Essential Measurements to be made at RHIC using the

PHOBOS Detector

Mark D. BakerBrookhaven National Laboratory

for the PHOBOS Experiment

BNL 08-SEP-2004Physics Advisory Committee Meeting

Mark D. Baker

Collaboration (Oct. 2004)

Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail

Bickley,

Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick

Decowski,

Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Clive Halliwell,

Joshua Hamblen, Adam Harrington, Michael Hauer, Conor Henderson, David Hofman,

Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane, Nazim

Khan,

Piotr Kulinich, Chia Ming Kuo, Willis Lin, Steven Manly, Alice Mignerey,

Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park,

Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Helen

Seals,

Iouri Sedykh, Wojtek Skulski, Chadd Smith, Maciej Stankiewicz, 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 Woźniak, Alan Wuosmaa, 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

Mark D. Baker

The PHOBOS Detector (2004)

Spectrometer

Paddle Trigger Counter

NIM A 499 (2003) 603

Octagon

TOF

SpecTrig

T0 counter

• 4- Multiplicity Detector– Comprehensive centrality measures

• Magnetic Spectrometer + ToF – Extends to very low pT– Good rejection of weak decays

Mark D. Baker

    

Phys. Rev. Lett. 85 , 3100 (2000)Phys. Rev. Lett. 87, 102301 (2001)Phys. Rev. Lett. 87, 102303 (2001)Phys. Rev. C 65 , 31901R (2002)Phys. Rev. Lett. 88 , 22302 (2002)Phys. Rev. C 65 , 061901R (2002)Phys. Rev. Lett. 89 , 222301 (2002)Phys. Rev. C 67, 021901R (2003)Phys. Rev. Lett. 91, 052303 (2003)nucl-ex/0301017, subm. to PRLnucl-ex/0302015, subm. to PLBPhys. Rev. Lett. 91, 072302 (2003)nucl-ex/0309013, subm. to PRC-RC

& Comparable # in the pipeline!

Physics Publications (Sept. 2003)

Mark D. Baker

Phys. Rev. Lett. 85 , 3100 (2000)Phys. Rev. Lett. 87, 102301 (2001) Phys. Rev. Lett. 87, 102303 (2001)Phys. Rev. C 65 , 31901R (2002)Phys. Rev. Lett. 88 , 22302 (2002) Phys. Rev. C 65 , 061901R (2002) Phys. Rev. Lett. 89 , 222301 (2002) Phys. Rev. C 67, 021901R (2003) Phys. Rev. Lett. 91, 052303 (2003)nucl-ex/0301017, subm. to PRLPhys. Lett. B 578, 072302 (2003)Phys. Rev. Lett. 91, 072302 (2003)Phys. Rev. C 70, 011901R (2004)Phys. Rev. Lett. 93, 082301 (2004) dN/d for dAunucl-ex/0401006, subm. to PRL PID at very low pT

nucl-ex/0405003, subm. to PRL Energy dependence of R(AA) Phys. Rev. C 70, 021902R (2004) Geometric dN/d scalingnucl-ex/0406017, subm. to PRC-RC R(dAu) vs. nucl-ex/0406021, subm. to PRL v2 vs. ’ at 4 energies

nucl-ex/0407012, subm. to PRC-RC v2 vs. , centrality, pT

nucl-ex/0409001, subm. to PRC-RC HBT vs pT, y at 62.4, 200

nucl-ex/0409003, subm. to PRC-RC pbar/p for pp

>700 citations total

~20 more in pipeline!

Physics Publications (Sept. 2004)

Mark D. Baker

Phys. Rev. Lett. 85 , 3100 (2000)Phys. Rev. Lett. 87, 102301 (2001) Phys. Rev. Lett. 87, 102303 (2001)Phys. Rev. C 65 , 31901R (2002)Phys. Rev. Lett. 88 , 22302 (2002) Phys. Rev. C 65 , 061901R (2002) Phys. Rev. Lett. 89 , 222301 (2002) Phys. Rev. C 67, 021901R (2003) Phys. Rev. Lett. 91, 052303 (2003)nucl-ex/0301017, subm. to PRLPhys. Lett. B 578, 072302 (2003)Phys. Rev. Lett. 91, 072302 (2003)Phys. Rev. C 70, 011901R (2004)Phys. Rev. Lett. 93, 082301 (2004) dN/d for dAunucl-ex/0401006, subm. to PRL PID at very low pT

nucl-ex/0405003, subm. to PRL Energy dependence of R(AA) Phys. Rev. C 70, 021902R (2004) Geometric dN/d scalingnucl-ex/0406017, subm. to PRC-RC R(dAu) vs. nucl-ex/0406021, subm. to PRL v2 vs. ’ at 4 energies

nucl-ex/0407012, subm. to PRC-RC v2 vs. , centrality, pT

nucl-ex/0409001, subm. to PRC-RC HBT vs pT, y at 62.4, 200

nucl-ex/0409003, subm. to PRC-RC pbar/p for pp

>700 citations total

~20 more in pipeline!

Physics Publications (Sept. 2004)

(1st Run IV paper)

(2nd Run IV paper)

(3rd Run IV paper)

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AuAu energies:19.6, 55.9, 62.4130., 200.

Mark D. Baker

Results from dAu - an updatePRL 91 (2003) 072302-5

dN/d data from nucl-ex/0403033

J.Phys.G30 (2004) S1133

RdA(pT)?

Mark D. Baker

Results from dAu - an update

dN/d data from nucl-ex/0403033

J.Phys.G30 (2004) S1133

RdA(pT)!

nucl-ex/0406017

Mark D. Baker

The program: vary energy and geometry

Varying the geometry (A,b):

Npart

eccentricity

• Initial state: NN, Ncoll/Npart, Qs(?) • System: , B, Nch • Partonic: xT, dE/dx

Varying the beam energy changes:

• jet quenching•vary overall path length•vary asymmetry

• Elliptic (and directed) flow • Study A dependence at fixed eccentricity.

Mark D. Baker

Surprise from 19.6 & 62.4 GeV AuAu: nucl-ex/0406021

Longitudinal scaling of elliptic flow

’=||-ybeam

v2

Mark D. Baker

Surprise from 19.6 GeV AuAu: PRC 70 (2004) 021902R

Where are the minijets?

NNpartNNpartmid sfNfsNR 21,

Energy & Centrality Dependences Factorize

Mark D. Baker

RAA ratios at 200 and 62.4 GeV (AuAu)

PHOBOS 62.4 GeV200 GeV

• Large variation of RAA with centrality

– <Npart> from 61 to 335

– <Ncoll> from 76 to 820

– 0 < b < 10.5 fmPLB (2004) 578297

arXiv:nucl-ex/0405003

Mark D. Baker

PHOBOS 62.4 GeV200 GeV

arXiv:nucl-ex/0405003

RAA ratios at 200 and 62.4 GeV (AuAu)

Mark D. Baker

PHOBOS 62.4 GeV200 GeV

TNNTpartNPC

NAA psfpNRR partpart ,, For b<10.5 fm:

arXiv:nucl-ex/0405003

RAA ratios at 200 and 62.4 GeV (AuAu)

Mark D. Baker

PHOBOS 62.4 GeV200 GeV

TNNTpartNPC

NAA psfpNRR partpart ,, For b<10.5 fm:

• Energy-independent

• Weak function of Npart, pT

arXiv:nucl-ex/0405003

RAA ratios at 200 and 62.4 GeV (AuAu)

Mark D. Baker

PHOBOS 62.4 GeV200 GeV

TNNTpartNPC

NAA psfpNRR partpart ,, For b<10.5 fm:

• Initial state: NN, Ncoll/Npart, Qs(?) • System: , B, Nch, • Partonic: xT, dE/dx

Varying the beam energy changes:arXiv:nucl-ex/0405003

Another surprise from energy variation

Why does the energy dependence factorize?

• We have discovered a strongly interacting medium with extremely high energy density whose description in terms of simple hadronic degrees of freedom is not appropriate.

Study the systematics of this “medium” (vary A & sNN).

• Furthermore, we have discovered that much of the data can be expressed in terms of simple scaling rules which suggest the existence of strong global constraints or some kind of universality in the mechanism of the production of hadrons in high energy collisions (possible connection to ideas of parton saturation).

Study these simple scaling rules systematically.

Will they survive further scrutiny?

What Have We Learned?& what are the essential measurements w/ ?

http://www.phobos.bnl.gov/Publications/PublicDocuments/PhobosWhitePaper.pdf (or .ps)

Mark D. Baker

Benefits of very light ions (SiSi e.g.)

• Clearly different from AuAu– study flow, “jet quenching”

• Extensive low energy comparison data exists (CC,SiSi,SiAl,SS...)– See BUP refs. 3-15 for a

partial listingNA49 (C. Hohne et al.), NPA715 (2003) 474c

Mark D. Baker

Benefits of intermediate ions (CuCu)

• Npart~100 is better determined for central CuCu than for AuAu

• Overlaps both AuAu & SiSi• Geometry different.

– study flow, “jet quenching”

nucl-ex/0301017

Mark D. Baker

Benefits of a short pp run @ 400-500 GeV

• Compare pp@400 to AA@200.– Better systematics within a single

experiment.– Better coverage than UA5– Better statistical power.

J.Phys.G30 (2004) S1133 nucl-ex/0403033

Mark D. Baker

Proposed scenario (updated)

• Boundary conditions– Run CuCu as the light ion species this year– RHIC will run 7 weeks of pp200 physics

• Phobos does not request any pp @ 200 GeV.

– 31 - 10 weeks of setup - 7 weeks pp200

• 14 weeks:– 200 GeV CuCu (10 weeks physics)– 62.4 GeV CuCu (3 weeks incl. setup)– 22.5 GeV CuCu (3 days incl. setup)– 400 GeV pp (4 days incl. setup)

Mark D. Baker

Fallback Scenario (updated)

• Constrained to 10 weeks– 27 weeks of cryo., still 7 weeks of pp200– RHIC becomes RppC

• 31 weeks, but 11 weeks for pp @ 200 GeV

• 10 weeks:– 200 GeV CuCu (7 weeks physics)– 62.4 GeV CuCu (2.5 weeks incl. setup)– 22.5 GeV CuCu (3 days incl. setup)

Mark D. Baker

Scenarios at a glance

* = including energy-change setup time

14 wks 10 wks

CuCu 200 10 7

CuCu 62.4 3* 2.5*

CuCu 22.5 0.5* 0.5*

pp 400 0.5* ---

d2Nch/ddd2N/dydpT

HBT

d2Nch/ddd2N/dydpT

HBT

d2Nch/dd

dNch/d

Mark D. Baker

Run VI + ??

• Highest priority: SiSi @ 3 energies

• Other possibilities depend on results– Longer 19.6 GeV AuAu– 200 GeV SiAu– Au-d(yellow)– ???

Mark D. Baker

Summary

• Many new interesting results from Phobos– Rate of publication growing exponentially.

• “Golden” opportunity in Run V– RHIC tuned for Cu ions – PHOBOS-specific features

• Unique coverage • Total Nch event-by-event• Unique centrality measures

– Run CuCu at 200, 62.4 and 22.5 GeV!

• Run VI– SiSi at 200, 62.4 and 24 GeV– & base further running on what we learn...