Standard missing pt
This is a documentation issue describing the computation of the type 1 corrected PF missing pT in the standard reconstruction.
Nominal missing pT
Produced by RunMETCorrectionsAndUncertainties
class using plugin based on PFJetMETcorrInputProducerT
with a configuration like this one. However, in a complete MiniAOD configuration from production, the collection of jets used for the type 1 correction is ak4PFJetsCHS
(from slimmedMETs
→ patMETs
→ pfMetT1
→ corrPfMetType1
). There is no selection on jet ID. Instead, jets are skipped if
jet.chargedEmEnergyFraction() + jet.neutralEmEnergyFraction() > 0.9
In addition, momenta of muons inside the jet are vectorially subtracted if they pass isGlobalMuon
or isStandAloneMuon
ID.
Momentum scale factors corresponding to the L1L2L3(+Res) and L1Offset JEC are computed for the jet with the muons included. Then they are applied to the muon-subtracted raw jet momentum. This means muons' momenta are effectively rescaled by the JEC.
Jets whose pT with thus applied L1L2L3(+Res) correction is above 15 GeV are used for the type 1 correction following the L1L2L3 - L1 scheme:
\vec p_\text{T}^\text{\,miss} \leftarrow \vec p_\text{T}^\text{\,miss} - \sum_\text{jets} \left(\vec p_\text{T}^\text{\,L1L2L3} - \vec p_\text{T}^\text{\,L1}\right),
where the momenta are with the muons subtracted.
In the main collection of jets in NanoAOD, the electromagnetic energy fractions are stored in branches Jet_chEmEF
and Jet_neEmEF
. The factor to scale the raw jet momentum to account for the subtraction of muons passing the ID specified above is available as 1 - Jet_muonSubtrFactor
(NanoAOD configuration and C++ code). This factor is also available in collection CorrT1METJet
, but the electromagnetic energy fractions are not.
JER smearing
It seems the procedure is identical to above, just starts from jets with the smearing applied. This just rescales the momentum, but the JEC factors in pat::Jet
are not updated. As a result, the JER smearing is propagated also in the L1-corrected momentum, which is not correct.
Variations in scale of jet momentum
Jet collections with rescaled momentum are created by this function. The source collection of jets seems to be created here. From a complete MiniAOD configuration, the jets are subjected to the cut on the electromagnetic energy fraction, the muon subtraction, and the type 1 pT threshold. In addition, they are cleaned (within ΔR < 0.5) against very loosely selected patMuons
and all patElectrons
.
Mitigation of EE noise in 2017
This method produces the collections of PF candidates and jets used as inputs for the computation of the type 1 corrected missing pT described above. From the collection of jets it removes those with raw pT < 50 GeV and 2.65 < |η| < 3.139. From the collection of PF candidates, the following candidates are removed:
- Constituents of a jet with raw pT < 50 GeV and 2.65 < |η| < 3.139, even if the pseudorapidity of the candidate itself is outside of this η range.
- Candidates in 2.65 < |η| < 3.139, provided that they are not included in a jet with raw pT > 50 GeV and 2.65 < |η| < 3.139, or an electron, a muon, a tau, or a photon given to the method.
In NanoAOD missing pT with the noise mitigation can be computed as
\vec m = \vec m_\text{raw} + \vec m_\text{fix} - \vec m_\text{std} - \sum_{j \in T \cap R} \left(\vec\tau_\text{L1L2L3*} - \vec\tau_\text{L1*}\right) - \sum_{j \in T \setminus R} \left(\vec\tau_\text{L1L2L3} - \vec\tau_\text{L1}\right).
Here \vec m_\text{raw}
, \vec m_\text{fix}
, and \vec m_\text{std}
are RawMET
, METFixEE2017
, and MET
from NanoAOD, respectively; \vec\tau
is vectorial pT of a jet corrected to the level specified in the subscript; the asterisk in the subscript indicates the version of the correction applied at the time of production of NanoAOD (which might be different from what is used in the analysis); T is the set of jets normally used for the type 1 correction; and R is the set of jets with raw pT < 50 GeV and 2.65 < |η| < 3.139. This computation is discussed here. It agrees with what is done in nanoAOD-tools
(this file, lines 212–221, 343–352, 435–446).