New physics effects in tree-level decays and the precision in the determination of the quark mixing angleγ

Abstract

(2015) 'New physics eects in tree-level decays and the precision in the determination of the quark mixing angle . ', Physical review D., 92 (3). 033002.Further information on publisher's website:http://dx.doi.org/10.1103/PhysRevD.92.033002Publisher's copyright statement:Reprinted with permission from the American Physical Society: Physical Review D 92, 033002 c 2015 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modied, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We critically review the assumption that no new physics is acting in tree-level B-meson decays and study the consequences for the ultimate precision in the direct determination of the Cabibbo-KobayashiMaskawa (CKM) angle γ. In our exploratory study we find that sizeable universal new physics contributions, ΔC 1;2 , to the tree-level Wilson coefficients C 1;2 of the effective Hamiltonian describing weak decays of the b quark are currently not excluded by experimental data. In particular, we find that ImΔC 1 and ImΔC 2 can easily be of order AE10% without violating any constraints from data. Such a size of new physics effects in C 1 and C 2 corresponds to an intrinsic uncertainty in the CKM angle γ of the order of jδγj ≈ 4°, which is slightly below the current experimental precision. The accuracy in the determination of γ can be improved by putting stronger constraints on the tree-level Wilson coefficients, in particular C 1 . To this end we suggest a more refined theoretical study as well as more precise measurements of the observables that currently provide the strongest bounds on hypothetical new weak phases in C 1 and C 2 . We note that the semileptonic CP asymmetries seem to have the best prospect for improving the bound on the weak phase in C 1 .

CP violation in the Bs0 system

“…In view of the increasing experimental precision this assumption should, however, be challenged. A recent study (Brod et al, 2015) found that current experimental bounds on different flavour observables that are dominated by tree-level effects, allow beyond SM effects to be as large as about ±0.1 in the tree-level Wilson coefficients C 1 and C 2 . A new physics contribution to the imaginary part of C 1 of about 0.1 would modify the measurement of γ from tree-level decays by about 4 • (Brod et al, 2015), which is smaller …”

“…Another enhancement mechanism would be new physics effects in tree-level decays, which are typically neglected. Such studies were performed systematically in (Bobeth et al, 2015(Bobeth et al, , 2014Brod et al, 2015) and could also lead to sizable enhancements of ∆Γ d . Here a more precise measurement of ∆Γ d would of course be very helpful.…”

“…Due to the dramatically improved experimental precision, this possibility has, however, to be considered. Taking only experimental constraints into account and no bias from model building, first studies performed by (Bobeth et al, 2014), (Bobeth et al, 2015) and (Brod et al, 2015) find that the tree-level Wilson coefficients C 1 and C 2 can easily be affected by new effects of the order of 0.1. Such a deviation can sometimes have dramatic effects, e.g.…”

Measurement of the CKM angle γ from a combination of LHCb results

“…Violation of CP symmetry can be studied by measuring the angles of the CKM unitarity triangle [5][6][7]. The least precisely known of these angles, γ ≡ arg[−V ud V * ub /V cd V * cb ], can be measured using only tree-level processes [8][9][10][11]; a method that, assuming new physics is not present in tree-level decays [12], has negligible theoretical uncertainty [13]. Disagreement between such direct measurements of γ and the value inferred from global CKM fits, assuming the validity of the SM, would indicate new physics beyond the SM.…”

Model-independent measurement of the CKM angle γ using B0 → DK∗0 decays with D → K S 0 π + π − and K S 0 K+K−

“…It is the only CKM angle easily accessible in tree-level processes and can be measured, with a small uncertainty from theory of δγ/γ ≤ 10 −7 [3]. Hence, in the absence of new physics effects at tree level [4], a precision measurement of γ provides an SM benchmark which can be compared with other CKM matrix observables that are more likely to be affected by physics beyond the SM. Such comparisons are currently limited by the uncertainty on direct measurements of γ, which is about 7 • [5,6].…”