CP Violation in {B_s}^0 -> J/psi.phi Decays: Measured with the Collider Detector at Fermilab PDF
Preview CP Violation in {B_s}^0 -> J/psi.phi Decays: Measured with the Collider Detector at Fermilab
Springer Theses Recognizing Outstanding Ph.D. Research Sabato Leo CP Violation in B 0 J/ψφ s Decays Measured with the Collider Detector at Fermilab 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 for its scientific excellence and the high impact of its contents for the pertinent fieldofresearch.Forgreateraccessibilitytonon-specialists,thepublishedversions includeanextendedintroduction,aswellasaforewordbythestudent’ssupervisor explaining the special relevance of the work for the field. As a whole, the series will provide a valuable resource both for newcomers to the research fields described, and for other scientists seeking detailed background information on specialquestions.Finally,itprovidesanaccrediteddocumentationofthevaluable 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 • They must be written in good English. • ThetopicshouldfallwithintheconfinesofChemistry,Physics,EarthSciences, Engineering andrelatedinterdisciplinaryfieldssuchasMaterials, Nanoscience, Chemical Engineering, Complex Systems and Biophysics. • The work reported in the thesis must represent a significant scientific advance. • Ifthethesisincludespreviouslypublishedmaterial,permissiontoreproducethis must be gained from the respective copyright holder. • They must have been examined and passed during the 12 months prior to nomination. • Each thesis should include a foreword by the supervisor outlining the signifi- cance of its content. • The theses should have a clearly defined structure including an introduction accessible to scientists not expert in that particular field. More information about this series at http://www.springer.com/series/8790 Sabato Leo CP Violation in 0 B ! J=ψφ Decays s Measured with the Collider Detector at Fermilab Doctoral Thesis accepted by the University of Pisa, Italy 123 Author Supervisors Dr. SabatoLeo Prof.GiovanniPunzi UniversityofIllinoisatUrbana-Champaign Universityof Pisa Urbana,IL Pisa USA Italy Dr. DiegoTonelli CERN Geneva Switzerland ISSN 2190-5053 ISSN 2190-5061 (electronic) ISBN 978-3-319-07928-8 ISBN 978-3-319-07929-5 (eBook) DOI 10.1007/978-3-319-07929-5 LibraryofCongressControlNumber:2014943127 SpringerChamHeidelbergNewYorkDordrechtLondon (cid:2)SpringerInternationalPublishingSwitzerland2015 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodology now known or hereafter developed. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purposeofbeingenteredandexecutedonacomputersystem,forexclusiveusebythepurchaserofthe work. Duplication of this publication or parts thereof is permitted only under the provisions of theCopyright Law of the Publisher’s location, in its current version, and permission for use must always be obtained from Springer. Permissions for use may be obtained through RightsLink at the CopyrightClearanceCenter.ViolationsareliabletoprosecutionundertherespectiveCopyrightLaw. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexempt fromtherelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. While the advice and information in this book are believed to be true and accurate at the date of publication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityfor anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,with respecttothematerialcontainedherein. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Supervisors’ Foreword Particle physics is now experiencing exciting and puzzling times. Recently, a massive spin-0 particle compatible with the Higgs boson predicted by the standard model (SM) was discovered. In addition, null results from experimental searches excluded non-SM particles as heavy as 1 TeV. These striking findings conclusivelyestablishthestandardmodelasanaccurateandconsistentdescription of the fundamental constituents of matter and their interactions at energies extendinguptothe‘‘Fermiscale’’(100GeV),atwhichelectromagneticandweak interactions act as an unified force—and beyond. However,anumberofexperimentalindicationsandsolidtheoreticalarguments support the idea that the standard model becomes necessarily incomplete at some energy higherthan the 1TeV scale directly probedthus far,andshouldbe rooted in a more general theory. The description of such a theory, and the search for its experimental signatures, is the chief goal of today’s fundamental physics. Direct observation offeebly interacting massive particles requires accelerators capable of producing collisions with multi-MHz rates, at energies a few times larger than the mass of the sought particles. This is a technologically and eco- nomically daunting task that requires ever-larger international collaboration enterprises, enduring for decades. The study of weak interactions of quarks, or quark-flavor physics, offers an attractive complementary path, since such interactions are sensitive to energy scalesfarhigherthanthosedirectlyaccessiblewithcurrentandforeseencolliders. Thepresenceofnon-SMdynamicscanbeindirectly,butunambiguously,inferred from quark transitions that allow exchanges of virtual non-SM particles. Thisrequiresfocusingonprocessesthatareexperimentallyaccessible,sensitiveto a broad class of SM extensions, and whose phenomenology is accurately predict- able.DiscrepanciesemergingfromthecomparisonofaccurateSMpredictionswith equally precise experimental results would reveal the presence of non-SM dynamics. Indeed,thediscoverypotentialofthisapproachisnonovelty.Indirectsearches have been instrumental in directing us toward discovery of some of the most v vi Supervisors’Foreword fundamentalbuildingblocksofthestandardmodelitself.Forinstance,theexistence ofthecharmedquarkwasconjecturedanditsmassestimated,afewyearspriortoits directdiscovery,basedontheobservationofananomaloussuppressioninKmeson decayrates. Intwodecadesofextensiveexplorations,nosearchinquark-flavorrevealedthe presence of non-SM physics. Nevertheless, sub-10 % contributions from non-SM dynamicsarenotruledout,especiallyinprocessesinvolvingtransitionsofbottom- strange mesons (B0 and B(cid:2)0). These bound states of a bottom and a strange quark s s offer a rich phenomenology that, at the time of this work, was only marginally explored.ThedecaysofB0andB(cid:2)0mesonsintothefinalstateinvolvingaJ/ψanda s s φmesonstandoutasoneofthefewgoldenchannelsthatofferthemostpromising discovery opportunities. Interference between direct decays and decays following particle–antiparticle transitions, B0 $B(cid:2)0 !J=ψφ, provides experimental access s s totheunderlyingmixingphase,aparameterthatisvery sensitivetoabroadclass of non-SM processes, and challenging to measure otherwise. Experimentally, a sizable decay rate into fully reconstructed final states, with intermediate resonances decaying into a muon pair and two charged particles makes the accuratereconstructionoflarge eventsamplesaccessibleinhadroncollisionsand aids effective suppression of backgrounds. The precision measurement of the B0 s mixing phase is one of the key goals of current experimental particle physics. This thesis reports the final measurement of the mixing phase performed in proton–antiproton collisions at center-of-mass energy of 1.96 TeV, provided by the Tevatron collider and recorded by the Collider Detector at Fermilab experi- ment (CDF). Sifting through 1014 collisions from 10 years of operations, a low-background sample of about 11,000 B0;B(cid:2)0 !J=ψφ decays is reconstructed. s s A sophisticated analysis of the data is then performed, which encompasses in a single measurement all most advanced experimental techniques employed in fla- vor-physicsathadroncolliders.Incollisionsthattypicallyyieldtenthstohundreds ofchargedparticles,thedistancetraveledbytheB0orB(cid:2)0mesonbeforedecayingis s s measuredwith30lmprecision.This,combinedwithafewpermilmeasurementof the meson’s momentum, provides a measurement of decay time with about 90 fs resolution. A suite of algorithms, specifically optimized for this thesis, is used to study the particle activity in the whole event searching for tiny correlations between particle species and their electrical charges, which allow determining whether the bottom-strange particle was produced as a meson or an antimeson. In addition, spatial correlations between the directions offinal-state particles are exploited in determining the value of the orbital angular momentum between decay products. All these informations are encapsulated into a technically challenging multivariate likelihood fitwith more than 30 parameterstodetermine the mixing phase. The relevance and impact of the results is well worth the effort. The determi- nation of the mixing phase and several supplementary quantities are among the most precise available from a single experiment. They have been published in a highlycitedlettertoPhysicalReview,PRL109,171802(2012),wherethisthesis Supervisors’Foreword vii is also cited. No indication of deviations from the SM predictions is found and significantlyimprovedboundsontheallowedphenomenologyofnon-SMparticles or interactions are obtained. The experimental exploration of the bottom-strange mixing phase is rapidly progressing owing to abundant samples available at the Large Hadron Collider, and promises many further new insights. But this thesis will remain a valuable resource, providing a clear and detailed description of a legacy measurement performed by the CDF experiment, where measurements of the bottom-strange mixingphasewerefirstperformed,andmanyofthekeytechniquesthathavenow become standard in hadron-collisions flavor physics had been pioneered and perfected. Pisa, 2014 Prof. Giovanni Punzi Dr. Diego Tonelli Abstract We report on the final measurement of the CP-violating B0 mixing phase p s βJ=ψφ in ffisffi¼1:96 TeV proton-antiproton collisions collected with the Collider s Detector at the Fermilab Tevatron collider. Using a sample corresponding to 9.6 fb-1 of integrated luminosity, we fit the decay-time evolution of B0 ? s J/ψ(?μ+μ-)φ(?K+K-)decaysinwhichtheb-quarkcontentatproductionand the CP parity of the final state are identified. The interference of decays with and without mixing renders the B0 mixing phase observable. The phase is determined s tobe-0.06\βJ/ψφ\0.30at 68% confidencelevel. Thedecay-width difference s between heavy and light B0 eigenstates, and the average B0 lifetime are also s s determined to be ΔΓ = 0.068 ± 0.027 ps-1 and τ = 1.528 ± 0.021 ps, s s respectively. These results are among the world’s most precise from a single experiment, and compatible with standard model predictions. ix Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Flavor as a Probe for Non-SM Physics. . . . . . . . . . . . . . . . . . . . . 5 2.1 The Current Landscape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Flavor as a Probe of Non-SM Physics . . . . . . . . . . . . . . . . . . . 6 2.3 CKM Matrix and CP-violation . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3.1 B0 Oscillations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 s 2.4 Analysis of the Time-Evolution of B0 !J=ψφ Decays . . . . . . . 14 s 2.4.1 Time Evolution of the ðSþPÞ-wave System. . . . . . . . . 21 2.4.2 Likelihood Symmetries. . . . . . . . . . . . . . . . . . . . . . . . 24 2.5 Experimental Status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.6 Experimental Aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.7 Analysis Strategy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3 The Collider Detector at the Fermilab Tevatron. . . . . . . . . . . . . . 33 3.1 The Fermilab Tevatron Collider . . . . . . . . . . . . . . . . . . . . . . . 33 3.1.1 Proton Production . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.1.2 Antiproton Production and Accumulation. . . . . . . . . . . 36 3.1.3 Injection and Collisions . . . . . . . . . . . . . . . . . . . . . . . 36 3.1.4 Run II Performances and Achievements. . . . . . . . . . . . 38 3.2 The CDF II Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.2.1 Coordinates and Notation. . . . . . . . . . . . . . . . . . . . . . 39 3.2.2 Tracking System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.2.3 Time of Flight Detector . . . . . . . . . . . . . . . . . . . . . . . 45 3.2.4 Calorimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.2.5 Muons Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.3 Trigger and Data Acquisition Systems. . . . . . . . . . . . . . . . . . . 48 3.3.1 Dimuon Trigger. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.3.2 Reconstruction of Physics Objects. . . . . . . . . . . . . . . . 52 xi
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