# Projects

**Competition :**

PN-II-ID-PCE-2011-3 – PROJECTS OF EXPLORATORY RESEACH

**Cod:** PN-II-ID-PCE-2011-3-0318

**Supported by CNCS-UEFISCDI, under the contract nr.:** 58/28.10.2011

**Project title (English) :**

Development of models and methods for computation of the nuclear matrix elements involved in the study of double-beta decay

**Project title (Romanian) :**

Dezvoltarea de modele si metode pentru calculul elementelor de matrice nucleare implicate in studiul dezintegrarii beta duble

**Domain :**

MATHEMATICS, PHYSICAL SCIENCES, INFORMATION AND COMMUNICATION, ENGINEERING, UNIVERSE AND EARTH SCIENCES

**Subdomain :**

Fundamental constituents of matter: particle, nuclear, plasma, atomic, molecular, gas, and optical physics

**Aria of reseach:** Nuclear physics

**Project leader :** Sabin Stoica

**Email :** sabin.stoica@unescochair-hhf.ro

**Project duration :** 36 months, starting 01.01.2012

**Project Host Institution**

Host Institution (without abbreviations) | Fundatia Horia Hulubei |

Institution Identification Code (CUI) | 9164783 |

Address | Str. Atomistilor, Nr.407, C.P. MG-12, Cod 077125 |

City | Magurele |

County | Ilfov |

Country | Romania |

Institutional Code in the Register of Potential Contractors* (Website): | 880 |

**Project abstract :**

The project proposes to develop new nuclear structure models and high performance computing codes based on the Shell Model to provide a reliable description of the nuclear matrix elements (NMEs) involved in the double-beta (ββ) decays. The NMEs are essential to improve the knowledge of the absolute neutrino masses, ando investigate the possibility of determining the leading mechanisms for the neutrinoless double beta (0νββ) decay mode. The specific ojectives of this project include: i)establish reliable effective shell model NN interactions that can adequately reproduce the spectroscopic properties of the nuclei in the mass-regions of the main ββ decay emitters; ii)develop an efficient code to calculate the two-body matrix elements of the 0νββ-decay operator, including high orders effects in the nucleon currents, short-range correlations and other nucleon-dressing effects; iii)estimate the effects of enlarging the size of the shell model spaces that may break general symmetries; iv)predict new limits and uncertainties for the effective 0νββ neutrino mass assuming a standard 0νββ decay half-life of 1026 years; v)derive explicit expressions for the transition amplitudes of other possible 0νββ decay mechanisms and investigate strength of their contributions; vi) disseminate the results to the experimentalists, which are using theoretical NMEs in the planning their ββ decay experiments.

**Key words :**

double-beta decay, neutrino mass, nuclear matrix elements, shell model, QRPA, standard model

**Project team**

- Sabin STOICA, cs1 – project director
- Mihai HOROI, cs1
- Mihai MIREA, cs1
- Andrei NEACSU, cs3
- Tudor PAHOMI, student

**Expected results**

- Development of an advanced numerical code for computing the nuclear matrix elements involved in double beta decay
- Development of an advanced numerical code for computing the phase space factors involved in double beta decay
- Calculation of the nuclear matrix elements for several DBD isotopes of experimental interest
- Clarification of the role of different nuclear ingredients/approximations involved in computation of the nuclear matrix elements
- Publication of the project results in ISI journals
- Dissemination of the results in national and international conferences, workshops, seminars
- Accomplishment of a PhD thesis (A. Neacsu)
- Establish international collaborations

**Scientific report (English) download:** (raport_stiintific_2012-2016.pdf).
**Results : **

**A) Publications**

**a) Journals, Conference Proceedings, Books**

- New phase space calculations for beta decay half-lives, S. Stoica, M. Mirea, O. Nitescu, J. Un Nabi and Z. Iftikhar,AHEP 2016, ID8729893 (2016).

- Theoretical aspects of double beta decay, Sabin Stoica, Proceedings of TAUP2015, Journal of Physics: Conference series 718, 062056 (2016).

- Shell model calculations for double beta decay, Sabin Stoica,Journal of Physics: Conference series 580, 012031 (2015).

- Neutrino properties probed by LNV at low and high energies, S. Stoica,Workshop of the SEE UNESCO network, on Quantum Field Theory and Hamiltonian Systems Craiova, 19-22 September; Rom. J. Phys., 58, no. 5-6, 665 (2013). ISSN 1221-146X.

- Fast Calculations of the Matrix Elements for Neutrinoless Double Beta Decay, A. Neacsu, S. Stoica, M. Horoi, International Summer School for Avanced Studies ”Dynamics of open nuclear systems”, Predeal July 9-20, 2012.

- Lepton number violating proceses at low and high energies, S. Stoica, lectie la Workshop “ Towards a resolution of the DBD problem”, ECT*, Trento, 3-7 September, 2012. (www.ectstar.eu).

- Study of nuclear effects in the computation of the 0νββ decay matrix elements, A. Neacsu and S. Stoica, accepted in J. Phys. G: Nucl. Part. Phys. 41 (2014).

- New Calculations for Phase Space Factors Involved in Double Beta Decay, S. Stoica and M. Mirea, Phys. Rev. C 88, 037303, (2013).

- Fast, efficient calculations of the two-body matrix elements of the transition operators forneutrinoless double-β decay, A. Neacsu, S. Stoica and M. Horoi, Phys.Rev. C 86, 067304 (2012). (abstract)

- Neutrino properties probed by lepton number violating processes at low and high energies, S. Stoica, Rom. J. Phys., 58, nos. 5-6, (2013).

- Shell model calculations for neutrinoless DBD through exchange of heavy neutrinos, A. Neacsu and S. Stoica, accepted in Rom. Rep. Phys. Vol 59, no. 2 (2014).

- Phase space calculations for β- β- decays to final excited 2+1 states, T. Pahomi, A. Neacsu, M. Mirea, S. Stoica, accepted in Rom. Rep. Phys., vol. 59, no.2 (2014).

- First forbidden β-decay rates for neutron-rich nickel isotopes in stellar matter, J. Un-Nabi and S. Stoica, arXiv:1211.6968 [nucl-th], Astrophys. & Space Science, 349, 843 (2013). ISSN: 0004-640X.

- Efficient double beta decay nuclear matrix elements computations, A. Neacsu, Proceedings of CSSP12, AIP Conf. Proceedings Vol.1498, 354 (2012).

- Neutrino properties deduced from the study of LNV processes at low and high energies, S. Stoica, Proceedings of CSSP12, AIP Conf. Proceedings Vol. 1498, 246 (2012).

- The double beta decay: theoretical challengies, M. Horoi, Proceedings of CSSP12, AIP Conf. Proceedings Vol. 1498, 97 (2012).

- New calculations of the phase spaces and nuclear matrix elements for double-beta decay, S. Stoica, Proceedings of MEDEX2013, to appear in AIP conference Proceedings, (2013).

- Neutrino properties probed by lepton number violating processes, Stoica Sabin, Open Journal of Microphysics, ISSN 2162-2450, DOI:10.4236/ojm2013, 3-4, (2013).

- Study of Nuclear Effects in the Computation of the 0νββ Decay Matrix Elements, A. Neacsu and S. Stoica, arXiv: 1308.1047 [nucl-th] and J. Phys. G. Nucl. Part. Phys. 41, 015201 (2014).

- Shell model calculations for neutrinoless DBD through exchange of heavy neutrinos, A. Neacsu and S. Stoica, Rom. Rep. Phys. Vol 66, no. 2, 376 (2014).

- Phase space calculations for β- β- decays to final excited 2+1 states, T. Pahomi, A. Neacsu, M. Mirea, S. Stoica, Rom. J. Phys., vol. 66, no.2, 370 (2014).

- Constraints on light neutrino parameters derived from the study of neutrinoless double beta decay, S. Stoica and A. Neacsu, arXiv:1405.0517 and Adv. High En. Phys., 2014 (2014), ID 745082.

- Constraints on heavy neutrino and SUSY Parameters Derived from the study of neutrinoless double beta decay, A. Neacsu, S. Stoica, arXiv:1308.1047 and Adv. High En. Phys. 2014, (2014), 2014 (2014), ID 724315.

- First forbidden transitions and stellar beta decay rates of Zn and Ge isotopes, J. Un Nabi, N. Cakmak, S. Stoica and Z. Iftikhar, Physica Scripta 90, 115301 (2015).

- Values of the Phase Space Factors Involved in Double Beta Decay, M. Mirea, T. Pahomi, S. Stoica, Rom. Rep. Phys., 67, nr. 3, 872 (2015).

- Shell model calculations for neutrinoless double beta decay, S. Stoica, ISCHIA-Italy, May 12-16, 2014, J. Phys.: Conference series, 580, 012031 (2015).

**b) Presentations at Conferences : **

- Theoretical challenges in double beta decay, Sabin Stoica, invited seminar at Institute of Physics – University of Zurich, Switzerland, 3 October, 2016

- Theoretical challenges in double beta decay, Sabin Stoica, invited seminar at l’Observatoire de la Cȏte d’Azur, Nice, France, 28 June, 2016

- Theoretical challenges in neutrinoless double beta decay, Sabin Stoica, International Nuclear Physics Conference (INPC2016), September 12 – 16, 2016, Adelaide, Australia (www.inpc2016.com), to be published in J. Phys.: Conference series 2017.

- Constraints of beyond standard model parametersfrom the study of neutrinoless double beta decay, Sabin Stoica, 5th International Conference on New Frontiers in Physics (ICNFP 2016) July 6 – 14, 2016, Kolymbari, Crete, Greece (http://indico.cern.ch/e/icnfp2016), to be published in EPJ-Conference series, 2017

- New calculations for phase space factors and NMEs involved in Double Beta Decay, Sabin Stoica, invited lecture at “Matrix Elements for Double Beta Decay Experiments”, June 11-14, Prague, 2013 (http://medex13.utef.cvut.cz/program.php)

- Theoretical aspects of Double Beta Decay, Sabin Stoica, invited lecture at NEMO & SuperNEMO collaboration meeting, March 18-21, Prague, 2013.(http://www.supernemo.utef.eu/index.php?p=26).

- Motivation for the search of LNV processes at high energy, Sabin Stoica, CERN Meeting - January (2013).

- Efficient double beta decay nuclear matrix elements computations, A. Neacsu, CSSP12, Sinaia, 24 June – 4 July, oral presentation, (2012).

- Neutrino properties deduced from the study of LNV processes at low and high energies, S. Stoica, CSSP12, Sinaia, 24 June – 4 July, invited lecture, (2012).

- The double beta decay: theoretical challengies, M. Horoi, , CSSP12, Sinaia, 24 June – 4 July, invited lecture, (2012).

- LNV processes at low and high energies, S. Stoica, workshop on “Towards a resolution of the double-beta decay problem”, ECT*-Trento, 3-7 September, invited lecture, (2012).

- A. Neacsu, Fast, Efficient Calculations of the Two-Body Matrix Elements of the Transition Operators for Neutrinoless Double Beta Decay Workshop “ Towards a resolution of the DBD problem”, ECT*, Trento, 3-7 September, (Website), (2012).

- Neutrino properties probed by lepton number violating processes at low and high energies, S. Stoica, SEE-UNESCO conference on QFTHS, 19-22 September 2012, Craiova, Romania (invited lecture).

- New results in the theory of double-beta decay, S. Stoica, SNEMO meeting, Prague, 15-18 March, 2013 (invited lecture).

- New calculations of the phase spaces and nuclear matrix elements for double-beta decay, S. Stoica, MEDEX2013, 11-15 June, Prague, 2013.

- Neutrino properties probed by lepton number violating processes, S. Stoica, oral presentation at the Conference: Molecular, Atomic, Nuclear and Particle Physics, 14-16 August, 2013, Beijing, China, Open Journal of Microphysics, 2013. ISSN 2162-2450, doi: 10.4236/ojm2013 , in press (Website) (2013).

- Nuclear Structure Calculations for Neutrinoless Double Beta Decay, S. Stoica, Int. Symp. on Phys. of Unstable Nuclei (ISPUN14), HoChiMinh-Vietnam, November 3-8, 2014 (invited lecture).

- Shell model calculations for neutrinoless double beta decay, S. Stoica, 11th International Spring Seminar on Nuclear Physics, ISCHIA-Italy, May 12-16, 2014 (invited lecture).

- Nuclear Structure Calculations for DBD and Neutrino Parameters Derived from LNV Processes at Low and High Energies, S. Stoica, Inst. of Phys., Vietnam Academy of Science and Technology, Hanoi, November 11, 2014 (invited seminar).

- Values of the phase space factors for double beta decay, S. Stoica and M. Mirea, WORKSHOP ON CALCULATION OF DOUBLE-BETA-DECAY MATRIX ELEMENTS (MEDEX’15), Prague, 9-12 June. 2015.

- Theoretical aspects of double beta decay, S. Stoica, XIV International Conference on Topics in Astroparticles and Underground Physics (TAUP15), Torino, 7-11 September, 2015.

**c) Other results **

- Following the results obtained in the field, project members were invited to give oral presentations and invited lectures at international conferences mentioned in the bibliography.

- Two members of the Project have been members of the Organizing Committee of the ECT* workshop: “Towards a Resolution of the DBD Problem”, 3-7 September, 2012, Trento, Italy.: S. Stoica-main organizer and M. Horoi) (Website);

- One of the project member, S. Stoica, with HHF affiliation, has become an associate member of SuperNEMO international collaboration (see the associate membership document).

- The project helped to develop international collaborations. Two foreign researchers visited Horia Hulubei Foundation: prof. Jameel Un- Nabi Jameel, dean at the GIK Institute, Pakistan and dr. Javier Menendez from Darmstadt, Germany, with which we started collaborations on topics related to the project theme .

- Completion of a PhD thesis in the project domain, double beta decay. A. Neacsu, a project team member, included part of the above described results in his doctoral thesis : " Charge-exchange exotic reactions” He defended his thesis in a public session, on October 24, 2013

A remarkable result is the receipt of our group, its leader (S. Stoica ) with HHF affiliation as associate member of the SuperNEMO prestigious international collaboration, which aims to build a new generation detector for measuring a DBD in the underground laboratory in Modane , France. The receipt was made after the presentation of our achievements in SuperNEMO meeting, from Paris, 22- 25 October 2012 .

S. Stoica was invited to join the conference program committee MANPP13 (http://www.engii.org/workshop/manpp2013august/ ).

With these results we consider, the appropriate objectives of the project have been fulfilled

Other projects, actually the most recent ones, can be found in the entry UNESCO Chair and in CIFRA website.