THE NUCLEUS AS A QCD LABORATORY: HADRONIZATION, 3D TOMOGRAPHY, AND MORE

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1 rhtjhtyhy EINN 2017 NOVEMBER 1, 2017 PAPHOS, CYPRUS THE NUCLEUS AS A QCD LABORATORY: HADRONIZATION, 3D TOMOGRAPHY, AND MORE KAWTAR HAFIDI Argonne National Laboratory is a U.S. Department of Energy laboratory managed by UChicago Argonne, LLC.

2 OUTLINE The nucleus from a QCD perspective Important questions to be addressed by current and future facilities Hadronization: How do quarks hadronize into hadrons? What did we learn from previous measurements? Anticipated measurement at JLab and the future EIC 3D tomography of nuclei First attempt Ambitious program at JLab and great potential for the EIC Summary and outlook

3 STUDYING NUCLEI FROM QCD PERSPECTIVE How do an energetic quark interact with the nuclear medium and subsequently neutralize its color and become confined inside a hadron? How are quarks and gluons distributed in space and momentum inside the nucleus? How are quarks and gluons distributions affected when they are embedded in nuclei compared to free nucleons? How these fundamental degrees of freedom of the strong interaction group themselves together to form nuclei and ultimately matter?

4 THE NUCLEUS AS A QCD LABORATORY electron electron Probe Medium Medium "QCD medium" "QCD vacuum" Probe Ø Studying the structure of the nucleus Ø Using the nucleus as a femtometer itself: EMC, SRC, 3D tomography detector to study hadronization, CT,..

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6 HOW DO ENERGETIC QUARKS BECOME HADRONS? Hadronization is a direct manifestation of confinement

7 SPACE TIME DYNAMICS OF HADRONIZATION Nuclei are used as detectors providing multiple scattering centers separated by only 1 2 fm e γ nucleon g g g Hadron propagation e Quark propagation Hadron q What is the interaction and the lifetime τ p of the struck quark before it neutralizes its color? q How long does it take to form the color field of a hadron τ f and which kind of interaction is in play?

8 COMPLEMENTARY PROCESSES TO STUDY HADRONIZATION SIDIS Quark propagation Hadron formation Final state effects Non perturbative FF DIS Frag. function DY Drell-Yan Quark propagation Initial state effects Perturbative conversion rate of lepton pair Cold QCD matter Test & calibrate tools used to determine properties of QGP Reduce syst. Effects when attenuation needs to be corrected for in neutrino experiments using nuclear targets RHIC Relativistic Heavy ion collisions Quark propagation in strongly interacting matter (unknown properties) Hadron formation Initial and final state effects

9 SEMI-INCLUSIVE DEEP INELASTIC SCATTERING (SIDIS) IN THE VACUUM e γ nucleon g g Color neutral object e g Parton energy loss via Gluon radiation in the vacuum Hadron Flavor tagging technique used to study Flavor decomposition of longitudinal unpolarized and polarized distributions Transverse momentum dependent distribution (TMDs) Parton fragmentation in the vacuum

10 SIDIS IN THE MEDIUM e e e nucleon g e g Hadron Hadron forms inside the medium Accessible at low energies Hadron forms outside the medium dominant at high energies q q q q Parton energy loss in the medium: Medium induced gluon emission Modification of the fragmentation functions in the medium Hadron/pre-hadron formation and interaction with the medium Low/Medium energy DIS offers a unique kinematic window with hadronization time scales comparable to the nuclei sizes

11 SIDIS OBSERVABLES Leptonic variables: ν (or x), Q 2 Hadronic variables: z and p T Different nuclei: size and density Different hadrons: quark s flavor Transverse momentum broadening Δ P T 2 = P T 2 A P T 2 D n Q 2 E h Multiplicity ratio z = k.p q.p = E h / ν z, p T (P T ) 2

12 GENERAL FEATURES OF MULTIPLICITY RATIOS HERMES NPB 780 (2007) ν (GeV) z Q 2 (GeV 2 ) Competing PLC and hard kick to parton? Mass effect Partonic: energy loss and modified Lorentz boost effect fragmentation functions Hadronic: Hadron formation length and absorption

13 FLAVOR DEPENDENCE OF MULTIPLICITY RATIOS (1) HERMES: All three pions and K - undergo similar attenuation

14 FLAVOR DEPENDENCE OF MULTIPLICITY RATIOS (2) HERMES: K + is less attenuated most likely due to contamination from π + p -> Λ + K (B. Kopeliovich et al.)

15 TRANSVERSE MOMENTUM BROADENING (TMB) HERMES l No broadening at high z Effect at the partonic level HERMES Saturation for large Nuclei? CLAS Smaller TMB for CLAS? Hadronization inside at CLAS energies? π + l l Dependence in A not conclusive Compatible with A 1/3 and A 2/3 Flavor dependence?

16 CLAS12 has 10 times more luminosity than CLAS and 1000 times more than HERMES - multidimensional measurements ü Improved particle identification ü Access to higher masses ü Much larger kinematical range ü Test models (parton energy loss vs. hadron attenuation vs. both) by providing multidimensional measurements

17 HADRONIZATION STUDIES AT THE FUTURE EIC Unprecedented range in photon energies Q 2 dependence/evolution of in medium hadronization Flavor scaling of in medium energy loss Mass dependence of Hadronization - Light vs. heavy quarks

18 Q 2 EVOLUTION q q Q 2 dependence allows to measure any modification of the DGLAP evolution in medium It is a very important tool to constrain energy loss calculations

19 FLAVOR SCALING OF P T BROADENING 20 GeV < ν < 30 GeV Pions Domdey et al Eta Accardi et al Simple PQCD scaling The Q 2 dependence of p T broadening can be used to check the simple pqcd scaling of in-medium energy loss as a function of quark flavors

20 Predictions depend on formation inside or outside the nucleus? Attenuation or enhancements? Mass dependence of hadronization? Integrated luminosity of 200 fb -1 per target

21 MULTIPLICITY RATIOS - MASS DEPENDENCE At RHIC, light and heavy quarks are equally suppressed? Hadronization outside D 0 Mass dependence of fragmentation function π D 0 π Semi-inclusive DIS Hadronization inside Red squares: combination of energy loss and hadron attenuation Solid lines: pure energy loss

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23 GENERALIZED PARTON DISTRIBUTIONS FOR HELIUM-4 Inner Calorimeter Radial Time Projection Chamber Measure Beam Spin Asymmetry for coherent 4 He(e,e g 4 He) and incoherent 4 He (e,e gp) channels

24 BEAM SPIN ASYMMETRIES A LU (φ) = dσ(φ) dσ(φ) dσ(φ) + dσ(φ) Leading order in a s and neglecting DVCS and interference part in denominator A LU (φ) Im{C I } sinφ C I = F 1 H + C I = H F ~ x B (F 1 + F 2 )H 2 x B 4 He nucleus Δ2 4 M F 2ε 2 nucleon 4 He spin 0 therefore has 1 chirally even GPD

25 CLAS 6 GEV MEASUREMENTS M. Hattawy et al. PRL 2017 First measurements of its kind Large asymmetries Limited statistics and kinematical coverage

26 MODEL INDEPENDENT EXTRACTION OF THE COMPTON FORM FACTORS A LU (φ) = I = Im{H 4 He } R = Re{H 4 He } α 0 (φ) I α 1 (φ) + α 2 (φ) R + α 3 (φ)( R 2 + I 2 ) First ever experimental extraction of the real and imaginary part of 4 He CFF ) A Im(H ) A Re(H Q [GeV ] x B Convolution Dual: V. Guzey, PRC 78, (2008) Convolution-VGG: M. Guidal, M. V. Polyakov, A. V. Radyushkin and M. Vanderhaeghen, PRD 72, (2005) Off-shell model: J. O. Gonzalez-Hernandez, S. Liuti, G. R. Goldstein and K. Kathuria, PRC 88, (2013) CLAS-EG6 Convolution-Dual Convolution-VGG Off-shell model CLAS-EG6 Convolution-Dual Convolution-VGG t [GeV 2 ]

27 APPROVED JLAB 12 GEV MEASUREMENTS: CLAS12-ALERT RUN GROUP 2 CLAS-EG6: x B = 0.17, Q = 1.5 GeV 2 Deep Virtual Compton Scattering ) (90 4 He A LU < < x B 2 HERMES: x B = 0.07, Q = 1.8 GeV 2 Off-shell: x B = 0.14, Q = 1.2 GeV 2 2 Deep Virtual Phi production < < x B < < x B t [GeV 2 ] Toward a complete tomography of 4 He Unique opportunity to compare gluon radius to charge radius in nuclei ρ[fm -2 ] Gluon density relative profiles < x v >=0.165 < x v >=0.215 < x v >=0.265 Provide a glimpse into gluon physics before the EIC xv b

28 SUMMARY AND OUTLOOK Hadronization Provides complementary way of studying confinement It allows testing and calibrating theoretical tools used to determine the properties of strongly coupled Quark-Gluon Plasma Good progress has been made by both HERMES and CLAS collaborations CLAS12 will provide the multi-dimensional data needed to constrain the existing models JLab 12 GeV will enable the next generation of experiments to study the 3D structure of light nuclei and other important nuclear effects via tagging of the recoil nucleus (A, A-1) EIC will allow the study of hadronization dynamics of heavy quarks in cold nuclear matter and obtain for the first time its dependence on the mass of the quarks (π, K, and D mesons) EIC will be the ultimate machine to access the 3D sea quark and gluon structure of fast moving nuclei with unprecedented precision

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