498 research outputs found
Charm suppression in Pb-Pb collisions at the LHC measured using D0 K-Ï + reconstruction with the ALICE experiment
Get PDFThe thesis is focused on the measurement of the nuclear modification of charm quark production, in lead-lead collisions at the Large Hadron Collider. This observable is sensitive to the interaction of this quark with the high-density strongly interacting medium formed in ultra-relativistic heavy-ion collisions and, thus, to the properties of the state of matter. The partons traversing the medium lose energy via gluon radiation or elastic collisions with other partons already present in the medium. The charm quark allows to study the mass and colour charge dependences of the energy loss, since heavy quarks are expected to behave differently from light partons.
The measurement presented in this thesis is performed for the first time in nucleus-nucleus collisions, with the full reconstruction of D mesons via their hadronic decay. The strategy to reconstruct D0 mesons in the two-prong decay D0->K-ÃÂÃÂ+, with the ALICE experiment, will be described. Results obtained in Pb-Pb collisions at the energy of 2.76 TeV in the centre of mass of the collision for nucleons pair will be shown. In particular, the selection cut optimization was studied to compute the raw signal of D mesons with an invariant mass analysis. Selection and reconstruction efficiencies were considered with the detector acceptance, to correct for experimental effects. The corresponding data systematic uncertainties were evaluated in detail.
The comparison with the production cross section obtained in proton-proton collisions at the same energy allows then to compute the nuclear modification of D0 meson, the first direct evidence of the charm quark energy loss.
The measurement was compared with other open heavy flavour results and with light-charged hadrons suppression, measured at the LHC, to test the mass and colour charge dependences of the interaction with the medium. Results have been also compared with models that compute the charm quark energy loss using different theoretical approaches.
These results were recently approved by the ALICE Collaboration and a publication has been proposed and is being review by the Collaboration.La tesi descrive la misura della modifica della produzione di quark charm, in collisioni tra ioni piombo al Large Hadron Collider. Questa misura permette di studiare l'interazione del quark charm con il mezzo ad alta densitÃÂàe fortemente interagente, formato in collisioni di ioni pesanti ad energie ultra-relativistiche e le proprietÃÂàdi questo stato della materia. I partoni che attraversano il mezzo perdono energia per emissione di gluoni (gluonnstrahlung) e collisioni elastiche con gli altri partoni del mezzo. Il quark charm permette di studiare come variano le proprietÃÂàdell'interazione in funzione della massa e della carica di colore del quark, poichÃÂé i modelli teorici prevedono un comportamento diverso dei quark pesanti nel mezzo, rispetto a quelli leggeri.
La misura presentata in questa tesi ÃÂÃÂ ̈ la prima fatta in collisioni tra nuclei pesanti, attraverso la ricostruzione esclusiva dei mesoni D nel loro decadimento adronico. In particolare, verrÃÂÃÂ presentata la strategia di ricostruzione del mesone D0 nel suo decadimento in due corpi D0->K-ÃÂÃÂ+, fatta con l'esperimento ALICE. Verranno, quindi, illustrati i risultati ottenuti con i dati di collisioni Pb-Pb ad un energia nel centro di massa per coppia di nucleoni di 2.76 TeV. In particolare, ÃÂÃÂ ̈ stata studiata l'ottimizzazione dei tagli di selezione per misurare il segnale, estratto con un'analisi di massa invariante. Le efficienze di selezione e ricostruzione delle particelle e gli effetti di accettanza del rivelatore, sono stati considerati con uno studio Monte Carlo, per considerare gli effetti sperimentali. Nella tesi viene anche descritto in dettaglio lo studio sulle incertezze sistematiche.
Il confronto delle sezioni d'urto di produzione ottenute in collisioni Pb-Pb e protone-protone, alla stessa energia, permette di misurare il fattore di modifica nucleare del mesone D0, prima evidenza diretta di perdita energia del quark charm nel mezzo.
La misura ÃÂÃÂ ̈ stata confrontata con altri risultati ottenuti nel settore dei quark pesanti alla stessa energia, e con la soppressione degli adroni carichi, per valutare le dipendenze dalla massa e dalla carica di colore del quark, nella sua interazione con il mezzo. I risultati sono stati confrontati con modelli teorici che descrivono la perdita di energia del quark charm, utilizzando diversi metodi di calcolo.
I risultati sono stati recentemente approvati dalla collaborazione ALICE, una pubblicazione ÃÂÃÂ ̈ stata proposta ed ÃÂÃÂ ̈ in fase di review nella collaborazione
Measurement of heavy-favour production in pp and Pb-Pb collisions at the LHC with ALICE
No full textLatest results on open heavy favour measurements in pp collisions at 7 TeV and Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV with the ALICE experiment are presented. The results of the single lepton analyses (electrons at central rapidity, muons at forward rapidity) and D meson reconstruction will be discussed.Latest results on open heavy favour measurements in pp collisions at 7 TeV and Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV with the ALICE experiment are presented. The results of the single lepton analyses (electrons at central rapidity, muons at forward rapidity) and D meson reconstruction will be discussed
Open heavy-flavour and quarkonium production in Pb-Pb and p-Pb collisions measured by the ALICE detector at the LHC
No full textOpen heavy-flavour and quarkonia measurements are important tools to study the hot and dense partonic medium formed in ultra-relativistic heavy-ion collisions. The modification of their production in those collisions, with respect to the pp and p-Pb ones, can help in the characterization of this medium. Quarkonia and open heavy-flavour production is measured in ALICE in the three different collision systems, at mid- and forward rapidity. A selection of those results recently obtained in Pb-Pb and p-Pb collisions by the ALICE Collaboration is presented
Measurement of the D meson elliptic flow in Pb-Pb collisions at sqrt(s_{NN}) = 2.76 TeV with ALICE
No full textWe present the measurements of D0, D+, D*+ meson v_2 as well as D0 R_{AA} in different directions with respect to the estimated reaction plane in Pb-Pb collisions at \sqrt{(s_{NN))}= 2.76 TeV with the ALICE detector at the LHC.We present the measurements of D^0, D^+, D^@?^+ meson v_2 as well as D^0R_A_A in different directions with respect to the estimated reaction plane in Pb-Pb collisions at =2.76TeV with the ALICE detector at the LHC.We present the measurements of D0 , D+ , D⁎+ meson v2 as well as D0 RAA in different directions with respect to the estimated reaction plane in Pb–Pb collisions at sNN=2.76TeV with the ALICE detector at the LHC.We present the measurements of D0, D+, D*+ meson v_2 as well as D0 R_{AA} in different directions with respect to the estimated reaction plane in Pb-Pb collisions at sqrt(s_{NN)) = 2.76 TeV with the ALICE detector at the LHC
D-meson reconstruction via cascade decays with the ALICE experiment
No full textDuring this internship, two D-meson decay channels involving were studied: and . In this report, the implementation of both cascade decay reconstructions in the ALICE analysis framework of the Charm-to-Hadron (D2H) group is presented. The performances in terms of memory consumption, running time and output size were evaluated on p-Pb data. Finally, cascade reconstructions were tested in pp Monte Carlo simulations
Functional characterization of various algal carotenoid ketolases reveals that ketolating zeaxanthin efficiently is essential for high production of astaxanthin in transgenic Arabidopsis
No full textExtending the carotenoid pathway to astaxanthin in plants is of scientific and industrial interest. However, expression of a microbial beta-carotene ketolase (BKT) that catalyses the formation of ketocarotenoids in transgenic plants typically results in low levels of astaxanthin. The low efficiency of BKTs in ketolating zeaxanthin to astaxanthin is proposed to be the major limitation for astaxanthin accumulation in engineered plants. To verify this hypothesis, several algal BKTs were functionally characterized using an Escherichia coli system and three BKTs were identified, with high (up to 85%), moderate (~38%), and low (~1%) conversion rate from zeaxanthin to astaxanthin from Chlamydomonas reinhardtii (CrBKT), Chlorella zofingiensis (CzBKT), and Haematococcus pluvialis (HpBKT3), respectively. Transgenic Arabidopsis thaliana expressing the CrBKT developed orange leaves which accumulated astaxanthin up to 2 mg g -1 dry weight with a 1.8-fold increase in total carotenoids. In contrast, the expression of CzBKT resulted in much lower astaxanthin content (0.24 mg g -1 dry weight), whereas HpBKT3 was unable to mediate synthesis of astaxanthin in A. thaliana. The none-native astaxanthin was found mostly in a free form integrated into the light-harvesting complexes of photosystem II in young leaves but in esterified forms in senescent leaves. The alteration of carotenoids did not affect chlorophyll content, plant growth, or development significantly. The astaxanthin-producing plants were more tolerant to high light as shown by reduced lipid peroxidation. This study advances a decisive step towards the utilization of plants for the production of high-value astaxanthin. Keywords: Arabidopsis thaliana, astaxanthin, beta-carotene ketolase, carotenoid, Haematococcus pluviali
Dynamics of photosynthetic complexes in the thylakoid membranes from higher plants
No full textPhDPhotosynthetic machinery in higher plants is localised in the thylakoids enclosed in
a chloroplast. To optimise and regulate the photosynthetic efficiency under different,
rapidly changeable environmental conditions the dynamics of the thylakoid
membrane components is required. It has been invoked in several contexts, for
example during assembly and turnover of the photosynthetic apparatus, regulation of
light-harvesting and photosynthetic electron transport. In this study, by employing
a confocal FRAP technique combined with freeze-fracture electron microscopy,
I addressed a fundamental problem of visualising the mobility and distribution of
photosynthetic complexes in a direct way close to the situation in vivo - the
thylakoids of intact chloroplasts isolated from green plants. Firstly, I provided direct
evidence that the dynamic changes in the distribution of photosynthetic complexes
are involved in two high-light related physiological phenomena, namely
photoinhibition and non-photochemical quenching. My study indicates that the
photoinhibited membranes exhibit an elevated level of protein mobility accompanied
by a decreased spacing between the complexes with the opposite effect observed in
the photoprotective state. Secondly, my work allowed the identification of some key
elements that are responsible for controlling the mobility under different
physiological conditions such as: (1) phosphorylation of PSII core complexes after
photoinhibition, (2) PsbS protein enhancing the membrane fluidity in a dark-adapted
state and decreasing it after light treatment, (3) different xanthophyll composition of
light-harvesting antenna with particular attention being paid to zeaxanthin which
decreases the size of mobile fraction, (4) the degree of macromolecular crowding and
the organisation of PSII-LHCII supercomplexes in the grana membranes which is
dependent strongly on individual light-harvesting proteins, the minor antenna
4
complexes in particular. Lastly, a completely new approach of visualising the
mobility of photosynthetic machinery in intact leaves has been introduced as a useful
tool to study different aspects of plant acclimation and physiology under natural
conditions.Biotechnology and Biological Science Research Council.
University of London Central Research fun
Publisher Correction: Unveiling the strong interaction among hadrons at the LHC (Nature, (2020), 588, 7837, (232-238), 10.1038/s41586-020-3001-6)
No full textIn Fig. 1c of this Article, owing to an error during the production process, the equation incorrectly began ‘C(k*, r*) = …’ instead of ‘C(k*) = …’. In addition, in affiliation 71 ‘Dipartimento di Fisica dell’Università degli studi di Bari Aldo Moro’ has been corrected to read ‘Dipartimento di Fisica dell’Università degli studi di Cagliari’. The original Article has been corrected online. *A list of authors and their affiliations appears online. © 2021, The Author(s), under exclusive licence to Springer Nature Limited
Publisher Correction: Direct observation of the dead-cone effect in quantum chromodynamics (Nature, (2022), 605, 7910, (440-446), 10.1038/s41586-022-04572-w)
No full textIn the version of this article initially published, there was a typographical error in the first sentence following the “Exposing the dead cone” heading, now reading, “The measurements of R(θ), in the three radiator (charmquark) energy intervals 5 < ERadiator < 10 GeV, 10 < ERadiator < 20 GeV and 20 < ERadiator < 35 GeV…,” where “35 GeV” initially appeared as “3 GeV.” The error has been corrected in the HTML and PDF versions of the article. *A list of authors and their affiliations appears online. © The Author(s) 2022
Neutral pion production at midrapidity in pp and Pb–Pb collisions at √ sNN TeV
No full textInvariant yields of neutral pions at midrapidity in the transverse momentum range (Formula presented.)c measured in Pb–Pb collisions at (Formula presented.) TeV are presented for six centrality classes. The pp reference spectrum was measured in the range (Formula presented.)c at the same center-of-mass energy. The nuclear modification factor, (Formula presented.), shows a suppression of neutral pions in central Pb–Pb collisions by a factor of up to about (Formula presented.) for (Formula presented.) ≲(Formula presented.)c. The presented measurements are compared with results at lower center-of-mass energies and with theoretical calculations. © 2014, The Author(s)
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