Strangeness enhancement at mid-rapidity in Pb-Pb collisions at 158 GeV/c

$K^{0}_{s}$, $\Lambda$, $\Xi$, $\Omega$ and negative particle yields and transverse mass spectra have been measured at central rapidity in Pb-Pb and p-Pb collisions at 158 $A$ GeV/$c$. The yields in Pb-Pb interactions % are presented as a function of the collision centrality and compared with those obtained from p-Pb collisions. Strangeness enhancement in Pb-Pb relative to p-Pb collisions increases with the strangeness content of the particle. Going from p-Pb to Pb-Pb, the strange particle yields increase faster than linearly with the number of participants $N_{part}$ up to $N_{part} \approx 100$, thereafter the increase becomes %linear with $N_{part}$. Yields are studied as a function of the number of nucleons participating in the collision $N_{part}$, which is estimated with the Glauber model. From p-Pb to Pb-Pb collisions the particle yields per participant increase substantially. The enhancement is more pronounced for multistrange particles, and exceeds an order of magnitude for the $\Omega$. For a number of participants, $N_{part}$, greater than $100$, however, all yields per participant appear to be constant

男子技巧“双重倒立坠落成颈上倒立”高难创新动作的可行性分析

将现役世界冠军作为研究对象,采用文献资料法和专家访问法,对此动作的创新性和动作性质进行了较为深入的研究和探讨,得出的结论为:一方面,此动作不仅完全具备作为难度储备动作的条件,即超前性和创新性,而且还为继续开发此类新的超高难创新系列动作奠定基础;另一方面,此动作性质的“特殊性”为拓宽技巧领域的动作范围和丰富动作形式创造了先决条件,在世界大赛中运用具有一定的可行性

A fast RICH detector for particle identification in ALICE at LHC

The ALICE collaboration proposes to investigate central ion-ion collisions (Pb-Pb) at the Large Hadron Collider operated in the ion mode. The core of the detector covers 1.8 units of rapidity centred at midrapidity. The maximum expected rapidity density is 8000 charged particles. The proposed detector is planned to measure the momentum, charge and mass of the majority of the particles in the range of transverse momentum of 0.05-2.0 GeV / c for pions and kaons, the ALICE detector envisages two alternatives currently actively investigated - a time of flight wall or a RICH detector. The RICH detector under study is of the proximity focusing type with a liquid C6F14 radiator, using a MWPC with pad readout equipped with a solid photocathode for UV light detection

Fast RICH detector with a caesium iodide photocathode at atmospheric pressure

CsI photocathodes of 30 30 cm2 size have been operated in a fast RICH detector composed of a NaF radiator and a multiwire proportional chamber with a cathode-pad readout. Results are presented from tests with a 3 GeV / c proton beam. A Cherenkov angular resolution of 8 mrad is obtained by detecting a mean of 8 photoelectrons per ring. Methods are described for counting the Cherenkov photon and evaluating the differential quantum efficiency of the CsI photocathode. The results obtained with photons impinging at a large angle on the CsI layer are presented and discussed in comparison with higher quantum efficiencies observed under different experimental conditions

Electronic detection of focused Cherenkov rings from aerogel

The recent development of highly transparent aerogel has permitted its use as a Cherenkov radiator in a focused (non-Rayleigh-scattered) mode. We report on the optical properties of this aerogel obtained by observation of Cherenkov rings with single-electron-sensitive phototubes. The dependence on aerogel radiator thickness of the number of Cherenkov ring hit points and background is shown and compared to expectations. A 5 cm thick radiator of this aerogel will permit pi/K identification up to 20 GeV/c