Direct observation of the dead-cone effect in quantum chromodynamics

ALICE Collaboration

doi:10.1038/s41586-022-04572-w

Direct observation of the dead-cone effect in quantum chromodynamics

ALICE Collaboration

Relativistic Nuclear Physics

Research output: Contribution to journal › Article › peer-review

48 Scopus citations

Abstract

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 shower², 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 emitter³. 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.

Original language	English
Pages (from-to)	440-446
Number of pages	7
Journal	Nature
Volume	605
Issue number	7910
DOIs	https://doi.org/10.1038/s41586-022-04572-w
State	Published - May 19 2022

Funding

The ALICE Collaboration is grateful to U. Wiedemann for his valuable suggestions and fruitful discussions. We are also grateful to D. Napoletano for providing the SHERPA configuration files and useful discussions. The ALICE Collaboration would like to thank all its engineers and technicians for their invaluable contributions to the construction of the experiment and the CERN accelerator teams for the outstanding performance of the LHC complex. The ALICE Collaboration gratefully acknowledges the resources and support provided by all Grid centres and the Worldwide LHC Computing Grid (WLCG) collaboration. The ALICE Collaboration acknowledges the following funding agencies for their support in building and running the 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) and Nationalstiftung f\u00FCr Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Cient\u00EDfico e Tecnol\u00F3gico (CNPq), Financiadora de Estudos e Projetos (Finep), Funda\u00E7\u00E3o de Amparo \u00E0 Pesquisa do Estado de S\u00E3o Paulo (FAPESP) and Universidade Federal do Rio Grande do Sul (UFRGS), Brazil; Ministry of Education of China (MOEC), Ministry of Science & Technology of China (MSTC) and National Natural Science Foundation of China (NSFC), China; Ministry of Science and Education and Croatian Science Foundation, Croatia; Centro de Aplicaciones Tecnol\u00F3gicas y Desarrollo Nuclear (CEADEN), Cubaenerg\u00EDa, Cuba; Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic; The Danish Council for Independent Research | Natural Sciences, the VILLUM FONDEN and Danish National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland; Commissariat \u00E0 l\u2019Energie Atomique (CEA), Institut National de Physique Nucl\u00E9aire et de Physique des Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France; Bundesministerium f\u00FCr Bildung und Forschung (BMBF) and GSI Helmholtzzentrum f\u00FCr 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) and 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) and Japan Society for the Promotion of Science (JSPS) KAKENHI, Japan; Consejo Nacional de Ciencia (CONACYT) y Tecnolog\u00EDa, through Fondo de Cooperaci\u00F3n Internacional en Ciencia y Tecnolog\u00EDa (FONCICYT) and Direcci\u00F3n General de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), the Netherlands; The Research Council of Norway, Norway; Commission on Science and Technology for Sustainable Development in the South (COMSATS), Pakistan; Pontificia Universidad Cat\u00F3lica del Per\u00FA, 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) and Knut & Alice Wallenberg Foundation (KAW), Sweden; European Organization for Nuclear Research, Switzerland; Suranaree University of Technology (SUT), National Science and Technology Development Agency (NSDTA) and 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) and United States Department of Energy, Office of Nuclear Physics (DOE NP), United States of America.

Funders	Funder number
Council of Scientific and Industrial Research, India
State Committee of Science and World Federation
Ministry of Communications and High Technologies
Ministry of Education and Science
Department of Atomic Energy, Government of India
National Academy of Sciences of Ukraine
National Science and Technology Development Agency
National Research Foundation of Korea
Villum Fonden
Ministry of Education of the People's Republic of China
Narodowe Centrum Nauki
University Grants Commission
Institut National de Physique Nucléaire et de Physique des Particules
Science and Technology Facilities Council
Institute of Atomic Physics, Romania
General Secretariat for Research and Technology, Ministry of Education, Research and Religions
Institute for Innovative Science and Technology, Nagasaki Institute of Applied Science
Nederlandse Organisatie voor Wetenschappelijk Onderzoek
Institute of Atomic Physics and Ministry of Research and Innovation
Korea Institute of Science and Technology Information
Knut och Alice Wallenbergs Stiftelse
Ministry of Science and Education and Croatian Science Foundation
Instituto Nazionale di Fisica Nucleare
Financiadora de Estudos e Projetos
Department of Science and Technology, Ministry of Science and Technology, India
Consejo Nacional de Ciencia y Tecnología
Helsinki Institute of Physics
Norges Forskningsråd
Yerevan Physics Institute
Natur og Univers, Det Frie Forskningsråd
Centre National de la Recherche Scientifique
Office of the Higher Education Commission
Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México
Bundesministerium für Bildung und Forschung
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
Danmarks Grundforskningsfond
Conselho Nacional de Desenvolvimento Científico e Tecnológico
Suranaree University of Technology
Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear
Nemzeti Kutatási Fejlesztési és Innovációs Hivatal
Russian Foundation for Basic Research
NRU
GSI Helmholtzzentrum für Schwerionenforschung
U.S. Department of Energy
Ministry of Education and Science of the Russian Federation
Indian Institute of Space Science and Technology
Fundação de Amparo à Pesquisa do Estado de São Paulo
Turkish Energy, Nuclear and Mineral Research Agency
National Nuclear Research Center
WUT ID-UB
National Research Center "Kurchatov Institute"
Ministry of Science and Technology of the People's Republic of China
Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic
Ministry of Education, Science, Research and Sport
Russian Science Foundation
Lembaga Ilmu Pengetahuan Indonesia
Fondo de Cooperación Internacional en Ciencia y Tecnología
Universidade Federal do Rio Grande do Sul
Österreichischen Akademie der Wissenschaften
University Grants Commission, Government of India
National Research Foundation
Ministry of Higher Education and Scientific Research
CERN
Joint Institute for Nuclear Research
Nuclear Physics
Vetenskapsrådet
Österreichische Nationalstiftung für Forschung, Technologie und Entwicklung
TENMAK
Ministry of Education, Culture, Sports, Science and Technology
National Natural Science Foundation of China
Austrian Science Fund	M 2467-N36
Austrian Science Fund
Japan Society for the Promotion of Science	21H04462
Japan Society for the Promotion of Science

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10.1038/s41586-022-04572-w

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@article{9f76af776397410b8aa78b5b35c72999,

title = "Direct observation of the dead-cone effect in quantum chromodynamics",

abstract = "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 shower2, 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 mQ and energy E, within a cone of angular size mQ/E around the emitter3. 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 techniques4,5 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.",

author = "{ALICE Collaboration} and S. Acharya and D. Adamova and A. Adler and J. Adolfsson and {Aglieri Rinella}, G. and M. Agnello and N. Agrawal and Z. Ahammed and S. Ahmad and Ahn, {S. U.} and I. Ahuja and Z. Akbar and A. Akindinov and M. Al-Turany and Alam, {S. N.} and D. Aleksandrov and B. Alessandro and Alfanda, {H. M.} and {Alfaro Molina}, R. and B. Ali and Y. Ali and A. Alici and N. Alizadehvandchali and A. Alkin and J. Alme and T. Alt and L. Altenkamper and I. Altsybeev and Anaam, {M. N.} and C. Andrei and D. Andreou and A. Andronic and M. Angeletti and V. Anguelov and F. Antinori and P. Antonioli and C. Anuj and N. Apadula and L. Aphecetche and H. Appelshauser and S. Arcelli and R. Arnaldi and Arsene, {I. C.} and M. Arslandok and A. Augustinus and R. Averbeck and S. Aziz and F. Bock and Read, {K. F.} and Schmidt, {N. V.}",

note = "Publisher Copyright: {\textcopyright} 2022, The Author(s).",

year = "2022",

month = may,

day = "19",

doi = "10.1038/s41586-022-04572-w",

language = "English",

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journal = "Nature",

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AU - ALICE Collaboration

AU - Acharya, S.

AU - Adamova, D.

AU - Adler, A.

AU - Adolfsson, J.

AU - Aglieri Rinella, G.

AU - Agnello, M.

AU - Agrawal, N.

AU - Ahammed, Z.

AU - Ahmad, S.

AU - Ahn, S. U.

AU - Ahuja, I.

AU - Akbar, Z.

AU - Akindinov, A.

AU - Al-Turany, M.

AU - Alam, S. N.

AU - Aleksandrov, D.

AU - Alessandro, B.

AU - Alfanda, H. M.

AU - Alfaro Molina, R.

AU - Ali, B.

AU - Ali, Y.

AU - Alici, A.

AU - Alizadehvandchali, N.

AU - Alkin, A.

AU - Alme, J.

AU - Alt, T.

AU - Altenkamper, L.

AU - Altsybeev, I.

AU - Anaam, M. N.

AU - Andrei, C.

AU - Andreou, D.

AU - Andronic, A.

AU - Angeletti, M.

AU - Anguelov, V.

AU - Antinori, F.

AU - Antonioli, P.

AU - Anuj, C.

AU - Apadula, N.

AU - Aphecetche, L.

AU - Appelshauser, H.

AU - Arcelli, S.

AU - Arnaldi, R.

AU - Arsene, I. C.

AU - Arslandok, M.

AU - Augustinus, A.

AU - Averbeck, R.

AU - Aziz, S.

AU - Bock, F.

AU - Read, K. F.

AU - Schmidt, N. V.

PY - 2022/5/19

Y1 - 2022/5/19

N2 - 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 shower2, 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 mQ and energy E, within a cone of angular size mQ/E around the emitter3. 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 techniques4,5 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.

AB - 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 shower2, 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 mQ and energy E, within a cone of angular size mQ/E around the emitter3. 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 techniques4,5 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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VL - 605

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EP - 446

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JF - Nature

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ER -

Direct observation of the dead-cone effect in quantum chromodynamics

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