594 research outputs found
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 . 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
Első mérések a CMS detektorral = First measurements with the CMS detector
A CMS kĂsĂ©rlet keretĂ©ben rĂ©szt vettem az elsĹ‘ 0,9 Ă©s 2.36 TeV tömegközĂ©pponti energiájĂş proton-proton ĂĽtközĂ©sek kiĂ©rtĂ©kelĂ©sĂ©ben Ă©s a publikáciĂł megĂrásában. Meghatároztam a keletkezĹ‘ töltött hadronok pszeudo-rapiditás Ă©s transzverz impulzus eloszlását, amely egy egyszerű fizikai modellel leĂrhatĂł. A kapott eredmĂ©nyek 0,9 TeV-en összhangban vannak korábbi mĂ©rĂ©sekkel Ă©s megerĹ‘sĂtik, hogy a proton-antiproton Ă©s a proton-proton ĂĽtközĂ©sekben közel azonos mennyisĂ©gű hadron keletkezik. A 2,36-TeV-en kapott hadronsűrűsĂ©g a modellek által jĂłsoltnál meredekebb energiafĂĽggĂ©sre utal. A LHC kĂ©sĹ‘i indulása folytán Ăşj adatkiĂ©rtĂ©kelĂ©si mĂłdszerekkel is foglalkoztam: javĂtott kölcsönhatási pont keresĂ©s ĂĽtközĹ‘nyalábos detektorokra, szilĂcium alapĂş detektor beĂĽtĂ©seinek javĂtott kiĂ©rtĂ©kelĂ©se, töltött rĂ©szecskĂ©k fajlagos energiavesztesĂ©g-becslĂ©sĂ©nek javĂtása, kis impulzusĂş töltött rĂ©szecskĂ©k azonosĂtása a track-illesztĂ©s chi^2 Ă©rtĂ©kĂ©vel. | 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
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
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 -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 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.
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 kĂsĂ©rletĂ©ben kifejlesztettĂĽk a töltött rĂ©szecskĂ©k nyomkövetĂ©sĂ©nek kis tĂ©vesztĂ©sű, nagyon kis impulzus esetĂ©n is jĂł hatásfokĂş mĂłdszerĂ©t. A szilĂciumdetektorokban leadott energia, valamint a bomlási topolĂłgia figyelembe vĂ©telĂ©vel kidolgoztuk a töltött Ă©s semleges rĂ©szecskĂ©k azonosĂtásának technikáját. Megmutattuk, hogy Ăşj matematikai eszközökkel a semleges pionok spektruma az egyfoton eloszlásbĂłl visszafejthetĹ‘. A fenti eszközök segĂtsĂ©gĂ©vel elkĂ©szĂtettĂĽk a 0.9-7-10 TeV-es proton-proton ĂĽtközĂ©sekben keletkezett hadronok számával Ă©s eloszlásával foglalkozĂł pĂ©lda-analĂziseket, melyek a 2009-es Ă©v vĂ©gĂ©n a CMS kĂsĂ©rlet elsĹ‘ publikáciĂłi lesznek. A Pb-Pb ĂĽtközĂ©sben keletkezett anyagon áthaladĂł partonok energiavesztesĂ©gĂ©nek vizsgálatához kidolgoztuk a nukleáris elnyomási faktorok mĂ©rĂ©sĂ©nek mĂłdszerĂ©t, nagy transzverzális impulzusokra, amely csak jet triggerek alkalmazásával Ă©rhetĹ‘ el. A mĂłdszerrel várhatĂłan többszörösĂ©re nĹ‘ majd az az impulzustartomány, ahol a mĂ©rĂ©s elvĂ©gezhetĹ‘. LĂ©trehoztunk egy megbĂzhatĂł, szcintillátorokon alapulĂł triggert, amely az elsĹ‘ nehĂ©zion mĂ©rĂ©sek alapvetĹ‘ 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
Large High-precision X-Ray Timing of Three Millisecond Pulsars with NICER: Stability Estimates and Comparison with Radio
The Neutron Star Interior Composition Explorer (NICER) is an X-ray astrophysics payload on the International Space Station. It enables unprecedented high-precision timing of millisecond pulsars (MSPs) without the pulse broadening and delays due to dispersion and scattering within the interstellar medium that plague radio timing. We present initial timing results from a year of data on the MSPs PSR B1937+21 and PSR J0218+4232, and nine months of data on PSR B1821-24. NICER time-of-arrival uncertainties for the three pulsars are consistent with theoretical lower bounds and simulations based on their pulse shape templates and average source and background photon count rates. To estimate timing stability, we use the sigma(z) measure, which is based on the average of the cubic coefficients of polynomial fits to subsets of timing residuals. So far we are achieving timing stabilities sigma(z) approximate to 3 x 10(-14) for PSR B1937+21 and on the order of 10 (-12) for PSRs B1821-24 and J0218+4232. Within the span of our NICER data we do not yet see the characteristic break point in the slope of sigma(z); detection of such a break would indicate that further improvement in the cumulative root-mean-square timing residual is limited by timing noise. We see this break point in our comparison radio data sets for PSR B1821-24 and PSR B1937+21 on timescales of 2 yr
- …