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Belle
Electromagnetic calorimeter reconstruction in Belle II.
2019-03–12, ACAT, Saas-Fee Torben Ferber ([email protected]) for the Belle II ECL group
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �2
SuperKEKB
7/34Torben Ferber, DESY
Nano beam scheme.
KEKB Super-KEKB
L=γ±
2er e
(1+σ y
*
σ x
*)I± ξ y±
βy±
RL
Rξy
vertical beta function at IP
beam current
factor 2-3factor 20
83mrad
KEKB e+/e-E (GeV): 3.5/8.0I (A): ~ 1.6/1.2β*y (mm): ~5.9/5.9Crossing angle (mrad): 22
7/34Torben Ferber, DESY
Nano beam scheme.
KEKB Super-KEKB
L=γ±
2er e
(1+σ y
*
σ x
*)I± ξ y±
βy±
RL
Rξy
vertical beta function at IP
beam current
factor 2-3factor 20
83mrad
SuperKEKB e+/e-E (GeV): 4.0/7.0I (A): ~ 3.6/2.6β*y (mm): ~0.27/0.3Crossing angle (mrad): 83→ Luminosity increase x40
4.0 GeV
7.0 GeV
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �3
Belle II at SuperKEKB
http://www-superkekb.kek.jp/img/ProjectedLuminosity_v20190128.png
Belle (1ab-1)
Belle II goal(50ab-1)
Belle II up to today:0.0005 ab-1
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �4
Belle II at SuperKEKB
positrons e+
electrons e-
KL and muon detector (KLM): Resistive Plate Counters (RPC) (outer barrel) Scintillator + WLSF + MPPC (endcaps, inner barrel)
Particle Identification (PID):Time-Of-Propagation counter (TOP) (barrel) Aerogel Ring-Imaging Cherenkov Counter (ARICH) (FWD)
Electromagnetic calorimeter (ECL):CsI(Tl) crystals, waveform sampling
Vertex detectors (VXD): 2 layer DEPFET pixel detectors (PXD) 4 layer double-sided silicon strip detectors (SVD)
Central drift chamber (CDC):He(50%):C2H6 (50%), small cells, fast electronics
Magnet:1.5 T superconducting
Trigger:Hardware: < 30 kHz Software: < 10 kHz
DEPFET: depleted p-channel field-effect transistorWLSF: wavelength-shifting fiberMPPC: multi-pixel photon counter
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �5
Belle II Calorimeter (ECL)
CrystalPhotodiode
Preamplifier
Sum
offline analysis
L1 trigger
Digitizer1.76 MHz
18 bitShaper
FPGA
• 8736 crystals
• ~5×5×30 cm3 CsI(Tl) →16.1 X0
• Crystals, photodiodes and preamplifiers reused from Belle experiment
• New shapers and digitizers/FPGAs
6
7
5 8
1
23
4
HdD
HaAaA
c C
bB
dD
_2
_1
_3
_4
dg68
dg24
dg57
dg13
1
2
9
3
4
5
6
10
7
8
_9
_2
_1 _4
_3
a
A
dD c C
b2
B2
b1
B1
HdD
HaA
dg68 dg57
dg13 dg24
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �6
Signal processing: Belle and Belle II
t
Shaper output (τ=0.5μs)
Waveform Digitizer, 1.76 MHz, 18 bit
FPGA fits to extract Amplitude and Time
Shaper output (τ=1.0μs)
Gate width (Δt=100ns)
t
Signal charge
Charge-to-time converter (QTC)
Digitizer (TDC)
Amplitude
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �7
Calorimeter tasks at Belle II
Calorimeter basics:Photon energy and position (30 MeV - 7 GeV)
Neutral trigger (L1 and HLT) Online luminosity
Multiple detectors:Track-cluster matching
Electron ID
Advanced: “Extra energy” (hermeticity at an e+e- collider)
Hadron IDPulse-shape discrimination Low pt muon identification
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �8
Calorimeter challenges at Belle II
Higher beam backgrounds
Higher collision rates (= tighter trigger conditions)
More demanding analyses
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �9
Calorimeter challenges at Belle II: L1 and HLT Trigger
Higher collision rates (= tighter trigger conditions)
0.5kHz, σ≈(5+450) nb(no HLT)20
18
10kHz, σ≈(5+8) nb (after HLT, compare to BaBar: (5+70) nb)20
25
Calibration, low multiplicity events:Dominated by ee→ee(γ) debris
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �10
Calorimeter challenges at Belle II: Beam background
Higher beam backgrounds
Belle II Simulation(2018)
Belle II Simulation(2025)
~20 cluster candidates per event
~100 cluster candidates per event
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �11
Offline reconstruction flow
Crystal calibration(time, energy)
User analysis
Track-Cluster Matching
Charged PID
Tracking
Cluster shapes
Energy Position Relation to track(s) and PID information Cluster shapes (similar to image moments) Crystal information is not available!
Seed Finder
Connected Region
Shower splitting
Clu
ster
ing
Energy calibration
Tail calibration
Leakage Correction
Cal
ibra
tion
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber)
x (cm)100 150 200 250 300 350
y (c
m)
250−
200−
150−
100−
50−
0
(E /
MeV
)10
Log
012
3
Crystal energy
x (cm)100 150 200 250 300 350
y (c
m)
250−
200−
150−
100−
50−
0Shower (no timing selection)
x (cm)100 150 200 250 300 350
y (c
m)
250−
200−
150−
100−
50−
0 > 20 MeV)
ClusterCluster (timing selection, E
θΦ
θΦ
θΦ
�12
Offline reconstruction in pictures
Clustering
Belle II Simulation Belle II Simulation Belle II Simulation
User analysis
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �13
Offline reconstruction For the case of the large pile-up noise the Belle algorithm for cluster reconstruction is not optimal
Belle 1: sum of the Ei in 5x5 matrix E
i>0.5 MeV
Other approach: Sum of N most energetic hits, N depends on energy and background
Cluster reconstruction
To get the photon energy: cluster energy is corrected by function depending on E, angles
and the background level
Background level is estimated from multiplicity off time events
Measured per event
#crystals in energy sums
[GeV]trueE1−10 1
/ E
[%]
Eσ
0
5
10
15BGx0.0 (no material) FWDBGx0.0 FWDBGx0.1 FWDBGx1.0 FWD
[GeV]trueE1−10 1
/ E
[%]
Eσ
0
5
10
15 BGx0.0 (no material) BarrelBGx0.0 BarrelBGx0.1 BarrelBGx1.0 BarrelBGx1.0 Barrel (MC5)
[GeV]trueE1−10 1
/ E
[%]
Eσ
0
5
10
15
20
25 BGx0.0 (no material) BWDBGx0.0 BWDBGx0.1 BWDBGx1.0 BWD
Fig. 16: Photon energy resolution as function of true photon energy for FWD endcap (a),
barrel (b), and BWD endcap (c). Note the di↵erent y–axis ranges of the plots. A smooth
curve has been fitted to the points to guide the eye. An older implementation of ECL
reconstruction (used in MC5) is also plotted in (b).
the cost of requiring analysis specific optimisation. The uncertainty on the selection e�ciency
cannot be pre-determined using this method.
The likelihood selectors rely on likelihood ratios constructed in the following way. First,
the PID log likelihoods from each detector are summed to create a combined PID likelihood
for each of six long-lived charged particle hypotheses: electron, muon, pion, kaon, proton
and deuteron. Next, the di↵erence in log likelihood between two particle hypotheses is used
to construct a PID value L(↵ : �) according to
L(↵ : �) =1
1 + eln L↵�ln L�
=
Qdet L(↵)Q
det L↵ +Q
det L�, (5)
where ↵ and � represent two di↵erent particle types and the product is over the active
detectors for the PID type of interest. The value L(↵ : �) is greater than 0.5 for a charged
track that more closely resembles a particle of type ↵ than one of type � and is less than
0.5 otherwise. More details on the PID types are given in the following sections.
The performance plots included in this section were generated from inclusive samples
of 106 cc̄ events generated during the fifth and sixth MC campaigns. These samples
were reconstructed with release-00-05-03 and release-00-07-00 of the Belle II software,
respectively.
68/689
Belle algorithm
arXiv:1808.10567 [hep-ex]
Belle II Simulation
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �14
Performance: π0
)2 (GeV/cγγm0.40 0.45 0.50 0.55 0.60 0.65 0.70
)2
Entri
es /
(0.0
03 G
eV/c
0
100
200
300 Data
> 0.30 GeVγE
Belle II 2018 (Preliminary)
-1 L dt = ~5 pb∫
FIG. 2: m�� distribution in Exp 3, runs 112-1355. A � peak at about 542 MeV/c2 is visible.
)2 (GeV/cγγm0.08 0.10 0.12 0.14 0.16 0.18
)2
Entri
es /
(0.0
01 G
eV/c
0.0
0.5
1.0
1.5
310×
Data
> 0.15 GeVγE
Belle II2018 (Preliminary)
-1 L dt = ~5 pb∫
FIG. 1: m�� distribution in Exp 3, runs 112-1355. A ⇡0 peak at about 132 MeV/c2 is visible.
6
Figure 1: This figure shows the invariant mass distribution of ⇡0 ! �� in 5 pb�1 of collisiondata. Events are required to contain at least three good tracks to purity the sample withprocesses of the type e+e� ! hadrons, while rejecting beam induced background, Bhabhascattering, and other low multiplicity background sources. The photon daughters of the⇡0 candidates are required to have an energy of greater than 150 MeV, and to be withinthe acceptance of the Central Drift Chamber (CDC). The internal document reference isBELLE2-NOTE-PH-2018-002.
1
BELLE2-NOTE-PL-2018-009
Few days after the start of data taking.
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �15
Offline reconstruction flow
Crystal calibration(time, energy)
User analysis
Track-Cluster Matching
Charged Particle Identification
Tracking
Cluster shapes
Energy Position Relation to track(s) Cluster shapes (similar to image moments) Crystal information is not available!
Seed Finder
Connected Region
Shower splitting
Clu
ster
ing
Energy calibration
Tail calibration
Leakage Correction
Cal
ibra
tion
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �16
Pulse-Shape Discrimination (PSD)• Online FPGA waveform fits use photon
templates only and provide time and amplitude fit results (2 variables)
• New: Exploit the fact that hadronic and electromagnetic scintillation components are different
• If crystal energy E > 30 MeV: Store waveform data (31 variables) and repeat fit offline with different templates.
• Third information from a crystal: PSDSavino Longo ([email protected]) ICHEP 2018
CsI(Tl) Pulse Shape Discrimination at Belle II
13
• Offline waveforms are characterized with photon+hadron component fit.
• Hadron response for all crystals is calibrated using Fourier analysis to compute the impulse response for each calorimeter crystals signal chain.
CsI(Tl) Diodes Preamp ShaperDSP
RHadron(t) = LHadron(t) ⇤ IShaperDSP(t)IShaperDSP(t) = IFT�FT (R�(t))FT (L�(t))
�FT = Fourier Transform IFT = Inverse Fourier Transform
Sample Fit of Hadron Pulse in Collision Data
Belle II Phase 2 data – preliminary
S. Longo, ICHEP2018
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �17
Pulse-Shape Discrimination (PSD)
• First time pulse shape discrimination (PSD) is used in an e+e- collider experiment
• New variable based on a BDT trained (on MC) to separate photons and K0L using all pulse shapes in a cluster
• Will be included in charged particle identification to improve muon vs. pion separation
Savino Longo ([email protected]) ICHEP 2018
First Beam = First Hadrons Observed!
• When SuperKEKB beams started circulating (April 2018) hadronic backgrounds in ECL allowed for hadronic pulse shapes to be observed at Belle II.
14
HER = 0.15 A LER < 0.001 A
ECL Data all barrel crystals
HER = 0A LER = 0A
(beams OFF)
ECL Data all barrel crystals
Observing Hadronic Pulse Shapes with Belle II Calorimeter
electromagnetic pulse shapes
proton bands
alphas Belle II Phase 2 data – 1st glimpse-preliminary
Belle II Phase 2 data – 1st glimpse-preliminary
SuperKEKB info: http://www-linac.kek.jp/skekb/snapshot/ring/dailysnap-20180404-0001.png
protons
alphas
Two component total energy [GeV]
Had
ron
Com
pone
nt In
tens
ity
Savino Longo ([email protected]) ICHEP 2018
First Beam = First Hadrons Observed!
• When SuperKEKB beams started circulating (April 2018) hadronic backgrounds in ECL allowed for hadronic pulse shapes to be observed at Belle II.
14
HER = 0.15 A LER < 0.001 A
ECL Data all barrel crystals
HER = 0A LER = 0A
(beams OFF)
ECL Data all barrel crystals
Observing Hadronic Pulse Shapes with Belle II Calorimeter
electromagnetic pulse shapes
proton bands
alphas Belle II Phase 2 data – 1st glimpse-preliminary
Belle II Phase 2 data – 1st glimpse-preliminary
SuperKEKB info: http://www-linac.kek.jp/skekb/snapshot/ring/dailysnap-20180404-0001.png
Electromagnetic pulse shapes
Had
ron
Com
pone
nt In
tens
ity
S. Longo, ICHEP2018
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �18
Low pt Particle Identification plans: Muon vs Pion
• Particles with low transverse momentum (pt < 0.5 GeV/c) do not reach our muon system:→ Baseline particle identification depends on E/p and is very poor→ Clustering itself difficult, since these particles leave long, charge dependent, trails in the calorimeter
ECL
High ptLow pt
muon system
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �19
Low pt Particle Identification plans• Approach under study:
• No clustering
• Extrapolate tracks to calorimeter
• Analyse 5×5 pixel calorimeter images around impact crystal using convolutional networks
Baseline identificationCalorimeter images + track extrapolation
Baseline identificationCalorimeter images + track extrapolation
Belle II Simulation (work in progress)
Belle II Simulation (work in progress)
Pions Electrons Muons
Electromagnetic calorimeter reconstruction in Belle II (Torben Ferber) �20
Summary
• Belle II is starting physics runs in ~7 days
• Calorimeter reconstruction priorities so far: Robust reconstruction, calibration
• Calorimeter reconstruction priorities now: Getting ready for high and varying beam backgrounds, and complex physics analyses
• Bonus: The knowledge of the initial state at an e+e- collider and the huge event rate makes this a perfect playground to develop data-driven ML applications
Deutsches Elektronen Synchrotron www.desy.de
Torben Ferber [email protected] ORCID: 0000-0002-6849-0427
Contact