Azimuthal asymmetries in lepton-pair production at a fixed-target experiment using the LHC beams (AFTER)

A multi-purpose fixed-target experiment using the proton and lead-ion beams of the LHC was recently proposed by Brodsky, Fleuret, Hadjidakis and Lansberg, and here we concentrate our study on some issues related to the spin physics part of this project (referred to as AFTER). We study the nucleon spin structure through pp and pd processes with a fixed-target experiment using the LHC proton beams, for the kinematical region with 7?TeV proton beams at the energy in center-of-mass frame of two nucleons $\sqrt{s}=115~\mathrm{GeV}$ . We calculate and estimate the cos2? azimuthal asymmetries of unpolarized pp and pd dilepton production processes in the Drell?CYan continuum region and at the Z-pole. We also calculate the sin(2??? _S ), sin(2?+? _S ) and sin2? azimuthal asymmetries of pp and pd dilepton production processes with the target proton and deuteron longitudinally or transversally polarized in the Drell?CYan continuum region and around Z resonances region. We conclude that it is feasible to measure these azimuthal asymmetries, consequently the three-dimensional or transverse momentum dependent parton distribution functions (3dPDFs or TMDs), at this new AFTER facility.     

Spin physics at a fixed-target experiment at the LHC (AFTER@LHC)

We outline the opportunities for spin physics which are offered by a next generation and multipurpose fixed-target experiment exploiting the proton LHC beam extracted by a bent crystal. In particular, we focus on the study of single transverse spin asymetries with the polarisation of the target.     

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.     

碱束斯特恩-盖拉赫实验

利用K束斯特恩－盖拉赫实验装置，通过对束源和表面电离探测器的改进，实现Li,Na,K,Rb,Cs全碱束斯特恩－盖拉赫实验。     

折射率调制深度误差对切趾啁啾光纤光栅特性的影响

从耦合模方程出发,用一种矩阵方法分析了折射率调制深度误差对切趾啁啾布拉格光纤光栅传输特性的影响。结果表明:折射率调制深度误差的分布频率越高,光栅传输特性受到的危害越小;误差平均幅值越高,光栅传输特性的劣化程度越大。因此,在光栅的制作过程中,应注意避免和减小高幅值误差,并注意减少低空间频率分布的误差。     

Quarkonium Physics at a Fixed-Target Experiment using the LHC Beams

We outline the many quarkonium-physics opportunities offered by a multi-purpose fixed-target experiment using the p and Pb Large Hadron Collider (LHC) beams extracted by a bent crystal. This provides an integrated luminosity of 0.5 fb^?1 per year on a typical 1?cm-long target. Such an extraction mode does not alter the performance of the collider experiments at the LHC. With such a high luminosity, one can analyse quarkonium production in great details in pp, pd and pA collisions at ${\sqrt{s_{NN}}\simeq 115}$ GeV and at ${\sqrt{s_{NN}}\simeq 72}$ GeV in PbA collisions. In a typical pp (pA) run, the obtained quarkonium yields per unit of rapidity are 2–3 orders of magnitude larger than those expected at RHIC and about, respectively, 10(70) times larger than for ALICE. In PbA, they are comparable. By instrumenting the target-rapidity region, the large negative-x _F domain can be accessed for the first time, greatly extending previous measurements by Hera-B and E866. Such analyses should help resolving the quarkonium-production controversies and clear the way for gluon PDF extraction via quarkonium studies. The nuclear target-species versatility provides a unique opportunity to study nuclear matter and the features of the hot and dense matter formed in PbA collisions. A polarised proton target?allows the study of transverse-spin asymmetries in J/ψ and ${\Upsilon}$ production, providing access to the gluon and charm Sivers functions.     

Single top production associated with a neutral scalar at LHC in topcolor-assisted technicolor

The topcolor-assisted technicolor(TC2)model predicts a number of neutral SCalars like the top-pion (π0t)and the top-Higgs(h0t).These scalar8 have flavor-changing neutral-current(FCNC)top quark couphngs,among which the top-charm transition couplings may be sizable.Such FCNC couplings induce single top productions associated with a neutral scalar at the CERN Large Hadron Collider(LHC)through the parton processes cg→tπ0t and cg→th0t.In this paper we examine these productions and find their production rates can exceed the 3σ sensitivity of the LHC in a large part of parameter space.Since in the Standard Model and the minimal supersymmetric model such rare productions have unobservably small production rates at the LHC.these rare processes will serve as a good probe for the TC2 model.     

Single top production associated with a neutral scalar at LHC in topcolor-assisted technicolor

The topcolor-assisted technicolor (TC2) model predicts a number of neutral scalars like the top-pion (π⁰_t) and the top-Higgs (h⁰_t). These scalars have flavor-changing neutral-current (FCNC) top quark couplings, among which the top-charm transition couplings may be sizable. Such FCNC couplings induce single top productions associated with a neutral scalar at the CERN Large Hadron Collider (LHC) through the parton processes cg→t π⁰_t and cg→t h⁰_t. In this paper we examine these productions and find their production rates can exceed the 3σ sensitivity of the LHC in a large part of parameter space. Since in the Standard Model and the minimal supersymmetric model such rare productions have unobservably small production rates at the LHC, these rare processes will serve as a good probe for the TC2 model.     

大型强子对撞机上的实验进展

大型强子对撞机的成功建成,使人类对微观世界的探索深入到了10^-18 m这样一个全新的领域。文章介绍大型强子对撞机上实验的最新进展。     

Higgs production cross-section in a Standard Model with four generations at the LHC

We present theoretical predictions for the Higgs boson production cross-section via gluon fusion at the LHC in a Standard Model with four generations. We include QCD corrections through NLO retaining the full dependence on the quark masses, and the NNLO corrections in the heavy quark effective theory approximation. We also include electroweak corrections through three loops. Electroweak and bottom-quark contributions are suppressed in comparison to the Standard Model with three generations.     

Exclusion of black hole disaster scenarios at the LHC

The upcoming high energy experiments at the LHC are one of the most outstanding efforts for a better understanding of nature. It is associated with great hopes in the physics community. But there is also some fear in the public, that the conjectured production of mini black holes might lead to a dangerous chain reaction. In this Letter we summarize the most straightforward arguments that are necessary to rule out such doomsday scenarios.     

From RHIC to LHC: a relativistic diffusion approach

We investigate the energy dependence of stopping and hadron production in high‐energy heavy‐ion collisions based on a three‐sources Relativistic Diffusion Model. The transport coefficients are extrapolated from Au + Au and Cu + Cu at RHIC energies ( = 19.6–200 GeV) to Pb + Pb at LHC energies = 5.52 TeV. Rapidity distributions for net protons, and pseudorapidity spectra for produced charged particles in central collisions are compared to data at RHIC energies, and discussed for several extrapolations to LHC energies.     

Franck-Hertz实验的物理过程

通过对Franck-Hertz实验中的电子能量分布及其动态变化的分析,对Franck-Hertz曲线的规律性波动现象作出了直观的解释.对充汞Franck-Hertz管,考虑了电子的额外加速程、汞原子的多能级共同激发以及电子与汞原子非弹性碰撞后电子具有剩余能量等因素,对Franck-Hertz实验的物理过程有了更全面的了解,并对Franck-Hertz曲线峰间距随加速电压增大而持续变大的现象作出了解释.     

Inflation,LHC and the Higgs boson

After the Higgs boson has been discovered, the Standard Model of particle physics became a confirmed theory, potentially valid up to the Planck scale and allowing one to trace the evolution of the Universe from the inflationary stage till the present days. We discuss the relation between the results from the LHC and the inflationary cosmology. We overview the Higgs inflation, and its relation to the possible metastability of the electroweak vacuum. A short overview of the bounds on the metastability of the electroweak vacuum in the models with inflation not related to the Higgs boson is presented.     

Associted Production of Z Boson and a Pair of New Quarks at LHC

The associated production of Z boson and a pair of new quarks at the Large Hadron Collider （LHC） is studied. The cross sections for both sequential fermions and vector-like fermions are presented. It is found that for sequential fermions the cross sections can reach 1 - 10^2 /b for heavy quark mass mQ from 1000 GeV to 200 GeV. For vector-like quarks, the cross sections are suppressed by mixing parameter sin OL. Focusing on process pp → b＇b＇, we investigate the possibility of detecting the 6l 4- 2j signal. For a b＇ with light mass and a large branching ratio of b＇ → bZ, it is found that only several signal events （ parton level ） can be produced with 1000 fb^-1 integrated luminosity. Although the signal events are rare, all the final states are produced centrally and multi lepton final states are clear at hadron collider, which could be easily detected.     

大学物理实验的双任务教学方法初探

为搭建课程改革与学习效果之间的桥梁，在大学物理实验中引入了双任务教学方法．本文介绍了双任务教学法的概念、优点及具体实施方法．     

The LHC collider

The first three year run of the Large Hadron Collider (LHC) ended in the spring of 2013. During this period, the collider was operated mainly at beam energies of 3.5 and 4 TeV. The performances that have been achieved during that first run and the challenges for commissioning and operating the LHC are presented. A brief outlook into the upcoming run at an energy of 6.5 TeV will be given.     

Associated production of Higgs boson and tt at LHC

One of the future goals of the LHC is to precisely measure the properties of the Higgs boson. The associated production of a Higgs boson and top quark pair is a promising process to investigate the related Yukawa interaction and the properties of the Higgs. Compared with the pure scalar sector in the Standard Model, the Higgs sector contains both scalars and pseudoscalars in many new physics models, which makes the ttH interaction more complex and provides a variety of phenomena. To investigate the ttH interaction and the properties of the Higgs, we study the top quark spin correlation observables at the LHC.