Palatable leptoquark scenarios for lepton flavor violation in exclusive b → sℓ 1 ℓ 2 modes

Received: September Palatable leptoquark scenarios for lepton avor D. Becirevic 0 1 3 N. Kosnik 0 1 3 4 5 O. Sumensari 0 1 2 3 R. Zukanovich Funchal 0 1 2 3 Open Access 0 1 3 c The Authors. 0 1 3 0 Jamova 39 , P.O. Box 3000, 1001 Ljubljana , Slovenia 1 Jadranska 19 , 1000 Ljubljana , Slovenia 2 Instituto de F sica, Universidade de Sa~o Paulo 3 CNRS and Univ. Paris-Sud, Universite Paris-Saclay , 91405 Orsay cedex , France 4 Departement of Physics, University of Ljubljana 5 Jozef Stefan Institute We examine various scenarios that involve a light O(1 TeV) leptoquark state and select those which are compatible with the current experimental values for B(Bs ! violation; in; exclusive; b; Beyond Standard Model; E ective eld theories - s`1`2 )large q2, RK = B0(B ! K consistent with other experimental data. We show that two such scenarios are phenomenoexperimental data as constraints, it is shown that the exclusive lepton avor violating decays, B(Bs ! ) and B(B ! K ), can be as large as O(10 5). 1 Introduction 2 3 4 E ective approach C`1`2 ( ) in leptoquark models Scalar leptoquarks Vector leptoquarks (3; 2)1=6 (3; 2)7=6 (3; 1) 1=3 (3; 1)2=3 (3; 3)2=3 Confronting LQ models with data Which leptoquark model? On (in)viability of (3; 1) 1=3 Results and discussion (3; 2)1=6 Comment on Bs ! (3; 3)2=3 A Formulas and hadronic quantities A.1 Scalar leptoquarks A.2 Vector leptoquark U3 A.3 Exclusive b ! s decay rates A.3.2 B ! K`1`2 A.4 Hadronic quantities Introduction The experimental searches of New Physics (NP) at the LHC are of great importance in our quest for solving the hierarchy and avor problems. Rare decays and low-energy precision measurements play a crucial role in searching for the e ects of physics beyond the Standard Model (BSM) because they are complementary to direct searches and even allow us to probe energy scales well above those that can be probed through them. Among the various types of rare decays, the lepton avor violating (LFV) ones are particularly appealing because they are absent in the Standard Model (SM), and their detection would represent a clean signal of NP. Theoretically, the LFV decays are predicted in various NP scenarios, such as in models with heavy sterile fermions [1{6], in models with a peculiar breaking of supersymmetry [7{ 10], in models involving an extra Z0-boson [11, 12], and in multiple scenarios founded on the paradigm of existence of one or more leptoquark (LQ) states [13]. Most of the current experimental e orts in searching for the e ects of LFV are focused onto lepton decays, `1 ! `2 , `1 ! 3`2 (with `1;2 2 fe; ; g), and on the e conversion in nuclei [14]. The experimental sensitivity to probe these decays is expected to be improved in the years to come by several orders of magnitude. The LFV decays of hadrons are complementary to the purely leptonic decays because they represent a convenient ground to test LQ models, and they also represent a di erent environment to test the result of the above-mentioned leptonic modes. For example, in the LQ models, which will be discussed in this paper, the rates of the LFV decays of hadrons are much larger than in radiative and three-body lepton decays. In this paper we will focus on the exclusive LFV modes, Bs ! `1`2 and B ! K( )`1`2. At present, the most constraining experimental bound is B(Bs ! e which has been recently improved by an order of magnitude [15]. The only dedicated experimental searches with a -lepton in the nal state have been made by the BaBar Collaboration which reported the upper limits B(B+ 10 5 [16]. The modes with one -lepton in the nal state are phenomenologically more appealing because the relevant couplings are less constrained by direct experimental limits and for that reason, in the following, we will focus on Bs ! recent observation of lepton avor universality (LFU) violation in1 One of the main motivations to study transitions based on b ! s`1`2 comes from the RK = B0(B+ ! K+ B0(B+ ! K+ee) B(B+ ! K+ee) q22[1;6] GeV2 where the squared dilepton mass is integrated in the bin q2 2 [1; 6] GeV2. LHCb found [17] RKexp = 0:745+00::009704(stat) uncertainties largely cancel in the ratio, if con rmed, this result would be an unambiguous manifestation of NP. Another experimental observation of LFU violation has been made in the processes mediated by the charged-current interaction, namely, 1Notice that, for shortness, we use B0(B ! K``) for the partial branching fraction corresponding to which turned out to be 2 (for RD) and 3:4 (for RD ) larger than predicted by the SM [20{ 24]. The possibility of connecting the observed LFU violation in neutral- and chargedcurrent processes triggered many interesting theoretical works, mostly based on introducing various LQ states or new gauge bosons (Z0 and W 0) [25{40, 43{46]. Remarkably, in most of the proposed scenarios, LFV in meson decays is induced at observable rates [41, 42]. In a previous work, we computed the general expressions for the full angular (...truncated)