The neutrino reaction on 71 Ga: new measurement of the neutrino - PowerPoint PPT Presentation

The neutrino reaction on 71 Ga: new measurement of the neutrino response of 71 Ge from terrestrial neutrinos and of the 71 Ge EC Q-value PI’s: D. Frekers, H. Ejiri, V.N. Gavrin, M.N. Harakeh, J. Dilling Annika Lennarz 16. November 2011

Reviewing the issue Neutrino flux measured via the ` ν e , e − ´ 71 Ge-reaction 71 Ga ◮ expected rate after the SSM: ≈ 132 SNU ◮ detected rate (GALLEX/GNO): 67.6 ± 4 . 0 ( stat . ) SNU ◮ detected rate (SAGE): 65.4 +3 . 1 − 3 . 0 SNU Calibration with 51 Cr ( 37 Ar) terrestrial ν -sources (EC-decay) E ν [keV] transition BR 500 keV 3/2 − Q EC =232keV K-EC → 51 V g.s. 747.3 81.6 % 175 keV 5/2 − L-EC → 51 V g.s. 752.1 8.5 % 0 keV 1/2 − K-EC → 51 V ∗ (320) 3/2 − 427.1 8.95 % 71 Ga 71 Ge L-EC → 51 V ∗ (320) 432.0 0.9 %

◮ Origin of this discrepancy?! ◮ lower detector efficiencies? exp. source ratio ◮ neutrino cross section? 51 Cr-1 0.95 ± 0.11 GALLEX 51 Cr-2 0.81 ± 0.11 GALLEX ◮ unknown properties of neutrinos? 51 Cr SAGE 0.95 ± 0.12 37 Ar SAGE 0.79 ± 0.10 51 Cr, 37 Ar Average 0.87 ± 0.05 ◮ ratio: # of measured 71 Ge atoms normalized to # of calculated atoms ◮ average value ≈ 2.5 σ away from unity Bahcall: Contribution from excited states: 5.1 % 2 3 6 7 6 7 6 7 1 + 0 . 669 B 1 ( GT ) +0 . 221 B 2 ( GT ) ` 51 Cr − ν ´ ` 51 Cr − ν ´ 6 7 = σ 0 6 7 σ 6 B 0 ( GT ) B 0 ( GT ) 7 6 7 | {z } | {z } 6 7 4 0 . 028 0 . 146 5 | {z } 5 . 1%

� 71 Ge-reaction @ RCNP Extracting the B(GT)-strength via the 71 Ga � 3 He , t � µ k i N D στ | J στ | 2 B ( GT ) � 2 k f d σ ( q tr =0) = π � 2 d Ω GT 35 N D στ : distorsion factor yield x10 2 / 5 keV /msr yield x103/ 5 keV /msr 32 71 Ga( 3 He, t ) 71 Ge IAS | J στ | : volume integral 30 E = 420 MeV 24 16 25 E x [keV] J π GT B (GT) 8 20 0 g.s. 1/2 − 92 % 0.0852(40) 8.5 9 Ex[MeV] 15 175 5/2 − 40 % 0.0034(26) 10 500 3/2 − 87 % 0.0176(14) 5 0 0 1 2 3 4 5 8 12 16 20 24 28 Ex[MeV] d σ /d Ω฀ [mb/sr] d σ /d Ω฀ [mb/sr] d σ /d Ω฀ [mb/sr] 71 Ga( 3 He,t) 71 Ge E x = 175 keV E x = 500 keV g.s. 3/2 − g.s. 1/2 − 3/2 − 5/2 − 3/2 − 3/2 − 10 -1 GT 110 10 -1 132 134 122 112 10 -2 10 -2 GT GT 110 110 134 144 112 10 -2 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 θ c.m. [deg.] θ c.m. [deg.] θ c.m. [deg.]

Results Contribution from the excited states: 7.2 ± 2.0 % ◮ 175 keV: 2.7 ± 2.0 % ◮ 500 keV: 4.5 ± 0.35 % as opposed to 5.1 % taken by Bahcall ◮ discrepancy confirmed/slightly increased ◮ Contributions from the excited states do NOT resolve the discrepancy ⇒ What else could contribute? ◮ What about the Q EC value of 71 Ge? � 51 Cr = F ( atom ) · 1 � σ 0 ft ft ∝ Q 2 EC · t 1 / 2

How was the Q EC -value measured before?? All measurements in context of 17 keV ν ! EC is accompanied by (IB)-photon (1/10 4 ) 1. End-point spectrum is sensitive to neutrino mass 2. Q-value is determined by end-point energy ⇒ Q EC only side effect! PROBLEMS: 1. Extremely strong sources needed ( ≈ 10 10 - 10 11 Bq; (n, γ ) activation) 2. Use of external source ⇒ atomic excitations on the end-point energy! 3. Pile-up issues 4. background issues after activation?? 5. detector efficiencies need to be known precisely!

71 Ge Q EC -value by Lee et al. (1995) None of the internal bremsstrahlungs (IB)-EC expmts. were aimed at a precise determination of the Q EC -value!! IB-spectrum IB-spectrum data / fit data / fit “17 keV” neutrino “17 keV” neutrino Q EC -value: 232.65 ± 0.15 keV

71 Ge Q EC -value by DiGrigorio et al. (1993) effect of atomic excitations on the end-point energy?? IB-spectrum IB-spectrum Q EC -value: 232.1 ± 0.1 keV data / fit data / fit pile-up studies pile-up studies “17 keV neutrino” normalized to

71 Ge Q EC -value by Zlimen et al. (1991) Also search for 17 keV ν with report of 17 keV ν ⇒ unreasonable error/calculation unclear IB-spectrum IB-spectrum data / fit data / fit Q EC -value: 229.0 ± 0.5 keV

71 Ge Q EC -value measurement at TRIUMF’s TITAN experiment - New approach: mass measurement via cyclotron frequencies ◮ Trap experiment ◮ radioactive beam of 71 Ge ◮ mass measurement of 71 Ge and 71 Ga via cyclotron frequencies

TITAN - TRIUMF’s Ion Trap for Atomic and Nuclear science 1. Radioactive beam provided by ISAC 2. Transfer to EBIT (Charge breeding - creating highly charged ions) 3. Transfer to Penning trap (frequency determination via TOF measurement)

Principle of mass measurement with Penning Trap 1. Single ion injection ◮ ions oscillate with cyclotron 2. Confinement by B-field + frequency: electrostatic quadrupole field q 1 ν c = m · B 2 π 3. Lorentz force ⇒ oscillation ◮ Precision: with cyclotron frequency δ m m m ≈ √ 4. Trap opening & transfer of q · B · T RF N energy to E kin ( T RF : Excitation time) ⇒ TOF-measurement ⇒ Precision increases with charge state and number of measurements CAVEAT: HCI ⇒ increase of systematic effects: 1. HCI’s interact with residual gas; i.e. increased damping 2. ion-ion interaction (when more than 1 ion in trap)

EBIT - Electron-Beam Ion Trap produces and traps highly charges ions (HCI’s) using a high-current electron beam Helmholtz geometry 3 - 5 Tesla ◮ e − -gun, trap center, e − -collector ◮ injected ions are accelerated towards trap center & compressed by B-field ◮ radial confinement by e − beam space charge ◮ Ionisation by intense e − Electrostatic potential beam (500mA) the ions “feel” ◮ Ions are captured deeper in TRIUMF trap potential with every loss of e −

Novel approach: Production of 71 Ga and radioactive 71 Ge 3-step photoionization ◮ Ta-target + 50 µ A, 500 MeV proton beam (developed @ TRIUMF) ⇒ produce 71 Ga/ 71 Ge production rate ≈ 10 7 - 10 8 p/s Autoionisation ◮ beam 1: surface ionized 71 Ga IP 63713.24 cm -1 IP 63713.24 cm -1 λ = 780.82 nm λ = 780.82 nm ( ≈ 10 7 p/s) 51011.4392 cm -1 51011.4392 cm -1 4s 2 4p5p 4s 2 4p5p 1 S 0 1 S 0 ◮ beam 2: surface ionized 71 Ga + laser λ = 909.85 nm λ = 909.85 nm ionized 71 Ge ( ≈ 10 6 p/s) 40020.5604 cm -1 40020.5604 cm -1 ◮ Beam transport to EBIT 4s 2 4p5s 4s 2 4p5s 1 P o1 1 P o1 ◮ Charge breeding to neon-like charge states λ = 253.4 nm λ = 253.4 nm ⇒ beam 1: Ga 21+ ⇒ beam 2: two species: Ga 21+ and Ge 22+ 557.1341 cm -1 557.1341 cm -1 4s 2 4p 2 3 P 1 4s 2 4p 2 3 P 1 ◮ high purity and high isobaric mass TRIUMF separation due to HCI’s ◮ assurance of single ion injection (minimize ion-ion interaction) into MPET

Typical TOF-resonances for 71 Ga and 71 Ge Excitation frequency versus the TOF Minimum of the resonance corresponds to the cyclotron frequency TOF [ µ s] 7.50 7.00 TOF [ µ s] 71 Ga 21+ 71 Ge 22+ 5.70 (neon-like) 5.40 (neon-like) 3.90 3.80 Tex : 117 ms 2.10 2.20 Tex : 117 ms CenFrq ( 71 Ga 21+ ): 17622108.586 Hz Error (CenFrq) : 0.188 Hz CenFrq ( 71 Ga 21+ ): 16821032.974 Hz 0.30 0.60 Error (CenFrq) : 0.158 Hz TOFEff: 21.13 % Scans : 100 TOFEff: 23.44 % Scans : 100 -1.50 -1.00 -5 +3 +11 +19 -21 -13 -20 -12 -4 +4 +12 +20 frequency + 16.821.033 [Hz] frequency +17.622.108 [Hz] TRIUMF

Example฀for฀SOMA฀plot Calculation of atomic mass excess ⇒ Q EC -value m 1 = q 1 q 2 · ν 2 ν 1 · m 2 ◮ stable nucleus ( 71 Ga) as reference ( m 2 ) ◮ ⇒ mass measurement of 71 Ge ( m 1 ) ◮ accounting for ionisation energies of each species ◮ additional calculations with other references (also highly charged) ⇒ Q EC -value: 233.0 ± 0.6 keV (Preliminary!)

Double resonance ◮ additional effect: ion-ion interaction of 2 species Independent measurement of ◮ resonance-resonance Q EC -value with two species trapped interaction at the same time ◮ increased damping 8.00 tof [ µ s] 71 Ga 21+ ◮ Effect on Q-value? 71 Ge 21+ 6.90 ◮ ⇒ Further investigation 5.80 4.70 Center Frq ( 71 Ga 21+ ): 16821031.075 Hz 3.60 Error (CenFrq) : 0.356 Hz Diff. : -60.431 Hz Error (Diff.) : 0.755 Hz Tex : 78 ms 2.50 -53 -31 -9 +13 +35 +57 frequency + 16.821.000 [Hz] ⇒ Q EC -value: 234.8 ± 0.95 keV (Preliminary!)

Systematic studies requiring further investigation 1. effect of excitation time (up to 156 ms) on charge exchange and frequency 2. effect of resonance damping (caused by charge exchange with residual gas) 3. ion-ion interaction 4. effect of Lorentz steering 5. calibration: study of well known (few eV) reference masses (i.e. 16 O 5+ , 84 Kr 25+ , 26+ , N 4+ ) 6. relativistic q/m shift due to magnetic field ⇒ attempt to reduce systematic error and study of systematics

Consequences of Q EC -value measurement ft ∝ Q 2 EC · t 1 / 2 F.i.: If Q EC is ≈ 1 keV higher ⇒ ft-value ≈ 1 % higher � 51 Cr − ν � ⇒ phase space factor for B 2 (GT) ≈ 14 % lower ⇒ σ 0 slightly reduced ⇒ Only slightly reduced discrepancy Conclusion nuclear physics aspect of the neutrino cross section has been investigated with high precision 1. contribution from excited states: 7.2 % ± 2.0 % (5.1 % by Bahcall) ⇒ slightly amplifies the discrepancy 2. Q EC will be close to the value employed by Bahcall & reduces @ most contrib. from exct. states from 7.2 % to 6.5 % 3. new calculations of phase space factors required the observed discrepancy is NOT due to any unknowns in Nuclear Physics!!