1a. gasparianhall d, march 7, 20081 primakoff experiments at 12 gev with gluex a. gasparian nc...

1A. Gasparian Hall D, March 7, 2008 1

Primakoff Experiments at 12 GeV with GlueX

A. GasparianNC A&T State University, Greensboro, NC

For the PrimEx Collaboration

Outline

The project and physics motivation: The first experiment @ 6 GeV: 0 lifetime

Development of precision technique Results for 0 lifetime

Experiments @ 12 GeV with GlueX Summary


The PrimEx Project at JLabThe PrimEx Project at JLab

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


Physics Motivation

Fundamental input to Physics:

precision test of chiral anomaly predictions determination of quark mass ratio -’ mixing angle 0, and ’ interaction electromagnetic radius is the ’ an approximate Goldstone boson?

4

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%

5

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→

6

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→


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.

)log(

2

2Pr

4Pr

2

2

Pr

EZd

Ed

dE

m

peak

peak

8

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, UResult: (0)=(7.920.42) eV

5.3%

All previous experiments used: Untagged bremsstrahlung beam Conventional Pb-glass calorimetry

9

PrimEx Experiment at Hall B

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

10

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

11

Fit to Extract 0 Decay Width:

Γ(0) 7.93 eV 2.1%(stat.) 2.0% (syst)

12

PrimEx Current Result

() = 7.93eV2.1%2.0%

0

Deca

y w

idth

(eV

)

±1.%

13

Estimated Systematic Errors Type of Errors Errors in current data Expected errors from

2nd run

Photon flux 1.0% 1.0%

Target number <0.1% <0.1%

Background subtraction 1.0% 0.4%

Event selection 0.5% 0.35%

HYCAL response function 0.5% 0.2%

Beam parameters 0.4% 0.4%

Acceptance 0.3% 0.3%

Model errors (theory) 1.0% 0.25%

Physics background 0.25% 0.25%

Branching ratio 0.03% 0.03%

Total 2.0% 1.3%


PrimEx @ 12 GeVPrecision 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


Physics Outcome from Experiment

Corr. )( ..0 meKKmm

)(2

1ˆ re whe,

22

222

duud

s mmmmm

mmQ

ΓΓ((ηη→→33)=)=ΓΓ((→→))××B.B.R.R.

- ’ mixing angle

light quark mass ratio


Primakoff Method

22

..4

43

3

2Pr

3

sin)(8

QFQ

E

m

Z

d

dme

ρ,ω


12C target

Primakoff

Nucl. Coherent

Interference

Nucl. Incoh.

17

)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 12 GeV?


Experiment with GlueXAdvantages:

High energy tagged photon beam Eγ=10 – 11.5 GeV High acceptance electromagnetic calorimeter (FCAL) Solenoid detector to veto charged particles, and reduce background on FCAL Targets (~1-5% R.L.):

LH2, LHe4, solid 12C

Challenges:

Photon flux stability and control: possible solutions:

e+e- pair spectrometer; Compton scattering;

High resolution FCAL needed for precision experiments: possible solution:

Pb-glass + PbWO4 crystals


FCAL Geometrical Coverage Forward Calorimeter FCAL (~2800 Pb-glass blocks

Radius = 120 cm: Central beam hole3x3 blocks removed (12x12 cm2)

FCAL has a good coverage for the forward → production


Geometrical Acceptances Forward Calorimeter FCAL (~2800 Pb-glass blocks

Radius = 120 cm: Central beam hole: 3x3 blocks removed (12x12 cm2)

A good geometrical acceptance can be reached for L = 6-9 m for η forward production angles needed for the experiment


Experimental Resolutions (prod. angle) Precision cross section measurement requires high resolutions in: luminosity (flux + target) production angle (for fit); invariant mass (background) …

FCAL with all Pb-glass

FCAL with Pb-glass andPbWO4 crystal insertion(75x75 blocks(150x150 cm2)


Experimental Resolutions (inv. mass)

FCAL with all Pb-glass

FCAL with Pb-glass andPbWO4 crystal insertion(75x75 blocks(150x150 cm2)


Experimental Resolutions (production angle vs. beam spot size)

Photon beam size up to 5 mm,as it is designed, seams reasonable


Experimental Resolutions(production angle vs. target length)

Reaction vertex can not be reconstructed in this experiment (recoil energies are too small T< 1 MeV)

Large size of the FCAL calorimeterprovides longer target to FCAL distance

That makes less sensitivity from the target length up to designed 30 cm liquid targets

25

Luminosity Control: Pair Spectrometer

Scint. Det.

Measured in experiment:

absolute tagging ratios: TAC measurements at low intensities

Uncertainty in photon flux at the level of 1% has been reached

Verified by known cross sections of EM processes

Compton scattering e+e- pair production

relative tagging ratios: pair spectrometer at low and high intensities

26

Luminosity Control: Pair Production Cross Section

Theoretical Inputs to Calculation:

Bethe-Heitler (modified by nuclear form factor)

Virtual Compton scattering

Radiative effects

Atomic screening

Electron field pair productionExperiment/Theory = 1.0004

27

Verification of Overall Systematics: Compton Cross Section

4.9 5.0 5.1 5.2 5.3 5.4 5.5

Energy (GeV)

0.055

0.060

0.065

0.070

0.075

0.080

0.085

Systematic Uncertainty

P R E L I M I N A R Y

Uncertainties:StatisticalSystematic

Compton Forward Cross Section

Klein-NishinaPrimex Compton Data

4.9 5.0 5.1 5.2 5.3 5.4 5.5

Energy (GeV)

-10

-5

0

5

10

Devi

atio

n (%

)

P R E L I M I N A R Y

Uncertainties:Statistical

Experiment To Theory Comparison

No DeviationExperiment / Theory Average stat. error:

0.6% Average syst. error: 1.2%

Total: 1.3%

Δσ

/ΔΩ

(m

b/6

.9 m

sra

d)

e e

Data with radiative corrections

28

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

29

Statistical

Target thickness

Photon flux

Acceptance misalignment

Background subtraction

Beam energy

Distorted form factor

Nuclear coherent contr.

Branching ratio

Total

0.5%

1.0%

1.0%

0.5%

0.4%

0.2%

0.3%

0.5%

0.8% (PDG)

2.0%

Estimated Error Budget


Summary

A state-of-the-art high resolution experimental setup has been designed, developed and constructed for the 6 GeV run.

New proposal for the 1.4% accuracy in Γ(0) has been approved for the second 6 GeV run.

PrimEx collaboration has developed an experimental program to perform precision test of chiral symmetry and anomaly effects in the light pseudoscalar meson sector.

The first experiment, the 0 lifetime measurement has been successfully performed in Hall B in 2004. Preliminary result: Γ(0) 7.93 eV 2.10%(stat.) 2.0%(syst.)

Reach experimental program for η, η’ widths measurements has been developed and approved by high energy PACs. These precision experiments can be performed with the upgraded GlueX experimental setup at 12 GeV.


The End


The Primakoff Effect

22

..4

43

3

2Pr

3

sin)(8

QFQ

E

m

Z

d

dme

ρ, ω



PbWO4 Energy Resolution

6 x 6 crystalsE/E = 1.3 %

1 x 1

3 x 3


PbWO4 Position Resolution

x = 1.3 mm


Experimental Setup Development: Pair Spectrometer

Pair spectrometer was designed for relative photon flux monitoring at high beam intensities:

Combination of: 16 KGxm dipole magnet 2 telescopes of 2x8

scintillating detectors

Dipole

Precision cross section measurements need control of photon flux at 1% level

e-

e+

HYCAL

Photon beam

Scint. Det.


(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%

1a. gasparianhall d, march 7, 20081 primakoff experiments at 12 gev with gluex a. gasparian nc...

Documents

bremsstrahlung beam

primakoff effect slide

primakoff method

gev proton beam

primex experiment

gasparianhall d

gev targets c

gluex summary slide