Thu·Sep 22, 2022Thursday·September 22, 2022

1. 01*

   Observation of the radiative decay of the ${}^{229}\mathrm{Th}$ nuclear clock isomer

   Sandro Kraemer🇧🇪 · Janni Moens🇧🇪 · Michail Athanasakis-Kaklamanakis🇨🇭 · Silvia Bara🇧🇪 · Kjeld Beeks🇦🇹 · Premaditya Chhetri🇧🇪 · Katerina Chrysalidis🇨🇭 · Arno Claessens🇧🇪 · Thomas E. Cocolios🇧🇪 · João M. Correia🇵🇹 · Hilde De Witte🇧🇪 · Rafael Ferrer🇧🇪 and 23 other authors

   The nucleus of the radioisotope thorium-229 (${}^{229}$Th) features an isomer with an exceptionally low excitation energy that enables direct laser manipulation of nuclear states. For this reason, it is a leading candidate for use in next-generation optical clocks. This nuclear clock will be a unique tool, amongst others, for tests of fundamental physics. While first indirect experimental evidence for the existence of such an extraordinary nuclear state is significantly older, the proof of existence has been delivered only recently by observing the isomer's electron conversion decay and its hyperfine structure in a laser spectroscopy study, revealing information on the isomer's excitation energy, nuclear spin and electromagnetic moments. Further studies reported the electron conversion lifetime and refined the isomer's energy. In spite of recent progress, the isomer's radiative decay, a key ingredient for the development of a nuclear clock, remained unobserved. In this Letter, we report the detection of the radiative decay of this low-energy isomer in thorium-229 (${}^{229\mathrm{m}}$Th). By performing vacuum-ultraviolet spectroscopy of ${}^{229\mathrm{m}}$Th incorporated into large-bandgap CaF${}_2$ and MgF${}_2$ crystals at the ISOLDE facility at CERN, the photon vacuum wavelength of the isomer's decay is measured as 148.71(42) nm, corresponding to an excitation energy of 8.338(24) eV. This value is in agreement with recent measurements, and decreases the uncertainty by a factor of seven. The half-life of ${}^{229\mathrm{m}}$Th embedded in MgF${}_2$ is determined to be 670(102) s. The observation of the radiative decay in a large-bandgap crystal has important consequences for the design of a future nuclear clock and the improved uncertainty of the energy eases the search for direct laser excitation of the atomic nucleus.

   nucl-exNature(2023)·96 citations
2. 02*

   Measurement of Hadron Production in ${\pi }^{-}$-C Interactions at 158 and 350 GeV/c with NA61/SHINE at the CERN SPS

   NA61/SHINE Collaboration: H. Adhikary · K.K. Allison · N. Amin · E.V. Andronov · T. Antićić · I.-C. Arsene · Y. Balkova · M. Baszczyk · D. Battaglia · S. Bhosale · A. Blondel · M. Bogomilov and 145 other authors

   We present a measurement of the momentum spectra of ${\pi }^{\pm }$, K${}^{\pm }$, p${}^{\pm }$, $\Lambda$, $\bar{\Lambda }$ and K${}_S^0$ produced in interactions of negatively charged pions with carbon nuclei at beam momenta of 158 and 350 GeV/c. The total production cross sections are measured as well. The data were collected with the large-acceptance spectrometer of the fixed target experiment NA61/SHINE at the CERN SPS. The obtained double-differential $p$-$p_T$ spectra provide a unique reference data set with unprecedented precision and large phase-space coverage to tune models used for the simulation of particle production in extensive air showers in which pions are the most numerous projectiles.

   nucl-exastro-ph.HEPRD(2023)·32 citations
3. 03*

   Quarkonia production in (ultra-)peripheral PbPb collisions at LHCb

   Xiaolin Wang🇨🇳

   The cross-sections of coherent \jpsi and \psitwos production in ultra-peripheral PbPb collisions at a nucleon-nucleon center-of-mass energy of $5.02\mathrm{TeV}$ are measured using a data sample collected in 2018 at $\text{lhcb}$, and the differential cross-sections are measured separately as a function of transverse momentum and rapidity. The photo-production of \jpsi mesons at low transverse momentum is studied in peripheral PbPb collisions, \jpsi candidates are reconstructed through the prompt decay into \mumu in the rapidity region of $2.0<y<4.5$. These results significantly improve previous measurements and are compared to the latest theoretical predictions.

   ↳ hep-exnucl-ex0 citations
4. 04*

   Theoretical discrepancies in the nucleon spin structure and the hyperfine splitting of muonic hydrogen

   Vladimir Pascalutsa (JGU)🇩🇪 · Franziska Hagelstein (JGU & PSI)🇩🇪 · Vadim Lensky (JGU)🇩🇪

   Two groups, ours (Mainz) and Bochum, have recently been re-evaluating the spin polarizabilities and spin structure functions at low $Q$, using the baryon chiral perturbation theory (B$\chi$PT), the manifestly-covariant counterpart of the heavy-baryon chiral perturbation theory (HB$\chi$PT). Whilst the two groups agree that the B$\chi$PT framework works better than HB$\chi$PT in this sector, their quantitative results disagree in some of the quantities; most notably, the proton spin polarizabilities ${\gamma }_0$ and ${\delta }_{LT}$. These discrepancies are especially intriguing in light of new experimental data coming from the Jefferson Lab "Spin Physics Program". The preliminary data on the proton are reported by Karl Slifer in a plenary session of this workshop. Another theoretical discrepancy is emerging in the proton-polarizability contribution to the hyperfine splitting (hfs) in hydrogen and muonic hydrogen. Our B$\chi$PT calculation shows a significantly smaller effect than the state-of-the-art data-driven evaluations based on empirical spin structure functions. The smaller polarizability contribution leads to a smaller Zemach radius of the proton. This discrepancy could be relevant for the planned first-ever measurement of the ground-state hfs in muonic hydrogen.

   ↳ hep-phnucl-exnucl-thPoS(2024)·2 citations
5. 05*

   Chiral spin symmetry and hot/dense QCD

   L. Ya. Glozman🇦🇹

   Above the chiral symmetry restoration crossover around T_{ch} ~ 155 MeV a new regime arises in QCD, a stringy fluid, which is characterized by an approximate chiral spin symmetry of the thermal partition function. This symmetry is not a symmetry of the Dirac Lagrangian and is a symmetry of the electric part of the QCD Lagrangian. In this regime the medium consists of the chirally symmetric and approximately chiral spin symmetric hadrons that are made of the chirally symmetric quarks connected into the color singlet compounds by a confining chromoelectric field. This regime is evidenced by the approximate chiral spin symmetry of the spatial and temporal correlators and by the breakdown of the thermal perturbation theory at the crossover between the partonic (the quark-gluon plasma) and stringy fluid regimes at ~ 3 T_{ch}. The chiral spin symmetry smoothly disappears above ~ 3T_{ch} which means that the chromoelectric confining interaction gets screened. A direct evidence that the stringy fluid medium consists of densely packed hadrons is the pion spectral function that shows a distinct pion state and its first radial excitation above T_{ch}. Another direct evidence of the hadron degrees of freedom in the stringy fluid is the bottomonium spectrum with the 1S,2S,3S and 1P,2P radial and orbital excitations that become broad with temperature. The hadrons between T_{ch} and ~ 3 T_{ch} in the stringy fluid interact strongly which makes the stringy fluid more a liquid rather than a gas. We discuss how this chiral spin symmetric regime extends into the finite chemical potentials domain and present a qualitative sketch of the QCD phase diagram.

   ↳ hep-lathep-phhep-thnucl-ex+1PPNP(2023)·35 citations
6. 06*

   Cumulants of net-strangeness multiplicity distributions at energies available at the BNL Relativistic Heavy Ion Collider

   Changfeng Li🇨🇳 · Deeptak Biswas🇮🇳 · Nihar Ranjan Sahoo🇨🇳

   The higher-order cumulants of net-proton number, net-charge, and net-strangeness multiplicity distributions are widely studied to search for the quantum-chromodynamics critical point and extract the chemical freeze-out parameters in heavy-ion collisions. In this context, the event-by-event fluctuations of the net-strangeness multiplicity distributions play important roles in extracting the chemical freeze-out parameter in the strangeness sector. Due to having difficulties in detecting all strange hadrons event by event, the kaon ($K$) and lambda ($\Lambda$) particles serve as a proxy for the strangeness-related observables in heavy-ion collisions. We have studied the net-$K$, net-$\Lambda$, and net-($K$ + $\Lambda$) multiplicity distributions and calculated their different order of cumulants using the ultrarelativistic quantum molecular dynamics model and hadron resonance gas calculation. To adequately account for the net-strangeness cumulants, it has been found that the inclusion of resonance decay contributions in $K$ and $\Lambda$ is necessary.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2023)·1 citation
7. 07*

   Unified Balance Functions

   Claude Pruneau🇺🇸 · Victor Gonzales · Brian Hanley🇺🇸 · Ana Marin🇩🇪 · Sumit Basu🇸🇪

   The use of charge balance functions in heavy-ion collision studies was initially proposed as a probe of delayed hadronization and two-stage quark production in these collisions. It later emerged that general balance functions can also serve as a probe of the diffusivity of light quarks as well as the evolution of the systems formed in heavy-ion collisions. In this work, we reexamine the formulation of general balance functions and consider how to best define and measure these correlation functions in terms of differences of conditional densities of unlike-sign and like-sign particle pairs. We define general balance functions in terms of associated particle functions and show these obey a simple sum rule. We additionally proceed to distinguish between balance functions expressed as differences of conditional densities valid irrespective of experimental acceptance boundaries and bound balance functions that explicitly account for the limited acceptance of experiments. General balance functions are additionally extended to accommodate strange, baryon, as well as charm and bottom quantum numbers based on the densities of these quantum numbers.

   ↳ hep-phnucl-exnucl-thPRC(2023)·16 citations
8. 08*

   Reply to "Comment on Sequential Single-pion Production Explaining the dibaryon $d^{\ast }(2380)$ peak''

   R. Molina🇪🇸 · N. Ikeno🇯🇵 · E. Oset🇪🇸

   In a comment [arXiv:2106.00494] to our paper on ``Sequential single-pion production explaining the dibaryon $d^{\ast }(2380)$ peak'' the authors provide arguments that apparently invalidate our claims and present what they call ``proofs'' of the dibaryon explanation of the $np\to {\pi }^0{\pi }^{0}d$ fusion reaction. In this reply we refute the arguments of the comment and show that no existing experiment proves the dibaryon nature of the peak of the fusion reaction.

   ↳ nucl-thnucl-exCPC(2023)·30 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.