1. Reconstruction status
Content
Particle tracking
Track finding and reconstruction
Primary vertex reconstruction
Secondary vertex finding
Pile-up removal with HLT
Charged particle identification
TPC dE/dx measurement
ITS particle identification
TOF particle identification
HMPID particle identification
12 June 2002
Karel Safarik: Reconstruction Status

2. Karel Safarik: Reconstruction Status
Tracking Status
Development since last year
We finish Kalman filter (version 2) of the tracker through ITS
Reverse propagation - smoothing
Tracking in TRD in the same way
Connection to other outer detectors (TOF, HMPID, PHOS)
General tracking strategy
Track seeding starts in TPC outer pad rows
uses rough (3cm) vertex constraint !(?)
Kalman filter in TPC
Kalman filter in ITS (use particle type hypothesis)
two passes, with and without ‘real’ (50-100mm) vertex constraint
Reverse filter go back through ITS and TPC (out-layers, smoothing)
Bridge filter to TRD
Extrapolation to other detectors
12 June 2002
Karel Safarik: Reconstruction Status

3. Tracking efficiencies
TPC tracking efficiency (100% event size means dN/dy=8000)
12 June 2002
Karel Safarik: Reconstruction Status

4. Tracking efficiencies
TPC+ITS tracking efficiency at dN/dy 8000
standard definition of good vs. fake tracks requires all 6 ITS hits to be correct
most of ‘incorrect’ tracks just has one bad point
when this definition is relaxed to 5 out of 6 hits the efficiency is better by % (fake track probability correspondingly lower)
12 June 2002
Karel Safarik: Reconstruction Status

5. Karel Safarik: Reconstruction Status
Tracking precision
Momentum resolution dependence on magnetic field
(high density)
Including TRD the estimated improvement in Dp/p at high momenta will be %
Dependence on particle density
up to dN/dy = 4000 independent on density and corresponds to simple estimates
above deteriorates - by factor 1.5 at the density dN/dy = 8000
TPC
TPC+ITS
magnetic field (T)
< pt > pt = 5 GeV/c
Dp/p (%)
12 June 2002
Karel Safarik: Reconstruction Status

6. Karel Safarik: Reconstruction Status
Tracking precision
Momentum resolution estimate (at high density)
TPC+ITS
TPC+ITS+TRD
Today the whole tracking chain TPC – ITS – TPC – TRD working
12 June 2002
Karel Safarik: Reconstruction Status

7. Electrons in Kalman Filter
Bremsstrahlung recovery a la Delphi
D.Stampfer at al. Comput. Phys. Comm. 79 (1994) 157
Later maybe to change likelihood function
maximize the likelihood (the prediction end measurement are not correlated)
L  exp [0.5 (An-1-A*n-1)T(V’n-1)-1(An-1-A*n-1)] x
x exp [0.5 (M(An-1)-Mn-1)T(Cn-1)-1(M(An-1)-Mn-1)]
12 June 2002
Karel Safarik: Reconstruction Status

8. Karel Safarik: Reconstruction Status
Primary vertex
Correlation of two innermost pixel layers (without tracking)
At beam axis
sx = 15 mm
sy = 15 mm
sz = 5 mm
1cm off beam axis
sx = 25 mm
sy = 25 mm
12 June 2002
Karel Safarik: Reconstruction Status

9. Karel Safarik: Reconstruction Status
Secondary vertices
For the moment restricted inside the beam pipe
Fiducial volume R < 2.5cm
Tracks found during 2nd ITS pass (without vertex constraint) are prolonged inside beam pipe and opposite charged pairs are combined in attempt to find secondary vertices
K0s and L added to full multiplicity events
Results at B = 0.2T
Position Mass Momentum Efficiency
resolution resolution resolution
K0s mm MeV % %
L 500mm MeV % %
Low efficiency mainly due to low reconstruction efficiency for secondary tracks, the loss due to vertexing itself only 1%
12 June 2002
Karel Safarik: Reconstruction Status

10. Karel Safarik: Reconstruction Status
Secondary vertices
K0s L
12 June 2002
Karel Safarik: Reconstruction Status

11. V0 and cascade production
Clear signal at highest particle densities
fiducial volume until now restricted to R<2.5cm
statistics per event (until now)
 7 K0s (however, for dN/dy=4000 will be the same)
 1 L
K0s L X-
12 June 2002
Karel Safarik: Reconstruction Status

12. Tracking – missing parts
As of today seeding still use an approximate vertex constraint
sigma is set to the size of beam pipe (3cm)
Consequently we are tracking well
primary tracks
secondary tracks – but only ‘close’ secondaries
In order to get better yields for strange particle decays and mainly charged kaons we need to change seeding strategy
on top of that we have improve also seeding performance (CPU)
Standalone ITS tracking for
high momentum tracks (above 1 GeV)  on the way
low momentum tracks (below 100 MeV)  much more difficult
And to write it !
12 June 2002
Karel Safarik: Reconstruction Status

13. Karel Safarik: Reconstruction Status
Muon tracking
New cluster finder
Development of Kalman filter underway
Writing  as previous
(However, they already requested the sample files…  so is underway)
12 June 2002
Karel Safarik: Reconstruction Status

14. Karel Safarik: Reconstruction Status
HLT filtering
we have first draft of pile-up removal for pp running
timing study  looks very good
we need detail efficiency study
as a function of pt
as function of background
we need implement beam-gas background
muons almost parallel to beam axis
12 June 2002
Karel Safarik: Reconstruction Status

15. Charged particle identification
ALICE has several PID systems for charged particle
dE/dx done by ITS, TPC and TRD
Time-of-Flight by multi-layer RPC
Higher momentum particles by RICH detector
Electron identification by Transition Radiation Detector
Muon identification by Forward Muon Detector
Underway the combining of PID significances together
however, allowed contamination level depends on the physics question under study
therefore also momentum range for particle separation is not uniquely defined
12 June 2002
Karel Safarik: Reconstruction Status

16. TPC particle identification
At dN/dy = At dN/dy = 4000
s dE/dx = 10 % s dE/dx = 7 %
electrons
electrons
12 June 2002
Karel Safarik: Reconstruction Status

17. Karel Safarik: Reconstruction Status
TPC dE/dx measurement
Results for dN/dy = 4300
Energy loss for 300<p<350 Mev
Today even better results:
for low multiplicities dE/dx just
above 5%
12 June 2002
Karel Safarik: Reconstruction Status

18. 4 ITS layers (silicon drift and strip) capable to measure dE/dx
ITS dE/dx
4 ITS layers (silicon drift and strip) capable to measure dE/dx
s dE/dx = %
Separation
12 June 2002
Karel Safarik: Reconstruction Status

19. Karel Safarik: Reconstruction Status
PID via Time Of Flight
Efficiency and contamination at high density (dN/dy = 8000)
B = 0.2 T
B = 0.4 T
12 June 2002
Karel Safarik: Reconstruction Status

20. Karel Safarik: Reconstruction Status
TOF for pp environment
Efficiency and contamination at low density (pp: dN/dy = 5-7)
possibility to detect low momentum electrons
12 June 2002
Karel Safarik: Reconstruction Status

21. Karel Safarik: Reconstruction Status
RICH PID
Efficiency and contamination of RICH PID for different configuration of (passive) material in front of it
12 June 2002
Karel Safarik: Reconstruction Status

22. Charged PID – missing parts
Different detector underway except:
TRD (they just finished tracking)
Combined PID from different detectors
study group started
Writing:
detector studies on different level
ordered list: TOF, HMPID+ITS, TPC
TRD  nothing
global PID  nothing
12 June 2002
Karel Safarik: Reconstruction Status

23. Karel Safarik: Reconstruction Status
g and p0 detection
Excellent energy
resolution:
stochastic 2.7%/E1/2
noise %/E
constant %
Fraction of
reconstructed
energy
(simulation GeV)
12 June 2002
Karel Safarik: Reconstruction Status

24. Photon identification status
Update of the text available
including first draft from PMD (without figures !)
However, mostly study of standalone detector performance
performance study in real environment
p0 detection
photon detection
hard photons
still has to be done (in the text is a ‘programme of work’)
12 June 2002
Karel Safarik: Reconstruction Status

25. Tracking development Strasbourg meeting
May 17th – 18th we had a two-days meeting in IReS, Strasbourg
First day – tracking itself
M.Ivanov: Progress on parallel tracking
M.Masera (J.Chudoba): TPC tracking – efficiencies using merged events
S.Radomski: Status on TPC tracking code
S.Sedykh: TRD tracking status
R.Schiker: TRD tracking with tilted pads
A.Pulverenti: Neural and combined tracking in ITS
12 June 2002
Karel Safarik: Reconstruction Status

26. Karel Safarik: Reconstruction Status
Parallel tracking
For a long time we plan to develop parallel Kalman filter
improvement in cluster deconvolution in TPC
improvement in ITS tracking, especially strip layers
First thing: we have to change seeding
in fact we have only work-around
Now the structure of parallel tracking is working in TPC
the study for deconvolution started
expect improvement in dE/dx (golden clusters)
12 June 2002
Karel Safarik: Reconstruction Status

27. Karel Safarik: Reconstruction Status
Merged events
Gives results well comparable to our standard chain
however much faster  partial TPC reconstruction
Technical provision for comparison: track reference information
at the moment we had for TPC a work-around: special hit
Now we have first implementation of track reference (similar structure to hits, one by M.Ivanov)
Technical discussion about structure of tracking code
static utility classes
multi-event per file processing
12 June 2002
Karel Safarik: Reconstruction Status

28. Standalone ITS tracking
TRD tracking
Ready for deployment
use the same structure as TPC and ITS reconstruction version 2
in this version the non-tilted pad geometry is implemented
seeding with TRD itself  slow and not optimized
Discussion on tilted pads
simple estimates gives expected improvement in z resolution
however, problems with ‘real’ implementation
implication for online triggering easy to recover
Standalone ITS tracking
Neural network algorithm with pre-filtering
work well above 1 GeV
12 June 2002
Karel Safarik: Reconstruction Status

29. Karel Safarik: Reconstruction Status
Second day
Long discussion about V0 vertexing:
Strasbourg group presented reconstruction of Omegas
background estimates not far from expected
has to be study using event merging already developed for TPC and now under development for ITS
(Yu.Belikov will tell you more)
status of V0 finding with version 1 (Catania group) gives compatible results
Status of fast simulation using parameterization of covariance matrix
now implemented for different particle types
can be used for other physics studies
12 June 2002
Karel Safarik: Reconstruction Status

30. Method for high statistics study
Parameterization of Track parameter covariance matrix after TPC
Regularization
of pt dependence
‘pulls’
Comparison with
full simulation
12 June 2002
Karel Safarik: Reconstruction Status

31. Impact parameter resolution
Basic parameter for charm and beauty study is impact parameter resolution
determined by ITS performance and namely pixel detector
Full simulation and approximation
12 June 2002
Karel Safarik: Reconstruction Status

32. Conclusions and outlook
Reconstruction development proceed well
lower than expected efficiency for secondary tracks
outstanding issues
improvement in seed finder
‘kink’ finder for charged K decays in TPC
V0 finding in larger fiducial volume
recovery for electron bremsstrahlung in Kalman filter ( started)
need an effort in calibration and alignment software
Charged particle identification
we have studies of performance on detector levels (ITS, TPC, TOF, HMPID)
dependence on particle density
‘correct’ connection with tracking detectors
global particle identification performance
Photon identification
study in the ‘real’ environment
12 June 2002
Karel Safarik: Reconstruction Status