The researchers from the Laboratory of the heavy quarks in hadron interactions participate in the LHCb experiment in CERN. The research program is aimed at observing the effects in New Physics beyond the Standard model of electroweak interactions. One of the aims of this joint project is the precision measurement of the value characterising CP-violation in B meson decays, namely, the angle ɣ of the Unitary Triangle.

CP-violation is responsible for the asymmetry of the matter and asymmetry in the Universe. Within the Standard model CP-violation is described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix, characterising transitions between different generations of quarks due to weak interactions. The so-called Unitary Triangle (UT) presents one of the representations of CKM matrix. Different processes sensitive to the length of the sides and values of angles of this triangle. The effects beyond the Standard model manifest themselves in the mismatch between the measurements of the UT (for example, in the deviation from 180 degrees of the sum of the angles of a triangle). Thus, UT precision measurement contributes to the direct searches for New Physics effects at high energy levels in such detectors as ATLAS or CMS.

Many processes violating CP-processes that are the most sensitive to the UT parameters are observed in B meson decays. At present, only one of the UT triangles (most frequently called ) has been measured with the precision of approximately 1 degree in Belle and BaBar experiments carried out on high luminosity electron positron colliders known as -factories. The experiment on LHCb will help to specify better many CP-violation parameters. In particular, the accuracy of angle ɣ measurement can reach several degrees.

The Laboratory has achieved the following results:
Bs0-meson decay to a pair of muons (μ+ и μ-) formed as a result of collision between protons has been discovered. Following the Standard model, such decay occurs in 3 or 4 cases per billion. Previously, all attempts to detect it failed. The experiments have demonstrated the correctness of the Standard model one more time and allowed dismissing a number of hypothesis broadening the Standard Model. The Unitary Triangle angle ɣ has been measured. At present the received value of ɣ = (62+15-14)° presents its most precise single measurement. An updated integrated angle ɣ measurement using several independent measurements made in 2014 and before for the first time gave the precision of less than 10°: γ = (73+9-10)°.

The Laboratory is a member of The Interdisciplinary Center for Elementary Particle Physics and Astrophysics.

The laboratory collaborates with CERN.

Research area expert: Associate professor Semen Isaakovich Eidelman (Sc. D., Physics and Mathematics) s.i.eidelman@inp.nsk.su

Elementary particle physics section
Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Siences