Physics perspectives of the ALICE experiment at the large hadron collider

The large hadron collider (LHC) under construction at CERN will deliver ion beams up to centre of mass energies of the order of 5.5 TeV per nucleon, in case of lead. If compared to the available facilities for the study of nucleus-nucleus collisions (SpS and RHIC), this represents a huge step forward in terms of both volume and energy density that can be attained in nuclear interactions. ALICE (a large ion collider experiment) is the only detector specifically designed for the physics of nuclear collisions at LHC, even though it can also study high cross-section processes occurring in proton-proton collisions. The main goal of the experiment is to observe and study the phase transition from hadronic matter to deconfined partonic matter (quark gluon plasma —QGP). ALICE is conceived as a general-purpose detector and will address most of the phenomena related to the QGP formation at LHC energies: for this purpose, a large fraction of the hadrons, leptons and photons produced in each interaction will be measured and identified.     

Tackling the kaon structure function at EicC

Measuring the kaon structure beyond proton and pion structures is a prominent topic in hadron physics, as it is one way to understand the nature of the Nambu-Goldstone boson of QCD and observe the interplay between the EHM and HB mechanisms for hadron mass generation. In this study, we present a simulation of the leading Λ baryon tagged deep inelastic scattering experiment at EicC (Electron-ion collider in China), which is engaged to unveil the internal structure of kaon via the Sullivan process. According to our simulation results, the suggested experiment will cover the kinematical domain of \begin{document}$ 0.05\lesssim x_{\rm K} \lesssim 0.85 $\end{document} and \begin{document}$ Q^2 $\end{document} up to 50 GeV\begin{document}$ ^2 $\end{document}, with the acceptable statistical uncertainties. In the relatively low-\begin{document}$ Q^2 $\end{document} region (\begin{document}$ <10 $\end{document} GeV\begin{document}$ ^2 $\end{document}), the Monte-Carlo simulation shows a good statistical precision (\begin{document}$ <5 $\end{document}%) for the measurement of the kaon structure function \begin{document}$ F_2^{\rm K} $\end{document}. In the high-\begin{document}$ Q^2 $\end{document} region (up to 50 GeV\begin{document}$ ^2 $\end{document}), the statistical uncertainty of \begin{document}$ F_2^{\rm K} $\end{document} is also acceptable (\begin{document}$ <10 $\end{document}%) for the data at \begin{document}$ x_{\rm K}<0.8 $\end{document}. To perform such an experiment at an electron-ion collider, a high-performance zero-degree calorimeter is suggested. The magnitude of the background process and the assumed detector capabilities are also discussed and illustrated in the paper.     

Direct photon and photon-jet measurement capability of the ATLAS experiment at the LHC

Direct photon and photon-jet correlations are perfect tools for tomographic studies of the dense medium produced in heavy ion collisions at LHC energies. Due to their weak interactions with the medium, direct photons serve as standard candles for hard-scattering processes, providing a clean calibration of the momentum of the associated jets. The ATLAS detector has powerful opportunities to carry out these measurements. The combination of fine granularity, longitudinal segmentation and large acceptance is unique for the LHC detectors. We show how it will provide optimal capability to distinguish direct photon clusters from neutral meson clusters based on their shower profile over a wide acceptance in η−?$\eta -?$ up to 200 GeV in pT$p_T$. We show that combined with a photon isolation cut ATLAS would be able to measure a relatively background-free direct photon yield from 50–200 GeV along with the corresponding gamma-jet correlations in one nominal LHC Pb+Pb year. These high pT$p_T$ photons provide clean and statistically significant measurements of gamma-jet correlations and the fragmentation function for photon-tagged jets.     

微弱信号检测实验教学研究

根据教学实践，阐述微弱信号检测实验开设的必要性，介绍了微弱信号检测的物理模型，设计了近代物理实验微弱信号检测专题实验的开设方案．     

铅球运动最佳出手角的理论分析和实验模拟研究

从理论上分析了铅球运动的初速度,出手高度,出手角度对成绩的影响,力求寻找它们之间的最佳组合,并通过模拟实验进行了论证.     

Duffing振子微弱信号检测盲区消除及检测统计量构造

针对Duffing振子进行同频微弱信号检测时存在的检测盲区, 提出了一种策动力移相法予以消除. 结合微弱信号特性对检测盲区表达式进行分析, 得出了策动力与待测信号的“相差”位于检测盲区时的角度范围, 通过使策动力相位产生相移量π后实现对同频信号的检测, 实验证明了方法的可行性. 为了克服定性分析的不足和有效区分振子系统信号检测过程中出现的不同状态, 构造了一个基于类Halmiton系统的检测统计量, 并设计了基于该统计量的任意频率信号检测方法步骤, 方法的核心是以检测统计量出现极大值处所在的连续两个频点作为待测信号的频率范围. 在不同检测过程的仿真实验基础上, 给出了混沌、间歇混沌和大周期的检测统计量数值范围, 进而利用该数值范围作为判据实现了对任意频率信号的检测. 实验结果表明, 该方法不仅为系统状态提供了定量的判据准则, 而且提高了信号检测性能, 进一步完善了现有利用Duffing振子进行微弱信号检测的方法.     

Photon statistics of pulse-pumped four-wave mixing in fiber with weak signal injection

We study the photon statistics of pulse-pumped four-wave mixing in fibers with weak coherent signal injection by measuring the intensity correlation functions of individual signal and idler fields. The experimental results show that the intensity correlation function of individual signal(idler) field g_(s(i))~(2) decreases with the intensity of signal injection. After applying narrow band filter in signal(idler) band, the value of g_(s(i))~(2) decreases from 1.9 ± 0.02(1.9 ± 0.02) to 1.03 ± 0.02(1.05 ± 0.02) when the intensity of signal injection varies from 0 to 120 photons/pulse. The results indicate that the photon statistics changes from Bose–Einstein distribution to Poisson distribution. We calculate the intensity correlation functions by using the multi-mode theory of four-wave mixing in fibers. The theoretical curves well fit the experimental results.Our investigation will be useful for mitigating the crosstalk between quantum and classical channels in a dense wavelength division multiplexing network.     

北京谱仪BESIII精确测量Y(4260)粒子

利用北京谱仪BESIII实验采集的约9fb^－1数据样本,BESIII测量了e^＋e^－→π^＋π^－J/ψ过程的产生截面,并对在该过程中观测到的Y(4260)粒子的质量和宽度做了目前世界上最精确的测量。BESIII的测量给出Y(4260)粒子的质量在4.22 GeV/c²左右,比之前的测量偏低;宽度约44 MeV,比之前的测量窄很多。相比之前的实验,BESIII对Y(4260)粒子参数的精确测量给解释该粒子的理论模型提供了更强的约束。另外,BESIII实验在4.32 GeV/c²附近还观测到一个新粒子信号,信号显著性为7.6σ。新粒子的质量和宽度和之前观测到的Y(4360)粒子的质量和宽度在误差范围内吻合,有可能是同一个粒子。     

Small x phenomenology on gluon evolution through the BFKL equation in light of a constraint in multi-Regge kinematics

We investigate the impact of so-called kinematic constraint on gluon evolution at small x.Implanting the constraint on the real emission term of the gluon ladder diagram, we obtain an integro-differential form of the Balitsky-Fadin-Kuraev-Lipatov(BFKL) equation. Later we solve the equation analytically using the method of characteristics. We sketch the Bjorken x and transverse momentum k_t~2 dependence of our solution of unintegrated gluon distributions f (x,k_t~2) in the kinematic constraint supplemented BFKL equation and contrasted the same with the original BFKL equation. Then we extract the integrated gluon density xg(x, Q~2) from unintegrated gluon distributions f (x,k_t~2) and compared our theoretical prediction with that of global data fits, namely NNPDF3.1 sx and CT14. Finally we illustrate the phenomenological implication of our solution for unintegrated gluon distribution f (x,k_T~2) towards exploring high precision HERA DIS data by the theoretical prediction of proton structure functions(F_2 and F_L).     

Measurement of forward-backward asymmetry A FB and of the weak mixing angle in processes of dilepton production in proton-proton collisions at \sqrt s = 7 TeV in the CMS experiment at the LHC

The results obtained by measuring the forward-backward asymmetry (A _FB ) of Drell-Yan lepton pairs in proton-proton collisions at $\sqrt s $ = 7 TeV at the LHC are presented. This asymmetry is measured as a function of the dilepton mass and rapidity in the dielectron and dimuon channels. The values of A _FB were found for invariant masses of dileptons in the range of 40 ? M _ll ? 600 GeV. The results for the effective weak mixing angle that were deduced from data on dimuon production in Drell-Yan processes are also presented. The respective data sample was collected by using the Compact Muon Solenoid (CMS) detector over the period spanning the years 2010 and 2011. The measured asymmetry and the effective weak mixing are consistent with the respective Standard Model predictions.     

The extended IEM mixing model in the framework of the composition PDF approach: applications to diesel spray combustion

A steady, two-dimensional corner flame is established when fuel and oxidizer enter the reaction zone in mutually perpendicular directions. A model problem in which the velocity fields are linear functions of spatial position is utilized to study the resulting flame. The flame structure is comprised of a diffusion flame surrounded on either side by fuel-rich and fuel-lean partially premixed laminar flames, similar to, but distinct from, triple flames. Using suitable coordinate transformations and change of variables, the governing equations in the thermodiffusive approximation are recast into a form akin to classical triple flames, with the strain rate appearing as the eigenvalue. A new exact integral representation of the solution to the mixture fraction equation is then utilized and high activation energy asymptotics are applied to solve approximately for the resulting flame shape, the imposed strain rate and, most significantly, the position of flame stabilization. This theoretically predicted flame is computed numerically, and comparisons are made between theory and computation.     

舵面角度测量中结构光光条图像自动定位方法

本文提出了一种在舵面角度测量中多平面结构光光条的自动定位方法.该方法首先基于Steger方法提取舵面中多个平面的光条图像中心;然后基于直线约束和距离约束提取出各小直线段,并根据各直线段的直线方向将各小直线段归类为最后的光条直线;最后根据光条直线的位置判断各光条直线所在光平面及所在舵平面.经实验验证,本文方法切实有效,具有较高的鲁棒性.     

Instability of the anomalies in the one-dimensional Anderson model at weak disorder

We study the asymptotic behavior of the invariant measure, the Lyapunov exponent, and the density of states in the weak disorder limit in the case where the single-site potential distribution is not centered and for the special energiesE=cos(p/q). We also prove that in general the above quantities can be continuously extended to zero disorder as continuous functions in the disorder parameter for all energiesE(–1, 1).     

密勒-库什实验过程中的气体分子分布函数

详细分析了密勒－库什实验过程中分子速率分布的变化情况，说明了实验数据与麦克斯韦速率分布之间的关系。     

刚体转动惯量实验中时间测量的改进方法

对传统的刚体转动实验仪时间的测量方法进行了改进,提高了实验测量的精度,拓展了实验内容．同时也可以作为开放、设计性实验．     

双光子共振非简并四波混频测量钡原子里德伯态碰撞展宽中的伴线研究

研究了采用双光子共振非简并四波混频技术测量原子里德伯态碰撞展宽时出现的伴线现象, 测量了不同缓冲气压下的钡原子里德伯态6snd ¹D₂ (n=16, 22, 36) 的四波混频谱线, 研究了伴线随主量子数n 的变化曲线以及伴线信号强度随缓冲气压压强的变化曲线, 分析了伴线对NFWM谱线的线宽的影响, 发现考虑伴线对四波混频谱线线宽的贡献, 可以对NFWM模型下测量到的碰撞展宽系数进行修正.     

Weak deflection angle and shadow cast by the charged-Kiselev black hole with cloud of strings in plasma

In this study, the gravitational deflection angle of photons in the weak field limit (or the weak deflection angle) and shadow cast by the electrically charged and spherically symmetric static Kiselev black hole (BH) in the string cloud background are investigated. The influences of the BH charge Q, quintessence parameter γ, and string cloud parameter a on the weak deflection angle are studied using the Gauss-Bonnet theorem, in addition to studying the influences on the radius of photon spheres and size of the BH shadow in the spacetime geometry of the charged-Kiselev BH in string clouds. Moreover, we study the effects of plasma (uniform and non-uniform) on the weak deflection angle and shadow cast by the charged-Kiselev BH surrounded by the clouds of strings. In the presence of a uniform/nonuniform plasma medium, an increase in the string cloud parameter a increases the deflection angle α. In contrast, a decrease in the BH charge Q decreases the deflection angle. Further, we observe that an increase in the BH charge Q causes a decrease in the size of the shadow of the BH. We notice that, with an increase in the values of the parameters γ and a, the size of the BH shadow increases, and therefore, the intensity of the gravitational field around the charged-Kiselev BH in string clouds increases. Thus, the gravitational field of the charged-Kiselev BH in the string cloud background is stronger than the field produced by the pure Reissner-Nordstrom BH. Moreover, we use the data released by the Event Horizon Telescope (EHT) collaboration, for the supermassive BHs M87* and Sgr A*, to obtain constraints on the values of the parameters γ and a.     

Planck's experiment on gas mixing,Gibbs' paradox and the definition of entropy in statistical mechanics

The interpretation of entropy provided by statistical thermodynamics is not adequate to represent the thermodynamic entropy of the gas of noninteracting particles considered in this theory. Planck's thought experiment on reversible mixing and Gibbs' paradox provide perhaps the best-known evidence of this. The assumption that the internal energy of an ideal gas depends only on its temperature is introduced both in the kinetic theory of gases and in the classical thermodynamics. Such an assumption is no doubt adequate to deal with real gases at appropriately low pressures and high temperatures. However, the present paper shows that the same assumption implies that the entropy of an ideal gas, like its internal energy, must also depend only on temperature. The paper calculates the expression of the entropy function that is consistent with the internal energy function of the gas. From this expression, the thermodynamic entropy of the ideal gas – as distinct from its statistical entropy – is finally expressed in terms of statistical mechanics variables.     

The LPCTrap experiment: measurement of the β–ν angular correlation in 6He using a transparent Paul trap

We report on the status of the LPCTrap experiment, devoted to measure the β–ν angular correlation in the pure Gamow–Teller decay of ⁶He. This measurement is motivated by the search for the presence of tensor type contributions to the weak interaction. The ⁶He ions are confined in a novel transparent Paul trap. The β particles and the recoil ions are detected in coincidence to deduce the angular correlation parameter. The commissioning run performed in 2005 has given the proof of principle of this experiment. Up to 10⁵ coincidences were recorded during a second run in 2006.