LHC constraints on scalar diquarks
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Springer
Received: June 26, 2020 Accepted: July 3, 2020 Published: July 21, 2020
Bruna Pascual-Dias,a Pratishruti Sahab and David Londona a
Physique des Particules, Universit´e de Montr´eal, C.P. 6128, succ. centre-ville, Montr´eal, QC H3C 3J7, Canada b Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211019, India
E-mail: [email protected], [email protected], [email protected] Abstract: A number of years ago, low-energy constraints on scalar diquarks, particles that couple to two quarks, were examined. It was found that the two most weakly-constrained diquarks are Du and Dd , colour antitriplets that couple to uiR ujR and diR djR , respectively. These diquarks have not been observed at the LHC. In this paper, we add the LHC measurements to the low-energy analysis, and find that the constraints are significantly improved. As an example, denoting xu as the Du coupling to the first and second generations, for MDu = 600 GeV, the low-energy constraint is |xu | ≤ 14.4, while the addition of the LHC dijet measurement leads to |xu | ≤ 0.13–0.15. Further improvements are obtained by adding the measurement of single top production with a pT cut. These new constraints must be taken into account in making predictions for other low-energy indirect effects of diquarks. Keywords: Beyond Standard Model, Heavy Quark Physics ArXiv ePrint: 2006.13385
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP07(2020)144
JHEP07(2020)144
LHC constraints on scalar diquarks
Contents 1
2 Scalar diquarks
2
3 Low-energy constraints
3
4 LHC constraints: direct searches
6
5 LHC constraints: single top production
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6 Conclusions
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12
Introduction
The Standard Model (SM) has been extremely successful in explaining almost all experimental measurements to date. However, for a variety of reasons — the hierarchy problem, dark matter, CP violation and the matter-antimatter asymmetry, etc. — it is generally believed that it is not complete. There must be physics beyond the SM. It was hoped that the LHC would produce new-physics (NP) particles directly, but so far this has unfortunately not happened. The scale of NP may be above the present reach of the LHC. Still, even if this is the case, all hope is not lost: one can also search for NP through indirect signals. (Indeed, there are currently indirect hints of NP in b → sµ+ µ− and b → cτ − ν¯τ transitions [1].) Of course, for a particular kind of NP, if one wants to examine how large the indirect effects can be in a given process, one must include the constraints on its mass and couplings derived from direct searches. One possible type of NP is a diquark, a particle that couples to two quarks. A diquark can be a scalar or a vector, and transforms as a 6 or ¯ 3 of SU(3)C . In this paper, we focus on scalar diquarks. These appear in models with E6 [2] or SU(2)L × SU(2)R × SU(4)C [3] symmetry, and in supersymmetry with R-parity violation [4]. Studies of diquark phenomenology mostly fall into three categories:
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