Mon·Mar 14, 2016Monday·March 14, 2016

1. 01*

   Centrality dependence of charged jet production in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   Measurements of charged jet production as a function of centrality are presented for p-Pb collisions recorded at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector. Centrality classes are determined via the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon-nucleon collisions is determined based on the particle production in the Pb-going rapidity region. Jets have been reconstructed in the central rapidity region from charged particles with the anti-$k_{\mathrm{T}}$ algorithm for resolution parameters $R=0.2$ and $R=0.4$ in the transverse momentum range 20 to 120 GeV/$c$. The reconstructed jet momentum and yields have been corrected for detector effects and underlying-event background. In the five centrality bins considered, the charged jet production in p-Pb collisions is consistent with the production expected from binary scaling from pp collisions. The ratio of jet yields reconstructed with the two different resolution parameters is also independent of the centrality selection, demonstrating the absence of major modifications of the radial jet structure in the reported centrality classes.

   nucl-exhep-exEur. Phys. J. C76 (2016) 271·60 citations
2. 02*

   Measurements of $d_2^n$ and $A_1^n$: Probing the neutron spin structure

   D. Flay · M. Posik · D. S. Parno · K. Allada · W. Armstrong · T. Averett · F. Benmokhtar · W. Bertozzi · A. Camsonne · M. Canan · G. D. Cates · C. Chen and 79 other authors

   We report on the results of the E06-014 experiment performed at Jefferson Lab in Hall A, where a precision measurement of the twist-3 matrix element $d_2$ of the neutron ($d_2^n$) was conducted. This quantity represents the average color Lorentz force a struck quark experiences in a deep inelastic electron scattering event off a neutron due to its interaction with the hadronizing remnants. This color force was determined from a linear combination of the third moments of the spin structure functions $g_1$ and $g_2$ on ${}^3$He after nuclear corrections had been applied to these moments. The kinematics included two average $Q^2$ bins of $3.2$ GeV${}^2$ and $4.3$ GeV${}^2$, and Bjorken-$x$ $0.25\le x\le 0.90$ covering the DIS and resonance regions. We found $d_2^n$ to be small and negative for $<Q^2>=3.2$ GeV${}^2$, and smaller for $<Q^2>=4.3$ GeV${}^2$, consistent with a lattice QCD calculation. The twist-4 matrix element $f_2^n$ was extracted by combining our $d_2^n$ with the world data on ${\Gamma }_1^n={\int }_0^1{g}_1^{n}dx$. We found $f_2^n$ to be roughly an order of magnitude larger than $d_2^n$. Utilizing the extracted $d_2^n$ and $f_2^n$ data, we separated the color force into its electric and magnetic components, $F_E^{y,n}$ and $F_B^{y,n}$, and found them to be equal and opposite in magnitude, in agreement with instanton model predictions but not with those from QCD sum rules. Additionally, we have extracted the neutron virtual photon-nucleon asymmetry $A_1^n$, the structure function ratio $g_1^n/F_1^n$, and the quark ratios $(\Delta u+\Delta \bar{u})/(u+\bar{u})$ and $(\Delta d+\Delta \bar{d})/(d+\bar{d})$. These results were found to be consistent with DIS world data and with the prediction of the constituent quark model but at odds with those of perturbative QCD at large $x$.

   nucl-exnucl-thPRD(2016)·64 citations
3. 03*

   A Capture-gated Fast Neutron Detection Method

   Yi Liu · Yigang Yang🇨🇳 · Yang Tai · Zhi Zhang🇨🇳

   To address the problem of the shortage of neutron detectors used in radiation portal monitors (RPMs), caused by the 3He supply crisis, research on a cadmium-based capture-gated fast neutron detector is presented in this paper. The detector is composed of many 1 cm * 1 cm * 20 cm plastic scintillator cuboids covered by 0.1 mm thick film of cadmium. The detector uses cadmium to absorb thermal neutrons and produce capture gamma-rays to indicate the detection of neutrons, and uses plastic scintillator to moderate neutrons and register gamma-rays. This design removes the volume competing relationship in traditional 3He counter-based fast neutron detectors, which hinders enhancement of the neutron detection efficiency. Detection efficiency of 21.66 +- 1.22% has been achieved with a 40.4 cm * 40.4 cm * 20 cm overall detector volume. This detector can measure both neutrons and gamma-rays simultaneously. A small detector (20.2 cm * 20.2 cm * 20 cm) demonstrated a 3.3 % false alarm rate for a 252Cf source with a neutron yield of 1841 n/s from 50 cm away within 15 seconds measurement time. It also demonstrated a very low (< 0.06%) false alarm rate for a 3.21 * 105 Bq 137Cs source. This detector offers a potential single-detector replacement for both neutron and the gamma-ray detectors in RPM systems.

   ↳ physics.ins-detnucl-exCPC(2016)·2 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.