Mon·Dec 18, 2017Monday·December 18, 2017

1. 01*

   Constraints on jet quenching in p-Pb collisions at $\sqrt{{\mathbf{s}}_{\mathbf{NN}}}$ = 5.02 TeV measured by the event-activity dependence of semi-inclusive hadron-jet distributions

   ALICE Collaboration

   The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high-transverse momentum trigger hadron in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. Jets are reconstructed from charged-particle tracks using the anti-$k_{\mathrm{T}}$ algorithm with resolution parameter $R=0.2$ and $0.4$. A data-driven statistical approach is used to correct the uncorrelated background jet yield. Recoil jet distributions are reported for jet transverse momentum $15<p_{\mathrm{T},\mathrm{jet}}^{\mathrm{ch}}<50$ GeV/$c$ and are compared in various intervals of p-Pb event activity, based on charged-particle multiplicity and zero-degree neutral energy in the forward (Pb-going) direction. The semi-inclusive observable is self-normalized and such comparisons do not require the interpretation of p-Pb event activity in terms of collision geometry, in contrast to inclusive jet observables. These measurements provide new constraints on the magnitude of jet quenching in small systems at the LHC. In p-Pb collisions with high event activity, the average medium-induced out-of-cone energy transport for jets with $R=0.4$ and $15<p_{\mathrm{T},\mathrm{jet}}^{\mathrm{ch}}<50$ GeV/$c$ is measured to be less than 0.4 GeV/$c$ at 90% confidence, which is over an order of magnitude smaller than a similar measurement for central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. Comparison is made to theoretical calculations of jet quenching in small systems, and to inclusive jet measurements in p-Pb collisions selected by event activity at the LHC and in d-Au collisions at RHIC.

   nucl-exhep-exPLB(2018)·118 citations
2. 02*

   Neutron lifetime measurements with the big gravitational trap for ultracold neutrons

   A. P. Serebrov🇷🇺 · E .A. Kolomensky🇷🇺 · A. K. Fomin🇷🇺 · I. A. Krasnoschekova · A. V. Vassiljev🇷🇺 · D. M. Prudnikov🇷🇺 · I. V. Shoka🇷🇺 · A. V. Chechkin🇷🇺 · M. E. Chaikovskiy🇷🇺 · V. E. Varlamov🇷🇺 · S. N. Ivanov🇬🇧 · A. N. Pirozhkov🇷🇺 and 5 other authors

   Neutron lifetime is one of the most important physical constants which determines parameters of the weak interaction and predictions of primordial nucleosynthesis theory. There remains the unsolved problem of a 3.9{\sigma} discrepancy between measurements of this lifetime using neutrons in beams and those with stored neutrons (UCN). In our experiment we measure the lifetime of neutrons trapped by Earth's gravity in an open-topped vessel. Two configurations of the trap geometry are used to change the mean frequency of UCN collisions with the surfaces - this is achieved by plunging an additional surface into the trap without breaking the vacuum. The trap walls are coated with a hydrogen-less fluorine-containing polymer to reduce losses of UCN. The stability of this coating to multiple thermal cycles between 80 K and 300 K was tested. At 80 K, the probability of UCN loss due to collisions with the trap walls is just 1.5% of the probability of beta-decay. The free neutron lifetime is determined by extrapolation to an infinitely large trap with zero collision frequency. The result of these measurements is 881.5 +/- 0.7_stat +/- 0.6_syst s which is consistent with the conventional value of 880.2 +/- 1.0 s presented by the Particle Data Group. Future prospects for this experiment are in further cooling to 10 K which will lead to an improved accuracy of measurement. In conclusion we present an analysis of currently-available data on various measurements of the neutron lifetime.

   nucl-exphysics.ins-detPRC(2018)·140 citations
3. 03*

   A 4-dimensional Langevin approach to low-energy nuclear fission of ${}^{236}$U

   Chikako Ishizuka🇯🇵 · Mark D. Usang · Fedir A. Ivanyuk · Joachim A. Maruhn🇩🇪 · Katsuhisa Nishio🇯🇵 · Satoshi Chiba🇯🇵

   We developed a four-dimensional Langevin model which can treat the deformation of each fragment independently and applied it to low energy fission of 236U, the compound system of the reaction n+${}^{235}$U. The potential energy is calculated with the deformed two-centerWoods-Saxon (TCWS) and the Nilsson type potential with the microscopic energy corrections following the Strutinsky method and BCS pairing. The transport coefficients are calculated by macroscopic prescriptions. It turned out that the deformation for the light and heavy fragments behaves differently, showing a sawtooth structure similar to that of the neutron multiplicities of the individual fragments $\nu$(A). Furthermore, the measured total kinetic energy TKE(A) and its standard deviation are reproduced fairly well by the 4D Langevin model based on the TCWS potential in addition to the fission fragment mass distributions. The developed model allows a multi-parametric correlation analysis among, e.g., the three key fission observables, mass, TKE, and neutron multiplicity, which should be essential to elucidate several long-standing open problems in fission such as the sharing of the excitation energy between the fragments.

   ↳ nucl-thnucl-exPRC(2017)·70 citations
4. 04*

   The three-pion decays of the $a_1(1260)$

   Xu Zhang🇨🇳 · Ju-Jun Xie🇨🇳

   We investigate the decay of $a_1^{+}(1260)\to {\pi }^{+}{\pi }^{+}{\pi }^{-}$ with the assumption that the $a_1(1260)$ is dynamically generated from the coupled channel $\rho \pi$ and $\bar{K}{K}^{\ast }$ interactions. In addition to the tree level diagrams that proceed via $a_1^{+}(1260)\to {\rho }^0{\pi }^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}$, we take into account also the final state interactions of $\pi \pi \to \pi \pi$ and $K\bar{K}\to \pi \pi$. We calculate the invariant ${\pi }^{+}{\pi }^{-}$ mass distribution and also the total decay width of $a_1^{+}(1260)\to {\pi }^{+}{\pi }^{+}{\pi }^{-}$ as a function of the mass of $a_1(1260)$. The calculated total decay width of $a_1(1260)$ is significantly different from other model calculations and tied to the dynamical nature of the $a_1(1260)$ resonance. The future experimental observations could test of model calculations and would provide vary valuable information on the relevance of the $\rho \pi$ component in the $a_1(1260)$ wave function.

   ↳ nucl-thhep-phnucl-exCommun.Theor.Phys.(2018)·12 citations
5. 05*

   Onset of $\eta$ nuclear binding

   Nir Barnea🇮🇱 · Betzalel Bazak🇮🇱 · Eliahu Friedman🇮🇱 · Avraham Gal🇮🇱 · Aleš Cieplý🇨🇿 · Jiří Mareš🇨🇿 · Martin Schäfer🇨🇿

   Recent studies of $\eta$ nuclear quasibound states by the Jerusalem-Prague Collaboration are reviewed, focusing on stochastic variational method self consistent calculations of $\eta$ few-nucleon systems. These calculations suggest that a minimum value Re$a_{\eta N}\approx 1$ fm (0.7 fm) is needed to bind $\eta {}^3$He ($\eta {}^4$He).

   ↳ nucl-thhep-phnucl-exEPJ Web Conf.(2018)·2 citations
6. 06*

   Multi moment cancellation of participant fluctuations

   Viktor Begun🇵🇱 · Maja Mackowiak-Pawlowska🇵🇱

   We summarize the new method for the correction of participant fluctuations in high energy nucleus-nucleus collisions. It allows to estimate a fluctuation baseline in comparison to a useful signal. In particular cases of a weak signal compared to baseline, it allows to cancel the baseline contribution from participants.

   ↳ nucl-thhep-exhep-phnucl-exPoS(2018)·1 citation

* 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.