Correction of the baseline fluctuations in the GEM-based ALICE TPC

The impact of the so-called common-mode effect and of the ion tail on the signal shapes in the upgraded ALICE Time Projection Chamber with gas-electron multiplier readout are investigated. These two effects lead to significant baseline fluctuations, degrading the particle identification and tracking performance, as well as to baseline bias affecting the amount of data collected. Since reconstruction and data compression are performed fully online during the Run~3 and Run~4 data-taking periods of the Large Hadron Collider, these effects must be corrected at the hardware level in the FPGA-based Common Readout Units. The characteristics of the common-mode effect and of the ion tail, as well as the algorithms developed for their online correction, are described. The common-mode dependencies are studied using machine learning techniques. Toy Monte Carlo simulations are performed to illustrate the importance of online corrections and to investigate the performance of the developed algorithms

Uncertainties of the CJK 5 Flavour LO Parton Distributions in the Real Photon

Radiatively generated, LO quark (u,d,s,c,b) and gluon densities in the real, unpolarized photon, calculated in the CJK model being an improved realization of the CJKL approach, have been recently presented. The results were obtained through a global fit to the experimental F2^gamma data. In this paper we present, obtained for the very first time in the photon case, an estimate of the uncertainties of the CJK parton distributions due to the experimental errors. The analysis is based on the Hessian method which was recently applied in the proton parton structure analysis. Sets of test parametrizations are given for the CJK model. They allow for calculation of its best fit parton distributions along with F2^gamma and for computation of uncertainties of any physical value depending on the real photon parton densities. We test the applicability of the approach by comparing uncertainties of example cross-sections calculated in the Hessian and Lagrange methods. Moreover, we present a detailed analysis of the chi^2 of the CJK fit and its relation to the data. We show that large chi^2/DOF of the fit is due to only a few of the experimental measurements. By excluding them chi^2/DOF approx 1 can be obtained.Comment: 28 pages, 8 eps figures, 2 Latex figures; FORTRAN programs available at http://www.fuw.edu.pl/~pjank/param.html; table 10, figure 10 and section 6 correcte

Heavy Flavour Production in Two-Photon Collisions

We review the production of charm and bottom quarks in two-photon collisions at e+e- colliders. The next-to-leading order QCD predictions for total cross sections and differential distributions are compared with recent experimental results.Comment: 6 pages, 2 figures. Talk given at the UK Phenomenology Workshop on Collider Physics, Durham, England, 19-24 Sep 199

Prospects for Pentaquark Searches in e+e−e^+e^- Annihilations and γγ\gamma\gamma Collisions

Recent strong experimental evidence of a narrow exotic S = +1 baryon resonance, $\Theta^+$, suggests the existence of other exotic baryons. We discuss the prospects of confirming earlier experimental evidence of $\Theta^+$ and the observation of additional hypothetical exotic baryons in $e^+e^-$ annihilations and $\gamma\gamma$ collisions at LEP and B Factories

Technical Design Report for the Upgrade of the ALICE Time Projection Chamber

An interaction rate of 50 kHz is expected for the Pb-Pb periods after the luminosity upgrade of the LHC during LS2, and the ALICE upgrade plans foresee to operate the experiment at these interaction rates. For this purpose, the MWPC-based TPC readout chambers will be replaced by Gas Electron Multipliers (GEMs), allowing a continuous readout of the TPC. The details of this upgrade are described in this Technical Design Report

Multiple Interactions and the Structure of Beam Remnants

Recent experimental data have established some of the basic features of multiple interactions in hadron-hadron collisions. The emphasis is therefore now shifting, to one of exploring more detailed aspects. Starting from a brief review of the current situation, a next-generation model is developed, wherein a detailed account is given of correlated flavour, colour, longitudinal and transverse momentum distributions, encompassing both the partons initiating perturbative interactions and the partons left in the beam remnants. Some of the main features are illustrated for the Tevatron and the LHC.Comment: 69pp, 33 figure

The Time Projection Chamber for the Alice Experiment

ICHEP08,Philadelphia,PA 29th July - 5th Aug.2008 ProceedingsThe Time Projection Chamber of the ALICE Experiment has been installed in the experimental setup in the underground area at the Large Hadron Collider at CERN in Geneva. The Alice TPC ReadOut (ALTRO) chip implements intelligent signal processing on the Front-End-Electronics. During the years of 2007 and 2008 commissioning and calibration of the TPC have been carried out with cosmic rays, radioactive Krypton isotopes and with tracks produced by a UV laser system. In addition to these in this publication we present first results on energy loss measurements and on the momentum resolution

Hadronic Cross-sections in two photon Processes at a Future Linear Collider

In this note we address the issue of measurability of the hadronic cross-sections at a future photon collider as well as for the two-photon processes at a future high energy linear $e^+e^-$ collider. We extend, to higher energy, our previous estimates of the accuracy with which the \gamgam\ cross-section needs to be measured, in order to distinguish between different theoretical models of energy dependence of the total cross-sections. We show that the necessary precision to discriminate among these models is indeed possible at future linear colliders in the Photon Collider option. Further we note that even in the $e^+e^-$ option a measurement of the hadron production cross-section via \gamgam processes, with an accuracy necessary to allow discrimination between different theoretical models, should be possible. We also comment briefly on the implications of these predictions for hadronic backgrounds at the future TeV energy $e^+e^-$ collider CLIC.Comment: 20 pages, 5 figures, LaTeX. Added an acknowledgemen

Experimental momentum spectra of identified hadrons at e+e−e^+e^- colliders compared to QCD calculations

Experimental data on the shape of hadronic momentum spectra are compared to theoretical predictions in the context of calculations in the Modified Leading Log Approximation (MLLA), under the assumption of Local Parton Hadron Duality (LPHD). Considered are experimental measurements at $e^+e^-$-colliders of $\xi_p^*$, the position of the maximum in the distribution of $\xi_p=\log(1/x_p)$, where $x_p=p/p_{beam}$. The parameter $\xi_p^*$ is determined for various hadrons at various centre of mass energies. The dependence on the hadron type poses some interesting questions about the process of hadron-formation. The dependence of $\xi^*_p$ on the centre of mass energy is seen to be described adequately by perturbation theory. A quantitative check of LPHD + MLLA is possible by extracting a value of $\alpha_s$ from an overall fit to the scaling behaviour of $\xi^*_p$.Comment: 9 pages latex, 7 eps figures and total ps fil

Hadronization in Z0 decay

The confinement transition from the quark and gluon degrees of freedom appropriate in perturbation theory to the hadrons observed by real world experiments is poorly understood. In this strongly interacting transition regime we presently rely on models, which to varying degrees reflect possible scenarios for the QCD dynamics. Because of the absence of beam and target remnants, and the clean experimental conditions and high event rates, e+e- annihilation to hadrons at the Z0 provides a unique laboratory, both experimentally and theoretically, for the study of parton hadronization. This review discusses current theoretical understanding of the hadronization of partons, with particular emphasis on models of the non-perturbative phase, as implemented in Monte Carlo simulation programs. Experimental results at LEP and SLC are summarised and considered in the light of the models. Suggestions are given for further measurements which could help to produce more progress in understanding hadronization.Comment: Topical review, to appear in J.Phys.G, 80 page