92Zr(n, γ) and (n,tot) measurements at the GELINA and n_TOF facilities

We are indebted to the anonymous referees for a careful reading of the manuscript and constructive remarks. This research was funded by the European Community Seventh Framework Programme FP7/2007-2011 under the Project CHANDA (Grant No. 605203) , by the European Commission within HORIZON2020 via the EURATOM project EUFRAT for transnational access and by the funding agencies of the participating institutes.Background: Stellar nucleosynthesis of elements heavier than iron is driven by neutron capture processes. Zr-92 is positioned at a strategic point along the slow nucleosynthesis path, given its proximity to the neutron magic number N = 50 and its position at the matching region between the weak and main slow processes. Purpose: In parallel with recent improved astronomical data, the extraction of accurate Maxwellian averaged cross sections (MACSs) derived from a more complete and accurate set of resonance parameters should allow for a better understanding of the stellar conditions at which nucleosynthesis takes place. Methods: Transmission and capture cross section measurements using enriched Zr-92 metallic samples were performed at the time-of flight facilities GELINA of JRC-Geel (BE) and n_TOF of CERN (CH). The neutron beam passing through the samples was investigated in transmission measurements at GELINA using a Li-glass scintillator. The gamma rays emitted during the neutron capture reactions were detected by C6D6 detectors at both GELINA and n_TOF. Results: Resonance parameters of individual resonances up to 81 keV were extracted from a combined resonance shape analysis of experimental transmissions and capture yields. For the majority of the resonances the parity was determined from an analysis of the transmission data obtained with different sample thicknesses. Average resonance parameters were calculated. Conclusions: Maxwellian averaged cross sections were extracted from resonances observed up to 81 keV. The MACS for kT = 30 keV is fully consistent with experimental data reported in the literature. The MACSs for kT less than or similar to 15 keV are in good agreement with those derived from the ENDF/B-VIII.0 library and recommended in the KADoNTS database. For kT higher than 30 keV differences are observed. A comparison with MACSs obtained with the cross sections recommended in the JEFF-3.3 and JENDL-4.0 libraries shows discrepancies even for kT less than or similar to 15 keV.European Commission 605203European Commission European Commission Joint Research Centr

Measurement of the 77Se(n, γ) cross section up to 200 keV at the n_TOF facility at CERN

The 77 Se ( n , γ ) reaction is of importance for 77 Se abundance during the slow neutron capture process in massive stars. We have performed a new measurement of the 77 Se radiative neutron capture cross section at the Neutron Time-of-Flight facility at CERN. Resonance capture kernels were derived up to 51 keV and cross sections up to 200 keV. Maxwellian-averaged cross sections were calculated for stellar temperatures between k T = 5 keV and k T = 100 keV , with uncertainties between 4.2% and 5.7%. Our results lead to substantial decreases of 14% and 19% in 77 Se abundances produced through the slow neutron capture process in selected stellar models of 15 M ⊙ and 2 M ⊙ , respectively, compared to using previous recommendation of the cross section.UK Science and Facilities Council (ST/M006085/1)MSMT of the Czech RepublicThe Charles University UNCE/SCI/013 projectEuropean Research Council ERC-2015-StG No. 67749

Measurement of the neutron-induced fission cross section of 230Th at the CERN n_TOF facility

Euratom "Support safe operation of nuclear systems" program MIS 5033021European Union (EU) European Social Fund (ESF)Greek national funds through the action 84755

Measurement of the Pu-242(n, γ) cross section from thermal to 500 keV at the Budapest research reactor and CERN n_TOF-EAR1 facilities

This measurement has received funding from the EC FP7 Programme under the projects NEUTANDALUS (Grant No. 334315) and CHANDA (Grant No. 605203), the Spanish Ministry of Economy and Competitiveness projects FPA2013-45083-P, FPA2014-53290-C2-2-P and FPA2016-77689-C2-1-R and the V Plan Propio de Investigacion Programme from the University of Sevilla. Support from the German Federal Ministry for Education and Research (BMBF), contract number 03NUK13A, is gratefully acknowledged.The design and operation of innovative nuclear systems requires a better knowledge of the capture and fission cross sections of the Pu isotopes. For the case of capture on Pu-242. a reduction of the uncertainty in the fast region down to 8-12% is required. Moreover, aiming at improving the evaluation of the fast energy range in terms of average parameters, the OECD NEA High Priority Request List (HPRL) requests high-resolution capture measurements with improved accuracy below 2 keV. The current uncertainties also affect the thermal point, where previous experiments deviate from each other by 20%. A fruitful collaboration betwen JGU Mainz and HZ Dresden-Rossendorf within the EC CHANDA project resulted in a Pu-242 sample consisting of a stack of seven fission like targets making a total of 95(4) mg of Pu-242 electrodeposited on thin (11.5 mu m) aluminum backings. This contribution presents the results of a set of measurements of the Pu-242(n,gamma) cross section from thermal to 500 keV combining different neutron beams and techniques. The thermal point was determined at the Budapest Research Reactor by means of Neutron Activation Analysis and Prompt Gamma Analysis, and the resolved (1 eV - 4 keV) and unresolved (1 - 500 keV) resonance regions were measured using a set of four Total Energy detectors at the CERN n_TOF-EAR1.EC FP7 Programme under the project NEUTANDALUS 334315EC FP7 Programme under the project CHANDA 605203Spanish Ministry of Economy and Competitiveness FPA2013-45083-P FPA2014-53290-C2-2-P FPA2016-77689-C2-1-RV Plan Propio de Investigacion Programme from the University of SevillaFederal Ministry of Education & Research (BMBF) 03NUK13

Measurement of the 14N(n, p) 14C cross section at the CERN n_TOF facility from subthermal energy to 800 keV

Background: The 14N(n, p) 14C reaction is of interest in neutron capture therapy, where nitrogen-related dose is the main component due to low-energy neutrons, and in astrophysics, where 14N acts as a neutron poison in the s process. Several discrepancies remain between the existing data obtained in partial energy ranges: thermal energy, keV region, and resonance region. Purpose: We aim to measure the 14N(n, p) 14C cross section from thermal to the resonance region in a single measurement for the first time, including characterization of the first resonances, and provide calculations of Maxwellian averaged cross sections (MACS). Method: We apply the time-of-flight technique at Experimental Area 2 (EAR-2) of the neutron time-of-flight (n_TOF) facility at CERN. 10B(n, & alpha;) 7Li and 235U(n, f ) reactions are used as references. Two detection systems are run simultaneously, one on beam and another off beam. Resonances are described with the R-matrix code SAMMY. Results: The cross section was measured from subthermal energy to 800 keV, resolving the first two resonances (at 492.7 and 644 keV). A thermal cross section was obtained (1.809 & PLUSMN; 0.045 b) that is lower than the two most recent measurements by slightly more than one standard deviation, but in line with the ENDF/B-VIII.0 and JEFF-3.3 evaluations. A 1/v energy dependence of the cross section was confirmed up to tens of keV neutron energy. The low energy tail of the first resonance at 492.7 keV is lower than suggested by evaluated values, while the overall resonance strength agrees with evaluations. Conclusions: Our measurement has allowed determination of the 14N(n, p) cross section over a wide energy range for the first time. We have obtained cross sections with high accuracy (2.5%) from subthermal energy to 800 keV and used these data to calculate the MACS for kT = 5 to kT = 100 keV.p>Instituto de Salud Carlos III Spanish Government PID2020-117969RB-I00Junta de Andalucia (FEDER Andalucia 2014-2020) P20-00665 B-FQM-156UGR20UK Science and Facilities Council ST/M006085/1 ST/P004008/1European Research Council (ERC) 677497Spanish Ministry of Science, Innovation and Universities under the FPU Grant FPU17/0230

Search for the Θˉ−→\bar{\Theta}^- \to K−^- nˉ\bar{n} with PHENIX

The PHENIX experiment at RHIC should be sensitive to decays of the the anti--pentaquark $\bar{\Theta}^-$ via the K$^-$ $\bar{n}$ channel. Charged kaons can be identified using the standard tracking and time of flight up to a momentum of 1.5 GeV/c. Anti--neutron candidates are detected via their annihilation signal in the highly segmented electromagnetic calorimeter (EMCal). In order to assess the quality of the anti--neutron identification we reconstruct the $\bar{\Sigma} \to \bar{n}\pi$. As an additional crosscheck the invariant mass of K$^+$ $\bar{n}$ is reconstructed where no resonance in the pentaquark mass range is expected. At the present time no enhancement at the expected pentaquark mass is observed in dAu collisions at $\sqrt{s_{NN}} = 200 GeV.Comment: 4 pages 5 figures contribution to the proceedings of the 17th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter, Oakland, January 11-17, 2004). To appear in the proceedings (Journal of Physics G

The n_TOF facility at CERN

The neutron Time-of-Flight facility (n_TOF) is an innovative facility operative since 2001 at CERN, with three experimental areas. In this paper the n_TOF facility will be described, together with the upgrade of the facility during the Long Shutdown 2 at CERN. The main features of the detectors used for capture fission cross section measurements will be presented with perspectives for the future measurements

Measurement of the 140Ce(n,γ) Cross Section at n_TOF and Its Astrophysical Implications for the Chemical Evolution of the Universe

140Ce(n, γ) is a key reaction for slow neutron-capture (s-process) nucleosynthesis due to being a bottleneck in the reaction flow. For this reason, it was measured with high accuracy (uncertainty ≈5%) at the n_TOF facility, with an unprecedented combination of a high purity sample and low neutron-sensitivity detectors. The measured Maxwellian averaged cross section is up to 40% higher than previously accepted values. Stellar model calculations indicate a reduction around 20% of the s-process contribution to the Galactic cerium abundance and smaller sizeable differences for most of the heavier elements. No variations are found in the nucleosynthesis from massive stars.U.S. National Science Foundation (Grants No. AST 1613536, No. AST 1815403/1815767, No. AST 2205847, and No. PHY 1430152—Joint Institute for Nuclear Astrophysics—Chemical Evolution of the Elements)European Union—NextGenerationEU RFF M4C2 1.1 PRIN 2022 project “2022RJLWHN URKA”INAF Theory Grant “Understanding R-process & Kilonovae Aspects (URKA)”MSMTof the Czech Republic, the Charles University UNCE/SCI/013 projec

1/N Expansion for Exotic Baryons

The 1/N expansion for exotic baryons is developed, and applied to the masses, meson couplings and decay widths. Masses and widths of the 27 and 35 pentaquark states in the same tower as the Theta+ are related by spin-flavor symmetry. The 27 and 35 states can decay within the pentaquark tower, as well as to normal baryons, and so have larger decay widths than the lightest pentaquark Theta. The 1/N expansion also is applied to baryon exotics containing a single heavy antiquark. The decay widths of heavy pentaquarks via pion emission, and to normal baryons plus heavy D^(*),B^(*) mesons are studied, and relations following from large-N spin-flavor symmetry and from heavy quark symmetry are derived.Comment: Major additions: plots of widths and branching ratios, discussion of strong decays of heavy pentaquarks, including consequences of heavy quark symmetr

High precision measurement of the associated strangeness production in proton proton interactions

A new high precision measurement of the reaction pp -> pK+Lambda at a beam momentum of 2.95 GeV/c with more than 200,000 analyzed events allows a detailed analysis of differential observables and their inter-dependencies. Correlations of the angular distributions with momenta are examined. The invariant mass distributions are compared for different regions in the Dalitz plots. The cusp structure at the N Sigma threshold is described with the Flatt\'e formalism and its variation in the Dalitz plot is analyzed.Comment: accepted for publication in Eur. Phys. J.