Definition of HLT2 lines for the dark photon search A'(-> e+ e-) produced in a D* decay.
Prompt lines:
D*0 -> D0 e+ e- with D0 -> K- pi+
D*0 -> D0 e+ e- with D0 -> K- pi- pi+ pi+
Ds*+ -> D(s)+ e+ e- with D(s)+ -> K- K+ pi+
K, pi and D are built inspired by the charm builders defined in d0_to_hh, d0_to_hhhh and d_to_hh. In the future, the cuts are expected to be tuned after a better understanding of the detector/data.
The dielectron pairs e+ e- are built including bremsstrahlung correction.
The range of the dark photon mass values is accessible within m(D*) - m(D) which is below 140 MeV, but extended to 250 MeV in the D* maker for background fitting.
The lines also preserve photons near the dielectron candidates to reconstruct, later, {pi0, eta} -> e+ e- gamma, for background studies. This is done using WeightedRelTableAlg, see Rec!2750 (merged), where a gamma E_T larger 100 MeV and combined mass m(e+e-gamma) below 600 MeV are desired.
A minimum electron p_T value of 50 MeV is chosen for all the trigger lines as it provides rates around 100 Hz with a minimal impact on the efficiency. The following table summarizes the results.
Line (cut at min p_T(e) = 50 MeV )
Rate [Hz]
Expected signal rate [Hz]
TrueSim Efficiency [%]
D*0 -> D0 e+ e-, D0 -> K- pi+
102.32
61.4
6.2
D*0 -> D0 e+ e-, D0 -> K- pi- pi+ pi+
55.66
-
-
Ds*+ -> D(s)+ e+ e-, D(s)+ -> K- K+ pi+
6.5
-
-
Note: Both D+ and Ds+ are used because the Ds*+ rate is very small.
Besides, the following plot shows the tradeoff between the TrueSim efficiency (red curve) and rate for the different trigger lines as a function of the minimum electron p_T.
Analysis
The trigger line is in the charm repository and gets inspired by some charm makers, but this analysis should also belong to QEE.
