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Flavor and LHC searches for new physics

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Abstract

Uncovering the physics of electroweak symmetry breaking (EWSB) is the raison-d’etre of the LHC. Flavor questions, it would seem, are of minor relevance for this quest, apart from their role in constraining the possible structure of EWSB physics. In this short review article, we outline, using flavor-dependent slepton physics as an example, how flavor can affect both searches for supersymmetry, and future measurements aimed at understanding the nature of any new discoveries. If the production cross-sections for supersymmetry are relatively low, as indicated by the fact that it has not revealed itself yet in standard searches, the usual assumptions about the superpartner spectra need rethinking. Furthermore, one must consider more intricate searches, such as lepton-based searches, which could be susceptible to flavor effects. We start by reviewing the flavor structure of existing frameworks for mediating supersymmetry breaking, emphasizing flavor-dependent models proposed recently. We use the kinematic endpoints of invariant mass distributions to demonstrate how flavor dependence can impact both searches for supersymmetry and the Inverse Problem. We also discuss methods for measuring small-mass splittings and mixings at the LHC, both in models with a neutralino LSP and in models with a charged slepton (N)LSP.

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Notes

  1. The term “flavor” is somewhat vague, and often redundant, since it can usually be replaced by “generation.” The matter fields of the SM carry both gauge indices and generation indices. The latter are often called flavor indices. Flavor-dependence simply means generation dependence, and flavor parameters refer to the generation-dependent parameters of the SM.

  2. For a review of EDM bounds on CP-violating phases, see the article by B. Batell in this chapter.

  3. To better understand these points, one should examine the structure of FV diagrams. See for example Eq. (20) of [17].

  4. Some of these are actual models, with a well-defined mechanism for generating the soft terms and controlling their structure. Others are simply ansatze, which may have some concrete realization(s).

  5. These models have additional features that contribute to the suppression of FV processes, including the absence of A terms and the Dirac nature of the gauginos (see items 5, 6 above).

  6. In gravity-mediated models, without additional ingredients, the scalar mass matrices could be arbitrary, so that bounds on FV are not satisfied.

  7. SU(3) L is further broken by the neutrino masses. Here, for simplicity, we will neglect the spurions associated with the neutrinos. This is justified if the seesaw scale is higher than the mediation scale. We can then take the charged lepton Yukawa to be a diagonal matrix without loss of generality.

  8. As mentioned above, AMSB is not universal but MFV.

  9. These small mixings are a generic result of the flavor symmetry.

  10. Flavor-dependent squark spectra and their impact on LHC searches were discussed for example in [36–38].

  11. The dilepton-invariant mass distribution is an important tool for measuring superpartner masses and we will return to it in Sects. 4 and 5. For now, however, we are mainly interested in it at the level of the discovery potential for SUSY.

  12. For early work on the collider signatures of generation-dependent sleptons, focused on lepton flavor violation, see, e.g., [56–60].

  13. Here and in the following we assume that the mass splitting is much bigger than the slepton decay width. The effect of non-zero width was studied in detail in [61].

  14. Apart from [70], these techniques rely on the low slepton speed. Sleptons produced in the decay of heavier particles can have large boosts, and therefore look like fake muons. Such sleptons may be detected by looking for a peak in the muon-lepton-invariant mass distribution [71].

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Acknowledgements

Research supported in part by the Israel Science Foundation (ISF) under grant No. 1367/11, by the United States-Israel Binational Science Foundation (BSF) under grant No. 2010221.

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    Yael Shadmi

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Shadmi, Y. Flavor and LHC searches for new physics. Eur. Phys. J. C 72, 2104 (2012). https://doi.org/10.1140/epjc/s10052-012-2104-0

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