A coherent gamma sourcethe GlueX experimentthe Hall D photon beamthe requirements for diamonds
Richard Jones, University of Connecticut
presented by
GlueX Tagged Photon Beam Working GroupUniversity of Glasgow
University of ConnecticutCatholic University of America
2Richard Jones, CHESS seminar, Aug. 15, 2006
What is GlueX?
ForwardCalorimeter
CerenkovCounter
Time ofFlight
Solenoid
BarrelCalorimeter
Tracking
Target
A new meson spectroscopy experiment at Jefferson Lab which requires:
the 12 GeV upgradethe 12 GeV upgrade
a new experimental halla new experimental hall
a polarized photon beama polarized photon beam
a multi-particle spectrometera multi-particle spectrometer
a new collaboration, presentlya new collaboration, presently~80 physicists~80 physicists~30 institutions~30 institutions
3Richard Jones, CHESS seminar, Aug. 15, 2006
Motivation: gluonic excitations
Consider QCD with Consider QCD with only heavy quarks:only heavy quarks:
the light mesons are glueballs
qq mesons have the conventional positronium low-energy spectrum
spectrum is distorted at higher excitations by a linear potential
for r >> 0.5 fm a tube of gluonic flux forms between q and q
0.4 0.8 1.2 1.6
1.0
2.0
0.0
r (fm)
V0(QQ)
(GeV)glueball decay threshold
4Richard Jones, CHESS seminar, Aug. 15, 2006
Motivation: gluonic excitations
Consider QCD with Consider QCD with only heavy quarks:only heavy quarks:
gluonic excitations give rise to new potential surfaces
for r >> r0 gluonic excitations behave like flux tube oscillations
inspires the flux tube modelflux tube model
5Richard Jones, CHESS seminar, Aug. 15, 2006
Motivation: normal vs hybrid mesons
m=0 CP=(-1)S+1
m=1 CP=(-1)S
Flux-tube Model
ground-state flux-tube m=0
excited flux-tube m=1
CP = (-1)L+S (-1)L+1
= (-1)S+1
S=0, L=0
J=1 CP=+
JPC=1++,1--
(not exotic)
S=1, L=0
J=1 CP=-
JPC = 0-+,00+-+-
11-+-+,1+-
2-+,22+-+-
exoticexotic
normal mesons
11-+-+ or 11+-+-
6Richard Jones, CHESS seminar, Aug. 15, 2006
Motivation: hybrid massesFlux-tube model: 8 degenerate nonetsFlux-tube model: 8 degenerate nonets 1++,1-- 0-+,0+-,1-+,1+-,2-+,2+- ~1.9 GeV/c2
Lattice calculations --- Lattice calculations --- 11-+-+ nonet is the lightest nonet is the lightest UKQCD (97) 1.87 0.20MILC (97) 1.97 0.30MILC (99) 2.11 0.10Lacock (99) 1.90 0.20Mei(03) 2.01 0.10Bernard (04) 1.79 0.14
~2.0 GeV/c2
In the charmonium sector:In the charmonium sector:1-+ 4.39 0.080+- 4.61 0.11 Splitting = 0.20
1-+
0+-
2+-
Splitting 0.20
S=0 S=1
7Richard Jones, CHESS seminar, Aug. 15, 2006
Lowest mass expected to be 1(1−+) at 1.9±0.2 GeV
Lattice 1-+ 1.9 GeV2+- 2.1 GeV0+- 2.3 GeV
8Richard Jones, CHESS seminar, Aug. 15, 2006
Experiment: hybrid searchesMost of what is presently known about the hybrid spectrum has come from one experiment: BNL E852BNL E852
- p X n at 18 GeV
1(1400) – seen in
1(1600) – seen in , f1, b1, ’
1(2000) – seen in f1b
General observations regarding these analyses exotic intensities are typically 1/10 dominant ones requires large samples (~106 in exclusive channels) requires good acceptance (uniform and well-understood) requires access to high-multiplicity final states
9Richard Jones, CHESS seminar, Aug. 15, 2006
Experiment: hybrid photoproduction
p p
BNL @ 18 GeV
Unexplored territory with unique advantages for hybrid search
ca. 1998@ 19 GeV
28
4
Eve
nts
/50
MeV
/c2
SLAC
p n
SLAC
1.0 2.52.01.5
ca. 1993
10Richard Jones, CHESS seminar, Aug. 15, 2006
Almost no data is available in the mass region
where we expect to find exotic hybridswhen flux tube is excited
Experiment: hybrid photoproduction
A pion or kaon beam, when scattering occurs,
can have its flux tube excitedor
beam
Quark spins anti-aligned
Data from these reactions show evidence for gluonic excitations(small part of cross section)
q
q
bef
ore
q
qaf
ter
q
q
afte
r
q
q
bef
ore
beam
Quark spins aligned
__
__
11Richard Jones, CHESS seminar, Aug. 15, 2006
Experiment: photoproduction phenomemology
N N
Xfinalstateforwardsystem
general framework: VMD in initial stateVMD in initial state t-channel exchanget-channel exchange
12Richard Jones, CHESS seminar, Aug. 15, 2006
GlueX ExperimentLead GlassDetector
Solenoid
Electron Beam from CEBAF
Coherent BremsstrahlungPhoton Beam
Tracking
Target
CerenkovCounter
Time ofFlight
BarrelCalorimeter
Note that tagger is80 m upstream of
detector
12 GeV electrons are required In order to produce a 9 GeV photon beam with a significant degree of linear polarization
9 GeV gamma beam MeV energy resolution high intensity (108 /s) linear polarization
www.gluex.org
13Richard Jones, CHESS seminar, Aug. 15, 2006
GlueX Experiment: beam polarization
L 0, 1, or 2
PV P PX 1 L
Suppose we want to distinguish theexchange: O+ from 0- ( AN from AU )
V = vectorphoton
m = 1
m = -1
R
L
AN AU
AN AU
For circular polarization: With linear polarization we
can isolate AN from AU
Circular polarization gives access to their interference
R J=0– or 0+
X
photon
for R with J = 0
Gottfried-Jackson frame
exchange particle
14Richard Jones, CHESS seminar, Aug. 15, 2006
GlueX Experiment: photon beam
flu
x
photon energy (GeV)
12 GeV electronsThe coherent bremsstrahlung technique provides requisite energy, flux and polarization
collimated
Incoherent &coherent spectrum
taggedwith 0.1% resolution
40%polarization
in peak
electrons in
photons out
spectrometer
diamondcrystal
15Richard Jones, CHESS seminar, Aug. 15, 2006
Requirements for photon beam
Energy 9 GeV
Linear polarization
High rates (consistent with tagging) Initial running at 107 /s in the coherent peak Design system with a clear path to 108 /s
Energy resolution E/E ~ 0.1% for use in event reconstruction
16Richard Jones, CHESS seminar, Aug. 15, 2006
6 GeV CEBAF
CHL-2CHL-2
Upgrade magnets Upgrade magnets and power and power suppliessupplies
12
Enhance equipment in Enhance equipment in existing hallsexisting halls
add Hall D (and beam line)
17Richard Jones, CHESS seminar, Aug. 15, 2006
1. energy 2. polarization 3. rate 4. resolution () () ()
5. background
The generic photon source
Techniques:A. Compton backscatterB. BremsstrahlungC. Coherent bremsstrahlung
A B C
() with tagging
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Incoherent vs coherent bremsstrahlung
Consider the electromagnetic form-factor of the target in q-space
q
no enhancement
q
strong enhancement
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Kinematics of Coherent Bremsstrahlung
effects of collimation at 80 m distance from radiatorincoherent (black) and coherent (red) kinematics
effects of collimation: to enhance high-energy flux and increase polarization
20Richard Jones, CHESS seminar, Aug. 15, 2006
No other solution was found that could meet all of these requirements at an existing or planned nuclear physics facility.
Coherent Bremsstrahlung with Collimation
A laser backscatter facility would need to wait for new construction of a new multi-G$ 20GeV+ storage ring (XFEL?).
Even with a future for high-energy beams at SLAC, the low duty factor <10-4 essentially eliminates photon tagging there.
The continuous beams from CEBAF are essential for tagging and well-suited to detecting multi-particle final states.
By upgrading CEBAF to 12 GeV, a 9 GeV polarized photon beam can be produced with high polarization and intensity.
UniqueUnique::
21Richard Jones, CHESS seminar, Aug. 15, 2006
circular polarization transfer from electron beam reaches 100% at end-point
linear polarization determined by crystal orientation vanishes at end-point not affected by electron
polarization
Polarization from Coherent Bremsstrahlung
Linear polarization arises from the two-body nature of the CB kinematics
Linear polarization has unique advantages for GlueX physics: a requirement
Changes the azimuthal coordinate from a uniform random variable to carrying physically rich information.
22Richard Jones, CHESS seminar, Aug. 15, 2006
Photon Beam Intensity Spectrum
4
nominaltagginginterval
Rates based on:• 12 GeV endpoint• 20m diamond crystal• 100nA electron beam
Leads to 107 /s on target
(after the collimator)
Design goal is to build an experiment with ultimate rate capability as high as 108 /s on target.
23Richard Jones, CHESS seminar, Aug. 15, 2006
II. Optimization
photon energy vs. polarization crystal radiation damage vs. multiple scattering collimation enhancement vs. tagging efficiency
Understanding competing factors is necessary to optimize the design
24Richard Jones, CHESS seminar, Aug. 15, 2006
Optimization: chosing a photon energy
A minimum useful energy for GlueX is 8 GeV;8 GeV; 9-10 GeV9-10 GeV is better for several reasons,
for a fixed endpoint of 12 GeV, the peak polarizationpeak polarization and the coherent gain factorcoherent gain factor are both steep functions of peak energysteep functions of peak energy.
CB polarization is a key factor in the choice of a energy range of 8.4-9.0 GeV for GlueX
but
25Richard Jones, CHESS seminar, Aug. 15, 2006
Optimization: choice of diamond thickness
Design calls for a diamond thickness of 2020mm which is approximately 1010-4-4 rad.len rad.len.
Requires thinningthinning: special fabrication steps and $$.
Impact from multiple-scattering is significant.
Loss of rate is recovered by increasing beam current,
up to a point…up to a point…
The choice of 20m is a trade-off between MS and radiation damage.
-3
-4
26Richard Jones, CHESS seminar, Aug. 15, 2006
Electron Beam Emittance
requirement : << 1010-8-8 m m••rr emittances are r.m.s. values
derivation : virtual spot size: 500 m radiator-collimator: 76 m crystal dimensions: 5 mm
In reality, one dimension (y) is much better than the other (x 2.5)
This is a key issue for achieving the requirements for the GlueX Photon Beam
Optics study: goal is achievable, but close to the limits according to 12 GeV machine models Optics study: goal is achievable, but close to the limits according to 12 GeV machine models
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V. Diamond crystal requirements
orientation requirements limitations from mosaic spread radiation damage assessment
28Richard Jones, CHESS seminar, Aug. 15, 2006
Diamond crystal: goniometer mount
temperature profile of crystalat full operating intensity
oC
29Richard Jones, CHESS seminar, Aug. 15, 2006
Diamond Orientation
orientation angle is relatively large at 9 GeV: 3 mr3 mr
initial setup takes place at near-normal incidence
goniometer precision requirements for stable operation at 9 GeV are not severe.
alignmentzone
operatingzone
fixed hodoscope
microscope(m
r)
30Richard Jones, CHESS seminar, Aug. 15, 2006
Driven by beam emittanceand spot size at collimator
X: r.m.s. = 1.7mmY: r.m.s. = 0.7mm
Minimum acceptable size:
5mm x 3mm
How large a diamond is needed?
31Richard Jones, CHESS seminar, Aug. 15, 2006
Mosaic spread goal:
Adds in quadraturewith beam divergence
50µr r.m.s.
25µr r.m.s.
How perfect a crystal is needed?
32Richard Jones, CHESS seminar, Aug. 15, 2006
A HTHP diamond ingot
seed
slice 1
slice 2
slice 3
We brought samples from 3 ingots to Daresbury January 2002
Stone 1407 Stone 1485A Stone 1532
SRS measurements (January, 2002)
33Richard Jones, CHESS seminar, Aug. 15, 2006
Stone 1407 slice 1
2mm
4mm x 4mm X-ray beam rocking curve
34Richard Jones, CHESS seminar, Aug. 15, 2006
Stone 1407 slice 1
2mm
0.5mm x 0.5mm X-ray beam rocking curve
35Richard Jones, CHESS seminar, Aug. 15, 2006
Stone 1482A slice 1
2mm
3mm x 5mm X-ray beam rocking curve
36Richard Jones, CHESS seminar, Aug. 15, 2006
Stone 1482A slice 2
4mm
5mm x 5mm X-ray beam rocking curve
37Richard Jones, CHESS seminar, Aug. 15, 2006
Stone 1482A slice 2 (rotated)
4mm
10mm x 10mm X-ray beam rocking curve
38Richard Jones, CHESS seminar, Aug. 15, 2006
Stone 1482A slice 3
4mm
10mm x 10mm X-ray beam rocking curve
39Richard Jones, CHESS seminar, Aug. 15, 2006
13
Stones not looked at
Stone 1407 slice 2
Stone 1407 slice 3
40Richard Jones, CHESS seminar, Aug. 15, 2006
Diamond Crystal Quality
rocking curve from X-ray scattering
natural fwhm
reliable source of high-quality synthetics from industry (Univ. of Glasgow contact)(Univ. of Glasgow contact)
established procedure in place for selection and assessment using X-rays
R&D is ongoing towards reliable operation of one 20m crystal (Hall B)(Hall B)
41Richard Jones, CHESS seminar, Aug. 15, 2006
conservative estimate (SLAC) for useful lifetime (before significant degradation):
during initial running at 107 /s this gives 600 hrs of running before a spot move
a “good” crystal accommodates 5 spot moves
R&D is planned that will improve the precision of this estimate.
Diamond Crystal Lifetime
0.25 C / mm0.25 C / mm22
42Richard Jones, CHESS seminar, Aug. 15, 2006
14
Conclusions
Doing X-ray topographs is not sufficient.
Topographs are relatively fast and easy to set up.
Rocking curves tell us what we need to know.
It is hard to tell from looking at the topograph what the rocking
curve will look like.
Large and high quality crystals are available.
Based on an example of 1.
New X-ray tests are needed after thinning, rad. damage.
43Richard Jones, CHESS seminar, Aug. 15, 2006
44Richard Jones, CHESS seminar, Aug. 15, 2006
GlueX ReviewsDecember 1999: PAC Requested Review of the GlueX ProjectD. Cassel (chair), J. Domingo, W. Dunwoodie, D. Hitlin, G. Young.
April 2001: NSAC Long Range Plan Committee.
July 2003: Electronics Review of the GlueX ProjectJ. Domingo, A. Lankford (chair), G. Young
October 2004: Detector ReviewM. Albrow, J. Alexander (Chair), W. Dunwoodie, B. Mecking.
December 2004: Solenoid AssessmentJ. Alcorn, B. Kephart (Chair), C. Rode.
January 2006: Photon Beam and Tagger ReviewJ. Ahrens (chair), B. Mecking, A. Nathan