INSTITUT MAX VON LAUE - PAUL LANGEVIN Measurement of parity-violating asymmetries in the reactions of light nuclei with polarized neutrons ( 6 Li, 10 B) 1.Motivation Li(n,  ) 3 H B(n,α) 7 Li*→γ→ 7 Li(g.s.) 4.Analysis. 5.Conclusions.

INSTITUT MAX VON LAUE - PAUL LANGEVIN Motivation. The choice of nuclei. The basic motivation consists in the measurement of a contribution of the weak neutral current into neutron-nuclear interaction. 1) Light nuclear → feasible (probably) theoretic interpretation. 2) Large interaction cross-sections → small false effects. 3) Large relative contribution of the weak neutral currents. 6Li(n,  )3H. 10B(n,α)7Li*→γ→7Li(g.s.) Small absolute asymmetry values (~10 -8 ) → severe limitations in terms of statistics and false effects. 1) the most intense neutron beams. 2) the (electric) current detection method instead of counting each event.

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)] Measurement of the parity-violating triton emission asymmetry in the reaction 6 Li(n,  ) 3 H with polarised cold neutrons. V. A. Vesna 1, Yu. M. Gledenov 2, V. V. Nesvizhevsky 3, A. K. Petoukhov 3, P. V. Sedyshev 2, T. Soldner 3, O. Zimmer 3,4, E. V. Shulgina 1 1 Petersburg Nuclear Physics Institute RAS, Gatchina, Leningrad Reg., Russia 2 Joint Institute for Nuclear Research, Dubna, Moscow Reg., Russia 3 Institut Laue-Langevin, F Grenoble Cedex 9, France 4 Physik-Department E18, TU München, D Garching, Germany VVR-M reactor at the PNPI, Gatchina, Russia (vertical channel) PF1B instrument at the ILL The average neutron wavelength is n = 4.7 Å The total neutron flux is F n ~ (2 – 5)∙10 10 s -1

INSTITUT MAX VON LAUE - PAUL LANGEVIN Contribution from  -exchange ~75%,  n  =760 b at E th 6 Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)]

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)] 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 The ionization chamber The detector is an assembly of ionization chambers placed in a cylindrical duralumin vessel. The entrance and the exit 70  150 mm windows are zirconium foils with the thickness of 0.5 mm. [Yu. M. Gledenov et. al. NIM A350 (1994) 517. ]

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)] The experiment scheme

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)] The detector consists of 24 identical double ionization chambers.

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)] The left-right asymmetry The P-odd asymmetry coefficient values measured for 3 angles between the neutron momentum and the chamber axis at the ILL The contribution of the left-right asymmetry to the measurement of the P-odd effect is smaller than the statistical uncertainties. [N.V. Borovikova et al., JETP Letters, 30(8) (1979) 495.]

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)] Flipper state: "+" OFF "-" ON Integration U1U1 U3 U3 U2U2 Reading of integrators U4U4 U1U1 T0T0 T1T1 T Single measurement  4T 1.Two-channel system. 2. Linear drift compensation. 3. Compensation of the reactor power fluctuations. 4. Reversal guiding neutron spin magnetic field at the detector.

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)] A typical variable component of the electrical signal at the entrance of the integrator as a function of time for two detectors

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)]

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)] A B C D  2 = 22, n=19  2 = 19.7, n=15

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)] A B C D  2 = 14.4, n=11  2 = 17.6, n=14

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)]

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)]

INSTITUT MAX VON LAUE - PAUL LANGEVIN Li(n,  ) 3 H [V.A. Vesna et al, Phys. Rev. C 77, (2008)]

INSTITUT MAX VON LAUE - PAUL LANGEVIN B(n,α)7Li*→γ→7Li(g.s.) V. A. Vesna, Yu. M. Gledenov, P. V. Lebedev, Stepanov, I. S. Okunev, A.V. Sinykov, Yu. M. Tchuvilsky, E. V. Shulgina.Phys. At. Nucl. 62 (1999) 522; S. Yu. Igashov, A. V. Sinykov, Yu. M. Tchuvilsky. In: Proc. ISINN-11. Dubna 2003, 34 a LR  0 The modern formalism of RGM was used on the solution of Schroedinger equation. P-odd asymmetry in the  -emission by the de-excitation of the 1st excited state of 7 Li for the reaction 10 B(n,  ) 7 Li* with polarized neutrons. Expected value   = 1.1  (DDH), contribution from  -exchange ~66%  n  =3940 b at E th

INSTITUT MAX VON LAUE - PAUL LANGEVIN B(n,α)7Li*→γ→7Li(g.s.)

INSTITUT MAX VON LAUE - PAUL LANGEVIN B(n,α)7Li*→γ→7Li(g.s.) The experiment scheme

INSTITUT MAX VON LAUE - PAUL LANGEVIN B(n,α)7Li*→γ→7Li(g.s.) Results Result of 3 previous runs:  P-odd = (2.9  2.7)  10 -8, Preliminary result of “0-experiment”:  0 = (2.1  2.8)  st + 2 nd Experiments (ILL, ): Main run:  P-odd = + (2.7  3.8)  d Experiment (ILL, 2007): Main run :  P-odd = + (3.1  3.8)  Preliminary result taking account the “0-experiment”:  P-odd = (0.8  3.9)  f  = (-1.5  2.4)  or f   2.4  (90% confidence level)

INSTITUT MAX VON LAUE - PAUL LANGEVIN _______________________________________________ a P-odd = (-8.8  2.1)  10 -8, f   1.1  (90%) (without 0-test) (with 0-test), f   2.6  (90%) _______________________________________________ a P-odd = (-0.8  3.9)  10 -8, f   2.4  (90%) Summary

INSTITUT MAX VON LAUE - PAUL LANGEVIN 18 F 6 Li 10 B pp pp np "Best values" Summary

INSTITUT MAX VON LAUE - PAUL LANGEVIN 1.We measured non-zero P-odd asymmetry of the triton emission in the reaction 6 Li(n,  ) 3 H with cold polarized neutrons. 2.A sensitivity of our measurement is as high as 2.1  It is achieved for the first time in neutron experiments. 3. The estimated value of f  coupling constant is small, close to that obtained in the 18 F measurements. 4.Thus, the neutral weak currents in the nucleon-nucleon interactions at low energy have not yet been observed. 5.The measurement of the P-odd asymmetry of  - quanta emission in the 10 B(n,  ) 7 Li*  7 Li+  reaction will continue. 6. The analysis of the 6 Li and 10 B results allows one to extract the h  0 coupling constant and to obtain stronger bounds on the f  constant. Summary