Fully Coherent Energy Loss

All FCEL particulars are bundled in the header file fcel.h, which includes the function channel(int i) the partonic 2->2 subprocess to be selected. This will prepare the appropriate SU(3) irreps of the final state and their colour probabilities as global quantities. The argument of channel(..) corresponds with the QCD processes

1. i=1 g, g -> g, g
2. i=2 q, g -> q, g
3. i=3 g, q -> q, g
4. i=4 g, g -> q, qbar

Here we consider two applications: i) LHC physics, ii) atmospheric neutrinos.

nuclear mod. factor @ LHC pA

Compute R_pA for light [1,2] and heavy mesons production, due solely to FCEL. The LHC parameters are the collisional energy, the nucleon number, and the strong coupling. Respectively, their default parameters are

double SQRTS = 8.16;  // TeV
double A = 208.;      // Pb
double alpha_s = 0.5; // coupling

Data is saved under pA/out/, where file names indicate the partonic subprocess {ab;cd} (for a,b -> c,d) and the fixed transverse momentum (pT) or rapidity (y).

• R_reps(double pT) generates a table of R(y)
• R_scan_y(double pT) generates a table of R(y)
• R_scan_pT(double y) generates a table of R(pT)

Uncertainty bands are generated by the Hessian method, which is applied to the parameter list:

#define PARAMS 5  // q0, xi, z, n,  m_Q
double dS[PARAMS] = {.02,.25,.2,1.,0.5};
double  S[PARAMS] = {.07,.50,.8,4.,1.5};

atmospheric neutrino flux nu/

Conventional and prompt ν's are produced by cosmic rays (CRs) colliding with Air nuclei (=14.5). Using the approximate Z-moment solution to the cascade equation, the flux on the earths surface can be expressed by a convolution of the charm cross-section with the CR flux. The cross-section dσ/dx_F is defined in sigma.h, as a functions of x_F and the proton energy E_p. Three CR fluxes are included in crflux.h:

• knee-spectrum
• H3a
• Global-spline fit