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1. chinaXiv:201608.00219 [pdf]

Analytical approximations for matter effects on CP violation in the accelerator-based neutrino oscillations with E $\lesssim$ 1 GeV

Zhi-zhong Xing; Jing-yu Zhu
Subjects: Physics >> Nuclear Physics

Given an accelerator-based neutrino experiment with the beam energy E \lesssim 1 GeV, we expand the probabilities of \nu_\mu \to \nu_e and \overline {\nu}_\mu \to \overline {\nu}_e oscillations in matter in terms of two small quantities \Delta_{21}/\Delta_{31} and A/\Delta_{31}, where \Delta_{21} \equiv m^2_2 - m^2_1 and \Delta_{31} \equiv m^2_3 - m^2_1 are the neutrino mass-squared differences, and A measures the strength of terrestrial matter effects. Our analytical approximations are numerically more accurate than those made by Freund in this energy region, and thus they are particularly applicable for the study of leptonic CP violation in the low-energy MOMENT, ESS\nuSM and T2K oscillation experiments. As a by-product, the new analytical approximations help us to easily understand why the matter-corrected Jarlskog parameter \widetilde{\cal J} peaks at the resonance energy E_* \simeq 0.14 GeV (or 0.12 GeV) for the normal (or inverted) neutrino mass hierarchy, and how the three Dirac unitarity triangles are deformed due to the terrestrial matter contamination. We also affirm that a medium-baseline neutrino oscillation experiment with the beam energy E lying in the E_* \lesssim E \lesssim 2 E_* range is capable of exploring leptonic CP violation with little matter-induced suppression.

submitted time 2016-08-31 Hits1143Downloads623 Comment 0

2. chinaXiv:201608.00218 [pdf]

Characterization study of a broad-energy germanium detector at CJPL

ZENG Zhi; MI Yuhao; ZENG Ming; MA Hao; YUE Qian; CHENG Jianping; LI Junli; QIU Rui; ZHANG Hui
Subjects: Physics >> Nuclear Physics

The ability of background discrimination using pulse shape discrimination (PSD) in broad-energy germanium (BEGe) detectors makes them as competitive candidates for neutrinoless double beta decay (0{\nu}\b{eta}\b{eta}) experiments. The measurements of key parameters for detector modeling in a commercial p-type BEGe detector are presented in this paper. Point-like sources were used to investigate the energy resolution and linearity of the detector. A cylindrical volume source was used for the efficiency calibration. With an assembled device for source positioning, a collimated 133Ba point-like source was used to scan the detector and investigate the active volume. A point-like source of 241Am was used to measure the dead layer thicknesses, which are approximately 0.17 mm on the front and 1.18 mm on the side. The described characterization method will play an important role in the 0{\nu}\b{eta}\b{eta} experiments with BEGe detectors at China JinPing underground Laboratory (CJPL) in the future.

submitted time 2016-08-31 Hits899Downloads514 Comment 0

3. chinaXiv:201608.00217 [pdf]

Strong decay mode $J/\psi p$ of hidden charm pentaquark states $P_c^+(4380)$ and $P_c^+(4450)$ in $\Sigma_c \barD^*$ molecular scenario

Qi-Fang Lu; Yu-Bing Dong
Subjects: Physics >> Nuclear Physics

We study the strong decay channels?P+c(4380)→J/ψp?and?P+c(4450)→J/ψp?under?ΣcD???molecular state ansatz. With various spin-parity assignments, the partial decay widths of?J/ψp?final state are calculated. Our results show that all the?P?wave?ΣcD???assignments are excluded, while?S?wave?ΣcD???pictures for?Pc(4380)?and?Pc(4450)?are both allowed by present experimental data. The?JP=3/2??Σ?cD??and?Σ?cD???molecules are also discussed in the heavy quark limit, and find that the?Σ?cD??system for?Pc(4380)?is possible. More experimental information on spin-parities and partial decay widths and theoretical investigations on other decay modes are needed to clarify the nature of the two?Pc?states.

submitted time 2016-08-31 Hits903Downloads454 Comment 0

4. chinaXiv:201608.00216 [pdf]

Performance of new 8-inch photomultiplier tube used for the Tibet muon-detector array

Ying Zhang; Jing Huang; Ding Chen; Liu-Ming Zhai; Xu Chen; Xiao-Bin Hu; Yu-Hui Lin; Hong-Bo Jin; Xue-Yao Zhang; Cun-Feng Feng: Huan-Yu Jia; Xun-Xiu Zhou; DANZENGLUOBU; Tian-Lu Chen; LABACIREN; Mao-Yuan Liu; Qi Gao; ZHAXICIREN
Subjects: Physics >> Nuclear Physics

A new hybrid experiment has been constructed to measure the chemical composition of cosmic rays around the "knee" in the wide energy range by the Tibet ASγ?collaboration at Tibet, China, since 2014. They consist of a high-energy air-shower-core array (YAC-II), a high-density air-shower array (Tibet-III) and a large underground water-Cherenkov muon-detector array (MD). In order to obtain the primary proton, helium and iron spectra and their "knee" positions in the energy range lower than?1016?eV, each of PMTs equipped to the MD cell is required to measure the number of photons capable of covering a wide dynamic range of 100 -?106?photoelectrons (PEs) according to Monte Carlo simulations. In this paper, we firstly compare the characteristic features between R5912-PMT made by Japan Hamamatsu and CR365-PMT made by Beijing Hamamatsu. This is the first comparison between R5912-PMT and CR365-PMT. If there exists no serious difference, we will then add two 8-inch-in-diameter PMTs to meet our requirements in each MD cell, which are responsible for the range of 100 - 10000 PEs and 2000 - 1000000 PEs, respectively. That is, MD cell is expected to be able to measure the number of muons over 6 orders of magnitude.

submitted time 2016-08-31 Hits1141Downloads683 Comment 0

5. chinaXiv:201608.00215 [pdf]

Quark matter in a parallel electric and magnetic field background: Chiral phase transition and equilibration of chiral density

M. Ruggieri; G. X. Peng
Subjects: Physics >> Nuclear Physics

In this article we study spontaneous chiral symmetry breaking for quark matter in the background of static and homogeneous parallel electric field?$\bm E$?and magnetic field?$\bm B$. We use a Nambu-Jona-Lasinio model with a local kernel interaction to compute the relevant quantities to describe chiral symmetry breaking at finite temperature for a wide range of?E?and?B. We study the effect of this background on inverse catalysis of chiral symmetry breaking for?E?and?B?of the same order of magnitude. We then focus on the effect of equilibration of chiral density,?n5, produced dynamically by axial anomaly on the critical temperature. The equilibration of?n5, a consequence of chirality flipping processes in the thermal bath, allows for the introduction of the chiral chemical potential,?μ5, which is computed self-consistently as a function of temperature and field strength by coupling the number equation to the gap equation, and solving the two within an expansion in?E/T2,?B/T2?and?μ25/T2. We find that even if chirality is produced and equilibrates within a relaxation time?τM, it does not change drastically the thermodynamics, with particular reference to the inverse catalysis induced by the external fields, as long as the average?μ5?at equilibrium is not too large.

submitted time 2016-08-31 Hits684Downloads312 Comment 0

6. chinaXiv:201608.00214 [pdf]

Sensitivity of YAC to measure the light-component spectrum of primary cosmic rays at the 'knee' energies

L M Zhai; J Huang; D Chen M Shibata; Y Katayose; Ying Zhang; J S Liu; Xu Chen; X B Hu; Y H Lin
Subjects: Physics >> Nuclear Physics

A new air-shower core-detector array (YAC : Yangbajing Air-shower Core-detector array) has been developed to measure the primary cosmic-ray composition at the "knee" energies in Tibet, China, focusing mainly on the light components. The prototype experiment (YAC-I) consisting of 16 detectors has been constructed and operated at Yangbajing (4300 m a.s.l.) in Tibet since May 2009. YAC-I is installed in the Tibet-III AS array and operates together. In this paper, we performed a Monte Carlo simulation to check the sensitivity of YAC-I+Tibet-III array to the cosmic-ray light component of cosmic rays around the knee energies, taking account of the observation conditions of actual YAC-I+Tibet-III array. The selection of light component from others was made by use of an artificial neural network (ANN). The simulation shows that the light-component spectrum estimated by our methods can well reproduce the input ones within 10\% error, and there will be about 30\% systematic errors mostly induced by the primary and interaction models used. It is found that the full-scale YAC and the Tibet-III array is powerful to study the cosmic-ray composition, in particular, to obtain the energy spectra of protons and helium nuclei around the knee energies.

submitted time 2016-08-31 Hits1061Downloads597 Comment 0

7. chinaXiv:201608.00213 [pdf]

ADMonium: Asymmetric Dark Matter Bound State

Xiao-Jun Bi; Zhaofeng Kang; P. Ko; Jinmian Li; Tianjun L
Subjects: Physics >> Nuclear Physics

We propose a novel framework for asymmetric scalar dark matter (ADM), which has interesting collider phenomenology in terms of an unstable ADM bound state (ADMonium) produced via Higgs portals. ADMonium is a natural consequence of the basic features of ADM: the (complex scalar) ADM is charged under a dark local?U(1)d?symmetry which is broken at a low scale and provides a light gauge boson?X. The dark gauge coupling is strong and then ADM can annihilate away into?X-pair effectively. Therefore, the ADM can form bound state due to its large self-interaction via?X?mediation. To explore the collider signature of ADMonium, we propose that ADM has a two-Higgs doublet portal. The ADMonium can have a sizable mixing with the heavier Higgs boson, which admits a large cross section of ADMonium production associated with?bb?. Of particular interest, our setup nicely explains the recent di-photon anomaly at 750 GeV via the events from?${\rm ADMonium}\ra 2X(\ra e^+e^-)$, where the electrons are identified as (un)converted photons. The remarkable prediction of an ADM near 375 GeV can be tested at the direct detection experiments in the near future.

submitted time 2016-08-31 Hits765Downloads383 Comment 0

8. chinaXiv:201608.00212 [pdf]

Design and optimization of resistive anode for a two-dimensional imaging triple-GEM detector

JU Xu-Dong; DONG Ming-Yi; ZHAO Yi-Chen; ZHOU Chuan-Xing; OUYANG Qun
Subjects: Physics >> Nuclear Physics

The optimization of resistive anode for two dimensional imaging detectors which consists of a series of high resistive square pads surrounding by low resistive strips has been studied by both numerical simulations and experimental tests. It has been found that to obtain good detector performance, the resistance ratio of the pad to the strip should be larger than 5, the nonuniformity of the pad surface resistivity had better be less than?20%, a smaller pad width leads to a smaller spatial resolution and when the pad width is?6mm, the spatial resolution (σ) can reach about?105μm. Based on the study results, a 2-D GEM detector prototype with the optimized resistive anode is constructed and a good imaging performance is achieved.

submitted time 2016-08-31 Hits1135Downloads576 Comment 0

9. chinaXiv:201608.00211 [pdf]

Constraints on $s-\bar s$ asymmetry of the proton in chiral effective theory

X. G. Wang; Chueng-Ryong Ji W. Melnitchouk; Y. Salamu; A. W. Thomas P. Wang
Subjects: Physics >> Nuclear Physics

We compute the?s?s??asymmetry in the proton in chiral effective theory, using phenomenological constraints based upon existing data. Unlike previous meson cloud model calculations, which accounted for kaon loop contributions with on-shell intermediate states alone, this work includes off-shell terms and contact interactions, which impact the shape of the?s?s??difference. Using a regularization procedure that preserves chiral symmetry and Lorentz invariance, we find that existing data limit the integrated value of the first moment of the asymmetry to the range??0.07×10?3≤?x(s?s?)?≤1.12×10?3?at a scale of?Q2=1GeV2. In contrast to some suggestions in the literature, the magnitude of this correction is too small to account for the NuTeV anomaly.

submitted time 2016-08-31 Hits408Downloads242 Comment 0

10. chinaXiv:201608.00210 [pdf]

Approximate degeneracy of heavy-light mesons with the same $L$

Takayuki Matsuki; Qi-Fang Lu; Yubing Dong; Toshiyuki Morii
Subjects: Physics >> Nuclear Physics

Careful observation of the experimental spectra of heavy-light mesons tells us that heavy-light mesons with the same angular momentum?L?are almost degenerate. The estimate is given how much this degeneracy is broken in our relativistic potential model, and it is analytically shown that expectation values of a commutator between the lowest order Hamiltonian and?L???2?are of the order of?1/mQ?with a heavy quark mass?mQ. It turns out that nonrelativistic approximation of heavy quark system has a rotational symmetry and hence degeneracy among states with the same?L. This feature can be tested by measuring higher orbitally and radially excited heavy-light meson spectra for?D/Ds/B/Bs?in LHCb and forthcoming BelleII.

submitted time 2016-08-31 Hits865Downloads419 Comment 0

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