Standard Model Higgs to gamma gamma Efficiency ( CMS DP-2018/039)

The plots show the efficiency of the trigger used in the Standard Model 𝐻 → 𝛾𝛾 analyses. The measurement uses the full dataset collected in 2017 by CMS, corresponding to 41.5 fb-1.

The trigger requires the presence of two photons at HLT. It is organized into two main parts: the first one requiring at least one photon matched to a Level-1 electron candidate and with ET > 30 GeV (referred to as the “seeded leg”), the second one requiring at least 2 photons with ET > 22 GeV, at least one of which survives the “seeded leg” selection (the other photon is referred to as “unseeded leg”).

The HLT decision is based on requirements on the photon transverse energy, on the ratio of the energy deposit in the hadronic and electromagnetic calorimeter, on shower shape and isolation variables, and on the mass of the di-photon system.

The selection is different in different categories defined depending on barrel/endcap photons and on the value of R9, which is defined as the ratio of the energy contained in an array of 5x5 crystals over the total supercluster energy.

The offline selection is similar to the trigger requirements, but more stringent.

The trigger efficiency is measured using the tag-and-probe technique on 𝑍→𝑒𝑒 events.

An offline isolated electron with a transverse momentum above 32 GeV matched to the HLT candidate firing the single electron trigger is used as a tag. The tag must pass the offline selection (inverting the requirement on the electron veto, which would reject most of electrons) and have |η|≤ 2.1 (excluding 1.4442 ≤ |η| ≤ 1.566). For the "unseeded leg" efficiency measurement, the tag is also required to match a Level-1 electron candidate.

The probe is required to pass the offline selection as well (with the inverted electron veto), to have |η| ≤ 2.5 and pT > 35(25) GeV for the seeded (unseeded) leg efficiency measurement.

For each electron passing the tag filter, the opposing electron is considered as a possible probe.

The efficiency is defined as efficiency= probes passing HLT/all probes

The 𝑍→𝑒𝑒 events are reweighted in R9 and η to match the H→𝛾𝛾 distribution for mH = 125 GeV.

Seeded Leg Efficiency The efficiency with respect to the probe electron transverse energy of the seeded leg of the di-photon trigger is shown for the four analysis categories, defined according to probe R9 (the ratio of the energy contained in an array of 5x5 crystals over the total supercluster energy) and η. It is measured on data for 𝑍→𝑒𝑒 events using the tag-and-probe method. The 𝑍→𝑒𝑒 events are reweighted in R9 and η to match the H→𝛾𝛾 distribution for m(H )= 125 GeV. The efficiency of the matching to the Level-1 electron candidate is also included. [Get pdf version] Contact: Linda Finco

Unseeded Leg Efficiency The efficiency with respect to the probe electron transverse energy of the unseeded leg of the di-photon trigger is shown for the four analysis categories, defined according to probe R9 (the ratio of the energy contained in an array of 5x5 crystals over the total supercluster energy) and η. It is measured on data for 𝑍→𝑒𝑒 events using the tag-and-probe method. The 𝑍→𝑒𝑒 events are reweighted in R9 and η to match the H→𝛾𝛾 distribution for mH = 125 GeV. The higher plateau value with respect to the seeded leg efficiency is due to the missing requirement on the matching to a Level-1 electron candidate. [Get pdf version] Contact: Linda Finco

-- ElisabettaGallo - 2018-07-03