Longitudinal density correlations in Au+Au collisions at √s NN = 200 GeV
Two-particle angular correlations in p+p and d+Au collisions
-
Upload
jamalia-mcmillan -
Category
Documents
-
view
36 -
download
1
description
Transcript of Two-particle angular correlations in p+p and d+Au collisions
Quark Matter 2005 8-Aug George S.F. Stephans
George S.F. StephansMassachusetts Institute of Technology
for the i
collaboration
Two-particle angular correlations in p+p and d+Au collisions
Quark Matter 2005 8-Aug George S.F. Stephans
Two-particle angular correlations in p+p and d+Au collisions
A hint of
Plus results for fluctuations of rapidity distributions in Au+Au
Quark Matter 2005 8-Aug George S.F. Stephans
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 Hołyński, 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 Woźniak, Shaun Wyngaardt, Bolek Wysłouch
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER
Quark Matter 2005 8-Aug George S.F. Stephans
Sample 2-particle correlation
Raw data
d+Au @ 200 GeV MinBias
Unique to Phobos
Quark Matter 2005 8-Aug George S.F. Stephans
Dominant physics in raw correlation
Detector effects (-e, etc.)
d+Au @ 200 GeV MinBias
Quark Matter 2005 8-Aug George S.F. Stephans
Dominant physics in raw correlation
Momentum conservation
d+Au @ 200 GeV MinBias
Quark Matter 2005 8-Aug George S.F. Stephans
Status of Phobos Results
Why do this in Phobos?Large available
Can look at or at large ||
Work ongoing to remove uninteresting effects.
Quark Matter 2005 8-Aug George S.F. Stephans
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
Quark Matter 2005 8-Aug George S.F. Stephans
Extended longitudinal scaling - I
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”).
Au+Au19.6 62.4 (Prelim) 130 200
Similar scaling observed for flow:Implies effect is set at an early stage.
Quark Matter 2005 8-Aug George S.F. Stephans
dN/d for Cu+Cu
Extended longitudinal scaling is also observed to hold for Cu data.
62.4 200
Cu+CuPhobosPrelim
Quark Matter 2005 8-Aug George S.F. Stephans
Extended longitudinal scaling - II
The shape is a function of centrality but the scaling with energy is repeated for each bin.
Quark Matter 2005 8-Aug George S.F. Stephans
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
RPCN part =
dNd 35−40%
NPart 35−40%
dNd 0−6%
NPart 0−6%
Quark Matter 2005 8-Aug George S.F. Stephans
Factorization of Energy and Centrality
dN/d for 35-40% over 0-6%, each normalized by Npart
TakePeriph overCentral
Quark Matter 2005 8-Aug George S.F. Stephans
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, it’s all the same %#&*% day” J. Joplin
Quark Matter 2005 8-Aug George S.F. Stephans
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…
Quark Matter 2005 8-Aug George S.F. Stephans
What we did - I
Used 3% most central event sample in high statistics 200 GeV Au+Au 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
Quark Matter 2005 8-Aug George S.F. Stephans
Results - Ia
There is a tail on the high-total-hit side
Cut
570 evts
More than one event??
Quark Matter 2005 8-Aug George S.F. Stephans
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.
Quark Matter 2005 8-Aug George S.F. Stephans
Results - IbWe found that these events are strongly
correlated with the beam rate ➩ Pileup?Rate of events extrapolated to low luminosity is
approximately consistent with zero
Quark Matter 2005 8-Aug George S.F. Stephans
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…
Quark Matter 2005 8-Aug George S.F. Stephans
Some details - IIa
Normalized each event total to remove remaining fluctuations in total yield.
Binned events in Z&Y vertex location.
X vertex didn’t vary significantly.
Used number of hit pads in bins in
Quark Matter 2005 8-Aug George S.F. Stephans
Some Details - IIb
Compared raw dN/d
Quark Matter 2005 8-Aug George S.F. Stephans
Some details - IIc
Important to use the measured variance in each bin, distributions are not Poisson
Quark Matter 2005 8-Aug George S.F. Stephans
Results - IIa
2 distribution shows a distinct tail
Cut200 evts
Quark Matter 2005 8-Aug George S.F. Stephans
Results - IIbHowever, 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
Quark Matter 2005 8-Aug George S.F. Stephans
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 Au+Au collisions @ 200 GeV indicates that both are very stable (at the rate of ~104 or possibly lower).