Measurement of the neutron-neutron scattering length<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>a</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">nn</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>with the reaction<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">−</mml:mi></mml:mrow></mml:msup></mml:mrow>

Schöri, O.; Joseph, C.; Perroud, J. P.; Ruegger, D.; Trân, M. T.; Truöl, P.; Winkelmann, E.; Dahme, W.

doi:10.1103/physrevc.35.2252

Cited by 65 publications

(32 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, the lack of stable A = 5 and A = 8 nuclei is often cited as the explanation for the dearth of nuclei formed with masses above helium-4 though the endothermicity of pure strong reactions such as 4 He(T, n) 6 Li, 4 He( 4 He, p) 7 Li and 4 He( 4 He, n) 7 Be plays a role. * Electronic address: Jim˙Kneller@ncsu.edu † Electronic address: Gail˙McLaughlin@ncsu.edu The focus in this paper is upon another nucleus that could also become stabilized -the dineutron 2 n. The dineutron, a member of the nucleon-nucleon isospin triplet, is a spin singlet and, by itself, the dineutron is weakly unbound 1 by ∼ 70 keV, the n-n scattering length being negative [40,41,42,43]. Early direct searches [44] did not see evidence for a stable dineutron but recently Bochkarev et al [45] claim that 45 ± 10% of the decay of an excited state of 6 He is through the dineutron state 2 and Seth & Parker [47], amongst others, find evidence for dineutrons in 5 H, 6 H and 8 He decay.…”

Section: Introductionmentioning

confidence: 99%

Effect of bound dineutrons upon big bang nucleosynthesis

Kneller

McLaughlin

2004

Phys. Rev. D

View full text Add to dashboard Cite

We have examined the effects of a bound dineutron, 2 n, upon big bang nucleosynthesis (BBN) as a function of its binding energy B2 n . We find a weakly bound dineutron has little impact but as B2 n increases its presence begins to alter the flow of free nucleons to helium-4. Due to this disruption, and in the absence of changes to other binding energies or fundamental constants, BBN sets a reliable upper limit of B2 n 2.5 MeV in order to maintain the agreement with the observations of the primordial helium-4 mass fraction and D/H abundance.PACS numbers: 99.99

show abstract

Section: Introductionmentioning

confidence: 99%

Effect of bound dineutrons upon big bang nucleosynthesis

Kneller

McLaughlin

2004

Phys. Rev. D

View full text Add to dashboard Cite

show abstract

“…Unfortunately, nn scattering is only poorly known experimentally. There is only one datum for the scattering length, which is still controversal [24,25,26,27,28,29,30,31]. AV18 is adjusted to a nn = −18.82 fm, whereas for CD-Bonn 2000 a nn results in −18.97 fm.…”

mentioning

confidence: 99%

Three-nucleon bound states using realistic potential models

et al. 2003

View full text Add to dashboard Cite

The bound states of 3 H and 3 He have been calculated using the Argonne v18 plus the Urbana threenucleon potential. The isospin T = 3/2 state have been included in the calculations as well as the n-p mass difference. The 3 H-3 He mass difference has been evaluated through the charge dependent terms explicitly included in the two-body potential. The calculations have been performed using two different methods: the solution of the Faddeev equations in momentum space and the expansion on the correlated hyperspherical harmonic basis. The results are in agreement within 0.1% and can be used as benchmark tests. Results for the CD-Bonn interaction are also presented. It is shown that the 3 H and 3 He binding energy difference can be predicted model independently.In the last years great efforts have been made to improve the description of the nucleon-nucleon (N N ) interaction. A new generation of potentials including explicitly charge independence and charge symmetry breaking (CIB,CSB) terms appeared. These interactions describe the N N scattering data below T lab = 300 MeV with a nearly perfect χ 2 /datum≈ 1. The CD-Bonn [1] and Argonne v 18 (AV18) [2] interactions also provide a neutron-neutron (nn) force, which has been adjusted to the experimental nn scattering length, whereas the Nijmegen interactions [3] are fitted only to proton-proton and proton-neutron data. Recently, the CD-Bonn potential has been updated to CD-Bonn 2000 [4]. In this paper we only present results for the AV18 and CD-Bonn 2000 interactions. Both are quite different from each other in their functional form, but their description of the N N data is almost equally accurate. Therefore a comparison of the results will give insights into the model dependence of our understanding of the three-nucleon (3N ) bound states.Following for example the notation of Ref.[2], all these N N potentials can be put in the general formThe short range part v R (N N ) of all of these interactions includes a certain number of parameters (around 40), which are determined by a fitting procedure to the N N scattering data and the deuteron binding energy (BE), whereas the long range part is represented by the one-pion-exchange potential v π (N N ) and an electromagnetic part v EM (N N ). For AV18, v EM (pp) consists of the one-and twophoton Coulomb terms plus the Darwin-Foldy term, vacuum polarization and magnetic moment interactions. The v EM (np) interaction includes a Coulomb term due to the neutron charge distribution in addition to the magnetic moment interaction. Finally, v EM (nn) is given by the magnetic moment interaction only. All these terms take into account the finite size of the nucleon charge distributions. The v EM (N N ) for CD-Bonn is much simpler:is given by the Coulomb force of point protons, whereas v EM (np) = v EM (nn) = 0. As it is well known, when these interactions are used to describe the 3N bound state, an underbinding of about 0.5 MeV to 0.9 MeV depending on the model is obtained (see for example Ref. [5]). The local potentials lead to less bin...

show abstract

“…The two reactions used to measure a nn that have the smallest theoretical uncertainties are pion-deuteron capture (π − + d → n + n + γ) and neutron-deuteron breakup (n+d → n+n+p). Curiously, measurements using these two reactions give significantly different values of a nn : from π − d capture measurements the average value for a nn is −18.6±0.4 fm [4][5][6] and from kinematically-complete nd breakup experiments the average value is −16.7 ± 0.5 fm [1]. It was suggested that the difference in these values has its origin in the threenucleon force (3NF), which would act in the nd breakup reaction [1] but not in the other.…”

mentioning

confidence: 99%

New Measurement of the1S0Neutron-Neutron Scattering Length Using the Neutron-Proton Scattering Length as a Standard

et al. 1999

View full text Add to dashboard Cite

The present paper reports high-accuracy cross-section data for the 2 H(n, nnp) reaction in the neutron-proton (np) and neutron-neutron (nn) final-state-interaction (FSI) regions at an incident mean neutron energy of 13.0 MeV. These data were analyzed with rigorous three-nucleon calculations to determine the 1 S0 np and nn scattering lengths, anp and ann. Our results are ann = -18.7 ±0.6 fm and anp = -23.5 ±0.8 fm. Since our value for anp obtained from neutron-deuteron (nd) breakup agrees with that from free np scattering, we conclude that our investigation of the nn FSI done simultaneously and under identical conditions gives the correct value for ann. Our value for ann is in agreement with that obtained in π − d measurements but disagrees with values obtained from earlier nd breakup studies. 25.10.+s,25.40.Fq The difference in the 1 S 0 neutron-neutron (nn) and proton-proton (pp) scattering lengths is an explicit measure of charge-symmetry breaking (CSB) of the the nuclear force. The high sensitivity of these scattering lengths to the nuclear potential strength makes them a valuable probe for detecting small potential-energy contributions like the isospin-dependent forces [1-3] that cause CSB. For realistic potentials, a 1% change in the potential strength results in a 30% shift in the scattering length. Since it is not technically viable to measure a nn directly by conducting free nn scattering experiments, one uses few-nucleon reactions that emit two neutrons with low relative momentum, i.e., a final-state interaction (FSI) configuration. The two reactions used to measure a nn that have the smallest theoretical uncertainties are pion-deuteron capture (π − + d → n + n + γ) and neutron-deuteron breakup (n+d → n+n+p). Curiously, measurements using these two reactions give significantly different values of a nn : from π − d capture measurements the average value for a nn is −18.6±0.4 fm [4-6] and from kinematically-complete nd breakup experiments the average value is −16.7 ± 0.5 fm [1]. It was suggested that the difference in these values has its origin in the threenucleon force (3NF), which would act in the nd breakup reaction [1] but not in the other.The goal of the present work was to measure a nn with the nd breakup reaction to an accuracy better than ±0.7 fm. To this aim a np was measured simultaneously and used as a standard for evaluating our methods and for determining the influence of the 3NF in nd breakup. We obtained a np and a nn from absolute cross-section measurements in the np and nn FSI regions, respectively, in nd breakup at an incident mean neutron energy of E n = 13.0 MeV. Rigorous nd breakup calculations with the Tucson-Melbourne (TM) 3NF potential [7] show that the percentage change in np and nn FSI cross sections from the addition of a 3NF are equal. Based on this observation and the fact that a np has been determined to high accuracy by np scattering [8], we used our extracted values of a np to set an upper limit on the 3NF influence on the value of a nn determined in the present experim...

show abstract

Measurement of the neutron-neutron scattering lengthannwith the reactionπ−

Cited by 65 publications

References 24 publications

Effect of bound dineutrons upon big bang nucleosynthesis

Effect of bound dineutrons upon big bang nucleosynthesis

Three-nucleon bound states using realistic potential models

New Measurement of the1S0Neutron-Neutron Scattering Length Using the Neutron-Proton Scattering Length as a Standard

Contact Info

Product

Resources

About