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BHWIDE 1.00: O(alpha) YFS Exponentiated Monte Carlo for Bhabha Scattering at Wide Angles for LEP1/SLC and LEP2

S. Jadach, W. Placzek, B. F. L. Ward

TL;DR

This work introduces BHWIDE 1.00, an $O(\alpha)$ YFS-exponentiated Monte Carlo generator for wide-angle Bhabha scattering at LEP1/SLC and LEP2 energies. It extends the BHLUMI framework to include $Z$-exchange and pure weak corrections, offering two electroweak libraries for flexible theoretical input, and computes the hard-photon residuals $\bar{\beta}_0$ and $\bar{\beta}_1$ from exact Born and one-loop amplitudes with mass corrections. Through extensive cross-checks against multiple established codes (ALIBABA, TOPAZ0, BHAGEN95, BHAGENE3, SABSPV, UNIBAB), the authors demonstrate a total precision of about $0.3\%$ near the $Z$ peak (rising to ~0.5% in a wider band) and $1.5\%$ at LEP2, representing a significant improvement over prior literature. This enables direct, event-level comparisons with detector data and strengthens the reliability of luminosity determinations at LEP1/SLC and LEP2.

Abstract

We present O(alpha) YFS exponentiated results for wide angle Bhabha scattering at LEP/SLC energies using a new Monte Carlo event generator BHWIDE 1.xx. Our calculations include two options for the pure weak corrections, as presented in Beenakker et al. and in Bohm et al. From comparison with the results of Beenakker et al., Montagna et al. and Cacciari et al., we conclude that the total precision of our BHWIDE results is 0.3% (0.5%) in the LEP1/SLC regime within +-100 MeV (+2.75/-2.5 GeV) of the Z peak. For LEP2, the corresponding precision is currently estimated at 1.5%; the latter could be improved if the data in LEP2 so require. Both precision tags represent clear improvements over what is currently available in the literature.

BHWIDE 1.00: O(alpha) YFS Exponentiated Monte Carlo for Bhabha Scattering at Wide Angles for LEP1/SLC and LEP2

TL;DR

This work introduces BHWIDE 1.00, an YFS-exponentiated Monte Carlo generator for wide-angle Bhabha scattering at LEP1/SLC and LEP2 energies. It extends the BHLUMI framework to include -exchange and pure weak corrections, offering two electroweak libraries for flexible theoretical input, and computes the hard-photon residuals and from exact Born and one-loop amplitudes with mass corrections. Through extensive cross-checks against multiple established codes (ALIBABA, TOPAZ0, BHAGEN95, BHAGENE3, SABSPV, UNIBAB), the authors demonstrate a total precision of about near the peak (rising to ~0.5% in a wider band) and at LEP2, representing a significant improvement over prior literature. This enables direct, event-level comparisons with detector data and strengthens the reliability of luminosity determinations at LEP1/SLC and LEP2.

Abstract

We present O(alpha) YFS exponentiated results for wide angle Bhabha scattering at LEP/SLC energies using a new Monte Carlo event generator BHWIDE 1.xx. Our calculations include two options for the pure weak corrections, as presented in Beenakker et al. and in Bohm et al. From comparison with the results of Beenakker et al., Montagna et al. and Cacciari et al., we conclude that the total precision of our BHWIDE results is 0.3% (0.5%) in the LEP1/SLC regime within +-100 MeV (+2.75/-2.5 GeV) of the Z peak. For LEP2, the corresponding precision is currently estimated at 1.5%; the latter could be improved if the data in LEP2 so require. Both precision tags represent clear improvements over what is currently available in the literature.

Paper Structure

This paper contains 5 sections, 14 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Born and ${\cal O}(\alpha)$ contributions to $\bar{\beta}_0$ for wide angle Bhabha scattering at high energies
  3. The YFS hard photon residual $\bar{\beta}_1$ for wide angle Bhabha scattering at high energies
  4. Results and comparisons
  5. Conclusions

Figures (3)

  • Figure 1: Monte Carlo results for BARE trigger, for two values ($10^o$ and $25^o$) of acollinearity cut. Center of mass energies (in GeV) close to $Z$ peak. In the plots cross section $\sigma_{\rm{REF}}$ from TOPAZ0 is used as a reference cross section. Cross sections in nb. Two horizontal dotted lines indicate the $0.3\%$ band, for reference.
  • Figure 2: Monte Carlo results for CALO trigger, for two values ($10^o$ and $25^o$) of acollinearity cut. Center of mass energies (in GeV) close to $Z$ peak. In the plots cross section $\sigma_{\rm{REF}}$ from TOPAZ0 is used as a reference cross section. Cross sections in nb. Two horizontal dotted lines indicate the $0.3\%$ band, for reference.
  • Figure 3: Monte Carlo results for CALO trigger, for two values ($10^o$ and $25^o$) of acollinearity cut. Center of mass energies close to $W$-pair production threshold ($E_{CM}$: 1. 175 GeV, 2. 190 GeV, 3. 205 GeV). In the plots cross section $\sigma_{\rm{REF}}$ from BHWIDE is used as a reference cross section. Cross sections in pb. Two horizontal dotted lines indicate the $1.5\%$ band, for reference.