Research Group for Advanced Theoretical Physics

Group Leader: HOSAKA Atsushi
Members: UTSUNO Yutaka, MARUYAMA Toshiki, KOURA Hiroyuki, Philipp GUBLER,NOMURA Kosuke, YOSHIDA Kazuki, SUZUKI Kei, Ahmad Jafar ARIFI, MORI Michiyasu,
IEDA Jun’ichi, ONISHI Hiroaki, NAKATA Koki, YAMAMOTO Kei, Araki YASUFUMI,HIYAMA Emiko, OTSUKA Takaharu, MIYASHITA Seiji

The Advanced Theoretical Physics (ATP) Group waslaunched in 2019 in ASRC/JAEA to conduct the research of thefundamental sciences related to the atomic energy. Our missions
are to support experimental researches at JAEA and to explore
interdisciplinary researches with new ideas. We are also trying
to form a platform to exchange new ideas, to stimulateinternational collaborations and to train young researchers. Core
members interests cover theoretical physics on hadrons andnuclei, the strongly interacting systems. In addition, condensed
matter physicists working on spintronics join the ATP.
As activities of 2019, we would like to report twoachievements, a crowdfunding to encourage the young
generation’s interest in nuclear science, and the collaboration
between theory and experiment in hadron physics.
“One Nuclear Chart for One High school” project:
Crowdfunding for making nuclear chart and visiting highschools to give a lecture
From this FY, we have started an outreach project for generalpublic and high schools in Japan. In JAEA, the Nuclear Data
Center has been publishing a nuclear chart, for researchers innuclear data and related areas since 1976. This JAEA nuclear
chart includes experimental data of nuclear decays for known
nuclei, and additionally theoretical decay data for unknown
nuclei, which have been provided through our theoretical work.
In order to popularize the use of nuclear chart to young people,
we have started the “one nuclear chart for one high school”
project. In the project, we try to distribute one sheet of nuclear
chart to every high-school in Japan, and to give a visiting lecturewith the chart (Fig. 1). For this purpose, we set a crowdfundingat the end of January in 2020 for eight weeks, which is the firstattempt of crowdfunding in JAEA. The target amount of
1,500,000 yen was set, and we finally obtained 1,731,000 yen
from 157 donators (Ref. [1]). This contribution will be used forthe project in FY 2020.

Universal features in the Roper-like resonances inspired by
the recent experimental observations
As motivated by the recent observation of Λb(6072) by CMSand LHCb collaborations, we have discussed it as a stateanalogous to the Roper resonance N(1440) [2], which is the firstexcited state of the nucleon of spin and parity JP =1/2+. It
remains a mysterious baryon because its properties such as
decay have not been easily explained by the conventional quarkmodel. In fact, candidates of similar nature have been reportedfor hyperons, Λ(1600) and Σ(1660), and possibly for charmed
baryons, Λc(2765), Ξc(2970). The observation of Λb(6072) has
added another member in the list of such states, implying auniversal feature in those states. LHCb reported not only themass and life time but also the decay property of Λb(6072)→Λbππ, providing useful information for theoretical studies.
In this occasion, an intern student from Osaka University,
Jafar Arifi, with advice of Kiyoshi Tanida in Hadron Group
performed analysis for the decay of Λb(6072) assuming theheavy quark symmetry. This is particularly useful to fix the yet
undetermined spin and parity of Λb(6072) and give suggestions
to further theoretical studies. The decay occurs through the socalled sequential processes, Λb(6072) → Σb(*)π → Λb ππ. Theintermediate state is in fact either Σb of JP = 1/2+ or Σb* of JP =3/2+, both of which contribute to the decay coherently, andtherefore quantum mechanical calculation with theirinterference is important. This has been done properly by Jafar,
and the results have been compared with the data. As shown in
Fig. 2, the agreement of the data and his calculation isremarkable. This agreement strongly indicates that the observedΛb(6072) is a family of the Roper resonance of spin and parity
1/2+.
A further theoretical study is then to clarify the origin of such
universal features in the Roper-like resonances. This will
provide an important direction for hadron physics research.

Fig. 2: Invariant mass plot of Λbπ [2].

Fig.1: Snapshot of visiting lecture with JAEA nuclear chart.

References[1] JAEA HP:
https://www.jaea.go.jp/news/newsbox/2020/013001/[2] A. J. Arifi, H. Nagahiro, A. Hosaka, and K. Tanida,Phys.Rev.D 101 (2020) 11, 111502.