research perspectives at jefferson lab

Duality05, Frascati, June 8, 2005, 1

Operated by the Southeastern Universities Research Association for the U.S. Department Of Energy

Thomas Jefferson National Accelerator Facility

Research Perspectives at Jefferson Lab

Kees de JagerJefferson LabDuality05 WorkshopLFN FrascatiJune 6-8, 2005




CEBAF @ 12 GeV, WHY?

• Gluonic Excitations and the Origin of Confinement

• Developing a Unified Description of Hadron Structure

Valence Quark Structure and Parton Distributions Form Factors – Constraints on the GPDs The Generalized Parton Distributions (GPDs) as Accessed via Deep(ly)

Exclusive Reactions Other Topics in Hadron Structure

• The Physics of Nuclei The Quark Structure of Nuclei (resolving the EMC effect) The Short-Range Behavior of the N-N Interaction and Its QCD Basis Quark propagation through Nuclear Matter (hadronization)

• Symmetry Tests in Nuclear Physics Precision Tests of the Standard Model Spontaneous Symmetry Breaking




Enhanced Kinematical Access to the DIS Regime

12 GeV will access the regime (x > 0.3), where valence quarks dominate




with enough luminosity to reach the high-Q2, high-x region

Counts/hour/ (100 MeV)2

(100 MeV2) for L=1035 cm-2 sec-1




Gluonic Excitations

from Alex Dzierba




Gluonic Excitations and the Origin of ConfinementThe quarks in a meson are sources of a color electric flux which is trapped in a flux tube connecting the quarks. The formation of the flux tube is related to the self-interaction of gluons via their color charge.

Flux

tube

forms

between

qq

linear potential

From G. Bali

• Flux tubes result in a linear confining potential

• Do flux tubes apply to light-quark systems? • Very little is known about gluonic (or flux-

tube) excitations




First excited state of flux tube has JPC=1+- or 1-

+ combined with S=1 for quarks results in

Photons couple to exotic mesons via VM transition (same spin configuration)

Photons Preferred for Flux Tube Excitations

JPC = 0-+ 0+- 1+- 1-+ 2-+ 2+-

exotic (mass ~ 1.7 – 2.3 GeV)

LSS12S = S + S12J = L + SC = (-1)L + SP = (-1)L + 1

Normal mesons: JPC = 0-+ 1+- 2-+

Double-blind Monte Carlo simulation: 2 % exotic signal clearly visible




• Use photons to produce meson final states with a mass up to 2.5 GeV

– tagged photon beam with 8 – 9 GeV– linear polarization to constrain production mechanism

• Use large acceptance detector– hermetic coverage for charged and neutral particles– typical hadronic final states: f1 KK KK

b1

– high data-acquisition rate

• Perform partial-wave analysis– identify quantum numbers as a function of mass– check consistency of results in different decay modes

Strategy for Exotic Meson Search




Hadron Structure

from Zein-Eddine Mezianiand Volkert Burkert




•In the large x region (x>0.5) theratio F2

n/F2

p is not well determined

due to the lack of a free neutron target

•Impact:• determine valence d quark momentum

distribution• extract helicity dependent quark

distributions through inclusive DIS

• high x and Q2 background in high energy particle searches.

• construct moments of structure functions

Unpolarized Neutron to Proton ratio




•Mirror symmetry of A=3 nuclei Extract F2

n/F2p from ratio of 3He/3H

structure functions and superratio R

R = ratio of ”EMC ratios” for 3He and 3H can be calculated to within 1%

•Most systematic and theoretical uncertainties cancel

• Nearly free neutron target by tagging low-momentum proton from deuteron at backward angles

•Small p (70-100 MeV/c) Minimize on-shell extrapolation (neutron

only 7 MeV off-shell)

•Backward angles (pq> 110o) Minimize final-state interactions

Spectator tagging

DIS from A=3 nuclei

Unpolarized Neutron to Proton ratio




Hall C 11 GeV with HMS

Hall B 11 GeV with CLAS12

Unpolarized Neutron to Proton Ratio




A1n at 11

GeVA1

p at 11 GeV

W>1.2

Inclusive measurements of asymmetries




Ee = 11 GeV polarized NH3 and 3He

Flavor decomposition

At RHIC with W production




•First data from HERMES

0 du Δ−Δ

. Predictions:

. Instantons (cQSM):

JLab @11 GeV

Flavor decomposition: polarized sea




Quark-gluon correlations and g2




g2 at JLab with 11 GeV




•Both d2 and f2 are required to determine the color polarizabilities•To extract f2, d2 needs to be determined first

target mass correction term

dynamical twist-3 matrix element

dynamical twist-4 matrix element

Moments of Structure Functions




Color “Polarizabilities”




d2 with 11 GeV at JLab




HMS+SHMS (11 GeV) projection

Where does the dynamics of the q-q interaction make a transition from the strong QCD (confinement) to the pQCD regime?

•It will occur earliest in the simplest systemsthe pion form factor F(Q2) provides a good starting system to

determine the relevant distance scale experimentally

•In asymptotic region, F 8s ƒ Q-2

Charged Pion Electromagnetic Form Factor




Proton Charge Form Factor




CLAS 12 : Neutron GMn

eD en(ps)ep en

With 12 GeV Upgrade




GPDs & Deeply Virtual Exclusive Processes

x

Deeply Virtual Compton Scattering (DVCS)

t

x+ x-

H(x,,t), E(x,,t), . .

hard vertices

– longitudinal momentum transfer

x – longitudinal quark momentum fraction

–t – Fourier conjugateto transverse impact parameter

“handbag” mechanism

xB

2-xB

=




Kinematics Coverage of the 12 GeV Upgrade

JLab Upgrade

Upgraded JLab hascomplementary& unique capabilities

unique to JLaboverlap with other experiments

High xB only reachablewith high luminosity H1, ZEUS




DVCS SSA Measures phase and amplitude directlyDVCS at 11 GeV can cleanly test correlations in nucleon structure(data shown – 2000 hours)

DVCS and Bethe-Heitler are coherent can measure amplitude AND phase




DVCS/BH Transverse Target Asymmetry

Asymmetry highly sensitive to the u-quark contributions to proton spin

Transversely polarized target

Δ~ sinIm{k1(F2H – F1E) +…}d

Q2=2.2 GeV2, xB = 0.25, -t = 0.5GeV2E = 11 GeVSample kinematics

AUTx Target polarized in scattering plane

AUTy Target polarized perpendicular to scattering plane

ep ↑→ ep




Exclusive 0 production on transverse target

2Δ (Im(AB*))/ T

t/4m2) - ReUT

Asymmetry depends linearlyon the GPD E, which enters Ji’s sum rule.

A ~ 2Hu + Hd

B ~ 2Eu + Ed0

K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001

A ~ Hu - Hd

B ~ Eu - Ed+

AUT

xB

CLAS12




Physics of Nuclei

from Will Brooks




Unpacking the EMC effect

•With 12 GeV, we have a variety of tools to unravel the EMC effect: Parton model ideas are valid over fairly wide kinematic range High luminosity High polarization

•New experiments, including several major programs: Precision study of A-dependence; x>1; valence vs. sea g1A(x) “Polarized EMC effect” – influence of nucleus on spin Flavor-tagged polarized structure functions ΔuA(xA) and ΔdA(xA) x dependence of axial-vector current in nuclei (can study via parity

violation) Nucleon-tagged structure functions from 2H and 3He with recoil

detector Study x-dependence of exclusive channels on light nuclei, sum up to

EMC




How do energetic quarks transform into hadrons? How quickly does it happen?What are the mechanisms?

Hadronization




12

12

12

12

Expected Results on Hadronization




Parity Violation

from Krishna Kumar




Electron-Quark Phenomenology

€

C1i ≡ 2gAe gV

i

€

C2i ≡ 2gVe gA

i

C1u and C1d will be determined to high precision by other experimentsC2u and C2d are small and poorly known: can be accessed in PV DIS

New physics such as compositeness, new gauge bosons:

Deviations to C2u and C2d might be fractionally large

A

V

V

A

Proposed JLab upgrade experiment will make it possible to improve knowledge of 2C2u-C2d by more than a factor of 20




Parity Violating Electron DIS

€

APV =GFQ2

2παa(x) + f (y)b(x)[ ]

€

a(x) =

C1iQi f i(x)i

∑

Qi2 f i(x)

i

∑

€

fi(x) are quark distribution functions

e-

N X

e-

Z* *

For an isoscalar target like 2H, structure functions largely cancel in the ratio:

€

a(x) =3

10(2C1u − C1d )[ ] +L

€

b(x) =3

10(2C2u − C2d )

uv (x) + dv (x)

u(x) + d(x)

⎡

⎣ ⎢ ⎤

⎦ ⎥+L

Provided Q2 >> 1 GeV2 and W2 >> 4 GeV2 and x ~ 0.2 - 0.4

Must measure APV to fractional accuracy better than 1%

• 11 GeV at high luminosity makes very high precision feasible• JLab is uniquely capable of providing beam of extraordinary stability• Systematic control of normalization errors being developed at 6 GeV

€

y ≡1− ′ E / E

€

b(x) =

C2iQi f i(x)i

∑

Qi2 f i(x)

i

∑

€

x ≡ xBjorken




2H Experiment at 11 GeV

E’ = 5.0 GeV ± 10% lab = 12.5o

APV = 217 ppm

Ibeam = 90 µA 60 cm LD2 target

• Use both HMS and SHMS to increase solid angle• ~2 MHz DIS rate, π/e ~ 2-3

xBj ~ 0.235, Q2 ~ 2.6 GeV2, W2 ~ 9.5 GeV2 1000 hours

(APV)=0.65 ppm

(2C2u-C2d)=±0.0086±0.0080

PDG (2004): -0.08 ± 0.24 Theory: +0.0986

Advantages over 6 GeV:•Higher Q2, W2, f(y)•Lower rate, better π/e•Better systematics: 0.7%




Physics Implications

Examples:•1 TeV extra gauge bosons (model dependent)•TeV scale leptoquarks with specific chiral couplings

Unique, unmatched constraints on axial-vector quark couplings:Complementary to LHC direct searches

(2C2u-C2d)=0.012

(sin2W)=0.0009




PV DIS and Nucleon Structure

•Analysis assumed control of QCD uncertainties

•Higher twist effects

•Charge Symmetry Violation (CSV)

•d/u at high x

•NuTeV provides perspective

•Result is 3 from theory prediction

•Raised very interesting nucleon structure issues: cannot be addressed by NuTeV

•JLab at 11 GeV offers new opportunities

•PV DIS can address issues directly

•Luminosity and kinematic coverage

•Outstanding opportunities for new discoveries

•Provide confidence in electroweak measurement




Search for CSV in PV DIS

Sensitivity will be further enhanced if u+d falls off more rapidly than u-d as x -> 1

•measure or constrain higher twist effects at x ~ 0.5-0.6•precision measurement of APV at x ~ 0.7 to search for CSV

Strategy:

•u-d mass difference•electromagnetic effects

•Direct observation of parton-level CSV would be very exciting•Important implications for high-energy collider pdfs•Could explain significant portion of the NuTeV anomaly€

up (x) = dn (x)?

d p (x) = un (x)?

For APV in electron-2H DIS:

€

APV

APV

= 0.28δu −δd

u + d

€

u(x) = up (x) − dn (x)

δd(x) = d p (x) − un (x)




APV in DIS on 1H

€

APV =GFQ2

2παa(x) + f (y)b(x)[ ]

€

a(x) =u(x) + 0.91d(x)

u(x) + 0.25d(x)

•Determine that higher twist is under control•Determine standard model agreement at low x•Obtain high precision at high x

•Allows d/u measurement on a single proton•Vector quark current (electron is axial-vector)

€

a(x) =3

2

2C1uu(x) − C1d (d(x) + s(x))

4u(x) + d(x) + s(x)

⎡

⎣ ⎢ ⎤

⎦ ⎥

€

b(x) =3

2

2C2uuv (x) − C2d dv (x)

4u(x) + d(x) + s(x)

⎡

⎣ ⎢ ⎤

⎦ ⎥

+ small corrections




d/u at High x

Deuteron analysis has nuclearcorrections

APV for the proton has no such corrections

Must simultaneously constrain higher twist effects

The challenge is to get statistical and systematic errors ~ 2%




Large Acceptance: Concept

•CW 90 µA at 11 GeV•40-60 cm liquid H2 and D2 targets•Luminosity > 1038/cm2/s

JLab Upgrade

•Need high rates at high x

•For the first time: sufficient rates to make precision PV DIS measurements

•solid angle > 200 msr•count at 100 kHz•online pion rejection of 102 to 103




CHL-2CHL-2

Upgrade magnets Upgrade magnets and power and power suppliessupplies

Enhance equipment in Enhance equipment in existing hallsexisting halls

6 GeV CEBAF1112Add new hallAdd new hall




Hall A w/ 2.2, 4.4, 6.6, 8.8 and 11 GeV Beam

• Retain High Resolution Spectrometer (HRS) pair for the continuation of research in which energy resolution comparable to nuclear level spacing is essential

• Use the hall infrastructure to support specialized large-installation experiments




CLAS12 - Acceptance for DVCS

Q2 > 2.5 GeV2ep ep

For small t, protons recoil at large polar angles

Forward Detector

Central Detector

Kinematic Limit

E = 11 GeV

Occupancy of DVCS events

10

20

30

40

50

60

70




CLAS12

Forward EC

Forward TOF

Preshower EC (not visible)

Low Threshold Cerenkov Counter (LTCC)

New Torus Coils

Forward Drift Chambers

High Threshold Cerenkov (HTCC)

Central Detector

Beamline

Coil EC

Inner EC (not visible)Reused CLAS element




Hall C: The SHMS and HMS

SuperHMS

HMS

SOS




GlueX DetectorLead Glass

Detector

Solenoid

Electron beam from CEBAF

Coherent BremsstrahlungPhoton Beam

Tracking

Target

CerenkovCounter

Time ofFlight

BarrelCalorimeter

Note that tagger is80 m upstream of

detector

Event rate to processor farm:10 kHz and later 180 kHz correspondingto data rates of 50 and 900 Mbytes/sec,respectively




DOE Critical Decisions

CD DOE Meaning

Implications of CD Approval

Time

CD-0 Approve Mission Need

Formal CDR work begins using DOE fundsR&D for CDR beginsPED funds can be requestedAcquisition plan developedSerious search for non-DOE/NP funding

April 2004

CD-1 Approve Preliminary Baseline Range

Lehman review of CDR and approvalPED funds can be spent

~August 2005

CD-2 Approve Performance Baseline

Second Lehman review to establish budget, schedule and performanceLong-lead procurements beginRequest construction funding

2006/7 ??

CD-3 Approve Start of Construction

Construction begins in earnest 2008/9 ??

CD-4 Approve Start of Operations

Science begins! 2013 ??




Status of 12 GeV project

•The 12 GeV JLab upgrade, a formal recommendation of the NSAC Long Range Plan, will permit a major step forward in the study of “strong” QCD and hadron structure

•Substantial progress has been made toward refining the experimental program and equipment designs

•DOE has provided a “mission need statement” (CD-0 approval)

•A recent DOE review of the science program was highly supportive

•JLab is in the process of obtaining CD-1 approval

•International involvement is essential to move this exciting project forward rapidly




Highlights of the 12 GeV Program Exploration of QCD in the Nonperturbative Regime:

• Existence and properties of exotic mesons Detailed study of hadronic structure

• Revolutionize Our Knowledge of Spin and Flavor Dependence of Valence PDFs

• Revolutionize Our Knowledge of Distribution of Charge and Current in the Nucleon

• Totally New View of Hadron (and Nuclear) Structure: • GPDs, Determination of the quark angular momentum

Nuclear Structure in Terms of QCD• Spin and flavor dependence of EMC Effect• Study quark propagation through nuclear matter

Parity Violation in Deep Inelastic Scattering • Factor 20 improvement in (2C2u-C2d)• Sensitive tests of Charge Symmetry Violation & valence region

research perspectives at jefferson lab

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