Heavy flavour capabilities of the ALICE transition radiation detector

The ALICE Transition Radiation Detector (TRD) enhances the detection sensitivity of heavy-flavour production of the ALICE experiment at the LHC by providing electron identification above and fast trigger capabilities above . The combined particle identification from the Inner Tracking System (ITS), the Time Projection Chamber (TPC) and the Transition Radiation Detector enables measurements of D-mesons and B-mesons and, potentially, the Λ_b, assuming the reconstruction of the .     

假根羽藻LHCⅡ的同质和异质三聚体的能量传递动力学研究

采用飞秒时间分辨荧光光谱技术在室温下用波长为495nm的光激发,研究了假根羽藻LHCⅡ的同质三聚体和异质三聚体这两种不同聚集形式蛋白复合物的光谱特性和传能特性.将实验获得的两样品的荧光光谱分别进行高斯解析,各得到5条亚谱带,并分析得出同质三聚体的四种特征Chl分子的光谱特性和异质三聚体的五种特征Chl分子光谱特性,另外还对两蛋白复合物的荧光光谱作了比较.利用Global优化处理方法,建立多指数拟合联立方程对荧光衰减曲线进行拟合处理,得到同质三聚体Chl分子传能的寿命：165±8.5 fs、2.2±0.6 ps、5.1±0.1 ns;异质三聚体Chl分子传能的寿命：255±6.3 fs、4±0.8 ps和3.8±0.1 ns;并且将这些时间常数作出归属.将其分析比较,快组分同质三聚体的传能速率较高,推断组成同质三聚体的同种脱辅基蛋白间的结合程度较组成异质三聚体的不同脱辅基蛋白间的更紧密,使其上结合的Chl分子空间位置更近,更有利于能量的迅速传递;而慢组分同质三聚体的偏大,可能是由于其经历的传能途径较长,传能机制上也和异质三聚体不同所致.     

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.     

Search for heavy sterile neutrinos in trileptons at the LHC

We present a search strategy for both Dirac and Majorana sterile neutrinos from the purely leptonic decays of W~±→e~±e~±μ~?ν and μ~±μ~± e~?ν at the 14 TeV LHC. The discovery and exclusion limits for sterile neutrinos are shown using both the Cut-and-Count(CC) and Multi-Variate Analysis(MVA) methods. We also discriminate between Dirac and Majorana sterile neutrinos by exploiting a set of kinematic observables which differ between the Dirac and Majorana cases. We find that the MVA method, compared to the more common CC method, can greatly enhance the discovery and discrimination limits. Two benchmark points with sterile neutrino mass m N =20 GeV and 50 GeV are tested. For an integrated luminosity of 3000 fb~(-1), sterile neutrinos can be found with 5σ significance if heavy-to-light neutrino mixings |U_(Ne)|~2~|U_(Nμ)|~2~10~(-6), while Majorana vs. Dirac discrimination can be reached if at least one of the mixings is of order 10~(-5).     

Feasibility study for the measurement of Bc meson mass and lifetime with the general purpose detector at the LHC

In this paper a feasibility study of the B_c meson to measure its mass and lifetime is described with the general purpose detector at the LHC. The study solely concentrated on the J/ψπ⁺, J/ψ→μ⁺μ^－ decay channel of the B_c and it was concluded that about 120 events can be selected in the first fb^－1 of data. With this data sample, the mass resolution was estimated to be 2.0(stat.)MeV/c² while the cτ resolution was found to be 13.1(stat.)μm, i.e. the lifetime resolution to be 0.044(stat.)ps.     

Revisiting wrong sign Yukawa coupling of type Ⅱ two-Higgs-doublet model in light of recent LHC data

In light of the recently obtained LHC Higgs data, we examine the parameter space of the type II twoHiggs-doublet model, in which the 125 GeV Higgs bosons exhibit wrong sign Yukawa couplings. Combining the relevant theoretical and experimental limits, we find that the LHC Higgs data exclude most of the parameter space of the wrong sign Yukawa coupling. For m_H 600 GeV, the allowed samples are mainly distributed across several corners and narrow bands of m_A 20 GeV, 30 m_A 120 GeV, 240 GeV m_A 300 GeV, 380 GeV m_A 430 GeV, and480 GeV m_A 550 GeV. For m_A 600 GeV, m_H is required to be lower than 470 GeV. The light pseudo-scalar with a mass of 20 GeV is still permitted in the case of the wrong sign Yukawa coupling of 125 GeV Higgs bosons.     

Randall–Sundrum reality at the LHC

The radion is expected to be the first signal of the Randall–Sundrum (RS) model. We explore the possibility of finding it in the ongoing Higgs searches at the LHC. The little RS model (LRS), which has a fundamental scale at ∼¹⁰³$\sim {10}^3$ TeV, is excluded over wide ranges of the radion mass from the latest WW and γγ data by ATLAS and CMS.     

Feasibility study on cross-section measurement of Y（1S） →μ^＋μ- by using early CMS data

One of the first physics results that CMS will hopefully obtain will be the analysis of heavy quarkonium productions, including the Υ cross-section measurement. Since the Υ production cross-section from p-p collisions is expected to be relatively large, the analysis should be viable with rather small datasets which will be available soon after the start-up of the LHC. This paper describes the methods and plans for measuring the differential cross-section of Y（1S） →μ^＋μ- production, by using data to be collected from the CMS detector in the first LHC run. In this study, about 80 thousand Υ are reconstructed corresponding to an integrated luminosity of 6.4 pb^-1 in 10 TeV proton-proton collisions by using Monte Carlo data. The precision of this measurement is estimated to be about 16%, which is limited by the systematic errors.     

Supermodels for early LHC

We investigate which new physics signatures could be discovered in the first year of the LHC, beyond the expected sensitivity of the Tevatron data by the end of 2010. We construct “supermodels”, for which the LHC sensitivity even with only 10 pb⁻¹ useful luminosity is greater than that of the Tevatron with 10 fb⁻¹. The simplest supermodels involve s  -channel resonances in the quark–antiquark and especially in the quark–quark channels. We concentrate on easily visible final states with small standard model backgrounds, and find that there are simple searches, besides those for Z^′$Z^{\prime }$ states, which could discover new physics in early LHC data. Many of these are well-suited to test searches for “more conventional” models, often discussed for multi-fb⁻¹ data sets.     

Prospectives of the hadron program in ATLAS

One of the first measurements that will be made at the LHC by ATLAS deals with the properties of inelastic collisions,namely the central charged particle density and transverse momentum distributions.Current predictions of these distributions have large uncertainties in the LHC energy range.We describe the ATLAS minimum bias triggers,designed to seleet all kind of inelastic interactions,and the performance of the track reconstruction software which was adapted to soft particle track reconstruction.The precision with which the minimum bias distributions can be measured with early data is presented and the uncertainties on the inelastic distributions due to trigger bias is discussed.