Wed·Feb 11, 2015Wednesday·February 11, 2015

1. 01*

   Measurement of the Target-Normal Single-Spin Asymmetry in Quasi-Elastic Scattering from the Reaction ${}^3$He${}^{\uparrow }(e,e^{\prime })$

   Y.-W. Zhang · E. Long🇺🇸 · M. Mihovilovič🇸🇮 · G. Jin🇺🇸 · K. Allada🇺🇸 · B. Anderson🇺🇸 · J. R. M. Annand🇬🇧 · T. Averett🇺🇸 · W. Boeglin🇺🇸 · P. Bradshaw🇺🇸 · A. Camsonne🇺🇸 · M. Canan🇺🇸 and 80 other authors

   We report the first measurement of the target single-spin asymmetry, $A_y$, in quasi-elastic scattering from the inclusive reaction ${}^3$He${}^{\uparrow }(e,e^{\prime })$ on a ${}^3$He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A non-zero $A_y$ can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the sub-structure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at $Q^2=$ 0.13, 0.46 and 0.97 GeV${}^2$. These measurements demonstrate, for the first time, that the ${}^3$He asymmetry is clearly non-zero and negative with a statistical significance of (8-10)$\sigma$. Using measured proton-to-${}^3$He cross-section ratios and the effective polarization approximation, neutron asymmetries of $-$(1-3)% were obtained. The neutron asymmetry at high $Q^2$ is related to moments of the Generalized Parton Distributions (GPDs). Our measured neutron asymmetry at $Q^2=0.97$ GeV${}^2$ agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions.

   nucl-exPRL(2015)·28 citations
2. 02*

   The Hot QCD White Paper: Exploring the Phases of QCD at RHIC and the LHC

   Yasuyuki Akiba (RIKEN)🇯🇵 · Aaron Angerami (Columbia University)🇺🇸 · Helen Caines (Yale University)🇺🇸 · Anthony Frawley (Florida State University)🇺🇸 · Ulrich Heinz (Ohio State University)🇺🇸 · Barbara Jacak (University of California, Berkeley)🇺🇸 · Jiangyong Jia (Stony Brook University)🇺🇸 · Tuomas Lappi (Jyväskylä University)🇫🇮 · Wei Li (Rice University)🇺🇸 · Abhijit Majumder (Wayne State University)🇺🇸 · David Morrison (Brookhaven National Laboratory)🇺🇸 · Mateusz Ploskon (Lawrence Berkeley National Laboratory)🇺🇸 and 8 other authors

   The past decade has seen huge advances in experimental measurements made in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and more recently at the Large Hadron Collider (LHC). These new data, in combination with theoretical advances from calculations made in a variety of frameworks, have led to a broad and deep knowledge of the properties of thermal QCD matter. Increasingly quantitative descriptions of the quark-gluon plasma (QGP) created in these collisions have established that the QGP is a strongly coupled liquid with the lowest value of specific viscosity ever measured. However, much remains to be learned about the precise nature of the initial state from which this liquid forms, how its properties vary across its phase diagram and how, at a microscopic level, the collective properties of this liquid emerge from the interactions among the individual quarks and gluons that must be visible if the liquid is probed with sufficiently high resolution. This white paper, prepared by the Hot QCD Writing Group as part of the U.S. Long Range Plan for Nuclear Physics, reviews the recent progress in the field of hot QCD and outlines the scientific opportunities in the next decade for resolving the outstanding issues in the field.

   nucl-exhep-exhep-lathep-ph+1162 citations
3. 03*

   Flavor decomposition of the nucleon electromagnetic form factors at low $Q^2$

   I. A. Qattan🇦🇪 · J. Arrington🇺🇸 · A. Alsaad🇯🇴

   The spatial distribution of charge and magnetization within the proton is encoded in the elastic form factors. These have been precisely measured in elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up- and down-quark contributions. In this work, we extract the proton and neutron form factors from world's data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucleon. From these, we separate the up- and down-quark contributions to the proton form factors. We combine cross section and polarization measurements of elastic electron-proton scattering to separate the proton form factors and two-photon exchange (TPE) contributions. We combine the proton form factors with parameterization of the neutron form factor data and uncertainties to separate the up- and down-quark contributions to the proton's charge and magnetic form factors. The extracted TPE corrections are compared to previous phenomenological extractions, TPE calculations, and direct measurements from the comparison of electron and positron scattering. The flavor-separated form factors are extracted and compared to models of the nucleon structure. With the inclusion of the precise new data, the extracted TPE contributions show a clear change ofsign at low $Q^2$, necessary to explain the high-$Q^2$ form factor discrepancy while being consistent with the known $Q^2\to 0$ limit. We find that the new Mainz data yield a significantly different result for the proton magnetic form factor and its flavor-separated contributions. We also observe that the RMS radius of both the up- and down-quark distributions are smaller than the RMS charge radius of the proton.

   nucl-exnucl-thPRC(2015)·32 citations
4. 04*

   Recoil-alpha-fission and recoil-alpha-alpha-fission events observed in the reaction Ca-48 + Am-243

   U. Forsberg · D. Rudolph · L.-L. Andersson · A. Di Nitto🇮🇹 · Ch.E. Düllmann · J.M. Gates · P. Golubev🇸🇪 · K.E. Gregorich · C.J. Gross🇩🇪 · R.-D. Herzberg🇬🇧 · F.P. Hessberger · J. Khuyagbaatar and 42 other authors

   Products of the fusion-evaporation reaction Ca-48 + Am-243 were studied with the TASISpec set-up at the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung. Amongst the detected thirty correlated alpha-decay chains associated with the production of element Z=115, two recoil-alpha-fission and five recoil-alpha-alpha-fission events were observed. The latter are similar to four such events reported from experiments performed at the Dubna gas-filled separator. Contrary to their interpretation, we propose an alternative view, namely to assign eight of these eleven decay chains of recoil-alpha(-alpha)-fission type to start from the 3n-evaporation channel 115-288. The other three decay chains remain viable candidates for the 2n-evaporation channel 115-289.

   nucl-exNPA(2016)·49 citations
5. 05*

   Preliminary study of feasibility of an experiment looking for excited state double beta transitions in tin

   Soumik Das🇮🇳 · S. K. Ghorui🇮🇳 · P. K. Raina🇮🇳 · A. K. Singh🇮🇳 · P. K. Rath🇮🇳 · F. Cappella🇮🇹 · R. Cerulli🇮🇹 · M. Laubenstein🇮🇹 · P. Belli🇮🇹 · R. Bernabei🇮🇹

   An attempt to study the feasibility of a new experiment to search for double beta decay in ${}^{112}$Sn and ${}^{124}$Sn was carried out by using ultra-low background HPGe detector (244 cm${}^3$) inside the Gran Sasso National Laboratory (LNGS) of the INFN (Italy). A small sample of natural Sn was examined for 2367.5 h. The radioactive contamination of the sample has been estimated. The data has also been considered to calculate the present sensitivity for the proposed search; half-life limits $\sim$ $10^{17}-10^{18}$ years for ${\beta }^{+}$EC and EC-EC processes in ${}^{112}$Sn and $\sim$ $10^{18}$ years for ${\beta }^{-}{\beta }^{-}$ transition in ${}^{124}$Sn were measured. In the last section of the paper the enhancement of the sensitivity for a proposed experiment with larger mass to reach theoretically estimated values of half-lives is discussed.

   nucl-exphysics.ins-detNucl.Instrum.Meth.A(2015)·6 citations
6. 06*

   Monte Carlo Study of a 137Cs calibration field of the China institute of atomic energy

   Fei Gao

   The MCNP code was used to study the characteristics of gamma radiation field with collimated beam geometry. A close-to-reality simulation model of the facility was used for calculation air-kerma along the whole range of source-detector-distance (SDD) along the central beam and air-kerma off-axis beam profiles at two different source-detector-distance (SDD). The simulation results were tested by the measured results which were acquired in the Radiation Metrology Center of CIAE. Other characteristics such as the individual contributions of photons scattered in collimator, floor, walls, mobile platform and other parts of the irradiation halls to the total air kerma rate on the beam axis were calculated for the purpose of future improvement of metrological parameters in CIAE. Finally, factors which influence the simulation results were investigated, including e.g., detector volume effects or source density effects.

   ↳ physics.ins-detnucl-ex0 citations
7. 07*

   A pilot study of the novel J-PET plastic scintillator with 2-(4-styrylphenyl)benzoxazole as a wavelength shifter

   A. Wieczorek🇵🇱 · P. Moskal🇵🇱 · Sz. Niedźwiecki🇵🇱 · T. Bednarski🇵🇱 · P. Białas🇵🇱 · E. Czerwiński🇵🇱 · A. Danel · A. Gajos🇵🇱 · A. Gruntowski · D. Kamińska🇵🇱 · Ł. Kapłon🇵🇱 · A. Kochanowski🇵🇱 and 21 other authors

   For the first time a molecule of 2-(4-styrylphenyl)benzoxazole containing benzoxazole and stilbene groups is applied as a scintillator dopant acting as a wavelength shifter. In this article a light yield of the plastic scintillator, prepared from styrene doped with 2 wt% of 2,5-diphenylbenzoxazole and 0.03 wt% of 2-(4-styrylphenyl)benzoxazole, is determined to be as large as 60% $\pm$ 2% of the anthracene light output. There is a potential to improve this value in the future by the optimization of the additives concentrations.

   ↳ physics.ins-detnucl-exActa Phys.Polon.A(2015)·15 citations
8. 08*

   Kinematic biases on centrality selection of jet events in pPb collisions at the LHC

   Nestor Armesto🇪🇸 · Doga Can Gulhan🇺🇸 · Jose Guilherme Milhano🇵🇹

   Centrality selection has been observed to have a large effect on jet observables in pPb collisions at the Large Hadron Collider, stronger than that predicted by the nuclear modification of parton densities. We study to which extent simple considerations of energy-momentum conservation between the hard process and the underlying event affect jets observables in such collisions. We develop a simplistic approach that considers first the production of jets in a pp collision as described by PYTHIA. From each pp collision, the value of the energy of the parton from the proton participating in the hard scattering is extracted. Then, the underlying event is generated simulating a pPb collision through HIJING, but with the energy of the proton decreased according to the value extracted in the previous step, and both collisions are superimposed. This model is able to capture the bulk of the centrality effect for central to semicentral collisions, for the two available sets of data: dijets from the CMS Collaboration and single jets from the ATLAS Collaboration. As expected, the model fails for peripheral collisions where very few nucleons from Pb participate.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2015)·41 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.