The European Muon Collaboration (EMC) was formed in 1973 to study the interactions of high energy muons at CERN. These experiments were motivated by the interest in determining the quark structure of the nucleon following the discovery of high levels of deep inelastic scattering at SLAC. [1] [2]
In 1972 two muon beams were proposed for the then new Super Proton Synchrotron (SPS) machine. One by Roger Clifft and Erwin Gabathuler and one by Friedhelm Brasse and Joerg Gayler. The two teams came together to design a high intensity muon beam of energy up to 280 GeV to do the experiments. The collaboration, which became known as the European Muon Collaboration (EMC), was formed around these people to carry out the experiments. A proposal for the beam and an apparatus to do the experiments was submitted to CERN in 1974 (the White Book). The experiments were approved and the apparatus was built between the years 1974–78. The collaboration grew in size to about 100 physicists. This was among the largest experimental collaborations at the time.
Several experiments were performed. Each experiment is denoted by a number NAxx where NA is for North Area experiments approved by CERN and xx is the number given to it by CERN.
NA2 was a single magnet spectrometer to measure the forward production products of deep inelastic scattering by muons. Data were taken for this experiment in the years between 1978–1981.
For this experiment a second magnet containing a streamer chamber was added upstream of the NA2 apparatus to detect and measure the products of the deep inelastic scattering reactions at wider angles. Further groups joined the EMC for these experiments and the collaboration grew to about 150 physicists. The experiments were performed between 1981–1983.
During the NA9 phase, a state of the art (at the time) processor was installed by the University of Uppsala group to trigger on scattered muons at very small angles to the beam (this was the NA28 experiment). This experiment was designed to investigate shadowing in nuclei. From 1984–1985 the experiment reverted to the single magnet spectrometer of NA2 and a large polarized target together with subsidiary nuclear targets were installed.
The first results of the NA2 phase of the experiment showed that charm production was mediated by the photon-gluon fusion process. The collaboration then went on to show that the scattering rate in iron and deuterium were different. This showed that the quark sub-structure of nucleons bound in nuclei is different from that of free nucleons. The effect became known as the EMC effect and aroused great interest among theoretical physicists. It was planned to replace the iron, deuterium and hydrogen targets with a polarized target in 1981. However, it proved to be difficult to build the large volume target necessary and this experiment was postponed until 1984. In addition the Lund model of quark fragmentation (which later became known as PYTHIA) became available and much of the data on forward produced hadrons were used to tune this model.
The NA9/NA28 phases of the experiment commenced taking data in 1981. The main results of these experiments were the confirmation of our understanding of the quark fragmentation process. Again the results were used to develop models of this process such as PYTHIA and the HERWIG model which had become available. The NA28 experiment discovered that the results of scattering in nuclei at small values of Bjorken x were much different from those at larger values. The process governing this behavior became known as shadowing in nuclei.
The final phase of the experiment with the polarized target produced the most dramatic result from the experiment with the discovery only a small part of the proton spin is carried by quarks, and that the strange quark sea is probably polarized. This is sometimes referred to as the "proton spin crisis".
Gargamelle was a heavy liquid bubble chamber detector in operation at CERN between 1970 and 1979. It was designed to detect neutrinos and antineutrinos, which were produced with a beam from the Proton Synchrotron (PS) between 1970 and 1976, before the detector was moved to the Super Proton Synchrotron (SPS). In 1979 an irreparable crack was discovered in the bubble chamber, and the detector was decommissioned. It is currently part of the "Microcosm" exhibition at CERN, open to the public.
Thomas Jefferson National Accelerator Facility (TJNAF), commonly called Jefferson Lab or JLab, is a US Department of Energy National Laboratory located in Newport News, Virginia.
In particle physics, deep inelastic scattering is the name given to a process used to probe the insides of hadrons, using electrons, muons and neutrinos. It was first attempted in the 1960s and 1970s and provided the first convincing evidence of the reality of quarks, which up until that point had been considered by many to be a purely mathematical phenomenon. It is an extension of Rutherford scattering to much higher energies of the scattering particle and thus to much finer resolution of the components of the nuclei.
ALICE is one of nine detector experiments at the Large Hadron Collider at CERN. The other eight are: ATLAS, CMS, TOTEM, LHCb, LHCf, MoEDAL, FASER and SND@LHC.
The Mainz Microtron, abbreviated MAMI, is a microtron which provides a continuous wave, high intensity, polarized electron beam with an energy up to 1.6 GeV. MAMI is the core of an experimental facility for particle, nuclear and X-ray radiation physics at the Johannes Gutenberg University in Mainz (Germany). It is one of the largest campus-based accelerator facilities for basic research in Europe. The experiments at MAMI are performed by about 200 physicists of many countries organized in international collaborations.
Nucleon spin structure describes the partonic structure of nucleon intrinsic angular momentum (spin). The key question is how the nucleon's spin, whose magnitude is 1/2ħ, is carried by its constituent partons. It was originally expected before the 1980s that quarks carry all of the nucleon spin, but later experiments contradict this expectation. In the late 1980s, the European Muon Collaboration (EMC) conducted experiments that suggested the spin carried by quarks is not sufficient to account for the total spin of the nucleons. This finding astonished particle physicists at that time, and the problem of where the missing spin lies is sometimes referred to as the proton spin crisis.
The High Luminosity Large Hadron Collider is an upgrade to the Large Hadron Collider, operated by the European Organization for Nuclear Research (CERN), located at the French-Swiss border near Geneva. From 2011 to 2020, the project was led by Lucio Rossi. In 2020, the lead role was taken up by Oliver Brüning.
CDHS was a neutrino experiment at CERN taking data from 1976 until 1984. The experiment was officially referred to as WA1. CDHS was a collaboration of groups from CERN, Dortmund, Heidelberg, Saclay and later Warsaw. The collaboration was led by Jack Steinberger. The experiment was designed to study deep inelastic neutrino interactions in iron.
The NA58 experiment, or COMPASS is a 60-metre-long fixed-target experiment at the M2 beam line of the SPS at CERN. The experimental hall is located at the CERN North Area, close to the French village of Prévessin-Moëns. The experiment is a two-staged spectrometer with numerous tracking detectors, particle identification and calorimetry. The physics results are extracted by recording and analysing the final states of the scattering processes.
CEBAF Large Acceptance Spectrometer (CLAS) is a nuclear and particle physics detector located in the experimental Hall B at Jefferson Laboratory in Newport News, Virginia, United States. It is used to study the properties of the nuclear matter by the collaboration of over 200 physicists from many countries all around the world.
Quark–gluon plasma is an interacting localized assembly of quarks and gluons at thermal and chemical (abundance) equilibrium. The word plasma signals that free color charges are allowed. In a 1987 summary, Léon van Hove pointed out the equivalence of the three terms: quark gluon plasma, quark matter and a new state of matter. Since the temperature is above the Hagedorn temperature—and thus above the scale of light u,d-quark mass—the pressure exhibits the relativistic Stefan-Boltzmann format governed by temperature to the fourth power and many practically massless quark and gluon constituents. It can be said that QGP emerges to be the new phase of strongly interacting matter which manifests its physical properties in terms of nearly free dynamics of practically massless gluons and quarks. Both quarks and gluons must be present in conditions near chemical (yield) equilibrium with their colour charge open for a new state of matter to be referred to as QGP.
The NA62 experiment is a fixed-target particle physics experiment in the North Area of the SPS accelerator at CERN. The experiment was approved in February 2007. Data taking began in 2015, and the experiment is expected to become the first in the world to probe the decays of the charged kaon with probabilities down to 10−12. The experiment's spokesperson is Cristina Lazzeroni. The collaboration involves 333 individuals from 30 institutions and 13 countries around the world.
The EMC effect is the surprising observation that the cross section for deep inelastic scattering from an atomic nucleus is different from that of the same number of free protons and neutrons. From this observation, it can be inferred that the quark momentum distributions in nucleons bound inside nuclei are different from those of free nucleons. This effect was first observed in 1983 at CERN by the European Muon Collaboration, hence the name "EMC effect". It was unexpected, since the average binding energy of protons and neutrons inside nuclei is insignificant when compared to the energy transferred in deep inelastic scattering reactions that probe quark distributions. While over 1000 scientific papers have been written on the topic and numerous hypotheses have been proposed, no definitive explanation for the cause of the effect has been confirmed. Determining the origin of the EMC effect is one of the major unsolved problems in the field of nuclear physics.
Fermilab E-906/SeaQuest is a particle physics experiment which will use Drell–Yan process to measure the contributions of antiquarks to the structure of the proton or neutron and how this structure is modified when the proton or neutron is included within an atomic nucleus.
The NA49 experiment was a particle physics experiment that investigated the properties of quark–gluon plasma. The experiment's synonym was Ions/TPC-Hadrons. It took place in the North Area of the Super Proton Synchrotron (SPS) at CERN from 1991-2002.
Richard Edward Taylor,, was a Canadian physicist and Stanford University professor. He shared the 1990 Nobel Prize in Physics with Jerome Friedman and Henry Kendall "for their pioneering investigations concerning deep inelastic scattering of electrons on protons and bound neutrons, which have been of essential importance for the development of the quark model in particle physics."
The polarized targets are used as fixed targets in scattering experiments. In high energy physics they are used to study the nucleon spin structure of simple nucleons like protons, neutrons or deuterons. In deep inelastic scattering the hadron structure is probed with electrons, muons or neutrinos. Using a polarized high energy muon beam, for example, on a fixed target with polarized nucleons it is possible to probe the spin dependent part of the structure functions.
The proton spin crisis is a theoretical crisis precipitated by a 1987 experiment by the European Muon Collaboration (EMC), which tried to determine the distribution of spin within the proton.
Volker D. Burkert is a German physicist, academic and researcher. He is a Principal Staff Scientist at the Thomas Jefferson National Accelerator Facility at Jefferson Lab (JLab) in Newport News, Virginia (USA). He has made major contributions to the design of the CEBAF Large Acceptance Spectrometer (CLAS) that made it suitable for high luminosity operation in experiments studying spin-polarized electron scattering.
Joel Marshall Moss is an American experimental nuclear physicist.
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