Analysis of the radiative $Λ_b\rightarrow Λγ$ transition in SM and scenarios with one or two universal extra dimensions

Analysis of the radiative A5 — > A7 transition in SM and scenarios with one or two universal extra dimensions K. Azizi 1 *, S. Kartal 2 t, A. T. Olgun 2 *, Z. Tavukoglu 2 § 1 Department of Physics, Dogu§ University, Acibadem-Kadikoy, 34722 Istanbul, Turkey 2 Department of Physics, Istanbul University, Vezneciler, 34134 Istanbul, Turkey Abstract We investigate the radiative process of the A& — > A 7 in the standard model as well as models with one or two compact universal extra dimensions. Using the form factors entered to the low energy matrix elements, calculated via light cone QCD in full theory, we calculate the total decay width and branching ratio of this decay channel. We compare the results of the extra dimensional models with those of the standard model on the considered physical quantities and look for the deviations of the results from the standard model predictions at different values of the compactification scale (1/R). PACS number(s): 12.60.-i, 13.30.-a, 13.30. Ce, 14.20.Mr *e-mail: kazizi@dogus.edu.tr 'e-mail: sehban@istanbul.edu.tr ■'■e-mail: a.t.olgun@gmail.com ^e-mail: z.tavukoglu@gmail.com 1 Introduction As it is well-known, the flavor changing neutral current (FCNC) transitions are prominent tools to indirectly search for the new physics (NP) effects. There are many mesonic and baryonic processes based on the b — > s transition at quark level investigated in the literature via different NP models and compared the obtained results with the experimental data to put constraints on the NP parameters. One of the most important channels in agenda of different experimental groups is the baryonic FCNC A b — y A£ + £~ decay channel. The CDF Collaboration at Fermilab reported the first observation on this mode at muon channel [1]. The measured branching ratio is comparable with the SM prediction [2] within the errors of form factors. Comparing the different NP models' predictions with the experimental data on this channel, it is possible to obtain information about and put limits on the parameters of the models. In our previous work, we put a lower limit to the compactification parameter of the universal extra dimension (UED) via this channel comparing the theoretical calculations with the experimental data [3]. Considering the above experimental progress and recent developments at LHC, we hope we will able to study more decay channels in the experiment in near future. Hence, the phenomenological works using different NP models can play crucial roles in this respect. In this context, we study the radiative A b — y A7 decay channel in SM as well as UED with a single ED (UED5) and two EDs (UED6) in the present work. There are many works dedicated to the analysis of different decay channels in UED5 in the literature (for some of them see [3-19]). However, the number of works devoted to the applications of the UED6 is relatively few. As the expression of the only Wilson coefficient Cy now is available in UED6 [20], it is possible to study the radiative channels based on the b —y 57. In [21], both the UED5 and UED6 are employed to analyze the B —y decay channel. In this work, by comparing the results with the experimental data, the lower limits 250 GeV and 400 GeV, respectively in UED5 and UED6 models are put to the compactification scale. The lower limit of the 1/R obtained via UED6 in this channel is close to the direct experimental limit [22] . For some other previous constraints on the compactification factor obtained via electroweak precision tests, some cosmological constraints and different hadronic channels in UED5 see [3,7,23-27]. Scenarios with EDs play crucial roles among models beyond the SM. The main feature that leads to the difference among ED models is the number of dimensions added to the SM. In the UED5, we have an extra universal compactified dimension compared to the SM, while in UED6 we consider two extra UEDs. Because of the universality, the SM particles 1 can propagate into the UEDs and interact with the Kaluza-Klein (KK) modes existing in EDs. As a result of these interactions, the new Feynman diagrams appear and this leads to a modification in the Wilson coefficients entered the low energy Hamiltonians defining the hadronic decay channels [6,20,28,29]. In the UED5, the ED is compactified to the orbifold S 1 /Z 2 , with the fifth coordinate x 5 — y changing from to 2irR. The points y = and y = ttR are fixed points of this orbifold. The boundary conditions at these points give the KK mode expansion of the fields. The masses of the KK particles in this model are obtained in terms of compactification scale as m n 2 = m 2 + n 2 /R 2 where n — 1,2, ... and m represents the zeroth mode mass referring to the SM particles (for more about model see [6,24,25,30-35]). Models with two EDs are more attractive since they reply to some questions existing in the SM [36]. In this model, cancellations of chiral anomalies allow the existence of the right-handed neutrinos and predict the correct nu