Transcript The Physics of Nuclei • History • Motivation • PN12 workshop and white paper framework • Major experimental thrusts for 12 GeV – Properties of.

The Physics of Nuclei
• History
• Motivation
• PN12 workshop and white paper framework
• Major experimental thrusts for 12 GeV
– Properties of quark systems in-medium (e.g., ‘EMC effect’)
– Quark propagation through nuclei
– Color transparency
– Universal scaling behavior
• Other important impacts of 12 GeV
Physics of Nuclei
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History – PAC 23 Report
Physics of Nuclei
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Why Study Nuclei at 12 GeV?
•
To understand QCD
– Contact with QCD and/or quarks is very direct and general in some experiments
– Can exploit nuclear symmetries and well-known properties to gain new understanding
– Example: chiral symmetry restoration in RHI – partial restoration in nuclei – manifested by
medium modification of hadron properties – QCD phase transition
•
To access a broader class of science by exploiting interdisciplinary opportunities –
experiments at Fermilab (both proton and n beams), RHIC, LHC, as well as classical
nuclear physics
– Example: constraining models to fit both EMC effect and Drell-Yan results
– Example: SRC – accessible at high momentum transfer, relevant at low energies
– Example: Cold dense matter – neutron stars: nucleons, strange matter, superconducting
quark matter, color condensate, …
Nuclei at high energies are poorly understood strongly interacting systems. Most simple
assumptions, when tested, fail. Opportunity for rapid progress and discoveries.
Physics of Nuclei
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The Workshop on
“The Physics of Nuclei with 12 GeV Electrons”
(“PN12”)
Physics of Nuclei
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PN12 – Goals and Deliverables
• Goals
– To identify new directions for the 12 GeV upgrade
– To refine existing upgrade initiatives
– To welcome new researchers to the JLab community, and identify connections
between the JLab program and initiatives at other laboratories, both at lower
and higher energies
– To define coherent themes of the nuclear physics JLab addresses
• Deliverables
– A white paper
• to define the compelling questions, coherent themes, and discovery potential
experiments related to the workshop
• Outlined at the workshop by session convenors, now filled in at zeroth draft
– A vision for a coherent, world-class program for studies with nuclei, at JLab
and elsewhere, addressing new, fresh, interesting questions
– The beginnings of a new community
Physics of Nuclei
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PN12 Program and Attendance
• Four major sessions:
– Quarks and Gluons in the Nuclear Medium
• Convenors: Stan Brodsky, Valeria Muccifora, Carl Carlson
– The QCD View of the Nucleus
• Convenors: Roy Holt, Pierre Guichon, Jerry Miller
– The Hadronic View of the Nucleus
• Convenors: [Francesco Iachello,] Franz Gross, Ron Ransome
– The Nature of Hadron-Hadron Interactions
• Convenors: Martin Savage, John Arrington, Jean-Marc Laget
• Well-attended
– Over 100 participants from institutions in eight countries
– Lots of interest and excitement
– Talks on web at
http://www.jlab.org/intralab/calendar/archive04/pn12/index.html
or can find link on JLab calendar for November 1, 2004.
Physics of Nuclei
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PN12 - White Paper Outline – Two Over-Arching Themes
“The Emergence of Nuclei from QCD”
and
“Fundamental QCD Processes in the Nuclear Arena”
(Document introduction written by Rolf Ent)
Physics of Nuclei
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The Emergence of Nuclei from QCD
• Fundamental Nature of Hadron-Hadron Interactions (Franz, Martin)
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–
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Origin of the intermediate-range attraction and the short-range repulsion
Quark mass dependence of hadronic properties and interactions
The role of fine-tuning in nuclear structure
Lattice description of deuteron
Form factors of light nuclei
• Short-Range Structure of Nuclei (Jean-Marc, John, Stan)
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–
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Multi-nucleon correlations
Hidden color
The role of glue
Constraining Fock state components
• Medium Modifications (Pierre, Jerry, John)
– Nuclear structure functions (the nucleus as a flavor laboratory)
– Nuclear generalized parton distributions
– Nucleon form factors in nuclei
• Scaling Laws and Conformal Symmetries (Stan, Carl)
Physics of Nuclei
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Fundamental QCD Processes in the Nuclear Arena
• Hadronization in the Nuclear Medium (Valeria, Will)
– Hadron formation times
– Quark energy loss
• Hadron-Hadron Interactions in Nuclei (Carl, Martin, Stan, John)
– Color transparency
– The role of heavy quarks (e.g., intrinsic charm)
– L-N and J/Y-N interaction
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PN12 – Theory Advances
• Chiral perturbation theory for the nucleus
– Talk by Evgeny Epelbaum
• Medium modifications of hadron properties from quark-level models of
nuclei, (e.g. QMC)
– Talks by Tony Thomas, Pierre Guichon, Wolfgang Bentz, Ian Cloet
• Lattice descriptions of hadron-hadron interactions and the deuteron
– Talks by Paulo Bedaque, Martin Savage
– “Nuclear Physics with Lattice QCD” collaboration
• Connections between color transparency and GPD’s
– Talks by Matthias Burkhardt and Swadin Taneja
• Hybrid models for large nuclei with partonic components
– Talks by James Vary and Pierre Guichon
Physics of Nuclei
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Properties of Quark Systems In-Medium
Physics of Nuclei
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The QCD
Lagrangian and
Nuclear Medium
Modifications
Lattice simulation
demonstrates reduction of
chiral condensate of QCD
vacuum in presence of
hadronic matter
Lasscock, Leinweber, Thomas, Williams
Physics of Nuclei
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The QCD Lagrangian and Nuclear Medium Modifications
Density dependence of proton form factor ratio
Polarization transfer ratio on 4He
Anticipated
uncertainties
of new experiment
Physics of Nuclei
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Related PN12 Talks
• Richard Milner, “Unique Phenomena in Nuclear High-Energy Lepton
Scattering”
• Antje Bruell, “Nuclear Effects on Parton Distributions”
• John Arrington, “Superfast Quarks”
• Jerry Miller, “The Light Front for Nuclear Physics”
• Steffen Strauch, “Experimental Signatures for Medium Modifications”
• Ulrich Mosel, “Hadrons in Nuclei – Predictions and Observables”
• Wolfgang Bentz, “Medium Modifications of Nucleon Structure Functions”
• Pierre Guichon, “The Role of Quarks in Nuclear Structure”
• Mark Strikman, “The Structure of Short-Range Correlations and the Origin
of the EMC Effect”
• Tony Thomas, “The QCD Many-Body Problem and 12 GeV Electrons”
Physics of Nuclei
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Properties of quark systems in-medium:
Origin of the EMC effect
• Observation that structure functions are altered in nuclei stunned and
electrified much of the HEP community 30 years ago
• Nearly one thousand papers have been generated, many models can fit the
curve, but data are insufficient to uniquely identify the origin
• What is it that alters the quark momentum in the nucleus?
J. Ashman et al., Z. Phys.
C57, 211 (1993)
J. Gomez et al., Phys.
Rev. D49, 4348 (1994)
Physics of Nuclei
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Unpacking the EMC effect
Propose to add this to the CDR executive summary
• With 12 GeV, we have a variety of tools to unravel the EMC effect:
– Parton model ideas are valid over fairly wide kinematic range (see PN12:
Richard Milner talk)
– High luminosity
– High polarization
• New experiments, including several major programs:
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Precision study of A-dependence; x>1; flavor decomposition uA(xA) and dA(xA)
g1A(x) “Polarized EMC effect” - double the size of the traditional EMC effect!
Flavor-tagged polarized structure functions Du(x) and Dd(x) vs. A
x dependence of axial-vector current in nuclei (can study via parity violation?)
Nucleon-tagged structure functions from 2H and 3He (e.g., BONUS)
Dependence of FL on A (low x and Q2)
Can study x-dependence of exclusive channels on light nuclei, sum up to EMC
Nuclear shell dependence?
Isospin dependence from comparison of 3He/2H with 3H/2H
Physics of Nuclei
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See PN12: Antje Bruell’s talk
Need much higher data precision,
especially at high x & light nuclei
A=4
A=12
A=40
Physics of Nuclei
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EMC Effect in 3He and 4He
Current data do not differentiate between models with either an A-dependence or a
r-dependence.
• Measure the shape in very light nuclei to distinguish
• Test models of the EMC effect in exact few-body calculations
• At 12 GeV, fill in high-x region and extend with high statistics to heavier nuclei to
determine A-dependence – can reach the interesting region 0.6 – 0.8
SLAC fit to heavy nuclei
(scaled to 3He)
Calculations by
Pandharipande and Benhar
for 3He and 4He
Approximate
uncertainties
for 12 GeV
coverage
Physics of Nuclei
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Flavor-tagged EMC effect
• Extend to semi-inclusive measurements for flavor-tagged uA(xA), dA(xA)
• Sea and valence expected to be quite different
• Global fit of electron and
muon DIS experiments and
Drell-Yan data by S. Kumano,
see “Nuclear Modification of
Structure Functions in Lepton
Scattering,” hep-ph/0307105
and NPB Proc. Supp. 112,
2002 42-48.
Physics of Nuclei
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g1(A) – “Polarized EMC Effect”
• New calculations indicate larger effect for polarized structure function than
for unpolarized (see PN12 talks by Ian Cloet, Wolfgang Bentz, Tony
Thomas)
• Spin-dependent parton distribution functions for nuclei nearly unknown
• Can take advantage of modern technology for polarized solid targets to
perform systematic studies – Dynamic Nuclear Polarization
F2 A
F2 p
g1 A
g1 p
Physics of Nuclei
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g1(A) – “Polarized EMC Effect” – Some Solid Target Possibilities
Nuclide
Compound
Polarization (%)
1H
NH3
90
C4H9OH
90
LiH
90
ND3
40
C4D9OH
40
LiD
50
6Li
6LiD
45
7Li
7LiD
90
11B
C2N2BH13
75
13C
13C H OH
4 9
65
14N
14NH
3
18
15N
15NH
3
20
19F
LiF
2H
Physics of Nuclei
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90
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“Polarized EMC Effect” – Flavor Tagging
• Can perform semi-inclusive DIS on sequence of polarized targets,
measuring p+ and p-, decompose to extract DuA(xA), DdA(xA).
• Challenging measurement, but have new tools
– High polarization for a wide variety of targets
– Large acceptance detectors to constrain systematic errors
– Uncertainties comparable to those from CLAS EG1b results
Theory: Cloet, Thomas, Bentz
Physics of Nuclei
(PN12 talk by Ian Cloet)
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Axial Vector Current EMC Effect
• Neutrino scattering probes axial-vector
current
• Models indicate EMC effect is different in
this sector, at high x and at x ~ 0.025
• Could access using parity violating electron
scattering
Physics of Nuclei
S. Kulagin and R. Petti, “Global Study of Nuclear
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Structure Functions,”
hep-ph/0412425.
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Nucleon-Tagged Structure Functions - e.g. F2n(D)(x,pm)
ps
e-
n
e-
Requires detection of a slow recoil
proton at backward angles and
with momenta ~60-150MeV/c
Can be used with, e.g., 3He or 3H
Measure Q2 dependence simultaneously
Physics of Nuclei
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EMC Effect in R=sL/sT
• Measurable effect (5-10%)
predicted in R at low Q2
• Calculation by S. Kumano, see
“Nuclear Modification of
Structure Functions in Lepton
Scattering,” hep-ph/0307105
and NPB Proc. Supp. 112,
2002 42-48.
• Density-dependent HartreeFock calculation in 14N
• Nucleus transverse structure
function impacted by nucleon
motion: admixture of nucleon
transverse and longitudinal
structure functions
Physics of Nuclei
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Nuclear Shell Dependence of
EMC Effect
• Models examined by Kumano and
Close predict dependence on nuclear
shell
• See “Dependence of the European
Muon Collaboration Effect on Nuclear
Structure,” S. Kumano and F. E. Close,
PRC 41, (1990) 1855.
• How to measure? Recoil detector?
Physics of Nuclei
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See PN12: Ron Ransome’s talk
EMC Effect in Tritium Compared to 3Helium
Physics of Nuclei
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Quark Propagation Through Nuclei
Physics of Nuclei
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Quark Propagation Through Nuclei
•
Can study propagation of quarks through nuclei using nuclear semi-inclusive DIS.
Accesses fundamental processes in QCD: gluon emission, hadronization
•
Derive hadron formation lengths via hadron attenuation
– Confinement mechanisms for producing a colorless final state after hadronization
– Fragmentation functions are modified in nuclear medium
– The modified fragmentation functions are needed for isolating EMC effect for flavortagged structure functions (previous topic)
•
Deduce quark energy loss via transverse momentum broadening
– Medium-induced quark energy loss via gluon emission gives a measure of the gluon
density of the medium
– There is an accessible quark-gluon correlation function associated with this process (Guo
and Qiu, PRD61, 096003, 2000)
– This partonic energy loss is a leading explanation for the jet quenching seen at RHIC,
which indicates a hot and dense region is formed, possibly the QGP
Physics of Nuclei
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Related PN12 Talks
• Valeria Muccifora, “Assessing Space-Time Characteristics of
Hadronization from Data”
• Boris Kopeliovich, “Hadronization – Theoretical Perspectives”
• Claudio Ciofi degli Atti, “Time Evolution of Hadronization: SemiExclusive DIS and Grey Tracks Production”
• Boris Kopeliovich, “Propagation of Partons in the Medium”
• Ulrich Mosel, “Hadrons in Nuclei – Predictions and Observables”
• Jen-Chien Peng, “Quark Energy Loss – Experimental”
• Will Brooks, “Hadronization and Nuclear Broadening in CLAS”
• Kebin Wang, “Semi-Inclusive DIS from Nuclei in Hall A”
Physics of Nuclei
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Nuclear Deep Inelastic Scattering and Hadronization
• We can learn about hadronization distance scales and reaction mechanisms
from nuclear DIS
• Nucleus acts as a spatial filter for outgoing hadronization products
Initial focus on properties of leading hadron;
correlations with subleading hadrons and soft
protons are also interesting
Physics of Nuclei
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Observables – Hadronic Multiplicity Ratio
In general,
Physics of Nuclei
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Summary of HERMES data to date:
• Mostly 27 GeV positron beam, some 12 GeV beam
• Targets include D, He, N, Kr, Xe (Xe results not yet released)
• Excellent PID (RICH) except for early nitrogen targets
• identify p+ - o, K+ -, proton and antiproton
• Limited luminosity -> typically 1D binning, lower Q2
Physics of Nuclei
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12 GeV Anticipated Data
Physics of Nuclei
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Bins
in yellow
are accessible
atWill6Brooks
GeV
Accessible Hadrons (12 GeV)
Physics of Nuclei
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Hayk Hakobyan, Yerevan State U.
CLAS EG2, very preliminary, 5% of total data set
DIS kinematics, Q2>1, all n
Carbon
Iron
Lead
No acceptance correction (small, two targets in the beam)
Not final calibrations (should be nearly irrelevant, bins are huge)
No fiducial cuts (probably ok, two targets in beam)
No radiative correction (effect primarily cancels in ratios)
No correction for pi+ from rho (need full statistics to correct for this)***
Few-percent kaon contamination in region 2-2.7 GeV
No isospin correction for heavy targets(~5%?)
No xF cuts
Physics of Nuclei
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Quark-Gluon
Dynamics
Transverse momentum
broadening from Fermilab
Drell-Yan experiments
L
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Struck quark emits gluons in vacuum because of confinement
In nuclear medium, multiple scattering will stimulate additional gluon radiation,
predicted to vary as L2
Gluon radiation creates dE/dx that can be connected to transverse momentum
broadening (an experimental observable):
Physics of Nuclei
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CLAS EG2 Preliminary
5% of data
No acceptance correction (small, two targets in the beam)
Not final calibrations (should be nearly irrelevant, bins are huge)
No fiducial cuts (probably ok, two targets in beam)
No radiative correction (effect primarily cancels in ratios)
No correction for pi+ from rho (need full statistics to correct for this)***
Few-percent kaon contamination in region 2-2.7 GeV
No isospin correction for heavy targets(~5%?)
No xF cuts
Physics of Nuclei
Catherine Silvestre (Nantes)
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12 GeV Anticipated Data
Physics of Nuclei
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Color Transparency
Physics of Nuclei
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Color Transparency
• A hadron is superposition of quark-gluon configurations of different space
size
• Small spatial size configurations interact with small cross-section with
target (QED : e+e- pair of a small size has a small cross-section determined
by its dipole moment)
• Particular hard processes can isolate minimal Fock state in the hadron wave
function such that the distance between the quarks is of the order of 1/Q
• Strategies for JLab experiments:
– Measure a reduced attenuation of particles as they exit the nucleus
– Measure a decrease in production of particles produced via two-step
rescattering mechanisms (few-body nuclei)
Physics of Nuclei
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Related PN12 Talks
• Matthias Burkardt, “Color Transparent Generalized Parton Distributions”
• Jerry Miller, “The QCD View of the Nucleus” (session summary)
• Kawtar Hafidi, “Color Transparency”
Physics of Nuclei
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Why are we still looking for the onset of color transparency?
• Color transparency was directly observed with dijets from 500 GeV/c pions
(E. M. Aitala, hep-ex/0010044). Equivalent Q2 is 10 GeV2, accessible to
the 12 GeV upgrade, so we should be able to see it.
• A null result at Jlab energies may cast doubt on factorization theorems
connected to DVMP
– “Factorization for hard exclusive electroproduction of mesons in QCD,” J.
Collins, L. Frankfurt, M. Strikman, PRD56(1997)2982 and hep-ph/9611433
• It is natural for such a process to occur in a quark-gluon picture, but would
be quite unexpected in a hadronic picture, thus it is one indication of a
transition from hadron to quark degrees of freedom.
• Recent theoretical work has identified connections between GPD’s and
color transparency
More details in PN12: Kawtar Hafidi’s talk
Physics of Nuclei
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Color Transparency: Theoretical Connections to GPD’s
• M. Burkardt and G. Miller (hep-ph/0312190, and PN12: Matthias
Burkardt’s talk) focus on pion CT:
– Derive the effective size of a hadron in terms of GPD’s:
– The existence of color transparency would place constraints on the analytic
behavior of H(x,0,Q2), and would provide testable predictions for GPD’s
• S. Liuti and S. K. Taneja (hep-ph/0405014, and PN12: Swadin Taneja’s
talk)
– Explored structure of GPD in impact parameter space to determine
characteristics of small transverse-separation components
– Nuclei as filters to map the transverse components of hadron wave function: a
new source of information on GPD’s
Physics of Nuclei
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GPD
Physics of Nuclei
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12 GeV Experiments: Reduced Attenuation
Pion electroproduction
Quasi-elastic 12C(e,e’p)
Physics of Nuclei
Pion electroproduction on copper
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12 GeV Experiments:
Reduced Attenuation
Incoherent r0 electroproduction at constant
coherence length, = 2n/(2Mr2 + Q2 )
Pion photoproduction from 4He
(E94-104 data published in D. Dutta
et al., PRC 68 021001(R) (2003))
Physics of Nuclei
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12 GeV Experiments:
Re-Interaction
Coherent r electroproduction from deuterium,
comparing Q2 dependence for low and high t
(longitudinal cross sections)
R=s(pm=400MeV/c)/s(pm=200MeV/c)
CT(I) : Calculation with ΔM2 = 0.7 GeV2
Farrar, Liu, Frankfurt and Strikman (1988)
CT(II) : Calculation with ΔM2 = 1.1GeV2
Sargsian, Private communication
Physics of Nuclei
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Universal Scaling Behavior
Physics of Nuclei
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Universal Scaling Phenomena
• It has been known for decades that scaling is seen in many reactions:
– Bjorken scaling in DIS (end of 1960’s)
– Dimensional scaling laws for exclusive processes from dimensional analysis
and pQCD (Brodsky et al, 1970’s)
• ds/dt(AB->CD)~1/(sm-2); e.g., for 2H(g,p)n, m=1+6+3+3, ~s-11
• New work has extended and improved these ideas
– Generalized counting rule for hard exclusive processes that takes into account
parton orbital angular momentum and hadron helicity flip (X. Ji et al, PRL90,
241601(2003))
• Provides new experimental opportunities for accessing orbital angular momentum
– ‘String theory derivation’ of dimensional scaling laws without resort to
perturbation theory (PN12: Stan Brodsky’s talk; also, “Scaling laws in hadronic
processes and string theory,” O. Andreev, PRD67, 046001(2003))
• Conformal invariance may provide a more fundamental basis for scaling behavior
• Makes connection with a realm of physics beyond QCD
Physics of Nuclei
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Will Brooks
Scaling in Deuteron
Photodisintegration
S-11 behavior observed for
pT>1.1 GeV
See “Onset of Asymptotic Scaling in
Deuteron Photodisintegration,”
P. Rossi et al. (CLAS collaboration),
PRL 94 012301(2005). Figure from
hep-ph/0405207v1.
Physics of Nuclei
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Deuteron Photodisintegration at 12 GeV
Physics of Nuclei
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Other Important Impacts of 12 GeV
Physics of Nuclei
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Threshold J/Y Photoproduction on Nuclei
• See PN12: Eugene Chudakov’s talk for full details
• Physics interest:
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–
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–
Essentially only produced by gluons ( cc )
Small color dipole probing the gluon field of the target
Can estimate J/Y–nucleon cross section; relevant for QGP, high theory interest
May form a stable bound state
On nuclear targets:
Production on proton
Physics of Nuclei
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Short Range Correlations and Cold Dense Matter
• Short range correlations are believed to
be the missing piece in the description
of intermediate and heavy nuclei
• They are associated with overlapping
nucleons and therefore may exhibit
quark-related properties
• Since the nucleons briefly overlap, it is
in a sense ‘dense matter,’ although not
in thermodynamic equilibrium
• See PN12: Talks by John Arrington,
Douglas MacGregor, and Kim Egiyan
Physics of Nuclei
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Wiringa, PRC 43 1585 (1991)
Proton momentum distribution in 4He
January 10, 2005
Will Brooks
Short Range Correlations and Cold Dense Matter
MF+multinucleon SRC
• SRC accessible at 12 GeV reach
baryon densities comparable to
neutron stars
• Experimental opportunities include
A(e,e’), A(e,e’p), A(e,e’NN), A(g,NN),
A(g,NNN), D(e,e’ps), etc.
• 12 GeV brings greatly expanded
kinematic coverage
Physics of Nuclei
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Will Brooks
Few-Body Physics
• A mature field, but some outstanding issues:
– No evidence yet that quark degrees of freedom are needed for elastic form
factors
•
•
•
•
higher Q2 may discover this region
Role of DD and other isobars
Kinematic coverage for T20 could be greatly increased with 12 GeV
See PN12: Ingo Sick’s talk
– Absence of any tritium data from JLab (PN12: Ron Ransome’s talk)
• Clean measurement of d/u ratio by comparing 3He to 3H, needs 12 GeV
• Elastic form factor, Coulomb sum rule, polarization transfer
• Information missing for fundamental few-body system which is accessible to
precise theoretical calculations
Physics of Nuclei
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Few-Body Physics – Form Factors to Higher Q2
Physics of Nuclei
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Conclusions
• With 12 GeV, poised to make a brilliant contribution to understanding
essentials of the Physics of Nuclei:
– Ideally equipped to solve the 30-year-old problem of the EMC effect
– Ideal energy range to study quark propagation through nuclei with orders of
magnitude more luminosity than previously
– An arsenal of color transparency experiments and a high probability of finding it
– Through scaling, the opportunity to make contact with physics beyond QCD
• Broad programs possible to study short range correlations and cold dense
matter, J/Y-N interaction, and topics in few-body physics
• A strong, coherent program coordinating theory and experiment, and a
highly motivated community to carry it out
The program of the Physics of Nuclei is sufficient justification for
the 12 GeV upgrade
Physics of Nuclei
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