Department of Physics

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Nuclear Structure, Nuclear Decays, Rare and Exotic Processes

The nuclear-theory group of JYFL develops nuclear-structure models and applies them to topics of weak-interaction physics. The topics include neutrino-nucleus interactions at supernova energies, rare weak decays like forbidden beta decays and double beta decays, and direct dark-matter detection. The group is theory member of the large experimental underground experiments SUPERNEMO and COBRA and collaborates with experimental groups at JYFL, RCNP, etc. The group has strong theory collaboration with La Plata in Argentina, Bucharest in Romania and Yale University in USA. The group hosts currently one professor, one post-doctoral researcher and five graduate students.

Contact person: Jouni Suhonen

  • Group members »
    • Jouni Suhonen, professor
    • Jenni Kotila, postdoctoral researcher
    • Wafa Almosly, doctoral student
    • Mikko Haaranen, doctoral student
    • Juhani Hyvärinen, doctoral student
    • Pekka Pirinen, doctoral student
    • Lotta Jokiniemi, MSc student
    • Joel Kostensalo, MSc student
    Previous years
    2015
  •  Recent research
    • Neutrinoless double beta decay probed by forbidden beta decays »

      Discovery of the neutrinoless double beta (0νββ) decay of atomic nuclei is at present one of the top priorities of particle physics. Its detection would imply that neutrino is a massive Majorana particle and that lepton-number conservation does not hold. Current experiments give only lower limits to the half-life of the decay but future experiments may be in a position to detect it.

      The measured half-life of 0νββ decay can be translated into neutrino mass through the nuclear matrix elements (NMEs). The 0νββ decay proceeds by virtual β-decay transitions from the 0+ ground state of the mother nucleus to the Jp multipole states of the neighboring odd-odd nucleus (here p is parity). These intermediate Jp states are, in turn, connected by virtual β-decay transitions to the 0+ ground state (or some excited state) of the even-even daughter nucleus. The corresponding NME can be divided into pieces corresponding to each of the Jp multipole channels. This Jp decomposition is shown in below for the 0νββ decay sequences 96Zr-96Nb-96Mo and 136Xe-136Cs-136Ba [1].

       

      Decomposition of NMEs for Zr and Xe
      Decomposition of the NMEs for the 0νββ decays of 96Zr and 136Xe.

      The virtual transitions can be studied by comparing their NMEs with the corresponding NMEs for the K-fold forbidden unique beta decays, where a single NME mediates the transition. In Figure below is shown the ratio k = M(pnQRPA)/M(qp) for the β-decay transitions between a 0+ state and the states Jp=2+,4-,5+,6-,7+,8- for K=2,3,4,5,6,7, respectively. The transitions occur in different nuclei identified by the mass number A of the horisontal axis. Here M(pnQRPA) is the NME computed by using the proton-neutron quasiparticle random-phase approximation and M(qp) is its simple two-quasiparticle reduction. The ratio k is indicative of the evolution of the NMEs when going from a simple quasiparticle approximation towards a more complex configuration-interaction framework, allowing extrapolation to the true (possibly measurable) NME [2].

       

      Ratio k as a function of the mass number A
      Ratio k as a function of the mass number A for the K-fold forbidden unique β-decay transitions.

      One further way to study the Jp multipole NMEs of the 0νββ decay is to relate them to the quenching of the value of the weak axial-vector coupling constant gA. This is a novel approach, introduced in [3] and further advanced in [4]. This approach, coined the spectrum-shape method (SSM), is based on the observed strong sensitivity of the theoretical shape of the electron spectrum of a K-fold forbidden non-unique (mediated by several NMEs) beta decay to the value of gA. In the SSM the extraction of the effective value of  gA is done by comparing the computed spectrum shape with that obtained in the present and future β-decay experiments. It turns out that the SSM is a robust tool, surprisingly independent of the details of the nuclear mean field or the adopted nuclear Hamiltonian. This is demonstrated in Figure below for the decay of 113Cd to the ground state of 113Sn, computed using three different theory frameworks: The microscopic quasiparticle-phonon model (MQPM), the nuclear shell model (NSM) and the microscopic interacting boson-fermion model (IBM). All three models point consistently to a quenched value gA=0.9 for this 4-fold forbidden transition.

       

      Comparison of the computed and experimental electron spectra
      Comparison of the computed and experimental electron spectra for the 4-fold forbidden non-unique β-decay transition from 113Cd(1/2+) to113Sn(9/2+).


      [1] J. Hyvärinen and J. Suhonen, Nuclear matrix elements for  0νββ decays with light or heavy Majorana-neutrino exchange, Phys. Rev. C 91 (2015) 024613.
      [2] J. Kostensalo and J. Suhonen, Spin-multipole nuclear matrix elements in the pn quasiparticle random-phase approximation: Implications for β and ββ half-lives, Phys. Rev. C 95 (2017) 014322.
      [3] M. Haaranen, P.C. Srivastava and J. Suhonen, Forbidden non-unique β decays and effective values of weak coupling constants, Phys. Rev. C 93 (2016) 034308.
      [4] M. Haaranen, J. Kotila and J. Suhonen, Spectrum-shape method and the next-to-leading-order terms of the β-decay shape factor, Phys. Rev. C, in press.

       

    • Rare weak decays, neutrino mass and effective weak coupling constants »


      Rare weak-decay processes owe their slow decay rates to (a) tiny decay energies (Q values), (b) large differences in spins of the initial and final states of decay and (c) decay channels of second order in weak interactions [1,2]. Decays with tiny Q values can be used for detection of the neutrino mass [1,2]. The decays of category (b) can be used, e.g., to probe the effective values of the vector coupling coefficient gV and axial-vector coupling coefficient gA as proposed in [3]. There the electron-spectrum shape of the high-forbidden non-unique beta-decay transitions is shown to be very sensitive to the values of gA and gV, thus enabling the extraction of these values by comparing with the present and future experimental data on the spectrum shape. The method was coined SSM (Spectrum Shape Method). The study has recently been extended in [4] to include now three different theory frameworks, namely the Microscopic Quasiparticle-Phonon Model (MQPM), the Nuclear Shell Model (NSM) and the microscopic Interacting Boson-Fermion Model (IBFM-2). Matching of the experimental and computed electron spectrum shapes for the decay of the 1/2+ ground state of  113Cd to the 9/2+ ground state of 113In yields the optimum spectra for the three theory models with  gA=0.9 and  gV=1.0. This is remarkable and shows that SSM is a robust tool to determine the effective value of the weak coupling constants, largely independent of the chosen nuclear Hamiltonian and the many-body approximations used to solve it.

      Comparison of the computed and experimental electron spectra
      Comparison of the computed and experimental electron spectra for the 4-fold forbidden non-unique β-decay transition from 113Cd(1/2+) to113Sn(9/2+).

      The effective value of gA can also be studied by comparing the computed results with the data for the Gamow-Teller type of single and double beta decays as discussed in [5-8]. The study of Ref. [9] shows that contributions from the Gamow-Teller 1+ and spin-dipole 2- states are conspicuous in the nuclear matrix elements related to neutrinoless double beta decays. It is thus of paramount importance to study the quenching effects of these contributions through the renormalization of gA. First step toward this direction is taken in Ref. [10]. Higher contributions have lately been addressed in a special case of mass A=96 nuclei in Ref. [11] where both beta and double-beta data can be used together with the computed nuclear matrix elements to pin down the effective value of  gin a unique way. In another recent work [12] a wide scan of different high-forbidden unique beta decays was done to follow the suppression of the spin-multipole nuclear matrix elements from the two-quasiparticle level, through the pnQRPA (proton-neutron Quasiparticle Random-Phase Approximation) level to the experimental one. The suppression was found to be rather uniform through different degrees of forbiddeness. A more extensive exploratory investigation of the candidates for the SSM is in progress [13].

       

      [1] J. Suhonen, Phys. Scripta 89 (2014) 054032
      [2] J. Suhonen, EPJ Web of Conferences 66 (2014) 08007
      [3] M. Haaranen, P. C. Srivastava and J. Suhonen, Phys. Rev. C 93 (2016) 034308
      [4] M. Haaranen, J. Kotila and J. Suhonen, Phys. Rev. C 95 (2017), 024327
      [5] J. Suhonen and O. Civitarese, Phys. Lett. B 725 (2013) 153 ; ibid Nucl. Phys. A 924 (2014) 1
      [6] H. Ejiri and J. Suhonen, J. Phys. G: Nucl. Part. Phys. 42 (2015) 055201
      [7] P. Pirinen and J. Suhonen, Phys. Rev. C 91 (2015) 054309
      [8] F. F. Deppisch and J. Suhonen, Phys. Rev. C 94 (2016) 055501
      [9] J. Hyvärinen and J. Suhonen, Adv. In High Energy Physics 2016 (2016) 4714829
      [10] H. Ejiri, N. Soukouti and J. Suhonen, Phys. Lett. B 729 (2014) 27
      [11] M. Alanssari et al., Phys. Rev. Lett. 116 (2016) 072501
      [12] J. Kostensalo and J. Suhonen, Phys. Rev. C 95 (2017) 014322
      [13] J. Kostensalo, M. Haaranen and J. Suhonen, submitted for publication



    • Neutrinoless double beta decays mediated by various mechanisms »


      In the search for massive Majorana neutrinos and their absolute mass scale the process of neutrinoless double beta (0νββ) decay of atomic nuclei plays a leading role, and once observed would offer new information on many fundamental aspects of elementary particle physics. As major experimental efforts are being made for the observation of this process, another essential step in the study of 0νββ decay is the calculation of nuclear matrix elements and phase-space factors, which are crucial for extracting information on physics beyond the standard model, like the neutrino mass, from the experimental half-lives.

      Several scenarios of neutrinoless double-beta decay have been considered, most notably, light neutrino exchange, heavy neutrino exchange, and Majoron emission. Lately, a comprehensive calculation of the nuclear matrix elements of the neutrinoless double beta decay, mediated by light or heavy Majorana neutrinos, was carried out in [1] by exploiting fast recursive methods [2] to allow computational feasibility. At the same time the effect of deformation on the rates of two-neutrino double beta decay was studied in [3] by using a consistent deformed approach. An extension to calculations of the neutrinoless mode is in progress. These modes of decay were studied experimentally by the NEMO (Neutrino Ettore Majorana Observatory) collaboration for 100Mo in [4], for 48Ca in [5], for 150Nd in [6] and for 116Cd in [7]. Majorons were introduced years ago as massless Nambu-Goldstone bosons arising from a global B − L symmetry, broken spontaneously in the low-energy regime. These bosons couple to the Majorana neutrinos and give rise to neutrinoless double-beta decay, accompanied by Majoron emission. Besides neutrinoless double beta decay the Majorons are of great interest since they may play important role also in cosmology and dark-matter searches. Recently we have done an extensive investigation of neutrinoless double beta decay proceeding through emission of one or two Majorons. Combining the obtained predictions with experimental lower bounds, limits on the effective Majoron-neutrino coupling constant can be set [8].

      In recent years, the possible occurrence of sterile massive neutrinos has attracted considerable attention, and searches are under way to detect their presence in oscillation experiments and in accelerator experiments. Several suggestions have been made for the presence of sterile neutrinos with masses from the eV mass all the way up to TeV mass range. Recently we have calculated the nuclear matrix elements and phase-space factors for the exchange of arbitrary mass sterile neutrinos [9] in double beta decay. The thus deduced theoretical 0νββ half-lives can be used to guide planning of future experiments.

      [1] J. Hyvärinen and J. Suhonen, Phys. Rev. C 91 (2015) 024613
      [2] J. Hyvärinen and J. Suhonen, Phys. Rev. C 91 (2015) 054308
      [3] D. S. Delion and J. Suhonen, Phys. Rev. C 91 (2015) 054329
      [4] R. Arnold et al., Phys. Rev. D 92 (2015) 072011
      [5] R. Arnold et al., Phys. Rev. D 93 (2016) 112008
      [6] R. Arnold et al., Phys. Rev. D 94 (2016) 072003
      [7] R. Arnold et al., Phys. Rev. D 95 (2017) 012007
      [8] J. Kotila, J. Barea and F. Iachello, Phys. Rev. C 91 (2015) 064310
      [9] J. Barea, J. Kotila and F. Iachello, Phys. Rev. D 92 (2015) 093001


       

    • Neutrino-nucleus scattering at supernova energies »
    • Direct WIMP detection rates in 83Kr and 125Te »

      Presently, there exists plenty of evidence of the existence of dark matter. One of the candidate constituents for dark matter is the weakly interacting massive particle (WIMP), motivated by various theoretical models going beyond the standard model. Currently, there are many experimental setups which search for the WIMP signal. In the recent work [1] we analyzed the possibility to use 83Kr as a detector material. The nucleus 83Kr would offer strong kinematic advantages over many other nuclei in the inelastic channel, due to its very low-lying excited state. We found that 83Kr would make a feasible detector material, although the nuclear-structure considerations seem to slightly weaken the promise of the nucleus as a WIMP target. Recently we have extended this work to 125Te target nucleus and specified the WIMP to be the supersymmetry-predicted stable particle, LSP (lightest supersymmetric particle) [2,3].

      [1] J. D. Vergados, F. T. Avignone III, P. Pirinen, P. C. Srivastava, M. Kortelainen and J. Suhonen, Phys. Rev. D 92 (2015) 015015
      [2] P. Pirinen, P. C. Srivastava, J. Suhonen and M. Kortelainen, Phys. Rev. D 93 (2016) 095012
      [3] J. D. Vergados, F. T. Avignone III, M. Kortelainen, P. Pirinen, P. C. Srivastava, J. Suhonen and A. W. Thomas, J. Phys. G: Nucl. Part. Phys. 43 (2016) 115002

    • Left-right mixing angle in the left-right extensions of the standard model »

      The minimal extension of the standard model of electroweak interactions allows for massive neutrinos, a massive right-handed boson and a left-right mixing angle. While an estimate of the light (electron) neutrino can be extracted from the non-observation of the neutrinoless double beta decay, the limits on the mixing angle and the mass of the right-handed boson may be extracted from a combined analysis of the double beta decay measurements (GERDA, EXO-200 and KamLAND-Zen collaborations) and ATLAS data on the two-jets two-leptons signals following the excitation of a virtual right-handed boson coupled to a heavy neutrino [1].

      [29] O. Civitarese, J. Suhonen and K. Zuber, Int. J. Mod. Phys. E 25 (2016) 1650081



  • Recent publications »


    M. Haaranen, P. C. Srivastava and J. Suhonen, Forbidden nonunique β decays and effective values of weak coupling constants, Phys. Rev. C 93 (2016) 034308

     M. Alanssari, D. Frekers, T. Eronen, L. Canete, J. Dilling, M. Haaranen, J. Hakala, M. Holl, M. Jeskovsky, A. Jokinen, A. Kankainen, J. Koponen, A. J. Mayer, I. D. Moore, D. A. Nesterenko, I. Pohjalainen, P. Povinec, J. Reinikainen, S. Rinta-Antila, P. C. Srivastava, J. Suhonen, R. I. Thompson, A. Voss, and M. E. Wieser, Single and double beta-decay Q values among the triplet 96Zr, 96Nb, and 96Mo, Phys. Rev. Lett. 116 (2016) 072501

    R. Arnold, C. Augier, A. M. Bakalyarov, J. D. Baker, A. S. Barabash, A. Basharina-Freshville, S. Blondel, S. Blot, M. Bongrand, V. Brudanin, J. Busto, A. J. Caffrey, S. Calvez, M. Cascella, C. Cerna, J. P. Cesar, A. Chapon, E. Chauveau, A. Chopra, D. Duchesneau, D. Durand, V. Egorov, G. Eurin, J. J. Evans, L. Fajt, D. Filosofov, R. Flack, X. Garrido, H. Gomez, B. Guillon, P. Guzowski, R. Hodak, A. Huber, P. Hubert, C. Hugon, S. Jullian, A. Klimenko, O. Kochetov, S. I. Konovalov, V. Kovalenko, D. Lalanne, K. Lang, V. I. Lebedev, Y. Lemiere, T. Le Noblet, Z. Liptak, X. R. Liu, P. Loaiza, G. Lutter, F. Mamedov, C. Marquet, F. Mauger, B. Morgan, J. Mott, I. Nemchenok, M. Nomachi, F. Nova, F. Nowacki, H. Ohsumi, R. B. Pahlka, F. Perrot, F. Piquemal, P. Povinec, P. Pridal, Y. A. Ramachers, A. Remoto, J. L. Reyss, B. Richards, C. L. Riddle, E. Rukhadze, N. I. Rukhadze, R. Saakyan, R. Salazar, X. Sarazin, Yu. Shitov, L. Simard, F. Simkovic, A. Smetana, K. Smolek, A. Smolnikov, S. Söldner-Rembold, B. Soule, I. Stekl, J. Suhonen, C. S. Sutton, G. Szklarz, J. Thomas, V. Timkin, S. Torre, Vl. I. Tretyak, V. I. Tretyak, V. I. Umatov, I. Vanushin, C. Vilela, V. Vorobel, D. Waters, S. V. Zhukov and A. Zukauskas, Measurement of the double-beta decay half-life and search for the neutrinoless double-beta decay of 48Ca with the NEMO-3 detector, Phys. Rev. D 93 (2016) 112008

     J. Hyvärinen and J. Suhonen, Neutrinoless ββ decays to excited 0+ states and the Majorana-neutrino mass, Phys. Rev. C 93 (2016) 064306

    J. Hyvärinen and J. Suhonen, Analysis of the intermediate-state contributions to neutrinoless double β- decays, Adv. in High Energy Physics 2016 (2016) 4714829

     R. Arnold, C. Augier, J. D. Baker, A. S. Barabash, A. Basharina-Freshville, S. Blondel, S. Blot, M. Bongrand, V. Brudanin, J. Busto, A. J. Caffrey, S. Calvez, M. Cascella, C. Cerna, J. P. Cesar, A. Chapon, E. Chauveau, A. Chopra, D. Duchesneau, D. Durand, V. Egorov, G. Eurin, J. J. Evans, L. Fajt, D. Filosofov, R. Flack, X. Garrido, H. Gomez, B. Guillon, P. Guzowski, R. Hodak, A. Huber, P. Hubert, C. Hugon, S. Jullian, A. Klimenko, O. Kochetov, S. I. Konovalov, V. Kovalenko, D. Lalanne, K. Lang, Y. Lemiere, T. Le Noblet, Z. Liptak, X. R. Liu, P. Loaiza, G. Lutter, F. Mamedov, C. Marquet, F. Mauger, B. Morgan, J. Mott, I. Nemchenok, M. Nomachi, F. Nova, F. Nowacki, H. Ohsumi, R. B. Pahlka, F. Perrot, F. Piquemal, P. Povinec, P. Pridal, Y. A. Ramachers, A. Remoto, J. L. Reyss, B. Richards, C. L. Riddle, E. Rukhadze, R. Saakyan, R. Salazar, X. Sarazin, Yu. Shitov, L. Simard, F. Simkovic, A. Smetana, K. Smolek, A. Smolnikov, S. Söldner-Rembold, B. Soule, I. Stekl, J. Suhonen, C. S. Sutton, G. Szklarz, J. Thomas, V. Timkin, S. Torre, Vl. I. Tretyak, V. I. Tretyak, V. I. Umatov, I. Vanushin, C. Vilela, V. Vorobel, D. Waters and A. Zukauskas, Measurement of the 2νββ half-life of 150Nd and the search for 0νββ decay processes with the full exposure from the NEMO-3 detector, Phys. Rev. D 94 (2016) 072003

    T. Grahn, J. Pakarinen, L. Jokiniemi, M. Albers, K. Auranen, C. Bauer, C. Bernards, A. Blazhev, P. A. Butler, S. Bönig, A. Damyanova, T. De Coster, H. De Witte, J. Elseviers, L. P. Gaffney, M. Huyse, A. Herzan, U. Jakobsson, R. Julin, N. Kesteloot, J. Konki, Th. Kröll, L. Lewandowski, K. Moschner, P. Peura, M. Pfeiffer, D. Radeck, P. Rahkila, E. Rapisarda, P. Reiter, K. Reynders, M. Rudiger, M.-D. Salsac, M. Sambi, M. Scheck, M. Seidlitz, B. Siebeck, T. Steinbach, S. Stolze, J. Suhonen, P. Thoele, M. Thuerauf, N. Warr, P. Van Duppen, M. Venhart, M. J. Vermeulen, V. Werner, M. Veselsky, A. Vogt, K. Wrzosek-Lipska and M. Zielinska, Collective 21+ excitations in 206Po and 208,210Rn, Eur. Phys. J. A 52 (2016) 340

    O. Civitarese, J. Suhonen and K. Zuber, Combining data from high-energy pp-reactions and neutrinoless double-beta decay: Limits on the mass of the right-handed boson, Int. J. Mod. Phys. E 25 (2016) 1650081

    L. Jokiniemi, J. Suhonen and H. Ejiri, Magnetic hexadecapole gamma transitions and neutrino-nuclear responses in medium-heavy nuclei, Adv. in High Energy Physics 2016 (2016) 8417598

    P. Pirinen, P. C. Srivastava, J. Suhonen and M. Kortelainen, Shell-model study on event rates of lightest supersymmetric particles scattering off 83Kr and 125Te, Phys. Rev. D 93 (2016) 095012

    F. F. Deppisch and J. Suhonen, Statistical analysis of β decays and the effective value of gA in the proton-neutron quasiparticle random-phase approximation framework, Phys. Rev. C 94 (2016) 055501

    J. D. Vergados, F. T. Avignone III, M. Kortelainen, P. Pirinen, P. C. Srivastava, J. Suhonen and A. W. Thomas, Inelastic WIMP-nucleus scattering to the first excited state in 125Te, J. Phys. G 43 (2016) 115002

    W. Almosly, B. G. Carlsson, J. Suhonen, J. Toivanen and E. Ydrefors, Theoretical estimates of supernova-neutrino cross sections for the stable even-even lead isotopes: Charged-current reactions, Phys. Rev. C 94 (2016) 044614

     J. Kotila and J. Barea, Occupation probabilities of single particle levels using the microscopic interacting boson model: Application to some nuclei of interest in neutrinoless double-β decay, Phys. Rev. C 94 (2016) 034320