Femtoscopy with identified hadrons in pp, pPb, and peripheral PbPb collisions in CMS

Short range correlations of identified charged hadrons in pp (sqrt(s) = 0.9, 2.76, and 7 TeV), pPb (sqrt(sNN) = 5.02 TeV), and peripheral PbPb collisions (sqrt(sNN) = 2.76 TeV) are studied with the CMS detector at the LHC. Charged pions, kaons, and protons at low pT and in laboratory pseudorapidity |eta| < 1 are identified via their energy loss in the silicon tracker. The two-particle correlation functions show effects of quantum statistics, Coulomb interaction, and also indicate the role of multi-body resonance decays and mini-jets. The characteristics of the one-, two-, and three-dimensional correlation functions are studied as a function of pair momentum and the charged-particle multiplicity of the event. The extracted radii are in the range 1-5 fm, reaching highest values for very high multiplicity pPb, also for similar multiplicity PbPb collisions, and decrease with increasing kT. The dependence of radii on multiplicity and kT largely factorizes and appears to be insensitive to the type of the colliding system and center-of-mass energy.Comment: 12 pages, 8 figures. Proceedings of the WPCF 2014 workshop, Gy\"ongy\"os, Hungar

Combination of analysis techniques for efficient track reconstruction in high multiplicity events

A novel combination of established data analysis techniques for reconstructing all charged-particle tracks in high energy collisions is proposed. It uses all information available in a collision event while keeping competing choices open as long as possible. Suitable track candidates are selected by transforming measured hits to a binned, three- or four-dimensional, track parameter space. It is accomplished by the use of templates taking advantage of the translational and rotational symmetries of the detectors. Track candidates and their corresponding hits, the nodes, form a usually highly connected network, a bipartite graph, where we allow for multiple hit to track assignments, edges. The graph is cut into very many minigraphs by removing a few of its vulnerable components, edged and nodes. Finally the hits are distributed among the track candidates by exploring a deterministic decision tree. A depth-limited search is performed maximising the number of hits on tracks, and minimising the sum of track-fit $\chi^2$. Simplified models of LHC silicon trackers, as well as the relevant physics processes, are employed to study the performance (efficiency, purity, timing) of the proposed method in the case of single or many simultaneous proton-proton collisions (high pileup), and for single heavy-ion collisions at the highest available energies.Comment: 11 pages, 12 figures, submitted to EPJ

Soft probes of high density QCD physics with CMS

The CMS heavy-ion program will probe QCD matter under extreme conditions. Its capabilities for the study of global observables and soft probes are described.Comment: 6 pages, 10 figures. Presented at the International Conference on Strangeness in Quark Matter 2007, Levoca, Slovakia, 28 June 200

Low pT Hadronic Physics with CMS

The pixel detector of CMS can be used to reconstruct very low pT charged particles down to about 0.1 GeV/c. This can be achieved with high efficiency, good resolution and a negligible fake rate for elementary collisions. In the case of central PbPb collisions the fake rate can be kept low for pT > 0.4 GeV/c. In addition, the detector can be employed for identification of neutral hadrons (V0s) and converted photons.Comment: 6 pages. Presented at the Poster Session of Quark Matter 2006 Conference, Shanghai, 14-20 November 2006. Submitted to IJMP

Első mérések a CMS detektorral = First measurements with the CMS detector

A CMS kísérlet keretében részt vettem az első 0,9 és 2.36 TeV tömegközépponti energiájú proton-proton ütközések kiértékelésében és a publikáció megírásában. Meghatároztam a keletkező töltött hadronok pszeudo-rapiditás és transzverz impulzus eloszlását, amely egy egyszerű fizikai modellel leírható. A kapott eredmények 0,9 TeV-en összhangban vannak korábbi mérésekkel és megerősítik, hogy a proton-antiproton és a proton-proton ütközésekben közel azonos mennyiségű hadron keletkezik. A 2,36-TeV-en kapott hadronsűrűség a modellek által jósoltnál meredekebb energiafüggésre utal. A LHC késői indulása folytán új adatkiértékelési módszerekkel is foglalkoztam: javított kölcsönhatási pont keresés ütközőnyalábos detektorokra, szilícium alapú detektor beütéseinek javított kiértékelése, töltött részecskék fajlagos energiaveszteség-becslésének javítása, kis impulzusú töltött részecskék azonosítása a track-illesztés chi^2 értékével. | In the CMS collaboration I took part in the analysis and publication of the first proton-proton collision data at 0.9 and 2.36 center-of-mass energies. I have determined the pseudo-rapidity and transverse momentum distribution of created charged hadrons. The latter is well described by a simple physical model. The obtained results confirm that proton-antiproton and proton-proton collisions produce nearly equal amount of hadrons. The measured particle density at 2.36 TeV points to a steeper-than-predicted increase with energy. Due to the late start of the LHC I had the possibility to work on new data analysis methods, such as: improved vertex finding for collider detectors; improved estimation of cluster properties for silicon detectors; optimized estimation of energy loss for charged particles; identification of low momentum charged particles with track fit chi^2

Another approach to track reconstruction: cluster analysis

A novel combination of data analysis techniques is proposed for the reconstruction of all tracks of primary charged particles, as well as of daughters of displaced vertices (decays, photon conversions, nuclear interactions), created in high energy collisions. Instead of performing a classical trajectory building or an image transformation, an efficient use of both local and global information is undertaken while keeping competing choices open. The measured hits of adjacent tracking layers are clustered first with the help of a mutual nearest neighbor search in the angular distance. The resulted chains of connected hits are used as initial clusters and as input for cluster analysis algorithms, such as the robust $k$-medians clustering. This latter proceeds by alternating between the hit-to-track assignment and the track-fit update steps, until convergence. The calculation of the hit-to-track distance and that of the track-fit $\chi^2$ is performed through the global covariance of the measured hits. The clustering is complemented with elements from a more sophisticated Metropolis-Hastings MCMC algorithm, with the possibility of adding new track hypotheses or removing unnecessary ones. Simplified but realistic models of today's silicon trackers, including the relevant physics processes, are employed to test and study the performance (efficiency, purity) of the proposed method as a function of the particle multiplicity in the collision event.Comment: Proceedings of "Connecting the Dots and Workshop on Intelligent Trackers (CTD/WIT 2019)"; 7 pages, 6 figure

Improved primary vertex finding for collider detectors

Primary vertex finding for collider experiments is studied. The efficiency and precision of finding interaction vertices can be improved by advanced clustering and classification methods, such as agglomerative clustering with fast pairwise nearest neighbor search, followed by Gaussian mixture model or k-means clustering.Comment: 12 pages, 10 figures, submitted to Nucl. Instrum. Meth.

Mid-rapidity π±\pi^\pm, K±K^\pm, and pˉ\bar{p} spectra and particle ratios from STAR

Results are presented on $\pi^\pm$, $K^\pm$, and $\bar{p}$ transverse mass spectra and particle multiplicity ratios at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$=130 and 200 GeV and in p+p collisions at $\sqrt{s}$=200 GeV. Comparisons are made to results from lower energies. The bulk properties of the collision inferred from these results are discussed.Comment: 4 pages, 3 figures, Talk presented at Quark Matter 2002, Nantes, France, July 200

Optimized differential energy loss estimation for tracker detectors

The estimation of differential energy loss for charged particles in tracker detectors is studied. The robust truncated mean method can be generalized to the linear combination of the energy deposit measurements. The optimized weights in case of arithmetic and geometric means are obtained using a detailed simulation. The results show better particle separation power for both semiconductor and gaseous detectors.Comment: 16 pages, 8 figures, submitted to Nucl. Istrum. Meth.

Hadronfizika a CMS detektorral = Hadronic physics at the CMS experiment

A CERN CMS kísérletében kifejlesztettük a töltött részecskék nyomkövetésének kis tévesztésű, nagyon kis impulzus esetén is jó hatásfokú módszerét. A szilíciumdetektorokban leadott energia, valamint a bomlási topológia figyelembe vételével kidolgoztuk a töltött és semleges részecskék azonosításának technikáját. Megmutattuk, hogy új matematikai eszközökkel a semleges pionok spektruma az egyfoton eloszlásból visszafejthető. A fenti eszközök segítségével elkészítettük a 0.9-7-10 TeV-es proton-proton ütközésekben keletkezett hadronok számával és eloszlásával foglalkozó példa-analíziseket, melyek a 2009-es év végén a CMS kísérlet első publikációi lesznek. A Pb-Pb ütközésben keletkezett anyagon áthaladó partonok energiaveszteségének vizsgálatához kidolgoztuk a nukleáris elnyomási faktorok mérésének módszerét, nagy transzverzális impulzusokra, amely csak jet triggerek alkalmazásával érhető el. A módszerrel várhatóan többszörösére nő majd az az impulzustartomány, ahol a mérés elvégezhető. Létrehoztunk egy megbízható, szcintillátorokon alapuló triggert, amely az első nehézion mérések alapvető triggere lehet 2010-ben. | Working in the CERN CMS experiment we have developed a new method of charged particle tracking that has good efficiency even at very low momentum. With help of the measured energy deposited in the silicon detectors, as well as by using the decay topology, we have worked out a technique of particle identification of charged and neutral hadrons. We have shown that with new mathematical methods the spectrum of neutral pions can be extracted from that of the photons. The above mentioned tools enabled us to prepare and accomplish the example analyses dealing with the measurement of the number distribution and momentum spectrum of hadrons produced in proton-proton collisions at 0.9-7-10 TeV. They will be the first publications of the CMS Collaboration at the end of 2009. For the study of energy loss of partons produced in Pb-Pb collisions, we have developed a method to measure the nuclear modification factors, for high transverse momenta. It was possible with help of jet triggers which multipled the reach of the measurement. We have created a reliable, scintillator based trigger, that can be a basic trigger for the first heavy ion collisions in 2010