cosmics in its: tracking & alignment
DESCRIPTION
Cosmics in ITS: tracking & alignment. A.Dainese (INFN Legnaro). ITS alignment group: LNL, PD, TS, CT, TO, Nikhef. Layout. ITS alignment strategy Cosmics reconstruction in ITS Summer cosmics sample for alignment First alignment results: Millepede Iterative residuals minimization - PowerPoint PPT PresentationTRANSCRIPT
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 1
Cosmics in ITS: Cosmics in ITS: tracking & alignmenttracking & alignment
A.DaineseA.Dainese(INFN Legnaro)(INFN Legnaro)
ITS alignment group: LNL, PD, TS, CT, TO, Nikhef ITS alignment group: LNL, PD, TS, CT, TO, Nikhef
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 2
Layout
ITS alignment strategy
Cosmics reconstruction in ITS
Summer cosmics sample for alignment
First alignment results:
Millepede
Iterative residuals minimization
Alignment monitoring
First attempts of TPC-ITS matching
S.Moretto
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 3
Inner Tracking System (ITS)
Silicon Pixel Detector (SPD):• ~10M channels• 240 sensitive vol. (60 ladders)
Silicon Drift Detector (SDD):• ~133k channels• 260 sensitive vol. (36 ladders)
Silicon Strip Detector (SSD):• ~2.6M channels• 1698 sensitive vol. (72 ladders)
SPDSSD
SDD
ITS total:2198 alignable sensitive volumes 13188 d.o.f.
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 4
ITS detector resolutions & target alignment precisions
Residual: expected misalignment left after applying the realignment procedure(s). Target ~0.7resol. ~20% degradation of the resolution
SPD(r = 4 & 7 cm)
SDD(r = 14 & 24 cm)
SSD(r = 39 & 44 cm)
nom. resolutions
xloc (yloc) zloc [m3] 12 (0) 120 38 (0) 20 20 (0) 830
residual mis. (shifts)
xlocyloczloc [m3] 10 10 20 20 20 20 15 15 100
yloc
zloc
xloc
detector local c.s.: xloc~rglob, yloc~rglob, zloc = zglob
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 5
ITS alignment with tracks:general strategy
Data sets: cosmics + first pp collisions (and beam gas)use cocktail of tracks from cosmics and pp to cover full detector surface and to maximize correlations among volumes
Start with B off, then switch on B (pp) possibility to select high-momentum (no multiple scattering) tracks for alignment
General strategy:
1) start with layers easier to calibrate: SPD and SSD good resol. in r (12-20m), worse in z (120-830m)
2) global ITS alignment relative to TPC (already internally aligned)
3) finally, inclusion of SDD, which need longer calibration (interplay between alignment and calibration)
Two independent track-based alignment methods in preparation:
global: Millepede (ported to ALICE for muon arm alignment)
local: iterative method based on residuals minimization
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 6
Cosmics!1st muon in SPD: Feb 17, 2008
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 7
Tracking cosmics in ITS
Cosmics tracking in ITS:adapted stand-alone ITS tracking (Torino)
enlarged search windows to account for large misalignments
start from “fake” vertex built from the two tracklets in inner two layers
ESD filewith track
space-points
ESD filewith track
space-points
Tree withSelected
Space points
Alignment procedures
Reconstruction Reconstruction
- select tracks (pt,, , #points)- can merge 2 cosmics tracks
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 8
AND
Cosmics with SPD trigger
Pixel FastOR trigger since May 25: first side C, then also side A
Trigger configuration:rate: 0.05 Hz (June) 0.18 Hz (Aug)
purity (reconstructed
with 3-4 cls/triggered): about 30%
about 85% of SPD
taking data in August
Statistics collected (till Sept 3rd): about 55k good eventsevents with 4-cls in SPD: 30k
events with 3-cls in SPD: 25k
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 9
ITS points
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 10
Cosmics statistics (SPD)220/240 (92%) modules with at least one hit200/240 (83%) modules with at least 50 hits
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 11
Cosmics statistics (SDD)Low statistics on inner layer (switched on later than outer)Limited statistics on the sides (outer layer: about 50% of modules have sufficient statistics to try alignment)
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 12
Cosmics statistics (SSD)Limited statistics on the side and edges in z
aligned in Millepede down to the ladder level: about 55/72 ladders have sufficient statiscs
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 13
SPDMillepede alignment quite advancedMost of the detectors that are currenltly switched on have some alignmentAlignment of side detectors may be less realiable
need quick checks with first pp data!
SDDCalibration of time offset is in progress (Torino)
Use Alignment Monitoring tool for validation (C.Bombonati)
Almost ready to be includedSurvey (modules on ladders) is ready to be used (M.Poghosyan)
SSDIncluded in Millepede since mid-JulyAlignment exercises usefull to spot / understand possible problems in geometry / hardware Survey (modules on ladders) ready to be used
S.Moretto
S.Moretto
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 14
Checking the quality of realignment
Main variable: track-to-track x at y=0
Acceptance overlaps “extra” clusters
Alignment monitoring tool
x
y
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 15
Millepede SPD realignment:x at y=0
realigned
not realignedSim, ideal geom:
43 m
DATA:
56 m
spatial=15 m spatial=11 m (Sim)
Expectedspread
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 16
Millepede SPD realignment:“extra” clusters
realigned
not realignedSim, ideal geom:
15 m
DATA:
22 m
spatial=16 m spatial=11 m (Sim)
Expectedspread
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 17
Alignment Monitoring: SPD
Track fit + residuals analysisCheck and monitor in time the quality of realignment
(try to “guess” high-level or correlated misalignments)
Millepede Ideal sim.
x residual [cm] x residual
C.Bombonati, A.Rossi
=70m =44mMille/Sim ~ 70/44 ~ 22/15
extraclusters
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 18
ITS alignment with tracks: iterative local method
Alignment params from minimization of track-to-points residuals
Local: works on a module-by-module basis
Iterations are used to take into account correlations between the alignment params of different modules
difficult with SPD alone: only 4 points (modules) per track
about 50% worse than Millepede;difficult to account for correlations
A.Rossi
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 19
SDD: time0 calibration and alignment
Residuals: fit su SPD+SSD
residuals su SDD (up, down)
Not indep. of misalignment
-130m -10m
C.Garcia, C.Bombonati
Complementary procedure: estimate time0 from minimum time (F.Prino)
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 20
TPC-ITS matching with large
misalignment/miscalibrationMisalignments (internal & TPC vs ITS) and miscalibration
(drift velocity, time0, ExB) reduce matching efficiency
A set of knobs to enlarge track/cluster errors should allow
to recover the efficiency
TPC: add systematic errors (drift velocity, time0, ExB) to the track
covariance matrix before prolongation to ITS
ITS: add misalignment errors to cluster errors (~ 1 mm)
Matching efficiency (prel.): TPC+ITS (4cls) / ITSsa
(4cls)
B=0: >90%
B=0.5T (enlarged errors): ~85%
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 21
B=0.5 T cosmics in ITS+TPC
pT = 1 GeV
pT = 0.2 GeV
pT = 2 GeV
noise SDDora risolto
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 22
Check of ITS alignment
with ITS+TPC tracks, B=0.5Use Millepede realignment SPD+SSD
Track-to-track distance x pull = x / √top
2+bottom
2
ITS+TPC
SPD+SSD+TPC
mean 6 m= 54 m
3or4 + 3or4 ITS points
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 23
SummaryLarge sample of cosmics collected during Summer
SPD FastOR trigger gave a big boost
All alignment machinery (reconstruction, realignment, monitoring) working from the very beginning
Good results from Millepede
Most of SPD realigned to 10 mneed cross-checks with pp, especially on the side
Started to include SSD (limited statistics for cosmics)
SDD will come soon
Next step: ITS-TPC alignmentneed to understand TPC calibration first...
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 24
EXTRA SLIDES
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 25
PrimaryVertex B
e
Xd0
rec. track
Impact of ITS misalignmenton tracking performance
Effect of misalignment on d0 (and pt) resolutions studied by reconstructing misaligned events with ideal geometry
Estimated effect on D0K significance
A.D, A.Rossi
nullresidualfullfull+
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 26
Millepede: cross-checks (3)
Use -acceptance overlaps in SPD (“extra” clusters)
Check on simulation with ideal geometry:
(xy) = 15 m (z) = 165 mouter SPD layer:
“extra” clusters not (yet) used for realignment cross-check
IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese 27
Millepede: cross-checks (3)
Use -acceptance overlaps in SPD (“extra” clusters)
Check on simulation with ideal geometry:
(xy) = 22 m (z) = 163 m
high-stats sectors
selected
outer SPD layer:
raw
realigned