[Paper Review] Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR

PANDA Collaboration, B. K. Singh+505 more|arXiv (Cornell University)|Jun 3, 2016

Particle physics theoretical and experimental studies6 references4 citations

TL;DR

This paper investigates the feasibility of measuring time-like proton electromagnetic form factors (FFs) at the PANDA experiment at FAIR using antiproton-proton annihilation. Through detailed Monte Carlo simulations with realistic detector modeling and event reconstruction, it demonstrates that PANDA can achieve statistical uncertainties comparable to BABAR at similar momentum transfers, enabling precise extraction of the FF ratio R over 5.4–13.9 (GeV/c²)², with total relative uncertainties of 2–48% for individual FFs and 3–57% for R.

ABSTRACT

Simulation results for future measurements of electromagnetic proton form factors at \PANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel $\bar p p o e^+ e^-$ is studied on the basis of two different but consistent procedures. The suppression of the main background channel, $ extit{i.e.}$ $\bar p p o π^+ π^-$, is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, simplified framework. However, a slightly better precision is achieved in the PandaRoot study in a large range of momentum transfer, assuming the nominal beam conditions and detector performance.

Motivation & Objective

• To assess the feasibility of measuring time-like proton electromagnetic form factors (FFs) at the PANDA experiment at FAIR.
• To evaluate the statistical precision achievable in extracting the ratio R of electric to magnetic proton FFs using realistic simulation frameworks.
• To investigate the impact of detector effects, event selection criteria, and fit functions on the uncertainty budget.
• To compare the expected performance of PANDA with existing experimental data and previous simulation studies.
• To determine the kinematic reach and systematic uncertainty contributions across the time-like region (5.4–13.9 (GeV/c²)²).

Proposed method

• Monte Carlo simulations of the process $\bar{p}p \to e^+e^-$ were performed using the PandaRoot software framework with full GEANT4-based detector simulation.
• Realistic tracking, pattern recognition, and particle identification (PID) algorithms were applied to digitized and reconstructed data to improve signal efficiency.
• Two different event selection criteria and two fit functions were used to extract the FF ratio R, with results compared across simulation setups.
• Statistical uncertainties were calculated in the angular range $|\cos\theta| \leq 0.8$ to ensure consistency with experimental analysis strategies.
• Systematic uncertainties were evaluated, including background misidentification, luminosity uncertainty, and statistical fluctuations due to low cross sections.
• The simulation framework was updated from previous studies (e.g., Sudol:2009vc) to include improved detector modeling and reconstruction algorithms.

Experimental results

Research questions

• RQ1 Can PANDA at FAIR achieve sufficient statistical precision to measure the proton electromagnetic form factor ratio R in the time-like region with uncertainties competitive with existing experiments?
• RQ2 How do different event selection criteria and fit functions affect the extraction of the FF ratio R in simulated PANDA data?
• RQ3 What are the dominant sources of systematic uncertainty in the measurement of R across the kinematic range 5.4–13.9 (GeV/c²)²?
• RQ4 To what extent does improved detector simulation and reconstruction in PandaRoot enhance signal efficiency compared to prior studies?
• RQ5 Can PANDA extend the kinematic coverage of time-like FF measurements beyond existing data, particularly at high $q^2$?

Key findings

• The statistical uncertainty on the proton FF ratio R is expected to be comparable to that achieved by the BABAR experiment at $q^2 \sim 7$ (GeV/c²)², even at higher $q^2$ values up to 13.9 (GeV/c²)².
• For $q^2 = 5.4$ and 8.2 (GeV/c²)², the results from two independent simulation setups assuming $R=1$ are consistent with each other.
• The total relative uncertainty on individual proton FFs is estimated to range from 2% to 48%, while the uncertainty on the ratio R ranges from 3% to 57% across the kinematic range.
• At lower $q^2$, background misidentification and luminosity uncertainty dominate the total uncertainty; at higher $q^2$, statistical fluctuations become the dominant source due to the decreasing $\bar{p}p \to e^+e^-$ cross section.
• Signal efficiency improved by 5–10% compared to previous studies due to enhanced selection procedures and PID capabilities in the PandaRoot framework.
• The absolute cross section measurement depends critically on luminosity precision, which is expected to be around 4%.