Status of dE/dx Offline Software WANG Dayong Institute of High Energy Physics Jan 10,2006

Outline  dE/dx software :OO design and development MdcDedxAlg : Reconstruction DedxCalibAlg : Calibration DedxCorrecSvc : Public service for dE/dx correction  Calibration and systematic corrections Important systematic and enviromental effects Calibration parameteriazation  Reconstruction algorithm studies: Different estimation of most prob Eloss Ionization Curve studies Resolution and residual bias correction  Summary

dE/dx :Particle ID with energy loss measurements  Principle: P = · m  Implementation: C++ programming under BOSS framework  Components: MdcDedxAlg, DedxCalibAlg, DedxCorrecSvc  Design goal: Resolution 6—7%, good seperation MDC trackin g dE/dx~f(v) Particle type info

Requirements and data flow MDC Tracking dE/dx Reconstruction Global Particle Identification Transient Data Store (TDS) MDC digits Tracks MDC digits Tracks 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

Overview of the software

dE/dx calibration package DedxCalibAlg

DedxCorrecSvc

Calibration data structure double m_wireg[6860]; double m_ggs[4][43]; double m_ddg[4][43]; double m_zdep[4][43]; double m_layerg[43]; double m_gain; double m_resol;

Sys. effects and dE/dx corrections  Gain variations among cells  Sampling length corrections  Drift distance dependence  Longitude position(z) dependence  Space charge effect  Charge gain non-linearity: from electronics  Corrections related to particle type  Run by run pulse height correction:Dependence on the sense wire voltage ， temperature, pressure and other environmental effects…

Parameterizations in calibration  Gas gain: Standard Landau distribution Vavilov distribution Asymmetric Gaussian distribution:  Space charge effect: general form of Q’=Q/(1-k(θ)*Q) BesII: fit with polynomial ： a=F(40°)/F(θ) Q’=Q*a CLEOII formulation: δ:longitude range of avalanche Babar formulation:  Parameterization of other effects: 3 order polynomials (presently implemented) Chebyshev series with the 1st kind of Chebyshev polynomials These parameterizations are to be tested by long-model data analysis

Comparison and choice of dE/dx curve Sternheimer(A) is better at high momentum end Va’vra(B) is relative better at low momentum end Practical global parameterization of curve is prefered Comparison of Sternheimer and Va’vra formula: A B Landau formula XP2~0 4-par fit X BESIII Simulation Preliminary

Global 5-parameter fit for phmp_nml vs  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 BESII data

1.In whole BesIII momentum range: 0.15—2GeV/c, good uniformity is seen with different particles and with momentum overlap; 2.Quality of curve fitting is good in the whole range 3.The fitting results is quite stable The best dE/dx curve obtained BESIII Simulation Preliminary

Algorithm studies: different estimation of most probable energy loss Landau 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 5.51%5.34% 6.06% 5.09% 5.75% 5.44% 5.71% 2.61% BOOST MC, MIP muon Truncation rate: 0.7

Different estimation of most probable energy loss: seperation power 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 BOOST MC, MIP muon Pi/K Pi/P 0.7GeV 1.2GeV Pi/K Pi/P 0.7GeV 1.2GeV Pi/K Pi/P 0.6GeV 1.1GeV Pi/K Pi/P 0.75GeV 1.3GeV

Comparison of linear&logorithm TM Cosmic rays Radiative Bhabha Pull width: Pull width: 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 like BESII 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

Calibration of σ dE/dx Empirical formula : Q dependence of σ dE/dx σ /Q= p0+p1*ln （ Q ） ， p0,p1 is fitting parameters Hits number and polar angle dependence

σ dE/dx ~ polar angle relationship

σ dE/dx ~ hits number relationship

Present performance(I) Software are robust Basic calibration and correction,and need more dE/dx resolution can reach design requirements: 6-7% 5.96%

χ distribution for Kaon sample Prob （ K ） distribution for Kaon sample Present performance(II) Distribution of is nearly a normal N(0,1)distribution Distributions of probability function are flat Our estimation is unbiased and can provide good partId info

dE/dx seperation for 5 particles(MC) seperation power with dE/dx Present performance(III) Good particle seperation in a wide range for different particles The important π/K seperation(3 σ )can reach nearly 800MeV/c Particle identification efficiency is more than 90% with MC samples

summary  OO designed dE/dx software is developed under BOSS, released and used for physics  Calibration algorithms and service are developed and many corrections performed to get unbiased estimation of dE/dx  Different reconstruction algorithms are explored to get best performance  Particle id is tested with MC samples, dE/dx resolution, distributions, pid efficiency is satisfactory.  To reach BESIII design goals, there are still much to understand and deal with

Thank you 谢谢！ Backed -up slides…