LHCb实验结果对新物理的限制.docx

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Introduction
The Large Hadron Collider beauty (LHCb) experiment is one of the four major experiments at the Large Hadron Collider (LHC), designed to study the physics of B hadrons. The experiment aims to determine the properties of B hadrons, search for new physics and CP violation, and test the standard model (SM) with high precision measurements. In this paper, we will discuss the limits on new physics from the recent LHCb results.
CP Violation
One of the primary objectives of the LHCb experiment is to study CP violation in B hadrons. So far, the results have been consistent with the SM predictions. However, the LHCb experiment has recently reported a measurement of the angular distribution in B0 → K*0μ+μ− decay that deviates from the SM predictions. This measurement has been confirmed by Belle and BaBar experiments and, hence, indicates a significant departure from the SM predictions.
The measurement is expressed in terms of several angular observables that describe the properties of the decay. These observables provide a way to test the SM predictions and to search for new physics beyond the SM. The deviation from the SM is seen in the angular observable P5′, which corresponds to the forward-backward asymmetry of the dimuon system. An anomalous behavior in P5′ indicates a violation of lepton flavor universality (LFU), which is a fundamental principle of the SM.
The LHCb result shows a deviation from the SM in P5′ at the level of . This result is consistent with the previous Belle measurement with smaller statistics and less precise angular resolution. The consistent measurements from Belle and LHCb indicate a systematic issue in the SM predictions rather than a statistical fluctuation.
Implications for New Physics
The anomalous measurement of P5′ in B0 → K*0μ+μ− decay opens the possibility of new physics beyond the SM. Several theoretical models have been proposed to explain this deviation, including leptoquarks, Z′ bosons, and supersymmetric particles. Leptoquarks are hypothetical particles that carry both baryon and lepton numbers and can mediate the flavor-changing neutral currents (FCNC) responsible for B0 → K*0μ+μ− decay. Z' bosons are hypothetical heavy gauge bosons that can arise in extensions of the SM, and supersymmetric particles are particles that appear in supersymmetry models that predict new particles as partners of the SM particles.
The LHCb experiment has set limits on several new physics models that can explain the anomalous behavior in P5′. In particular, leptoquark models have been constrained by the LHCb data. The constraints on leptoquarks depend on their masses and the nature of their couplings to the quarks and leptons. The LHCb data have set bounds of TeV and TeV on vector and scalar leptoquarks, respectively, assuming that they couple only to the third generation quarks and leptons.
In addition to the leptoquarks, the LHCb results also constrain the Z' boson models, which predict the existence of a new gauge boson that can mediate the FCNC interactions. The LHCb experiment has set bounds on the mass and couplings of several Z' models, which predict an enhancement in P5′. The bounds depend on the specific models and can range from TeV to TeV for Z' bosons that couple to muons.
Finally, the LHCb experiment has also set constraints on the supersymmetric particles that may contribute to B0 → K*0μ+μ− decay. The most relevant supersymmetric particles are the charginos and the neutralinos, which are the superpartners of the W and Z bosons and the Higgs boson. The LHCb experiment has set constraints on the masses and couplings of the charginos and neutralinos that depend on the specific supersymmetry models and on the compositions of the particles.
Conclusion
The recent LHCb results on B0 → K*0μ+μ− decay have shown a significant deviation from the SM prediction in the angular observable P5′, which can be interpreted as a violation of LFU. The anomalous behavior in P5′ indicates the possibility of new physics beyond the SM, including leptoquark models, Z' boson models, and supersymmetric particles. The LHCb experiment has set constraints on several new physics models, including leptoquarks, Z' bosons, and supersymmetric particles, which can provide useful guidance for future theoretical and experimental studies. The LHCb experiment will continue to play an important role in the search for new physics beyond the SM and in the determination of the properties of B hadrons with high precision measurements.