富中子物质中质子跃迁动量的影响与探测

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"探索富中子物质中的质子跃迁动量" 在核物理学领域，研究核物质的内部结构和动态对于理解基本粒子行为以及天体物理现象至关重要。富中子物质是指含有大量中子的核系统，如中子星或某些核反应过程中的中间状态。标题和描述提到的"质子跃迁动量"是指在核物质中，质子从一个能态跃迁到另一个能态时所携带的动量。在正常情况下，核物质中的核子（质子和中子）动量分布n(k)通常在核费米动量附近经历一个转变，由常数分布转变为1/k^4的形式。这种转变对核物质的性质有显著影响，因为它决定了核子间的相互作用和能量分布。然而，对于在富中子物质中，尤其是少数族裔（例如质子）的这种转变动量，目前的研究相对较少，其确切值尚未被确定。本文引用的Physics Letters B 776 (2018) 447–450中，作者Gao-Chan Yong利用了IBUU（Isospin-Basic-Urca-Urca）输运模型来首次深入研究了质子在富中子环境中的跃迁动量。IBUU模型是一种用于模拟中子星和核反应过程中核物质动力学的理论工具，它考虑了同位旋效应，使得在不同中子-质子比例的物质中都能进行准确的计算。研究发现，质子的跃迁动量与π-/π+比值（负介子与正介子的比例）以及高能光子的产生密切相关。这两个观测指标在核反应和天体物理事件中具有重要意义。π介子是强相互作用的产物，而光子则反映了核反应中的能量释放。质子跃迁动量的敏感性揭示了在富中子物质中，质子的行为可能与传统的核物质模型预测有所不同，这将对我们理解这些极端条件下的核反应和中子星的内部动力学产生深远影响。质子动量分布的变化不仅影响核物质的宏观性质，也可能影响中子星的冷却机制、星震活动，甚至可能影响中子星合并后产生的引力波信号。因此，对质子跃迁动量的深入研究对于构建更精确的天体物理模型和理解宇宙中极端环境下的物理过程至关重要。这篇研究工作在探索富中子物质中的质子跃迁动量方面迈出了重要的一步，为今后的核物理实验和理论研究提供了新的视角和挑战，也为解析中子星等天体的内部秘密打开了新的窗口。

Physics Letters B 776 (2018) 447–450

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Probing proton transition momentum in neutron-rich matter

Gao-Chan Yong

Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China

a r t i c l e i n f o a b s t r a c t

Article history:

Received

8 July 2017

Received

in revised form 26 October 2017

Accepted

30 November 2017

Available

online 2 December 2017

Editor: W.

Haxton

Around the nuclear Fermi momentum, there is a transition of nucleon momentum distribution n(k) in

nuclear matter, i.e., from a constant to the 1/k

nucleon momentum distribution. While nowadays the

transition momentum of minority in asymmetric matter is rarely studied and thus undetermined. In the

framework of the IBUU transport model, proton transition momentum in nuclei is ﬁrst studied. It is

found that the transition momentum of proton is sensitive to the π

−

/π

ratio as well as the energetic

photon production in neutron-rich nuclear reaction. This result may push the study of how the proton

momentum is distributed in neutron-rich matter forward and help us to better understand the dynamics

of both neutron-rich nuclear reactions and neutron stars.

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

In recent two years, the study of nuclear short-range correla-

tions

attracts much attention [1–6]. It has been shown that about

20% nucleons in nuclei are correlated [7–9]. Because of the nucleon

short-range interactions [10,11], nucleons in nuclei can form pairs

with larger relative momenta and smaller center-of-mass momenta

[12,13]. The nucleon short-range correlations (SRC) in nuclei cause

a high-momentum tail (HMT) in single-nucleon momentum distri-

bution

above the Fermi-momentum [14–18]. And the HMT shape

caused by two-nucleon SRC is almost identical for all nuclei from

deuteron to very heavier nuclei [19–22], i.e., roughly exhibits a

1/k

tail [23–26]. And in the HMT, the number of neutron–proton

correlated pairs is about 18 times that of the proton–proton or

neutron–neutron correlated pairs [9].

Proton

transition momentum, i.e., the starting point of proton

1/k

momentum distribution in neutron-rich matter directly af-

fects

proton average kinetic energy in nuclear matter, thus affects

the dynamics of neutron-rich nuclear reactions and the dynamics

of neutron stars, such as the cooling of a Neutron Star, the super-

ﬂuidity

of protons [27], etc. While for neutron-rich matter, it is not

straightforward to determine the transition momentum of proton.

One general considers that below the Fermi momentum, proton or

neutron have independent movements while above their respective

Fermi momenta, i.e., k

, k

, they respectively have 1/k

distri-

butions

starting from their respective Fermi momenta. This naive

opinion, however, is not consistent with the correlation picture

of neutron–proton pair [23]. The correlated neutron and proton

should have almost the same momentum whether in symmetric

E-mail address: yonggaochan@impcas.ac.cn.

or in asymmetric matter. In asymmetric matter or neutron matter,

such as the neutron stars, neutron and proton may have very dif-

ferent

Fermi momenta. If each correlated neutron and proton have

1/k

distributions starting from their respective Fermi momenta,

then the correlated neutron and proton would have very different

momenta. This point evidently contradicts the thought of the n–p

dominance model [23].

neutron-rich matter, because protons become more promi-

nent

at high momenta as their concentration decreases [28], the

starting momentum of minority 1/k

distribution should be not

the minority Fermi momentum. Because the minority Fermi mo-

mentum

would become very small in magnitude if proton concen-

tration

decreases sharply. Apart from its own Fermi momentum,

the left case is using the majority Fermi momentum as the start-

ing

momentum of minority 1/k

distribution. For very asymmetric

nuclear matter, it is hard to obtain the minority transition mo-

mentum

from microscopic theory. The ladder self-consistent Green

function approach could not get the nucleon momentum distribu-

tion

at Zero temperature [16] and the Brueckner theory with a

microscopic Three-body force gives a noncontinuous nucleon mo-

mentum

distribution [29]. That is to say, the microscopic theory

can not answer the question of minority transition momentum in

asymmetric matter, especially in the neutron matter. However, the

minority transition momentum could be checked by nuclear exper-

iments

with unequal numbers of proton and neutron.

One

way to check the starting point of proton 1/k

distribution,

i.e., whether the HMT starts from proton Fermi momentum or from

the correlated majority Fermi momentum, is using heavy-ion col-

lisions

with neutron-rich nuclei. In nucleus–nucleus collisions at

intermediate energies, different proton energies may cause the dif-

https://doi.org/10.1016/j.physletb.2017.11.075

0370-2693/

SCOAP

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