J/psi production as a function of charged particle multiplicity in pp collisions at root s=7 TeV

The ALICE Collaboration reports the measurement of the relative J/psi yield as a function of charged particle pseudorapidity density dN(ch)/d eta in pp collisions at root s = 7 TeV at the LHC. J/psi particles are detected for p(t) > 0, in the rapidity interval vertical bar y vertical bar < 0.9 via decay into e(+)e(-), and in the interval 2.5 < y < 4.0 via decay into mu(+)/mu(-) pairs. An approximately linear increase of the J/psi yields normalized to their event average (dN(J/psi)/dy)/(dN(J/psi)/dy) with (dN(ch)/c eta)/(dN(ch)/d eta) is observed in both rapidity ranges, where dN(ch)/d eta is measured within vertical bar eta vertical bar < 1 and p(t) > 0. In the highest multiplicity interval with (dN(ch)/d eta)(bin)) = 24.1, corresponding to four times the minimum bias multiplicity density, an enhancement relative to the minimum bias J/psi yield by a factor of about 5 at 2.5 < y <4 (8 at vertical bar y vertical bar < 0.9) is observed. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.

Light vector meson production in pp collisions at root s=7 TeV ALICE Collaboration

The ALICE experiment has measured low-mass dimuon production in pp collisions at root s = 7 TeV in the dimuon rapidity region 2.5 < y < 4. The observed dimuon mass spectrum is described as a superposition of resonance decays (eta, rho, omega, eta', phi) into muons and semi-leptonic decays of charmed mesons. The measured production cross sections for omega and phi are sigma(omega)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 5.28 +/- 0.54(stat) +/- 0.49(syst) mb and sigma(phi)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 0.940 +/- 0.084(stat) +/- 0.076(syst) mb. The differential cross sections d(2)sigma/dy dp(t) are extracted as a function of p(t) for omega and phi. The ratio between the rho and omega cross section is obtained. Results for the phi are compared with other measurements at the same energy and with predictions by models. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.

Entrevista al Dr. Javier Santaolalla, ingeniero de telecomunicación y fisico español, participante en las investigaciones del boson Higgs en el CERN.

Entrevista a Javier Santaolalla investigador en el experimento del CERN que describió recientemente una nueva partícula: el bosón de Higgs, que trata de explicar el origen de la masa de las partículas elementales. La existencia del bosón de Higgs y su campo asociado intentan explicar la razón de la existencia de masa en las partículas elementales. El 4 de julio de 2012, el CERN anunció la observación de una nueva partícula «consistente con el bosón de Higgs», pero se necesitaría más tiempo y datos para confirmarlo. El 14 de marzo de 2013 el CERN, con dos veces más datos de los que disponía en el anuncio del descubrimiento en julio de 2012, encontraron que la nueva partícula se ve cada vez más como el bosón de Higgs. Javier Santaolalla es ingeniero de telecomunicación por la Universidad de las Palmas de Gran Canaria y licenciado en ciencias físicas por la Universidad Complutense de Madrid. Investigador del CIEMAT (Madrid) y Dr. por esta última universidad en ciencias físicas. El Dr. Javier Santaolalla se encuentra unos días de escala en Las Palmas de Gran Canaria procedente de Brasil y con destino a Ginebra. Le agradecemos cuantas facilidades nos ha proporcionado en la realización de la presente entrevista así como sus aportaciones.

Sensitivity of the Top quark mass measurement with the CMS experiment at LHC using t-tbar multijet simulated events

This thesis comes after a strong contribution on the realization of the CMS computing system, which can be seen as a relevant part of the experiment itself. A physics analysis completes the road from Monte Carlo production and analysis tools realization to the final physics study which is the actual goal of the experiment. The topic of physics work of this thesis is the study of tt events fully hadronic decay in the CMS experiment. A multi-jet trigger has been provided to fix a reasonable starting point, reducing the multi-jet sample to the nominal trigger rate. An offline selection has been provided to reduce the S/B ratio. The b-tag is applied to provide a further S/B improvement. The selection is applied to the background sample and to the samples generated at different top quark masses. The top quark mass candidate is reconstructed for all those samples using a kinematic fitter. The resulting distributions are used to build p.d.f.’s, interpolating them with a continuous arbitrary curve. These curves are used to perform the top mass measurement through a likelihood comparison

Evaluation of a multi variated analysis for the selection of t-tbar multijet events in the current CMS implemented environment at LHC

In the present study we are using multi variate analysis techniques to discriminate signal from background in the fully hadronic decay channel of ttbar events. We give a brief introduction to the role of the Top quark in the standard model and a general description of the CMS Experiment at LHC. We have used the CMS experiment computing and software infrastructure to generate and prepare the data samples used in this analysis. We tested the performance of three different classifiers applied to our data samples and used the selection obtained with the Multi Layer Perceptron classifier to give an estimation of the statistical and systematical uncertainty on the cross section measurement.

The Time-Of-Flight detector of ALICE at LHC: construction, test and commissioning with cosmic rays

The Time-Of-Flight (TOF) detector of ALICE is designed to identify charged particles produced in Pb--Pb collisions at the LHC to address the physics of strongly-interacting matter and the Quark-Gluon Plasma (QGP). The detector is based on the Multigap Resistive Plate Chamber (MRPC) technology which guarantees the excellent performance required for a large time-of-flight array. The construction and installation of the apparatus in the experimental site have been completed and the detector is presently fully operative. All the steps which led to the construction of the TOF detector were strictly followed by a set of quality assurance procedures to enable high and uniform performance and eventually the detector has been commissioned with cosmic rays. This work aims at giving a detailed overview of the ALICE TOF detector, also focusing on the tests performed during the construction phase. The first data-taking experience and the first results obtained with cosmic rays during the commissioning phase are presented as well and allow to confirm the readiness state of the TOF detector for LHC collisions.

Hardware and software development of a multichannel readout board named CARLOSrx for the ALICE experiment

ALICE, that is an experiment held at CERN using the LHC, is specialized in analyzing lead-ion collisions. ALICE will study the properties of quarkgluon plasma, a state of matter where quarks and gluons, under conditions of very high temperatures and densities, are no longer confined inside hadrons. Such a state of matter probably existed just after the Big Bang, before particles such as protons and neutrons were formed. The SDD detector, one of the ALICE subdetectors, is part of the ITS that is composed by 6 cylindrical layers with the innermost one attached to the beam pipe. The ITS tracks and identifies particles near the interaction point, it also aligns the tracks of the articles detected by more external detectors. The two ITS middle layers contain the whole 260 SDD detectors. A multichannel readout board, called CARLOSrx, receives at the same time the data coming from 12 SDD detectors. In total there are 24 CARLOSrx boards needed to read data coming from all the SDD modules (detector plus front end electronics). CARLOSrx packs data coming from the front end electronics through optical link connections, it stores them in a large data FIFO and then it sends them to the DAQ system. Each CARLOSrx is composed by two boards. One is called CARLOSrx data, that reads data coming from the SDD detectors and configures the FEE; the other one is called CARLOSrx clock, that sends the clock signal to all the FEE. This thesis contains a description of the hardware design and firmware features of both CARLOSrx data and CARLOSrx clock boards, which deal with all the SDD readout chain. A description of the software tools necessary to test and configure the front end electronics will be presented at the end of the thesis.

Laserionisation und Laserionenquelle an ISOLDE, CERN

Es wurden im Rahmen des COMPLIS Experimentes laserspektroskopische Untersuchungen der neutronenarmen Platinisotope 178-185Pt durchgeführt. Die Kerndeformation der geraden Platinisotope baut sich ab dem Isotop 188Pt langsam auf und erreicht ein Maximum bei A=180. Danach nimmt die Deformation bis zum 178Pt wieder leicht ab. Zudem zeigen die Kernladungsradien um die Mitte der Neutronenschale bei N=104 einen inversen Gerade-Ungerade-Effekt. Die ungeraden Platinisotope werden durch eine axial-prolate Kernform, die geraden Platinisotope durch eine triaxiale Struktur beschrieben. Im zweiten Teil der Arbeit werden Messungen an der Laserionenquelle bei ISOLDE vorgestellt. Die Resonanzionisation mit abstimmbaren Lasern wird zur chemisch selektiven Ionisation in der Target-Ionenquelleneinheit eingesetzt. Die Entwicklung einer Frequenzverdreifachung für das hochrepetierende Farbstofflasersystem ermöglichte die selektive Präparation von Ionenstrahlen der Elemente Beryllium, Cadmium und Zink an ISOLDE. Dabei wurde bei Beryllium eine Ionisationseffizienz von 9% erreicht. Zum ersten Male wurden in der Laserionenquelle laserspektroskopische Untersuchungen an exotischen Isotopen mit der Messung der Isotopieverschiebung von 7-14Be durchgeführt und bei den Silberisotopen wurde eine Isomerenseparation über die Hyperfeinstruktur erziehlt. Damit ergeben sich neue Anwendungen der Laserspektroskopie und der Laserseparation.

Zeitaufgelöste Fluoreszenzmessungen zur Faltung und Pigmentbindung des Lichtsammlerproteins LHC II aus Photosystem II

Zusammenfassung Der Lichtsammlerkomplex (LHCII) aus PhotosystemII hoeherer Pflanzen kann in vitro rekonstituiert werden. Es werden drei Reaktionszeiten (<10 s; <1 min; <10 min) aufgeloest. Dabei werden bei allen Reaktionszeiten Pigmente durch das Apoprotein gebunden. Chlorophylle (Chl a und Chl b) und Xanthophylle wirken limitierend auf die Rekonstitution. Chl a beschleunigt die zweite Reaktionszeit, ein ausgeglichenes Chl a/b-Verhaeltnis verkürzt die dritte Reaktionszeit. Ein molekularer Mechanismus als Interpretation dieser Effekte wird vorgeschlagen. Native Lipide verlaengern nichtspezifisch die Rekonstitution. Abiotische Faktoren haben einen spezifischen Einfluss auf die Rekonstitution. Spezifische Einfluesse der o. a. Bedingungen auf die thermische Stabilitaet des rekonstituierten LHCII wurden bestimmt.

Design of a beam stopper for the new CERN linear accelerator Linac4

In this paper I will present the work I have completed during a five months work placement at CERN, European Organisation for Nuclear Research, from March to July 2011. This stage was done in the EN Department (ENgineering Department), STI Group (Sources, Targets and Interactions), TCD Section (Targets, Collimators and Dumps) under the supervision of Dr Cesare Maglioni. The task I was given concerned all the beam stoppers in the PS Complex, in detail: - General definition and requirements - Creation of a digital archive - Verification of the stoppers of the PS Complex - Design of the L4T.STP.1

Identified primary hadron spectra with the TOF detector of the ALICE experiment at LHC

In this thesis the analysis to reconstruct the transverse momentum p_{t} spectra for pions, kaons and protons identified with the TOF detector of the ALICE experiment in pp Minimum Bias collisions at $\sqrt{s}=7$ TeV was reported. After a detailed description of all the parameters which influence the TOF PID performance (time resolution, calibration, alignment, matching efficiency, time-zero of the event) the method used to identify the particles, the unfolding procedure, was discussed. With this method, thanks also to the excellent TOF performance, the pion and kaon spectra can be reconstructed in the 0.5

Study of the forward photons productions in pp collisions at sqrt{s} = 7 TeV with the ZDC detector of the ATLAS experiment

The Zero Degree Calorimeter (ZDC) of the ATLAS experiment at CERN is placed in the TAN of the LHC collider, covering the pseudorapidity region higher than 8.3. It is composed by 2 calorimeters, each one longitudinally segmented in 4 modules, located at 140 m from the IP exactly on the beam axis. The ZDC can detect neutral particles during pp collisions and it is a tool for diffractive physics. Here we present results on the forward photon energy distribution obtained using p-p collision data at sqrt{s} = 7 TeV. First the pi0 reconstruction will be used for the detector calibration with photons, then we will show results on the forward photon energy distribution in p-p collisions and the same distribution, but obtained using MC generators. Finally a comparison between data and MC will be shown.

Measurement of the differential cross section of tt pairs in pp collision at sqrt(s) = 7TeV with the ATLAS detector at the LHC

In this thesis three measurements of top-antitop differential cross section at an energy in the center of mass of 7 TeV will be shown, as a function of the transverse momentum, the mass and the rapidity of the top-antitop system. The analysis has been carried over a data sample of about 5/fb recorded with the ATLAS detector. The events have been selected with a cut based approach in the "one lepton plus jets" channel, where the lepton can be either an electron or a muon. The most relevant backgrounds (multi-jet QCD and W+jets) have been extracted using data driven methods; the others (Z+ jets, diboson and single top) have been simulated with Monte Carlo techniques. The final, background-subtracted, distributions have been corrected, using unfolding methods, for the detector and selection effects. At the end, the results have been compared with the theoretical predictions. The measurements are dominated by the systematic uncertainties and show no relevant deviation from the Standard Model predictions.

Measurement of K(892)*0 resonance production in Pb-Pb collisions with the ALICE experiment at the LHC

The analysis of the K(892)*0 resonance production in Pb–Pb collisions at √sNN = 2.76 TeV with the ALICE detector at the LHC is presented. The analysis is motivated by the interest in the measurement of short-lived resonances production that can provide insights on the properties of the medium produced in heavy-ion collisions both during its partonic (Quark-Gluon Plasma) and hadronic phase. This particular analysis exploits particle identification of the ALICE Time-Of-Flight detector. The ALICE experiment is presented, with focus on the performance of the Time-Of-Flight system. The aspects of calibration and data quality controls are discussed in detail, while illustrating the excellent and very stable performance of the system in different collision environments at the LHC. A full analysis of the K*0 resonance production is presented: from the resonance reconstruction to the determination of the efficiency and the systematic uncertainty. The results show that the analysis strategy discussed is a valid tool to measure the K∗0 up to intermediate momenta. Preliminary results on K*0 resonance production at the LHC are presented and confirmed to be a powerful tool to study the physics of ultra-relativistic heavy-ion collisions.