Tue·Mar 6, 2018Tuesday·March 6, 2018

1. 01*

   Identification of significant $E0$ strength in the $2_2^{+}\to 2_1^{+}$ transitions of ${}^{58,60,62}$Ni

   L.J. Evitts🇨🇦 · A.B. Garnsworthy🇨🇦 · T. Kibédi🇦🇺 · J. Smallcombe🇨🇦 · M.W. Reed🇦🇺 · B.A. Brown🇺🇸 · A.E. Stuchbery🇦🇺 · G.J. Lane🇦🇺 · T.K. Eriksen🇳🇴 · A. Akber🇦🇺 · B. Alshahrani · M. de Vries and 14 other authors

   The $E0$ transition strength in the $2_2^{+}\to 2_1^{+}$ transitions of ${}^{58,60,62}$Ni have been determined for the first time following a series of measurements at the Australian National University (ANU) and the University of Kentucky (UK). The CAESAR Compton-suppressed HPGe array and the Super-e solenoid at ANU were used to measure the $\delta (E2/M1)$ mixing ratio and internal conversion coefficient of each transition following inelastic proton scattering. Level half-lives, $\delta (E2/M1)$ mixing ratios and $\gamma$-ray branching ratios were measured at UK following inelastic neutron scattering. The new spectroscopic information was used to determine the $E0$ strengths. These are the first $2^{+}\to 2^{+}$ $E0$ transition strengths measured in nuclei with spherical ground states and the $E0$ component is found to be unexpectedly large; in fact, these are amongst the largest $E0$ transition strengths in medium and heavy nuclei reported to date.

   nucl-exnucl-thPLB(2018)·13 citations
2. 02*

   On the possibility to observe neutron dark decay in nuclei

   Marek Pfützner🇵🇱 · Karsten Riisager🇩🇰

   As proposed recently by Fornal and Grinstein, neutrons can undergo a dark matter decay mode which was not observed before. Such a decay could explain the existing discrepancy between two different methods of neutron lifetime measurements. If such neutron decay is possible, then it should occur also is nuclei with sufficiently low neutron binding energy. We examine a few nuclear candidates for the dark neutron decay and we consider possibilities of their experimental identification. In more detail we discuss the case of ${}^{11}$Be which appears as the most promising nucleus for the observation of the neutron dark decay.

   nucl-exPRC(2018)·51 citations
3. 03*

   Robust extraction of proton charge radius from electron-proton scattering data

   Xuefei Yan🇺🇸 · Douglas W. Higinbotham🇺🇸 · Dipangkar Dutta🇺🇸 · Haiyan Gao🇺🇸 · Ashot Gasparian🇺🇸 · Mahbub A. Khandaker🇺🇸 · Nilanga Liyanage🇺🇸 · Eugene Pasyuk🇺🇸 · Chao Peng🇺🇸 · Weizhi Xiong🇺🇸

   Extracting the proton charge radius from electron scattering data requires determining the slope of the charge form factor at $Q^2$ of zero. But as experimental data never reach that limit, numerous methods for making the extraction have been proposed, though often the functions are determined after seeing the data which can lead to confirmation bias. To find functional forms that will allow for a robust extraction of the input radius for a wide variety of functional forms in order to have confidence in the extraction from upcoming low $Q^2$ experimental data such as the Jefferson Lab PRad experiment, we create a general framework for inputting form-factor functions as well as various fitting functions. The input form factors are used to generate pseudo-data with fluctuations intended to mimic the binning and random uncertainty of a given set of real data. All combinations of input functions and fit functions can then be tested repeatedly against regenerated pseudo-data. Since the input radius is known, this allows us to find fit functions that are robust for radius extractions in an objective fashion. For the range and uncertainty of the PRad data, we find that a two-parameter rational function, a two-parameter continued fraction and the second order polynomial expansion of $z$ can extract the input radius regardless of the input charge form factor function that is used. We have created an easily expandable framework to search for functional forms that allow for a robust extraction of the radius from a given binning and uncertainty of pseudo-data generated from a wide variety of trial functions. This method has enabled a successful search for the best functional forms to extract the radius from the upcoming PRad data and can be used for other experiments.

   nucl-exhep-phnucl-thPRC(2018)·46 citations
4. 04*

   Charm Program of NA61/SHINE: Motivation and Measurements

   Aleksandra Snoch · the NA61/SHINE collaboration

   Recently, the NA61/SHINE experiment at the CERN SPS has extended its program on physics of strong interactions by measurements of charm hadron production in nucleus-nucleus collisions. This charm program is here briefly summarized.

   nucl-ex1 citation
5. 05*

   Effective-energy universality approach describing total multiplicity centrality dependence in heavy-ion collisions

   Edward K. Sarkisyan-Grinbaum🇨🇭 · Aditya Nath Mishra🇲🇽 · Raghunath Sahoo🇮🇳 · Alexander S. Sakharov🇺🇸

   The recently proposed participant dissipating effective-energy approach is applied to describe the dependence on centrality of the multiplicity of charged particles measured in heavy-ion collisions at the collision energies up to the highest LHC energy of 5 TeV. The effective-energy approach relates multihadron production in different types of collisions, by combining, under the proper collision energy scaling, the constituent quark picture with Landau relativistic hydrodynamics. The measurements are shown to be well described in terms of the centrality-dependent effective energy of participants and an explanation of the differences in the measurements at RHIC and LHC are given by means of the recently introduced hypothesis of the energy-balanced limiting fragmentation scaling. A similarity between the centrality data and the data from most central collisions is proposed pointing to the central character of participant interactions independent of centrality. The findings complement our recent investigations of the similar midrapidity pseudorapidity density measurements extending the description to the full pseudorapidity range in view of the considered similarity of multihadron production in nucleon interactions and heavy-ion collisions.

   ↳ hep-phhep-exnucl-exnucl-thEPL(2019)·21 citations
6. 06*

   Elliptic flow of hadrons via quark coalescence mechanism using Boltzmann transport equation for Pb+Pb collision at $\sqrt{s_{NN}}$=2.76 TeV

   Mohammed Younus🇮🇳 · Sushanta Tripathy🇮🇳 · Swatantra Kumar Tiwari🇮🇳 · Raghunath Sahoo🇮🇳

   Elliptic flow of hadrons observed at relativistic heavy-ion collision experiments at Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC), provides us an important signature of possible de-confinement transition from hadronic phase to partonic phase. However, hadronization processes of de-confined partons back into final hadrons are found to play a vital role in the observed hadronic flow. In the present work, we use coalescence mechanism also known as Recombination (ReCo) to combine quarks into hadrons. To get there, we have used Boltzmann transport equation in relaxation time approximation to transport the quarks into equilibration and finally to freeze-out surface, before coalescence takes place. A Boltzmann-Gibbs Blast Wave (BGBW) function is taken as an equilibrium function to get the final distribution and a power-like function to describe the initial distributions of partons produced in heavy-ion collisions. In the present work, we try to estimate the elliptic flow of identified hadrons such as $\pi$, $K$, $p$ etc., produced in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV at the LHC for different centralities. The elliptic flow ($v_2$) of identified hadrons seems to be described quite well in the available $p_{\mathrm{T}}$ range. After the evolution of quarks until freeze-out time, has been calculated using BTE-RTA, the approach used in this paper consists of combining two or more quarks to explain the produced hadrons at intermediate momenta regions. The formalism is found to describe elliptic flow of hadrons produced in Pb+Pb collisions to a large extent.

   ↳ hep-phhep-exnucl-exnucl-thAdv.High Energy Phys.(2020)·7 citations
7. 07*

   The high voltage system for the novel MPGD-based photon detectors of COMPASS RICH-1

   J. Agarwala🇮🇹 · R. Birsa🇮🇹 · F. Bradamante🇮🇹 · A. Bressan🇮🇹 · C. Chatterjee🇮🇹 · P. Ciliberti🇮🇹 · S. Dalla Torre🇮🇹 · S. Dasgupta🇮🇹 · B. Gobbo🇮🇹 · M. Gregori🇮🇹 · G. Hamar🇮🇹 · S. Levorato🇮🇹 and 4 other authors

   The architecture of the novel MPGD-based photon detectors of COMPASS RICH-1 consists in a large-size hybrid MPGD multilayer layout combining two layers of Thick-GEMs and a bulk resistive MICROMEGAS. Concerning biasing voltage, the Thick-GEMs are segmented in order to reduce the energy released in case of occasional discharges, while the MICROMEGAS anode is segmented in pads individually biased at positive voltage, while the micromesh is grounded. In total, there are ten different electrode types and more than 20000 electrodes supplied by more than 100 HV channels. Commercial power supply units are used. The original elements of the power supply system are the architecture of the voltage distribution net, the compensation, by voltage adjustment, of the effects of pressure and temperature variation affecting the detector gain and a sophisticated control software, which allows to protect the detectors against errors by the operator, to monitor and log voltages and current at 1 Hz rate and to automatically react to detector misbehaviors. The HV system and its performance are described in detail as well as the electrical stability of the detector during the operation at COMPASS.

   ↳ physics.ins-dethep-exnucl-exPoS(2019)·1 citation
8. 08*

   Measurement of two-particle correlations with respect to second- and third-order event planes in Au$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV

   A. Adare · S. Afanasiev · C. Aidala · N.N. Ajitanand · Y. Akiba · H. Al-Bataineh · J. Alexander · M. Alfred · K. Aoki · Y. Aramaki · E.T. Atomssa · R. Averbeck and 446 other authors

   We present measurements of azimuthal correlations of charged hadron pairs in $\sqrt{s_{{}_{NN}}}=200$ GeV Au$+$Au collisions for the trigger and associated particle transverse-momentum ranges of $1<p_T^t<10$~GeV/$c$ and $0.5<p_T^a<10$~GeV/$c$. After subtraction of an underlying event using a model that includes higher-order azimuthal anisotropy $v_2$, $v_3$, and $v_4$, the away-side yield of the highest trigger-\pt ($p_T^t>4$~GeV/$c$) correlations is suppressed compared to that of correlations measured in $p$$+$$p$ collisions. At the lowest associated particle $p_T$ ($0.5<p_T^a<1$ GeV/$c$), the away-side shape and yield are modified relative to those in $p$$+$$p$ collisions. These observations are consistent with the scenario of radiative-jet energy loss. For the low-$p_T$ trigger correlations ($2<p_T^t<4$ GeV/$c$), a finite away-side yield exists and we explore the dependence of the shape of the away-side within the context of an underlying-event model. Correlations are also studied differentially versus event-plane angle ${\Psi }_2$ and ${\Psi }_3$. The angular correlations show an asymmetry when selecting the sign of the difference between the trigger-particle azimuthal angle and the ${\Psi }_2$ event plane. This asymmetry and the measured suppression of the pair yield out of plane is consistent with a path-length-dependent energy loss. No ${\Psi }_3$ dependence can be resolved within experimental uncertainties.

   ↳ hep-exnucl-exPRC(2019)·31 citations
9. 09*

   Centrality fluctuations in heavy-ion collisions

   Mingliang Zhou🇺🇸 · Jiangyong Jia🇺🇸

   Volume or centrality fluctuations (CF) is one of the main uncertainties for interpreting the centrality dependence of many experimental observables. The CF is constrained by centrality selection based on particle multiplicity in a reference subevent, and contributes to observables measured in another subevent. Using a Glauber-based independent source model, we study the influence of CF on several distributions of multiplicity $N$ and eccentricities ${ϵ}_n$: $p(N)$, $p({ϵ}_n)$, $p({ϵ}_n,{ϵ}_m)$ and $p(N,{ϵ}_n)$, where the effects of CF is quantified using multi-particle cumulants of these distributions. In mid-central collisions, a general relation is established between the multiplicity fluctuation and resulting CF in the reference subevent. In ultra-central collisions, where distribution of particle production sources is strongly distorted, we find these cumulants exhibit rich sign-change patterns, due to observable-dependent non-Gaussianity in the underlying distributions. The details of sign-change pattern change with the size of the collision systems. Simultaneous comparison of these different types cumulants between model prediction and experimental data can be used to constrain the CF and particle production mechanism in heavy-ion collisions. Since the concept of centrality and CF are expected to fluctuate in the longitudinal direction within a single event, we propose to use pseudorapidity-separated subevent cumulant method to explore the nature of intra-event fluctuations of centrality and collective dynamics. The subevent method can be applied for any bulk observable that is sensitive to centrality, and has the potential to separate different mechanisms for multiplicity and flow fluctuations happening at different time scales. The forward detector upgrades at RHIC and LHC will greatly enhance such studies in the future.

   ↳ nucl-thhep-phnucl-exPRC(2018)·48 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.