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Terzo Convegno Nazionale sulla Fisica di ALICE Frascati (Italy) – November 12-14, 2007. Multiplicity analysis and dN/d h reconstruction with the silicon pixel detector. Maria Nicassio (Univ. and INFN Bari) in collaboration with D. Elia, B. Ghidini (Univ. and INFN Bari) - PowerPoint PPT Presentation
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Multiplicity analysis Multiplicity analysis and and
dN/ddN/dreconstructionreconstructionwith the with the
silicon pixel detectorsilicon pixel detector
Terzo Convegno Nazionale sulla Fisica di ALICETerzo Convegno Nazionale sulla Fisica di ALICEFrascati (Italy) – November 12-14, 2007Frascati (Italy) – November 12-14, 2007
Maria Nicassio Maria Nicassio (Univ. and INFN Bari)(Univ. and INFN Bari)
in collaboration within collaboration with
D. Elia, B. Ghidini (Univ. and INFN Bari)D. Elia, B. Ghidini (Univ. and INFN Bari)T. Virgili (Univ. Salerno)T. Virgili (Univ. Salerno)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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ContentsContents
Introduction: physics motivation tracklet reconstruction algorithm
Status of the analysis: study of the corrections:
geometrical acceptance detector efficiency background from secondaries vertex reconstruction efficiency minimum bias trigger acceptance
Summary and outlook
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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IntroductionIntroduction
Why multiplicity: first measurement in p-p collisions for ALICE global observable characterizing the event comparison with results obtained at lower energies
Why multiplicity with pixels: available in a short time advantages over reconstructed tracks (ITS+TPC)
larger acceptance coverage only alignment of the two pixel layers required
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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IntroductionIntroduction
Acceptance coverage:
SPD layers:-2.0 < < 2.0 (inner)
-1.5 < < 1.5 (outer)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Multiplicity reconstruction: (a) counting clusters on the inner layer (|| < 2.0)
no detector alignment required
reliable at high multiplicity
(b) counting tracklets (|| < 1.5) alignment, vertex needed
more reliable (e.g. good noise rejection)
Pseudorapidity reconstruction: vertex needed for both methods the angle of the cluster on the inner layer is used
IntroductionIntroduction
Fiducial window
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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dN/ddN/d distributions distributions (uncorrected)(uncorrected)
asymmetry due to the detector efficiency losses in PDC06
Inner layer clusters Tracklets
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Corrections: SPD acceptance Corrections: SPD acceptance (I) (I)
MC data samples: Pb-Pb (HijingParam) collisions @ 5.5 TeV:
20,000 tracks/evt, within [-4,4]
event vertex-Z within [-20,20] cm
fully efficient SPD 2,500 evts pure
geom acceptance
standard PDC06 SPD dead chip map 2,500 evts
convoluted acc+eff
Correction matrix:
binning and range: within [-3,3] nEtabins = 120 d = 0.05
vtx-Z within [-20,20] cm nVtxzbinx = 40 dVtx-Z = 1 cm
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Calculation method: detectable_tracks (fDenAcc):
primary charged
no decay, no secondary interactions up to the sensitive layer
detected_tracks (fNumAcc): detectable tracks with associated (label) cluster on the sensitive
layer
if there are 2 clusters on adjacent modules: track is counted twice
this takes into account the overlapping regions
( 2%)
compute acceptance and error in each bin
(fAcc,fErrAcc)
statistics in each bin: detectable tracks: 104
resulting error on the acceptance: 10-3
Corrections: SPD acceptance Corrections: SPD acceptance (II) (II)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Results: convoluted acceptance & efficiency:
Tracklets
Inner layer
Outer layer
Corrections: SPD acceptance Corrections: SPD acceptance (III) (III)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Correction applied:
Corrections: Corrections: acceptance & efficiency (I)acceptance & efficiency (I)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Corrections: Corrections: acceptance & efficiency (II)acceptance & efficiency (II)
Correction applied:
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Corrections: Corrections: background from secondaries background from secondaries (I)(I)
Studied using the SPD cluster labels
Definition of background:
for clusters on the inner layer:
clusters having secondary track labels only
for tracklets:
at least one of the two clusters in the
tracklet
having secondary track labels only
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Clusters (inner layer):
Corrections: Corrections: background from secondaries background from secondaries (II)(II)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Clusters (inner layer):
correction(to be multiplied by)
Corrections: Corrections: background from secondaries background from secondaries (III)(III)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Tracklets:
Tracklets from primaries
Tracklets from secondaries
Tr(P+P)
Tr(P+P’)
Tr(P+P)+Tr(P+P’)
Tr(S+S) + Tr(P+S)
Tr(S+S) Tr(P+S)
to be subtracted
P, P’ = cluster with a label of a primary track
S = cluster with all labels of secondary tracks
(total bkg fraction: 7.5%)
Corrections: Corrections: background from secondaries background from secondaries (IV)(IV)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Tracklets:
correction(to be multiplied by)
Corrections: Corrections: background from secondaries background from secondaries (V)(V)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Corrections: Corrections: vertex reconstruction (I)vertex reconstruction (I)
Generated dNch/d
N.B. The correction is integrated, but it should be a function of multiplicity and vertex position
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Correction (to be multiplied by)
Corrections: Corrections: vertex reconstruction (III)vertex reconstruction (III)
The correction depends both on and on multiplicity at low multiplicityTo be checked as a function of Z-vtx
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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All corrections applied: inner layer clusters
Final dN/dFinal dN/d distributions distributions
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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All corrections applied: tracklets
Final dN/dFinal dN/d distributions distributions
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Multiplicity distributions Multiplicity distributions (uncorrected)(uncorrected)
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Multiplicity distributionsMultiplicity distributions
Background correction:
16% 7%
Background fractionsfor each event
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Multiplicity distributionsMultiplicity distributions
All corrections applied:
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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MB2 =(GFO.and.V0OR).and.notBG
triggerwithEvents
eventsAllCorrection
__
_
Effect of trigger selection: Effect of trigger selection: first look (I)first look (I)
Trigger correction:
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Effect of trigger selection: Effect of trigger selection: first look (II)first look (II)
Generated dN/d:MB2 =(GFO.and.V0OR).and.notBG
All events
No triggerNo vertex
vertextriggerwithEvents
eventsAllCorrection
&__
_
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Summary and outlookSummary and outlook
Multiplicity and pseudorapidity density in p-p: first measurement in ALICE reconstruction with the Silicon Pixel Detector only
Status of the analysis: raw reconstructed distributions with PDC06 data study of the main corrections:
acceptance, efficiency, background from secondaries, vertex, trigger
What next: check correction dependence on multiplicity, Z-vtx estimate of the systematics tests with PDC07 data
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Backup slidesBackup slides
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Couples of clusters associated with the same
track
Tracklet algorithm efficiency in p-pTracklet algorithm efficiency in p-p
Maria Nicassio Convegno Nazionale sulla Fisica di ALICE Frascati - November 12, 2007
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Using the default cuts the algorithm efficiency is 99%
Tracklet algorithm efficiency in p-pTracklet algorithm efficiency in p-p
Couples of clusters associated with the same
track