Measurement of the P-odd asymmetry of triton emission in the 6 Li(n, ) 3 Hreaction withcold polarized neutrons V. A. Vesna 1, Yu. M. Gledenov 2, V. V. Nesvizhevsky 3, A. K. Petukhov 3, P. V. Sedyshev 2, T. Soldner 3, E. V. Shulgina 1, O. Zimmer 4 1 Petersburg Nuclear Physics Institute of RAS, Gatchina, Russia. 2 Frank Laboratory of Neutron Physics, JINR, Dubna, Russia. 3 Institut Laue-Langevin, Grenoble, France. 4 Technische Universität, München, Germany The goal of experiment is to determine the value of the weak -meson-nucleon exchange constant f . Fundamental problems: Search for the neutral currents in the weak NN-interaction. Test of the validity of the meson exchange description of the weak NN-force. Interpretation of the P-odd observables in complex nuclei and in the eN scattering experiments. Electro-weak interaction at low energy as useful tools to study the strongly interacting limit of QCD.
One meson exchange model N N N N , , PVPC
Weak meson-nucleon coupling constants (in units of ): T = 0, 2 – charged currents T = 1 – neutral currents DDH – B. Desplanques, J. F. Donoughu, B. R. Holstein; DZ – V. M. Dubovik, S. V. Zenkin; FCDH - G. B. Feldman, G. A. Crawford, J. Dubach, B. R. Holstein; KM – N. Kaiser, U. G. Meissner. G. A. Lobov: f = 3.4∙10 -7
The PNC Constraints 18 F(1.081 MeV), P : -1.0∙10 -7 f 1.2∙10 -7 best values
P-odd effects in extremely light nuclei Cluster and multiclaster schemes for 6,7 Li, 9 Be, 10,11 B N. N. Nesterov, I. S. Okunev. JETPh Let. 48 (1988): P-odd asymmetry in the 6 Li(n, ) 3 H reaction with cold polarized neutrons. n + { d’} {n,d’} + Expected asymmetry size (with DDH best values):
Experiments 1 exp. (2002): 18 days main run; polarizer: 10 5 cm 2 exp. (2005): 48 days main run; polarizer: 8 8 cm; 3 exp. (2006): 25 days, 0-exp.; polarizer: 8 8 cm ILL, Grenoble, France PF1B instrument: n = 4.7 Å F n ~ (3 – 5)∙10 10 s -1
Experimental scheme – polarizer; 2 – resonance spin-flipper; 3 – ionization chamber; 4 – guiding field; 5 – beam-stop. p n - neutron momentum; n - neutron spin. Geometry of experiment: n || P n || P t : target plate is perpendicular to the beam axis. The accuracy of the alignment: < Spin-flipper state was changed every 1 s. Current method of event detection
Ionization chamber The detector is an assembly of ionization chambers placed in a cylindrical duralumin vessel. The entrance and exit 70 150 mm windows are zirconium foils of thickness 0.5 mm.
Ionization chamber The double ionization chamber: H – high-voltage electrode; C – signal electrode; T – target electrode. Distances: TC=CH=10.5 mm The working gas: Ar, p=2 at. Detector includes 24 identical double jonization chambers. PnPn nn The detector was designed as a two-channel system. The signs of investigated P-odd effect in the detector channels was opposite at synchronous measurements.
Targets max The lithium targets are 450 g/cm 2 layers of LiF (the enrichment with 6 Li of 95 %) with size of 140х60 мм. Lithium fluoride is evaporated onto 14 m aluminum foil and covered with the foil of the same thickness. Targets absorbed 60% of beam intensity. cos = 0.75
Circuit diagram of current signal preamplifier Feedback capacitance and resistance Input U const u PA switch Calibration signal input U const I det u +-+ I U converter: U out = I det R fb
Circuit diagram of the integrator K7K7 K6K6 K 10 Input Output to ADC K 6, K 7 - switches for the integration and reset of the integrator; K 10 – switch connecting the integrator and the ADC Programmable counter-timer card. Accuracy of the integrator key control signals is 2∙ Accuracy of the flipper state control signal is 2.5∙10 -7.
The electronics and data acquisition system Flowchart of control over an experiment and measurement of the current signals. Control computer ADC (ACL-8112pg) Counter-Timer (ACL 7120) Flipper control Interface controlling the integrator gates Interator Integrator D1 PA U U const U U c D2 Guiding field control
Reactor power fluctuations f, Hz Power of the reactor neutron flux fluctuation as a function of frequency
Data acquisition procedure -Values are measuring synchronously for each detector channel. 4 sequence values are jointed with a pattern: - A single measurement The N sequence single measurements are joined into series: N = 128.
Data acquisition procedure U c +, U c - - are recorded one time per series. U out = I det R fb K is an amplification coefficient of varying part of signal.
Compensation of the reactor power fluctuations Synchronous values L – compensation coefficient
Compensation of the the reactor power fluctuations Compensation coefficient is determined over a series meeting the requirement of minimal subtraction dispersion Method decreased the error in factor of 80.
Suppression of the apparatus asymmetries Main sources: signal of the flipper control; signals in the ground circuit; scattering electromagnetic fields of the working facilities B + /B - : 4 min. Pn Pn nn B+B+ B-B- Test of the system without the beam: noise = (1.7 2.4)∙10 -10
Suppression of the apparatus asymmetries
The left-right asymmetry: 6 Li(n, ) 3 H : lr = (1.06 0.04)∙10 -4
Test of LR-asymmetry Pn Pn nn PnPn
Constant components and LR-asymmetry vs. angle between neutron and proton momenta. , rad t, ~ 4.2 Averaged value -9.3 2.5 P-odd asymmetry coefficient vs. the angle between neutron and triton momenta Additional test of the LR-asymmetry t LR ~ [p n p t ] t PNC ~ p t
0-experiment 1. 8 Li, -, E max = 16.0 MeV, T 1/2 = 0.84 s, = -(0.08 0.01) F, -, E max = 7.0 MeV, T 1/2 = 11.0s, - ? Cl(n,p) 35 S, E p = 0.6 MeV, = -(1.5 0.34)· Al, Ar, N: , , , p - ? All targets were cloused by aluminum foils with the thickness of 20 m. 0 = -(0.0 0.5)
Results P PNC 00 PNPI0.66 -(5.4 6.0)∙10 -8 (2.0 1.7)·10 -8 ILL, PF1B0.66 -(8.1 3.9)∙10 -8 ILL, PF1B0.70 -(9.3 2.5)∙10 -8 ILL, PF1B0.70 (0.0 0.5)· (8.6 2.0)∙10 -8 (0.2 0.5)·10 -8
Results
Measurements of the P-odd asymmetry of emitted -quanta in the 10 B(n, ) 7 Li* 7 Li+ (E = MeV) Expected value = 5.2 (DDH) Result of 2 previous runs: = (5.1 3.8) 10 -8, “0-experiment”: 0 = -(0.7 3.7)