FODA SECTOR BIOPLASTICO
AMENAZAS MATRIZ DE
The method employed to derive the photon fake factors, called the abcd method, makes use of
the isolation profiles expected for real and mis-identified photons. Similarly to the 2x2D sideband method, a two dimensional plane is constructed with identification and isolation variables. The dif- ference, other than only requiring one signal photon, between this and the 2x2D sideband method is that only the number of jet-to-photon fakes in the signal region is desired. The photon is identified as eitherTightor “pseudo”, which isLoose-but-not-Tightand defined in a way to be less correlated with isolation variables, as described in Section 5.1.3. In the isolation axis, the photon candidate can either be isolated or non-isolated, as determined by the “corrected topocone40” = topoetcone40−0.022pT, where the topoetcone40 is the transverse energy in a cone of radius∆R= 0.4 around the photon. This leads to four distinct areas of phase space described below or illustrated in Figure 7.27.
Corrected topoetcone40 [GeV]
topoetcone40 - pT*0.022
Identification
Non-Tight, Isolated Tight, Non-Isolated Tight, Isolated Non-Tight, Non-Isolated Isolation gapA
B
D
C
FFiso FFIDFigure 7.27: Cartoon of theabcdregions in the two dimensional plane of identification and isolation.
• A:Tight ID photon with track isolation and corrected topocone40 < 0 GeV
• B: Tight ID photon with corrected topocone40 > 8 GeV
• C: Pseudo photon with track isolation and corrected topocone40 < 0 GeV
7. Search for Exotic Higgs Decays 154
Theabcdmethod establishes three control regions (denoted B,C,D), which are composed of the mis-identified and looser photons(referred to as background photons), and a “signal region” in A. Assuming no signal contamination and correlation in the regions (this is a first order conjecture), the following holds: NBb
Nb A
=NDb
Nb C
, that is the ratio of background events in B to A is the same as D to C. Thus two photon fake factors can be written:
FFIso= NC ND , FFID= NB ND . (7.4)
With these factors designated, to estimate the number of jet-to-photon events in region A, the different fake factors can be applied in regions B or C:
Nj→γ(pT, η) =NAb =FFIso(pT, η)×NB=FFID(pT, η)×NC (7.5)
By construction, using either FFIso or FFID will give the same prediction for the signal region. The choice is up to the analyzer. In this analysis the isolation fake factors were larger than one in some important areas of phase space. This implies one event in control regions would be used to predict more than one signal region event, leading to large statistical errors of the final prediction. Therefore the ID fake factors were chosen to be used in the analysis. To be explicit, in order to infer theZ+ jets background in a given region, isolated pseudo photons would be selected and the FFID would be applied. The signal contamination in the control regions can be quantified and the fake factors are modified:
Nj→γ(pT, η) =NAb = NB−NBs ND−NDs ×(NC−NCs) =FF corr ID (pT, η)×(NC−NCs) ; (7.6) whereNsdenotes the number of real prompt photons in each region. This number is extracted from truth matched photons in Monte Carlo. Lastly, to gauge the correlation of the regions (R), one can calculate: R=N b ANDb Nb BNCb , (7.7)
which will equal 1 in the case of no correlation. Unfortunately R cannot be measured in data as background photons cannot be distinguished, therefore a similarly definedR0 is computed in a data region rich in background:
R0 =N 0 AN 0 D NB0 NC0 ; (7.8)
where the primed regions are:
• B0: Tight ID photon with 15 < corrected topocone40 < 27 GeV
• C0: Pseudo photon with track isolation and 9 < corrected topocone40 < 15 GeV
• D0: Pseudo photon with 15 < corrected topocone40 < 27 GeV
The 9 GeV choice to start the R0 regions is arbitrary but aims to define a background enriched
region for measuring the correlation while retaining sufficient statistics. The final formula for the estimated jet-to-photon events in a signal region with the correlation included would then be:
Nj→γ(pT, η) =NAb = R0NB−N s B ND−NDs ×(NC−NCs) = R0NB−N s B ND−NDs (1−N s C NC ) ×NC=FFcorrID (pT, η)×NC . (7.9)
In the analysis, the jet-to-photon mis-identified background arises from mostlyZ+ jets so nat- urally the fake factors should be measured in a Z+ jets region distinct from the signal region. Unfortunately, with photon like objects, the region is dominated by Standard ModelZγ leading to enormous subtractions of the signal photon contamination and large statistical uncertainties. In- stead, the measurement is performed in a diphoton topology, tagging the first photon asTight and
isolated, and allowing the second photon to be Tight or pseudo. To further complicate matters,
the 2017 trigger used to collect the sample was tighter and contained an additional calorimeter requirement, changing the composition of theLoose-but-not-Tightphotons. In order to expedite the analysis further studies were left for the full Run 2 search, and it was decided to perform the photon fake factor extraction with the 2015–2016 diphoton sample collected with the same trigger as the
H →γγ analysis (detailed in Section 6.2.1).
A comparison between theZ+ jets fake factor calculated with79.8fb−1of data and the diphoton fake factor determined with36.1fb−1of data in a different dataset is shown in Figure 7.28. The fake factors are calculated independently for the barrel (red) and endcap (blue) regions for the following studies. The shapes of the distributions are similar to each other and although the uncertainties in the fake factor determined from the Z+ jets samples are large, they are consistent with the magnitude and dependence onpTseen in the diphoton derivation. As long as theZ+ jets fake factors were not contingent on the topology of the event, then the fake factors derived in the diphoton region could be employed for the final calculation. Figure 7.29 shows theZ+ jets fake factors as a function ofp``T andETmiss. The values are relatively constant.
The diphoton fake factors were then investigated for reliance on kinematic variables. The fake factors as a function ofETmiss,∆φ(ETmiss, γ),mγ,E
miss T
T are shown in Figure 7.30. Considering the fake
factors are not sensitive to most important kinematic variables, the fake factors parameterized by
7. Search for Exotic Higgs Decays 156
(a) Diphoton (b)Z+ jets
Figure 7.28: (a) Diphoton and (b)Z+ jets jet-to-photon ID fake factors as a function of pT. The measurements are split between barrel (red) and endcap objects (blue). The diphoton fake fac- tors were calculated using36.1fb−1 of 2015–2016 data while theZ+ jets fake factors were derived utilizing79.8fb−1 of data collected in 2015–2017.
(a)p``
T (b)ETmiss
Figure 7.29: Jet-to-photon ID fake factor as a function of (a)p``
T and (b)ETmissin theZ+ jets region. The fake factors are derived in the barrel (red) and endcap (blue) regions.
factors, statistical errors, andR0 parameters are presented inpTbins for both the barrel and endcap regions. This factor is measured to be0.4-0.7in the barrel region and0.45-0.95in the endcap region of the detector, depending on the pT of the photon. The correlation R0 derived in the data was within15% of1.0 (no correlation) for most bins.
Table 7.7: Jet-to-photon ID fake factors, binned inpTand split between barrel and endcap regions.
pTBin [GeV] 0.0<|η|<1.37 Stat. Err. R
0 1.52<|η|<2.37 Stat. Err. R0 25≤pT<35 0.59 0.01 0.86 0.87 0.02 0.86 35≤pT<50 0.63 0.01 0.85 0.91 0.02 0.83 50≤pT<65 0.66 0.02 0.93 0.92 0.05 0.90 65≤pT<80 0.69 0.04 0.90 0.76 0.06 0.92 80≤pT<100 0.57 0.05 0.90 0.58 0.07 0.90 100≤pT<150 0.46 0.05 0.86 0.50 0.08 1.09 150≤pT<∞ 0.51 0.07 1.16 0.45 0.10 1.02 (a)Emiss T (b)∆φ(ETmiss, γ) (c)mγ,E miss T T
Figure 7.30: Diphoton photon-to-jet ID fake factors as a function of (a)ETmiss, (b)∆φ(EmissT , γ), (c)
mγ,E miss T
T . The fake factors are calculated in the barrel (red) and endcap (blue) regions.
Correlation Measurements
The previous section details the photon fake factors derived in the data. InZ+ jets and γj Monte
Carlo one can do the same calculations and confirm the assumptions are reasonable. The R0 pa-
rameter, which measures the correlation of the regions, in the fake rate calculation is measured in primed regions rather than the actual abcd regions. As a simple check, the actualR = NAbNDb
Nb BNCb
is calculated in Monte Carlo and compared with theR0 used in the fake rate derivation. Table 7.8
7. Search for Exotic Higgs Decays 158
shows the comparison between data and Monte Carlo correlation factors, binned coarser to compare the correlation in bothZ+ jets andγj events. The majority ofR0 andRparameters are consistent
with each other and1.0.
Table 7.8: Rand R0 parameters measured in theZ+ jets andγj Monte Carlo and data.
BarrelZ+ jets Barrel Diphoton EndcapZ+ jets Endcap Diphoton
pT[GeV] R 0 R R0 R R0 R R0 R 25≤pT<50 0.99±0.03 1.16±0.06 1.12±0.09 1.30±0.06 0.83±0.07 1.23±0.07 0.87±0.15 1.13±0.10 50≤pT<100 0.96±0.05 1.22±0.08 0.99±0.11 1.15±0.09 0.94±0.11 0.88±0.17 0.94±0.14 1.32±0.16 100≤pT<150 0.98±0.11 1.07±0.16 1.04±0.15 0.93±0.18 1.16±0.17 0.79±0.21 0.77±0.21 0.85±0.32 150≤pT<∞ 0.96±0.06 1.18±0.23 1.07±0.06 1.01±0.10 0.89±0.07 1.59±0.61 1.11±0.23 1.17±0.23