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 core of the detector consisted of 19 (later 20) magnetized iron modules. In the spacings between these, drift chambers for track reconstruction were installed. Additionally, plastic scintillators were inserted into the iron. Each iron module therefore served successively as an interaction target, where the neutrinos hit and produced hadron showers, a calorimeter that measured those hadrons' energy and a spectrometer, determining the momenta of produced muons via magnetic deflection. [1] [2]
At the time of its completion in 1976, the overall detector was 20 m long and weighed approximately 1250 tons.
The experiment was located in CERN's West Area, in building 182. The neutrinos (and antineutrinos) were produced by protons from the Super Proton Synchrotron (SPS) at energies of around 400 GeV, which were shot onto a beryllium target. [1]
The experiment was first proposed in July 1973 by a group led by Jack Steinberger as a two-piece detector. The front should serve as the neutrino target and hadronic shower detector, the following second part should detect the muon traces. [3] It was planned that the four proposing groups from Saclay, Dortmund, Heidelberg and CERN would contribute with complementary expertise and manpower. For example, Saclay was assigned to be in charge of the drift chambers, whereas CERN should handle the iron core magnets. It were also these four groups that gave the experiment its name: CERN Dortmund Heidelberg Saclay (CDHS). Approximately 30 people should form the final experiment group. [4]
After prolonged discussions with the SPS Committee, that was in charge of approving the proposals and distributing available money, an updated proposal for the new detector was submitted in March 1974. The suggested detector was a modular setup consisting of magnetized iron modules in combination with drift chambers and plastic scintillators. [5] This new proposal was approved by the committee in April 1974. Construction started soon after and was completed in 1976. The experiment's official name was WA1, since it was the first approved experiment at CERN's West Area. The estimated cost of the detector ranged between 6 and 8 million CHF. [3]
In 1979, an upgrade of the experimental setup was proposed. [6] The main reason for this upgrade was the comparably low resolution of eight of the 19 detector modules. This situation should be improved by inserting twelve new and better modules, resulting in a slightly longer and significantly more accurate machine. The proposal also included the suggestion for a group from Warsaw University, led by Adam Para, to join the project. Starting with the long shutdown of the Super Proton Synchrotron (SPS) from summer 1980 on, the requested changes were implemented. Eventually, half of the experiment's target calorimeters got replaced and the total number of detector modules was increased from 19 to 20. This led to four times higher spatial resolution of the produced particles as well as 25% more accurate measurements of the deposited hadronic energy. Additionally, four new drift chambers were installed, improving the reconstruction of muon tracks. [7] [8] Later, a liquid hydrogen tank was added in front of the detector as a target to measure the structure function of protons. [9]
CDHS took data with neutrinos delivered by the SPS from late 1976 until September 1984.
The scientific goal of the CDHS experiment was to study high energy neutrino interactions. When the incoming neutrinos (or antineutrinos) were interacting with the target iron, either charged current (
ν
+ Fe →
μ+
+ anything) or neutral current (
ν
+ Fe →
ν
+ anything) events could be produced. [2]
One of the main objectives of the experiment was to determine the ratio between the neutral and the charged inclusive neutrino cross sections, from which the Weinberg angle could be inferred. [10] Neutral currents had previously been discovered by the Gargamelle experiment, which had also provided first estimates of the Weinberg angle. The results were confirmed and measured with much higher precision by CDHS, allowing to predict the mass of the top quark, before it was discovered at the Tevatron, with approximately ±40 GeV precision. [11] [10]
Other measurements regarding the electroweak interaction within the standard model included the measurement of more than one muon; i.e. dimuon and trimuon events. [12] [13]
Results obtained at CDHS provided experimental validation of the standard model, at a time when this model was still in the testing phase. An important step in this regard was the falsification of the alleged "high-y anomaly". The value y characterizes the inelasticity of neutrino collisions, i.e. it measures the amount of energy that an incoming neutrino transfers to the hadrons during their collision. Experiments at Fermilab had found the so-called "high-y anomaly", which challenged the standard model. However, results from CDHS disproved those findings, strengthening the standard model. [14]
CDHS examined the nucleon structure functions, which enabled scientists to confirm the theory of quantum chromodynamics (QCD). [15] [8] This work included the determination of the QCD coupling constant , verification of the quark's (s = 1/2) and gluon's (s = 1) spin, as well as the falsification of both abelian theories of strong interactions and theories based on scalar gluons. [9] [15] Additionally, the experiments provided insights into the structure of the nucleon, examining the distribution of gluons, quarks and antiquarks within it. Results from CDHS were in line with the quark parton model, that assigned quarks to be point-like partons. [10] In this context, it was also confirmed that the number of valence quarks in a nucleon is 3. [16] Finally, the CDHS results allowed to determine the momentum distribution of strange quarks and antiquarks within a nucleon. [17]
During its last years of operation, the CDHS collaboration engaged in the search for neutrino oscillations. Although this phenomenon could not be confirmed using CERN's large energy neutrino beam, this attempt influenced the following experiments that eventually discovered neutrino oscillations. [18]
A proton is a stable subatomic particle, symbol
p
, H+, or 1H+ with a positive electric charge of +1 e (elementary charge). Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton-to-electron mass ratio). Protons and neutrons, each with masses of approximately one atomic mass unit, are jointly referred to as "nucleons" (particles present in atomic nuclei).
The Standard Model of particle physics is the theory describing three of the four known fundamental forces in the universe and classifying all known elementary particles. It was developed in stages throughout the latter half of the 20th century, through the work of many scientists worldwide, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks. Since then, proof of the top quark (1995), the tau neutrino (2000), and the Higgs boson (2012) have added further credence to the Standard Model. In addition, the Standard Model has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy.
In particle physics, the W and Z bosons are vector bosons that are together known as the weak bosons or more generally as the intermediate vector bosons. These elementary particles mediate the weak interaction; the respective symbols are
W+
,
W−
, and
Z0
. The
W±
bosons have either a positive or negative electric charge of 1 elementary charge and are each other's antiparticles. The
Z0
boson is electrically neutral and is its own antiparticle. The three particles each have a spin of 1. The
W±
bosons have a magnetic moment, but the
Z0
has none. All three of these particles are very short-lived, with a half-life of about 3×10−25 s. Their experimental discovery was pivotal in establishing what is now called the Standard Model of particle physics.
ATLAS is the largest general-purpose particle detector experiment at the Large Hadron Collider (LHC), a particle accelerator at CERN in Switzerland. The experiment is designed to take advantage of the unprecedented energy available at the LHC and observe phenomena that involve highly massive particles which were not observable using earlier lower-energy accelerators. ATLAS was one of the two LHC experiments involved in the discovery of the Higgs boson in July 2012. It was also designed to search for evidence of theories of particle physics beyond the Standard Model.
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.
The Underground Area 2 (UA2) experiment was a high-energy physics experiment at the Proton-Antiproton Collider — a modification of the Super Proton Synchrotron (SPS) — at CERN. The experiment ran from 1981 until 1990, and its main objective was to discover the W and Z bosons. UA2, together with the UA1 experiment, succeeded in discovering these particles in 1983, leading to the 1984 Nobel Prize in Physics being awarded to Carlo Rubbia and Simon van der Meer. The UA2 experiment also observed the first evidence for jet production in hadron collisions in 1981, and was involved in the searches of the top quark and of supersymmetric particles. Pierre Darriulat was the spokesperson of UA2 from 1981 to 1986, followed by Luigi Di Lella from 1986 to 1990.
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.
ALICE is one of eight detector experiments at the Large Hadron Collider at CERN. The other seven are: ATLAS, CMS, TOTEM, LHCb, LHCf, MoEDAL and FASER.
T2K is a particle physics experiment studying the oscillations of the accelerator neutrinos. The experiment is conducted in Japan by the international cooperation of about 500 physicists and engineers with over 60 research institutions from several countries from Europe, Asia and North America and it is a recognized CERN experiment (RE13). T2K collected data within its first phase of operation from 2010 till 2021. The second phase of data taking (T2K-II) is expected to start in 2023 and last until commencement of the successor of T2K – the Hyper-Kamiokande experiment in 2027.
Hyper-Kamiokande is a neutrino observatory and experiment under construction, conducted in Japan by the collaboration of institutes from 21 countries from six continents. As a successor of the Super-Kamiokande (SK) and T2K experiments, it is designed to search for proton decay and detect neutrinos from natural sources such as the Earth, the atmosphere, the Sun and the cosmos, as well as to study neutrino oscillations of the man-made accelerator neutrino beam. The beginning of data-taking is planned for 2027.
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 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.
The K2K experiment was a neutrino experiment that ran from June 1999 to November 2004. It used muon neutrinos from a well-controlled and well-understood beam to verify the oscillations previously observed by Super-Kamiokande using atmospheric neutrinos. This was the first positive measurement of neutrino oscillations in which both the source and detector were fully under experimenters' control. Previous experiments relied on neutrinos from the Sun or from cosmic sources. The experiment found oscillation parameters which were consistent with those measured by Super-Kamiokande.
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.
Luigi Di Lella is an Italian experimental particle physicist. He has been a staff member at CERN for over 40 years, and has played an important role in major experiments at CERN such as CAST and UA2. From 1986 to 1990 he acted as spokesperson for the UA2 Collaboration, which, together with the UA1 Collaboration, discovered the W and Z bosons in 1983.
The Enhanced NeUtrino BEams from kaon Tagging or ENUBET is an ERC funded project that aims at producing an artificial neutrino beam in which the flavor, flux and energy of the produced neutrinos are known with unprecedented precision.
An accelerator neutrino is a human-generated neutrino or antineutrino obtained using particle accelerators, in which beam of protons is accelerated and collided with a fixed target, producing mesons which then decay into neutrinos. Depending on the energy of the accelerated protons and whether mesons decay in flight or at rest it is possible to generate neutrinos of a different flavour, energy and angular distribution. Accelerator neutrinos are used to study neutrino interactions and neutrino oscillations taking advantage of high intensity of neutrino beams, as well as a possibility to control and understand their type and kinematic properties to a much greater extent than for neutrinos from other sources.
In quantum field theory, a sum rule is a relation between a static quantity and an integral over a dynamical quantity. Therefore, they have a form such as:
The Scattering and Neutrino Detector (SND) at the Large Hadron Collider (LHC), CERN, is an experiment built for the detection of the collider neutrinos. The primary goal of SND is to measure the p+p --> +X process and search for the feebly interacting particles. It will be operational from 2022, during the LHC-Run 3 (2022-2024). SND will be installed in an empty tunnel- TI18 that links the LHC and Super Proton Synchrotron, 480m away from the ATLAS experiment interaction point in the fast forward region and along the beam collision axis.
