Strange prospects for LHC energies

Strange quark and hadron production will be studied at the large hadron collider (LHC) energies in order to explore the properties of both pp and heavy-ion collisions. The ALICE experiment will be specifically efficient in the strange sector with the identification of baryons and mesons over a wide range of transverse momentum. Dedicated measurements are proposed for investigating chemical equilibration and bulk properties. Strange particles can also help to probe kinematical regions where hard processes and pQCD dominate. We try to anticipate here several ALICE analyses to be performed as the first Pb–Pb and pp data will be available. PACS 25.75.-q; 25.75.Dw     

Strange particle production in relativistic nucleus-nucleus collisions at RHIC and LHC energy regions

PACIAE, a parton and hadron cascade model, is utilized to systematically investigate strange particle production and strangeness enhancement in Au+Au collisions and in Pb+Pb collisions with the √s_NN=200 GeV at the RHIC and 2.76 TeV at the LHC, respectively. The experimental results at different centralities, using data from the STAR collaboration and the ALICE collaboration, are well described by the PACIAE model. This may represent the importance of the parton and hadron rescatterings, as well as the reduction mechanism for strange quark suppression, that are implemented in the PACIAE model.     

Proton-proton physics with the ALICE muon spectrometer at the LHC

ALICE, the dedicated heavy-ion experiment at the LHC, has also an important proton-proton physics program. The ALICE muon spectrometer will be presented and the corresponding physics analysis will be reviewed. A particular emphasis will be placed on heavy-flavor measurement. (for the ALICE Collaboration) The text was submitted by the author in English.     

Effects of inelastic (re)scattering processes s→gg and gg→s on strange hadron production in pp collisions at RHIC and LHC energies

The rapidity densities at mid-rapidity and the transverse momentum distributions for strange hadrons produced in pp collisions are analyzed using the modified PACIAE model by considering the effect of inelastic (re)scattering processes s→gg and gg→s in parton (re)scattering. The calculated results of the transverse momentum spectra of the strangeness fitting with data measured by STAR and ALICE Collaborations can be improved, especially at large transverse momentum levels. This demonstrates that the effect of inelastic (re)scattering processes of s→gg and gg→s is not negligible at RHIC and LHC energy levels.     

Multi-strange-quark states at ultra-relativistic heavy-ion collisions

We examine the possibility of producing and evidencing exotic strange matter (strangelets and metastable multi-hypernuclear objects, MEMO’s), including also pure hyperonic bound states ((ΛΛ)_b, (ξΛ)_b), at RHIC and LHC. Simulations are presented to estimate the sensitivity of the STAR and ALICE experiments to the detection of these objects, focusing mainly on metastable short-lived (weak decaying) strange dibaryons, with a particular emphasis on theH-dibaryon, a six quark-bag bound state (uuddss).     

ALICE实验内径迹系统探测器升级

大型重离子对撞实验(A Large heavy-Ion Collision Experiment,ALICE)按计划在大型强子对撞机(Large Hadron Collider,LHC)的第二次停机(2019—2021)期间进行探测器升级工作。为了对强相互作用物质——夸克胶子等离子体(Quark-Gluon Plasma,QGP)的性质进行更细致的研究,作为升级计划中重要的一个内容是把ALICE实验现有的内径迹系统探测器(Inner Tracking System,ITS)全面升级为基于单片有源像素传感器(Monolithic Active Pixel Sensor,MAPS)技术的硅像素探测器(习惯称之为ITS2),并在Run 3和Run 4期间采集更多的铅核-铅核碰撞数据。新的ITS2共由7层(内3层,中间2层和外2层)探测桶面组成,共由24 000余片尺寸为3 cm × 1.5 cm的MAPS硅像素芯片(该芯片称之为ALPIDE)构成,有效探测面积达10 m2,共约120亿像素。ALPIDE芯片厚度为50 μm,单个像素的尺寸是27 μm × 29 μm,该芯片具有低功耗、高空间分辨率和高速读出等特点。ITS2将使ALICE探测器在测量极低横动量粒子时具备优异的探测效率和碰撞参数分辨率,同时也使ALICE探测器适应于LHC高束流亮度环境。目前ITS2的探测器模块量产和测试已于2019年完成,并在欧洲核子中心(CERN)洁净室完成了7层桶面的组装与安装,于2020年完成试运行测试。2021年1月启动ITS2在ALICE探测器中的安装与试运行工作,计划于2021年5月底完成ITS2的安装与测试。本工作将对ALICE/ITS2的探测器结构、ALPIDE芯片和升级进展等方面进行介绍。     

Low-<Emphasis Type="Italic">p</Emphasis><Subscript>T</Subscript> proton-proton physics at low luminosity at LHC

This review of low-p _T proton-proton physics at low luminosity at the large hadron collider (LHC) should cover all LHC experiments, but in practice, is mainly related to ALICE, for reasons which will be explained. However, the relevance to other LHC experiments is clear, as low-p_T. phenomena represent an important component of the background to their high-p_T. phenomena which needs to be calibrated. The ALICE collaboration will study proton-proton collisions as part of their heavy-ion programme, where most signals are relative to the proton-proton system. In addition, the ALICE detector’s unique acceptance at low p_T as well as its unique particle identification capability will make it possible to carry out a program of genuine proton-proton physics complementary to those of other LHC experiments.     

High-p t and jet physics from RHIC to LHC

The observation of the strong suppression of high-p t hadrons in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) at BNL has motivated a large experimental program using hard probes to characterize the deconfined medium created. However, what can be denoted as “leading particle” physics accessible at RHIC presents some limitations which motivate at higher energy the study of much more penetrating objects: jets. The gain in center-of-mass energy expected at the Large Hadron Collider (LHC) at CERN will definitively improve our understanding on how the energy is lost in the system, opening a major new window of study: the physics of jets on an event-by-event basis. We will concentrate on the expected performance for jet reconstruction in ALICE using the EMCal calorimeter. (for the ALICE Collaboration) The text was submitted by the author in English.     

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.     

Recent results from CERN SPS experiments and the future heavy ion programme

We describe the important results from the recent experiments using lead beams at the CERN SPS. The results of the WA98 experiment, which has substantial Indian participation along with the photon multiplicity detector is described in some detail. Combining the preliminary results from various experiments looking at different signals of phase transition, one finds enough evidences to suggest that phase transition has taken place in nuclear collisions at the SPS. Future programme of heavy ion physics at the LHC is being greared around the ALICE experiment. This will comprise of detector subsystems capable of studying almost all the signals in the same event. The photon multiplicity detector will be an important component of the ALICE experiment, being a totally Indian contribution to ALICE.     

Simulations of the PHOS detector in the ALICE experiment at CERN

In 2005 the ALICE experiment will start at the Large Hadron Collider at CERN. It will investigate hot and dense strongly interacting matter formed in heavy ion collisions. The photon spectrometer of the ALICE detector will be designed to identify direct photons. To optimize the detector, simulations will be carried out.     

Investigation of the ALICE muon forward spectrometer performances for upsilon measurement

ALICE (A Large Ion Collider Experiment) is the LHC detector dedicated to the study of nucleus–nucleus collisions, in which the formation of the quark–gluon plasma (QGP) is expected. Heavy quarkonia, especially the Upsilon states, are relevant for studying the QGP since they provide an essential probe of the earliest and hottest stages of heavy ion collisions. They will be measured via their dimuon decay channel in ALICE in the muon spectrometer. The muon spectrometer performance has been studied in simulations, the results will be presented with emphasis on the trigger efficiency and rate in Pb–Pb collisions. The expected yields of Upsilon states will be extracted from a simulation based on a global fit of the dimuon mass spectra for different collision centralities.     

Construction and testing of the ALICE TRD chambers at LHE,JINR

The current status of construction and testing of Transition Radiation Detectors (TRD) for ALICE at LHE, JINR, is presented. The main purpose of this detector is electron identification at intensive pion background. The whole ALICE TRD system is comprised of 540 wire chambers of total sensitive area ∼750 m². Each chamber consists of drift and amplifying gaps and a radiator. One hundred such TRD chambers will be constructed at LHE, JINR. The text was submitted by the authors in English.     

Flow with photon multiplicity detector: Past and future

Measurements of azimuthal distribution of inclusive photons using the fine granularity pre-shower photon multiplicity detector (PMD) at CERN SPS are used to obtain anisotropy in the azimuthal distributions. These results are used to estimate the anisotropy in the neutral pion distributions. The results are compared with results of charged particle data, both for first order and second order anisotropy. Assuming the same anisotropy for charged and neutral pions, the anisotropy in photons is estimated and compared with the measured anisotropy. The effect of neutral pion decay on the correlation between the first order and the second order event plane is also discussed. Data from PMD can also be used to estimate the reaction plane for studying any anisotropy in particle emission characteristics in the ALICE experiment at the large hadron collider (LHC). In particular, we show that using the event plane from the PMD, it will be possible to measure the anisotropy inJ/Ψ absorption (if any) in the ALICE experiment.     

ALICE perspectives for the study of charm and beauty energy loss at the LHC

At LHC energy, heavy quarks will be abundantly produced and the design of the ALICE detector will allow us to study their production using several channels. The expected heavy-quark in-medium energy loss in nucleus-nucleus collisions at the LHC is calculated within a model, that is compared to the available heavy-quark quenching measurements at RHIC. The nuclear modification factors and heavy-to-light ratios of charm and beauty mesons are considered. The capability of the ALICE experiment for addressing this phenomenology is discussed. PACS 25.75.-q; 14.65.Dw; 13.25.Ft     

ALICE FIT Data Processing and Performance during LHC Run 3

Physics of Atomic Nuclei - During the upcoming Run 3 and Run 4 at the LHC the upgraded ALICE (A Large Ion Collider Experiment) will operate at a significantly higher luminosity and will collect two...     

在大型强子对撞机上探索物质本源的大型重离子实验

欧洲核子研究中心的大型重离子实验探测器(ALICE),利用2008年开始运行的大型强子对撞机(LHC),将核物质加热到太阳中心温度的几十万倍,研究在高温高密的极端环境下生成的新物质形态（夸克胶子等离子体或夸克物质）的性质.这样的实验有可能从本源上探索:强作用力如何支配物质结构？夸克作为强作用力的基本量子,如何禁闭于质子和中子内部？夸克作为物质的基本组成单元,质量从何而来？文章介绍了在大型强子对撞机上探索物质本源的大型重离子实验,内容包括：强作用力与夸克模型、渐进自c由与夸克禁闭、重离子碰撞与夸克物质、LHC上的ALICE实验、连通夸克和宇宙.     

Event-by-event fluctuation studies in the ALICE experiment

Event-by-event (E-by-E) fluctuations are considered to be one of the possible indications that a phase transition from ordinary hadronic matter to a plasma of quarks and gluons has occurred, as it is expected to happen in ultra-relativistic heavy-ion collisions. In this article, the results of a study concerning the observability of E-by-E fluctuations for the ALICE experiment at the LHC collider at CERN is presented. In particular, an estimate of the E-by-E statistical sensitivity in the measurement of the inverse slope parameter from the transverse momentum spectra of hadrons and of their particle ratios is discussed. The analysis relies on the excellent performance of ALICE in terms of particle identification.     

Space charge limited avalanche growth in multigap resistive plate chambers

The European Physical Journal C - The ALICE TOF array will be built using the Multigap Resistive Plate Chamber(MRPC) configured as a double stack. Each stack contains 5 gas gaps with width of...     

Adaption of a diffractometer for time‐resolved X‐ray resonant magnetic scattering

A new set‐up is presented to measure element‐selective magnetization dynamics using the ALICE chamber [Grabis et al. (2003), Rev. Sci. Instrum. 74 , 4048–4051] at the BESSY II synchrotron at the Helmholtz‐Zentrum Berlin. A magnetic‐field pulse serves as excitation, and the magnetization precession is probed by element‐selective X‐ray resonant magnetic scattering. With the use of single‐bunch‐generated X‐rays a temporal resolution well below 100 ps is reached. The ALICE diffractometer environment enables investigations of thin films, described here, multilayers and laterally structured samples in reflection or diffuse scattering geometry. The combination of the time‐resolved set‐up with a cryostat in the ALICE chamber will allow temperature‐dependent studies of precessional magnetization dynamics and of damping constants to be conducted over a large temperature range and for a large variety of systems in reflection geometry.