110) o Both Double-Distribution based models (VGG&KMS12) overestimate the helicity- dependence cross-section o KMS12 tuned on vector-meson data at low-to- very-low 𝑦 𝐶 o KM10a shows good agreement → model parameters already constrained from CLAS (Hall-B) asymmetry data on the same kinematical region. o KM10a underestimates DVCS contribution around 𝜒 = 180° o Lack of strength around 𝜒 = 180° partly compensates by Target-Mass Corrections (TMS) o Need a refit of KMS12 including valence data M. Defurne et. al., hep-ex :1504.05453 PacificSpin2015 – October 6 th , 2015.

Hall-A@11 GeV: E12-06-114 + 𝑙𝐺 2 𝓕 𝑒𝜒 ∆𝜏 𝑀𝑉 ∝ sin 𝜒 𝐽𝑛 𝐺 1 𝓘 + ξ 𝐺 1 + 𝐺 2 𝓘 Beam-polarized and unpolarized cross sections with high precision at three electron-beam energies to get:  increased kinematic coverage Test of scaling → 𝑅 2  dependence of 𝑒𝜏 at fixed 𝑦 𝐶 Large 𝑹 𝟑 region explored with high statistics 12 PacificSpin2015 – October 6 th , 2015.

Hall-B: DVCS cross-section on the proton in Hall-B (E01-113) Extraction in a LARGE kinematic domain 𝑒 4 𝜏 𝑓𝑞→𝑓 ′ 𝑞′𝛿 𝑒𝑅 2 𝑒𝑦 𝐶 𝑒𝑢𝑒𝜒 ----- KMS H. S. Jo et. al., hep-ex :1504.02009, accepted by PRL PacificSpin2015 – October 6 th , 2015. 13

Hall-B: DVCS cross-section on the proton in Hall-B (E01-113) o VGG model 𝐵𝑓 𝑐𝑢 o 𝐵, 𝑐 increases with 𝑦 𝐶 → the partonic content of the nucleon increases when probing smaller 𝑦 𝐶 H. S. Jo et. al., hep-ex :1504.02009, accepted by PRL PacificSpin2015 – October 6 th , 2015.

Mapping GPDs: Beam-spin asymmetries - ℋ 𝑱𝒏 First CLAS DVCS devoted experiment on unpolarized 𝐼 2 𝐭𝐣𝐨 𝝌 𝑩 𝑴𝑽 F. X. Girod et al., Phys. Rev. Lett. 100, 162002 (2008). PacificSpin2015 – October 6 th , 2015. 15

𝑱𝒏 Comparing charge distributions: 𝑩 𝑴𝑽 ∝ ℋ 𝑱𝒏 , 𝑩 𝑽𝑴 ∝ ℋ 𝑩 𝑴𝑽 𝟏. 𝟓 𝟏. 𝟑 𝟏. 𝟑 𝟏. 𝟓 𝑩 𝑽𝑴 𝟏. 𝟓 𝟏. 𝟑 𝟏. 𝟑 𝑱𝒏 ℋ , 𝑱𝒏 ℋ 𝟏. 𝟓 𝑰 𝒓 𝒚, 𝟏, 𝟏 = 𝒈 𝟐 𝒚 𝒓 𝒚, 𝟏, 𝟏 = 𝒉 𝟐 𝒚 𝑰 𝟐. 𝟏 (for 𝒚 > 0; antiquark 𝑩 𝑴𝑴 High statistics extraction of Single for 𝒚 <0) and Double-Spin Asymmetries 𝟏. 𝟔 → axial charge is more concentrated in the nucleon centre than the electric charge → simultaneous CFF extraction 𝟏. 𝟏 from three observables in a E. Seder et al, Phys. Rev. Lett. 114, 032001 (2015) common kinematics S.P. et al, Phys. Rev. D 91, 052014 (2015) 16 PacificSpin2015 – October 6 th , 2015.

JLab 12 GeV data: impact on ℋ M. Guidal, H. Moutarde, M. Vanderhaeghen: hep-ph > arXiv:1303.6600 PacificSpin2015 – October 6 th , 2015. 17

JLab 12 GeV data: impact on ℋ M. Guidal, H. Moutarde, M. Vanderhaeghen: hep-ph > arXiv:1303.6600 PacificSpin2015 – October 6 th , 2015. 18

Quark orbital angular momentum 𝐾 𝑟 = 𝑀 𝑟 + 𝑇 𝑟 𝑇 𝑟 → accessible through Inclusive Deep-Inelastic Scattering Quark Orbital Angular Momentum can be extracted To access 𝐹 𝑣 &𝐹 𝑒 both 𝐹 𝑞 &𝐹 𝑜 are needed so to perform a flavor separation 𝑇 𝑟 𝑀 𝑟 𝑰, 𝑭 𝒗 𝝄, 𝝄, 𝒖 = 𝟘 𝟐𝟔 𝟓 𝑰, 𝑭 𝒒 𝝄, 𝝄, 𝒖 − 𝑰, 𝑭 𝒐 𝝄, 𝝄, 𝒖 𝐾 𝑕 𝑰, 𝑭 𝒆 (𝝄, 𝝄, 𝒖) = 𝟘 𝟐𝟔 𝟓 𝑰, 𝑭 𝒐 𝝄, 𝝄, 𝒖 − 𝑰, 𝑭 𝒒 𝝄, 𝝄, 𝒖 Neutron GPD 𝑭 𝒐 : 𝐵 𝑀𝑉 on the neutron Proton GPD 𝑭 𝒒 : cos 𝜒 modulation in 𝜏 𝑉𝑈 on proton PacificSpin2015 – October 6 th , 2015. 19