Measurement of the D0 Meson Production in Pb–Pb and p–Pb Collisions: A Study Performed with the ALICE Experiment at the LHC PDF
Preview Measurement of the D0 Meson Production in Pb–Pb and p–Pb Collisions: A Study Performed with the ALICE Experiment at the LHC
Springer Theses Recognizing Outstanding Ph.D. Research Andrea Festanti Measurement of the D0 Meson Production in Pb–Pb and p–Pb Collisions A Study Performed with the ALICE Experiment at the LHC Springer Theses Recognizing Outstanding Ph.D. Research Aims and Scope The series “Springer Theses” brings together a selection of the very best Ph.D. theses from around the world and across the physical sciences. Nominated and endorsed by two recognized specialists, each published volume has been selected foritsscientificexcellenceandthehighimpactofitscontentsforthepertinentfield of research. For greater accessibility to non-specialists, the published versions includeanextendedintroduction,aswellasaforewordbythestudent’ssupervisor explainingthespecialrelevanceoftheworkforthefield.Asawhole,theserieswill provide a valuable resource both for newcomers to the research fields described, and for other scientists seeking detailed background information on special questions. Finally, it provides an accredited documentation of the valuable contributions made by today’s younger generation of scientists. Theses are accepted into the series by invited nomination only and must fulfill all of the following criteria (cid:129) They must be written in good English. (cid:129) ThetopicshouldfallwithintheconfinesofChemistry,Physics,EarthSciences, Engineeringandrelatedinterdisciplinary fields such asMaterials,Nanoscience, Chemical Engineering, Complex Systems and Biophysics. (cid:129) The work reported in the thesis must represent a significant scientific advance. (cid:129) Ifthethesisincludespreviouslypublishedmaterial,permissiontoreproducethis must be gained from the respective copyright holder. (cid:129) They must have been examined and passed during the 12 months prior to nomination. (cid:129) Each thesis should include a foreword by the supervisor outlining the signifi- cance of its content. 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More information about this series at http://www.springer.com/series/8790 Andrea Festanti 0 Measurement of the D – Meson Production in Pb Pb – and p Pb Collisions A Study Performed with the ALICE Experiment at the LHC Doctoral Thesis accepted by the University of Padua, Italy 123 Author Supervisor Dr. Andrea Festanti Dr. Andrea Dainese Department ofPhysics INFN-Sezione di Padova INFN-Sezione diPadova Padua Universitàdegli Studi diPadova Italy Padua Italy ISSN 2190-5053 ISSN 2190-5061 (electronic) SpringerTheses ISBN978-3-319-43454-4 ISBN978-3-319-43455-1 (eBook) DOI 10.1007/978-3-319-43455-1 LibraryofCongressControlNumber:2016946963 ©SpringerInternationalPublishingSwitzerland2016 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authorsortheeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinor foranyerrorsoromissionsthatmayhavebeenmade. Printedonacid-freepaper ThisSpringerimprintispublishedbySpringerNature TheregisteredcompanyisSpringerInternationalPublishingAGSwitzerland ’ Supervisor s Foreword The aim of experimental high-energy heavy-ion physics is to study strongly interacting matter, quarks and gluons, in conditions of high density and tempera- ture; high with respect to the conditions characterizing the ordinary nuclear matter that constitutes the known Universe. Theoretical calculations predict that at a critical temperature of about 160 MeV, corresponding to an energy density εc ’ 1 GeV/fm3, nuclear matter undergoes a phase transition to a deconfined state of quarks and gluons, the quark-gluon plasma (QGP). The phase transition can be produced in the laboratory in ultra-relativistic heavy-ion collisions, where one attains energy densities that reach and exceed the critical value εc. The ALICE experiment is devoted to the study of heavy-ion collisions at the CERN Large Hadron Collider (LHC). Its goal is to use nucleus–nucleus, proton– proton and proton–nucleus collisions at unprecedented high energy to characterize the properties of the quark-gluon plasma. Andrea Festanti obtained his Ph.D. with measurements of charmed-hadron production in Pb–Pb and p–Pb collisions using data from the first LHC run. Charm quarks are regarded as effective probes of the conditions of the QGP, because they traverse this “medium” and interact with its constituents (quarks and gluons), via both gluon radiation and elastic scatterings. The study of the medium-induced suppression (nuclear modification factor R ) and of the azi- AA muthal anisotropy of the production yields in non-central collisions (elliptic flow v ),providesinsightintothetransportpropertiesofheavyquarksintheQGP.This 2 includes the role of the different energy loss processes, the degree to which heavy quarks are thermalizedand participateinthe collectiveexpansionof theQGP, and the heavy-quark hadronization mechanisms in the presence of a high-density par- tonic system. Andrea carried out the first measurement of the charmed D0 meson production relative to the reaction plane in Pb–Pb collisions and the measurement of the D0 production in p–Pb collisions. The measurement of the D0 azimuthal anisotropy with respect to the reaction plane indicates that low-momentum charm quarks participateinthecollectiveexpansionoftheQGP,despitetheirlargemassofabout v vi Supervisor’sForeword 1.5 GeV/c2. This observation can be explained by charm hadronization via recombination with light quarks from the QGP and elastic interactions with the expanding QGP constituents. The measurement of the D0 production in p–Pb collisions is crucial to disentangle the effects induced by cold nuclear matter, like thereductionofthepartondensitiesinnuclei,fromthefinal-stateeffectsinducedby the hot QGP formed in Pb–Pb collisions. The D0 production in p–Pb collisions is consistent with the binary collision scaling of the production in pp collisions, demonstratingthatthemodificationofthemomentumdistributionobservedinPb– Pb collisions with respect to pp is induced by final-state effects such as the energy loss of charm quarks in the QGP. In sum, the measurements described in the thesis, which are in many aspects unique at the LHC, provide a clear indication that heavy quarks undergo strong energy loss via interactions within the quark-gluon plasma and take part in its collective expansion. Padua Dr. Andrea Dainese April 2016 Abstract ThisthesispresentsthemeasurementofthecharmedD0mesonproductionrelative tothereactionplaneinPb–Pbcollisionsatthecentre-of-massenergypernucleon– pffiffiffiffiffiffiffi nucleoncollisionof psNffiNffiffiffiffi¼ffiffi 2:76TeV,andthemeasurementoftheD0production in p–Pb collisions at sNN ¼5:02 TeV with the ALICE detector at the CERN Large Hadron Collider. TheD0azimuthalanisotropywithrespecttothereactionplaneissensitivetothe interaction of the charm quarks with the high-density strongly interacting medium formed in ultra-relativistic heavy-ion collisions and, thus, to the properties of this state of matter. In particular, this observable allows to establish whether low-momentum charm quarks participatein thecollective expansion ofthe system andwhethertheycanreachthermalequilibriumwiththemediumconstituents.The azimuthalanisotropyisquantifiedintermsofthesecondcoefficientv inaFourier 2 expansionoftheD0azimuthaldistributionandintermsofthenuclearmodification factorRAA,measuredinthedirectionofthereactionplaneandorthogonaltoit.The measurement of the D0 production in p–Pb collisions is crucial to disentangle the effectsinducedbycoldnuclearmatterfromthefinal-stateeffectsinducedbythehot medium formed in Pb–Pb collisions. TheD0productionismeasuredinbothsystemsbyreconstructingthetwo-prong hadronicdecayD0!K−π+inthecentralrapidityregion,exploitingtheseparation of the decay vertex from the primary vertex. The raw signal is obtained with an invariant mass analysis, and corrected for selection and reconstruction efficiency. Apositive elliptic flow v isobservedinPb–Pbcollisionsinthecentrality class 2 30–50%,withameanvalueof0:204þ0:099 intheinterval2<p <6GeV/c,which (cid:2)0:036 T decreases towards more central collisions. Consequently, the nuclear modification factor shows a stronger suppression in the direction orthogonal to the reaction plane. The v2 and the RAA measured in two azimuthal regions with respect to the reactionplanearecomparedtotheoreticalcalculationsofcharmquarktransportand energy loss in high-density strongly-interacting matter. The models that include substantial elastic interactions with an expanding medium provide a good description of the observed anisotropy. vii viii Abstract The D0 nuclear modification factor RpPb in p–Pb collisions is compatible with unity within uncertainties. The measured RpPb is compared to theoretical models includinginitial-stateeffects,aswellastothenuclearmodificationfactormeasured incentralPb–Pbcollisions.TheD0RpPb resultsareconsistentwiththemodification of the nucleon parton distribution functions induced by the nuclear environment, and provide experimental evidence that the modification of the D meson momen- tum spectrum observed in Pb–Pb with respect to pp collisions is due to strong final-state effects induced by the hot medium. Acknowledgements I would like to thank my supervisor, Andrea Dainese, for his constant support during my Ph.D. and for being always available for discussion in case of any questions or doubts I had in these 3 years, his suggestions were fundamental to improve this write-up. Iamalso verygrateful toRosario Turrisi for hisexperience and the stimulating discussions I had with him, and to all the ALICE group in Padova,thatgavemethepossibilitytoattendschoolsandconferencesandallowed metospendanamazing andfruitfulyearatCERN.Itwasapleasuretoworkwith Davide on the analysis and I am very grateful to him for his help and suggestions andforthetimespentlearninganddiscussingaboutphysics,hebecamealsoagood friend.ThanksalsotoZaida,FrancescoandRalf,theyhavebeengreatcoordinators andIlearntalotaboutheavy-flavourphysicsfromthediscussionswiththemduring themeetingsoftheworkinggroup.IthankAndrea,Riccardo,CristinaandGrazia,it was a pleasure to cooperate with them in the D meson analysis. Iamverythankfultomyparentsfortheirloveandforallowingmetopursuemy studies and researches, to my sister for being always with me, and to my grand- parents for being always proud of my work even if so far from their experiences. Last,IwishtothankmydearfriendsAndrea, Luca,Emanuela,Carlo,Emiland Federica, they accompanied me during these years and we shared many enjoying and relaxing moments. ix
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