Thu·Jun 22, 2017Thursday·June 22, 2017

1. 01*

   Nuclear modification of forward $D$ production in pPb collisions at the LHC

   Hirotsugu Fujii🇯🇵 · Kazuhiro Watanabe🇺🇸

   We study nuclear modification factors for single $D$ meson and semileptonic decay lepton $l$ ($=e,\mu$) production in minimum bias proton-nucleus (p$A$) collisions at the LHC in the color-glass-condensate (CGC) framework at leading order in strong coupling. In our numerical computations, transverse momentum ($k_{\perp }$) dependent multi-point Wilson line correlators are employed for describing target nucleus for p$A$ and proton for pp. The projectile proton is treated with unintegrated gluon distribution function, which is also $k_{\perp }$-dependent. The rapidity evolutions of these functions in the small Bjorken $x$ region are taken into account by solving running coupling Balitsky-Kovchegov (BK) equation at leading logarithmic accuracy. For simplicity, we employ Kartvelishvili's type fragmentation function and a simple model for lepton energy distribution from seileptonic decay, respectively, to compute differential cross sections for $D$ and $l$ production. The gluon saturation scale inside the heavy nucleus is enhanced and dependent on $x$, which we take into account by replacing the initial saturation scale in the BK equation with a larger value for the heavy nucleus. We show that the saturation effect leads to perceptible nuclear suppression of $D$ production at forward rapidity. Our numerical results predict similar nuclear suppressions in p$A$ collisions for forward $l$ production at lower transverse momentum $p_{\perp }<2\mathrm{GeV}$. Numerical tables on the nuclear modifications of $D$ and $l$ are listed in this note.

   ↳ hep-phhep-exnucl-exnucl-th21 citations
2. 02*

   Measurement of the fast neutron background at the China Jinping Underground Laboratory

   Qiang Du (1 and 2)🇨🇳 · Shin-Ted Lin (1)🇨🇳 · Shu-Kui Liu (1)🇨🇳 · Chang-Jian Tang (1)🇨🇳 · Li Wang (3)🇨🇳 · Wei-Wei Wei (2)🇨🇳 · Henry T. Wong (4)🇹🇼 · Hao-Yang Xing (1)🇨🇳 · Qian Yue (3)🇨🇳 · Jing-Jun Zhu (2) ((1) College of Physical Science and Technology, Sichuan University, Chengdu, (2) Institute of Nuclear Science and Technology, Sichuan University, Chengdu, (3) Key Laboratory of Particle and Radiation Imaging (Ministry of Education) and Department of Engineering Physics, Tsinghua University, Beijing, (4) Institute of Physics, Academia Sinica, Taipei)🇨🇳

   We report on the measurements of the fluxes and spectra of the environmental fast neutron background at the China Jinping Underground Laboratory (CJPL) with a rock overburden of about 6700 meters water equivalent, using a liquid scintillator detector doped with 0.5% gadolinium. The signature of a prompt nuclear recoil followed by a delayed high energy $\gamma$-ray cascade is used to identify neutron events. The large energy deposition of the delayed $\gamma$-rays from the $(n,\gamma )$ reaction on gadolinium, together with the excellent n-$\gamma$ discrimination capability provides a powerful background suppression which allows the measurement of a low intensity neutron flux. The neutron flux of $(1.51\pm 0.03(stat.)\pm 0.10(syst.))\times 10^{-7}$ cm${}^{-2}$s${}^{-1}$ in the energy range of 1 -- 10 MeV in the Hall A of CJPL was measured based on 356 days of data. In the same energy region, measurement with the same detector placed in a one meter thick polyethylene room gives a significantly lower flux of $(4.9\pm 0.9(stat.)\pm 0.5(syst.))\times 10^{-9}$ cm${}^{-2}$s${}^{-1}$ with 174 days of data. This represents a measurement of the lowest environmental fast neutron background among the underground laboratories in the world, prior to additional experiment-specific attenuation. Additionally, the fast neutron spectra both in the Hall A and the polyethylene room were reconstructed with the help of GEANT4 simulation.

   ↳ physics.ins-dethep-exnucl-exNucl.Instrum.Meth.A(2018)·12 citations
3. 03*

   A determination of the fragmentation functions of pions, kaons, and protons with faithful uncertainties

   Valerio Bertone🇳🇱 · Stefano Carrazza🇨🇭 · Nathan P. Hartland🇳🇱 · Emanuele R. Nocera🇬🇧 · Juan Rojo🇳🇱

   We present NNFF1.0, a new determination of the fragmentation functions (FFs) of charged pions, charged kaons, and protons/antiprotons from an analysis of single-inclusive hadron production data in electron-positron annihilation. This determination, performed at leading, next-to-leading, and next-to-next-to-leading order in perturbative QCD, is based on the NNPDF methodology, a fitting framework designed to provide a statistically sound representation of FF uncertainties and to minimise any procedural bias. We discuss novel aspects of the methodology used in this analysis, namely an optimised parametrisation of FFs and a more efficient ${\chi }^2$ minimisation strategy, and validate the FF fitting procedure by means of closure tests. We then present the NNFF1.0 sets, and discuss their fit quality, their perturbative convergence, and their stability upon variations of the kinematic cuts and the fitted dataset. We find that the systematic inclusion of higher-order QCD corrections significantly improves the description of the data, especially in the small-$z$ region. We compare the NNFF1.0 sets to other recent sets of FFs, finding in general a reasonable agreement, but also important differences. Together with existing sets of unpolarised and polarised parton distribution functions (PDFs), FFs and PDFs are now available from a common fitting framework for the first time.

   ↳ hep-phhep-exnucl-exnucl-thEPJC(2017)·214 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.