B-physics trigger efficiencies

In these plots, the efficiency of three requirements used in B-Physics triggers in CMS is shown. It has been measured on a fraction of the data collected in the middle of the 2017 data-taking period, corresponding to 9.8 fb-1. Each of these requirements is used in several trigger paths, for dfferent physics channels.

The efficiencies have been measured on a set of J/Psi candidates or of B+/- -> J/Psi K+/- candidates, in order to have a negligible amount of background contamination after selection criteria have been applied.

To select the J/Psi candidates, muons passing a set of generic quality and identification criteria optimized for B-Physics and Quarkonium channels, and with |eta(muon)|< 2:4 are used, with a dimuon invariant mass in the range [2.9,3.3] GeV and a dimuon vertex probability greater than 0.001. In addition, each muon used in the analysis is matched with the corresponding muon firing the high level trigger used to collect the sample, which is different for each efficiency.

The B+/- -> J/Psi K+/- candidates are reconstructed as follows. A J/Psi candidate is formed using the same selections described above. In addition, a track with pT > 2 GeV is required for the kaon candidate. The overall invariant mass is required to be in the range [5.123,5.423] GeV, and the three object vertex probability should be greater than 0.1.

For both J/Psi and B+/- -> J/Psi K+/- candidates, if more than one candidate per event is passing the selection criteria, only the one with highest vertex probability is used.

To estimate each efficiency a reference method is used, computing the ratio of number of candidates passing a numerator trigger in a sample of events collected by a trigger not presenting the investigated requirement, called denominator trigger.

The efficiency is defined as: Eff = events satisfying the denominator and firing the numerator trigger/events with one selected candidate and firing the denominator trigger.

L1 DeltaR efficiency
The efficiency of the Level-1 Trigger requirement DeltaR(mumu) < 1.2, used to select events with dimuon candidates with invariant mass lower than 6 GeV, is shown against the pseudorapidity of the J/Psi candidate. DeltaR(mumu) is defined as sqrt(Deltaphi2+Deltaeta2).
The efficiency is computed with the reference method, on a sample of J/Psi candidates selected using the criteria described in the introduction and requiring pT (J/Psi) > 27 GeV. The sample is collected with a denominator trigger that requires a pair of opposite-sign muons with pT(mu) at the L1T> 4 GeV , and forming a common vertex at HLT.
The numerator trigger additionally requires that the pair of muons has DeltaR(mumu) at the L1T < 1.2, and has a dimuon invariant mass compatible with the J/Psi mass and a dimuon pT > 25 GeV, at HLT.
The efficiency loss for candidates with module of the pseudorapidity greater than 1.2 can be attributed to the lower resolution on the muon kinematic variables in that region, that propagates to a lower resolution of the DeltaR(mumu) value.
[Get pdf version]
Contact: Alessio Boletti
imgfd3cbdae0a2c9b9fe0fde35054d4d510.png

Inclusive vertex efficiency
The efficiency of the High-Level Trigger requirement of a vertex between two muons, with no displaced topology, is shown against the offline dimuon vertex probability.
The efficiency is computed with the reference method, on a sample of J/Psi candidates selected using the criteria described in the introduction and requiring pT (J/Psi) > 27 GeV.
The sample is collected with a denominator trigger that requires a pair of opposite-sign muons with pT(mu) at the L1T > 4 GeV and DeltaR(mumu) at the L1T< 1.2, or a pair of opposite-sign muons with eta(mu) at the L1T< 1.5 and DeltaR(mumu) at the L1T< 1.4, and with a dimuon invariant mass compatible with the J/Psi mass at the HLT.
The numerator trigger additionally requires that the muon pair is forming a common vertex, and has a dimuon pT > 25 GeV, at HLT.
[Get pdf version]
Contact: Alessio Boletti
imgca894b2e482a35a36dd2599edb1345bf.png

Displaced vertex efficiency
The efficiency of the High-Level Trigger requirement of a displaced vertex between two muons, used to select B-hadron decays, is shown against the significance of the dimuon transverse flight length. The significance of dimuon transverse flight length is defined as the offline dimuon flight length from the beam interaction point projected on the transverse plane of the detector, divided by its uncertainty.
The efficiency is computed with the reference method, on a sample of B -> J/Psi K+/- candidates selected using the criteria described in the introduction.
The sample is collected with a denominator trigger that requires a pair of opposite-sign muons with pT(mu) at the L1T> 4 GeV and DeltaR(mumu) at the L1T < 1.2, or a pair of opposite-sign muons with abs(eta(mu)) at the L1T < 1.5 and DeltaR(mumu) at the L1T < 1.4, and with pT(mu) at the HLT > 4 GeV and with a dimuon invariant mass compatible with the J/Psi mass at the HLT.
The numerator trigger additionally requires that the dimuon pair is forming a common vertex with a displacement significance on the transverse plane, with respect to the beam interaction point, greater than 3, at the HLT.
[Get pdf version]
Contact: Alessio Boletti
img77f8f6942163f21c6468a8d3aa709fc1.png

-- ElisabettaGallo - 2018-05-15

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