George S.F. Stephans

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Two-particle angular correlations in pp and dAu
collisions

• George S.F. Stephans
• Massachusetts Institute of Technology
• for the i
• collaboration

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Two-particle angular correlations in pp and dAu
collisions
A hint of
Plus results for fluctuations of rapidity
distributions in AuAu
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Collaboration (August 2005)
Burak Alver, Birger Back, Mark Baker, Maarten
Ballintijn, Donald Barton, Russell Betts, Richard
Bindel, Wit Busza (Spokesperson), Zhengwei Chai,
Vasundhara Chetluru, Edmundo García, Tomasz
Gburek, Kristjan Gulbrandsen, Clive Halliwell,
Joshua Hamblen, Ian Harnarine, Conor Henderson,
David Hofman, Richard Hollis, Roman Holynski,
Burt Holzman, Aneta Iordanova, Jay Kane,Piotr
Kulinich, Chia Ming Kuo, Wei Li, Willis Lin,
Constantin Loizides, Steven Manly, Alice
Mignerey, Gerrit van Nieuwenhuizen, Rachid
Nouicer, Andrzej Olszewski, Robert Pak, Corey
Reed, Eric Richardson, Christof Roland, Gunther
Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith,
Maciej Stankiewicz, Peter Steinberg, George
Stephans, Andrei Sukhanov, Artur Szostak,
Marguerite Belt Tonjes, Adam Trzupek, Sergei
Vaurynovich, Robin Verdier, Gábor Veres, Peter
Walters, Edward Wenger, Donald Willhelm, Frank
Wolfs, Barbara Wosiek, Krzysztof Wozniak, Shaun
Wyngaardt, 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
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Sample 2-particle correlation
dAu _at_ 200 GeV MinBias
Raw data



??
Unique to Phobos
??
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Dominant physics in raw correlation
dAu _at_ 200 GeV MinBias
Detector effects (?-e?, etc.)


??
??
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Dominant physics in raw correlation
dAu _at_ 200 GeV MinBias
Momentum conservation


??
??
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Status of Phobos Results

• Why do this in Phobos?
• Large ?? available
• Can look at ?? or ?? ?? at large ?
• Work ongoing to remove uninteresting effects.

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Change of Topic

• In addition to looking at correlations in ?,
  Phobos can study essentially all of dN/d? either
  averaged or on event-by-event basis.
• Many physics possibilities
• Dependence on energy, system, and centrality
• Event-by-event correlations and fluctuations

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Extended longitudinal scaling - I
AuAu
When effectively viewed in the rest frame of one
of the colliding nuclei, dN/d? appears to be
independent of energy over a very large range of
?', denoted extended longitudinal scaling
(previously limiting fragmentation).
19.6
62.4 (Prelim)
130
200
Similar scaling observed for flow Implies effect
is set at an early stage.
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dN/d? for CuCu

• Extended longitudinal scaling is also observed to
  hold for Cu data.

62.4
200
CuCu Phobos Prelim
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Extended longitudinal scaling - II

• The shape is a function of centrality but the
  scaling with energy is repeated for each bin.

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Extended longitudinal scaling - III

• The factorization of the centrality and energy
  dependence is quite remarkable.

Take the peripheral dN/d?, normalize by
Npart, divide by the central dN/d?, also
normalized by Npart
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Factorization of Energy and Centrality
dN/d? for 35-40 over 0-6, each normalized by
Npart
Take Periph over Central
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Observations on dN/d?

• Complete factorization of centrality and energy
  observed in all data studied to date.
• It seems inappropriate to separate longitudinal
  phase space into distinct fragmentation and
  central regions governed by different physics.
• Differences in particle density will produce
  variations in final-state effects but the overall
  shape is set by the initial energy and centrality.

As we discovered on the train, tomorrow never
happens, its all the same day J. Joplin
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Some Related Studies

• Do regions of ? correlate event-by-event?
• P.Steinberg talk last Saturday
• Are there events with very large multiplicity?
• Does the shape of dN/d? vary event-by-event?
• These constitute the remainder of this talk

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What we did - I

• Used 3 most central event sample in high
  statistics 200 GeV AuAu data set.
• About 1.96M events pass all quality cuts
• Looked at the distribution of the total number of
  hits in the multiplicity detectors.
• Note that these analyses required multiple passes
  through the entire data sample (not just the 3),
  each pass took about 2-4 hours using PROOF and
  distributed disk storage.
• See poster by M. Ballintijn

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Results - Ia

• There is a tail on the high-total-hit side

Cut
570 evts
More than one event??
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Could it be pileup?

• Pileup means a single event in which the data
  is affected by more than one actual collision,
  including beam-gas and halo from upstream.
• Scintillators and Si have different integration
  times. Result also depends strongly on vertex
  location and is different for beam gas,
  beam-beam, halo, etc.
• Collisions from different or same bunches.
• Rate of each depends on how the beam is
  distributed into bunches, bunch crossing time,
  etc.
• Pileup within the Si detector integration time,
  or in the same bunch crossing, estimated at 6000
  and 800 events, respectively, out of 2M.

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Results - Ib

• We found that these events are strongly
  correlated with the beam rate ? Pileup?
• Rate of events extrapolated to low luminosity is
  approximately consistent with zero

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What we did - II

• Divided dN/d? distribution into individual bins
  and calculated average and variation.
• Compared each event to the average and looked for
  highly unusual events

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Some details - IIa

• Normalized each event total to remove remaining
  fluctuations in total yield.
• Binned events in ZY vertex location.
• X vertex didnt vary significantly.
• Used number of hit pads in bins in ??

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Some Details - IIb

• Compared raw dN/d?

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Some details - IIc

• Important to use the measured variance in each ?
  bin, distributions are not Poisson

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Results - IIa

• ?2 distribution shows a distinct tail

200 evts
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Results - IIb

• However, these events are also strongly
  correlated with the beam rate ? Pileup again?
• Rate of events extrapolated to low luminosity is
  again approximately consistent with zero

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Summary

• Many results are in progress
  for correlations and fluctuations.
• Extended longitudinal scaling indicates that mid-
  and far-from-mid-rapidity cannot be treated as
  totally distinct.
• First event-by-event investigation of total
  number of hits and overall shape of dN/d? in the
  most central AuAu collisions _at_ 200 GeV indicates
  that both are very stable (at the rate of 10?4
  or possibly lower).