Production of pions, kaons and protons in pp collisions at $\sqrt{s}= 900~\mathrm{GeV}$ with ALICE at the LHC

Abstract

The production of π + , π − , K + , K − , p, and p at mid-rapidity has been measured in proton-proton collisions at √ s = 900 GeV with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta. Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon transverse momentum (p t ) spectra. Since these various particle identification tools give the best separation capabilities over different momentum ranges, the results are combined to extract spectra from p t = 100 MeV/c to 2.5 GeV/c. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and the mean p t are compared with previous measurements, and the trends as a function of collision energy are discussed.t Deceased.

Measurement of charm production at central rapidity in proton-proton collisions at $ \sqrt {s} = 7{ }TeV $

“…The procedure for track reconstruction in the central barrel detectors [15,25] starts with a first determination of the primary vertex position, performed by correlating hit pairs (tracklets) in the two layers of the Silicon Pixel Detector. The same algorithm is used to search for vertices from pile-up collisions starting from the tracklets that do not point to the first found vertex.…”

A warm and friendly memorial session for Helmut Oeschler

“…He was also one of the key contributors for topics related to particle identification using the central detectors and lead the efforts for the preparation of the publication on identified hadrons (illustrated by Fig. 4) for the very first proton-proton collisions recorded at the LHC at the center of mass energy of 0.9 TeV [7]. Among many roles he had in the collaboration, he served as chair of the ALICE Editorial Board for several years.…”

Thermalisation properties of various field theories

“…The temperature (T ) of the system is calculated by the following formula [9]: 2) where N 3 is the number of lattice sites and Π k is the Fourier-transformed momentum field. We use this formula to check whether the system reached thermal equilibrium by verifying that |Π k | 2 is independent of k (equipartition).…”

“…One may anticipate that the p t distribution of particle yields is Boltzmannian. However, it seems not to be correct in p-p collisions according to ALICE, CMS, STAR and PHENIX collaborations, respectively [2][3][4] [5]. Instead of Boltzmannian, the Tsallis-distribution is proposed.…”