Journal
NATURE
Volume 605, Issue 7910, Pages 440-+Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41586-022-04572-w
Keywords
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Categories
Funding
- Worldwide LHC Computing Grid (WLCG) collaboration
- ALICE detector: A. I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation (ANSL)
- State Committee of Science and World Federation of Scientists (WFS), Armenia
- Austrian Academy of Sciences, Austrian Science Fund (FWF) [M 2467-N36]
- Nationalstiftung fur Forschung, Technologie und Entwicklung, Austria
- Ministry of Communications and High Technologies
- National Nuclear Research Center, Azerbaijan
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)
- Financiadora de Estudos e Projetos (Finep)
- Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)
- Universidade Federal do Rio Grande do Sul (UFRGS), Brazil
- Ministry of Education of China (MOEC)
- Ministry of Science AMP
- Technology of China (MSTC)
- National Natural Science Foundation of China (NSFC), China
- Ministry of Science and Education and Croatian Science Foundation, Croatia
- Centro de Aplicaciones Tecnologicas y Desarrollo Nuclear (CEADEN), Cubaenergia, Cuba
- Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic
- Danish Council for Independent Research \ Natural Sciences, the VILLUM FONDEN
- Danish National Research Foundation (DNRF), Denmark
- Helsinki Institute of Physics (HIP), Finland
- Commissariat a l'Energie Atomique (CEA)
- Institut National de Physique Nucleaire et de Physique des Particules (IN2P3)
- Centre National de la Recherche Scientifique (CNRS), France
- Bundesministerium fur Bildung und Forschung (BMBF)
- GSI Helmholtzzentrum fur Schwerionenforschung GmbH, Germany
- General Secretariat for Research and Technology
- Ministry of Education, Research and Religions, Greece
- National Research, Development and Innovation Office, Hungary
- Department of Atomic Energy Government of India (DAE)
- Department of Science and Technology, Government of India (DST)
- University Grants Commission
- Government of India (UGC)
- Council of Scientific and Industrial Research (CSIR), India
- Indonesian Institute of Science, Indonesia
- Istituto Nazionale di Fisica Nucleare (INFN), Italy
- Institute for Innovative Science and Technology
- Nagasaki Institute of Applied Science (IIST)
- Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- Japan Society for the Promotion of Science (JSPS) KAKENHI, Japan
- Consejo Nacional de Ciencia (CONACYT) y Tecnologia, through Fondo de Cooperacion Internacional en Ciencia y Tecnologia (FONCICYT)
- Direccion General de Asuntos del Personal Academico (DGAPA), Mexico
- Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), the Netherlands
- Research Council of Norway, Norway
- Commission on Science and Technology for Sustainable Development in the South (COMSATS), Pakistan
- Pontificia Universidad Catolica del Peru, Peru
- Ministry of Education and Science
- National Science Centre and WUT ID-UB, Poland
- Korea Institute of Science and Technology Information and National Research Foundation of Korea (NRF), Republic of Korea
- Ministry of Education and Scientific Research
- Institute of Atomic Physics and Ministry of Research and Innovation and Institute of Atomic Physics, Romania
- Joint Institute for Nuclear Research (JINR)
- Ministry of Education and Science of the Russian Federation
- National Research Centre Kurchatov Institute
- Russian Science Foundation and Russian Foundation for Basic Research, Russia
- Ministry of Education, Science, Research and Sport of the Slovak Republic, Slovakia
- National Research Foundation of South Africa, South Africa
- Swedish Research Council (VR)
- Knut AMP
- Alice Wallenberg Foundation (KAW), Sweden
- European Organization for Nuclear Research, Switzerland
- Suranaree University of Technology (SUT)
- National Science and Technology Development Agency (NSDTA)
- Office of the Higher Education Commission under NRU project of Thailand, Thailand
- Turkish Energy, Nuclear and Mineral Research Agency (TENMAK), Turkey
- National Academy of Sciences of Ukraine, Ukraine
- Science and Technology Facilities Council (STFC), United Kingdom
- National Science Foundation of the United States of America (NSF)
- United States Department of Energy, Office of Nuclear Physics (DOE NP), United States of America
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In particle collider experiments, the direct observation of the QCD dead cone effect in the parton shower of charm quarks has been achieved using new iterative declustering techniques. This observation confirms a fundamental feature of QCD and provides a direct experimental observation of the non-zero mass of the charm quark.
In particle collider experiments, elementary particle interactions with large momentum transfer produce quarks and gluons (known as partons) whose evolution is governed by the strong force, as described by the theory of quantum chromodynamics (QCD)(1). These partons subsequently emit further partons in a process that can be described as a parton shower(2), which culminates in the formation of detectable hadrons. Studying the pattern of the parton shower is one of the key experimental tools for testing QCD. This pattern is expected to depend on the mass of the initiating parton, through a phenomenon known as the dead-cone effect, which predicts a suppression of the gluon spectrum emitted by a heavy quark of mass m(Q) and energy E, within a cone of angular size m(Q)/E around the emitter(3). Previously, a direct observation of the dead-cone effect in QCD had not been possible, owing to the challenge of reconstructing the cascading quarks and gluons from the experimentally accessible hadrons. We report the direct observation of the QCD dead cone by using new iterative declustering techniques(4,5) to reconstruct the parton shower of charm quarks. This result confirms a fundamental feature of QCD. Furthermore, the measurement of a dead-cone angle constitutes a direct experimental observation of the non-zero mass of the charm quark, which is a fundamental constant in the standard model of particle physics.
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