The 12 GeV CEBAF Upgrade at Jefferson Lab

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The 12 GeV CEBAF Upgrade at Jefferson Lab

Bernhard A. Mecking Jefferson Lab (ret.)
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Jefferson Lab Today

• Laboratory for studying electromagnetic structure
  of nucleons and nuclei. Serves gt1000 member
  international user community.
• Sponsored by U.S. Department of Energy

C
B
A

• Continuous Electron Beam Accelerator Facility,
  CEBAF, electron accelerator provides CW beams of
  unprecedented quality with a maximum beam energy
  of 6 GeV.

• CEBAF allows delivery of electron beams to three
  experimental halls simultaneously.

• Each of the three halls has complementary
  experimental capabilities and allows for large
  equipment installations to extend scientific
  reach.

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Continuous Electron Beam Accelerator (CEBAF) Today

• Main physics programs
• nucleon electromagnetic form factors (incl.
  strange)
• N N electromagnetic transition form factors
• spin structure functions of the nucleon
• form factors and structure of light nuclei
• Superconducting recirculating electron
  accelerator
• max. energy 5.7 GeV
• max current 200 mA
• e polarization 85
• Experimental equipment in 3 halls (simultaneous
  operation) L cm-2s-1
• A 2 High Resolution Spectrometers (pmax 4
  GeV/c) 1039
• C spectrometers (pmax7 and 1.8 GeV/c)
  special equipment 1039
• B Large Acceptance Spectrometer for e and g
  reactions 1034

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Physics Drivers for CEBAF Upgrade

• New capabilities
• search for the origin of confinement (JPC exotic
  mesons)
• determine parton distributions (high Q2 and W)
  via
• polarized and unpolarized inclusive scattering
• semi-inclusive (tagged) structure functions
• exclusive processes (DVCS, meson production)
• Push present program to higher Q2
• form factors of mesons, nucleons, and light
  nuclei

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Overview of 12 GeV Physics Program
Hall D exploring origin of confinement by
studying exotic mesons
Hall B understanding nucleon structure via
generalized parton distributions
Hall C precision determination of valence quark
properties in nucleons and nuclei
Hall A short range correlations, form factors,
hyper-nuclear physics, future specialized
equipment
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Search for Exotic Mesons Basic idea
Color field due to gluon self interaction,
confining flux tubes form between static color
charges
Original idea by Nambu, now verified by Lattice
QCD calculations
Excitation of the flux tube can lead to exotic
quantum numbers
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Excited Flux Tube Quantum Numbers
Normal mesons JPC 0- 1- 2-
First excited state of flux tube has J1
combined with S1 for quarks
JPC 0- 0- 1- 1- 2- 2-
exotic (mass 1.7 2.3 GeV)
Photons couple to exotic mesons via g VM
transition (same spin configuration)
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Strategy for Exotic Meson Search

• Use photons to produce meson final states
• tagged photon beam with 8 9 GeV to cover mass
  range up to 2.5 GeV
• linear polarization to constrain production
  mechanism
• Use large acceptance detector
• hermetic coverage for charged and neutral
  particles
• typical hadronic final states
• f1h KKh KKppp
• b1p wp pppp
• rp ppp
• high data acquisition rate
• Perform partial-wave analysis
• identify quantum numbers as a function of mass
• check consistency of results in different decay
  modes

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Why photoproduction of hybrid mesons?
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Comparison of g and p beams
Phys. Rev. D43, 2787 (1991)
Phys. Rev. D73, 072001 (2006)
a2
18 GeV
19 GeV
a2
p2
a1
SLAC
BNL
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GlueX Experiment Detector Requirements
The GlueX detector design has been driven by the
need to carry out amplitude analysis.
?1 ?1 ?1 b2 h2 h2 b0 h0 h0
1-
2-
0-
h1 ? a1p- ? (?o?)(?-) ? ??-??-
(all charged)
h0 ? bo1po ? (??o)gg ? ??-gggggg
(many photons)
h2 ? K1K- ? ?o K K- ? ??-KK-
(strange particles)
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HALL B Key Physics Programs

• Generalized Parton Distributions and
  femto-tomography of the nucleon.
• Quark orbital angular momentum contributions to
  the nucleon spin
• Spin structure functions of the nucleon in the
  valence quark domain.
• Free neutron structure function and moments in
  neutron tagging,
• Neutron magnetic form factor at highest Q2.
• EMC effect for spin structure function g1p(x,Q2)
  in various polarized nuclei.
• Quark propagation and quark hadronization using
  the nucleus as a laboratory.
• Quark confinement in the 3-quark system through
  baryon excitations
• - High operating luminosity of 1035 cm-2sec-1
• - Particle ID to higher momentum (e-/p-, p/K/p,
  g/po)
• - More complete detection of hadronic final
  state
• - Compatibility with all target configurations

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Proton charge density and quark momentum
distribution
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Link to DIS and elastic form factors
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Accessing GPDs in exclusive processes

• Deeply virtual Compton scattering (clean probe,
  flavor blind)

Sensitive to all GPDs. Insensitive to quark
flavor

g
ep
e
p
'
'
L

• Hard exclusive meson production (quark flavor
  filter)

• 4 GPDs in leading order, 2 flavors (u, d) ? 8
  measurements

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Deeply Virtual Compton Scattering, DVCS
Physics issue constrain GPDs from DVCS
measurement
XB 0.45
e
g
rate low
e
p
GPDs
p
XB 0.15
Experimental problem isolate small DVCS cross
section
Q2 low
Solution for CEBAF Upgrade - use CLAS to detect
all final state particles - observe interference
term DVCS-BH
CLAS acceptance for DVCS
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DVCS/BH- Beam Asymmetry
Ee 11 GeV
With large acceptance, measure large Q2, xB, t
ranges simultaneously. A(Q2,xB,t)
Ds(Q2,xB,t) s (Q2,xB,t)
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CLAS12 - DVCS/BH- Beam Asymmetry
Luminosity 720fb-1
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CLAS12 - DVCS/BH Beam Asymmetry
e p epg
E 11 GeV
DsLUsinfImF1H..df
Selected Kinematics

• L 1x1035
• T 2000 hrs
• DQ2 1 GeV2
• Dx 0.05

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Exclusive r0 production on transverse target
2D (Im(AB))/p
T
A 2Hu Hd
AUT -
r0
A2(1-x2) - B2(x2t/4m2) - Re(AB)2x2
B 2Eu Ed
AUT
A Hu - Hd B Eu - Ed
r
Asymmetry depends linearly on the GPD E, which
enters Jis sum rule.
K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001
xB
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Motivation for Hall C Upgrade

• Pion and nucleon form factors at high Q2
• Deep inelastic scattering at high Bjorken x
• Semi-inclusive scattering at high hadron momenta
• Polarized and unpolarized scattering on nuclei

• Highest Luminosity (L1038 nucleons/cm2/s)
• Detection of charged particles with highest
  momenta
• Accuracy and reproducibility
• Small angle capability
• Very good particle identification
• Compatibility with all target configurations

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Pion Form Factor
Physics issue p electromagnetic structure, can
be predicted in pQCD
Experimental technique isolate g p p
vertex
e
e
p
n
p
CEBAF Upgrade - use HMS to detect e - use SHMS
to detect p
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Inclusive Deep-Inelastic Scattering

• Unpolarized structure functions F1(x,Q2) and
  F2(x,Q2)
• Proton neutron measurements provide d/u ratio
• Polarized structure functions
• g1(x,Q2) and g2(x,Q2)
• Proton neutron measurements combined with d/u
  provide the spin-flavor distributions Du/u Dd/d

U
Q2 Four-momentum transfer x Bjorken
variable n Energy transfer M Nucleon mass W
Final state hadrons mass
L
T
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Example for the existing data
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Limited knowledge of
and spin dependence at large x (here A1n is shown)
d-quarks at large x
Resolution e.g., F2n tagging spectator proton
from deuterium, and 3He(e,e)
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Unambiguous Resolution _at_ 12 GeV
F2n/F2p at 11 GeV
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CEBAF Upgrade Plan

• Upgrade accelerator to 12 GeV max. energy
• maintain 100 duty cycle
• keep RF system (beam power constant at 1MW
  max. current 80mA)
• Build new experimental hall for meson
  spectroscopy (Hall D)
• polarized tagged photon beam (coherent
  bremsstrahlung)
• large acceptance detector for real photons only
• Upgrade Halls B (CLAS) and C (SHMS) with new
  detection equipment
• Upgrade Hall A beam line for the higher beam
  energy (keep 2 HRS)

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CEBAF Accelerator Upgrade

• keep present accelerating system
• add ten new cryomodules at 100MeV energy gain
• present cryomodules provide 30 MeV
• increased performance can be achieved by
• increased effective cavity length (5-cell ?
  7-cell)
• Increased average gradient (7.5 MV/m ? 17.5
  MV/m)
• need to double cryogenic system capacity
• upgrade recirculating arcs
• add new beam line to Hall D

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New experimental area for GlueX Hall D
Top View
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Coherent Bremsstrahlung
This technique provides the necessary g energy,
flux, and polarization
photon energy spectrum for 12 GeV electrons
flux
photons out
electrons in
spectrometer
diamond crystal
photon energy (GeV)
Hadronic Backgrounds
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Hall D Detector
leadglass counters
barrel calorimeter
solenoid magnet
coherent bremsstrahlung photon beam
tagging magnet (located 80 m upstream of
detector)
time-of-flight
tracking
Cerenkov Counter
electron beam from CEBAF
target
tagging detectors
Event rate to processor farm 10 kHz and later
180 kHz corresponding to data rates of 50 and
900 Mbytes/sec, respectively
crystal radiator
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Calorimetry
BCAL
Forward Calorimeter Pb Glass Existing
lead glass detector 2500 blocks ?E/E
0.036 0.073/vE 100 MeV E? 8 GeV
Pb Glass
UPV
Expected ?o and ? resolutions
Barrel Calorimeter BCAL Lead
scintillating fiber sandwich 4m long cylinder
?E/E 0.020 0.05/vE 20MeV E? 3
GeV st (150 50/vE) ps z-position of
shower via timing time-of-flight
Upstream Photon Veto UPV Veto photons
20MeV E? 300 MeV
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Charged Particle Tracking
Forward Region FDC 4 packages of planar
drift chambers anode cathode readout six
planes per package ?xy150?m active close
to the beam line.
Central Region CDC cylindrical
straw-tube chamber 23 layers from 14cm to
58cm 6o stereo layers ?r?150?m ?z
2mm minimize downstream endplate
Additional layers at r lt 14cm dE/dx for p lt
450 MeV/c
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Particle Identification
Time-of-flight Systems Forward tof 60 ps
BCAL (150 50/vE) ps Start
counter
Cerenkov Detector Gas Cerenkov ? K p
separation
central
dE/dx Information The CDC will do dE/dx p
lt 450 MeV/c The FDC can do dE/dx
very forward
forward
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Hall B Upgrade

• Requirements
• Need high statistics capabilities for exclusive
  processes
• high operating luminosity of gt1035 cm-2sec-1
• particle ID to higher momentum (e-/p-, p/K/p,
  g/po)
• more complete detection of hadronic final state
  

Solution

• Reduce DC occupancies to reach higher
  luminosities
• reduce DC cell sizes (decrease solid angle and
  sensitive time)
• improved magnetic shielding for Møller electrons

..

• Upgrade CLAS forward detection system
• additional threshold Cerenkov detector pp gt 5
  GeV/c
• improve time-of-flight resolution to 60 80 ps
• increase calorimeter granularity for po/g
  separation

• Complement CLAS detection system with new
  Central Detector
• tracking and magnetic analysis
• particle identification

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CLAS12 - Detector
Forward Calorimeter
Preshower Calorimeter
Forward Cerenkov (LTCC)
Forward Time-of-Flight Detectors
Forward Drift Chambers
Superconducting Torus Magnet
Inner Cerenkov (HTCC)
Central Detector
In blue are re-used detectors from CLAS
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CLAS12 Single Sector (exploded view)
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CLAS12 Central Detector
(B0 5T)
Cryostat vacuum jacket
TOF light-guide
SiliconTracker
Space for e.m. calorimeter
Main coil
Central TOF
Shielding coil
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Silicon Vertex Tracker

• detector geometry to optimize tracking acceptance
  resolution
• 6 layer (3 double layers) with 5 cm distances
  between them, changing pitch of silicon strips to
  150 mm
• support structure with minimal material to
  optimize coverage for tracking
• Support structure with carbon-fiber rods
  (ongoing)

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High Threshold Cerenkov

• Purpose separate e and pions in the polar angle
  range from 5o to 40o
• Problem detector resides before main tracking
  detectors.
• Solution use composite materials to minimize
  mirror material thickness

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Central Time-of-flight Counters

• Purpose timing at the 50ps level for particle
  ID in the Central Detector region
• Problem light detectors reside in gt2 Tesla
  magnetic field
• Readout options
• - long bent light guides
• - magnetic field insensitive devices
  (Micro-Channel Plate, Avalanche Photo Diodes).

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Torus Design (ITEP-Kurchatov-TRINITI)
6.5
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Super-High Momentum Spectrometer in Hall C
SHMS properties
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12 GeV Upgrade Project Schedule
Critical Decision1 Approval in February 2006 12
GeV Upgrade included in DOE 5-Year Business Plan
in March 2006

• 2004-2005 Conceptual Design (CDR)
• 2004-2008 Research and Development (RD)
• 2006 Advanced Conceptual Design (ACD)
• 2007-2009 Project Engineering Design (PED)
• 2008 Long Lead Procurement
• 2008-2012 Construction
• 2012-2013 Pre-Ops (beam commissioning)

NOTE schedule shown per Feb 2006 CD-1
Documents, new funding profile received in April,
update of project plan in progress
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Summary

• CEBAF 12 GeV upgrade focused on elucidating the
  quark substructure of mesons and nucleons
• experimental program requires
• new and upgraded equipment
• luminosities between 1035 and 1039 cm-2s-1
• upgrade is a cost-effective extension
• strong community support and endorsement
• construction start expected in 2008