Vcb fitter for Bs -> Ds(*) mu nu decays

This repository contains the code that will allow the users to perform a fit to the data published by the LHCb collaboration in Phys. Rev. D101 (2020) 072004. This fit will additionally employ several theory and experimental inputs, such as: * Bs -> Ds mu nu (f+ function) * HPQCD, PRD101 (2020) 7, 074513 * MILC, PRD85 (2012) 114502 * LCSR, EPJC80 (2020) 4, 347 * Bs -> Ds* mu nu (V, A1 and A2 functions) * HPQCD, arXiv:2105.11433 * HPQCD, PRD99 (2019) 114512 * LCSR, EPJC80 (2020) 4, 347 * LHCb, JHEP12 (2020) 144

The fit can be performed using the CLN parameterisation or the BGL parameterisation (up to order 10 of the series).

Running the code

The code has been test with ROOT 6.22.06. In order to run the code this version of ROOT must be used (earlier versions might work too). The first thing to be done is to generate the signal templates that will be used inside the fit. This is done issuing the following command: root -l runGeneration.C. This command executes a function (generateSignalTemplates) that generates the signal templates. This function takes four arguments that can be customised: * filename: a string specifying the configuration file that needs to be read by the script. This configuration file contains the form-factor parameters used during the generation of the signal templates; * nentries: the number of events that will be generated for Ds and Ds* decays. * rateDS_4D: set this to true if you want to generate the signal template for Ds* using the 4-dimensional decay rate (q2 and three helicity angles). If you set this value to false, the 1-dimensional decay rate will be used instead. N.B: the 4-dimensional generation may take a long time. * _res2D: set this to true to use the 2-dimensional resolution for the p_perp observable available in the supplementary material of the paper at this link. If set to false, the 1-dimensional resolution is used instead.

The acceptance due to the LHCb detector and selection will be automatically taken into account and applied after the data have been generated.

A file called file_templates.root that contains the signal templates for Ds and Ds* with 500k events is already added to the repository. After the signal templates have been generated, one can lauch the fit via the command root -l RunFit.C. This macro has just one argument, configFile, that specifies which configuration file needs to be used for the fit.

Configuration files

The configuration files are contained in the directory config/ and have the following structure (taking as example the CLN parameterisation):

```

Templates file_templates.root templTree

FF-Model-Ref-P CLN 2 G0 1.074

rho2P 1.27

FF-Model-Ref-V CLN 4 F1 0.902 rho2V 1.23 R1 1.34

R2 0.83

FF-Model-Fit-P CLN 2 G0 1.07 0.04 0 0 0

rho2P 1.23 0.05 0 0 0

FF-Model-Fit-V CLN 4 F1 0.902 0.013 0 0 1 rho2V 1.23 0.1 0 0 0
R1 1.34 0.1 0 0 0

R2 0.83 0.1 0 0 0

Other-Parameters 15 Vcb 40e-3 0.1 0 0 0 etaEW 1.0066 0.0050 0 0 1 tauBs 1.510 0. 0 0 0 fsfdBrDs 0.01265 0.00053 0 0 1
BrD 0.00993 0.00024 0 0 1 BrDst 0.323 0.006 0 0 1 BrBdD 0.0231 0.001 0 0 1 BrBdDst 0.0505 0.0014 0 0 1 NrefD 36.4e3 1.6e3 0 0 1 NrefDst 27.8e3 1.2e3 0 0 1
effRD 1.568 0.008 0 0 1 effRDst 1.464 0.007 0 0 1 physBkg 15560 0. 0 0 0 combBkg 5940 0. 0 0 0

normLHCb 0.6812 0.1 0 0 0

Correlations 1

NrefD NrefDst -0.703

Theory-Inputs 5 HPQCD LCSRDsS LCSRDs LHCb-PAPER-2019-046 MILC

`` The first line (Templates) is formed by the name of the file containing the signal templates and by the name of theTTreethat needs to be read. It should not be necessary to change it. The lines containingFF-Model-Ref-VandFF-Model-Ref-P` specify the model used during the generation of the signal templates (CLN in both cases) and the number of parameters of the model. These parameters are set to the values measured by the LHCb collaboration in Phys. Rev. D101 (2020) 072004.

The lines FF-Model-Fit-P and FF-Model-Fit-V indicate the model used during the fit to the data (CLN or BGL) and the number of parameters. The parameters that will be used are indicated via the following syntax parName parValue parError parLowLimit parUpperLimit isGaussianConstrained, which specifies the parameter name, central value, uncertainty, lower and upper limits and if the parameter is Gaussian constrained in the fit (1 if yes, 0 if not).

The line Other-Parameters indicates the number of other parameters used in the fit.

The line Correlations is followed by the a number that indicates the number of correlated parameters used in the fit (excluding the form-factor parameters). The correlations are simply indicated using the name of both parameters followed by the value of the correlation coefficient.

The line Theory-Inputs contains the number and the names of the theory/experimental inputs that will be used in the fit. Available options are: HPQCD_Ds, HPQCD_DsS, LCSRDs, LCSRDsS, LHCb-PAPER-2019-046 and MILC. The fit will automatically include these additional inputs and minimise the chi2 simultaneously.