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:
- 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
andD
are built inspired by the charm builders defined ind0_to_hh
,d0_to_hhhh
andd_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 gammaE_T
larger 100 MeV and combined massm(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.