The GPD program in Halls A & C Carlos Mu˜ noz Camacho Institut de Physique Nucl´ eaire, CNRS/IN2P3 (France) June 21, 2018 Joint Hall A and C Summer Meeting C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 1 / 35
Introduction Outline 1 Introduction 2 Nucleon 3D-imaging & Generalized Parton Distributions (GPDs) 3 Deeply Virtual Compton Scattering (DVCS): ep → epγ 4 Experimental program at Jefferson Lab Recent results on DVCS and π 0 production Experiments at 12 GeV 5 Summary C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 2 / 35
Introduction Studying the structure of the nucleon experimentally Elastic scattering Deeply Inelastic Scattering Hard exclusive processes y y δ ~ 1 z Q y ⊥ ~ 1 δ z Q ⊥ xp xp r ⊥ r ⊥ z x z x z x p p p ρ ( ⊥ r ) f x ( ) ( , ) f x r ⊥ 0 r 0 0 r ⊥ r ⊥ ⊥ x x 1 1 Form factors Parton distributions Generalized Parton Nobel prize, 1969 Nobel prize, 1961 Nobel prize, 1990 Distributions (GPDs) C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 3 / 35
GPDs & DVCS Deeply Virtual Compton Scattering (DVCS): γ ∗ p → γ p High Q 2 Perturbative QCD Non-perturbative GPDs Handbag diagram Bjorken limit : � Q 2 = − q 2 → Q 2 ∞ x B = 2 Mν fixed ν → ∞ C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 4 / 35
GPDs & DVCS DVCS experimentally: interference with Bethe-Heitler At leading order in 1 /Q (leading twist) : d 5 → σ − d 5 ← ℑ m ( T BH · T DV CS ) σ = d 5 → σ + d 5 ← | BH | 2 + ℜ e ( T BH · T DV CS ) + | DV CS | 2 σ = � +1 dx H ( x, ξ, t ) T DV CS = x − ξ + iǫ + · · · = − 1 � +1 dxH ( x, ξ, t ) P − iπ H ( x = ξ, ξ, t ) + . . . x − ξ − 1 � �� � � �� � Access in helicity-independent cross section Access in helicity-dependent cross-section C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 5 / 35
GPDs & DVCS Leading twist GPDs 8 GPDs related to the different combination of quark/nucleon helicities 4 chiral-even GPDs: conserve the helicity of the quark Access through DVCS (and DVMP) C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 6 / 35
GPDs & DVCS Leading twist GPDs 8 GPDs related to the different combination of quark/nucleon helicities 4 chiral-odd GPDs: flip helicity of the quark “transversity GPDs” Experimental access more complicated ( π 0 electroproduction?) C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 7 / 35
GPDs & DVCS Kinematic coverage Kinematic complementarity between different facilities: C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 8 / 35
DVCS @ JLab The GPD experimental program at Jefferson Lab Hall A: high accuracy, limited kinematic coverage Hall B: wide kinematic range, limited precision Hall C: high precision program at 11 GeV Partially overlapping, partially complementary programs with different experimental setups The roadmap: Early results (2001) from non-dedicated experiment (CLAS) 1 st round of dedicated experiments in Halls A/B in 2004/5 2 nd round on 2008–2010: precision tests + more spin observables Compeling DVCS experiments in Halls A+B+C at 11 GeV ( � 2017) C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 9 / 35
DVCS @ JLab Recent results Experimental setup High Resolution Spectrometer 100-channel scintillator array 132-block PbF 2 electromagnetic calorimeter C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 10 / 35
DVCS @ JLab Recent results DVCS cross sections: azimuthal analysis Q 2 = 2 . 36 GeV 2 , x B = 0 . 37 , − t = 0 . 32 GeV 2 d 4 σ = T 2 BH + T BH R e ( T DVCS ) + T 2 DVCS R e ( T DVCS ) ∼ c I 0 + c I 1 cos φ + c I 2 cos 2 φ DVCS ∼ c DVCS + c DVCS T 2 cos φ 0 1 ∆ 4 σ = d 4 − → σ − d 4 ← − σ = I m ( T DVCS ) 2 I m ( T DVCS ) ∼ s I 1 sin φ + s I 2 sin 2 φ M. Defurne et al. Phys. Rev. C 92, 055202 (2015) C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 11 / 35
DVCS @ JLab Recent results DVCS cross sections: Q 2 –dependance No Q 2 -dependance within limited range ⇒ leading twist dominance C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 12 / 35
DVCS @ JLab Recent results DVCS cross sections: kinematical power corrections KM10a: global fit to HERA x-sec & HERMES + CLAS spin asymmetries Kumericki and Mueller (2010) C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 13 / 35
DVCS @ JLab Recent results DVCS cross sections: kinematical power corrections KM10a: global fit to HERA x-sec & HERMES + CLAS spin asymmetries Kumericki and Mueller (2010) Target-mass corrections (TMC): ∼ O ( M 2 /Q 2 ) and ∼ O ( t/Q 2 ) Braun, Manashov, Mueller and Pirnay (2014) C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 13 / 35
DVCS @ JLab E07-007 Rosenbluth-like separation of the DVCS cross section | BH | 2 | DV CS | 2 σ ( ep → epγ ) = + I ( BH · DV CS ) + � �� � � �� � � �� � Known to ∼ 1 % Linear combination of GPDs Bilinear combination of GPDs I∝ 1 /y 3 = ( k/ν ) 3 , � T DV CS � � � 2 ∝ 1 /y 2 = ( k/ν ) 2 BKM-2010 – at leading twist → 7 independent GPD terms: � � C I , C I ,V , C I ,A � � C DV CS ( F , F∗ ) . ℜ e , ℑ m ( F ) , and ϕ -dependence provides 5 independent observables: ∼ 1, ∼ cos ϕ, ∼ sin ϕ , ∼ cos(2 ϕ ) , ∼ sin(2 ϕ ) The measurement of the cross section at two or more beam energies for exactly the same Q 2 , x B , t kinematics, provides the additional information in order to extract all leading twist observables independently. C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 14 / 35
DVCS @ JLab E07-007 E07-007: DVCS beam-energy dependence Cross section measured at 2 beam energies and constant Q 2 , x B , t E = 4 . 5 GeV E = 5 . 6 GeV Leading-twist and LO simultaneous fit of both beam energies (dashed line) does not reproduce the data Light-cone axis in the ( q , q ′ ) plane (Braun et al.) : H ++ , � H ++ , E ++ , � E ++ C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 15 / 35
DVCS @ JLab E07-007 Beyond Leading Order (LO) and Leading Twist (LT) Two fit-scenarios: Light-cone axis in the ( q , q ′ ) plane (Braun et al.) LO/LT + HT H ++ , � H ++ , H 0+ , � H 0+ LO/LT + NLO H ++ , � H ++ , H − + , � H − + C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 16 / 35
DVCS @ JLab E07-007 E07-007: DVCS beam-energy dependence Cross section measured at 2 beam energies and constant Q 2 , x B , t 4 4 nb/GeV nb/GeV 4 σ Fit LT/LO d 0.2 ∆ σ Fit HT 4 0.1 KM15 0.1 0.05 0 0 0 100 200 300 0 100 200 300 Φ Φ (deg) (deg) Leading-twist and LO simultaneous fit of both beam energies (dashed line) does not reproduce the data Including either NLO or higher-twist effects (dark solid line) satisfactorily reproduce the angular dependence C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 17 / 35
DVCS @ JLab E07-007 DVCS 2 and I (DVCS · BH) separation DVCS 2 and I (DVCS · BH) separated in NLO and higher-twist scenarios 4 4 nb/GeV nb/GeV 0.04 0.01 0.03 DVCS 2 & I significantly 0.02 0.005 different in each scenario 0.01 0 0 Sizeable DVCS 2 contribution in the − 0.01 higher-twist scenario in − 0.005 − 0.02 the helicity-dependent 2 DVCS ++/-+ Interference ++/-+ cross section − 0.03 2 − DVCS ++/0+ 0.01 Interference ++/0+ − 0.04 0 100 200 300 0 100 200 300 Nature Commun. 8, 1408 (2017) Φ Φ (deg) (deg) C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 18 / 35
π 0 electroproduction DVCS @ JLab π 0 electroproduction ( ep → epπ 0 ) At leading twist: � dσ L dt = 1 N , h N ) | 2 ∝ 1 σ T ∝ 1 |M L ( λ M = 0 , h ′ 2Γ Q 6 Q 8 h N ,h N ′ � � 1 � � 1 � � � � dz φ π ( z ) 1 1 M L ∝ Γ 1 � H π 0 + Γ 2 � dx x − ξ + × E π 0 z x + ξ − 1 0 Different quark weights: flavor separation of GPDs � 2 � 1 H u + 1 u � − | d ¯ � � H d � | π 0 � = 1 2 {| u ¯ d �} H π 0 = √ √ 3 3 2 H DV CS = 4 9 H u + 1 9 H d | p � = | uud � C. Mu˜ noz Camacho (IPNO, CNRS/IN2P3) 3D structure of hadrons @ JLab & EIC 06/21/2018 19 / 35
Recommend
More recommend
