, the Early Years

4-Jan-2002G.S.F.Stephans Epiphany 2002

, the Early Years

The Ghost of PastWhat was built and why

The Ghost of PresentWhat has been accomplished

The Ghost of FutureWhat is still to come

Presented in the spirit(s) of Charles Dickens:


Collaboration (Jan 2002)

ARGONNE NATIONAL LABORATORYBirger Back, Alan Wuosmaa

BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Alan Carroll, Joel Corbo, Nigel George, Stephen Gushue, Dale Hicks, Burt Holzman, Robert Pak, Marc Rafelski, Louis Remsberg, Peter Steinberg, Andrei Sukhanov

INSTITUTE OF NUCLEAR PHYSICS, KRAKOWAndrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak

MASSACHUSETTS INSTITUTE OF TECHNOLOGYWit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Michel Rbeiz, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch

NATIONAL CENTRAL UNIVERSITY, TAIWANChia Ming Kuo, Willis Lin, Jaw-Luen Tang

UNIVERSITY OF ROCHESTERJoshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly,Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs

UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Edmundo Garcia, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer

UNIVERSITY OF MARYLANDAbigail Bickley, Richard Bindel, Alice Mignerey


Goals of ,

Measure numerous observables quickly & accurately

Perform several unique measurementsLarge multiplicity phase space coverage

Particle measurements extended to low p

Large event sample

Eliminate the word “preliminary” from relativistic heavy ion vocabulary

Good (to be)published data: Thanks to the collaboration

Wild physics speculation: Blame GSFS


Detectors used by ,

Multiplicity array (Si sensors)Almost 4 coverage and high granularity

2 Arm Spectrometer (Si sensors)2 Tesla magnetic field

PID using dE/dx

Time-of-Flight wall for extended PID

Trigger counters (Scintillator Paddles & Cherenkov T0)

ZDCs common to all RHIC experiments


Frodo (to scale)


~4 Multiplicity array

Trigger paddles Spectrometer

The 42-ton monster

All held together by excellent engineering!

Spectrometer module


Detector Performance IDetectors signals stable and well understood


Excellent signal/noise

Very few dead channels (even after RHIC assault)

Detector Performance II

Before RHIC blasts

10%

15~137,000 total Si channels


Triggering on Interactions

t (ns)

Eve

nts

Negative

Paddles

Positive Paddles

ZDC N

ZDC PAu Au

x

z

PPPN

3<||<4.5

ValidCollision


For more discussion, see later talk by

Andrzej Olszewski…

Determining Centrality of Interaction

Data

Paddle signal

Nparticipants

Data+MC

HIJING +GEANT Glauber calculation Model of paddle trigger


Multiplicity Measurements

Unrivaled phase space coverage

High granularity in and Low mass detectors situated very close to the

beam pipe

Multiple detectors and/or independent analysis methods for the same observable

MC and data combined for a very detailed understanding of systematics


-5.4 +5.4

Single-event display

Octagon&Ring hits

Vertextracklets


Energy Dependence of Central Multiplicity

||1 6% most central AA collisions

Phys Rev Lett 85, 3100 (2000) & 88, 22302 (2002)


nucl-ex/0105011Accepted: Phys Rev C

Kharzeev/Nardi

Centrality Dependence I

HIJING: PRL 86, 3496 (2001)EKRT: hep-ph/0106330KN scaling PLB 507,121 (2001)

||1 AuAu

dN

ch/d

/<

Np

art>

/2


Centrality Dependence II

To be submitted to PRLSee: Kharzeev and Levin, Phys. Lett. B523, 79 (2001)

||1 AuAu


“soft” “hard”

Two Component Parameterization

collpppart

pp NxnN

nxddN

2)1(

(mini)jet

(mini)jet

Hard ScatteringSoft Scattering

x is the fraction of particles produced by hard scatteringAt RHIC: npp~2.3, x~10%


Two Component Parameterization

4.13.1~ PairColl NN

In old language:PairColl NN

From geometry, the number of collisions:

For Symmetric systems, colliding pairs:

where is the average number of binary collisions

4.03.0 PairN

11

xnNddN

ppPair Ratio to pp is a mix

of nuclear geometry and the fraction of hard scatteringNote: Asymmetric systems (pAu,

SiAu, etc.) will have different ratiosbetween NColl and NPart

2Part

PairNN


Model Comments

Fit of AuAu centrality data to two component parameterization extrapolates very close to pp data.

Underlying physics of two-component model and saturation model are very different!

Hopefully, further study (as well as other systems including pA) will help to differentiate the two.

Note: Several different ‘saturation’ calculations agree that gluon densities are “large” on the QCD

scale.


2-Component Energy Prediction

37.0

291.0 25.0 0078.0 PairCollNN

NNsx

~20 at LHCdN/d~3500


PRL 87, 102303 (2001)

Shapes I

Distributions get narrower for more central collisions.

130 GeV AuAu Data

Full dN/d distribution yields the total number of charged particles.

For 3% most central<Nch> = 4200 470

Peripheral

Central


Shapes II

PRL 87,102303(2001)

130 GeV

Notecrossover


beamy

FragmentationFragmentation

UA5: Alner et al., Z. Phys. C33,1 (1986) PHOBOS 2000/2001

7-10% syst error

Shapes III

200 GeV shape from Phys Rev Lett 88, 22302 (2002)


Multiplicity Conclusions (so far)Whatever measure or model is used, systems

being created are dense & denser.

Extensive results on energy, centrality, andrapidity dependence

Data have significant impact on theoryInitial conditions and subsequent evolution

Global properties and fundamental interactions

Rules out or severely restricts many proposed exotic processes

Much more to come…


Charged Multiplicity Future

Soon: 20 GeV AuAu (RHIC injection energy, run in November specifically for Phobos) and

200 GeV pp (currently running)

Later: More details, fluctuations, event shape…

Next Run: More species and energies


Observation: Centrality data at both beam energies rise for the most central events (systematics? physics? mean p?) ||1

AuAu


Spectrometer

z

-x

10 cm

y

70 cm Magnetic Field


dE/dx resolution 7%

Particle ID using dE/dx

Momentum resolution

Spectrometer Characteristics

2%

10 GeV

K

p d


130 GeV Data Phys.Rev.Lett. 87, 102301 (2001)

06.004.060.0

06.007.091.0

02.001.000.1

p

p

K

K

Stat. Syst.

Spectrometer I: Chemistry

Using model of Redlich (QM ’01) T~165 implies B=45


K-/K+ vs Energy

Particle Ratios @ 130 GeV

p/p vs Energy

Phys Rev Lett 87, 102301 (2001)


Spectrometer II: Stopping ParticlesThe Ultimate in Low p

X[c

m] A

BC

D

E F

Z[cm]

Beam pipe

For tracks stopping in the 5th Si layer:

p 50 MeV/cpK 140 MeV/c pp 200 MeV/c

Note: At low p, particles are at y~0 for any angle


High signals fromnuclear fragmentation

can identify -

dE/dx from in Individual Layers

0 2

0 20


Eloss

Mp

K

P

Eloss = (ΣdEi )/nhits , i=A-E

Mi = (dE/dx)i * Ei

(~1/2) (m2)

MC Results


Spectrometer Future

Soon: Particle ratios from 200 GeV AuAu

Later: Spectra (with and without PID)

Extended PID

Low and high p

HBT

Beyond: Reaction plane, resonances (especially at low p), and much more…


Future for ,

Eagerly awaiting more beam energies and beam species (including pA) for systematic study

Continue the program discussed as well as many additional physics topics (flow…)

Far Future: Considering addition of electron identification to study charm production


• Add

• ALICE prototype TRD Electron-ID

• EM-Calorimeter

• Micro-Vertex Detector

Micro-Vertex

Transition Radiation Detector

EM-Calorimeter

Use existing spectrometer

Discussing upgrade to focus on charm production at RHIC.

Measure single electrons from displaced vertices.

One Possible Charming Future…


Conclusion

Early results have proven more robust and more interesting than (I) expected.

Detector (and analysis teams) have performed spectacularly.

Bright prospects for productive years ahead.

An even Happier 2002!

G.S.F.Stephans Epiphany 2002 4-Jan-2002

PHOBOS web-site: www.phobos.bnl.gov Physics Results

Charged particle multiplicity near mid-rapidity in central Au+Au collisions at 56 and 130 GeV Phys. Rev. Lett. 85, 3100 (2000)

Ratios of charged antiparticles-to-particles near mid-rapidity in Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102301 (2001)

Charged-particle pseudorapidity density distributions from Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102303 (2001)

Energy dependence of particle multiplicities in central Au+Au collisions Phys. Rev. Lett. 88, 22302 (2002)

Centrality Dependence of Charged Particle Multiplicity at h=0 in Au+Au Collisions at 130 GeV Accepted to Phys. Rev. C (December 2001); nucl-ex/0105011

Technical Array of Scintillator Counters for PHOBOS at RHIC

Nucl. Instr. Meth. A474, 38-45 (2001) Silicon Pad Detectors for the PHOBOS Experiment at RHIC

Nucl. Instr. Meth. A461, 143-149 (2001)

Development of a double metal, AC-coupled silicon pad detectorThe silicon detector for the PHOBOS experiment at RHICNucl. Instr. Meth. A389, 415 (1997)

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