Search for Heavy Bosons at the LHC

Scientists at the ATLAS detector have been looking for new heavy particles called Bosons produced from proton-proton Collisions. These collisions took place at the Large Hadron Collider (LHC) with a high energy of 13 TeV. The focus of this research was on events that produced four Leptons (which can be electrons or muons) and missing energy or jets. The Data analyzed were collected from 2015 to 2018, amounting to a total of 139 fb of integrated luminosity.

#Basics of the Study

The researchers wanted to find evidence of heavy bosons that might decay into leptons and potentially connect to dark matter. They were particularly interested in two types of bosons: one that could behave like the standard Higgs boson but heavier, and another that could be a new type of particle that does not interact directly with regular matter.

The mass of these bosons was expected to be in specific ranges: from 390 to 1300 GeV for one type of boson and from 220 to 1000 GeV for another.

#The Role of the ATLAS Detector

The ATLAS detector is a sophisticated piece of equipment designed to capture and analyze the data from particle collisions. It is built to monitor nearly all angles around the collision point. It has several components including tracking devices, calorimeters to measure energy, and muon detectors.

The inner tracking detector helps track particles generated from the collision. Surrounding it are calorimeters, which are crucial for measuring the energy of different particles. Lastly, the muon spectrometer measures the paths of muons, which are a type of lepton.

#Data Collection and Triggers

The data for this research were collected through various collision events where some particles were detected while others were missing. This missing energy is crucial because it may indicate the presence of dark matter particles.

The event selection process involved using specific triggers designed to collect data based on certain conditions, ensuring that the significant collisions were recorded. Different triggers were employed depending on the type of lepton detected, resulting in a diverse data set.

#Simulation of Events

To understand what to expect in real collision events, scientists used Monte Carlo simulations. These simulations generate artificial data that mimic possible outcomes from collisions based on known physics principles. Different kinds of background events, including those that may resemble the signal, were also simulated for comparison.

#Selection of Relevant Signals

The actual analysis involved selecting events that matched predefined criteria for four-lepton states and associated Energies. This would help narrow down the search for new bosons amidst a background of other possible interactions.

Events were categorized based on specific characteristics, such as the number of jets produced and the missing energy. The search focused on cases where the combined energy of the lepton pairs was above 200 GeV.

#Background Processes

Understanding the background processes is crucial. It is essential to distinguish potential signals of new physics from standard model processes that occur more frequently. In this case, the primary background source came from the decay of Z bosons, which themselves decay into lepton pairs. The analysis showed that most background events came from quark-antiquark annihilation.

#Analysis Techniques

A detailed analysis was carried out to determine which events could potentially be linked to the presence of heavy bosons. Specific kinematic variables were examined to optimize the sensitivity of the search.

The analysis involved fitting the observed data against the expected behavior of standard model backgrounds. If the data showed deviations, it could suggest the presence of heavy new bosons.

#Systematic Uncertainties

Throughout the analysis, systematic uncertainties were considered. These include factors that could affect measurements, like the efficiency of the detectors and the accuracy of simulations. Each uncertain factor was evaluated based on its potential impact on the results.

#Results

After extensive analysis, no significant deviations from the standard model predictions were found. This means that no new heavy bosons were conclusively detected in the data. Instead, researchers were able to set upper limits on the possible production rates of these bosons.

For the heavy bosons searched, the observed limits ranged from 6.8 fb to 119.2 fb in one category, while for the other category of bosons, limits were between 2.1 fb to 32.3 fb.

#Conclusion

The research into heavy bosons at the LHC contributes to the broader understanding of particle physics. While no new heavy particles were found, the results from this study provide important constraints on theoretical models predicting such particles. The findings help improve the overall picture of the particle physics landscape and guide future searches for new phenomena.

#Acknowledgments

The successful operation of the LHC and the efficient running of the ATLAS experiment relied heavily on the support of various institutions and organizations. Their contributions are essential for advancing knowledge in the field of particle physics and understanding the fundamental structures of matter.