11 primakoff experiments with eic a. gasparian nc a&t state university, greensboro, nc for the...
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11
Primakoff Experiments with EIC
A. GasparianNC A&T State University, Greensboro, NC
For the PrimEx Collaboration
Outline
Physics motivation: The first experiment at JLab: 0 lifetime
Development of precision technique Results for 0 lifetime
Experiments with EIC Summary
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chiral limit: is the limit of vanishing quark masses mq→ 0.
QCD Lagrangian with quark masses set to zero:
s
d
u
q
GgD
GGqiDqqiDqL
LR
s
RRLLoQCD
)1(2
1
2/
4
1
5,
)(
Large global symmetry group:Large global symmetry group:
)1()1()3()3( BARL UUSUSU
The QCD LagrangianThe QCD Lagrangian
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Fate of QCD SymmetriesFate of QCD Symmetries
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• Chiral SUL(3)XSUR(3) spontaneously broken Goldstone mesons π0, η8
• Chiral anomalies Mass of η0 P→γγ ( P: π0, η, η׳)
• Quark flavor SU(3) breaking
The mixing of π0, η and η׳
The The 00, , ηη and and ηη’ system provides a rich ’ system provides a rich laboratory to study the symmetry structure of laboratory to study the symmetry structure of
QCD at low energyQCD at low energy..
Lightest Pseudoscalar MesomsLightest Pseudoscalar Mesoms
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The PrimEx Experimental ProjectThe PrimEx Experimental Project
Experimental program Precision measurements of:
Two-Photon Decay Widths: Γ(0→), Γ(→), Γ(’→)
Transition Form Factors at low Q2 (0.001-0.5 GeV2/c2): F(*→ 0), F(* →), F(* →)
Test of Chiral Symmetry and Anomalies via the Primakoff Effect
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Physics Outcome
Fundamental input to Physics:
precision test of chiral anomaly predictions determination of quark mass ratio -’ mixing angle 0, and ’ interaction electromagnetic radii is the ’ an approximate Goldstone boson?
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First experiment: 0 decay width
eVF
mNc 725.7576 23
3220
0→ decay proceeds primarily via the chiral anomaly in QCD. The chiral anomaly prediction is exact for massless quarks:
Corrections to the chiral anomaly prediction: (u-d quark masses and mass differences)
Calculations in NLO ChPT:(J. Goity, at al. Phys. Rev. D66:076014, 2002)Γ(0) = 8.10eV ± 1.0%
~4% higher than LO, uncertainty: less than 1%
Precision measurements of (0→) at the percent level will provide a stringent test of a fundamental prediction of QCD.
0→
Recent calculations in QCD sum rule: (B.L. Ioffe, et al. Phys. Lett. B647, p. 389, 2007)
Γ() is only input parameter 0- mixing includedΓ(0) = 7.93eV ± 1.5%
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Decay Length Measurements (Direct Method)
1x10-16 sec too small to measure
solution: Create energetic 0 ‘s,
L = vE/m
But, for E= 1000 GeV, Lmean 100 μm very challenging experiment
Measure 0 decay length
1984 CERN experiment: P=450 GeV proton beamTwo variable separation (5-250m) foilsResult:(0) = 7.34eV3.1% (total)
Major limitations of method unknown P0 spectrum needs higher energies for improvement
0→
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e+e- Collider Experiment
e+e-e+e-**e+e-0e+e-
e+, e- scattered at small angles (not detected)
only detected
DORIS II @ DESY
Results: Γ(0) = 7.7 ± 0.5 ± 0.5 eV ( ± 10.0%)
Not included in PDG average
Major limitations of method knowledge of luminosity unknown q2 for **
0→
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Primakoff Method
22
..4
43
3
2Pr
3
sin)(8
QFQ
E
m
Z
d
dme
ρ,ω
Challenge: Extract the Primakoff amplitude
from the experimental cross section
12C target
Primakoff Nucl. Coherent
Interference Nucl. Incoh.
)log(
2
2Pr
4Pr
2
2
Pr
EZd
Ed
dE
m
peak
peak
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Previous Primakoff Experiments
DESY (1970) bremsstrahlung beam,
E=1.5 and 2.5 GeVTargets C, Zn, Al, Pb Result: (0)=(11.71.2) eV
10.%
Cornell (1974) bremsstrahlung beam
E=4 and 6 GeV targets: Be, Al, Cu, Ag, U Result: (0)=(7.920.42) eV
5.3%
All previous experiments used: Untagged bremsstrahlung beam Conventional Pb-glass calorimetry
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PrimEx Experiment at Hall B JLab
JLab Hall B high resolution, high intensity photon tagging facility
New pair spectrometer for photon flux control at high intensities New high resolution hybrid multi-channel calorimeter (HYCAL)
Requirements of Setup: high angular resolution (~0.5 mrad)
high resolutions in calorimeter small beam spot size (‹1mm)
Background: tagging system needed
Particle ID for (-charged part.) veto detectors needed
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Fit to Extract Γ(0) Decay Width Theoretical angular distributions smeared with experimental
resolutions are fit to the data
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C 208Pb
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14L. Gan APS, April 15, 2008 14
Estimated Systematic Errors
Contributions Errors
Photon flux 1.0%
Target number 0.1%
Background subtraction 0.9%
Event selection 0.5%
HYCAL response function 0.5%
Beam parameters 0.4%
Acceptance 0.3%
Model errors (theory) 0.25%
Physics background 0.24%
Branching ratio (PDG) 0.03%
Total 1.6%
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Current PrimEx Result
() = 7.93eV2.3%1.6%
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Next Run
16
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PrimEx @ High Energies with EICPrimEx @ High Energies with EIC
Experimental program
Precision measurements of:
Transition Form Factors at low Q2 (0.001-0.5 GeV2/c2):
F(*→ 0), F(* →), F(* →)
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Primakoff Method
22
..4
43
3
2Pr
3
sin)(8
QFQ
E
m
Z
d
dme
ρ,ω
Challenge: Extract the Primakoff amplitude
12C target
Primakoff
Nucl. Coherent
Interference
Nucl. Incoh.
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)log( 2
Pr4Pr EZdE
d
d
peak
Increase Primakoff cross section:
Better separation of Primakoff reaction from nuclear processes:
Momentum transfer to the nuclei becomes less reduce the incoherent background
3/12
2
Pr
2
2 AEE
mNCpeak
Why do we need high energy?
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Direct measurements of slopes:
F(*→ 0), F(* →), F(* →)
Interaction radii:
Fγγ*P(Q2) ≈ 1 - 1/6▪<r2>PQ2
ChPT for large Nc predicts relation between the slopes.
Extraction of Ο(p6) low-energy constant in the chiral Lagrangian
Extraction of decay widths:
Γ(0→), Γ(→), Γ(’→)
Precision test of chiral anomaly predictions
Transition Form Factors at Law Q2
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Experimental Status for Experimental Status for F(*→ 0)
F(*→ 0) ≈ 1 – a Q2/m2
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Experimental Status for Experimental Status for F(* →)
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PrimEx @ High Energies with EIC Precision Measurement of → decay width
All decay widths are calculated from decay width and experimental Branching Ratios (B.R.):
ΓΓ((η→η→ decay) = decay) = ΓΓ((→→) × B.R.) × B.R.
Any improvement in ΓΓ((→→))
will change the whole will change the whole - sector in PDB- sector in PDB
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)(2
1ˆ ,
22
222
duud
s mmmmm
mmQ
..)()3( RB
There are two ways to determine the quark mass ratio:
•Γ(η→3π) is the best observable for determining the quark mass ratio, which is obtained from Γ(η→γγ) and known branching ratios:
•The quark mass ratio can also be given by a ratio of The quark mass ratio can also be given by a ratio of meson masses: meson masses:
)(1)(
222
22
2
22 m
mm
mm
m
mQ
QCDKK
kk
o
Determination of quark mass ratioDetermination of quark mass ratio
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Corr. )( ..0 meKKmm
)(2
1ˆ re whe,
22
222
duud
s mmmmm
mmQ
ΓΓ((ηη→→33)=)=ΓΓ((→→))××B.B.R.R.
Determination of quark mass ratioDetermination of quark mass ratio
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• Mixing corrections:
)(cos)(sin
)(sin)(cos00
0
008
008
• DecayDecay constant corrections:
000
888
000
888
cos ,sin
sin ,cos
ffff
ffff
Γ(η/η´→γγ) widths are crucial inputs for obtaining fundamental mixing parameters.
Mixing Angles Mixing Angles
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Summary
Extrapolation to Q2=0 will define the radiative decay widths: Γ(0→), Γ(→), Γ(’→)
It looks possible to perform high precision transition form factor measurements of light pseudoscalar mesons at low Q2 with EIC at high energies
Fundamental input to Physics:
precision test of chiral anomaly predictions 0, and ’ interaction electromagnetic radii
extraction of Ο(p6) low-energy constant in the chiral Lagrangian
determination of quark mass ratio -’ mixing angle is the ’ an approximate Goldstone boson?
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28A. Gasparian Hall D, March 7, 2008 28
The End
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The Primakoff Effect
22
..4
43
3
2Pr
3
sin)(8
QFQ
E
m
Z
d
dme
ρ, ω
Challenge: Extract the Primakoff amplitude
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(0→) World Data
0 is lightest quark-antiquark hadron
The lifetime:
= B.R.( 0 →γγ)/(0 →γγ) 0.8 x 10-16 second
Branching ratio: B.R. ( 0→γγ)= (98.8±0.032)% 0
→
±1%
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Estimated Systematic Errors
Contributions Errors
Photon flux 1.0%
Target number 0.1%
Background subtraction 0.9%
Event selection 0.5%
HYCAL response function 0.5%
Beam parameters 0.4%
Acceptance 0.3%
Model errors (theory) 0.25%
Physics background 0.24%
Branching ratio (PDG) 0.03%
Total 1.6%
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Electromagnetic Calorimeter: HYCAL Energy resolution Position resolution Good photon detection efficiency @ 0.1 – 5 GeV; Large geometrical acceptance
PbWO4 crystals resolutionPb-glass budget
HYCALonly
Kinematicalconstraint
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15 Days
Beam Time and Statistics
Target: L=20 cm, LHe4 NHe = 4x1023 atoms/cm2 Nγ = 1x107 photon/sec (10-11.5 GeV part)<Δσ(prim.)> = 1.6x10-5 mb
N() = NHexNγx<Δσ>xεx(BR)
= 4x1023x 1x107x 1.6x10-32x0.7x0.4 = 64 events/hour = 1500 events/day = 45,000 events/30 days
Will provide sub-percent systematic error