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Outline
dE/dx package:OO design and software development
Calibration and systematic corrections
Reconstruction algorithm studies:A. Different estimation of most prob Eloss
B. Curve studies based on BESII data
C. Resolution and residual bias correction
dE/dx :Particle ID with energy loss measurements
Components: calibration and reconstruction
Implementation: C++ programming under BOSS framework
Design goal: Resolution 6—7%, good seperation
MDC
tracking
dE/dx~f(v)
Particle type info
Principle:
P = · m
Requirements and data flow
MDC Tracking
dE/dx Reconstruction
Global Particle Identification
TransientData Store
(TDS)
MDC digits
Tracks
MDC digitsTracks
Recon dE/dx
Recon dE/dx
partId info
physics analysis Real dataflow
Apparent dataflow
Tracks
Recon dE/dx
MDC digits
。。。
AIM: to give the partID information from the list of pulse heights of hits on the MDC track, and store them into TDS
some corrections are performed to get unbiased dE/dx information.
Some proper dE/dx estimators are constructed
Some implementation features
Uniform interface: Alternative algorithms with the same interface
Uniform data I/O format: MDC recon data model: MdcRecEvent
Input from MC : MdcFakeData package
Output:MdcDedx in MdcRecEvent
int m_id; float m_dedx; // measured value of dE/dx float m_dedx_exp[5]; // expected value of dE/dx for 5
particle hypotheses float m_sigma_dedx[5]; // sigma value of dE/dx for 5
particle hypotheses float m_pid_prob[5]; // probability for each of the 5
particle hypotheses int m_stat; // status flag SmartRef<MdcTrack> m_trk; // reference to the track
Calibration issues
Systematic and run-by-run calibrations is important for dE/dx correction
Calibration consts ~7200 are designedCalib consts stored in DataBase. They can be
retrieved from DB in reconstruction nowIn future, calib consts in ROOT format and
DB only contains meta data
dE/dx calibration and corrections
① Gain variations among cells ② Gas Gain variation within one cell ③ Sampling length corrections④ Drift distance dependence ⑤ Longitude position(z) dependence ⑥ Dependence of the sense wire voltage ⑦ Space charge effect ⑧ Gas gain saturation : from electronics⑨ Temperature,pressure and environmental effects⑩ Corrections related to particle type ⑪ Variations of the pulse height run by run
Algorithm studies: different estimation of most probable energy
lossLandau distribution has no definite mean. The
algorithm used must estimate the most probable energy loss
Truncated mean Double truncated mean: truncate at both ends Median Geometric mean
Harmonic mean
Transformation:
Logorithm truncated mean: studies based on BESII data
idea:these methods give less bias to large values,then the satured hits have less effect to give better shape and better seperation
Different estimation of most probable energy loss: resolution(1)
Truncation rate 0.7
5.51% 5.34%
6.06% 5.09%
0.05~0.75 truncation
BOOST MC, MIP muon
Different estimation of most probable energy loss: resolution(2)
5.75%5.44%
5.71% 2.61%
Truncation rate: 0.7
BOOST MC, MIP muon
Different estimation of most probable energy loss: seperation
power(1)
Pi/K Pi/P
0.7GeV 1.2GeV
Pi/K Pi/P
0.7GeV 1.2GeV
Pi/K Pi/P
0.6GeV 1.1GeVPi/K Pi/P
0.75GeV 1.3GeV
Different estimation of most probable energy loss: seperation
power(2)
Pi/K Pi/P
0.7GeV 1.2GeV
Pi/K Pi/P
0.7GeV 1.3GeV
Pi/K Pi/P
0.7GeV 1.3GeV
Pi/K Pi/P
0.75GeV 1.3GeV
Comparison of linear&logorithm TM
Cosmic rays Radiative Bhabha
Pull width: 1.020 0.9995 Pull width: 0.8477 0.9304
shape is more Gaussian-like shape is more Gaussian-like
Logorithm TM(right figure),compared to plain TM(left figure):
Suppress high-end residual Landau tail
The distribution more Gaussian likeBESII DATA, J/Psi hadrons
Study of truncated mean method
Well established method of dE/dx estimation
Simple and robust
Rejection of lower end hits to remove contributions from noise and background fluctuation
Truncation of higher tail to remove Landau tail due to hard collisions
Just cooresponding to ~5% lower cut
After truncation, distribution just Gaussian-like
Landau tail
BOOST MC, 1GeV electrons
Resolution curve with different truncation rates
70% truncation ratio is adopted for the algorthm
Number of good hits is required to no less than 10 for each track
Resolution from perfect MC consistent with empirical formula
BOOST MC, 1GeV electrons
Different most probable energy loss formulations(1)
Bethe-Bloch formula
Landau formula with density correction
Sternheimer correction : Cobb-Allison correction:
PAI: Photo-Absorption Ionization model
A
dE/dx curve studies with BesII data
Purpose: 1. Comparison of different formula to find
the best curve to calculate expectation in reconstruction
2. A test-bed for BESIII reconstruction
data samples used: Pion:J/Psirho+pi & J/PsiKKPiPi
Kaon:J/PsiK*(892)+K(1430)KKPiPi
Proton:J/psiPPbarPi0&J/PsiPPbarEta
electron: (radiative) Bhabha
muon: dimu +cosmic rays
“Garbage” events: beam-gas protons, cosmic-rays, rad. Bhabha
To get pure samples:
Use Tof and BSC information ONLY to identify particles
use relative probability only
Strict kinetic and invariant mass cut
The cuts are checked with GENBES
Example:Cuts for Bhabha
Comparison between data and dE/dx curve
Sternheimer(A) is better at high momentum end
Va’vra(B) is relative better at low momentum end
Data need careful calibration
Practical global parameterization of curve is prefered
Sternheimer
Comparison of Sternheimer and Va’vra formula:
AB
A
B
Global 5-parameter fit for phmp_nml vs
5
44
13ln2
1p
pp
ppp
dx
dE
binning with nearly the same statisticsat each point to reduce the error
Using garbage events in order to fastly calibrate this curve for BESIII in future
A uniform formula to avoid discrete expression for density effect
The curve fit the BESII data OK
Beam-gas proton
Cosmic rays
Radiative bb
Residual theta dependence before correction (Hadron events)
After correction
The correction is then parameterized and used in mass data process
σdE/dx~ hits number relationship
35.2
0.8132.0
46.0
In
n
Empirical formula :
reso
luti
on
number of hits number of hits
reso
luti
on
J/Psi dimuon events
J/Psi radiative Bhabha events
data of different momenta bins
2
1153.0
t
A
Z
summary
OO designed BESIII dE/dx package now runs smothly under BOSS
Calibration algorithm are designed and many corrections considered
Different reconstruction algorithms are explored to get best performance
To reach design goals, there are still a long way to go