# T Chen / B Yu – G Loffhagen / A Rai Match Prediction | 06-09-2019 02:00

The red curves represent the trajectories of the muons from the candidate decay. a, The LHCb detector and its components; see ref. 21 for details. The protonproton collision occurs on the left-hand side, at the origin of the trajectories depicted with the orange curves. b, A candidate decay produced in protonproton collisions at 7 TeV in 2011 and recorded in the LHCb detector.

The study presented in this Letter uses data collected at energies of 3.5 TeV per beam in 2011 and 4 TeV per beam in 2012 by the CMS and LHCb experiments located at two of these IPs. At the Large Hadron Collider (LHC), two counter-rotating beams of protons, contained and guided by superconducting magnets spaced around a 27 km circular tunnel, located approximately 100 m underground near Geneva, Switzerland, are brought into collision at four interaction points (IPs).

1f and g, that can considerably modify the SM branching fractions. In particular, theories with additional Higgs bosons10, 11 predict possible enhancements to the branching fractions. Alternatively, a measurement compatible with the SM could provide strong constraints on BSM theories. Many theories that seek to go beyond the standard model (BSM) include new phenomena and particles8, 9, such as in the diagrams shown in Fig. A significant deviation of either of the two branching fraction measurements from the SM predictions would give insight on how the SM should be extended.

## Determination of the quark coupling strength |Vub| using baryonic decays

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The type of MVA used is a boosted decision tree (BDT)24, 25, 26. The final classification of data events is done in categories of the response of a multivariate discriminant (MVA) combining information from the kinematics and vertex topology of the events. The resulting candidate is further required to point back to the PV, for example, to have a small impact parameter, consistent with zero, with respect to it. Pairs of high-quality oppositely charged particle tracks that have one of the expected patterns of hits in the muon detectors are fitted to form a common vertex in three dimensions, which is required to be displaced from the primary interaction vertex (PV) and to have a small 2 in the fit. The data analysis procedures in the two experiments follow similar strategies. The branching fractions are then obtained by a fit to the dimuon invariant mass, , of all categories simultaneously.

They are also helicity and CKM suppressed. 1c, is forbidden at the elementary level because the Z0 cannot couple directly to quarks of different flavours, that is, there are no direct flavour changing neutral currents. The corresponding decay of the B0 meson, where a d quark replaces the s quark, is even more CKM suppressed because it requires a jump across two quark generations rather than just one. However, it is possible to respect this rule and still have this decay occur through higher order transitions such as those shown in Fig. The neutral meson is similar to the B+ except that the u quark is replaced by a second generation strange (s) quark of charge 1/3. The decay of the meson to two muons, shown in Fig. These are highly suppressed because each additional interaction vertex reduces their probability of occurring significantly. Consequently, the branching fraction for the decay is expected to be very small compared to the dominant b antiquark to c antiquark transitions. 1d and e.

For each of the two branching fractions, a one-dimensional profile likelihood scan is likewise obtained by fixing only the single parameter of interest and allowing the other to vary during the fits. In the simultaneous fit to both the CMS and LHCb data, the branching fractions of the two signal channels are common parameters of interest and are free to vary. An unbinned extended maximum likelihood fit to the dimuon invariant-mass distribution, in a region of about 500 MeV/c2 around the mass, is performed simultaneously in all categories (12 categories from CMS and eight from LHCb). The ratio of the hadronization probability into B+ and mesons and the branching fraction of the normalization channel B+J/K+ are common, constrained parameters. In the case of CMS, they are further categorized according to the data-taking period, and, because of the large variation in mass resolution with angle, whether the muons are both produced at large angles relative to the proton beams (central-region) or at least one muon is emitted at small angle relative to the beams (forward-region). Other parameters in the fit are considered as nuisance parameters. Likelihood contours in the plane of the parameters of interest, (B0+) versus (), are obtained by constructing the test statistic 2lnL from the difference in log-likelihood (lnL) values between fits with fixed values for the parameters of interest and the nominal fit. Those for which additional knowledge is available are constrained to be near their estimated values by using Gaussian penalties with their estimated uncertainties while the others are free to float in the fit. Additional fits are performed where the parameters under consideration are the ratio of the branching fractions relative to their SM predictions, , or the ratio of the two branching fractions. Candidate decays are categorized according to whether they were detected in CMS or LHCb and to the value of the relevant BDT discriminant.

## B Mousley/R Purcell vs T Chen/B Yu Sets

The SM is represented by the (red) vertical lines. The SM point is shown as the (red) square located, by construction, at . The dark and light (cyan) areas define the 1 and 2 confidence intervals, respectively. Each contour encloses a region approximately corresponding to the reported confidence level. The SM branching fractions are assumed uncorrelated to each other, and their uncertainties are accounted for in the likelihood contours. a, The (black) cross marks the central value returned by the fit. b, c, Variations of the test statistic 2lnL for and are shown in b and c, respectively.

4. Finally, the fit for the ratio of branching fractions yields which is compatible with the SM at the 2.3 level. 6. The measurements are compatible with the SM branching fractions of the and B0+ decays at the 1.2 and 2.2 level, respectively, when computed from the one-dimensionalhypothesis tests. The one-dimensional likelihood scan for this parameter is shown in Fig. Associated likelihood contours and one-dimensional likelihood scans are shown in Extended Data Fig. The fit for the ratios of the branching fractions relative to their SM predictions yields .

b, A candidate decay produced in protonproton collisions at 7 TeV in 2011 and recorded in the LHCb detector. a, The LHCb detector and its components; see ref. 21 for details. The red curves represent the trajectories of the muons from the candidate decay. The protonproton collision occurs on the left-hand side, at the origin of the trajectories depicted with the orange curves.

Therefore, the decay vertex, from which the muons originate, is required to be displaced with respect to the production vertex, the point where the two protons collide. The separation between genuine decays and random combinations of two muons (combinatorial background), most often from semi-leptonic decays of two different b hadrons, is achieved using the dimuon invariant mass, , and the established characteristics of -meson decays. For example, because of their lifetimes of about 1.5 ps and their production at the LHC with momenta between a few GeV/c and ~100 GeV/c, mesons travel up to a few centimetres before they decay. The experiments follow similar data analysis strategies. Decays compatible with (candidate decays) are found by combining the reconstructed trajectories (tracks) of oppositely charged particles identified as muons. Furthermore, the negative of the candidates momentum vector is required to point back to the production vertex.

## Contents

Experimental particle physicists have been testing the predictions of the standard model of particle physics (SM) with increasing precision since the 1970s. Theoretical developments have kept pace by improving the accuracy of the SM predictions as the experimental results gained in precision. It also fails to explain the origin of the asymmetry between matter and antimatter, which after the Big Bang led to the survival of the tiny amount of matter currently present in the Universe3, 4. In the course of the past few decades, the SM has passed critical tests derived from experiment, but it does not address some profound questions about the nature of the Universe. Many theories have been proposed to modify the SM to provide solutions to these open questions. For example, the existence of dark matter, which has been confirmed by cosmological data3, is not accommodated by the SM.