Suchergebnisse

Measurement of Z-boson production in p-Pb collisions at √sNN = 8.16 TeV and Pb-Pb collisions at √sNN = 5.02 TeV is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity −4 20 GeV/c in the laboratory frame. The invariant yield and nuclear modification factor are measured for opposite-sign dimuons with invariant mass 60 < mμμ < 120 GeV/c2 and rapidity 2.5 < ycmsμμ< 4. They are presented as a function of rapidity and, for the Pb-Pb collisions, of centrality as well. The results are compared with theoretical calculations, both with and without nuclear modifications to the Parton Distribution Functions (PDFs). In p-Pb collisions the center-of-mass frame is boosted with respect to the laboratory frame, and the measurements cover the backward (−4.46 < ycmsμμ < −2.96) and forward (2.03 < ycmsμμ < 3.53) rapidity regions. For the p-Pb collisions, the results are consistent within experimental and theoretical uncertainties with calculations that include both free-nucleon and nuclear-modified PDFs. For the Pb-Pb collisions, a 3.4σ deviation is seen in the integrated yield between the data and calculations based on the free-nucleon PDFs, while good agreement is found once nuclear modifications are considered. ; A. I. Alikhanyan National Science Laboratory (Yerevan Physics Insti- tute) 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 fu ̈r Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Cient ́ıfico e Tecnol ́ogico (CNPq), Financiadora de Estudos e Projetos (Finep), Fundac ̧ ̃ao de Amparo `a Pesquisa do Estado de S ̃ao 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 ́ogicas y Desarrollo Nuclear (CEADEN), Cubaenerg ́ıa, Cuba; Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic; The Danish Council for Independent Re- search — Natural Sciences, the VILLUM FONDEN and Danish National Research Foun- dation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland; Commissariat `a l'Energie Atomique (CEA) and Institut National de Physique Nucl ́eaire et de Physique des Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France; Bundesministerium fu ̈r Bildung und Forschung (BMBF) and GSI Helmholtzzentrum fu ̈r Schwerionenforschung GmbH, Germany; General Secretariat for Research and Technology, Ministry of Education, Research and Religions, Greece; National Research, Develop- ment 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; Centro Fermi - Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi and Istituto Nazionale di Fisica Nucleare (INFN), Italy; Institute for Innovative Science and Technology , Nagasaki Insti- tute of Applied Science (IIST), Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and Japan Society for the Promotion of Science (JSPS) KAK- ENHI, Japan; Consejo Nacional de Ciencia (CONACYT) y Tecnolog ́ıa, through Fondo de Cooperaci ́on Internacional en Ciencia y Tecnolog ́ıa (FONCICYT) and Direcci ́on Gen- eral de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway, Nor- way; Commission on Science and Technology for Sustainable Development in the South (COMSATS), Pakistan; Pontificia Universidad Cat ́olica del Peru ́, Peru; Ministry of Sci- ence and Higher Education, National Science Centre and WUT ID-UB, Poland; Korea Institute of Science and Technology Information and National Research Foundation of Ko- rea (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 Foun- dation 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 Technol- ogy Development Agency (NSDTA) and Office of the Higher Education Commission under NRU project of Thailand, Thailand; Turkish Atomic Energy Agency (TAEK), Turkey; Na- tional 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

The first measurements of dielectron production at midrapidity (|η_e| < 0.8) in proton–proton and proton–lead collisions at √sNN = 5.02 TeV at the LHC are presented. The dielectron cross section is measured with the ALICE detector as a function of the invariant mass m_ee and the pair transverse momentum p_T,ee in the ranges m_ee < 3.5 GeV/c^2 and p_T,ee < 8 GeV/c, in both collision systems. In proton–proton collisions, the charm and beauty cross sections are determined at midrapidity from a fit to the data with two different event generators. This complements the existing dielectron measurements performed at √s = 7 and 13 TeV. The slope of the √s dependence of the three measurements is described by FONLL calculations. The dielectron cross section measured in proton–lead collisions is in agreement, within the current precision, with the expected dielectron production without any nuclear matter effects for e+e− pairs from open heavy-flavor hadron decays. For the first time at LHC energies, the dielectron production in proton–lead and proton–proton collisions are directly compared at the same √sNN via the dielectron nuclear modification factor RpPb. The measurements are compared to model calculations including cold nuclear matter effects, or additional sources of dielectrons from thermal radiation. ; 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 für Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Financiadora de Estudos e Projetos (Finep), Fundação de Amparo à Pesquisa do Estado de São 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 Tecnológicas y Desarrollo Nuclear (CEADEN), Cubaenergía, 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 à l'Energie Atomique (CEA) and Institut National de Physique Nucléaire et de Physique des Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France; Bundesministerium für Bildung und Forschung (BMBF) and GSI Helmholtzzentrum für 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; Centro Fermi - Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi and 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 Tecnología, through Fondo de Coop- eración Internacional en Ciencia y Tecnología (FONCICYT) and Dirección General de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway, Norway; Commission on Science and Technology for Sustainable Development in the South (COM- SATS), Pakistan; Pontificia Universidad Católica del Perú, Peru; Ministry of Science and Higher Education, 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 Edu- cation Commission under NRU project of Thailand, Thailand; Turkish Atomic Energy Agency (TAEK), Turkey; National Academy of Sciences of Ukraine, Ukraine; Science and Technology Facilities Council (STFC), United Kingdom; National Science Foundation of the USA (NSF) and United States Department of Energy, Office of Nuclear Physics (DOE NP), USA.

This Letter presents the first experimental observation of the attractive strong interaction between a proton and a multistrange baryon (hyperon) Ξ−. The result is extracted from two-particle correlations of combined p−Ξ−⊕¯p−¯Ξ+ pairs measured in p−Pb collisions at √sNN=5.02 TeV at the LHC with ALICE. The measured correlation function is compared with the prediction obtained assuming only an attractive Coulomb interaction and a standard deviation in the range [3.6, 5.3] is found. Since the measured p−Ξ−⊕¯p−¯Ξ+ correlation is significantly enhanced with respect to the Coulomb prediction, the presence of an additional, strong, attractive interaction is evident. The data are compatible with recent lattice calculations by the HAL-QCD Collaboration, with a standard deviation in the range [1.8, 3.7]. The lattice potential predicts a shallow repulsive Ξ− interaction within pure neutron matter and this implies stiffer equations of state for neutron-rich matter including hyperons. Implications of the strong interaction for the modeling of neutron stars are discussed. ; 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 für Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Universidade Federal do Rio Grande do Sul (UFRGS), Financiadora de Estudos e Projetos (Finep) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Brazil; Ministry of Science & Technology of China (MSTC), National Natural Science Foundation of China (NSFC) and Ministry of Education of China (MOEC), China; Croatian Science Foundation and Ministry of Science and Education, Croatia; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Cubaenergía, Cuba; Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic; The Danish Council for Independent Research—Natural Sciences, the Carlsberg Foundation and Danish National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland; Commissariat à l'Energie Atomique (CEA), Institut National de Physique Nucléaire et de Physique des Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS) and Rlégion des Pays de la Loire, France; Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) and GSI Helmholtzzentrum für 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; Centro Fermi—Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi and Istituto Nazionale di Fisica Nucleare (INFN), Italy; Institute for Innovative Science and Technology, Nagasaki Institute of Applied Science (IIST), Japan Society for the Promotion of Science (JSPS) KAKENHI and Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan; Consejo Nacional de Ciencia (CONACYT) y Tecnología, through Fondo de Cooperación Internacional en Ciencia y Tecnología (FONCICYT) and Dirección General de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway, Norway; Commission on Science and Technology for Sustainable Development in the South (COMSATS), Pakistan; Pontificia Universidad Católica del Perú, Peru; Ministry of Science and Higher Education and National Science Centre, 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; National Science and Technology Development Agency (NSDTA), Suranaree University of Technology (SUT) and Office of the Higher Education Commission under NRU project of Thailand, Thailand; Turkish Atomic Energy Agency (TAEK), 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.

United States National Science Foundation (NSF) ; Science and Technology Facilities Council (STFC) of the United Kingdom ; Max-Planck-Society (MPS) ; State of Niedersachsen/Germany ; Italian Istituto Nazionale di Fisica Nucleare (INFN) ; French Centre National de la Recherche Scientifique (CNRS) ; Australian Research Council ; International Science Linkages program of the Commonwealth of Australia ; Council of Scientific and Industrial Research of India ; Department of Science and Technology, India ; Science & Engineering Research Board (SERB), India ; Ministry of Human Resource Development, India ; Spanish Ministerio de Economia y Competitividad ; Conselleria d'Economia i Competitivitat and Conselleria d'Educaci, Cultura i Universitats of the Govern de les Illes Balears ; Netherlands Organisation for Scientific Research ; National Science Centre of Poland ; European Union ; Royal Society ; Scottish Funding Council ; Scottish Universities Physics Alliance ; National Aeronautics and Space Administration ; Hungarian Scientific Research Fund (OTKA) ; Lyon Institute of Origins (LIO) ; National Research Foundation of Korea ; Industry Canada ; Province of Ontario through the Ministry of Economic Development and Innovation ; Natural Science and Engineering Research Council, Canada ; Brazilian Ministry of Science, Technology, and Innovation ; Carnegie Trust ; Leverhulme Trust ; David and Lucile Packard Foundation ; Research Corporation ; Alfred P. Sloan Foundation ; NSF ; STFC ; MPS ; INFN ; CNRS ; Science and Technology Facilities Council ; Science and Technology Facilities Council: ST/L000938/1 Gravitational Waves ; Science and Technology Facilities Council: 1362895 ; Science and Technology Facilities Council: ST/L000962/1 ; Science and Technology Facilities Council: ST/I006285/1 Gravitational Waves ; Science and Technology Facilities Council: ST/L003465/1 ; Science and Technology Facilities Council: ST/L000962/1 Gravitational Waves ; Science and Technology Facilities Council: ST/I006285/1 ; Science and Technology Facilities Council: ST/I006242/1 Gravitational Waves ; Science and Technology Facilities Council: ST/J000019/1 ; Science and Technology Facilities Council: ST/N00003X/1 ; Science and Technology Facilities Council: ST/L000946/1 ; Science and Technology Facilities Council: ST/N000064/1 ; Science and Technology Facilities Council: ST/L000954/1 Gravitational Waves ; Science and Technology Facilities Council: ST/K000845/1 ; Science and Technology Facilities Council: ST/I006269/1 ; Science and Technology Facilities Council: ST/L000938/1 ; Science and Technology Facilities Council: Gravitational Waves ; Science and Technology Facilities Council: ST/K005014/1 ; Science and Technology Facilities Council: ST/I006269/1 Gravitational Waves ; We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4 x 10(-5) and 9.4 x 10(-4) Mpc(-3) yr(-1) at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves.

Advanced LIGO ; Science and Technology Facilities Council (STFC) of the United Kingdom ; Australian Research Council ; Council of Scientific and Industrial Research of India, Department of Science and Technology, India ; Science & Engineering Research Board (SERB), India ; Ministry of Human Resource Development, India ; Spanish Ministerio de Economia y Competitividad ; Conselleria d'Economia i Competitivitat and Conselleria d'Educacio, Cultura i Universitats of the Govern de les Illes Balears ; National Science Centre of Poland ; FOCUS Programme of Foundation for Polish Science ; European Union ; Royal Society ; Scottish Funding Council ; Scottish Universities Physics Alliance ; Lyon Institute of Origins (LIO) ; National Research Foundation of Korea ; Industry Canada ; Province of Ontario through the Ministry of Economic Development and Innovation ; National Science and Engineering Research Council Canada ; Brazilian Ministry of Science, Technology, and Innovation ; Research Corporation, Ministry of Science and Technology (MOST), Taiwan ; Kavli Foundation ; Science and Technology Facilities Council ; Science and Technology Facilities Council: ST/L000954/1 Gravitational Waves ; Science and Technology Facilities Council: ST/L000946/1 ; Science and Technology Facilities Council: ST/I006269/1 Gravitational Waves ; Science and Technology Facilities Council: ST/I006242/1 Gravitational Waves ; Science and Technology Facilities Council: ST/L003465/1 ; Science and Technology Facilities Council: ST/J000019/1 ; Science and Technology Facilities Council: ST/N000072/1 ; Science and Technology Facilities Council: ST/K000845/1 ; Science and Technology Facilities Council: ST/I006269/1 ; Science and Technology Facilities Council: ST/N000633/1 ; Science and Technology Facilities Council: ST/M000931/1 ; Science and Technology Facilities Council: ST/K005014/1 ; Science and Technology Facilities Council: PPA/G/S/2002/00652 ; Science and Technology Facilities Council: Gravitational Waves ; Science and Technology Facilities Council: ST/N00003X/1 ; We present a possible observing scenario for the Advanced LIGO and Advanced Virgo gravitational-wave detectors over the next decade, with the intention of providing information to the astronomy community to facilitate planning for multi-messenger astronomy with gravitational waves. We determine the expected sensitivity of the network to transient gravitational-wave signals, and study the capability of the network to determine the sky location of the source. We report our findings for gravitational-wave transients, with particular focus on gravitational-wave signals from the inspiral of binary neutron-star systems, which are considered the most promising for multi-messenger astronomy. The ability to localize the sources of the detected signals depends on the geographical distribution of the detectors and their relative sensitivity, and 90% credible regions can be as large as thousands of square degrees when only two sensitive detectors are operational. Determining the sky position of a significant fraction of detected signals to areas of 5 deg(2) to 20 deg(2) will require at least three detectors of sensitivity within a factor of similar to 2 of each other and with a broad frequency bandwidth. Should the third LIGO detector be relocated to India as expected, a significant fraction of gravitational-wave signals will be localized to a few square degrees by gravitational-wave observations alone.

United States National Science Foundation (NSF) ; Science and Technology Facilities Council (STFC) of the United Kingdom ; MaxPlanck- Society (MPS) ; State of Niedersachsen/Germany ; Australian Research Council ; Netherlands Organisation for Scientific Research ; EGO consortium ; Council of Scientific and Industrial Research of India, Department of Science and Technology, India ; Science AMP; Engineering Research Board (SERB), India ; Ministry of Human Resource Development, India ; Spanish Ministerio de Economia y Competitividad ; Conselleria d'Economia i Competitivitat and Conselleria d'Educacio Cultura i Universitats of the Govern de les Illes Balears ; National Science Centre of Poland ; European Union ; Royal Society ; Scottish Funding Council ; Scottish Universities Physics Alliance ; Lyon Institute of Origins (LIO) ; National Research Foundation of Korea, Industry Canada ; Province of Ontario through the Ministry of Economic Development and Innovation ; National Science and Engineering Research Council Canada ; Brazilian Ministry of Science, Technology, and Innovation ; Leverhulme Trust ; Research Corporation, Ministry of Science and Technology (MOST), Taiwan ; Kavli Foundation ; NSF ; STFC ; MPS ; INFN ; CNRS ; Science and Technology Facilities Council ; State of Niedersachsen/Germany: GEO600 ; Science and Technology Facilities Council: ST/K005014/1 ; Science and Technology Facilities Council: ST/L000938/1 Gravitational Waves ; Science and Technology Facilities Council: ST/N000072/1 ; Science and Technology Facilities Council: PPA/G/S/2002/00652 ; Science and Technology Facilities Council: ST/I006269/1 ; Science and Technology Facilities Council: ST/L000962/1 ; Science and Technology Facilities Council: ST/J00166X/1 ; Science and Technology Facilities Council: ST/M006735/1 ; Science and Technology Facilities Council: ST/I006285/1 Gravitational Waves ; Science and Technology Facilities Council: ST/J000019/1 Gravitational Waves ; Science and Technology Facilities Council: ST/I006285/1 ; Science and Technology Facilities Council: ST/J000019/1 ; Science and Technology Facilities Council: 1362895 ; Science and Technology Facilities Council: ST/M000931/1 ; Science and Technology Facilities Council: ST/L000962/1 Gravitational Waves ; Science and Technology Facilities Council: ST/L000938/1 ; Science and Technology Facilities Council: ST/K000845/1 ; Science and Technology Facilities Council: ST/I006242/1 Gravitational Waves ; Science and Technology Facilities Council: ST/L003465/1 ; Science and Technology Facilities Council: ST/G504284/1 ; Science and Technology Facilities Council: ST/I006269/1 Gravitational Waves ; Science and Technology Facilities Council: ST/L000954/1 Gravitational Waves ; Science and Technology Facilities Council: ST/N00003X/1 ; Science and Technology Facilities Council: Gravitational Waves ; Science and Technology Facilities Council: ST/N000633/1 ; Science and Technology Facilities Council: ST/L000946/1 ; The discovery of the gravitational-wave (GW) source GW150914 with the Advanced LIGO detectors provides the first observational evidence for the existence of binary black hole (BH) systems that inspiral and merge within the age of the universe. Such BH mergers have been predicted in two main types of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively heavy BHs (greater than or similar to 25M(circle dot)) can form in nature. This discovery implies relatively weak massive-star winds and thus the formation of GW150914 in an environment with a metallicity lower than about 1/2 of the solar value. The rate of binary-BH (BBH) mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions (greater than or similar to 1 Gpc(-3) yr(-1)) from both types of formation models. The low measured redshift (z similar or equal to 0.1) of GW150914 and the low inferred metallicity of the stellar progenitor imply either BBH formation in a low-mass galaxy in the local universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-BH formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and GW detectors in space.