A class for the \(M \to P l^+ l^-\) decay. More...
#include <MPll.h>
A class for the \(M \to P l^+ l^-\) decay.
This class is used to compute all the functions needed in order to build the observables relative to the \(M \to P l^+ l^-\) decays, where \(M\) is a generic meson and \(P\) is a pseudoscalar meson.
The mandatory parameters of MPll are summarized below:
| Label | LaTeX symbol | Description |
|---|---|---|
| r_1_fplus, r_2_fplus, m_fit2_fplus | \(r_1^{f_+}, r_2^{f_+}, m_{fit}^{2,f_+}\) | The fit parameters for the LCSR form factor \(f_+\) of the \(B\to K\). |
| r_1_fT, r_2_fT, m_fit2_fT | \(r_1^{f_T}, r_2^{f_T}, m_{fit}^{2,f_T}\) | The fit parameters for the LCSR form factor \(f_T\) of the \(B\to K\). |
| r_2_f0, m_fit2_f0 | \(r_2^{f_0}, m_{fit}^{2,f_0}\) | The fit parameters for the LCSR form factor \(f_0\) of the \(B\to K\). |
| absh_0_MP, absh_0_1_MP | \(\mathrm{Abs}h_0^{(0)}, \mathrm{Abs}h_0^{(1)}\) | The constant and linear terms of the absolute value of the hadronic parameter \(h_0\) of the \(B\to K\). |
| argh_0_MP, argh_0_1_MP | \(\mathrm{Arg}h_0^{(0)}, \mathrm{Arg}h_0^{(1)}\) | The constant and linear terms of the argument of the hadronic parameter \(h_0\) of the \(B\to K\). |
This kind of decays can be described by means of the \(\Delta B = 1 \) weak effective Hamiltonian
\[ \mathcal{H}_\mathrm{eff}^{\Delta B = 1} = \mathcal{H}_\mathrm{eff}^\mathrm{had} + \mathcal{H}_\mathrm{eff}^\mathrm{sl+\gamma}, \]
where the first term is the hadronic contribution
\[ \mathcal{H}_\mathrm{eff}^\mathrm{had} = \frac{4G_F}{\sqrt{2}}\Bigg[\sum_{p=u,c}\lambda_p\bigg(C_1 Q^{p}_1 + C_2 Q^{p}_2\bigg) -\lambda_t \bigg(\sum_{i=3}^{6} C_i P_i + C_{8}Q_{8g} \bigg)\Bigg] \,, \]
involving current-current, chromodynamic penguin and chromomagnetic dipole operators, while the second one, given by
\[ \mathcal{H}_\mathrm{eff}^\mathrm{sl+\gamma} = - \frac{4G_F}{\sqrt{2}}\lambda_t \bigg( C_7Q_{7\gamma} + C_9Q_{9V} + C_{10}Q_{10A} \bigg) \,, \]
includes the electromagnetic penguin plus the semileptonic operators.
Considering the matrix element of \(\mathcal{H}_\mathrm{eff}^{\Delta B = 1}\) between the initial state \(M\) and the final state \(P l^+ l^-\), only the contribution of \(\mathcal{H}_\mathrm{eff}^\mathrm{sl+\gamma}\) clearly factorizes into the product of hadronic form factors and leptonic tensors at all orders in strong interactions. Following [144], we implemented the amplitude in the helicity basis; hence we made use of the helicity form factors \( \tilde{V}_0(q^2), \tilde{T}_0(q^2)\) and \(\tilde{S}(q^2) \), which are related to the ones in the transverse basis through the following relations :
\[ \tilde{V}_0(q^2) = i \frac{\sqrt{\lambda(q^2)}}{2m_M\sqrt{q^2}}f_+(q^2)\,,\\ \tilde{T}_0(q^2) = i \frac{\sqrt{\lambda(q^2)q^2}}{2m_M^2(m_M+m_P)}f_T(q^2)\,,\\ \tilde{S}(q^2) = -\frac{m_M^2-m_P^2}{2m_M(m_b+m_s)}\frac{1+m_s/m_b}{1-m_s/m_b}f_0(q^2)\,, \]
where \(\lambda(q^2) = 4m_M^2|\vec{k}|^2\), with \(\vec{k}\) as the 3-momentum of the meson \(P\) in the \(M\) rest frame.
The effect of the operators of \(\mathcal{H}_\mathrm{eff}^\mathrm{had}\) due to exchange of soft gluon can be reabsorbed in the following parameterization,
\[ h_0(q^2) = \frac{\epsilon^*_\mu(\lambda)}{m_M^2} \int d^4x e^{iqx} \langle \bar P \vert T\{j^{\mu}_\mathrm{em} (x) \mathcal{H}_\mathrm{eff}^\mathrm{had} (0)\} \vert \bar M \rangle = h_0^{(0)} + \frac{q^2}{1\,\mathrm{GeV}^2} h_0^{(1)}\,. \]
The amplitude can be therefore parametrized in terms of the following helicity amplitudes:
\[ H_V = -i\, N \Big\{C_{9} \tilde{V}_{L,0} +C_{9}' \tilde{V}_{R,0} + \frac{m_M^2}{q^2} \Big[\frac{2\, m_b}{m_M} (C_{7} \tilde{T}_{L,0} + C_{7}' \tilde{T}_{R,0}) - 16 \pi^2 h_0 \Big] \Big\} \,, \\ H_A = -i\, N (C_{10} \tilde{V}_{L,0} + C_{10}'\tilde{V}_{R,0}) \,, \\ H_S = i\, N \frac{ m_b}{m_W} (C_S \tilde{S}_L + C_S' \tilde{S}_R)\,, \\ H_P = i\, N \Big\{ \frac{ m_b}{m_W} (C_P \tilde{S}_L + C_P' \tilde{S}_R) + \frac{2\,m_\ell m_b}{q^2} \left[C_{10} \Big(\tilde{S}_L - \frac{m_s}{m_b} \tilde{S}_R \Big) + C_{10}' \Big(\tilde{S}_R - \frac{m_s}{m_b} \tilde{S}_L\Big) \right] \Big\} \,, \]
where \( N = - \frac{4 G_F m_M}{\sqrt{2}}\frac{e^2}{16\pi^2}\lambda_t\) and we have defined
\[ \tilde{V}_{L,0}(q^2) = -\tilde{V}_{R,0}(q^2)=\tilde{V}_0(q^2)\,,\\ \tilde{T}_{L,0}(q^2) = -\tilde{T}_{R,0}(q^2)=\tilde{V}_0(q^2)\,,\\ \tilde{S}_L(q^2) = -\tilde{S}_R(q^2)=\tilde{S}(q^2)\,. \]
Squaring the amplitude and summing over the spins it is possible to obtain the fully differential decay rate, which is
\[ \frac{d^{(4)} \Gamma}{dq^2\,d(\cos\theta_l)} = \frac{9}{32\,\pi} \Big( I^c_1 +I^c_2\cos2\theta_l + I_6^c \cos\theta_l \Big) \]
The angular coefficients involved in the differential decay rate are related to the helicity amplitudes according to the following relations:
\[ I_1^c = F \left\{ \frac{1}{2}\left(|H_V^0|^2+|H_A^0|^2\right)+ |H_P|^2+\frac{2m_\ell^2}{q^2}\left(|H_V^0|^2-|H_A^0|^2\right) + \beta^2 |H_S|^2 \right\}\,,\\ I_2^c = -F\, \frac{\beta^2}{2}\left(|H_V^0|^2+|H_A^0|^2\right)\,,\\ I_6^c = 2 F \frac{\beta\, m_\ell}{\sqrt{q^2}} {\rm Re} \left[ H_S^* H_V^0 \right]\,,\\ \]
where
\[ F=\frac{ \lambda^{1/2}\beta\, q^2}{3 \times 2^{5} \,\pi^3\, m_M^3}\,, \qquad \beta = \sqrt{1 - \frac{4 m_\ell^2}{q^2} }\,. \]
The final observables are hence build employing CP-averages \(\Sigma_i\) or CP-asymmetries \(\Delta_i\) of such angular coefficients; however, since on the experimental side the observables are averaged over \( q^2 \) bins, an integration of the coeffiecients over such bins has to be performed before they are combined in order to build the observables.
The class is organized as follows: after the parameters are updated in updateParameters() and the cache is checked in checkCache(), the form factor are build in the transverse basis in the functions f_plus(), f_0() and f_T() [31]. They are consequentely translated in the helicity basis through the functions V_L(), V_R(), T_L(), T_R(), S_L() and S_R(). Form factors and parameters are combined together in the functions H_V(), H_A(), H_S() and H_P() in order to build the helicity amplitudes, which are consequentely combined to create the angular coefficients in the function I(). Those coefficients are used to create the CP averaged coefficients in the function Sigma() ad the CP asymmetric coefficients in the function Delta(). Form factors, CP averaged and asymmetric coefficients and hadronic contributions are integrated in the functions integrateSigma() and integrateDelta() in order to be further used to build the observables.
Public Member Functions | |
| gslpp::complex | DeltaC9_KD (double q2) |
| gslpp::complex | funct_g (double q2) |
| double | getSigma (int i, double q_2) |
| The value of \( \Sigma_{i} \) from \(q_{min}\) to \(q_{max}\). More... | |
| double | getwidth () |
| The width of the meson M. More... | |
| gslpp::complex | H_A (double q2) |
| The helicity amplitude \( H_A^{\lambda} \) . More... | |
| gslpp::complex | h_lambda (double q2) |
| The non-pertubative ccbar contributions to the helicity amplitudes. More... | |
| gslpp::complex | H_P (double q2) |
| The helicity amplitude \( H_P^{\lambda} \) . More... | |
| gslpp::complex | H_S (double q2) |
| The helicity amplitude \( H_S^{\lambda} \) . More... | |
| gslpp::complex | H_V (double q2) |
| The helicity amplitude \( H_V^{\lambda} \) . More... | |
| std::vector< std::string > | initializeMPllParameters () |
| A method for initializing the parameters necessary for MPll. More... | |
| double | integrateDelta (int i, double q_min, double q_max) |
| The integral of \( \Delta_{i} \) from \(q_{min}\) to \(q_{max}\). More... | |
| double | integrateSigma (int i, double q_min, double q_max) |
| The integral of \( \Sigma_{i} \) from \(q_{min}\) to \(q_{max}\). More... | |
| MPll (const StandardModel &SM_i, QCD::meson meson_i, QCD::meson pseudoscalar_i, QCD::lepton lep_i) | |
| Constructor. More... | |
| virtual | ~MPll () |
| Destructor. More... | |
Private Attributes | |
| double | ale |
| bool | dispersion |
| bool | FixedWCbtos |
| double | GF |
| QCD::lepton | lep |
| double | Mb |
| double | mb_pole |
| double | Mc |
| double | mc_pole |
| QCD::meson | meson |
| double | mJ2 |
| double | Mlep |
| double | MM |
| double | MP |
| std::vector< std::string > | mpllParameters |
| double | Ms |
| double | mu_b |
| double | mu_h |
| std::unique_ptr< F_1 > | myF_1 |
| std::unique_ptr< F_2 > | myF_2 |
| const StandardModel & | mySM |
| QCD::meson | pseudoscalar |
| double | spectator_charge |
| double | width |
| MPll::MPll | ( | const StandardModel & | SM_i, |
| QCD::meson | meson_i, | ||
| QCD::meson | pseudoscalar_i, | ||
| QCD::lepton | lep_i | ||
| ) |
Constructor.
| [in] | SM_i | a reference to an object of type StandardModel |
| [in] | meson_i | initial meson of the decay |
| [in] | pseudoscalar_i | final pseudoscalar meson of the decay |
| [in] | lep_i | final leptons of the decay |
Definition at line 19 of file MPll.cpp.
| gslpp::complex MPll::DeltaC9_KD | ( | double | q2 | ) |
| gslpp::complex MPll::funct_g | ( | double | q2 | ) |
| double MPll::getSigma | ( | int | i, |
| double | q_2 | ||
| ) |
The value of \( \Sigma_{i} \) from \(q_{min}\) to \(q_{max}\).
| [in] | i | index of the angular coefficient \( I_{i} \) |
| [in] |
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| gslpp::complex MPll::H_A | ( | double | q2 | ) |
| gslpp::complex MPll::h_lambda | ( | double | q2 | ) |
| gslpp::complex MPll::H_P | ( | double | q2 | ) |
| gslpp::complex MPll::H_S | ( | double | q2 | ) |
| gslpp::complex MPll::H_V | ( | double | q2 | ) |
| std::vector< std::string > MPll::initializeMPllParameters | ( | ) |
A method for initializing the parameters necessary for MPll.
Definition at line 76 of file MPll.cpp.
| double MPll::integrateDelta | ( | int | i, |
| double | q_min, | ||
| double | q_max | ||
| ) |
The integral of \( \Delta_{i} \) from \(q_{min}\) to \(q_{max}\).
| [in] | i | index of the angular coefficient \( I_{i} \) |
| [in] | q_min | minimum q^2 of the integral |
| [in] | q_max | maximum q^2 of the integral |
Definition at line 1232 of file MPll.cpp.
| double MPll::integrateSigma | ( | int | i, |
| double | q_min, | ||
| double | q_max | ||
| ) |
The integral of \( \Sigma_{i} \) from \(q_{min}\) to \(q_{max}\).
| [in] | i | index of the angular coefficient \( I_{i} \) |
| [in] | q_min | minimum q^2 of the integral |
| [in] | q_max | maximum q^2 of the integral |
Definition at line 1174 of file MPll.cpp.
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