Hadronization and Quark Propagation in Nuclear Medium
Jian-ping Chen, Jefferson LabINT09 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.
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
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 distributionsTransverse 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 4He• Color Transparency • Quark propagation in cold and hot nuclear matter
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)
Nuclear Medium Effects (II) Coulome Sum Rule
Probing a nucleon inside a nucleus
Possible modification of thenucleons’ property inside nuclei
E01-015
Precision Measurement of Coulomb Sum at q=0.5-1 GeV/c
Spokespersons: J. P. Chen, S. Choi and Z. E. MezianiPhD students: Y. Oh, H. Yao, X. Yan,
• New NaI detector for
background control
• Data taking last year
• Analysis well underway
• Expect preliminary results in a few
months
Nuclear Medium Effects (V)
• Quark propagation in cold and hot matter
SIDIS A-A Collision
Eh = z~ 2 - 20 GeV Eh = pT ~ 2 – 20 GeV(HERMES/JLab) (RHIC)
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)
PT - broadening
PT-broadening help to study production time, multiple scattering and beyond.
A, z, , Q2 dependence
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?)
• PT-broadening: study production/formation length, multiple scattering, …
• Preliminary JLab CLAS 6 data: multi-variable binning
• What’s next?
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• E12-07-101, conditional approval• At selected kinematics, precision study
• What should be the choice of kinematics?
E12-07-101
• Overview: • SIDIS, A(e,e’/K+-)X• Targets: 1H, 2H, 12C, 64Cu and 184W• Q2: 2.5 – 6 GeV2, focus on high Q2
• = 6 GeV
• PT up to 0.8 GeV/c
• z ~ 0.5-0.9, focus on large z• Good PID for pions and Kaons
• Study Q2 dependence
PT/z dependence at high Q2
A dependence
Spokespersons: J. P. Chen, H. Lu, B. Norum, K. Wang
PT-broadening
• PT broadening provides (almost direct) information on formation length (Kopeliovich model)
sensitive to z (at large z)
and A
Discussion
• HMS/SHMS (High luminosity, small acceptance) measurements complementary to large acceptance CLAS12 measurements
• What should be the choice of kinematics?• need inputs
Solenoid detector for SIDIS at 11 GeVProposed for PVDIS at 11 GeV
FGEMx4
LGEMx4 LSGas Cherenkov
HG
Aerogel
GEMx2
SH
PS
Z[cm]
Y[cm
]
Yoke
Coil
3HeTarget
Discussion• Large acceptance (~700 msr) and high luminosity (1037) provide
the unprecedented precision to map multi-variable dependence of nuclear SIDIS for hadronization study• RM and <PT>
• +, - and K+, K- and other particles
• Measure A, Q2, , PT 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 ?