Femtoscopy BNL Workshop 6/21/2005George Stephans Very Low p T in x Past, Present, and Prospects.

Femtoscopy BNL Workshop 6/21/2005George Stephans

Very Low pT in x

Past, Present, and Prospects


Collaboration (March 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, 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


Kinematic Regions at RHICAu+Au Centrality: 0-15%

200 GeV Mid-rapidity

(+)/2 Phys. Rev. C70, 051901(R) (2004)

(h+h)/2 PLB 578 (2004) 297

TAIL

BULK

HEAD

Physics Topics:

Bulk - Particle production, sets

the stage

Tail - Jet quenching,

probes medium

Head - Sensitive to global

properties


Spectrometer

The PHOBOS Detector (2001/2002)


The Low pT Part


The TechniqueSimple in principle, Si gives dE/dx which sums to total energy

Combination of dE/dx and ETot gives mass

Complicated in practice

Energy in last plane is unreliable (decays, interactions, etc.)

Need to iterate that energy until (dE/dx)i and Ei consistent

Many corrections: decays, secondaries, ghosts, tracking efficiency, PID efficiency, mis-identified particles, etc.


X[c

m] A

BC

DE F

Z[cm]

Beam pipe

0 10 20 Z [cm]

. .

.

Particle Measurements at Very Low pT

For now: Only find particles stopped in the 5th spectrometer plane

Reconstruction is based on the analysis of the measured energy depositions in the first 5 layers.

Fewer than 5 planes per track leads to more background.

Beyond that, magnetic field becomes a serious issue.

Single stopping particles fromGEANT simulations are used tocalibrate the method.


Comparison of dE/dx for low momentum pions (red) PR01 data (black) HIJING events


Particle Measurements at Very Low pT

Summary of data reconstruction

Au+Au sNN=200 GeV (RHIC Run II)

Centrality: 15% most central events

Vertex: -7cm < Zvtx < 15cm

Event statistics: 2,070,000

Total reconstructed tracks: ( + ) 14,000 (K+ K) 1,900 (p+p) 1,000

+ + –

Dominant background: Feed-down, ghost, mis-identified K& p

pT-dependent corrections from

0.69 to 0.78

Use HIJING simulations with yields tuned to our measurements


Published Result Au+Au 200 GeV 0-15%PHENIX - open symbolsPHOBOS –closed symbols

Solid curves: Fits to PHENIX onlyDashed curves: Extrapolations

Log scale!

PRC 70051901 (R)

Used PHENIXbecause 0-15% data published


Published Result (Blown Up)

Au+Au 15% central

Extrapolation of fit to PHENIX data

for pT>0.25 GeV/c

PRC 70051901 (R)


Comparison to Cramer et al.

PRL curve, data fit problem

Star data, fixed fit

Fit to modified data

Phobos 0-15% data

Estimated yield 0-5%

Data is ( Au+Au 0-15% central

Cramer, et al.PRL 94, 102302& private comm.

nucl-ex0506008 {}


Procedure to Estimate 0-5% Yield

PHENIX pion data for pT=250-450 MeV/c

STAR pion data for pT=126-214 MeV/c (estimate 15%

numbers using 5-10, 10-20% data)

PHOBOS charged hadron data for pT=250-450 MeV/c

PHOBOS summed charged hadron data

These ratios range from 16.2 to 20.1%

Our extrapolation band spans 15-20%

Of course, the final answer is to have the data…


Near-Term Future

d+Au 200 GEV

— Study system size dependence

Au+Au 62.4 & 200 GEV

— Study energy & centrality dependence

✔ Important to determine where any interesting

properties “turn off”


Far-Term FutureAu+Au 200 GEV – high statistics data from RHIC Run 4

— Study low pT yields vs many event parameters

Could identify negatives using excess energy in last

plane

— Attempt to get BE correlation function at very low mT

Momentum and angular resolutions are encouraging

R0

(fm

)

KT (MeV/c)

Cramer, et al.

PRL


Far-Term FutureAu+Au 200 GEV – high statistics data from RHIC Run 4

R0

(fm

)

KT (MeV/c)

We will try, but the reality is that this data set is unlikely to yield usable pair statistics using very low pT stopping

particles.

There are several other options to explore to see how low in KT Phobos can reach.


Conclusions

i low pT data can play an important role in evaluating model(s) of the exotic systems formed at RHIC

More data for yields will be available soon

Looking forward to detailed comparison to theory(ies)

Very low KT HBT would likely require a dedicated experiment

Femtoscopy BNL Workshop 6/21/2005George Stephans Very Low p T in x Past, Present, and Prospects.

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