Refining the Standard Model and Exploring Fundamental Forces

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This study investigates the ttW process and its implications for the scientific community and humanity. By refining the Standard Model and understanding fundamental particle interactions, researchers can uncover the principles governing the universe and potentially contribute to breakthroughs in various fields. Continued exploration of particle physics may lead to innovative technologies and advancements that benefit society.

Unexpected Abundance of Particle Triplet Discovered at Large Hadron Collider

The ATLAS experiment has verified that a trio of particles, consisting of a top-antitop quark pair and a W boson, appears more frequently than anticipated following proton-proton collisions within the Large Hadron Collider (LHC). The formation of these three particles, known as ttW, is a rare occurrence, as only one in every 50,000 collisions at the LHC results in their creation. Due to the short-lived nature of top quarks and W bosons, which decay almost instantly, the researchers identified ttW events based on the electrons and muons they decay into.

Over the past three years, the ATLAS team at the Department of Energy’s SLAC National Accelerator Laboratory has conducted an intricate analysis to measure this process. The researchers developed innovative methods to estimate and eliminate background and detector effects, ensuring the accuracy and precision of the analysis. These findings will aid in testing theories of elementary particle physics and support experimentalists working on other particle physics processes.

Brendon Bullard, research associate at SLAC National Accelerator Laboratory and head of this data analysis, stated, “The only measurements of ttW production come from the LHC — it is the first collider that can produce these types of events at a large enough rate to be measured.”

Discrepancy in Particle Triplet Production Raises Questions About the Standard Model

The ttW process was initially observed by ATLAS in 2015 using data collected during the LHC’s Run 1, which spanned from 2010 to 2012. Later measurements using a portion of the data obtained during Run 2 (2015–2018) hinted that ttW was appearing more frequently than predicted by the Standard Model of particle physics, which serves as a framework for understanding subatomic particle behavior.

The most recent measurement, utilizing the entire dataset gathered by ATLAS during Run 2, resulted in a more accurate assessment of ttW, revealing the overall production rate to be approximately 20 percent higher than theoretical estimates. This excess has been supported by new findings from the CMS experiment.

Bullard mentioned that the reason for this inconsistency remains uncertain, but the results seem to suggest an unaccounted factor is at play. It is possible that new physics beyond the Standard Model is involved.

Alternatively, it may be that current models are missing essential components for accurately predicting ttW production. Theorists make predictions from the Standard Model using stepwise approximations of increasing complexity, and it is possible that unaccounted-for subtle effects in these approximations can explain the inconsistency.

In either case, theorists must now attempt to uncover the truth by considering these yet-to-be-calculated subtle effects while approximating ttW production.

Bullard noted, “This is something that hasn’t been done before because it’s very hard. But now, with our result, there’s already theorists who are interested in putting in the effort.” He added, “This measurement will be very useful to continue to better understand the Standard Model and maybe even identify some beyond-the-Standard-Model effects if we’re lucky.”

Enhanced Understanding of Particle Interactions Offers New Insights into Fundamental Forces

By further examining the characteristics of ttW events, scientists can gain valuable insights into the fundamental forces acting between the two quarks and the W boson, including the strong interaction, which holds quarks together, and the electroweak interaction, responsible for electromagnetism and radioactive decay.

Improved measurements will also assist in the investigation of even scarcer processes occurring during proton collisions. ttW serves as a significant background for two other processes observed at the LHC. Previously, physicists had to estimate ttW production and remove it from the data to identify the signal they were seeking. With a more precise measurement of ttW now available, these rare signals can be more accurately detected.

One such process is the production of two top quarks and a Higgs boson, the particle responsible for giving mass to certain particles, such as quarks and W bosons. This event, known as ttH, is 10 times rarer than ttW when considering the electrons and muons into which it decays. Enhanced measurements of ttH will enable physicists to assess the strength of the Higgs’ interaction with the top quark, a crucial test of the Standard Model that can reveal insights into the origin of mass.

The other process affected by ttW is the production of four top quarks, an event that is 50 times rarer and was recently observed for the first time by both ATLAS and CMS. Further study will allow physicists to investigate new physics potentially involving top quarks, the heaviest particle in the Standard Model.

Zhi Zheng, a research associate at SLAC who supervised the four top quark analysis at ATLAS and assisted Bullard with the ttW analysis, stated, “Improved understanding of the ttW process, especially with this result, can further improve the four top measurements and precision, allowing us to explore more properties of this process.” Their collaboration at SLAC enabled the pair to crosscheck these interconnected measurements.

Bullard added, “Being at SLAC together has allowed a greater connection and collaboration between these two measurements.”

What Does All This Mean?

The significance of all these findings for humanity and the scientific community lies in advancing our understanding of fundamental particle physics. By probing and refining the Standard Model, researchers can uncover the fundamental principles governing the universe at the subatomic level. This knowledge can potentially lead to breakthroughs in various scientific fields, such as material science, energy production, and understanding the origins of the universe.

Moreover, the discovery of new particles or interactions beyond the Standard Model could pave the way for novel technologies and innovations that we cannot yet foresee. By continually pushing the boundaries of our knowledge, we can unlock the potential for future advancements that will ultimately benefit humanity.

Deep Dive

  1. Aaboud, M., Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Abeloos, B., … & Abreu, R. (2017). Measurement of the top quark mass in the tt¯→ lepton+jets and tt¯→ dilepton channels using √s= 7 TeV ATLAS data. The European Physical Journal C, 77(7), 1–30.
  2. Aad, G., Abajyan, T., Abbott, B., Abdallah, J., Abdel Khalek, S., Abdelalim, A. A., … & Aben, R. (2012). Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC. Physics Letters B, 716(1), 1–29.
  3. Chatrchyan, S., Khachatryan, V., Sirunyan, A. M., Tumasyan, A., Adam, W., Aguilo, E., … & Amsler, C. (2012). Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC. Physics Letters B, 716(1), 30–61.
  4. Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Aben, R., Abolins, M., … & Abreu, R. (2016). Measurements of top-quark pair differential cross-sections in the eμ channel in pp collisions at √s= 13 TeV using the ATLAS detector. Journal of High Energy Physics, 2016(8), 1–53.
  5. Sirunyan, A. M., Tumasyan, A., Adam, W., Ambrogi, F., Asilar, E., Bergauer, T., … & Dragicevic, M. (2018). Observation of tt¯H production. Physical review letters, 120(23), 231801.


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