The beta decay of $$^{77}$$ Ge and $$^{77\textrm{m}}$$ Ge, both produced by neutron capture on $$^{76}$$ Ge, is a potential background for Germanium based neutrinoless double-beta decay search experiments such as GERDA or the LEGEND experiment. In this work we present a search for $$^{77}$$ Ge decays in the full GERDA Phase II data set. A delayed coincidence method was employed to identify the decay of $$^{77}$$ Ge via the isomeric state of $$^{77}$$ As ( $$9/2^+$$ , $${475}\,\hbox {keV}$$ , $${T_{1/2} = {114}\,{\upmu }\hbox {s}}$$ , $$^{77\textrm{m}}$$ As). New digital signal processing methods were employed to select and analyze pile-up signals. No signal was observed, and an upper limit on the production rate of $$^{77}$$ Ge was set at $$<0.216$$ nuc/(kg $$\cdot $$ yr) (90% CL). This corresponds to a total production rate of $$^{77}$$ Ge and $$^{77\textrm{m}}$$ Ge of $$<{0.38}$$ nuc/(kg $$\cdot $$ yr) (90% CL), assuming equal production rates. A previous Monte Carlo study predicted a value for in-situ $$^{77}$$ Ge and $$^{77\textrm{m}}$$ Ge production of (0.21 ± 0.07) nuc/(kg.yr), a prediction that is now further corroborated by our experimental limit. Moreover, tagging the isomeric state of $$^{77\textrm{m}}$$ As can be utilised to further suppress the $$^{77}$$ Ge background. Considering the similar experimental configurations of LEGEND-1000 and GERDA, the cosmogenic background in LEGEND-1000 at LNGS is estimated to remain at a sub-dominant level.

United Kingdom

M. Agostini

A. Alexander

Switzerland

G. Araujo

Russia

A. Bakalyarov

Italy

M. Balata

I. Barabanov

L. Baudis

Germany

C. Bauer

S. Belogurov

A. Bettini

L. Bezrukov

V. Biancacci

E. Bossio

V. Bothe

R. Brugnera

A. Caldwell

S. Calgaro

C. Cattadori

A. Chernogorov

P.J. Chiu

T. Comellato

V. D’Andrea

E. Demidova

N. Marco

E. Doroshkevich

M. Fomina

A. Gangapshev

A. Garfagnini

C. Gooch

P. Grabmayr

V. Gurentsov

K. Gusev

United States

J. Hakenmüller

S. Hemmer

W. Hofmann

J. Huang

Belgium

M. Hult

L. Inzhechik

Hungary

J. Janicskó Csáthy

J. Jochum

M. Junker

V. Kazalov

Y. Kermaïdic

H. Khushbakht

T. Kihm

K. Kilgus

I. Kirpichnikov

A. Klimenko

K. Knöpfle

O. Kochetov

V. Kornoukhov

P. Krause

V. Kuzminov

M. Laubenstein

M. Lindner

I. Lippi

A. Lubashevskiy

B. Lubsandorzhiev

G. Lutter

C. Macolino

B. Majorovits

W. Maneschg

G. Marshall

Poland

M. Misiaszek

M. Morella

Y. Müller

I. Nemchenok

M. Neuberger

L. Pandola

K. Pelczar

L. Pertoldi

P. Piseri

A. Pullia

C. Ransom

L. Rauscher

M. Redchuk

S. Riboldi

N. Rumyantseva

C. Sada

S. Sailer

F. Salamida

S. Schönert

J. Schreiner

A.K. Schütz

O. Schulz

M. Schwarz

B. Schwingenheuer

O. Selivanenko

E. Shevchik

M. Shirchenko

L. Shtembari

H. Simgen

A. Smolnikov

D. Stukov

S. Sullivan

A. Vasenko

A. Veresnikova

C. Vignoli

K. Sturm

T. Wester

Search for the in-situ production of $$^{77}$$ Ge in the GERDA neutrinoless double-beta decay experiment

The fragmentation reactions of neutron-rich unstable nuclei $^{81}$Ga and $^{82}$Ge at 250 MeV/nucleon have been studied in order to search the optimal mean for the production of very neutron-rich nuclei in the vicinity of $^{78}$Ni. The newly measured cross sections were compared with various calculations, showing a good agreement with EPAX3.01. The present work provides experimental insights into the two-step scheme—fragmentation following fission—as a method to produce very neutron-rich nuclei through a combination of ISOL and fragmentation of post-accelerated beams of unstable nuclei. Our results enable an evaluation of the potential of the two-step scheme in the production of very neutron-rich nuclei for the $^{78}$Ni region. The two-step scheme using fragmentation of a post-accelerated $^{81}$Ga beam could be an option to produce neutron-rich nuclei around $^{78}$Ni when the $^{81}$Ga beam intensity reaches <math><mn>1.0</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>8</mn></mrow></msup></math> pps, compared to the one-step scheme with fission of $^{238}$U.

China

X.H. Sun

Japan

H. Wang

K. Yoneda

N. Aoi

H. Baba

P. Bednarczyk

Zs. Dombrádi

P. Doornenbal

Zs. Fülöp

S. Go

T. Hashimoto

E. Ideguchi

K. Kobayashi

Y. Kondo

Hong Kong

J. Lee

H.N. Liu

W.P. Liu

J.L. Lou

M. Matsushita

R. Minakata

T. Motobayashi

D. Nishimura

H. Otsu

H. Sakurai

Y. Shiga

Y.P. Shen

D. Sohler

D. Steppenbeck

Y.L. Sun

S. Takeuchi

A. Tamii

R. Tanaka

Z.Y. Tian

Zs. Vajta

T. Yamamoto

X.F. Yang

Z.H. Yang

Y.L. Ye

R. Yokoyama

J. Zenihiro

Production of neutron-rich nuclei in the vicinity of Ni: Fragmentation reactions of unstable Ga and Ge beams

The bubble nuclei are important components of exotic nuclear structures characterized by special depletions of central densities. Focusing on bubble structures of $^{36}$Ar, the characterizations of bubble nuclei were explored with the framework of the extended quantum molecular dynamics model. Three density distribution modes were uncovered for the first time, i.e. micro-bubble, bubble, and cluster resonances, which show unique spectral signature compared to the monopole resonance spectrum as the excitation intensity was increased in bubbles. Of pivotal importance is the revelation that the bubble mode's oscillation frequency closely resembles macroscopic bubble dynamics, building a connection between classical macroscopic phenomena and the quantum complexity of the nuclear structure. The discovery marks a crucial step forward in deciphering the relationship between classical and quantum domains within the enigmatic world of atomic nuclei.

Ge Ren

Chun-Wang Ma

Xi-Guang Cao

Yu-Gang Ma

Bubble Ar and its new breathing modes

The yields of  $$K^0_S$$  <math> <msubsup> <mi>K</mi> <mi>S</mi> <mn>0</mn> </msubsup> </math>   mesons have been measured in inelastic p+p interactions at incident projectile momenta of 31, 40 and 80  $$\text {Ge}\hspace{-1.00006pt}\text {V}\!/\!c$$  <math> <mrow> <mtext>Ge</mtext> <mspace width="-1.00006pt"></mspace> <mtext>V</mtext> <mspace width="-0.166667em"></mspace> <mo>/</mo> <mspace width="-0.166667em"></mspace> <mi>c</mi> </mrow> </math>   ( $$\sqrt{s_{NN}}=7.7, 8.8$$  <math> <mrow> <msqrt> <msub> <mi>s</mi> <mrow> <mi>NN</mi> </mrow> </msub> </msqrt> <mo>=</mo> <mn>7.7</mn> <mo>,</mo> <mn>8.8</mn> </mrow> </math>   and 12.3  $$\text {Ge}\hspace{-1.00006pt}\text {V}$$  <math> <mrow> <mtext>Ge</mtext> <mspace width="-1.00006pt"></mspace> <mtext>V</mtext> </mrow> </math>  , respectively). The data were recorded by the NA61 $$/$$  <math> <mo>/</mo> </math>  SHINE spectrometer at the CERN Super Proton Synchrotron and the  $$K^0_S$$  <math> <msubsup> <mi>K</mi> <mi>S</mi> <mn>0</mn> </msubsup> </math>   mesons identified via their decays into  $$\pi ^{+} \pi ^{-}$$  <math> <mrow> <msup> <mi>π</mi> <mo>+</mo> </msup> <msup> <mi>π</mi> <mo>-</mo> </msup> </mrow> </math>   pairs. Double-differential distributions are presented as function of transverse momentum and rapidity. The mean multiplicities of  $$K^0_S$$  <math> <msubsup> <mi>K</mi> <mi>S</mi> <mn>0</mn> </msubsup> </math>   mesons were determined to be  $$(5.95 \pm 0.19 (stat) \pm 0.30 (sys)) \times 10^{-2}$$  <math> <mrow> <mrow> <mo>(</mo> <mn>5.95</mn> <mo>±</mo> <mn>0.19</mn> <mrow> <mo>(</mo> <mi>s</mi> <mi>t</mi> <mi>a</mi> <mi>t</mi> <mo>)</mo> </mrow> <mo>±</mo> <mn>0.30</mn> <mrow> <mo>(</mo> <mi>s</mi> <mi>y</mi> <mi>s</mi> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>×</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>2</mn> </mrow> </msup> </mrow> </math>   at 31  $$\text {Ge}\hspace{-1.00006pt}\text {V}\!/\!c$$  <math> <mrow> <mtext>Ge</mtext> <mspace width="-1.00006pt"></mspace> <mtext>V</mtext> <mspace width="-0.166667em"></mspace> <mo>/</mo> <mspace width="-0.166667em"></mspace> <mi>c</mi> </mrow> </math>  ,  $$(7.61 \pm 0.13 (stat) \pm 0.43 (sys)) \times 10^{-2}$$  <math> <mrow> <mrow> <mo>(</mo> <mn>7.61</mn> <mo>±</mo> <mn>0.13</mn> <mrow> <mo>(</mo> <mi>s</mi> <mi>t</mi> <mi>a</mi> <mi>t</mi> <mo>)</mo> </mrow> <mo>±</mo> <mn>0.43</mn> <mrow> <mo>(</mo> <mi>s</mi> <mi>y</mi> <mi>s</mi> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>×</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>2</mn> </mrow> </msup> </mrow> </math>   at 40  $$\text {Ge}\hspace{-1.00006pt}\text {V}\!/\!c$$  <math> <mrow> <mtext>Ge</mtext> <mspace width="-1.00006pt"></mspace> <mtext>V</mtext> <mspace width="-0.166667em"></mspace> <mo>/</mo> <mspace width="-0.166667em"></mspace> <mi>c</mi> </mrow> </math>   and  $$(11.58 \pm 0.12 (stat) \pm 0.55 (sys)) \times 10^{-2}$$  <math> <mrow> <mrow> <mo>(</mo> <mn>11.58</mn> <mo>±</mo> <mn>0.12</mn> <mrow> <mo>(</mo> <mi>s</mi> <mi>t</mi> <mi>a</mi> <mi>t</mi> <mo>)</mo> </mrow> <mo>±</mo> <mn>0.55</mn> <mrow> <mo>(</mo> <mi>s</mi> <mi>y</mi> <mi>s</mi> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>×</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>2</mn> </mrow> </msup> </mrow> </math>   at 80  $$\text {Ge}\hspace{-1.00006pt}\text {V}\!/\!c$$  <math> <mrow> <mtext>Ge</mtext> <mspace width="-1.00006pt"></mspace> <mtext>V</mtext> <mspace width="-0.166667em"></mspace> <mo>/</mo> <mspace width="-0.166667em"></mspace> <mi>c</mi> </mrow> </math>  . The results on  $$K^{0}_{S}$$  <math> <msubsup> <mi>K</mi> <mi>S</mi> <mn>0</mn> </msubsup> </math>   production are compared with the production of charged kaons in corresponding reactions and with model calculations (Epos1.99, SMASH 2.0 and PHSD) as well as with published data from other experiments.

N. Abgrall

H. Adhikary

P. Adrich

K. Allison

N. Amin

E. Andronov

Croatia

T. Antićić

Norway

I.C. Arsene

M. Bajda

Y. Balkova

M. Baszczyk

D. Battaglia

A. Bazgir

S. Bhosale

M. Bielewicz

France

A. Blondel

Bulgaria

M. Bogomilov

Y. Bondar

N. Bostan

A. Brandin

A. Bravar

W. Bryliński

J. Brzychczyk

M. Buryakov

A. Camino

Serbia

M. Ćirković

M. Csanád

J. Cybowska

T. Czopowicz

C. Dalmazzone

N. Davis

A. Dmitriev

P. Doetinchem

$$K^0_S$$  <math> <msubsup> <mi>K</mi> <mi>S</mi> <mn>0</mn> </msubsup> </math>   meson production in inelastic p+p interactions at 31, 40 and 80  $$\text {Ge}\hspace{-1.00006pt}\text {V}\!/\!c$$  <math> <mrow> <mtext>Ge</mtext> <mspace width="-1.00006pt"></mspace> <mtext>V</mtext> <mspace width="-0.166667em"></mspace> <mo>/</mo> <mspace width="-0.166667em"></mspace> <mi>c</mi> </mrow> </math>   beam momentum measured by NA61 $$/$$  <math> <mo>/</mo> </math>  SHINE at the CERN SPS