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LHC tau-pair production constraints on $a_\tau$ and $d_\tau$
by Ulrich Haisch, Luc Schnell, Joachim Weiss
|Authors (as registered SciPost users):||Ulrich Haisch|
|Preprint Link:||scipost_202308_00018v1 (pdf)|
|Date submitted:||2023-08-14 15:42|
|Submitted by:||Haisch, Ulrich|
|Submitted to:||SciPost Physics|
We point out that relevant constraints on the anomalous magnetic ($a_\tau$) and electric ($d_\tau$ ) moment of the tau lepton can be derived from tau-pair production measurements performed at the LHC. Our conclusion is based on the observation that the leading relative deviations from the Standard Model prediction for $pp \to \tau^+ \tau^-$ due to aτ and dτ are enhanced at high energies. Less precise measurements at hadron colliders can therefore offer the same or better sensitivity to new physics with respect to high-precision low-energy measurements performed at lepton machines. We derive bounds on aτ and dτ using the full LHC Run II data set on tau-pair production and compare our findings with the current best limits on the tau anomalous moments.
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This article provides a nice analysis of tau pair DY production and its relevance for the tau anomalous couplings. The conclusions rest on a range of assumptions, which are, however, not entirely clear.
(i) all effects are attributed to the tau lepton-sector. How does this compare to the competing coupling modifications that can be expected in other fermion interactions that DY is sensitive to?
(ii) the Z contribution is chosen to vanish. Is this a reasonable assumption? I would expect through Z-photon mixing to see correlated effects away from the Z resonance that can become relevant at large momentum transfers that are highlighted as particularly relevant by the authors.
This work is precise and succinct, yet detailed enough, highlighting a key insight into probing new physics in anomalous dipole moments of the tau lepton. The authors effectively set limits on the relevant SMEFT dipoles using high-mass Drell-Yan tails. Notably, the determined limits are the most competitive for the anomalous magnetic moment. Before I recommend this for publication, I have two areas I would like the authors to address:
1. Could the authors briefly comment on the UV models where these bounds are of interest? It is my understanding that perturbative models typically generate these effects at the one-loop level. Referring to eq. (13), this seems pertinent primarily for lighter particle mediators, where the EFT methodology might not be applicable and direct searches come into play.
2. The authors suggest that the SM target at the HL-LHC will be met. Could they elaborate on the implications for the high-mass tails? Specifically, which SM corrections will become more significant? Additionally, how adequate is the SM prediction at such a precision level?