Hadronization and Quark Propagation in Nuclear Medium Jian-ping Chen, Jefferson Lab INT09 on JLab 12 GeV, Oct.26-30, 2009  Introduction  Hadronization and Nuclear medium effects  Current status of nuclear SIDIS to study hadronization  JLab 12 GeV program on hadronization  CLAS12 (large acceptance) (Will Brook’s talk)  SHMS+HMS (high luminosity/small acceptance) What can high luminosity/small acceptance measurements contribute?  Opportunity with SoLID (high luminosity/large acceptance)  Summary Acknowledgement: Thanks to A. Accardi, K. Wang and B. Norum for providing plots and nice pictures. Also “borrowed” from colleague’s talks.

Introduction Nuclear Medium as a Laboratory to Study QCD

Strong Interaction and QCD Strong interaction, running coupling ~1 -- QCD: accepted theory for strong interaction -- asymptotic freedom (2004 Nobel) perturbation calculation works at high energy -- interaction significant at intermediate energy quark-gluon correlations -- interaction strong at low energy confinement -- gluons self interacting A major challenge in fundamental physics: -- Understand QCD in all regions, including strong (confinement) region Fundamental degrees of freedom: quarks, gluons Natural effective degrees of freedom: hadrons -- transition and relation between two pictures E ss

Confinement and Nucleon Colors are confined in hadronic system Can not directly detect quarks/gluons (colored objects) Only hadron (color singlet) properties are observables Observables are gauge invariant Both nucleon and nucleus are good laboratories to study QCD Nucleon: simpler, often can use fundamental DOF to describe processes pQCD, description of hadronic properties in terms of quarks/gluons It is only an approximation at any finite Q2 power (twist) corrections and order (as) corrections Multi-parton correlations Partons in-separable from gluon field due to gauge invariance Beyond co-linear factorization Multi-dimensional structure and distributions Transverse dimension is crucial for complete understanding QCD

Confinement and Hadronization Confinement from a simple experimentalist point of view: DIS directly probe partons, which always hadronize on the way out  can not directly detect partons Hadronization is one of the fundamental processes in QCD Colored objects always interact with gluon field/sea to become color neutral before being detected Nuclear medium provides a natural laboratory to study hadronization Understanding cold matter quark propagation important for hot matter study

QCD and Nuclei Most of the strong interaction confined in nucleon, only residual strong interaction remains among nucleons in a nucleus (exponential tail?) Effective N-N interaction with meson exchange Study QCD with nuclei Short range not well understood: Short range correlations Nuclei at extreme conditions: QGP, CGC (gluon saturation) Nuclear medium effects EMC effect Coulomb Sum Rule quenching(?) Form Factor Modification(?) in 4 He Color Transparency Quark propagation in cold and hot nuclear matter

Short-Range Correlation Pair Factions R. Subedi et al., Science 320 (2008) 1476). 7

Short Range Correlations and Cold Dense Matter Mean field MF+2-N SRC MF+multinucleon SRC SRC accessible at 12 GeV reach baryon densities comparable to neutron stars CDR

Nuclear Medium Effects (I) EMC effect, shielding and anti-shielding J. Ashman et al., Z. Phys. C57, 211 (1993) J. Gomez et al., Phys. Rev. D49, 4348 (1994)

Polarized EMC effect (Ian Cloet, Wolfgang Bentz, Tony Thomas)

EMC Effect in PVDIS: CSV in Heavy Nuclei Can be measured with SoLID (Cloet, Bentz, and Thomas) 5%

Nuclear Medium Effects (II) Coulome Sum Rule Probing a nucleon inside a nucleus Possible modification of the nucleons’ property inside nuclei

E Precision Measurement of Coulomb Sum at q=0.5-1 GeV/c Spokespersons: J. P. Chen, S. Choi and Z. E. Meziani PhD students: Y. Oh, H. Yao, X. Yan, New NaI detector for background control Data taking last year Analysis well underwa y Expect preliminary results in a few months

Nuclear Medium Effects (III) G E /G M with polarization transfer in 4 He

Nuclear Medium Effects (IV) Color Transparency 12 C(e,e’p)

Nuclear Medium Effects (V) Quark propagation in cold and hot matter SIDIS A-A Collision E h = z  ~ GeV E h = p T ~ 2 – 20 GeV (HERMES/JLab) (RHIC)

Nuclei as Laboratories to Study Hadronization What have we learned?

Nuclei: Laboratories to study Hadornization Use different size of nuclei to filter hadronization

SIDIS to study hadronization Quark propagation

Mechanism for Quark Propagation Non-perturbative in nature Models: Accardi et al., Wang et al., Kopeliovich, et al.

Attenuation in SIDIS HERMES results help to sort out models and to understand mechanisms Energy loss (gluon bremsstrahlung) Hadronization outside Pre-hadron absorption Color neutralization inside)

 -Scaling Pre-hadron absorption  > 0 Energy loss < 0

P T - broadening P T -broadening help to study production time, multiple scattering and beyond. A, z,, Q 2 dependence

PT-Broadening

Summary of Current Status HERMES results have made an impact in the study of a hadronization Clear attenuation in nuclear medium Scaling (prefer absorption mechanism?) P T -broadening: study production/formation length, multiple scattering, … Preliminary JLab CLAS 6 data: multi-variable binning What’s next?

Planned 12 GeV Measurements CLAS12 (Hall B) and SHMS+HMS (Hall C)

12 GeV Upgrade Kinematical Reach Reach a broad DIS region Precision SIDIS for hadronization study Many other opportunities (Valence quark, TMDs, GPDs)

Planned 12 GeV Measurements CLAS12 measurements (Will Brooks’ talk) Large acceptance, extensive coverage HMS/SHMS measurements High luminosity, small acceptance E , conditional approval At selected kinematics, precision study What should be the choice of kinematics?

E Overview: SIDIS, A(e,e’  /K +- )X Targets: 1 H, 2 H, 12 C, 64 Cu and 184 W Q 2 : 2.5 – 6 GeV 2, focus on high Q 2 = 6 GeV P T up to 0.8 GeV/c z ~ , focus on large z Good PID for pions and Kaons Study Q 2 dependence P T /z dependence at high Q 2 A dependence Spokespersons: J. P. Chen, H. Lu, B. Norum, K. Wang

E Accessible phase space with HMS/SHMS

P T -broadening P T broadening provides (almost direct) information on formation length (Kopeliovich model) sensitive to z (at large z) and A

E Projection Projected R M vs. z for  + and proton on 3 targets 12 C, 64 Cu, 184 W

E Projection Projected R M vs. P T for 3 bins of z Z=0.65, 0.75, 0.85

Discussion HMS/SHMS (High luminosity, small acceptance) measurements complementary to large acceptance CLAS12 measurements What should be the choice of kinematics? need inputs

A new possibility Solenoid Detector for SIDIS in Hall A

Solenoid detector for SIDIS at 11 GeV Proposed for PVDIS at 11 GeV FGEMx4 LGEMx4 LS Gas Cherenkov HG Aerogel GEMx2 SH PS Z[cm] Y[cm] Yoke Coil 3 He Target

Power of SOLid for Sivers

Discussion Large acceptance (~700 msr) and high luminosity (10 37 ) provide the unprecedented precision to map multi-variable dependence of nuclear SIDIS for hadronization study R M and  +,  - and K +, K - and other particles Measure A, Q 2,, P T and z dependence Extract production length and formation length Understand mechanisms: energy loss, absorption, … Study current fragmentation and target fragmentation Isolate different effects, differentiate models Gain solid understanding of quark propagation in cold matter, forming a baseline for hot matter study Shed light on fundamental processes of QCD: effects due to gluon field, sea (QCD vacuum) and confinement.

Summary Hadronization is a fundamental process of QCD  Non-perturbative effect  Related to QCD gluon field/sea/vacuum and confinement  Nuclear medium is an idea lab to study hadronization Current status  Our understanding is still primitive, a lot to be learned  Many models, different mechanisms  HERMES results provide valuable information and constraints to models  CLAS 6 GeV started to provide precision measurements with multi-variables JLab 12 GeV  SHMS/HMS, small acceptance with high luminosity complementary to CLAS12 large acceptance measurements Needs input to optimize choice of kinematics  An opportunity for high-precision multi-variable measurements with SOLID (large acceptance and high luminosity) Help understanding fundamental QCD processes  Lead to breakthrough ?