精确分析伪标量在极化中子β衰变中的作用
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本文主要探讨了中子β衰变过程中的伪标量相互作用精确分析。这项研究关注的是在标准模型（SM）框架外引入的额外伪标量交互对一-极交换（OPP）的影响，特别是对于极化中子、极化电子和非极化质子之间的中子β-衰变相关系数。OPP交换的贡献被量化为有效耦合常数Cps（OPP），其数值大约在10^-5的量级，显示了这类相互作用在衰变过程中的相对较小但并非可以忽视的作用。
作者分析了强低能相互作用与BSM（超出标准模型）伪标量交互的联合效应，其中BSM的有效耦合常数Cps（BSM）的实部和虚部受到了严格的限制，具体来说是ReCps（BSM）在-3.5×10^-5到0之间，而ImCps（BSM）则小于-2.3×10^-5。这些限制条件对于理解BSM在极化中子β衰变中的潜在影响至关重要，因为它们确定了新物理效应的可探测范围。
研究利用了González-Alonso等人（2019）的研究成果，将所得结果置于理论研究的背景中，特别是在检测BSM效应时，这些结果提供了关于精度的指导，即理论上能够达到10^-5或更低的测量误差，这比先前Abele（2016）的工作更为精确。这一领域的研究对于检验粒子物理学的基本原理和探索新的物理现象具有重要意义，因为它可能揭示出超出标准模型的新粒子或力的证据。
文章发表于《核物理学B》（Nuclear Physics B）杂志，2020年951期，114891篇，并可在ScienceDirect和Elsevier网站上获取。该论文由编辑Hong-Jian He审阅，提供了一个严谨的科学框架，有助于进一步推进对中子β衰变及其背后基本粒子相互作用的理解。
4 A.N. Ivanov et al. / Nuclear Physics B 951 (2020) 114891
per should be tangible and important for a correct analysis of experimental data on searches
of contributions of interactions BSM with an accuracy of a few parts of 10
−5
. We give also a
comparative analysis of the results obtained in this work with those in [4,47–54]. This allows us
to argue that the corrections, caused by pseudoscalar interactions, calculated for the correlation
coefficients of the neutron β
−
–decays, induced by correlations of the electron spin with the neu-
tron spin and 3-momenta of decay fermions with standard correlation structures introduced by
Jackson et al. [24], are fully new. Moreover all terms in Eq. (A.6) with correlation structures be-
yond the standard ones by Jackson et al. [24] and proportional to the ef
fective coupling constants
C
ps
and C
ps
were never calculated in literature. In the Appendix we give a detailed calculation
of the contributions of pseudoscalar interactions caused by the OPP exchange and BSM to the
correlation coefficients of the neutron β
−
–decays for a polarized neutron, a polarized electron
and an unpolarized proton, completing the analysis of contributions of interactions BSM to the
correlation coefficients of the neutron β
−
–decays carried out in [10–12].
2. Amplitude of the neutron β
−
–decay with contributions of OPP exchange and
pseudoscalar interaction BSM
Since the expected order of contributions of pseudoscalar interactions of about 10
−5
, we take
them into account in the linear approximation additively to the corrections of order 10
−4
−10
−3
calculated in [1–34]. In such an approximation and following [9,11,12]the amplitude of the
neutron β
−
–decay we take in the form
M(n →pe
−
¯ν
e
)
=−
G
F
√
2
V
ud
p(
k
p
,σ
p
)|J
(+)
μ
(0)|n(
k
n
,σ
n
)
¯u
e
(
k
e
,σ
e
)γ
μ
(1 −γ
5
)v
¯ν
(
k
¯ν
, +
1
2
)
+¯u
p
(
k
p
,σ
p
)γ
5
u
n
(
k
n
,σ
n
)
¯u
e
(
k
e
,σ
e
)(C
p
+
¯
C
P
γ
5
)v
¯ν
(
k
¯ν
, +
1
2
)
, (1)
where G
F
and V
ud
are the Fermi couping constant and the Cabibbo–Kobayashi–Maskawa
(CKM) matrix element [14]. Then, p(
k
p
, σ
p
)|J
(+)
μ
(0)|n(
k
n
, σ
n
) is the matrix element of the
charged hadronic current J
(+)
μ
(0) = V
(+)
μ
(0) − A
(+)
μ
(0), where V
(+)
μ
(0) and A
(+)
μ
(0) are the
charged vector and axial–vector hadronic currents [15,18,19]. The fermions in the initial and
final states are described by Dirac bispinor wave functions u
n
, u
p
, u
e
and v
¯ν
of free fermions
[9,62]. In the second term of Eq. (1)we take into account the contribution of the pseudoscalar
interaction BSM [22–27] with two complex phenomenological coupling constants C
P
and
¯
C
P
in the notation of [9,11,12].
For the analysis of contrib
utions of pseudoscalar interactions to the neutron β
−
–decays for a
polarized neutron, a polarized electron and an unpolarized proton we define the matrix element
p(
k
p
, σ
p
)|J
(+)
μ
(0)|n(
k
n
, σ
n
) as follows
p(
k
p
,σ
p
)|J
(+)
μ
(0)|n(
k
n
,σ
n
)
=¯u
p
(
k
p
,σ
p
)
γ
μ
(1 +λγ
5
) +
2Mλq
μ
m
2
π
−q
2
−i0
γ
5
u
n
(
k
n
,σ
n
), (2)
where λ is the axial coupling constant with recent experimental value λ =−1.27641(45)
stat.
(33)
syst.
[41]. The first term in Eq. (1)is written in agreement with the standard V −A effective
theory of weak interactions [15,18,19](see also [20,21]). The term proportional to q
μ
γ
5
defines
the contribution of the OPP exchange, caused by strong low–energy interactions (see also [18])
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