NERVIOSO Y ENDOCRINO

A summary of the software used for different processes is shown in Table 10.1. The simulated events are weighted such that the final pileup distribution matches the one observed in data. Also several other corrections are applied to the simulated samples as described in Chapter 13.

10.4 Combination with the leptonic final state

The final states of all H± _→τ±_ν

τ signal events do not correspond to the τh + jets

final state. Electrons or muons can be produced either from the decays of the tau leptons from H± _{decays, or from a W}± _{boson decay. Thus the leptonic final states}

of the H± _→τ±_ν

τ process contain a single isolated lepton (electron or muon), pmissT

(due to neutrinos), and hadronic jets. For maximal signal sensitivity, the results of the analysis presented in this thesis, targeting the hadronic final state, are combined with those from a separate analysis targeting the leptonic final states, detailed in Ref. [73]. In the analysis of leptonic final states, single electron and single muon triggers are used in the online selection. In the offline selection, events with a single isolated electron or muon and one, two or three hadronic jets are selected.

At least one of the jets is required to be b-tagged. Leptonic final states containing a hadronically decaying tau lepton (τh), originating from the H± or from the W±

decay, and those without a τh are considered in separate categories. The latter case

corresponds to events where the H± _{decays leptonically while the W}± _{boson decays}

hadronically, or where either H± _{or W}± _{decay produces a τhbut it does not pass the}

identification criteria.

In the leptonic final states, the dominant background is tt production. This and other backgrounds are estimated from simulation. The number of QCD multijet events with jets misidentified as leptons is reduced to a negligible level by requiring a high pmiss_T and by applying angular selections based on ∆φ(`,~p<sub>T</sub>miss), ∆φ(leading jet,~p<sub>T</sub>miss), and min(∆φ(`, jet_n)), where jet_n refers to any of the 2–3 selected jets in the events.

The selected events are classified into several categories for statistical analysis, based on the presence or absence of a τh candidate, the jet multiplicity, the number of b-

tagged jets and on the magnitude of pmiss

T . Together with the separate electron and

muon final states, this results in 34 different categories.

The analyses of the hadronic and leptonic final states complement each other, because the relatively high trigger thresholds limit the sensitivity of the hadronic final state

150 10. Analysis strategy

Table 10.2: A summary of the phase space regions used in different H± _analyses.

No isolated electrons or muons 1 isolated electron or muon

2 jets —

H± _→τ±_ν

τ, leptonic final states 3 jets

H± _→τ±_ν

τ, τh + jets final state

>3 jets H± _→tb, leptonic final states

in the low-mH± region (below mt), making the leptonic final states experimentally

the most sensitive ones for the H± _{signal. In the high-m}

H± region (above mt) the

hadronic final state dominates the sensitivity, since the selection efficiency is higher as a result of more inclusive jet multiplicity requirements.

The object definitions and event selection requirements used in the hadronic and leptonic analyses are coordinated to ensure that the analyses use disjoint phase space regions, so that they have no events in common after all selections. This way the statistical combination of the results is straightforward as the data used in the two analyses are uncorrelated. In practice, this is ensured by common definitions in the lepton identification and isolation: the event selection in the hadronic channel rejects all events with isolated electrons and muons, whereas the leptonic analysis only uses these events. In the analysis of leptonic final states, events with more than 2–3 jets are not selected, because the high jet multiplicity events are expected to be more sensitive in the H± _{→tb decay channel. In order to allow statistical combination of the results}

from τ±_ν

τ and tb channels, the jet selection criteria are used to ensure that the two analyses do not use the same events. The different phase space regions defined by the lepton isolation and the jet multiplicity, used by the different analyses, are summarized in Table 10.2.

Shared object definitions, such as identification algorithms, isolation criteria and working points, also mean that most sources of systematic uncertainties are shared between the hadronic and leptonic final states of the H± _→τ±_ν

τchannel. Correlation of these systematic uncertainties in the combined statistical analysis allows the data from one final state to constrain the systematic uncertainties in another final state. In Chapter 14, after the final results of the analysis of the τh + jets final state are

presented, also the combined results from the hadronic and leptonic final states are shown and the contribution of each analysis in the final results is discussed.

Chapter 11

Event selection

This chapter describes the consecutive event selection steps applied in order to max- imize the signal sensitivity. Table 11.1 summarizes the online and offline selection steps described in Sections 11.1 and 11.2, with the final selection thresholds optimized as described in Section 11.3. The resulting signal selection efficiency is reported in Section 11.4.

Table 11.1: A summary of the online and offline event selection criteria. Selection steps 3–5 are

referred to as baseline selections. Steps 6–8 efficiently reduce the background from jets misidentified as τh, and step 9 discriminates between genuine taus from signal

and backgrounds events.

Selection Description

1 τh+pmissT trigger Selection of signal-like events using a dedicated trigger

2 Data quality filters Events required to pass the pmiss T filters

3 τhidentification ≥1 τhcandidates with pT >50 GeV,|η| <2.1 (loose MVA τhID)

4 Lepton veto No isolated electrons (muons) with pT>15(10)GeV,|η| <2.5

5 Jets selection ≥3 jets with pT >30 GeV,|η| <4.7 and passing the loose jet ID

6 b jet selection ≥1 b-tagged jet with pT >30 GeV and|η| <2.4 (CSVv2 medium WP)

7 pmiss

T Type-I corrected pmissT >90 GeV

8 Angular selection Rmin

bb >40◦to reduce the jet→τhbackground

9 Rτ categorization Reconstruct mTseparately for events with Rτ >0.75 and Rτ <0.75