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 muon is an elementary particle similar to the electron, with an electric charge of −1 e and spin-1/2, but with a much greater mass. It is classified as a lepton. As with other leptons, the muon is not thought to be composed of any simpler particles.
A neutrino is an elementary particle that interacts via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The rest mass of the neutrino is much smaller than that of the other known elementary particles. The weak force has a very short range, the gravitational interaction is extremely weak due to the very small mass of the neutrino, and neutrinos do not participate in the electromagnetic interaction or the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected.
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.
The muon neutrino is an elementary particle which has the symbol
ν
μ and zero electric charge. Together with the muon it forms the second generation of leptons, hence the name muon neutrino. It was discovered in 1962 by Leon Lederman, Melvin Schwartz and Jack Steinberger. The discovery was rewarded with the 1988 Nobel Prize in Physics.
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.
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.
Jack Steinberger was a German-born American physicist noted for his work with neutrinos, the subatomic particles considered to be elementary constituents of matter. He was a recipient of the 1988 Nobel Prize in Physics, along with Leon M. Lederman and Melvin Schwartz, for the discovery of the muon neutrino. Through his career as an experimental particle physicist, he held positions at the University of California, Berkeley, Columbia University (1950–68), and the CERN (1968–86). He was also a recipient of the United States National Medal of Science in 1988, and the Matteucci Medal from the Italian Academy of Sciences in 1990.
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In particle physics, lepton number is a conserved quantum number representing the difference between the number of leptons and the number of antileptons in an elementary particle reaction. Lepton number is an additive quantum number, so its sum is preserved in interactions. The lepton number is defined by where
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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.
