Determination of Jet Energy Calibration and Transverse Momentum Resolution in CMS (1107.4277v1)

Abstract: Measurements of the jet energy calibration and transverse momentum resolution in CMS are presented, performed with a data sample collected in proton-proton collisions at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 36 inverse picobarns. The transverse momentum balance in dijet and gamma/Z+jets events is used to measure the jet energy response in the CMS detector, as well as the transverse momentum resolution. The results are presented for three different methods to reconstruct jets: a calorimeter-based approach, the "Jet-Plus-Track" approach, which improves the measurement of calorimeter jets by exploiting the associated tracks, and the "Particle Flow" approach, which attempts to reconstruct individually each particle in the event, prior to the jet clustering, based on information from all relevant subdetectors.

• The paper presents advanced calibration techniques that achieve sub-3% energy uncertainty for jets with pT > 50 GeV.
• It compares three jet reconstruction methods, demonstrating improved accuracy with Jet-Plus-Track and Particle-Flow approaches over CALO jets.
• It measures transverse momentum resolution using dijet asymmetry and γ+jet balancing, highlighting close agreement between simulation and observed data.

Jet Energy Calibration and Transverse Momentum Resolution in CMS

Overview

The CMS (Compact Muon Solenoid) experiment, conducted at CERN's LHC, necessitates precise calibration of jet energy measurements and resolution of transverse momentum for executing various high-energy physics analyses. The paper under discussion explores methodologies adopted for calibration and resolution using data from proton-proton collisions at a center-of-mass energy of 7 TeV, with an integrated luminosity of 36 pb$^{-1}$.

Jet Reconstruction Techniques

Jets are reconstructed employing three distinct methods:

1. Calorimeter-based jets (CALO jets) rely on energy deposits in calorimeter towers.
2. Jet-Plus-Track (JPT) methods enhance CALO jets by incorporating tracking information, refining both the energy resolution and accuracy of direction.
3. Particle-Flow (PF) approach combines information from all relevant sub-detectors, aiming at a comprehensive particle reconstruction before jet clustering.

Calibration and Resolution Measurement

Energy Calibration

The calibration strategy focuses on aligning the detected energy with the true particle jet energy. It consists of multiple stages:

• Offset Correction: This removes excess energy contributions like pile-up and noise using methods such as jet area and hybrid offset techniques.
• MC Calibration: A Monte Carlo-based simulation that adjusts the detector's non-linear and non-uniform responses over different jet $p_T$ and $\eta$ ranges.
• Residual Corrections: Address any remaining discrepancies between data and simulation.

The calibration establishes not only a more uniform energy scale but also reduces systematic uncertainties, achieving sub-3% uncertainty for $p_T >50 \text{ GeV}$ across most detector regions, though it rises in forward areas.

Transverse Momentum Resolution

The paper employs dijet asymmetry and $\gamma$+jet balancing to gauge $p_T$ resolution. Dijet asymmetry harnesses the expected balance in back-to-back jets, while the $\gamma$+jet method correlates jet $p_T$ with that of an accurately measurable photon.

MC simulated events present a resolution baseline which is further refined based on observed data, revealing broader resolutions in measurements than predicted by simulation. With efforts to mitigate various biases, the research achieves insightful agreements between simulation and experimental data.

Key Findings and Implications

The results underscore a need for excellent control over systematic uncertainties to leverage high-energy physics studies that rely heavily on jet measurements. With improved calibration and resolution strategies, detectors can achieve higher precision in identifying and measuring jet properties, which is crucial for unraveling phenomena like potential new particles beyond the Standard Model.

Forward-Thinking Considerations

The paper serves as a reference for future enhancements in detector technology and algorithms, facilitating more accurate high-energy physics investigations. This is crucial as research pushes toward exploring uncharted energies and particle interactions at colliders. Indirectly, advancements in technologies associated with jet calibration and resolution could also improve systems relying on similar detection principles, like those in medical imaging modalities.