Lepton flavor violation and dilepton tails at the LHC

Abstract

Abstract Starting from a general effective Lagrangian for lepton flavor violation (LFV) in quark-lepton transitions, we derive constraints on the effective coefficients from the high-mass tails of the dilepton processes $$pp \rightarrow \ell _k \ell _l$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>p</mml:mi><mml:mi>p</mml:mi><mml:mo>→</mml:mo><mml:msub><mml:mi>ℓ</mml:mi><mml:mi>k</mml:mi></mml:msub><mml:msub><mml:mi>ℓ</mml:mi><mml:mi>l</mml:mi></mml:msub></mml:mrow></mml:math> (with $$k\ne l$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>k</mml:mi><mml:mo>≠</mml:mo><mml:mi>l</mml:mi></mml:mrow></mml:math> ). The current (projected) limits derived in this paper from LHC data with $$36~\mathrm {fb}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>36</mml:mn><mml:mspace/><mml:msup><mml:mrow><mml:mi>fb</mml:mi></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> ( $$3~\mathrm {ab}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>3</mml:mn><mml:mspace/><mml:msup><mml:mrow><mml:mi>ab</mml:mi></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> ) can be applied to generic new physics scenarios, including the ones with scalar, vector and tensor effective operators. For purely left-handed operators, we explicitly compare these LHC constraints with the ones derived from flavor-physics observables, illustrating the complementarity of these different probes. While flavor physics is typically more constraining for quark-flavor violating operators, we find that LHC provides the most stringent limits on several flavor-conserving ones. Furthermore, we show that dilepton tails offer the best probes for charm-quark transitions at current luminosities and that they provide competitive limits for tauonic $$b\rightarrow d$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>b</mml:mi><mml:mo>→</mml:mo><mml:mi>d</mml:mi></mml:mrow></mml:math> transitions at the high-luminosity LHC phase. As a by-product, we also provide general numerical expressions for several low-energy LFV processes, such as the semi-leptonic decays $$K\rightarrow \pi \ell ^{\pm }_k \ell ^{{\mp }}_l$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>K</mml:mi><mml:mo>→</mml:mo><mml:mi>π</mml:mi><mml:msubsup><mml:mi>ℓ</mml:mi><mml:mi>k</mml:mi><mml:mo>±</mml:mo></mml:msubsup><mml:msubsup><mml:mi>ℓ</mml:mi><mml:mi>l</mml:mi><mml:mo>∓</mml:mo></mml:msubsup></mml:mrow></mml:math> , $$B\rightarrow \pi \ell ^{\pm }_k \ell ^{{\mp }}_l$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>B</mml:mi><mml:mo>→</mml:mo><mml:mi>π</mml:mi><mml:msubsup><mml:mi>ℓ</mml:mi><mml:mi>k</mml:mi><mml:mo>±</mml:mo></mml:msubsup><mml:msubsup><mml:mi>ℓ</mml:mi><mml:mi>l</mml:mi><mml:mo>∓</mml:mo></mml:msubsup></mml:mrow></mml:math> and $$B\rightarrow K^{(*)} \ell ^{\pm }_k \ell ^{{\mp }}_l$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>B</mml:mi><mml:mo>→</mml:mo><mml:msup><mml:mi>K</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mrow/><mml:mo>∗</mml:mo><mml:mo>)</mml:mo></mml:mrow></mml:msup><mml:msubsup><mml:mi>ℓ</mml:mi><mml:mi>k</mml:mi><mml:mo>±</mml:mo></mml:msubsup><mml:msubsup><mml:mi>ℓ</mml:mi><mml:mi>l</mml:mi><mml:mo>∓</mml:mo></mml:msubsup></mml:mrow></mml:math> .

Topics & Concepts