improvements to bremsstrahlung energy loss correction for electron momentum ... · 2015-04-10 ·...
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Improvements to Bremsstrahlung energy loss correctionfor electron momentum reconstruction
PANDA Collaboration Meeting
Ermias ATOMSSA
Institut de Physique Nucleaire d’Orsay
March 17, 2015
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 1 / 17
Effect of Bremsstrahlung radiation
Photon emission by electrons before exiting the tracking system
Some or all of the tracking points are created after the track loses momentum
Leads to mis-reconstruction of the momentum that shows as a tail in resolutiondistributions and invariant mass spectra
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 2 / 17
General approach
Thesis work by Binsong Ma, 23 Sept 2014, Universite Paris SudEnergy distribution highly non Gaussian: Can not be corrected easily with Kalman FilterSearch for clusters in the EMC generated by the Bremsstrahlung photons associated witheach track and add the total energy to the track’s momentum
Relies on the observation that90% of Bremsstrahlung photons are emitted within a cone of 2 mradThe angular separation of the reconstructed electron momentum and photon clusterposition is a reliable predictor of the radius at which the photon was emitted
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 3 / 17
Cluster merging
Depending on the momentum and point of emission, Bremsstrahlung photon clusters canbe reconstructed separately from or merged with that of the electron
Higher momentum tracks and late emission of photons tend to result in merging, whereaslower momenta and early emission result in separate clusters
The method has to handle both cases for every track
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 4 / 17
Separate bumps
Dominant at low momentum and late emissionSearch for bumps in the EMC with Ebump > 1%Etrack
Apply angular selection on ∆φ = ±(φbump − φe∓ ) and ∆θ = ±(θbump − θe∓ )∆θ: |∆θ| < 2◦ (no bending assumed in theta)∆φ (Barrel): −1◦ < ∆φ < 2 arcsin((0.3 · B · Rext
TRK )/precT )∆φ (Forward): −1◦ < ∆φ < (0.3 · B · ZSTT+MVD+GEM · tan θrec )/Prec
T
Corrected momentum: pCOR = pKF + ETOTγ,sep , where ETOT
γ,sep =∑
EBrem cutγ,sep. bumps
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 5 / 17
Merged bumps
Project the energy deposits in the cluster associated to the electron in φ direction
Split the phi projection along local minima into “φ-bumps”
The right (left) most φ-bump with sufficient energy is considered as originating from thee+ (e−) and the total energy of the phi bumps to the left (right) is added to themomentum of the track depending on charge
pCOR = pKF + ETOTγ,sep + ETOT
γ,mrg , where ETOTγ,mrg =
∑Eφ−bumps
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 6 / 17
Performance of the method
MC)/p
COR - p
MC(p
0.1− 0.05− 0 0.05 0.1 0.15 0.2 0.25 0.30
200
400
600
800
1000
1200
1400
UncorrectedSep. bumps onlyFull corr.
= 0.5 GeV/cT
p < 45θ 30 <
BARREL
MC)/p
COR - p
MC(p
0.1− 0.05− 0 0.05 0.1 0.15 0.2 0.25 0.30
200
400
600
800
1000
1200
1400 = 1.0 GeV/cT
p
< 45θ 30 <
BARREL
MC)/p
COR - p
MC(p
0.1− 0.05− 0 0.05 0.1 0.15 0.2 0.25 0.30
200
400
600
800
1000 = 2.0 GeV/cT
p < 45θ 30 <
BARREL
MC)/p
COR - p
MC(p
0.1− 0.05− 0 0.05 0.1 0.15 0.2 0.25 0.30
200
400
600
800
1000
1200
1400
1600
= 0.5 GeV/cT
p
< 20θ 10 <
FWD. ENDCAP
MC)/p
COR - p
MC(p
0.1− 0.05− 0 0.05 0.1 0.15 0.2 0.25 0.30
200
400
600
800
1000
1200
1400
= 1.0 GeV/cT
p
< 20θ 10 <
FWD. ENDCAP
MC)/p
COR - p
MC(p
0.1− 0.05− 0 0.05 0.1 0.15 0.2 0.25 0.30
200
400
600
800
1000 = 2.0 GeV/cT
p
< 20θ 10 <
FWD. ENDCAP
Significantly improved resolution at all angles (L:Barrel, R:FWD) and momenta
Correction with separated only and both separated and merged photons
Contribution from merged increases with momentum
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 7 / 17
Neutral candidates vs. bumps
Initial code used neutral candidates for separated bump correction to avoid adding bumpsalready associated with the electron
Results in a dependence on track-cluster association criteriaIssue first noticed in recent PANDAroot releases (≈ scrut14 and above)Possibly due to bumps being assigned to secondary electrons/fake tracks?
All bumps used now with a condition that EmcIndex(bump) 6= EmcIndex(track)
MC - p)/p
MC(p
0.2− 0.1− 0 0.1 0.2 0.30
1000
2000
3000
4000
5000
6000
7000UncorrectedNeut. candsBumps
= 0.5T
p
< 45θ 30 <
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 8 / 17
Over-correction
Visible asymmetry of corrected resolution, too much energy is being added back
For tracks that emit late, the momentum reconstruction is mostly based on “good” hits
Adding the full energy of the photon for such tracks over-corrects momentum
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 9 / 17
Emission radius dependence of resolution degradation
Photons emitted in later half of tracking system do not affect the reconstructedmomentum as much as photons emitted early
Reconstructed momentum resolution improves with increasing MC radius (RTrue) ofemission (ie. fraction of tracking points before emission)
MC)/p
KF - p
MC(p
0.2− 0 0.2 0.4 0.6 0.8 1
4−10
3−10
2−10
1−10
Resolution of reconstructed momentum
< 45θ 30 <
= 0.5T
p
(cm) < 7True0 < R
Resolution of reconstructed momentum
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 10 / 17
Emission radius dependence of resolution degradation
Photons emitted in later half of tracking system do not affect the reconstructedmomentum as much as photons emitted early
Reconstructed momentum resolution improves with increasing MC radius (RTrue) ofemission (ie. fraction of tracking points before emission)
MC)/p
KF - p
MC(p
0.2− 0 0.2 0.4 0.6 0.8 1
4−10
3−10
2−10
1−10
Resolution of reconstructed momentum
< 45θ 30 <
= 0.5T
p
(cm) < 14True7 < R
Resolution of reconstructed momentum
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 10 / 17
Emission radius dependence of resolution degradation
Photons emitted in later half of tracking system do not affect the reconstructedmomentum as much as photons emitted early
Reconstructed momentum resolution improves with increasing MC radius (RTrue) ofemission (ie. fraction of tracking points before emission)
MC)/p
KF - p
MC(p
0.2− 0 0.2 0.4 0.6 0.8 1
4−10
3−10
2−10
1−10
Resolution of reconstructed momentum
< 45θ 30 <
= 0.5T
p
(cm) < 21True14 < R
Resolution of reconstructed momentum
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 10 / 17
Emission radius dependence of resolution degradation
Photons emitted in later half of tracking system do not affect the reconstructedmomentum as much as photons emitted early
Reconstructed momentum resolution improves with increasing MC radius (RTrue) ofemission (ie. fraction of tracking points before emission)
MC)/p
KF - p
MC(p
0.2− 0 0.2 0.4 0.6 0.8 1
3−10
2−10
1−10
Resolution of reconstructed momentum
< 45θ 30 <
= 0.5T
p
(cm) < 28True21 < R
Resolution of reconstructed momentum
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 10 / 17
Emission radius dependence of resolution degradation
Photons emitted in later half of tracking system do not affect the reconstructedmomentum as much as photons emitted early
Reconstructed momentum resolution improves with increasing MC radius (RTrue) ofemission (ie. fraction of tracking points before emission)
MC)/p
KF - p
MC(p
0.2− 0 0.2 0.4 0.6 0.8 1
3−10
2−10
1−10
Resolution of reconstructed momentum
< 45θ 30 <
= 0.5T
p
(cm) < 35True28 < R
Resolution of reconstructed momentum
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 10 / 17
Emission radius dependence of resolution degradation
Photons emitted in later half of tracking system do not affect the reconstructedmomentum as much as photons emitted early
Reconstructed momentum resolution improves with increasing MC radius (RTrue) ofemission (ie. fraction of tracking points before emission)
MC)/p
KF - p
MC(p
0.2− 0 0.2 0.4 0.6 0.8 1
3−10
2−10
1−10
Resolution of reconstructed momentum
< 45θ 30 <
= 0.5T
p
(cm) < 42True35 < R
Resolution of reconstructed momentum
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 10 / 17
Emission radius weighted correction
Solution: Add a smaller fraction of the energy for photons emitted later:ETOTγ,sep =
∑W (R)× EBrem cut
γ,sep. bumps
Constraints on weight function: W (0) = 1 and W (RextTRK ) = 0.
Estimator of R based on the relation between RTrue ,∆φ, pT : RCalc = K× 2pT sin (∆φ/2)0.3B
Correlation plot: Events with single Bremsstrahlung photon (Remission < RTRK ) and singleidentified separate bump (cut on ∆φ, ∆θ), MC matching requiredWeight: Fermi function with inflection point at the middle of tracking system
0
50
100
150
200
250
300
350
Calculated radius vs. true radius
True R0 5 10 15 20 25 30 35 40
Cal
c R
0
5
10
15
20
25
30
35
40
= 0.5 GeV/cT
p
Calculated radius vs. true radius
CalcR0 5 10 15 20 25 30 35 40
)C
alc
W(R
0
0.2
0.4
0.6
0.8
1(R-R0)/R11+e1W(R) =
/2)TRKextR0 = 21 cm (= R
/10)TRKext R≈R1 = 5.0 cm (
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 11 / 17
Results with weighted correction (Barrel Region)
MC)/p
COR - p
MC(p
0.2− 0.1− 0 0.1 0.2 0.30
1000
2000
3000
4000
5000
6000
7000
8000Full corr.
Full corr. (wtd)
= 0.5T
p
< 45θ 30 <
Resolution of fully corrected (with weight) momentum
MC)/p
COR - p
MC(p
0.2− 0.1− 0 0.1 0.2 0.30
1000
2000
3000
4000
5000
6000
7000
8000Full corr.
Full corr. (wtd)
= 1.0T
p
< 45θ 30 <
Resolution of fully corrected (with weight) momentum
Weighting fixes over-correction at all momenta and angles (more plots in backup)
The same function is used everywhere
Particularly useful for low momentum tracks where search window can be wide
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 12 / 17
Full event simulation
Presence of other particles that generate hits in the EMC can bias the correctionPotential issue especially at low momenta, where ∆φ search window is largeTo test the stability in presence of other particles: π0J/ψ and π0π+π−
Significantly improved J/ψ mass resolution with minimal effect on π+π− spectrumModifications (discussed on PANDAroot forum, msg:17933) to the track-cluster matching algorithms were usedReason: A failed association can result in adding the energy of the electron’s cluster back to the momentum
Allows for much tighter mass cut while improving efficiency
-e+eM0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
0
200
400
600
800
1000
1200
1400
1600
inv. massψJ/ inv. massψJ/
-π+πM0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
0
50
100
150
200
250
300
inv. mass-π+π
Raw (eid)
Corrected (eid)
inv. mass-π+π
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 13 / 17
Implementation in PANDAroot (1/3)
φ-bumps are created for all clusters and stored separately in PndEmcPhiBumpSpiltter.cxx(called from XYZ..). No change required in “official” simulation macros for this step
Corrected momentum calculated for all reconstructed tracks and stored separately in aTCA by PndPidBremCorrector.cxx. Add the following to pid complete.C:
// after all the Pid modules...
PndPidBremCorrector *bremCorr = new PndPidBremCorrector();
fRun->AddTask(bremCorr);
...
In analysis macro, request RhoCandidate objects to be filled with corrected momenta byadding “Brem” to the selection string
PndAnalysis* theAnalysis = new PndAnalysis();
RhoCandList eplus;
while (theAnalysis->GetEvent() && i++<nevts) {
...
theAnalysis->FillList(eplus, "BremElectronVeryTightMinus");
...
}
...
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 14 / 17
Implementation in PANDAroot (2/3)
Alternatively, working directly with charged candidates
// MyTask.h:
TClonesArray* fBremCorr;
...
// MyTask.cxx
#include "PndPidBremCorrected4Mom.h"
// in MyTask::Init() method
fBremCorr =
dynamic_cast<TClonesArray *> (ioman->GetObject("BremCorrected4Mom"));
...
// in MyTask::Exec() method
for (int j=0; j<fChargedCandList.GetLength(); ++j) {
int trk_id = fChargedCandList[j]->GetTrackNumber();
PndPidBremCorrected4Mom *bremCorr =
(PndPidBremCorrected4Mom*) fBremCorr->At(trk_id);
TVector3 mom_corrected = bremCorr->GetMomentum());
double energy_corrected = bremCorr->GetEnergy());
...
}
...
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 15 / 17
Implementation in PANDAroot (3/3)
Does not affect any analysis that doesn’t request it explicitly (separate storage)
PID consideration:
All PID probabilities are still calculated with uncorrected momentumNot advisable to use corrected momenta as input for PID algorithms at this pointunless PID probabilities are recomputedPotential to use the corrected momentum as additional input to PID algorithms
Will be available soon in trunk release (pending approval)
In the meantime all the relevant source files can be found here:https://github.com/atomssa/brempatch
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 16 / 17
Conclusion
Bremsstrahlung correction method for electrons fully debugged and implemented inPANDAroot with some improvements
Offers improved spectra for signals with electrons in the exit channel and improved masscut efficiency for resonances
Simple usage instructions for simulations are provided
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 17 / 17
Backup
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 1 / 4
Performance with varying momentum (Barrel Region)
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
100
200
300
400
500
No weight
W/ weight
= 0.15 GeV/cT
p
< 45θ 30 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400 = 0.25 GeV/cT
p
< 45θ 30 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400
1600
1800
2000 = 0.50 GeV/cT
p
< 45θ 30 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400
1600
1800
2000 = 1.00 GeV/cT
p
< 45θ 30 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400
1600
1800= 1.50 GeV/c
Tp
< 45θ 30 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400 = 2.00 GeV/cT
p
< 45θ 30 <
BARREL
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 2 / 4
Performance with varying energy (FWD Region)
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400
No weight
W/ weight
= 0.15 GeV/cT
p
< 20θ 10 <
FWD.ENDCAP
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400= 0.25 GeV/c
Tp
< 20θ 10 <
FWD.ENDCAP
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400
1600
1800
2000 = 0.50 GeV/cT
p
< 20θ 10 <
FWD.ENDCAP
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400
1600
1800 = 1.00 GeV/cT
p
< 20θ 10 <
FWD.ENDCAP
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400
1600 = 1.50 GeV/cT
p
< 20θ 10 <
FWD.ENDCAP
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400= 2.00 GeV/c
Tp
< 20θ 10 <
FWD.ENDCAP
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 3 / 4
Performance with varying angles (Barrel Region)
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
200
400
600
800
1000
1200
1400
1600
1800
2000
No weight
W/ weight
= 0.50 GeV/cT
p
< 45θ 30 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
500
1000
1500
2000
2500 = 0.50 GeV/cT
p
< 60θ 45 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
500
1000
1500
2000
2500= 0.50 GeV/c
Tp
< 75θ 60 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
500
1000
1500
2000
2500
= 0.50 GeV/cT
p
< 90θ 75 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
500
1000
1500
2000
2500= 0.50 GeV/c
Tp
< 105θ 90 <
BARREL
MC)/p
COR - p
MC(p
0.2− 0.15− 0.1− 0.05− 0 0.05 0.1 0.15 0.20
500
1000
1500
2000
2500 = 0.50 GeV/cT
p
< 120θ105 <
BARREL
Ermias ATOMSSA (IPNO) PCM, Bremsstrahlung Correction Mar. 17, 2015 4 / 4