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## B. CP asymmetry in B$_{s}$ → X$_{s}$ℓν 

In this section we shall concentrate on semileptonic CP asymmetry ( A$_{SL}$ ) in B$_{s}$ system $^{2}$. In general the CP asymmetry in semileptonic B$_{s}$ decays defined as, 

<img src='content_image/335469.jpg'>

depends on the relative phase between the absorptive and dispersive parts of B$_{s}$ − ¯ B$_{s}$ mixing amplitude [77], 

<img src='content_image/335468.jpg'>

with φ$_{s}$ = arg ( − M s 12 Γ s 12 ) , the relative phase between B$_{s}$ − ¯ B$_{s}$ mixing and the corresponding b → c ¯ cs decays and | Δ$_{s}$ | parametrises the NP effect in M s 12 [6]. | Γ$_{12}$ /M$_{12}$ | = O ( m 2 $_{b}$/M 2 $_{W}$) suppresses A$_{SL}$ to the percent level, apart from this there is a GIM suppression factor m 2 $_{c}$/m 2 b reducing A$_{SL}$ by another order of magnitude. Because of these suppression factors it is very small in SM, for B$_{s}$ system it is O (10 − $^{5}$). The GIM suppression is lifted if new physics contributes to arg( M$_{12}$ ). Therefore A$_{SL}$ is very sensitive to new CP phases [78, 79]. The situation where new physics could enhance A$_{SL}$ by a factor O (10-100) makes this asymmetry a sensitive probe of new physics. 

Recently the search for CP violation in semileptonic B$_{s}$ decays achieved a much more improved sensitivity [80, 81]: 

Present world average is given by [82], 

<img src='content_image/335467.jpg'>

<img src='content_image/335466.jpg'>

In near future more precise measurements can exclude SM prediction if it is much enhanced then the SM prediction. It is important to note that the scenarios like SM4 can significantly 

