Charm physics confronts high-pT lepton tails

Abstract

We present a systematic survey of possible short-distance new-physics effects in (semi)leptonic charged- and neutral-current charmed meson decays. Using the Standard Model Effective Field Theory (SMEFT) to analyze the most relevant experimental data at low and high energies, we demonstrate a striking complementarity between charm decays and high invariant mass lepton tails at the LHC. Interestingly enough, high-pT Drell-Yan data offer competitive constraints on most new physics scenarios. Furthermore, the full set of correlated constraints from K, π and τ decays imposed by SU(2)L gauge invariance is considered. The bounds from D(s) decays, high-pT lepton tails and SU(2)L relations chart the space of the SMEFT affecting semi(leptonic) charm flavor transitions.

Bottom-flavored mono-tau tails at the LHC

“…Since quadratic terms are formally of order ∼ 1/M 4 NP , like the interference of possible dimension-8 operators with the SM, the validity and generality of the approach could be questioned if their inclusion were to affect the results. Nevertheless, in case of single tree-level mediators this is not an issue, since it turns out that the interference of dimension-8 operators with the SM is always smaller than the interference of dimension-6 terms with SM, if M 2 NP >ŝ, as shown in [10]. A cancellation between dimension-six and eight contributions would require a specific multimediator scenario with tuned couplings.…”

“…In case of an exchange in the t or u channel, instead, the true signal can be smaller but, as shown in [7], the EFT limits approximate well those obtained in the complete model. We refer to [10] for a more detailed discussion of possible caveats due to the EFT expansion in the pp → τ ν(+b) process at the LHC.…”

“…In this section we discuss what information on the flavor structure of New Physics can be extracted from high-p T tails of pp → τ ν(+b) at LHC, and how this compares with limits from low-energy flavor processes. This topic has already been the focus of several works in recent years, see [7,10] for τ ν searches and [1][2][3][4][5][8][9][10][11][12] for other leptonic final states.…”

“…This enhancement of new physics effects at high energies can be leveraged to compensate JHEP12(2020)035 the limited statistical and systematic precision of these processes, allowing the limits obtained in this way to be competitive with those derived from precision low-energy data. For instance, it has already been shown that high-energy tails of 2 to 2 processes at LHC can provide complementary information to low-energy flavor physics on the flavor structure of New Physics [1][2][3][4][5][6][7][8][9][10][11] or even be competitive with LEP in putting constraints on electroweak precision tests [12][13][14][15][16].…”

“…1 Since the mass scale of new resonances indicated by these deviations lies in the few-TeV range, testing this process in high-energy scattering at the LHC is clearly particularly motivated. CMS [30] and ATLAS [31] searches in the τ ν channel have been recasted to provide limits on EFT operators in [7,10].…”