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Jun 10, 2024

ATLAS chases long-lived particles with the Higgs boson

Posted by in categories: cosmology, information science, particle physics, robotics/AI

The Higgs boson has an extremely short lifespan, living for about 10–22 seconds before quickly decaying into other particles. For comparison, in that brief time, light can only travel about the width of a small atomic nucleus. Scientists study the Higgs boson by detecting its decay products in particle collisions at the Large Hadron Collider. But what if the Higgs boson could also decay into unexpected new particles that are long-lived? What if these particles can travel a few centimeters through the detector before they decay? These long-lived particles (LLPs) could shed light on some of the universe’s biggest mysteries, such as the reason matter prevailed over antimatter in the early universe and the nature of dark matter. Searching for LLPs is extremely challenging because they rarely interact with matter, making them difficult to observe in a particle detector. However, their unusual signatures provide exciting prospects for discovery. Unlike particles that leave a continuous track, LLPs result in noticeable displacements between their production and decay points within the detector. Identifying such a signature requires dedicated algorithms. In a new study submitted to Physical Review Letters, ATLAS scientists used a new algorithm to search for LLPs produced in the decay of Higgs bosons. Boosting sensitivity with a new algorithm Figure 1: A comparison of the radial distributions of reconstructed displaced vertices in a simulated long-lived particle (LLP) sample using the legacy and new (updated) track reconstruction configurations. The circular markers represent reconstructed vertices that are matched to LLP decay vertices and the dashed lines represent reconstructed vertices from background decay vertices (non-LLP). (Image: ATLAS Collaboration/CERN) Despite being critical to the LLP searches, dedicated reconstruction algorithms were previously so resource intensive that they could only be applied to less than 10% of all recorded ATLAS data. Recently, however, ATLAS scientists implemented a new “Large-Radius Tracking” algorithm (LRT), which significantly speeds up the reconstruction of charged particle trajectories in the ATLAS Inner Detector that do not point back to the primary proton-proton collision point, while drastically reducing backgrounds and random combinations of detector signals. The LRT algorithm is executed after the primary tracking iteration using exclusively the detector hits (energy deposits from charged particles recorded in individual detector elements) not already assigned to primary tracks. As a result, ATLAS saw an enormous increase in the efficiency of identifying LLP decays (see Figure 1). The new algorithm also improved CPU processing time more than tenfold compared to the legacy implementation, and the disk space usage per event was reduced by more than a factor of 50. These improvements enabled physicists to fully integrate the LRT algorithm into the standard ATLAS event reconstruction chain. Now, every recorded collision event can be scrutinized for the presence of new LLPs, greatly enhancing the discovery potential of such signatures. Physicists are searching for Higgs bosons decaying into new long-lived particles, which may leave a ‘displaced’ signature in the ATLAS detector. Exploring the dark with the Higgs boson Figure 2: Observed 95% confidence-limit on the decay of the Higgs boson to a pair of long-lived s particles that decay back to Standard-Model particles shown as a function of the mean proper decay length ( of the long-lived particle. The observed limits for the Higgs Portal model from the previous ATLAS search are shown with the dotted lines. (Image: ATLAS Collaboration/CERN) In their new result, ATLAS scientists employed the LRT algorithm to search for LLPs that decay hadronically, leaving a distinct signature of one or more hadronic “jets” of particles originating at a significantly displaced position from the proton–proton collision point (a displaced vertex). Physicists also focused on the Higgs “portal” model, in which the Higgs boson mediates interactions with dark-matter particles through its coupling to a neutral boson s, resulting in exotic decays of the Higgs boson to a pair of long-lived s particles that decay into Standard-Model particles. The ATLAS team studied collision events with unique characteristics consistent with the production of the Higgs boson. The background processes that mimic the LLP signature are complex and challenging to model. To achieve good discrimination between signal and background processes, ATLAS physicists used a machine learning algorithm trained to isolate events with jets arising from LLP decays. Complementary to this, a dedicated displaced vertex reconstruction algorithm was used to pinpoint the origin of hadronic jets originating from the decay of LLPs. This new search did not uncover any events featuring Higgs-boson decays to LLPs. It improves bounds on Higgs-boson decays to LLPs by a factor of 10 to 40 times compared to the previous search using the exact same dataset (see Figure 2)! For the first time at the LHC, bounds on exotic decays of the Higgs boson for low LLP masses (less than 16 GeV) have surpassed results for direct searches of exotic Higgs-boson decays to undetected states. About the event display: A 13 TeV collision event recorded by the ATLAS experiment containing two displaced decay vertices (blue circles) significantly displaced from the beam line showing “prompt” non displaced decay vertices (pink circles). The event characteristics are compatible with what would be expected if a Higgs boson is produced in association with a Z boson (decaying to two electrons indicated by green towers), and decayed into two LLPs (decaying into two b-quarks each). Tracks shown in yellow and jets are indicated by cones. The green and yellow blocks correspond to energy deposition in the electromagnetic and hadronic calorimeters, respectively. (Image: ATLAS Collaboration/CERN) Learn more Search for light long-lived particles in proton-proton collisions at 13 TeV using displaced vertices in the ATLAS inner detector (Submitted to PRL, arXiv:2403.15332, see figures) Performance of the reconstruction of large impact parameter tracks in the inner detector of ATLAS (Eur. Phys. J. C 83 (2023) 1,081, arXiv:2304.12867, see figures) Search for exotic decays of the Higgs boson into long-lived particles in proton-proton collisions at 13 TeV using displaced vertices in the ATLAS inner detector (JHEP 11 (2021) 229, arXiv:2107.06092, see figures)

Jun 10, 2024

Physicists overcome two key operating hurdles in fusion reactions

Posted by in categories: energy, physics

A team of physicists from several institutions across the U.S. working with a colleague from China, at the DIII-D National Fusion Facility, in San Diego, California, has devised a way to overcome two key hurdles standing in the way of using fusion as a general power source.

Jun 10, 2024

Cancer-fighting antibodies inject chemo directly into tumor cells, upping effectiveness

Posted by in category: biotech/medical

Oncologists have grown increasingly excited about “antibody drug conjugates,” which allow for the use of more potent chemotherapy agents with fewer side effects.

Jun 10, 2024

‘Quantum optical antennas’ provide more powerful measurements on the atomic level

Posted by in categories: particle physics, quantum physics

Similar to how a radio antenna plucks a broadcast from the air and concentrates the energy into a song, individual atoms can collect and concentrate the energy of light into a strong, localized signal that researchers can use to study the fundamental building blocks of matter.

Jun 10, 2024

Large-scale, lab-grown meat: Step inside a cultivated meat factory

Posted by in categories: futurism, sustainability

Lab-grown meat, cultivated meat, cell-based meat, slaughter-free meat: All of these terms refer to the process of creating real meat from animal cells, despite names that may allude to a vegan product.

What benefits are there to growing meat from chicken cells rather than raising animals for slaughter? Industrial animal agriculture is responsible for an estimated 15 percent of total global greenhouse gas emissions, and with demand for meat projected to double in the next decade, this technology could offer a more sustainable option for future carnivores.

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Jun 10, 2024

LEE LECTURE: WILCZEK, Frank, “My Life With QCD” — 04/09/2024

Posted by in category: quantum physics

FRANK WILCZEK Herman Feshbach Professor of Physics, MIT; Chief Scientist, T. D. Lee Institute and Wilczek Quantum Center, Shanghai Jiao Tong University; Distinguished Professor, Arizona State University; Professor of Physics, Stockholm University; 2004 Nobel Prize in Physics My Life With QCD: A…


David M. Lee Historical Lecture in Physics: FRANK WILCZEKHerman Feshbach Professor of Physics, MIT;Chief Scientist, T. D. Lee Institute and Wilczek Quantum Ce…

Jun 10, 2024

Elon Musk Speaks: All Starship Tiles will be Replaced After Flight 4 Issues!

Posted by in categories: 3D printing, Elon Musk, space travel

Elon revealed details about Starship Flight 4 outcome, Flight 5, and beyond during a gaming livestream in X.

Video Credit: Elon Musk.

Continue reading “Elon Musk Speaks: All Starship Tiles will be Replaced After Flight 4 Issues!” »

Jun 10, 2024

New material records mechanical stress through luminescence

Posted by in categories: innovation, materials

Identifying crumbling infrastructure is sometimes as difficult as rectifying it. Yet, this process has been made easier thanks to an innovative new material developed by Tohoku University researchers. Details of the findings were published in the journal Applied Physics Letters on April 25, 2024.

Jun 10, 2024

Digital twins are helping scientists run the world’s most complex experiments

Posted by in category: futurism

Engineers use the high-fidelity models to monitor operations, plan fixes, and troubleshoot problems.

Jun 10, 2024

Research team uses CRISPR/Cas9 to alter photosynthesis for the first time

Posted by in categories: biotech/medical, food, genetics

A team from the Innovative Genomics Institute at the University of California, Berkeley (UCB) has produced an increase in gene expression in a food crop by changing its upstream regulatory DNA. While other studies have used CRISPR/Cas9 gene-editing to knock out or decrease the expression of genes, new research published in Science Advances is the first unbiased gene-editing approach to increase gene expression and downstream photosynthetic activity.

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