Separation of converted and unconverted photons:
!
New geometry MC sample of single photons and
photons from radiative Z decay
Yee Chinn Yap
1
Single photon samples
•
Moving from the old geometry to new geometry samples, a strange bump at
F1=0.1 is observed.
•
This is due to the different ET spectra of the two samples.
•
Old geometry sample : mc12_8TeV.
159020.ParticleGenerator_gamma_Et7to80.merge.NTUP_PHOTON.e1173_s1
479_s1470_r3586_r3549_p1344
•
New geometry sample : mc12_8TeV.
184001.ParticleGenerator_gamma_ETspectrumMVAcalib.merge.NTUP_PHOTO
N.e2173_s1748_s1741_r4807_r4540_p1344
2
ET spectrum
•
Old sample uses flat ET from 7-80GeV.
•
New sample has pT spectrum that covers the full range up to 3 TeV while
maximising the statistics in the region between 7–100 GeV.
3
F1(Fraction of energy in strip layer)
•
Old geometry
!
!
•
New geometry
4
5
Emaxs1 (Energy of strip with maximal energy deposit)
•
Converted photons and electrons has same emaxs1 distribution. Despite
electrons from converted photons having lower energy than unconverted
photons, the fact that electron starts showering earlier contributes to the larger
emaxs1 value.
6
Radiative Z decays (Z→μμγ) Monte Carlo samples
7
Radiative Z decays
•
Motivation: able to make comparison between data and Monte Carlo.
•
To check reconstruction and identification algorithm.
•
Thanks to Kun for the sample of photons selected from radiative Z decay.
•
Start by checking how this sample compares to the single photon samples.
Due to vastly different pT distributions of the two samples, a selection cut on
pT<50GeV is applied. (See next slide)
•
Good agreement on the distribution of shower shape variables between the
two, taking into account the different pT spectra and pile-up conditions (0 for
single photons and ~20 for radiative Z decays).
8
pT distribution
pT mostly
contained in
10-50GeV
up to 3TeV, max
stats in 7-100GeV
9
Photon selection from Z→μμγ sample
•
Generated with Sherpa
•
Selection criteria :
1. at least two leptons and one photon, with two lepton invariant mass within
[40, 83] GeV and three body invariant mass within [45, 125] GeV.
2. photon pT>10GeV (ph_cl_corrected)
10
Rɸ (layer-2 variable)
•
Radiative Z decays
!
!
!
•
Single photons
11
ws,tot (strip layer variable)
•
Radiative Z decays
!
!
!
•
Single photons
12
Next steps
•
Learn to use TMVA
•
Shower shape variables as input for the BDT for separation of converted and
unconverted photons
•
η and pT bins for BDT
•
With TMVA, able to rank variables according to discriminating power
13
Backup
14
ηs2 distribution
•
Radiative Z decay
•
Single photon
!
!
!
!
!
15
Rη (layer-2 variable)
•
Ratio of the energy in 3x7 cells over the energy in 7x7 cells centered at the
electron cluster position
16
Single photon (pT<50GeV)
17
Rɸ (layer-2 variable)
•
Ratio of energy deposited in 3x3 versus 3x7 cells
18
Single photon
19
wη2 (layer-2 variable)
•
Lateral width of the shower in η, over a region of 3x5 cells in Δη x Δɸ around
the center of the photon cluster
20
Single photon
21
F1 (strip layer variable)
•
Fraction of energy in strip layer
22
Single photon
23
Fside (strip layer variable)
•
Fraction of energy outside core of three central strips but within seven strips
24
Single photon
25
ws,3 (strip layer variable)
•
Shower width for three strips around maximum strip
26
Single photon
27
ws,tot (strip layer variable)
•
Total lateral shower width, identical to ws,3, except it is measured over all strips
20x2 strips in Δη x Δɸ
28
Single photon
29
ΔEs (strip layer variable)
•
Difference between energy associated with the second largest energy deposit
and energy associated with the minimal value between the first and second
maxima
30
Single photon
31