Looking for heavy new particles with the ATLAS Experiment

Determine 1: Publish-fit distributions of the mixed mass of the W boson and Higgs boson candidates in a single sign area of curiosity for W’. (Right here the two b-tag, merged area.) The strong coloured area signifies the Normal Mannequin background, the black factors with error bars point out the experimental knowledge, and the dashed line signifies hypothetical occasions for a 2 TeV W’ boson. The underside plot reveals the ratio of knowledge to the full Normal Mannequin background. Credit score: ATLAS Collaboration/CERN

Since discovering the Higgs boson in 2012, the ATLAS Collaboration at CERN has been working to know its properties. One query particularly stands out: why does the Higgs boson have the mass that it does? Experiments have measured its mass to be round 125 GeV—but the Normal Mannequin implies it has a lot bigger mass and requires a really giant correction to the arithmetic as a way to align principle with statement, resulting in the “naturalness downside.”

This discrepancy may very well be resolved if a brand new sort of interplay existed, along with the 4 identified basic forces (gravity, electromagnetism, sturdy and weak). This interplay would lead to new force-carrying particles (bosons) with plenty a lot bigger than something at the moment within the Normal Mannequin. Amongst a number of theories describing this interplay are the “heavy vector triplet” (HVT) fashions, which recommend {that a} new particle—the “W prime” (W’) boson—may very well be produced with the collision energies accessible on the LHC. Because the identify implies, these new heavy particles would work together with the electroweak power and, after being produced in a collision, would in a short time decay right into a W boson and Higgs boson.

A brand new search from the ATLAS Collaboration, launched this week on the Giant Hadron Collider Physics convention (LHCP 2021), units limits on the mass of the W’ boson, utilizing the total LHC Run 2 dataset collected between 2015 and 2018. The search targets the “semileptonic” closing state, the place the Higgs boson decays right into a pair of b-quarks, and the W boson decays into each a neutrino and one electron, muon or tau lepton.

Searching for heavy new particles with the ATLAS Experiment
Determine 2: Mixed 95% noticed (anticipated) exclusion limits on the manufacturing cross part of the W’ boson are proven by the black (blue) line. The purple and blue dashed strains point out the theoretical cross part vs mass for a model of the HVT principle with a selected worth of the coupling to the Normal Mannequin W boson. All W’ plenty under and to the left of every dashed line are excluded for that worth of the coupling. Credit score: ATLAS Collaboration/CERN

The wide selection of potential plenty for the W’ boson—from 400 GeV to five TeV—offered ATLAS physicists with some distinctive challenges. If the W’ mass is on the heavier finish of the predictions, it could produce Higgs bosons with larger energies and the ensuing b-quarks would emit two “jets” (collimated sprays of particles) which can be so shut collectively as to seem as a single jet with a big radius within the ATLAS detector. Smaller W’ plenty, then again, would seem as two distinct jets. To account for this nice variation of options, the brand new ATLAS evaluation studied a number of distinct channels, every particularly optimized to supply the perfect sensitivity to the brand new particle.

As seen in Determine 2, many much more frequent Normal Mannequin processes might lead to the identical signature because the W’ decay, so it is crucially vital to get rid of as a lot of this Normal Mannequin background as potential. ATLAS physicists employed a multi-variate algorithm that used sure kinematic options of b-quark decays to attempt to distinguish their decay jets from different, lighter flavors of hadrons, creating “one b-tag” and “two b-tag” areas. Moreover, enhancing on the earlier seek for W’ bosons with a partial Run 2 dataset, researchers utilized novel strategies to determine and measure jets within the detector. “TrackCaloCluster” jets mixed info from ATLAS’ interior monitoring system and electromagnetic calorimeter, whereas “Variable Radius” jets may extra effectively determine Higgs bosons by permitting the radius of its decay jets to vary with totally different quantities of momentum.

Physicists discovered no statistically important proof of a deviation from the Normal Mannequin of their search. The outcomes have been used to set new limits, proven right here, on the mass of a hypothetical W’ boson, excluding plenty as much as 3.15 TeV, which is an almost 12% enhance from the earlier ATLAS seek for a HVT W’ boson with a partial Run 2 dataset. The hunt for brand spanking new physics continues!


ATLAS experiment searches for ‘charming’ decay of the Higgs boson


Extra info:
Seek for heavy resonances decaying right into a W boson and a Higgs boson in closing states with leptons and b-jets in 139 fb−1 of proton–proton collisions at 13 TeV with the ATLAS detector (ATLAS-CONF-2021-026): atlas.net.cern.ch/Atlas/GROUPS … ATLAS-CONF-2021-026/

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Looking for heavy new particles with the ATLAS Experiment (2021, June 10)
retrieved 10 June 2021
from https://phys.org/information/2021-06-heavy-particles-atlas.html

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