Collision Geometry Scaling of MidRapidity Charged Particle Multiplicity in PHOBOS from vsNN 19'6 to - PowerPoint PPT Presentation

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Collision Geometry Scaling of MidRapidity Charged Particle Multiplicity in PHOBOS from vsNN 19'6 to

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Title: Collision Geometry Scaling of MidRapidity Charged Particle Multiplicity in PHOBOS from vsNN 19'6 to


1
Collision Geometry Scaling of Mid-Rapidity
Charged Particle Multiplicity in PHOBOS from
vsNN 19.6 to 200 GeV
  • Aneta Iordanova
  • University of Illinois at Chicago
  • For the collaboration

DNP04/Chicago
2
Outline
  • Multiplicity Analysis Technique
  • Vertex Tracklet reconstruction method
  • Results
  • Mid-rapidity charged-particle multiplicity and
    its centrality dependence for 19.6 and 200GeV
  • Compare the results with model predictions
  • Conclusions

3
Collaboration (October 2004)
Burak Alver, Birger Back, Mark Baker, Maarten
Ballintijn, Donald Barton, Russell Betts, Abigail
Bickley, Richard Bindel, Wit Busza
(Spokesperson), Alan Carroll, Zhengwei Chai,
Vasundhara Chetluru, Patrick Decowski, Edmundo
García, Tomasz Gburek, Nigel George, Kristjan
Gulbrandsen, Clive Halliwell, Joshua Hamblen,
Ian Harnarine, Conor Henderson, David Hofman,
Richard Hollis, Roman Holynski, Burt Holzman,
Aneta Iordanova, Jay Kane, Nazim Khan, Piotr
Kulinich, Chia Ming Kuo, Wei Li, Willis Lin,
Steven Manly, Alice Mignerey, Gerrit van
Nieuwenhuizen, Rachid Nouicer, Andrzej
Olszewski, Robert Pak, Heinz Pernegger, Corey
Reed, Christof Roland, Gunther Roland, Joe
Sagerer, Iouri Sedykh, Wojtek Skulski, Chadd
Smith, Peter Steinberg, George Stephans, Andrei
Sukhanov, Marguerite Belt Tonjes, Adam Trzupek,
Carla Vale, Sergei Vaurynovich, Robin Verdier,
Gábor Veres, Peter Walters, Edward Wenger, Frank
Wolfs, Barbara Wosiek, Krzysztof Wozniak, Alan
Wuosmaa, Bolek Wyslouch ARGONNE NATIONAL
LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITU
TE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS
INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL
UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
4
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5
Multiplicity measurement at mid-rapidity (hlt1)
6
Vertex Detector
  • 8192 silicon channels
  • Outer Layer 2 2048 channels, 0.47mm 24.1mm
  • Inner Layer 2 2048 channels, 0.47mm 12.0mm

7
Tracklet Reconstruction
  • Tracklet
  • Two-hit combination from Outer and Inner Vertex
    (Top or Bottom), pointing to the reconstructed
    vertex.
  • Reconstructed vertex
  • from Spectrometer Detector
  • 19.6GeV
  • sx,y,z0.3,0.3,0.4 mm (central)
  • sx,y,z0.6,0.5,0.8 mm (mid-central)

8
Tracklet Reconstruction
First Pass
  • df fSearch fSeed lt 0.3
  • dh hSearch hSeed lt 0.1
  • smallest dh combination.

fSearch ,hSearch
Extrapolate fSeed ,hSeed
hit
Search Layer
hit
Seed Layer
Top Vertex
Second Pass
Reconstructed Vertex
  • Tracklets with a common hit
  • in the Search Layer
  • smallest dh combination.

9
Multiplicity Determination
  • formed by rotating Inner Vertex Detector layers
    1800 about the beam pipe
  • corrects for
  • azimuthal acceptance of the detector
  • tracklet reconstruction efficiency
  • secondary decays

10
Results
11
Centrality Determination
  • Select the same regions at 200 and 19.6 GeV
  • Have two centrality methods at each energy
  • One at mid-rapidity
  • One away from mid-rapidity
  • Mechanism for comparing like regions to see
    systematic effects
  • Results presented here
  • for a) and c)

Regions are matched according to the ratio of
beam rapidities (a) with (c) (b) with (d)
12
Measured pseudorapidity density per participant
pair as a function of ltNpartgt
  • Geometry-normalized multiplicity in Au-Au
    collisions higher than corresponding values for
    inelastic
  • Percentile cross-section
  • 0-50 for 200 GeV
  • 0-40 for 19.6 GeV

90 C.L.
13
Measured pseudorapidity density per participant
pair as a function of ltNpartgt
  • Model predictions
  • Hijing
  • does not follow data trend
  • Saturation Model (KLN)
  • Phys.Lett.B523 79 (2001)
  • arXivhep-ph/0111315
  • better agreement

90 C.L.
14
Ratio of the two data sets systematic errors
  • Most of the systematic errors on the individual
    measurements at the two energies will cancel in
    the ratio
  • Analyses performed with the same method
  • Detector
  • Centrality determination
  • Percentile cross-section used in ratio
  • top 40
  • Errors are estimated as 1-s.

15
Ratio of the two data sets systematic and
statistical errors
  • Final 1-s systematic and statistical error
  • Centrality dependent
  • central events 3
  • mid-central events 7

16
Ratio for the data sets
  • Data ratio
  • AuAu1 (fixed fraction of cross-section)

1-s errors
17
Ratio for the data sets
  • Data ratio
  • AuAu1 (fixed fraction of cross-section)
  • No centrality (geometry) dependence
  • R 2.03 0.02 0.05 (simple scale-factor
    between 19.6 and 200GeV)

1-s errors
18
Ratio for the data sets
  • Data ratio
  • AuAu1 (fixed fraction of cross-section)
  • No centrality dependence
  • R 2.03 0.02 0.05
  • AuAu2 (fixed ltNpartgt)
  • No centrality dependence

1-s errors
19
Ratio for the data sets
  • Models
  • Hijing
  • increase in mid-rapidity with centrality
  • Saturation Model (KLN)
  • flat centrality dependence as in data

1-s errors
Phys. Rev. C70, 021902(R)(2004)
20
Other Geometry Scaling observations in
  • Multiplicity
  • 200/130 GeV mid-rapidity ratio
  • Phys.Rev.C65 061901(R) (2002)
  • 19.6-200GeV Nch/ltNpart/2gt
  • Plot from QM 2002 talks

21
Other Geometry Scaling observations in
  • Charged hadron pT spectra
  • Ratio of yield for 200 and 62.4 GeV is centrality
    independent for all measured pT bins

22
Conclusions
  • We measured charged-particle pseudorapidity
    density at mid-rapidity for Au-Au collisions at
    200 and 19.6GeV
  • Centrality, derived from different h-regions for
    each of the two Au-Au collision energies, yield
    consistent results
  • An increase in particle production per
    participant pair for Au-Au compared to the
    corresponding values for collisions
  • The ratio of the measured yields for the top 40
    in the cross section gives a simple scaling
    factor between the two energies
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