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


Two-particle angular correlations in p+p and d+Au collisions

A hint of

Plus results for fluctuations of rapidity distributions in Au+Au


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


Sample 2-particle correlation

Raw data

d+Au @ 200 GeV MinBias

Unique to Phobos


Dominant physics in raw correlation

Detector effects (-e, etc.)



Dominant physics in raw correlation

Momentum conservation



Status of Phobos Results

Why do this in Phobos?Large available

Can look at or at large ||

Work ongoing to remove uninteresting effects.


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


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.


dN/d for Cu+Cu

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

62.4 200

Cu+CuPhobosPrelim


Extended longitudinal scaling - II

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


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%


Factorization of Energy and Centrality

dN/d for 35-40% over 0-6%, each normalized by Npart

TakePeriph overCentral


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


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…


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


Results - Ia

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

Cut

570 evts

More than one event??


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.


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


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…


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


Some Details - IIb

Compared raw dN/d


Some details - IIc

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


Results - IIa

2 distribution shows a distinct tail

Cut200 evts


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


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).

two-particle angular correlations in p+p and d+au collisions

Documents

d au collisionsgeorge

au collaboration

au au19

prelim130200similar

energy dependence

event correlations

central dnd

npartfactorization of