[Paper Review] Heavy chiral bosons search at hadron colliders

M. V. Chizhov|ArXiv.org|May 27, 2007

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper proposes a search strategy for heavy spin-1 chiral bosons at the Fermilab Tevatron and CERN LHC, using differential cross-section calculations via CalcHEP to identify resonant production and distinctive decay signatures. It identifies a potential 500 GeV signal in Tevatron data and predicts that the LHC could discover all chiral bosons up to 1 TeV if the signal is confirmed.

ABSTRACT

The production of new spin-1 chiral bosons at the hadron colliders, the Fermilab Tevatron and the CERN LHC, is considered. The masses of the chiral bosons can be determined on the basis of experimental data of precise low-energy experiments, which already indicate indirectly their existence. They can explain, for example, the serious 4.5 sigma discrepancy between the measured and the predicted two pion branching ratio of the tau decay and the sign of the 3.3 sigma deviation of the muon (g-2) theoretical prediction from the experimental value. Quantitative evaluations of the various differential cross-sections of the chiral boson production at hadron colliders are made using the CalcHEP package. It is noteworthy that the Tevatron data already hint the existence of the lightest charged chiral boson with a mass around 500 GeV. New Tevatron data and the LHC results will definitely confirm or reject this indication. In the positive case the LHC would be able to discover all predicted charged and neutral chiral bosons spanning in mass up to 1 TeV.

Motivation & Objective

• To identify experimental signatures for heavy spin-1 chiral bosons at hadron colliders, motivated by anomalies in low-energy precision measurements.
• To address the 4.5σ discrepancy in the τ decay two-pion branching ratio and the 3.3σ deviation in muon (g-2) via new chiral gauge bosons.
• To provide a phenomenological model for chiral bosons that explains existing anomalies and guides detection at the Tevatron and LHC.
• To enable simulation of chiral boson production and decays by modifying the PYTHIA event generator with corrected angular distributions.
• To predict discovery potential at the LHC, especially in dilepton and lepton+jets final states, based on differential cross-sections.

Proposed method

• Uses the CalcHEP package to compute differential cross-sections for chiral boson production in pp collisions at Tevatron and LHC energies.
• Applies model-independent properties of chiral bosons, including non-universal vector and axial-vector couplings to quarks and leptons.
• Modifies the PYTHIA event generator to correctly simulate chiral boson decays, replacing the standard gauge boson angular distribution (WT = 1 + ASYM·cosθ + cos²θ) with WT = 4cos²θ for chiral bosons.
• Introduces parameter sets in PYTHIA (PARU(131)-(134)) to model chiral bosons with specific couplings, such as the U boson with (3/2, -1/2, 1/2, -1/2).
• Analyzes transverse momentum and invariant mass distributions of decay products (leptons, jets) to distinguish chiral bosons from SM W/Z bosons.
• Compares Jacobian peaks (at pT ≈ M/2) in gauge bosons to the broad bump at lower pT (well below M/2) expected for chiral bosons.

Experimental results

Research questions

• RQ1 Can the observed 4.5σ discrepancy in the τ decay two-pion branching ratio and the 3.3σ (g-2) anomaly be explained by the existence of heavy chiral bosons?
• RQ2 What are the distinctive kinematic signatures—especially in transverse momentum and angular distributions—of chiral boson production at hadron colliders?
• RQ3 How can the PYTHIA event generator be modified to correctly simulate chiral boson decays, given their different angular distributions compared to standard gauge bosons?
• RQ4 What is the expected discovery reach of the LHC for chiral bosons, particularly in the Drell–Yan dilepton channel?
• RQ5 Can the Tevatron data already show evidence for a light charged chiral boson with mass around 500 GeV?

Key findings

• Tevatron data already hint at the existence of a light charged chiral boson with a mass of approximately 500 GeV, based on a shoulder in the lepton transverse momentum distribution.
• The differential cross-section for resonant production of the lightest charged chiral boson (U±) reaches about 0.03 pb/GeV at transverse lepton momentum around 200 GeV.
• At peak luminosity, approximately 10 events per 10 GeV bin in transverse momentum are expected within one hour of data-taking for the light U± boson.
• The second shoulder in the distribution, corresponding to a heavier charged chiral boson, requires more than a day of data-taking to observe due to lower statistics.
• The LHC is expected to discover all predicted charged and neutral chiral bosons up to 1 TeV if the 500 GeV signal in the Tevatron data is confirmed.
• The key distinguishing feature in the Drell–Yan channel is the absence of a Jacobian peak at pT ≈ M/2 for chiral bosons, instead showing a broad bump at significantly lower pT, which can be used to identify them.