Tag Archives: CERN

CERN Physicists Witness the Transformation of Lead into Gold

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Collisions involving high-energy lead nuclei at CERN’s Large Hadron Collider generate a powerful electromagnetic field capable of displacing protons and converting lead into ephemeral gold nuclei.

The lead ions (208Pb) in the LHC pass by one another without direct collision. During electromagnetic dissociation, photons interact with the nucleus, causing internal vibrations that result in the ejection of a small number of neutrons (2) and protons (3), leaving behind the nucleus of gold (before gold 203Au). Image credit: CERN.

The transformation of base metal lead into the precious metal gold was a long-held aspiration of medieval alchemists.

This enduring pursuit, known as Chrysopia, may have been spurred by the recognition that the relatively common lead, with its dull gray color, bears resemblance to gold.

It has since been established that lead and gold are fundamentally different chemical elements, and that chemical means cannot facilitate their conversion.

The advent of nuclear physics in the 20th century uncovered the possibility of transforming heavy elements into others through processes such as radioactive decay or in laboratory settings involving bombardment by neutrons or protons.

Gold has been artificially generated through such means previously, but physicists from the Alice Collaboration at CERN’s Large Hadron Collider (LHC) have recently measured lead’s conversion into gold using a novel mechanism that relies on close interactions between lead nuclei at the LHC.

High-energy collisions between lead nuclei can lead to the formation of quark-gluon plasma, a state of high temperature and density believed to represent conditions shortly after the Big Bang, initiating phenomena we now recognize.

Simultaneously, in more frequent instances where nuclei narrowly miss each other without direct contact, the strong electromagnetic fields they generate can provoke photon-nucleus interactions, potentially uncovering more exploration avenues.

The electromagnetic field produced by the nucleus is particularly potent due to its 82 protons, each carrying a fundamental charge.

Additionally, when lead nuclei are accelerated to extreme speeds at the LHC, the electromagnetic field lines become compressed into thin layers, extending laterally in the motion direction, generating transient pulses of photons.

This phenomenon often triggers electromagnetic dissociation, where photons interact with the nucleus, causing vibrations in its internal structure and leading to the release of a limited number of neutrons and protons.

To fabricate gold (with 79 protons), three protons must be removed from the lead nuclei in the LHC beam.

“It is remarkable to witness our detectors managing direct collisions that produce thousands of particles, while being sensitive to scenarios where merely a few particles are generated,” said a researcher.

The Alice team employed a zero degree calorimeter (ZDC) to quantify the number of photon-nucleus interactions, correlating them to the emission of zero, one, two, and three protons related to the production of lead, thallium, mercury, and gold, respectively.

While the creation of thallium and mercury occurs more frequently, results indicate that the LHC currently generates gold at a rate of approximately 89,000 nuclei from lead collisions at the Alice collision point.

These gold nuclei emerge from collisions at extremely high energies, colliding with LHC beam pipes or collimators at various downstream points and swiftly fragmenting into individual protons, neutrons, and other particles, lasting mere seconds.

The analysis from Alice shows that roughly 86 billion gold nuclei were produced during four significant experiments across two runs of the LHC, equating to only 29 picograms (2.9*10-11 g) in mass.

With ongoing upgrades to the LHC enhancing its brightness, Run 3 yielded almost double the amount of gold as observed in Run 2, although the overall quantity remains trillions of times less than what is necessary for jewelry production.

Though the technological aspirations of medieval alchemists have been partially fulfilled, their dreams of acquiring wealth have yet again been dashed.

“Thanks to the distinctive capabilities of Alice’s ZDC, our current analysis marks the inaugural systematic detection and examination of gold production signatures at the LHC,” states Dr. Uliana Dmitrieva, a member of the Alice Collaboration.

“These results extend beyond fundamental physics interests and serve to test and refine theoretical models of electromagnetic dissociation, improving our understanding of beam loss— a significant factor influencing the performance limitations of the LHC and future colliders,” adds Dr. John Jowett, also of the Alice Collaboration.

A new study will be published in the journal Physical Review C.

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S. Acharya et al. (Alice Collaboration). √sNN= 5.02 Proton emission in ultra-fine Pb-Pb collisions at TeV. Phys. Rev. C 111, 054906; doi:10.1103/PhysRevC.111.054906

Source: www.sci.news

Physicists at CERN witness the creation of weak boson triplet

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The physicist with Atlas collaboration We presented our first observations of VVZ production at Cern's large Hadron Collider. This is a rare combination of three giant vector bosons.

Three vector boson events recorded by Atlas are when one W-boson collapses into electrons and neutrinos, one collapses into moons and neutrinos, and two moons collapses into z boson. Muons are shown with a red line, electrons are shown with a green line, and a white line where “loss of energy” from Neutrino is destroyed. Image credits: Atlas/Cern.

As carriers of weak forces, W and Z bosons are central to standard models of particle physics.

Accurate measurements of multiboson production processes provide excellent testing of standard models and shed light on new physical phenomena.

“The production of three vector (V) bosons is a very rare process in LHC,” says Dr. Fabio Cerutti, Ph.D., Atlas Physics Coordinator.

“The measurement provides information about the interactions between multiple bosons linked to the symmetry underlying the standard model.”

“It is a powerful tool to uncover new physics phenomena, such as new particles that are too heavy to be produced directly in LHC.”

The Atlas team observed the generation of VVZ with statistical significance of 6.4 standard deviations, exceeding the five standard deviation thresholds needed to assert the observations.

This observation extends previous results from Atlas and CMS collaborations, including observations of VVV production by CMS and observations of WWW production by Atlas.

As some of the heaviest known particles, W and Z bosons can collapse in countless different ways.

In a new study, Atlas physicists focused on seven attenuation channels with the highest discovery potential.

These channels were further refined using a machine learning technique called Boosted Decision Trees, where the algorithms for each channel were trained to identify the desired signal.

By combining the attenuation channels, researchers were able to observe the production of VVZ and set limits on the contributions of new physical phenomena to the signal.

“The resulting limitations confirm the validity of the standard model and are consistent with previous results on the generation of three vector bosons,” they said.

“Analyzing the third run of LHC and the large dataset from future HLHCs will further improve the measurements of the generation of three vector bosons. We will deepen our understanding of these basic particles and our role in the universe.”

Team's result It will be published in journal Physical character b.

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Atlas collaboration. 2025. Observation of VVZ production at S√=13 TEV using an ATLAS detector. Phys. Rhett. bin press; Arxiv: 2412.15123

Source: www.sci.news

Physicists at CERN investigate potential Lorentz symmetry violations in top quark pair production

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A physicist in charge of CERN’s large -scale Hadronco Rider has tested whether top queks follow Albert Einstein’s special theory.

Installation of CMS beam pipe. Image credit: CERN / CMS collaboration.

In addition to quantum mechanics, Albert Einstein’s special relativity is functioning as the basis of the standard model of particle physics.

In that mind, there is a concept called Lorentz symmetry. The experimental results do not depend on the direction or speed of the experiment in which they were taken.

Special relativity has endured the trials of time. However, some theories, including specific models in string rationale, predict that very high energy does not work with special relativity and experimental observation depends on the direction of space -time experiments.

Lorentz’s remnants of the symmetry destruction can be observed with low -energy, such as the energy of a large hoodron co -rider (LHC), but has not been found on LHC or other colliders despite previous efforts.

In a new study, CMS physicists have searched for Lorentz symmetry on LHC using the top quark pair, the most known basic particles.

“In this case, relying on the direction of the experiment means that the speed at which the top quark pair is generated by the LHC collision in the LHC is different over time,” they said.

“To be more accurate, the average direction of the top quark generated in the center of the LHC proton beam and the center of the CMS experiment also changes because the earth rotates around the axis.”

“As a result, and if there is a priority in space -time, the production rate of the highest pair varies by era.”

“Therefore, finding a deviation from a certain speed will discover the direction of space -time priority.”

The new results of the team based on the LHC’s second execution data consistent with a certain speed. In other words, Lorentz’s symmetry is not broken, and Einstein’s special relativity remains effective.

Researchers have used results to limit the size of the parameters that are predicted to be null when symmetry is maintained.

The obtained restrictions have improved up to 100 times with the previous search results, which were destroyed by Lorentz symmetry in the previous Tevatron accelerator.

“The results will open a way to search for the future in which Lorentz symmetry will be destroyed based on the top quark data from the third run of LHC,” said scientists.

“Open the door to scrutinization of processes including other heavy particles that can only be investigated on LHC, such as Higgs Boson, W and Z Bosons.”

study Published in the October 2024 issue of the journal Physics B.

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CMS collaboration. 2024. Use the Dilepton Event in the 13 TEV Proton Proton collision to search for Lorentz invaluity in the production of top quark pairs. Physics B 857: 138979; DOI: 10.1016/j.physletb.2024.138979

Source: www.sci.news

Physicists at CERN make groundbreaking discovery: Evidence of antihyperhelium-4 detected for the first time

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Physicists are Alice Collaboration. Evidence of antihyperhelium-4 has been seen for the first time at CERN’s Large Hadron Collider (LHC). Antihyperhelium-4 consists of two antiprotons, an antineutron, and an antilambda. New results are also the first evidence of the heaviest antimatter hypernuclear still at the LHC.

Illustration of the production of antihyperhelium-4 in a lead-lead collision. Image credit: AI-assisted J. Ditzel.

Collisions between heavy ions at the LHC created quark-gluon plasma, a hot, dense state of matter that is thought to have filled the universe about a millionth of a second after the Big Bang.

Heavy ion collisions also create conditions suitable for the production of atomic nuclei, exotic hypernuclei, and their antimatter counterparts, antinuclei and antihypernuclei.

Measuring these forms of matter is important for a variety of purposes, including helping to understand the formation of hadrons from quarks and gluons, the building blocks of plasma, and the matter-antimatter asymmetry seen in the modern universe.

Hypernuclei are exotic atomic nuclei formed by a mixture of protons, neutrons, and hyperons, the latter of which are unstable particles containing one or more strange types of quarks.

More than 70 years after their discovery in cosmic rays, hypernuclei continue to be a source of fascination for physicists. This is because hypernuclei are rarely found in nature and are difficult to create and study in the laboratory.

Collisions of heavy ions produce large numbers of hypernuclei, and until recently, the lightest hypernuclei, hypertriton (composed of protons, neutrons, and lambda), and its antimatter partner, antihypertriton, have been observed.

Following recent observations of antihyperhydrogen-4, ALICE physicists have detected antihyperhelium-4.

This result has a significance of 3.5 standard deviations and is also the first evidence of the heaviest antimatter hypernucleus ever at the LHC.

The ALICE measurements are based on lead-lead collision data taken in 2018 at an energy of 5.02 teraelectronvolts (TeV) for each colliding pair of nucleons (protons and neutrons).

The researchers examined data for the signals of hyperhydrogen-4, hyperhelium-4, and their antimatter partners using machine learning techniques that go beyond traditional hypernuclear search techniques.

Candidates for (anti)hyperhydrogen-4 were identified by looking for an (anti)helium-4 nucleus and a charged pion with which it decays; identified by. -Three atomic nuclei, an (anti)proton, and a charged pion.

In addition to finding evidence for antihyperhelium-4 with a significance of 3.5 standard deviations and evidence for antihyperhydrogen-4 with a significance of 4.5 standard deviations, the ALICE team found that the production yields of both hypernuclei and measured the mass.

“For both hypernuclei, the measured masses are consistent with current global average values,” the scientists said.

“The measured production yields were compared with predictions from a statistical hadronization model that adequately accounts for the formation of hadrons and nuclei in heavy ion collisions.”

“This comparison shows that the model's predictions closely match the data when both the excited hypernuclear state and the ground state are included in the prediction.”

“This result confirms that the statistical hadronization model can also adequately explain the production of hypernuclei, which are compact objects about 2 femtometers in size.”

The authors also determined the antiparticle-to-particle yield ratios for both hypernuclei and found that they agreed within experimental uncertainties.

“This agreement is consistent with ALICE's observation that matter and antimatter are produced equally at LHC energy and further strengthens ongoing research into the matter-antimatter imbalance in the Universe.” concluded.

Source: www.sci.news

Physicists at CERN witness a top quark pair in lead-lead collision

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The generation of top quark pairs is observed This process of interaction between atomic nuclei was observed for the first time in lead-lead collisions at CERN's Large Hadron Collider (LHC) and the ATLAS detector.

We show lead-lead collisions at 5.02 TeV per nucleon pair, resulting in the production of candidate pairs of top quarks that decay into other particles. This event contains four particle jets (yellow cone), one electron (green line), and one muon (red line). The inlay shows an axial view of the event. Image credit: ATLAS/CERN.

In quark-gluon plasma, quarks (matter particles) and gluons (strong force transmitters), which are the basic constituents of protons and neutrons, are not bound within particles and exist in an unconfined state of matter, and almost It forms a complete dense fluid.

Physicists believe that quark-gluon plasma filled the universe shortly after the Big Bang, and their study provides a glimpse into conditions at earlier times in the universe's history.

However, the lifespan of quark-gluon plasma produced by heavy ion collisions is extremely short, approximately 10 years.-twenty three Seconds — means not directly observable.

Instead, physicists study the particles produced in these collisions that pass through the quark-gluon plasma and use them as probes of the plasma's properties.

In particular, the top quark is a very promising probe of the evolution of quark-gluon plasmas over time.

The top quark, the heaviest elementary particle known, decays into other particles an order of magnitude faster than the time required to form a quark-gluon plasma.

The delay between the collision and the decay products of the top quark interacting with the quark-gluon plasma may serve as a “time marker” and provide a unique opportunity to study the temporal dynamics of the plasma.

In addition, physicists could potentially extract new information about the nuclear parton distribution function, which describes how the momentum of a nucleon (proton or neutron) is distributed among its constituent quarks and gluons.

In the new study, physicists from the ATLAS collaboration studied lead ion collisions that occurred during LHC Experiment 2 at a collision energy of 5.02 teraelectronvolts (TeV) per nucleon pair.

They observed the production of a top quark in a dilepton channel, where the top quark decays into a bottom quark and a W boson, which then decays into an electron or muon and its associated neutrino.

This result has statistical significance with a standard deviation of 5.0, and is the first observation of the production of a top quark pair in a nucleus-nucleus collision.

“We measured the production rate, or cross section, of the top quark pair with a relative uncertainty of 35%,” the physicists said.

“The overall uncertainty is primarily driven by the size of the dataset, which means new heavy ion data from the ongoing Experiment 3 will improve the accuracy of the measurements.”

“The new results open the door to the study of quark-gluon plasmas,” the researchers added.

“Future studies will also consider semi-leptonic decay channels for top quark pairs in heavy ion collisions. This may provide the first glimpse of the evolution of quark-gluon plasmas over time.” ”

Source: www.sci.news

Physicists at CERN study the characteristics of enigmatic particles

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Physicists have been intrigued by χc1(3872), also known as X(3872), since its discovery two decades ago. They have been exploring whether it is a conventional charmonium state composed of two quarks or an exotic particle made up of four quarks. The LHCb collaboration at CERN’s Large Hadron Collider (LHC) set out to find the answer.

Artist's impression of a tetraquark, made up of two charm quarks and an up and down antiquark. Image courtesy of CERN.

In the quark model of particle physics, there are heavy particles (composed of three quarks), mesons (consisting of quark-antiquark pairs), and exotic particles (comprising an unusual number of quarks).

To determine the composition of χc1(3872), physicists must measure properties like mass and quantum numbers.

According to theory, χc1(3872) could be a standard charmonium state made of a charm quark and an anticharm quark, or it could be an exotic particle consisting of four quarks.

These exotic particles could be tightly bound tetraquarks, molecular states, cc-gluon hybrid states, vector glueballs, or a combination of various possibilities.

Recent measurements by LHCb physicists revealed that its quantum number is 1++, and in 2020 they obtained precise data on the particle’s width (lifetime) and mass.

They also examined low-energy scattering parameters.

Their findings indicated that the mass of χc1(3872) is slightly less than the combined masses of the D0 and D*0 mesons.

These results have sparked debate within the theoretical community, with some proposing that χc1(3872) is a molecular state made up of spatially separated D0 and D*0 mesons.

However, this hypothesis faces challenges, as physicists anticipate molecular matter to be suppressed in hadron-hadron collisions, yet significant amounts of χc1(3872) are produced.

Other theorists suggest that the particle contains “compact” components, indicating a smaller size and potentially consisting of tightly bound charmonium or tetraquarks.

One method to uncover the composition of χc1(3872) is to calculate the branching ratio, which involves the probabilities of decay into different lighter particles.

By comparing the decay into a photon of the excited charmonium state, physicists can gain insights into the nature of the particle.

A key theoretical indicator is a non-zero ratio, suggesting the presence of compact components and countering a purely molecular model.

Using data from LHC Run 1 and Run 2, LHCb scientists found significant ratios beyond six standard deviations, ruling out a pure D0D*0 molecular hypothesis for χc1(3872).

Instead, the results support various predictions based on alternative hypotheses for the structure of χc1(3872, such as a mix of conventional (compact) charmonium, tetraquarks, light quarks, or molecules with a substantial compact core element.

Thus, the findings provide compelling evidence in favor of a χc1(3872) structure including a compact component.

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R. Aiji others (LHCb Collaboration). 2024. Probing the properties of the χc1(3872) state using radiative decay. arXiv: 2406.17006

This article is based on the original release from CERN.

Source: www.sci.news

CERN physicists witness exceptionally rare hyperon decay

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A hyperon is a particle that contains three quarks, like a proton or a neutron, and one or more strange quarks. Physicists from the LHCb collaboration at the Large Hadron Collider (LHC) at CERN say they have observed a hyperon decay Σ+→pμ+μ- in proton-proton collisions.

A view of the LHCb detector. Image courtesy of CERN.

“Rare decays of known particles are a promising tool for exploring physics beyond the Standard Model of particle physics,” said the LHCb physicist.

“In the Standard Model, the Σ+ → pμ+μ- process is only possible through a loop diagram, meaning that the decay does not occur directly, but intermediate states have to be exchanged within the loop.”

“In quantum field theory, the probability of such a process occurring is the sum of the probabilities of all particles, both known and unknown, that can possibly be exchanged in this loop.”

“This is what makes such processes sensitive to new phenomena.”

“If a discrepancy is observed between experimental measurements and theoretical calculations, it may be caused by the contribution of some unknown particle.”

“These particles can either be exchanged within the loop or directly mediate this decay, interacting with the quarks and decaying into pairs of muons.”

“In the latter case, the new particle would leave a signature on the properties of the two muons.”

The study of the Σ+ → pμ+μ- decay has been particularly exciting thanks to hints of structure observed in the properties of muon pairs by the HyperCP collaboration in 2005.

With only three occurrences the structure was far from conclusive, and it was hoped that new research would shed light on the situation.

Finally, the LHCb data did not show any significant peak structure in the two-muon mass region highlighted by HyperCP, thus refuting the hint.

However, the new study observes the decay with a high degree of significance, followed by precise measurements of the decay probability and other parameters, which will allow further investigation of the discrepancy with the Standard Model predictions.

“In data collected in Run 2 of pp collisions at the LHCb experiment, the Σ+ → pμ+μ− decay is observed with very high significance, with a yield of NΣ+→pμ+μ− = 279 ± 19,” the authors write in their paper. paper.

“We do not see any structure in the two-muon invariant mass distribution that is consistent with the Standard Model predictions.”

“The collected signal yield allows for measurements of integral and differential branching rates, as well as other measurements such as charge-parity symmetry breaking and front-to-back asymmetry.”

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LHCb Collaboration. 2024. Observation of rare Σ+→pμ+μ− decays at LHCb. CERN-LHCb-CONF-2024-002

Source: www.sci.news

CERN Scientists Aim to Produce Enigmatic Higgs Particle Duplicates

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Physicists from the ATLAS Collaboration at the Large Hadron Collider (LHC) at CERN have announced the results of the most sensitive search to date for double Higgs production and self-coupling, achieved by combining five double Higgs studies from LHC Run 2 data.

Event display of a double Higgs candidate event, photographed in 2017. Image courtesy of ATLAS Collaboration / CERN.

Remember how hard it was to find one Higgs boson? Now try and find two of them in the same place at the same time.

This intriguing process, known as double Higgs production, can teach scientists about the Higgs particle's self-interaction.

By studying it, physicists can measure the strength of the Higgs particle's self-binding, a fundamental aspect of the Standard Model that links the Higgs mechanism to the stability of the universe.

Searching for the creation of double Higgs particles is a particularly challenging task.

This is an extremely rare process, about 1,000 times rarer than the creation of a single Higgs particle.

While LHC Run 2 produced 40 million collisions per second, ATLAS is expected to produce just a few thousand double Higgs events.

So how can physicists find these rare needles in a mountain of data?

One way to make it easier to find double Higgs production is to search in multiple locations.

By investigating the different ways in which the double Higgs decay (decay modes) and combining them, physicists can maximise their chances of discovering and studying the creation of the double Higgs.

The new results from the ATLAS collaboration are the most comprehensive search to date, covering more than half of all possible double Higgs events with ATLAS.

Each of the five individual studies in this combination focuses on a different mode of damping, each with its own strengths and weaknesses.

For example, the most likely double-Higgs decay mode is the decay into four bottom quarks.

However, the Standard Model QCD process likely also produces four bottom quarks, making it difficult to distinguish this background process from a double Higgs event.

The double-Higgs decay into two bottom quarks and two tau leptons involves moderate background contamination, but it occurs five times less frequently and there are neutrinos that escape undetected, complicating physicists' efforts to recreate the decay.

Decays into multiple leptons are not uncommon, but they have complex characteristics.

Other double Higgs decays are even rarer, such as the decay into two bottom quarks and two photons.

This final state accounts for only 0.3% of all double Higgs decays, but has a cleaner signature and much smaller background contamination.

Combining their findings for each of these decays, ATLAS physicists were able to find that the probability of producing two Higgs particles rules out more than 2.9 times the Standard Model prediction.

This result has a confidence level of 95% and an expected sensitivity of 2.4 (assuming this process does not exist in nature).

They were also able to provide constraints on the strength of the Higgs particle's self-coupling, achieving the highest sensitivity to date for this important observable.

They found that the magnitude of the Higgs self-coupling constant and the strength of the interaction between two Higgs particles and two vector particles are consistent with the Standard Model predictions.

“This overall result marks a milestone in the study of double Higgs particle production,” the researchers said.

their result will be published in journal Physics Review Letter.

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ATLAS Collaboration. 2024. Combined search for Higgs pair production in pp collisions at s√=13 TeV with the ATLAS detector. Physiotherapy Rev Lett,in press; arXiv:2406.09971

Source: www.sci.news

CERN researchers direct attention towards theoretical magnetic monopole

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American theoretical physicist Joseph Polczynski once said that the existence of magnetic monopoles is “one of the safest bets you can make about physics that has yet to be seen.” In the search for these particles that have magnetic charges and are predicted by several theories that extend the standard model, Moedal (Monopole and Exotic Detectors at the LHC) Although the collaboration has yet to prove Polczynski correct, its latest discovery represents a major advance. The new results narrow the search window for these hypothetical particles.

Generation of monopole pairs by Schwinger mechanism. Image credit: MoEDAL Collaboration / CERN.

At CERN's Large Hadron Collider (LHC), interactions between protons or heavy ions can produce pairs of magnetic monopoles.

In collisions between protons, protons can be formed from a single virtual photon (Dorrell-Yang mechanism) or from the fusion of two virtual photons (photon fusion mechanism).

Through a process called the Schwinger mechanism, pairs of magnetic monopoles can also be generated from the vacuum of huge magnetic fields produced by near-miss collisions of heavy ions.

Since starting data acquisition in 2012, MoEDAL has achieved several firsts, including conducting the first search for magnetic monopoles produced by photon fusion and Schwinger mechanisms at the LHC. Ta.

inside First part of the latest researchMoEDAL physicists explored monopoles and highly charged objects (HECOs) produced via the Dorell-Yang mechanism and the photon fusion mechanism.

This search was based on proton-proton collision data collected during Experiment 2 at the LHC using the complete MoEDAL detector for the first time.

The complete detector consists of two main systems that sense magnetic monopoles, HECO, and other highly ionizing virtual particles.

First, magnetic monopole and HECO trajectories can be permanently registered without background signals from standard model particles. The second system consists of an approximately 1-ton capture volume designed to capture magnetic monopoles.

Although the researchers did not find any magnetic monopoles or HECOs in their latest scan of the trapping volume, the masses and production rates of these particles were determined for different values ​​of particle spin, a unique form of angular momentum. limits have been set.

For magnetic monopoles, a mass limit of 1 to 10 times the Dirac charge (gD), the basic unit of magnetic charge, is set, excluding the existence of monopoles with masses as high as about 3.9 trillion electron volts (TeV). I did. .

For HECO, a mass limit was established for charges from 5e to 350e, where e is the electronic charge, and the presence of HECO with masses in the range up to 3.4 TeV was excluded.

“MoEDAL's search reach for both monopoles and HECOs allows the collaboration to explore vast swaths of the theoretical 'discovery space' for these hypothetical particles,” said a spokesperson for the MoEDAL collaboration. said Dr. James Pinfold.

in their second studyMoEDAL scientists focused on searching for monopoles produced via the Schwinger mechanism in heavy ion collision data collected during LHC Experiment 1.

In a unique effort, we scanned a decommissioned section of the CMS experimental beam pipe for trapped monopoles instead of the trapping volume of the MoEDAL detector.

Again, the team found no monopoles, but set the strongest mass constraints yet for Schwinger monopoles with charges between 2 gD and 45 gD, ruling out the existence of monopoles with masses up to 80 GeV. did.

“A crucial aspect of the Schwinger mechanism is that the production of complex monopoles is not suppressed compared to the production of elementary monopoles, as is the case with Dorell-Yang and photon fusion processes,” Pinfold said. Ta.

“Therefore, if monopoles are composite particles, this and the previous Schwinger monopole search may have been the first ever chance to observe monopoles.”

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Moedal collaboration. 2024. Searching for highly ionized particles in pp collisions in LHC Run-2 using the Full MoEDAL detector. arXiv: 2311.06509

B. Acharya other. 2024. MoEDAL explores magnetic monopoles generated by the Schwinger effect in CMS beam pipes. arXiv: 2402.15682

Source: www.sci.news

Physicists at CERN release data on the discovery of the Higgs particle

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Physicist from CMS cooperation at CERN just published the combination of CMS measurements that helped establish the discovery of the Higgs boson in 2012.

CMS event display showing a Higgs boson candidate decaying into two photons. It is one of two decay channels that were key to the particle’s discovery. Image credit: CERN.

“Physical measurements based on data from CERN’s Large Hadron Collider (LHC) are typically reported as central values and corresponding uncertainties,” the CMS physicists said.

“For example, shortly after observing the Higgs boson in the LHC’s proton-proton collision data, CMS determined its mass to be 125.3 plus or minus 0.6 GeV (the mass of a proton is about 1 GeV).”

“But this figure is just a quick summary of the measurements, and is like the title of a book.”

In measurement, the complete information extracted from the data is encoded into a mathematical function known as a likelihood function. This function includes measurements of quantities and dependence on external factors.

“For CMS measurements, these factors include the calibration of the CMS detector, the accuracy of the CMS detector simulation used to facilitate the measurements, and other systematic effects,” the researchers said.

“To fully understand the nasty collisions that occur at the LHC, many aspects need to be determined, so the likelihood function for measurements based on LHC data can be complex.”

“For example, the likelihood function for the combined CMS Higgs boson discovery measurement that CMS just released in electronic form has nearly 700 parameters for a fixed value of the Higgs boson mass.”

“Only one of these, the number of Higgs bosons found in the data, is an important physical parameter, and the rest model systematic uncertainties.”

“Each of these parameters corresponds to a dimension of a multidimensional abstract space in which the likelihood function can be drawn.”

“It is difficult for humans to visualize spaces that contain multiple dimensions, much less spaces that contain many dimensions.”

The new release of the CMS Higgs boson discovery measurement likelihood function, the first publicly available likelihood function from this collaboration, allows researchers to avoid this problem.

Using a publicly accessible likelihood function, physicists outside the CMS Collaboration can now accurately incorporate CMS Higgs boson discovery measurements into their studies.

“The release of this likelihood function and the Combine software used to model likelihood and fit data marks another milestone in CMS’s 10-year commitment to fully open science.” said the people.

“This joins hundreds of open access publications, the release of nearly 5 petabytes of CMS data on the CERN Open Data Portal, and the publication of the entire software framework on GitHub.”

Source: www.sci.news

Physicists at CERN successfully measure a key parameter of the Standard Model

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Physicists from the CMS Collaboration at CERN’s Large Hadron Collider (LHC) have successfully measured the effective leptonic electroweak mixing angle. The results were presented at the annual general meeting. Rencontre de Morion Conference is the most accurate measurement ever made at the Hadron Collider and is in good agreement with predictions from the Standard Model of particle physics.

Installation of CMS beam pipe. Image credit: CERN/CMS Collaboration.

The Standard Model is the most accurate description of particles and their interactions to date.

Precise measurements of parameters, combined with precise theoretical calculations, provide incredible predictive power that allows us to identify phenomena even before we directly observe them.

In this way, the model has succeeded in constraining the masses of the W and Z particles, the top quark, and recently the Higgs boson.

Once these particles are discovered, these predictions serve as a consistency check on the model, allowing physicists to explore the limits of the theory’s validity.

At the same time, precise measurements of the properties of these particles provide a powerful tool for exploring new phenomena beyond the standard model, so-called “new physics.” This is because new phenomena appear as mismatches between different measured and calculated quantities.

The electroweak mixing angle is a key element of these consistency checks. This is a fundamental parameter of the Standard Model and determines how unified electroweak interactions give rise to electromagnetic and weak interactions through a process known as electroweak symmetry breaking.

At the same time, we mathematically connect the masses of the W and Z bosons that transmit weak interactions.

Therefore, measurements of W, Z, or mixed angles provide a good experimental cross-check of the model.

The two most accurate measurements of the weak mixing angle were made by experiments at CERN’s LEP collider and by the SLD experiment at the Stanford Linear Accelerator Center (SLAC).

These values ​​have puzzled physicists for more than a decade because they don’t agree with each other.

The new results are in good agreement with standard model predictions and are a step towards resolving the discrepancy between standard model predictions and measurements of LEP and SLD.

“This result shows that precision physics can be performed at the Hadron Collider,” said Dr. Patricia McBride, spokesperson for the CMS Collaboration.

“The analysis had to deal with the challenging environment of LHC Run 2, with an average of 35 simultaneous proton-proton collisions.”

“This paves the way for even more precise physics, where more than five times as many proton pairs collide simultaneously at the high-luminosity LHC.”

Precise testing of Standard Model parameters is a legacy of electron-positron collider such as CERN’s LEP, which operated until 2000 in the tunnel that now houses the LHC.

Electron-positron collisions provide a clean environment ideal for such high-precision measurements.

Proton-proton collisions at the LHC are more challenging for this type of research, even though the ATLAS, CMS, and LHCb experiments have already yielded numerous new ultra-high-precision measurements.

This challenge is primarily due to the vast background from physical processes other than those studied, and the fact that protons, unlike electrons, are not subatomic particles.

With the new results, it seemed impossible to reach accuracy similar to that of the electron-positron collider, but now it has been achieved.

The measurements presented by CMS physicists use a sample of proton-proton collisions collected from 2016 to 2018 at a center of mass energy of 13 TeV and a total integrated luminosity of 137 fb.−1 or about 11 billion collisions.

“The mixing angle is obtained through analysis of the angular distribution in collisions in which pairs of electrons or muons are produced,” the researchers said.

“This is the most accurate measurement ever made at the Hadron Collider and improves on previous measurements by ATLAS, CMS, and LHCb.”

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Physicists at CERN witness the creation of two tau leptons from two photons during a proton-proton collision

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According to physicists, CMS cooperation This is the first time this process has been observed in proton-proton collisions at CERN's Large Hadron Collider (LHC). This is also the most accurate measurement of tau's anomalous magnetic moment and provides a new way to constrain the existence of new physics.

We reproduced candidate events of the γγ →ττ process in proton-proton collisions measured by the CMS detector. Tau can decay into muons (red), charged pions (yellow), and neutrinos (not visible). Energy is stored in green in an electromagnetic calorimeter and cyan in a hadronic calorimeter. Image credit: CMS Collaboration.

of TauIt is a special particle of the lepton family, also called tauon.

In general, leptons, together with quarks, constitute the matter content of the Standard Model.

Tau was first discovered in the 1970s, and its associated neutrino (tau neutrino) was discovered by Fermilab's DONUT collaboration in 2000 to complete the tangible matter part.

However, tau has a very short lifetime and can remain stable for only 290*10 hours, making it quite difficult to study it accurately.-15 seconds.

Two other charged leptons, electrons and muons, are fairly well studied.

Much is also known about their magnetic moments and their associated anomalous magnetic moments.

The former can be understood as the strength and direction of a virtual bar magnet within the particle.

However, this measurable quantity requires correction at the quantum level resulting from the virtual particles pulling on the magnetic moment and deviates from the predicted value.

The quantum correction, called the anomalous magnetic moment, is about 0.1%.

If the theoretical and experimental results do not agree, this anomalous magnetic momentIopens the door to physics beyond the Standard Model.

The anomalous magnetic moment of the electron is one of the most accurately known quantities in particle physics and is in perfect agreement with models.

Its muon counterpart, on the other hand, is one of the most studied, and research is ongoing.

So far, theory and experiment are largely in agreement, but recent results raise tensions that require further investigation.

But for Tau, the race is still on. Its anomalous magnetic moment is particularly difficult to measure.τThis is because tau has a short lifespan.

The first attempt wasτ After the discovery of tau, there was an uncertainty 30 times higher than the size of the quantum correction.

Experimental efforts at CERN improved the constraints and reduced the uncertainty to 20 times the size of the quantum correction.

In collisions, physicists look for special processes. That is, two photons interact to produce two tau leptons (also called a ditau pair), which then decay into muons, electrons, or charged pions, and neutrinos.

So far, both ATLAS and CMS collaborations have observed this in ultraperipheral lead-to-lead collisions.

Now, CMS physicists report: first observation The same process occurs during proton-proton collisions.

These collisions provide greater sensitivity to physics over the standard model, as new physical effects increase with collision energy.

Taking advantage of the superior tracking capabilities of the CMS detector, the collaboration will isolate this particular process from other processes by selecting events that produce a tau with no other tracking within a distance of just 1 mm. I was able to separate it.

“This remarkable achievement in detecting proton-proton collisions in the super-periphery sets the stage for many breakthrough measurements of this kind from CMS experiments,” said Dr. Michael Pitt, a member of the CMS team. said.

This new method provided a new way to constrain tau's anomalous magnetic moments, and the CMS Collaboration quickly put it to the test.

Future driving data will likely improve the significance, but their new measurements impose the tightest constraints to date, with greater precision than ever before.

This reduces the prediction uncertainty to just three times the size of the quantum correction.

“We're really excited to finally be able to narrow down some of the fundamental properties of the elusive tau lepton,” said CMS team member Dr. Isaac Neutelings.

“This analysis introduces a new approach to investigating tau g-2 and revitalizes a measurement that has been stagnant for more than 20 years,” said CMS team member Dr. Xuelong Qin.

Source: www.sci.news

Physicists at CERN Discover Intriguing New Decay Mode of Mesons

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Physicists from LHCb collaboration at CERN’s Large Hadron Collider (LHC) have made the first observation of the collapse of the Bc+ meson. This results in a J/ψ charm-anticharm quark bound state (consisting of two heavy quarks, b and c) and a pair of pions π+π0. This new decay process shows a contribution from an intermediate particle, the ρ+ meson, which forms for a short time and then decays into π+π0 pairs.

September 2016, LHCb experimental cave at LHC IP8. Image courtesy of CERN.

The Bc+ is the heaviest meson and decays only through weak interactions due to the decay of one heavy constituent quark.

It decays into an odd number of optical hadrons, and J/ψ (or another attractive and anti-attractive quark-bound state called Charmonia) has been intensively studied and found to be in remarkable agreement with theoretical predictions.

The decay of Bc+ to J/ψ and π+π0 pairs is the simplest decay to charmonium and even-numbered optical hadrons.

This has never been observed before. The main reason for this is that in the LHC proton-proton collision environment, it is very difficult to accurately reconstruct low-energy π0 mesons through their decay into a pair of photons.

“Accurate measurements of the Bc+→J/ψπ+π0 decay will allow us to better understand its possible contribution as a background source for the study of other decays of Bc mesons and rare decays of B0 mesons,” said the LHCb physicist.

From a theoretical point of view, J/ψ and the decay of Bc into an even number of pions are closely related to the decay of the τ lepton into an even number of pions and the e+e- annihilation into an even number of pions.

Accurate measurements of e+e- annihilation into two pions in the ρ mass region (like the Bc decay discussed here) are possible using the Fermilab G-2 experiment, which measures the anomalous magnetic dipole moment of the muon and is important for interpreting the results. The annihilation of low-energy e+e- into hadrons is an important source of uncertainty in g-2 measurements.

The ratio of the probability of a new decay to the probability of a decay from Bc+ to J/ψπ+ has been calculated by various theorists over the past 30 years.

Now these predictions can finally be compared with experimental measurements. Most predictions agree with the new result 2.80±0.15±0.11±0.16.

The large number of b quarks produced in LHC collisions and the excellent detectors allow LHCb researchers to study the formation, decay, and other properties of Bc+ mesons in detail.

“Since the discovery of the meson by the Tevatron Collider’s CDF experiment, 18 new Bc+ decays (with more than 5 standard deviations) have been observed, all from the LHCb,” the researchers said.

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LHCb collaboration. 2024. Observation of B+c→J/ψπ+π0 collapse. arXiv: 2402.05523

Source: www.sci.news