src.detector module

Toy detector model: photon transport to a forward EM calorimeter.

• Geometry: plane at z = z_cal, circular active area of radius R.

• Escape: exponential survival in target with lambda = (9/7) X0 (pair production).

• Measurement: smear (x,y) on calorimeter and smear energy. Possibly include additional material-dependent smearing terms based on photon path length in target.

• Selection: energy threshold on measured energy, cluster separation.

• Reconstruction: eta, phi from (x_meas, y_meas, z_cal - z_vtx).

L-dependence via:

• path length in material before exiting target

• vertex depth z_vtx which affects geometry and separation at the calorimeter plane.

• smearing via material-dependent terms based on path length.

src.detector.intersect_calo_plane(photon_p4, z_vtx_cm, z_cal_cm)

Intersect photon trajectory with a plane z = z_cal.

Parameters:

• photon_p4 (ROOT.TLorentzVector) – Photon 4-vector in LAB.

• z_vtx_cm (float) – Production vertex z (cm).

• z_cal_cm (float) – Calorimeter plane position z (cm).

Returns:

• ok (bool) – True if the photon goes forward and intersects the plane.

• x_cm, y_cm (float) – Intersection coordinates on the plane (cm).

src.detector.passes_calo_aperture(x_cm, y_cm, R_cm)

Circular active area cut.

Parameters:

• x_cm (float) – Impact point on calo plane.

• y_cm (float) – Impact point on calo plane.

• R_cm (float) – Active radius.

Returns:

ok (bool) – True if inside active area.

src.detector.photon_exit_length_cm(photon_p4, z_vtx_cm, L_cm, R_tgt_cm)

Geometric path length (cm) a photon must travel to exit the target.

Verify both forward and lateral exit.

Parameters:

• photon_p4 (ROOT.TLorentzVector) – Photon 4-vector in LAB.

• z_vtx_cm (float) – Production depth inside target.

• L_cm (float) – Target thickness.

• R_tgt_cm (float) – Target radius (cm).

Returns:

path_length (float) – Photon path length in cm.

src.detector.photon_escape_prob(photon_p4, z_vtx_cm, L_cm, R_tgt_cm)

Survival probability for a photon to exit the target.

Parameters:

• photon_p4 (ROOT.TLorentzVector) – Photon 4-vector in LAB.

• z_vtx_cm (float) – Production depth inside target.

• L_cm (float) – Target thickness.

• R_tgt_cm (float) – Target radius (cm).

Returns:

p_esc (float) – Escape probability in [0,1].

src.detector.smear_energy(rng, E_GeV, a=0.12, b=0.02, c=0.0, path_length=None)

Implement simple calorimeter energy resolution model.

The relative energy resolution is given by the quadratic sum of three terms: stochastic, constant, and noise. If path_length is provided, an additional material-dependent smearing term is added to the constant term based on the photon path length in the target.

Parameters:

• rng (np.random.Generator) – Random number generator.

• E_GeV (float) – Expected photon energy.

• a (float) – Resolution parameters.

• b (float) – Resolution parameters.

• c (float) – Resolution parameters.

• path_length (float or None) – Photon path length. If None, no extra smearing.

Returns:

E_meas (float) – Smeared energy (GeV), clipped to be >= 0.

src.detector.smear_position(rng, x_cm, y_cm, sigma_xy_cm=0.2, path_length=None)

Gaussian smearing of the shower centroid on calo plane.

If path_length is provided, an additional material-dependent smearing term is added to the constant term based on the photon path length in the target.

Parameters:

• rng (np.random.Generator) – Random number generator.

• x_cm (float) – Impact point on calo plane.

• y_cm (float) – Impact point on calo plane.

• sigma_xy_cm (float) – Position resolution (cm).

• path_length (float or None) – Photon path length. If None, no extra smearing.

Returns:

x_meas, y_meas (float) – Measured hit coordinates.

src.detector.eta_phi_from_hit(x_cm, y_cm, z_vtx_cm, z_cal_cm)

Reconstruct direction (eta, phi) from measured hit position.

Parameters:

• x_cm (float) – Measured hit coordinates.

• y_cm (float) – Measured hit coordinates.

• z_vtx_cm (float) – Production vertex z (cm).

• z_cal_cm (float) – Calorimeter plane position z (cm).

Returns:

eta, phi (float) – Reconstructed direction in (eta, phi) space.

src.detector.deltaR(eta1, phi1, eta2, phi2)

Compute cluster separation in (eta, phi) space.

Parameters:

• eta1 (float) – Direction from cluster 1.

• phi1 (float) – Direction from cluster 1.

• eta2 (float) – Direction from cluster 2.

• phi2 (float) – Direction from cluster 2.

Returns:

dR (float) – Delta R separation between the two clusters.

src.detector.detect_two_photons(rng, g1_lab, g2_lab, z_vtx_cm, L_cm, z_cal_cm=1000.0, R_calo_cm=100.0, R_tgt_cm=10.0, E_thr_GeV=0.1, deltaR_min=0.02, sigma_xy_cm=0.2, res_a=0.12, res_b=0.01, en_material_smearing=True, xy_material_smearing=True)

Full detection chain for two photons.

Steps (per photon):

• escape in target (stochastic)

• intersect plane and aperture cut

• smear energy and position

• apply energy threshold on measured energy

Finally:

• reconstruct eta/phi from smeared (x,y)

• apply cluster separation deltaR > deltaR_min

Parameters:

• rng (np.random.Generator) – Random number generator.

• g1_lab (ROOT.TLorentzVector) – Photon 4-vectors in LAB.

• g2_lab (ROOT.TLorentzVector) – Photon 4-vectors in LAB.

• z_vtx_cm (float) – Production vertex z (cm).

• L_cm (float) – Target thickness (cm).

• z_cal_cm (float) – Calorimeter plane position z (cm).

• R_calo_cm (float) – Calorimeter active radius (cm).

• R_tgt_cm (float) – Target radius (cm).

• E_thr_GeV (float) – Energy threshold on MEASURED energy (GeV).

• deltaR_min (float) – Minimum separation between the two clusters.

• sigma_xy_cm (float) – Position resolution (cm).

• res_a (float) – Energy resolution parameters.

• res_b (float) – Energy resolution parameters.

• en_material_smearing (bool) – If True include material-dependent smearing in energy.

• xy_material_smearing (bool) – If True include material-dependent smearing in position.

Returns:

• ok (bool) – True if the event is reconstructed as two resolved photons.

• out (dict) – If ok, contains measured kinematics for both photons and deltaR.