Fri·Mar 30, 2018Friday·March 30, 2018

1. 01*

   Search for dark matter decay of the free neutron from the UCNA experiment: n $\to \chi +e^{+}{e}^{-}$

   X. Sun · E. Adamek · B. Allgeier · M. Blatnik · T. J. Bowles · L. J. Broussard · M. A.-P. Brown · R. Carr · S. Clayton · C. Cude-Woods · S. Currie · E. B. Dees and 49 other authors

   It has been proposed recently that a previously unobserved neutron decay branch to a dark matter particle ($\chi$) could account for the discrepancy in the neutron lifetime observed in experiments that use two different measurement techniques. One of the possible final states discussed includes a single $\chi$ along with an $e^{+}{e}^{-}$ pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with $\sim 4\pi$ acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). The summed kinetic energy ($E_{e^{+}{e}^{-}}$) from such events is used to set limits, as a function of the $\chi$ mass, on the branching fraction for this decay channel. For $\chi$ masses consistent with resolving the neutron lifetime discrepancy, we exclude this as the dominant dark matter decay channel at $\gg 5\sigma$ level for $100\text{keV}<E_{e^{+}{e}^{-}}<644\text{keV}$. If the $\chi +e^{+}{e}^{-}$ final state is not the only one, we set limits on its branching fraction of $<10^{-4}$ for the above $E_{e^{+}{e}^{-}}$ range at $>90\%$ confidence level.

   nucl-exphysics.ins-detPRC(2018)·65 citations
2. 02*

   New determination of the spectroscopic factor of ${}^7$Be ground state and the ${}^6$Li($p,\gamma$)${}^7$Be astrophysical S(E) factors

   Zhi-Hong Li · Er-Tao Li · Jun Su🇨🇳 · Yun-Ju Li🇨🇳 · You-Bao Wang · Sheng-Quan Yan🇨🇳 · Bing Guo · Ding Nan · Wei-Ping Liu

   The `lithium problem' in Big Bang Nucleosynthesis (BBN) has recently focused on the reactions involving ${}^7$Be. The ${}^6$Li($p,\gamma$)${}^7$Be reaction can provide us not only the information for destroying ${}^6$Li but also the information for producing ${}^7$Be. In the present work, the proton spectroscopic factor in ${}^7$Be was extracted to be 0.70 $\pm$ 0.17 from the angular distribution of ${}^7$Be($d$, ${}^3$He)${}^6$Li at $E_{c.m.}$ = 6.7 MeV. The value was then used to compute the direct component of the astrophysical ${}^6$Li($p,\gamma$)${}^7$Be${}_{g.s.}$ S(E) factors and determine the resonance parameters from the total S(E) factors.

   nucl-exnucl-thCPC(2018)·8 citations
3. 03*

   Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains

   I. Mukha🇩🇪 · L.V. Grigorenko🇷🇺 · D. Kostyleva🇩🇪 · L. Acosta🇮🇹 · E. Casarejos🇪🇸 · A.A. Ciemny🇵🇱 · W. Dominik🇵🇱 · J.A. Dueñas🇪🇸 · V. Dunin🇷🇺 · J. M. Espino🇪🇸 · A. Estradé🇬🇧 · F. Farinon🇩🇪 and 36 other authors

   The proton-unbound argon and chlorine isotopes have been studied by measuring trajectories of their decay-in-flight products by using a tracking technique with micro-strip detectors. The proton ($1p$) and two-proton ($2p$) emission processes have been detected in the measured angular correlations "heavy-fragment"+$p$ and "heavy-fragment"+$p$+$p$, respectively. The ground states of the previously unknown isotopes ${}^{30}$Cl and ${}^{28}$Cl have been observed for the first time, providing the $1p$-separation energies $S_p$ of $-0.48(2)$ and $-1.60(8)$ MeV, respectively. The relevant systematics of $1p$ and $2p$ separations energies have been studied theoretically in the core+$p$ and core+$p$+$p$ cluster models. The first-time observed excited states of ${}^{31}$Ar allow to infer the $2p$-separation energy $S_{2p}$ of 6(34) keV for its ground state. The first-time observed state in ${}^{29}$Ar with $S_{2p}=-5.50(18)$ MeV can be identified either as a ground or an excited state according to different systematics.

   nucl-exPRC(2018)·19 citations
4. 04*

   Ordinary muon capture studies for the matrix elements in $\beta \beta$ decay

   D. Zinatulina🇷🇺 · V. Brudanin🇷🇺 · V. Egorov🇷🇺 · C. Petitjean🇨🇭 · M. Shirchenko🇷🇺 · J. Suhonen🇫🇮 · I. Yutlandov

   Precise measurement of $\gamma$-rays following ordinary (non-radiative) capture of negative muons by natural Se, Kr, Cd and Sm, as well as isotopically enriched ${}^{48}$Ti, ${}^{76}$Se, ${}^{82}$Kr, ${}^{106}$Cd and ${}^{150}$Sm targets was performed by means of HPGe detectors. Energy and time distributions were investigated and total life time of negative muon in different isotopes was deduced. Detailed analysis of $\gamma$-lines intensity allows to extract relative yield of several daughter nuclei and partial rates of ($\mu$,$\nu$) capture to numerous excited levels of the ${}^{48}$Sc, ${}^{76}$As, ${}^{82}$Br, ${}^{106}$Ag and ${}^{150}$Tc isotopes which are considered to be virtual states of an intermediate odd-odd nucleus in 2$\beta$-decay of ${}^{48}$Ca, ${}^{76}$Ge, ${}^{82}$Se, ${}^{106}$Cd and ${}^{150}$Nd, respectively. These rates are important as an experimental input for the theoretical calculation of the nuclear matrix elements of 2$\beta$-decay.

   nucl-exPRC(2019)·53 citations
5. 05*

   Improved limit on neutrinoless double beta decay of ${}^{76}$Ge from GERDA Phase II

   M. Agostini🇮🇹 · A.M. Bakalyarov🇷🇺 · M. Balata🇮🇹 · I. Barabanov🇷🇺 · L. Baudis🇨🇭 · C. Bauer🇩🇪 · E. Bellotti🇮🇹 · S. Belogurov🇷🇺 · A. Bettini🇮🇹 · L. Bezrukov🇷🇺 · J. Biernat🇵🇱 · T. Bode🇩🇪 and 96 other authors

   The GERDA experiment searches for the lepton number violating neutrinoless double beta decay of ${}^{76}$Ge (${}^{76}$Ge $\to$ ${}^{76}$Se + 2e${}^{-}$) operating bare Ge diodes with an enriched ${}^{76}$Ge fraction in liquid argon. The exposure for BEGe-type detectors is increased threefold with respect to our previous data release. The BEGe detectors feature an excellent background suppression from the analysis of the time profile of the detector signals. In the analysis window a background level of $1.0_{-0.4}^{+0.6}\cdot 10^{-3}$ cts/(keV$\cdot$kg$\cdot$yr) has been achieved; if normalized to the energy resolution this is the lowest ever achieved in any 0$\nu \beta \beta$ experiment. No signal is observed and a new 90 \% C.L. lower limit for the half-life of $8.0\cdot 10^{25}$ yr is placed when combining with our previous data. The median expected sensitivity assuming no signal is $5.8\cdot 10^{25}$ yr.

   nucl-exphysics.ins-detPRL(2018)·360 citations
6. 06*

   Nuclear parton density functions from dijet photoproduction at the EIC

   M. Klasen🇩🇪 · K. Kovarik🇩🇪

   We study the potential of dijet photoproduction measurements at a future electron-ion collider (EIC) to better constrain our present knowledge of the nuclear parton distribution functions. Based on theoretical calculations at next-to-leading order and approximate next-to-next-to-leading order of perturbative QCD, we establish the kinematic reaches for three different EIC designs, the size of the parton density function modifications for four different light and heavy nuclei from He-4 over C-12 and Fe-56 to Pb-208 with respect to the free proton, and the improvement of EIC measurements with respect to current determinations from deep-inelastic scattering and Drell-Yan data alone and when also considering data from existing hadron colliders.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2018)·24 citations
7. 07*

   Event engineering studies for heavy flavor production and hadronization in high multiplicity hadron-hadron and hadron-nucleus collisions

   Yan-Qing Ma🇨🇳 · Prithwish Tribedy🇺🇸 · Raju Venugopalan🇺🇸 · Kazuhiro Watanabe🇺🇸

   Heavy flavor measurements in high multiplicity proton-proton and proton-nucleus collisions at collider energies enable unique insights into their production and hadronization mechanism because experimental and theoretical uncertainties cancel in ratios of their cross-sections relative to minimum bias events. We explore such event engineering using the Color Glass Condensate (CGC) effective field theory to compute short distance charmonium cross-sections. The CGC is combined with heavy-quark fragmentation functions to compute $D$-meson cross-sections; for the $J/\psi$, hadronization is described employing Nonrelativistic QCD (NRQCD) and an Improved Color Evaporation model. Excellent agreement is found between the CGC computations and the LHC heavy flavor data in high multiplicity events. Event engineering in this CGC+NRQCD framework reveals a very rapid growth in the fragmentation of the ${}^3{S}_1^{[8]}$ state in rare events relative to minimum bias events.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2018)·73 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.