Composition | Elementary particle |
---|---|
Family | Boson |
Interactions | Fifth force |
Status | Unconfirmed |
Symbol | X17 |
Theorized | 2015 |
Mass | 17.01±0.16 MeV/c2 [1] |
Mean lifetime | 10−14 s [2] |
Decays into | one electron and one positron |
Electric charge | 0 e |
The X17 particle (X17 boson) is a hypothetical subatomic particle proposed by Attila Krasznahorkay and his colleagues to explain certain anomalous measurement results; these anomalous measurements are known as ATOMKI anomaly or beryllium (8Be) anomaly or X17 anomaly. [2] [3] The particle has been proposed to explain wide angles observed in the trajectory paths of particles produced during a nuclear transition of beryllium-8 nuclei and in helium nuclei. [4] The X17 particle could be the force carrier for a postulated fifth force, possibly connected with dark matter, [4] and has been described as a protophobic (i.e., ignoring protons) [5] vector boson with a mass near 17 MeV/c2. [4]
In 2015, Krasznahorkay and his colleagues at ATOMKI, the Hungarian Institute for Nuclear Research, posited the existence of a new, light boson with a mass of about 17 MeV/c2 (i.e., 34 times heavier than the electron). [6] In an effort to find a dark photon, the team fired protons at thin targets of lithium-7, which created beryllium-8 nuclei in an excited state, which then decayed to the ground state and produced pairs of electrons and positrons. [2] Excess decays were observed at an opening angle of 140° between the
e+
and
e−
particles and a combined energy of approximately 17 MeV/c2. This indicated that a small fraction of the excited beryllium-8 might shed its excess energy in the form of a new particle. The result was successfully repeated by the team. [4]
Feng et al. (2016) [7] proposed that a "protophobic" X boson, with a mass of 16.7 MeV/c2, suppressed couplings to protons relative to neutrons and electrons at femtometre range, could explain the data. The force may explain the g − 2 muon anomaly and provide a dark matter candidate. As of 2019 [update] , several research experiments are underway to attempt to validate or refute these results. [6] [7]
Krasznahorkay (2019) [8] posted a preprint announcing that he and his team at ATOMKI had successfully observed the same anomalies in the decay of stable helium atoms as had been observed in beryllium-8, strengthening the case for the existence of the X17 particle. [8]
This was covered in science journalism, focusing largely on the implications that the existence of the X17 particle and a corresponding fifth force would have in the search for dark matter. [9] [10] [11]
In 2021 the workshop "Shedding light on X17" was held at Centro Enrico Fermi in Rome, Italy. The workshop discussed the ATOMKI anomaly and its theoretical interpretation and future experiments to confirm and explain it. [12] One of the experiments that plans to repeat the original ATOMKI lithium–beryllium experiment is MEG II at PSI institute; the measurement was planned (in 2021) to be completed in 2022. [13] [14] [15] Also Universite de Montreal's 6 MV (6 megavolt) Tandem Van de Graaff Facility in Montreal has an experiment that attempts to reproduce the ATOMKI measurement; data taking should take place in early 2023. [16]
In 2022, another preprint was published by Krasznahorkay et al. supporting the X17 particle hypothesis. [17]
CERN's NA64 experiment and NA62 experiment have reported in 2021 [18] [19] and 2023 [20] [21] respectively results of conducted searches that have put stringent limits for the existence of the X17 particle.
In early 2023 the MEG II experiment performed its replication of the ATOMKI lithium–beryllium experiment; as of January 2024 the results have not yet been published (although the measurements were made in early 2023). [22] As of September 2024, the analysis of measurement results has been done but an article has not been published. [23]
This section needs to be updated. The reason given is: are the articles still not peer-reviewed?.(October 2023) |
As of December 2019 [update] , the ATOMKI paper describing the particle has not been peer reviewed and should therefore be considered preliminary. [24] In late 2019, a follow-up paper was published in Acta Physica Polonica B . [1] Efforts by CERN and other groups to independently detect the particle have been unsuccessful so far. [25]
The ATOMKI group had claimed to find various other new particles earlier in 2016 but abandoned these claims later, without an explanation of what caused the spurious signals. The group has also been accused of cherry-picking results that support new particles while discarding null results. [5] [26]
The X17 particle is not consistent with the Standard Model, so its existence would need to be explained by another theory. [3]
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.
In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron. The proton decay hypothesis was first formulated by Andrei Sakharov in 1967. Despite significant experimental effort, proton decay has never been observed. If it does decay via a positron, the proton's half-life is constrained to be at least 1.67×1034 years.
In physics, a fifth force refers to a hypothetical fundamental interaction beyond the four known interactions in nature: gravitational, electromagnetic, strong nuclear, and weak nuclear forces. Some speculative theories have proposed a fifth force to explain various anomalous observations that do not fit existing theories. The specific characteristics of a putative fifth force depend on which hypothesis is being advanced. No evidence to support these models has been found.
The top quark, sometimes also referred to as the truth quark, is the most massive of all observed elementary particles. It derives its mass from its coupling to the Higgs field. This coupling yt is very close to unity; in the Standard Model of particle physics, it is the largest (strongest) coupling at the scale of the weak interactions and above. The top quark was discovered in 1995 by the CDF and DØ experiments at Fermilab.
The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundreds of universities and laboratories across more than 100 countries. It lies in a tunnel 27 kilometres (17 mi) in circumference and as deep as 175 metres (574 ft) beneath the France–Switzerland border near Geneva.
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.
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 LHCb experiment is a particle physics detector experiment collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the parameters of CP violation in the interactions of b-hadrons. Such studies can help to explain the matter-antimatter asymmetry of the Universe. The detector is also able to perform measurements of production cross sections, exotic hadron spectroscopy, charm physics and electroweak physics in the forward region. The LHCb collaborators, who built, operate and analyse data from the experiment, are composed of approximately 1650 people from 98 scientific institutes, representing 22 countries. Vincenzo Vagnoni succeeded on July 1, 2023 as spokesperson for the collaboration from Chris Parkes. The experiment is located at point 8 on the LHC tunnel close to Ferney-Voltaire, France just over the border from Geneva. The (small) MoEDAL experiment shares the same cavern.
In particle physics, flavor-changing neutral currents or flavour-changing neutral currents (FCNCs) are hypothetical interactions that change the flavor of a fermion without altering its electric charge.
The DØ experiment was a worldwide collaboration of scientists conducting research on the fundamental nature of matter. DØ was one of two major experiments located at the Tevatron Collider at Fermilab in Batavia, Illinois. The Tevatron was the world's highest-energy accelerator from 1983 until 2009, when its energy was surpassed by the Large Hadron Collider. The DØ experiment stopped taking data in 2011, when the Tevatron shut down, but data analysis is still ongoing. The DØ detector is preserved in Fermilab's DØ Assembly Building as part of a historical exhibit for public tours.
Leptoquarks are hypothetical particles that would interact with quarks and leptons. Leptoquarks are color-triplet bosons that carry both lepton and baryon numbers. Their other quantum numbers, like spin, (fractional) electric charge and weak isospin vary among models. Leptoquarks are encountered in various extensions of the Standard Model, such as technicolor theories, theories of quark–lepton unification (e.g., Pati–Salam model), or GUTs based on SU(5), SO(10), E6, etc. Leptoquarks are currently searched for in experiments ATLAS and CMS at the Large Hadron Collider in CERN.
Beryllium-8 is a radionuclide with 4 neutrons and 4 protons. It is an unbound resonance and nominally an isotope of beryllium. It decays into two alpha particles with a half-life on the order of 8.19×10−17 seconds. This has important ramifications in stellar nucleosynthesis as it creates a bottleneck in the creation of heavier chemical elements. The properties of 8Be have also led to speculation on the fine tuning of the Universe, and theoretical investigations on cosmological evolution had 8Be been stable.
The Higgs boson, sometimes called the Higgs particle, is an elementary particle in the Standard Model of particle physics produced by the quantum excitation of the Higgs field, one of the fields in particle physics theory. In the Standard Model, the Higgs particle is a massive scalar boson with zero spin, even (positive) parity, no electric charge, and no colour charge that couples to mass. It is also very unstable, decaying into other particles almost immediately upon generation.
The search for the Higgs boson was a 40-year effort by physicists to prove the existence or non-existence of the Higgs boson, first theorised in the 1960s. The Higgs boson was the last unobserved fundamental particle in the Standard Model of particle physics, and its discovery was described as being the "ultimate verification" of the Standard Model. In March 2013, the Higgs boson was officially confirmed to exist.
Terence Richard Wyatt is a Professor in the School of Physics and Astronomy at the University of Manchester, UK.
The 750 GeV diphoton excess in particle physics was an anomaly in data collected at the Large Hadron Collider (LHC) in 2015, which could have been an indication of a new particle or resonance. The anomaly was absent in data collected in 2016, suggesting that the diphoton excess was a statistical fluctuation. In the interval between the December 2015 and August 2016 results, the anomaly generated considerable interest in the scientific community, including about 500 theoretical studies. The hypothetical particle was denoted by the Greek letter Ϝ in the scientific literature, owing to the decay channel in which the anomaly occurred. The data, however, were always less than five standard deviations (sigma) different from that expected if there was no new particle, and, as such, the anomaly never reached the accepted level of statistical significance required to announce a discovery in particle physics. After the August 2016 results, interest in the anomaly sank as it was considered a statistical fluctuation. Indeed, a Bayesian analysis of the anomaly found that whilst data collected in 2015 constituted "substantial" evidence for the digamma on the Jeffreys scale, data collected in 2016 combined with that collected in 2015 was evidence against the digamma.
When embedded in an atomic nucleus, neutrons are (usually) stable particles. Outside the nucleus, free neutrons are unstable and have a mean lifetime of 877.75+0.50
−0.44 s or 879.6±0.8 s. Therefore, the half-life for this process is 611±1 s.
In theoretical physics, the dual photon is a hypothetical elementary particle that is a dual of the photon under electric–magnetic duality which is predicted by some theoretical models, including M-theory.
Bradley Cox is an American physicist, academic and researcher. He is a Professor of Physics and the founder of the High Energy Physics Group at the University of Virginia.
NA64 experiment is one of the several experiments at CERN's Super Proton Synchrotron (SPS) particle collider searching for dark sector particles. It is a fixed target experiment in which an electron beam of energy between 100-150 GeV, strikes fixed atomic nuclei. The primary goal of NA64 is to find unknown and hypothetical particles such as dark photons, axions, and axion-like particles.
A lab in Hungary has reported an anomaly that could lead to a physics revolution. But even as excitement builds, closer scrutiny has unearthed a troubling backstory.
{{cite arXiv}}
: CS1 maint: numeric names: authors list (link)