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Searching for heavy new particles with the ATLAS Experiment


Figure 1: Post-fit distributions of the mixed mass of the W boson and Higgs boson candidates in a single sign area of curiosity for W’. (Here the two b-tag, merged area.) The stable coloured area signifies the Standard Model background, the black factors with error bars point out the experimental information, and the dashed line signifies hypothetical occasions for a 2 TeV W’ boson. The backside plot exhibits the ratio of information to the total Standard Model background. Credit: ATLAS Collaboration/CERN

Since discovering the Higgs boson in 2012, the ATLAS Collaboration at CERN has been working to grasp its properties. One query specifically 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 Standard Model implies it has much larger mass and requires a really massive correction to the arithmetic in an effort to align concept with statement, resulting in the “naturalness problem.”


This discrepancy could possibly be resolved if a brand new kind of interplay existed, along with the 4 recognized (gravity, electromagnetism, sturdy and weak). This interplay would end in new force-carrying particles (bosons) with plenty a lot bigger than something at the moment within the Standard Model. Among a number of theories describing this interplay are the “heavy vector triplet” (HVT) fashions, which recommend {that a} new particle—the “W prime” (W’) —could possibly be produced with the collision energies accessible on the LHC. As the title implies, these new heavy particles would work together with the electroweak pressure and, after being produced in a collision, would in a short time decay right into a W boson and Higgs boson.

A new search from the ATLAS Collaboration, launched this week on the Large 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” last 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
Figure 2: Combined 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 concept with a selected worth of the coupling to the Standard Model W boson. All W’ plenty beneath and to the left of every dashed line are excluded for that worth of the coupling. Credit: ATLAS Collaboration/CERN

The wide selection of attainable 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 might produce Higgs bosons with larger energies and the ensuing b-quarks would emit two “jets” (collimated sprays of particles) which are so shut collectively as to look 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 offer the very best sensitivity to the brand new particle.

As seen in Figure 2, many way more frequent Standard Model processes could end in the identical signature because the W’ decay, so it is crucially necessary to remove as a lot of this Standard Model background as attainable. 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. Additionally, bettering on the earlier seek for W’ bosons with a partial Run 2 dataset, researchers utilized novel strategies to establish and measure jets within the detector. “TrackCaloCluster” jets mixed data from ATLAS’ interior monitoring system and electromagnetic calorimeter, whereas “Variable Radius” jets may extra effectively establish Higgs bosons by permitting the radius of its decay jets to vary with completely different quantities of momentum.

Physicists discovered no statistically important proof of a deviation from the Standard Model of their search. The outcomes have been used to set new limits, proven here, on the 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 new physics continues!


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


More data:
Search for heavy resonances decaying right into a W boson and a Higgs boson in last 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.web.cern.ch/Atlas/GROUPS … ATLAS-CONF-2021-026/

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ATLAS Experiment

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Searching for heavy new particles with the ATLAS Experiment (2021, June 10)
retrieved 10 June 2021
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