Photoreactions with tensor-polarized deuterium target at VEPP–3 I.A.Rachek Budker Institute of Nuclear Physics, Novosibirsk, Russia September 18, 2009 experimental approach two-body deuteron photodisintegration coherent pion photoproduction on the deuteron upgrade: almost-real photon tagging system • charge pion photoproduction → next talk I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 1
Experimental SetUp Method Method of Superthin Internal Target conception – in BINP first use – in BINP: VEP–1, VEPP–2, VEPP–3 later – in many Laboratories: electron storage rings: NIKHEF, Bates, HERA . . . ion rings: IUCF, CELCIUS, COSY . . . allows to increase substantially the efficiency of utilization of target material and beam particles, thus making feasible measurements: with exotic targets: polarized ones; of rare-isotopes, etc. with exotic beams: positrons, antiprotons, ions of isotopes etc. with slow or heavy or strong-ionizing reaction products. review of the method: S.G. Popov, Internal targets in storage rings of charged particles, Yad.Fiz. 62(1999)291 I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 2
Experimental SetUp Internal Polarized Target Atomic Beam Source Liquid He Liquid Nitrogen Turbo Pump S1–S5 – sextupole magnets MFT, SFT – RF-transition units IT – inlet tube 8 · 10 16 at/sec Flux of deuterium atoms Degree of tensor polarization > 98% Degree of vector polarization < 2% I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 3
Experimental SetUp Internal Polarized Target Storage Cell 30 m-thick aluminum foil µ covered by drifilm Gain over a jet target: 40 cm From ABS s K = 1 . 1 ( L / 2) 2 T jet To BRP D 2 T cell for our cell K ≈ 65 13mm e-beam Liquid Nitrogen 24mm New problems: depolarization in atom-wall collisions depolarization by mag. field of e-beam aperture limitation Solutions: special wall coating – drifilm mag. field strength >> H c = 117 Gs local modification of VEPP–3 beam optics I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 4
Experimental SetUp VEPP–3 storage ring VEPP–3 VEPP–3 parameters Electron energy E 0 2 GeV Mean beam current I 0 150 mA Energy spread ∆ E / E 0.05% RF HV magnitude U 72 0.8 MV VEPP-3 revolution period T 248.14 ns bunch length σ L 15 cm vertical beam size ∗ σ z 0.5 mm horizontal beam size ∗ σ x 2.0 mm vert. β -function ∗ β z 2 m horiz. β -function ∗ β x 6 m Injection beam energy E inj 350 MeV 1.5 · 10 9 s − 1 ˙ Injection rate I inj ∗ parameters in the center of 2nd straight section shift graph (beam current vs. time) Internal Target Area I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 5
Photodisintegration Introduction two-body deuteron photodisintegration Heavy hydrogen was chosen as the element first to be examined, because the diplon is the simplest of all nuclear systems and its properties are as important in nuclear theory as the hydrogen is in atomic theory. J. Chadwick and M. Goldhaber, Nature 134 (1934)237. γ p d n two-body deuteron photodisintegration ✞ ☎ γ + d → p + n ✝ ✆ PC T-matrix: n = 2 × 3 × 2 × 2 = 24 → 12 complex amplitudes; − − in total 2 n 2 = 288 various observables, but only 2 n − 1 = 23 are independent any such “set-of-23” must include tensor asymmetries. H. Arenh¨ ovel, W. Leidemann, E.L. Tomusiak, “Complete sets of polarization observables in electromagnetic deuteron breakup”, FBS 28(2000)147. I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 6
Photodisintegration Overview of theoretical models Theoretical models H.A.Bethe & R.Peierls, “Quantum theory of the diplon”, Proc. Roy. Soc. A148( 1935 )146 . . . E1-multipole only, simplest NN-potential V ( r ) = − V 0 δ ( r ) : = e 2 ( η − 1) 3 / 2 e 2 ( η − 1) 3 / 2 d σ BP σ BP ( ω ) = 8 π sin 2 θ, α 2 η 3 α 2 η 3 d Ω 3 where η = E γ / E b , α = √ M d E b , E b = 2 . 224 MeV M.Schwamb and H. Arenh¨ ovel, Nucl. Phys. A690(2001)682 M. Schwamb, habilitation thesis, Johannes Gutenberg-Universit¨ at at Mainz, 2006 static retarded coupled–channels approach: NN , N ∆, π NN π π π pion retardation in NN-potential and in MEC; π π π π π π mutual interactions between the involved π π three particles in the propagating π NN -system is taken into account π nonperturbatively π π π no free parameters with respect to deuteron photodisintegration, all π ρ/ω π parameters have been fitted in advance by ρ/ω considering other reactions. ρ/ω π ρ/ω ρ/ω π π From static approach to meson retardation MEC. I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 7
Photodisintegration Cross section Cross Section in case of polarized spin-1 target and unpolarized photon beam: ( r d Ω = d σ 0 d σ 3 4 P Z sin θ H sin φ H · T 11 ( E γ, θ CM 1 − ) p d Ω » 3 cos 2 θ H − 1 r 1 · T 20 ( E γ, θ CM + 2 P ZZ ) p 2 r 3 8 sin 2 θ H cos φ H · T 21 ( E γ, θ CM ) − p #) r 3 8 sin 2 θ H cos 2 φ H · T 22 ( E γ, θ CM + ) p P z = n + − n − – degree of target vector polarization Surface of constant density ρ = 0 . 24 fm − 3 in deuteron P zz = 1 − 3 · n 0 – degree of target tensor polarization H n + , n − , n 0 – population numbers for spin projections +1 , − 1 and 0 , respectively. P zz = -2 P zz = +1 I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 8
Photodisintegration Almost-real photon approach Almost–real photon approach Electro-disintegration Photo-disintegration orientation orientation plane plane H H k p ϕ H k p ϕ θ e → 0 CM θ p θ k θ lab e Q 2 → 0 E k γ γ H θ , θ H p θ n q CM θ n k scattering plane k n k n reaction plane reaction plane „ 1 − ρ L « ≈ T photo T electro for θ e ≈ 0 : · 2 M 2 M ρ T ξ = Q 2 ρ T = 1 η = tan 2 θ e ρ L = ξ 2 ; 2 ξ + η ; q | 2 ; | � 2 – 2 » 1 − r for small θ e : ρ L /ρ T = r (1 − r / 2) · θ e , where r = E γ / E e . = 1 ◦ and E γ / E e = 0 . 1 e.g. for θ cut δ T 2M / T 2M ≤ 10 − 3 e I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 9
Photodisintegration Particle Detector Detector Layout Neutron arm #2 Neutron arm #1 • 2 pairs of arms in vertical plane: veto counters arm I II θ p 20 ◦ -40 ◦ 55 ◦ -95 ◦ 127 ◦ -145 ◦ 68 ◦ -92 ◦ θ n ∆ φ 25 ◦ 19 ◦ • proton arm: drift chambers + 3 scintillator e-arm of LQ-polarimeter layers storage cell e • neutron arm: vertex chamber drift chamber DC1 thin veto-counter + thick drift chamber DC2 scintillator 3 scintillator 23.5x50x2 cm 3 scintillator 27.5x50x12 cm Proton arm #1 3 scintillator 35x50x12 cm Proton arm #2 I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 10
Photodisintegration Particle Detector neutron arms I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 11
Photodisintegration Separation of tensor observables Separation of T IM √ a T = σ + − σ − 2 zz σ + → c 0 T 20 + c 1 T 21 + c 2 T 22 Tensor asymmetry: P + zz σ − − P − c 0 ( θ H , φ H ) , c 1 ( θ H , φ H ) , c 2 ( θ H , φ H ) VEPP–3 (2003) 1 φ H = 180 ◦ θ H = 180 ◦ a 0 ∼ c 0 T 20 0.75 θ H = 54 . 7 ◦ a 1 ∼ + c 1 T 21 + c 2 T 22 0.5 0.25 θ H = 125 . 3 ◦ a 2 ∼ − c 1 T 21 + c 2 T 22 0 -0.25 → T 20 ∼ a 0 -0.5 -0.75 T 21 ∼ a 1 − a 2 -1 0 o 30 o 60 o 90 o 120 o 150 o 180 o T 22 ∼ a 1 + a 2 θ H 1 0.75 regime 0 regime 1 regime 2 0.5 H H 0.25 125.3 o H 54.7 o 0 -0.25 k γ k γ k γ -0.5 -0.75 -1 0 o 45 o 90 o 135 o 180 o 225 o 270 o 315 o 360 o φ H I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 12
Photodisintegration The Run Data taking run beam integral vs. time 4-month run: Oct-2002 – Jan-2003 200 electron energy 2000 MeV, mean beam current beam current integral [KCoulomb] 175 regime 0 62.3 kC 80 mA, total beam integral 200 KCoulomb regime 1 64.8 kC 150 regime 2 71.7 kC target thickness 3 × 10 13 at/cm 2 125 100 target polarization measured by the 75 LQ-polarimeter: P zz = 0 . 341 ± 0 . 025 ± 0 . 013 50 raw events collected: 37.5M 25 selected PD events: 540K 0 OCT-2002 NOV-2002 DEC-2002 JAN-2003 -3 -2 -1 0 1 event distributions: . . . vs. photon energy . . . vs. proton angle ARM2 25000 ARM2 ( Θ p =60 o ...95 o ) events per 5MeV 10 4 20000 events per 1 o 15000 ARM1 ( Θ p =20 o ...40 o ) 10 3 ARM1 10000 5000 10 2 0 20 o 30 o 40 o 50 o 60 o 70 o 80 o 90 o 100 o 110 o 0 50 100 150 200 250 300 350 400 450 500 cm E γ , MeV θ p I.A.Rachek Photoreactions with tensor-polarized deuterium target at VEPP–3 September 18, 2009 13
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