New HLT2 trigger lines for dark photon search from charm decays

Description of the lines

Definition of HLT2 lines for the dark photon search A'(-> e+ e-) produced in a D* decay.

Prompt lines:

1. D*0 -> D0 e+ e- with D0 -> K- pi+
2. D*0 -> D0 e+ e- with D0 -> K- pi- pi+ pi+
3. 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.

Efficiency and rates

The efficiency is calculated using MC signal:

- MagDown : "/MC/Upgrade/27184010/Beam7000GeV-Upgrade-MagDown-Nu7.6-25ns-Pythia8/Sim10aU1/XDIGI"
- MagUp   : "/MC/Upgrade/27184010/Beam7000GeV-Upgrade-MagUp-Nu7.6-25ns-Pythia8/Sim10aU1/XDIGI"

and the rates using minbias:

- MagDown : /MC/Upgrade/30000000/Beam7000GeV-Upgrade-MagDown-Nu7.6-Pythia8/Sim10aU1/XDIGI
- MagUp   : /MC/Upgrade/30000000/Beam7000GeV-Upgrade-MagUp-Nu7.6-Pythia8/Sim10aU1/XDIGI

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.

Contact people

• Carlos Cocha @cacochat
• Martino Borsato @mborsato