Abstract
We study the leptoquark model of Buchm\"uller, R\"uckl and Wyler, focusing on a particular type of scalar ($R_2$) and vector ($U_1$) leptoquark. The primary aim is to perform the calculations for leptoquark production and decay at next-to-leading order (NLO) to establish the importance of the NLO contributions and, in particular, to determine how effective the narrow-width-approximation (NWA) is at NLO. For both the scalar and vector leptoquarks it is found that the NLO contributions are large, with the larger corrections occurring for the case vector leptoquarks. For the scalar leptoquark it is found that the NWA provides a good approximation for determining the resonant peak, however the NWA is not as effective for the vector leptoquark. For both the scalar and vector leptoquarks there are large contributions away from the resonant peak, which are missing from the NWA results, and these make a significant difference to the total cross-section.
Highlights
Mass) and that the interference between the different helicity states for the production and decay processes is negligible
The primary aim is to perform the calculations for leptoquark production and decay at next-to-leading order (NLO) to establish the importance of the NLO contributions and, in particular, to determine how effective the narrow-width-approximation (NWA) is at NLO
For both the scalar and vector leptoquarks it is found that the NLO contributions are large, with the larger corrections occurring for the case vector leptoquarks
Summary
In general the NWA involving an intermediate scalar particle should give a good approximation to the full result close to the resonant region. Away from the resonant peak there are differences in the invariant mass distributions between the NWA and full non-factorisable process. The enhancement to the distribution away from the resonant peak does make a large contribution to the total cross-section (see tables 2 and 4) and we see a large difference between the cross-sections calculated in the NWA and full non-factorisable process. The NWA gives a symmetric distribution around the resonance, but the full non-factorisable process shows an enhancement to the distribution for values of the invariant mass minv < mLQ. This enhancement makes a sizeable difference to the total cross-section (see tables 6 and 8). From the non-factorisable results there are substantial corrections below the resonance, with regards to the vector leptoquarks, and its is possible these could be observed to give an indirect hint of the presence of leptoquarks
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