Domenico Elia / INFN BariII Convegno Fisica di ALICE / Vietri, 30 Maggio - 1 Giugno 20061 Attività...

Domenico Elia / INFN Bari II Convegno Fisica di ALICE / Vietri, 30 Maggio - 1 Giugno 2006

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Attività di Attività di OfflineOfflinenel progetto nel progetto SPDSPD

Domenico Elia (INFN Bari)

II Convegno Nazionale sulla Fisica di ALICEVietri sul Mare (SA), 30 Maggio - 1 Giugno 2006


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Attività di Offline nel progetto SPD

ContentsContents

Main issues in the SPD Offline: Detector response simulation (diffusion model)

Alignment and calibration

Reconstruction (multiplicity with tracklets)

Trigger (Fast-OR based MB pp selection)

Analysis studies in Bari: Additional FO applications (high multiplicity pp, etc)

Contribution to 1st Physics Paper

Secondary vertex and charm reconstruction


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2 barrel layers (z = 28.3 cm, r = 3.9 and 7.6 cm)40+20 staves, 10 sectors

240 silicon sensors & ladders (200 m thick)

1200 readout chips (150 m thick), 10 per half-stave

9.83 M pixels, 50 x 425 m2, 8192 on each chip

spatial precision (in r) 12 m (ALICE ITS TDR, 1999) low material budget (< 1% X0 per layer)

SPD numbers

Physics goals:

primary vertexing secondary vertexing for open charm and beauty

L0 trigger in pp multiplicity

The SPD in ALICEThe SPD in ALICE


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SPD spatial precisionSPD spatial precision

Plane dimensions: 13.6 mm x 12.8 mm

test detector: single chip assemblies two additional doublets of single chip assemblies used as tracking system

Measurements in beam tests: H4 line at the CERN SPS, 350 GeV/c proton beam

measurements at different thresholds various inclination angle settings (0-30o)


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SPD spatial precisionSPD spatial precision

Normal track incidenceand 200 DAC threshold

Data from 2002 testwith 200 m sensor

Track not well definedin the long pixel side(x) coordinate due to tracking doubletconfiguration

Residuals in the short pixel side (y ) coordinate:y

x

425 m

50 m

Global (all clusters) precision:

Ly / √12 = 14.4 m

Spatial precision: Tracking error estimatedby simulation: track (y) 6 m


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Response simulationResponse simulation

Two models compared with beam test data:

Experimental data Geometrical model

Track impact position on the pixel cell

Diffusion model

diffusion model better suited for precision studies


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Updates in the diffusion model code: speeding-up of the diffusion algorithm (B.S. Nilsen)

fine tuning of diffusion parameters (G.E. Bruno, R.

Santoro):

~

x-x0

y-y0 ●

Fdv = sensor thickness / bias voltage

Fda = asymmetry parameter for the x/y diffusion

Fcr = coupling along the row direction (percentage of charge)


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Updates in the diffusion model code: fine tuning of diffusion parameters (cont’d):


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Layer 1:- ladders at 0o wrt radial direction- at ladder edges: track angle ± 10o

Updates in the diffusion model code: fine tuning checked to work at different thresholds

detailed cross-check on the spatial precisions: for different cluster patterns

at different track inclination angles

Layer 2:- ladders at 18o wrt radial direction- at ladder edges: track angle 18o ± 5o


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Updates in the diffusion model code: fine tuning checked to work at different thresholds

detailed cross-check on the spatial precisions: for different cluster patterns

at different track inclination angles

Spatial precision (m) – Exp. data vs Simulation

0° 5° 10°

All clusters 10,4 10,2 9,4 9.2 9,1 8.3

Single pixel 11,4 10,7 10,2 9,6 8,3 7,3

Double-y clusters

6,4 6,9 7,3 7,1 9,5 8,4


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Geometry and alignmentGeometry and alignment

Basic ideas for PDC06:

produce hit and digits with misplaced geometry ITS-TPC and intra-ITS alignments critical for strangeness and charm

amount of displacement: expected residual mis-alignment after standard software alignment

for the SPD ladders: 10 m in r, 20 m in Z, 0.3 mrad rotation global ITS shift: 50 m

reconstruction and tracking with nominal geometry: check the effect of residual mis-alignment on physical quantities

(e.g. decrease of tracking and vertexing performances)


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Calibration and preprocessingCalibration and preprocessing

Basic ideas:

create a framework to use calibration objects: partially implemented (E. Crescio, M. Masera, L. Gautichet, B. Nielsen)

create preprocessing: classes to fill data members of calibration objects (i.e. calibration data)

link to input sources: e.g. DAQ (calibration runs), DCS

pioneering work, existing preprocessor class for SPD (P. Nilsson)

basic need for PDC06: run simulation with reasonable “de-calibration”

(i.e. how many dead channels, how distributed in the modules, etc)


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Calibration and preprocessingCalibration and preprocessing

- 1% dead pixels - 1% dead chips - 5% dead columns in 5% of the chips - 5% dead modules (2 inner, 4 outer layer)

input SPD dead channels (CDB file for PDC06):

Inner Layer


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Trigger (Fast-OR)Trigger (Fast-OR)

The basic idea:

the SPD layout:

each SPD chip outputs a digital signal (FO) if >=1 pixel is fired

full SPD can provide a total of 1200 FO signals (400 from the inner layer + 800 from the outer layer)

FO signal combinations can provide an input for the L0 trigger (within a timing constraint of 900 nsec)

Sector: 4 (outer) + 2 (inner) staves

Half-Stave: 10 chips

SPD: 10 sectors (1200 chips)


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Fast-OR as minimum bias trigger in p-p

studies by J. Conrad, J.G. Conteras and C. Jorgensen

full description in ALICE-INT-2005-025

simulated beam-gas and p-p collisions (PDC04 data)

total of 10 possible SPD FO algorithms tested

18 possible MB trigger combinations investigated (SPD and VZERO)

3 possible MB trigger combinations finally proposed

best candidate:

MB1: (GLOBAL.FO) or (VZERO.OR) and (notBG) *

* See ALICE-INT-2005-025, ALICE PPR vol.II chap.VI


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Code implementation in AliRoot

recent work in AliITSTrigger.cxx : updated trigger class (in collaboration with C. Jorgensen)

two different methods implemented:

MultiplicityTrigger() providing 2 basic inputs:

ITS_SPD_GFO_L0 (for min-bias p-p)

ITS_SPD_HMUL_L0 (for high-multiplicity p-p)

GeometricalTrigger() left for additional inputs (not activated)

based on topological correlation between Fast-ORs

e.g. trigger for HMPID in p-p

trigger for ultra-peripheral in Pb-Pb


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New data samples:

larger statistics wrt to previous studies (factor 5)

full production done on the Bari PC-farm sample of p-p minimum bias:

- AliRoot v4-03-06 (PDC05 compatible version)

- Config = PYTHIA 6.214, kPyMb process

- total statistics currently available: 50 K events

sample of beam-background:

- same AliRoot version, HIJING generation of pO collisions

- vertex Z in [-50m,+30m] (beam-gas, beam-halo)

- total statistics currently available: 20 K events


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Minimum bias trigger:

cross checks with existing results*

* See ALICE-INT-2005-025, ALICE PPR vol.II chap.VI

INEL

ND

SDDD

50K pp events

Charged multiplicity in || < 1.5


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Global FO

MB1

MB1 = GlobFO .or. VzeroOR .and. notBG

MB2 = GlobFO .and. VzeroOR .and. notBG


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Global FO

MB1

ND SD DD INEL

MB1 1.00 0.74 0.88 0.94

MB2 0.99 0.60 0.69 0.88

MB1 = GlobFO .or. VzeroOR .and. notBG

MB2 = GlobFO .and. VzeroOR .and. notBG

Efficiency on pp:

but: MB2 more effectiveon bkg rejection


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Minimum bias trigger (cont’d)

new features implemented in the analysis code SPD dead channels as from CDB file for PDC06 (~ 6% dead)

FO inefficiency parameter

effect on the MB trigger negligible

effect on multiplicity selection being checked

Multiplicity trigger analysis ongoing, current results in the next slides


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nFO > 100nFO > 150

nFO > 200


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Multiplicity reconstructionMultiplicity reconstruction

Tracklets for multiplicity (T. Virgili)

analysis macro finalized, tested (fake associations estimated)

coded in a new class: AliITSMultReconstructor.cxx

checks on PDC06 data ongoing

Contribution to 1st Physics paper:

multiplicity measurement in pp collisions @14 TeV

coordinated effort for the SPD part (with Tiziano)

few main issues to be finalized (see next slide)


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Contribution to 1st Phys. PaperContribution to 1st Phys. Paper

Main issues for the SPD: Data selection

mult reconstruction implemented in the trigger analysis code trigger studies and effects on multiplicity: to be finalized

Vertex determination < 1 mm precision required no-vtx events: using clusters on the 1st layer, clusters in the ESD ?

Corrections acceptance, decays, rec-efficiency: already done background (beam-gas): to be estimated

dN/d estimation sistematics (from corrections): being evaluated


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Secondary vertex and charmSecondary vertex and charm

Ongoing activity: Secondary vertexer performance (R. Romita)

checks (eg CPU consumption) of the standard vertexer comparison with an alternative method (D. Di Bari, for charged kaons)

Charm decay channels in pp (G.E. Bruno, R. Romita)

DS ( K K ), C ( p K ) decays

test sample of p-p events:

- AliRoot v4-04-Rev01 (PDC06 version)

- Config = kCharmpp14000wmi process, kHadr decay

- total statistics currently available: 16K events


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SummarySummary

Offline for the SPD: main updates and developments for the PDC06 done

geometry, calibration issues in evolution

multiplicity and trigger codes up to date

Analysis activity: work for 1st Physics Paper ongoing

additional Fast-OR trigger combinations under study

vertex and charm reconstruction just started

Domenico Elia / INFN BariII Convegno Fisica di ALICE / Vietri, 30 Maggio - 1 Giugno 20061 Attività...

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