STUDY OF nn-interaction IN nd- AND dd-reactions

Transcription

1 INTERNATIONAL SEMINAR ISINN Dubna, Russia, May 22 26, 2017 STUDY OF nn-interaction IN nd- AND dd-reactions E.Konobeevski 1, A.Kasparov 1, V.Lebedev 2, M.Mordovskoy 1, A.Spassky 2, S.Zuyev 1 1 Institute for Nuclear Research, Russian Academy of Sciences 2 Skobeltsyn Institute of Nuclear Physics, Moscow State University

2 NN-Interaction pp and np Interaction A huge amount of data on pp and np interactions has been accumulated. Careful analysis of these data led to constructing NN interaction potentials describing vast majority of experimental data. nn Interaction The situation around neutron neutron interaction is more ambiguous. Because of the absence of neutron target, data on this interaction are obtained primarily from reactions with two neutrons in the final state. But in many cases, there are serious discrepancies between available experimental data and the results of the current precise calculations on the basis of Faddeev equations. 2

3 Unresolved Problems in Nd-breakup nd- and pd-breakup in SS-configuration nn-quasifree scattering Experimental CS for pd- and nd- breakup differ greatly while the theoretical CS are almost identical and do not agree with the experimental data Experimental CS for nn-qfs exceed theoretical estimates by about 18%. At the same time, the theory describes well the CS obtained for np QFS The analysis performed by several authors showed that theoretical results remain quite stable using different standard NN-potentials and introducing modern three-nucleon forces 3

4 Data on proton-proton and neutron-neutron scattering lengths The results obtained by now testify significant uncertainty of a nn Neutron values Proton-proton - which neutron are clustered scattering near length -16.3±0.4 is determined (Bonn) and from using -18.5±0.4 the mostly pp- n+d p+n+n fm scattering (TUNL, and LAMPF), (a - pp +d =-17.3±0.4 so +n+n there reactions fm); is even its accuracy uncertainty and investigating is about mainly the connected sign region of of the n-n the with FSI difference model-dependent where dependent two a nn -a neutrons pp which corrections fly is a together measure of Coulomb with of CSB small effects relative energy 4

5 3 He(ppn) and 3 H(nnp) Systems Two protons in 3 He are mainly in opposite spin states Two neutrons in 3 H are also in a spinsinglet state 3 He n p p 3 H n p n Strong discrepancies observed in Nd-breakup can be explained by a significant strengthening of nn- and ppcorrelations of attractive character in the third nucleon field. 5

6 Dibaryon Model (Kukulin et al) New mechanism arising in the Dibaryon Model: New force meson exchange between the nucleon and dibaryon Nd or t ( 3 He) dd D + D n+n+p+p Our plans: study of nd p+nn, nt d+nn and dd pp+nn and. In these reactions nn-correlated pair can be produced dynamically in the intermediate state. Thus, measured nn-correlation, in particular energy of nn virtual singlet state, may be different from those inherent for the free NN-systems.

7 Determination of nn-virtual Virtual-State Energy and Scattering Length in n + 2 H n + n + p Reaction 7

8 nd Breakup Reaction Setup for Determination nn-scattering Length FSI ε=(e n1 +E n2 2(E n1 E n2 ) 1/2 cosδθ)/2 dn d WM E nn Neutron beam is produced in the beam stop of INR proton accelerator A CD 2 disk (~ 100 mg cm 2 ) is used as the scattering target. Registration in coincidence of one proton and two neutrons Protons are detected by a plastic detector located at 75 6 Neutrons are detected by a six-detector hodoscope at Energies of secondary neutrons are determined by a TOF technique Incident neutron energy and p are reconstructed from kinematics 8

9 Experimental and simulated dependences N( ) for various values of E nn ; = 6º, E 0 = 40 ± 5 MeV N, events a nn m E E nn = 170 kev E nn = 130 kev E nn = 80 kev 1/ 2 n nn mnenn 2 nn 2 1 r , MeV The best fit is obtained for E nn = 129 ± 14 kev.

10 Determination of E nn from 2 versus E nn curve = 6º; E 0 = 40 ± 5 MeV 2 value for 2 experimental 2 and theoretical points is given by the expression эксп мод dn ( ) dn ( ) A 2 d 2 min+1 d ( a nn) эксп 2 dn ( ) d where A is the normalization coefficient, determined as the ratio of the integrals of the experimental and theoretical spectra over a wide range of (0 0.8 MeV), and dn эксп ( ) d is the statistical error of experimental points. The values of 2 (E nn ) are approximated by a quadratic polynomial. The minimum of the curve determines E nn. Statistical uncertainty E nn is given as 2 E nn E nn = 129 ± 14 kev a nn = ± 0.9 fm 10

11 Determination of nn-virtual Virtual-State Energy and Scattering Length in d + 2 H (nn) S + (pp) S n+n+p+p Reaction 11

12 Simulation of d + 2 H 2 n s + 2 p s Reaction; E d = 15 MeV Output parameters: Θ p1 =Θ p2 =27 ; Θ n =36 (red areas) Corresponding energies: E( 2 p)~6 MeV; E( 2 n)~4 MeV

13 Simulation of d + 2 H n + n + p + p Reaction: E d = 15 MeV, p1 = 27º, p2 = 27º, n1 = 36º E n1 vs E n2 E nn Spectrum E nn = [E 1 + E 2 2(E 1 E 2 ) 1/2 CosΔΘ] / 2 For democratic breakup two neutrons can have a relative energy in the range MeV

14 Simulation of d + 2 H n + n + p + p Reaction: E n1 vs E n2 E nn Spectrum Democratic breakup Democratic breakup E nn = 120 kev, nn = 50 kev E nn = 120 kev, nn = 50 kev This structure in spectrum is due to the fact that to reach detector, installed at angle of emitting nn-system in two-body reaction, may only breakup particles emitted in c.m. system in forward or in backward direction 14

15 Simulation of d + 2 H n + n + p + p Reaction: Different Energies of Singlet State E nn = 50 kev, nn = 30 kev E nn = 200 kev, nn = 100 kev E nn = 120 kev, nn = 70 kev The distance between peaks depends on the excitation energy (excess mass of two-nucleon system over the sum of masses of its constituents) 15

16 Simulation of d + 2 H n + n + p + p Reaction: Different Widths of Singlet State; E nn = 120 kev nn = 110 kev nn = 70 kev nn = 20 kev One The can shape see that of time the spectra change of is sensitive the state to width values affects of the mainly state energy on degradation and width, of "valley" that will between allow us to the peaks determine and on a slight these shift quantities of the from peak a with comparison larger time of experimental to the middle data of distribution. and simulation results 16

17 Experimental: Setup for Study d + 2 H p+p+n+n E d = 15 MeV Conditions: 15 MeV deuteron beam of U120 cyclotron of SINP MSU CD 2 -target p- and n-detectors are set at angles of 2 p and 2 n emitting both protons are detected in one E-E telescope n-detector at 83 was used for timing calibration in dd 3 He+n reaction

18 Experimental E-E E Plot and Simulated Plot for Two-Proton Events Selecting events on p+p region and determining the neutron time of flight for these events we obtained neutron timing spectrum 18

19 Experimental: Neutron Time-of-flight flight Spectrum vs Simulated events ns 19

20 2 -Fitting on nn for Different E nn 2 ( E nn, nn ) t N th E, nn nn ( t) AN N exp ( t) exp 2 ( t) 2 20

21 2 -Fitting over E nn Dependence of 2 on E i nn. E nn = 76 ± 6 kev a nn = ± 0.6 fm To determine E nn the dependence of minimum value on Еnn was fitted by a quadratic polynomial. The minimum value of 2 determines the most probable value of the quasibound state energy. Error in determining E nn is given as E 2 ( ) E 2 ( 1) The minimum value of the polynomial is achieved at E nn = 76 kev, E nn = ± 6 kev nn E nn min nn min 21

22 -ann (fm) (fm) Analysis of a nn data obtained in nd- and dd-breakup a nn m E 1/ 2 n nn mnenn 2 nn 2 1 r 2 ann=(15.5+/- 0.13) /r^1,9 Xi2/N= R с ( E 1 Q)( M 3 M 4 ) M 3 M 4 E M Year R (fm) For each experiment we introduced parameter R which corresponds to distance between nn pair and proton (or diproton in dd experiment) for arbitrary time interval

23 The neutron-neutron 1 S 0 scattering length a nn has been determined from a kinematically complete nd breakup experiment at E n = 40 MeV. The values of a nn = 16.6 ± 0.9 fm and E nn = 129 ± 14 kev were obtained performing the shape analysis of the FSI dependence of reaction yield on relative energy of nn pair. For the first time, in d+ 2 H 2 n S + 2 p S n+n+p+p reaction the energy of virtual state of 2 n-system and nn-scattering length were determined - E nn = 76 ± 6 kev; a nn = ± 0.6 fm. The obtained values of scattering lengths were compared with experimental values of 1 S 0 nn-scattering length obtained in nd-breakup reaction. One can conclude that the difference in the scattering lengths obtained under different kinematic conditions can be explained by the influence of 3N-forces depending on the relative velocity between the nn-pair and the charged fragment. clusions

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25 E fast 2D-Plot E-E fast

26 Experimental 2D-plot E-E de d p p? d? E

27 Summary We investigated d+ 2 H 2 n S + 2 p S n+n+p+p reaction, passing through a formation in the intermediate state of dineutron and diproton singlet pairs. For the first time, in a kinematically complete experiment the energy virtual state of 2n-system is determined. The energy of the state is determined by comparing the experimental TOF spectrum of neutrons from breakup of this state with simulated spectra depending on this energy. The obtained value E nn = 76 ± 6 kev was compared with experimental values of 1 So nn-scattering length obtained in nd-breakup reaction. One can conclude that the difference in the scattering lengths obtained under different kinematic conditions can be explained by the influence of 3N-forces depending on the relative velocity between the nn-pair and the charged fragment.

28 E fast Experimental 2D-plot E-Ef Ef (400 μm) 1-2 полное поглощение, пролет 1 d p 2 p,d 3

29 E fast Experimental 2D-plot E-Ef Ef (400 μm) 1-2 полное поглощение, пролет 2 3

30 E-E: E: пролетный локус (2-3) de E

31 E fast Experimental 2D-plot E-Ef Ef (400 μm) 1-2 полное поглощение, пролет 1 d p 2 p,d

32 de-e: E: полное поглощение (1-2) de d p E

33 PSD: n-γ разделение (EJ-301) PSD n E

34 PSD - Spectrum N n PSD

35 Предварительные результаты по эксперименту dp ppn Проведено моделирование реакции dp ppn Отлажена детектирующая система ( E-E и n-детекторы) Отлажена методика выделения p+n событий Начат набор статистики

36 Experimental Spectrum vs Simulated 36

37 Analysis: Fitting Procedure

38 Simulation of d + 2 H n + n + p + p Reaction: Democratic vs Quasibound state E nn = 120 kev, nn = 50 kev Democratic breakup Simulated time-of-flight spectra of neutrons: 1 for events of democratic breakup, 2 for events with E nn = 120 kev, nn = 50 kev. Neutron timeof-flight base 0.79 м. 38

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45 Space Star (SS) Anomaly SS Anomaly was first found in 1989 in nd breakup reaction at 13 MeV. E N =13 MeV ~30% nd exp. Erlangen & TUNL (1989) (1996) ( ) nd calc. ( ) Space Star (c.m. system) Space Star pd exp. Koeln (1991) 90 J.STRATE et al., Nucl. Phys. A501 (1989) 51 H.R.Setze et al., Physics Letters B388 (1996) 229 G.RAUPRICH et al., Nucl. Phys. A535 (1991) 313 equilateral triangle In Star configuration, outgoing 3 nucleons have the same energy and form an equilateral triangle. In Space Star (SS), the star plane is perpendicular to the beam axis in c.m. system. 31 August th International IUPAP Conference on Few-Body Problems in Physics 45

46 The Search for for NN-Correlations in 3N-Systems In 3 He neutron causes a correlation of two protons leading to an appearance of quasibound 1 S 0 diproton state In 3 H proton causes a correlation of two neutrons leading to an appearance of quasibound 1 S 0 dineutron state 3 He 2 He n n p p p p p p 3 2 n H n p p n n n Removal of proton from 3 H and/or neutron from 3 He provide conditions advantageous for NN-correlations to search 46

47 Space Star (SS) Anomaly in pd breakup pd calc. were made by Deltuva et al. and by Ishikawa. pd calc. by Deltuva et al. (2005) E N =13 MeV nd calc. ~15% pd exp. Koeln( )& KUTL( ) (2002) E N =13 MeV ~30% Space Star nd exp. Erlangen & TUNL (1989) (1996) ( ) nd calc. pd exp. Koeln (1991) ( ) A.Deltuva et al., PRC72, (2005) J.STRATE et al., Nucl. Phys. A501 (1989) 51 H.R.Setze et al., Physics Letters B388 (1996) 229 G.RAUPRICH et al., Nucl. Phys. A535 (1991) 313 At pd SS, exp. cross section is smaller than pd calc. At nd SS, exp. cross section is larger than nd calc. 47

48 Our Preliminary Results of d+d 2 He+2n Neutron TOF TOF Base 1 m N Experiment: 2He 2He =27 ; n =36 Simulation: E nn = 80 kev T n Spectrum t, ns

49 The Search for NN-Correlations Результаты кинематического моделирования реакции d + 2H 2 n s + 2 p s двумерные диаграммы 2n - 2p (a) и E 2n -E 2p (б), где 2n и 2p углы вылета, а E 2n и E 2p энергии двухнейтронной и двухпротонной систем. Красные области соответствуют вылету системы 2 p s под углом 27 ±

50 nd-breakup configurations and unresolved problems 50

51 Modification of 1 S 0 nn force H. Witala & W. Gloeckle suggested V nn ( 1 S 0 ) = λ V CDBonn ( 1 S 0 ) nn 25MeV H. Witala & W. Gloeckle, Phys. Rev. C83, (2011) =1.08 No arguments for this modification X.C.Ruan et al., Phys. Rev. C 75, (2007) 51

52 Kinematical curves for FSI geometry in nd-breakup E 0 = 40 5 MeV, n1 = -36º, p = 75º 1-neutron, 2-proton 1-neutron 3-neutron E 2 E S E E 1 FSI E 13 =ε= (E 1 + E 2 2(E 1 E 2 ) 1/2 cosδθ)/2 0, 1 2 3N Faddeev equation d d 1 d 3 ds WM-approximation dn d WM 0 INR RAS 2012 E FSI E 1 E 1-3 E FSI

53 -ann (fm) nn- и pp -длины рассеяния Year

54 Charge Independence and Charge Symmetry of Nuclear Forces pp and np Interaction A huge amount of data on pp and np interactions has been accumulated. Careful analysis of these data led to constructing NN interaction potentials describing vast majority of experimental data. nn Interaction The situation around neutron neutron interaction is more ambiguous. Because of the absence of neutron target, data on this interaction are obtained primarily from reactions with two neutrons in the final state. But in many cases, there are serious discrepancies between available experimental data and the results of the current precise calculations on the basis of Faddeev equations. 54