material budget, energy losses and multiple scattering
TRANSCRIPT
Material budget, energy losses and multiple scattering
Barrel tracking
Momenta resolution for low momenta tracks determined mainly by energy losses and multiple scattering
Left side – momentum resolution for pion Right side - proton
Energy loss between vertex and TPC
Left - rel. loss as a function of particle velocity Right – function of particle momenta
Energy losses (Bethe Bloch)
-particle velocity material density Z - atomic number of absorber A – mass number of absorber I – mean excitation energy – density effect correction factor –
material dependent and dependent
2)1(
2ln
1/ 2
2
22
21
I
cm
A
ZkdxdE e
Energy losses (Reconstruction)
- particle velocity material density K1 and K2 – Effective parameters
22
2
221 )1(ln
1/
kkdxdE
Energy loses correction
Left side - correction shift as function of particle velocity
Right side – correction shift as function of particle momenta (pion)
Energy loses correction
Left side - correction shift as function of particle momenta (kaon)
Right side – correction shift as function of particle momenta (proton)
Multiple scattering (Gaussian approximation)
-particle velocity material density P - particle momenta
0
2
2 *6.13
X
x
cp
MeV
Energy losses correction (Current) Material budget and radiation length
hardwired in the code Using symmetry of the detectors
Correction layer by layer during propagation Intervals in y and z in the local coordinate
frames Fast access Difficult to describe non symmetric parts
(big problem in TRD)
Geo modeler (0) Used to get information necessary for
energy loss calculation and multiple scattering Local information - in each point density,
radiation length, Z, A defined (mean excitation energy missing)
Mean query time ~ 15 s Mean number of queries
~15 – between 2 ITS layer ~15 – between 2 TRD layers
Geo modeler (1) Two option considered
1. Propagate track up to material boundary defined by modeler – get local material parameters
Time consuming - too many propagations 2. Calculate mean parameters between
start and end point <density>, <density*Z/A>, <radiation length> Faster (only one propagation), reusable in the
case of parallel hypothesis (ITS), not big changes in the tracking
Implementation
AliKalmanTrack::MeanMaterialBudget(Double_t *start, Double_t *end, Double_t *param)
First test Track references in inner volume of
the TPC – propagated to the vertex
TRD tracking
FollowProlongatioBackG implemented Using mean material budget 14 steps
Propagate to first plane Loop over TRD planes
Propagate and update in the sensitive layer Propagate to the next plane
Propagate to the outer volume of TRD
Energy loss estimate resolution
Left side - old propagation Right side – new propagation
Relative Pt resolution
Left side - old propagation Right side – new propagation
Relative Pt resolution
Left side - old propagation Right side – new propagation
Pt pulls
Left side - old propagation Right side – new propagation
Time pulls
Left side - old propagation Right side – new propagation
Conclusion First results in TRD tracking
Indication of improvements in the momentum and the time resolution
Test with propagation to the vertex using AliExternalParameter and GeoMedeler – better vertex position resolution Better interface required – without
user intervention
Conclusion
Default access to the TGeoManager required Currently loaded by hand
Better energy loss parameterization- options: 1. Mean Energy loss and multiple
scattering calculation using TGeoManager
2. Tuning 1 free parameter -