ππ00-threshold measurements-threshold measurements((unpol. photonsunpol. photons))

► Date : Date : Sep-Oct 2007.Sep-Oct 2007.

► Ebeam: Ebeam: 450.0 MeV.450.0 MeV.

► EEγγ : : 130 – 420 MeV.130 – 420 MeV.

► NMR : NMR : 0.539456(run1), 0.539456(run1), 0.538114 (run2).0.538114 (run2).

σσtottot ( (γγ+p+pp+p+ππ00))runrun11 & SAID & SAID

σtot σtot * 1.05

σσtottot ( (γγ+p+pp+p+ππ00))runrun11 & SAID & SAID

two regions:

high & low Eγ

σσtottot at low & highat low & high E Eγγ

low Eγ: shift ~ -2 MeV high Eγ: shift ~ +4 MeV

Moeller scatteringMoeller scattering

Background for Moeller:Background for Moeller:Triplet ElectroproductionTriplet Electroproduction

σ ~ Z2

two electrons – in Tagger,

a positron – out.

Detection of Moeller electrons in TaggerDetection of Moeller electrons in Tagger

►Coincidence of two electrons:Coincidence of two electrons:

| T| T11 – T – T22 | < 1 ns | < 1 ns

►Difference of electrons energies:Difference of electrons energies:

| E| E11 - E - E22 |> 10 MeV |> 10 MeV

Moeller in TaggerMoeller in Tagger

6 MeV shift of Moeller peak6 MeV shift of Moeller peak

Tagger channel vs Moeller peakTagger channel vs Moeller peak

3.5 MeV shift3.5 MeV shift in 2007in 2007

Oct2007, 883 MeV Jul2007, 1508 MeV

2.3 MeV shift in Jun20042.3 MeV shift in Jun2004

((ππ00-threshold, linpol)-threshold, linpol)

radiator = Diamond

Ebeam = 450 MeV

Old Tagger measurementsOld Tagger measurements

Radiator = Diamond

Ebeam = 882 MeV

Jul04, Sep04, Dec95

shifted CB-data, SAID & MAIDshifted CB-data, SAID & MAID

Control region: 165 – 175 MeV

Shift: ~ 2 MeV

shifted CB-data & TAPS shifted CB-data & TAPS Dec95Dec95

TAPS-95 : A.Schmidt, Mainz

Fine step photon energies:

no Microscope,just change Tagger field

CB-data, SAID & MAIDCB-data, SAID & MAIDnear thresholdnear threshold

γ+pp+ξ( ξ γ γ )

Ethr=147.5 +/- 0.5 MeV

mξ=137.5 +/- 0.5 MeV

Investigation of TaggerInvestigation of Taggerwith Moeller scatteringwith Moeller scattering

►Tagger channels: Tagger channels: 1 – 352.1 – 352.►EEbeambeam: : 180, 450, 8180, 450, 88383, 1508 , 1508

MeV.MeV.►Radiator: Radiator: Diamond.Diamond.►Beam current: Beam current: 1nA, 10nA, 50nA.1nA, 10nA, 50nA.

AttenuationAttenuation length of NaIlength of NaI

PM

AmBe

Eγ=4.44 MeV

ΝαΙ

Attenuation length of NaIAttenuation length of NaI

PM

AmBe

Eγ=4.44 MeVAmBe

ΝαΙ