# Presentation: 456957

## A Year At RHIC First Data, New Phenomena

**W.A. Zajc****Columbia University**

- W.A. Zajc

- 29-Nov-01

## Conclusions

**RHIC is a hadron collider of unprecedented versatility.**
**The four RHIC experiments have a broad coverage ideally suited to exploit RHIC’s potential.**
**RHIC and its experiments provide a superb environment for the study of QCD as a fundamental theory:**
**Phase transition(s) associated with**
**Confinement**
**Chiral symmetry breaking**
**Origin of proton spin**
**Initial results from RHIC show superb agreement between the experiments  *****and*****  indications of new phenomena**

- W.A. Zajc

- 29-Nov-01

## Standard Model 

## Relevant Parts of SM

**Players:**
**Quarks (u, d, s, eventually c, b) with any of three color charges (r,g,b)**
** ****with gauge couplings that generate interactions via exchange of**
**Gluons with 8 varieties of color charge**

- W.A. Zajc

- 29-Nov-01

## QCD is not QED

**QED (Abelian):**
**Photons have do not carry charge**
**Flux is not confined ******** 1/r potential   ******** 1/r****2**** force**
**QCD (Non-Abelian):**
**Gluons carry charge (red, green, blue)********(anti-red, anti-green, anti-blue)**
**Flux tubes form         ******** potential ~ r   ******** constant force**

**+**

**+...**

- W.A. Zajc

- 29-Nov-01

## Making Something from Nothing

**Experimental method:**
**Energetic collisions of heavy nuclei**
**Experimental measurements:****Use probes that are**
**Auto-generated**
**Sensitive to all time/length scales**

**Explore non-perturbative “vacuum”  ****that confines color flux by **_***melting it***_

**Particle production**
**Our ‘perturbative’ region ****is filled with**** **
**gluons**
**quark-antiquark pairs**
**A Quark-Gluon Plasma (QGP)**

- W.A. Zajc

- 29-Nov-01

## Why is RHIC?

**Why is RHIC?**

**We have a theory of the strong interaction:**

**Where does the proton get its spin?**

**How does nuclear matter “melt”?**

**To understand fundamental features of the strong interaction:**

**(This works well except when the interaction is strong...)**

- W.A. Zajc

- 29-Nov-01

## Experimental Gauge Theory

**QCD is the only fundamental gauge *****theory *****amenable to  *****experimental*****  study in both**
**Weak and strong coupling limits**
**Particle and bulk limits**
**RHIC**
**(Large g, bulk       )  limit ******** heavy ion collisions**
**(Large g, particle)  limit ******** spin physics**
**(Small  g, particle)  limit ******** W’s as helicity probes**
**(Small  g, bulk       )  limit ******** high p****T**** probes of plasma state **

## NOT

**Here’s what RHIC (heavy ion) experiments are **_***not ***_**:**
**Scattering**
**Rutherford, Hofstader, Kendall/Friedman/Taylor**
**(New)***** Particle*****  Production**
**Positron, anti-proton, ... Omega ... Top ... Higgs**

- W.A. Zajc

- 29-Nov-01

## Phase Diagrams

**Phase Diagrams**

**Water**

**Nuclear Matter**

- W.A. Zajc

- 29-Nov-01

## Relevant Nuclear Physics

**Normal nuclei have   ~ constant density:**
******0**** ~ 0.16 GeV / fm****3**
**M****PROTON**** ~ M****NEUTRON**** ~ 1 GeV**
**R(A) = 0.92 A****1/3 ****(rms)**** , ****where A = Atomic**** ****Number**

- W.A. Zajc

- 29-Nov-01

## Relevant Thermal Physics

**Need better control of dimensional analysis:**

**Relevant Thermal Physics**

**Q. How to liberate quarks and gluons from**** ~1 fm confinement scale?**
**A. Create an energy density  **

- W.A. Zajc

- 29-Nov-01

## Slightly More Refined Estimate

**Slightly More Refined Estimate**

***Compare***

****** ****Phase transition at T ~ 140 MeV****      with latent heat ~0.8 GeV / fm****3**** **

***Select*****  system with higher pressure:**

**Compare to best estimates ****(Karsch, QM01)**** ****from lattice calculations:****T ~ 150-170 MeV****  latent heat ~ 0.7********0.3 GeV / fm****3**** **

- W.A. Zajc

- 29-Nov-01

## Aside 1

**Aside 1**

**Previous approach ****(using a “pure” pion gas) ****works because**** QCD is a theory ****with a mass gap**

- {

**This gap is a ****manifestation of ****the approximate ****SU(2)****R**** x SU(2)****L**** ****chiral symmetry of QCD ****with pions as the ****Nambu-Goldstone bosons**** **** **

- W.A. Zajc

- 29-Nov-01

## Aside 2

**The frightening density of hadronic levels led to concepts of **
**A “limiting temperature” T****H**** (Hagedorn, 1965)**
**A phase transition(?) in hadronic matter**
** *****before *****quarks were understood as underlying constituents**

- W.A. Zajc

- 29-Nov-01

## Aside 3

**Aside 3**

**What lattice QCD does superbly (uniquely?):**
**Study potential V(r) = ****-********/r + ******** r****as a function of temperature T**

- F. Karsch, hep-ph/0103314

- 29-Nov-01

## Previous Attempts

** ****First attempt at QGP formation **_***was***_** successful**
**                                            ****(~10****10**** years ago)**

**  ****( Effective number of degrees-of-freedom per relativistic particle )****                                                     ****                                                   **

- W.A. Zajc

- 29-Nov-01

## RHIC Specifications

**RHIC Specifications**

**3.83 km circumference**
**Two independent rings**
**120 bunches/ring**
**106 ns crossing time**
**Capable of colliding ****~any nuclear species ****on ****~any other species**
**Energy:**
**500 GeV for p-p**
**200 GeV for Au-Au****(per N-N collision)**
**Luminosity**
**Au-Au: 2 x 10****26**** cm****-2**** s****-1**
**   ****p-p  : 2 x 10****32**** cm****-2**** s****-1**** ****(**_***polarized***_**) **

**1**

**3**

**4**

**1’**

**2**

**6**

**5**

- W.A. Zajc

- 29-Nov-01

## How is RHIC Different?

**It’s a **_**collider**_
**Detector systematics independent of E****CM**
**(No thick targets!)**
**It’s **_**dedicated**_
**Heavy ions will run 20-30 weeks/year**
**It’s **_**high energy**_
**Access to perturbative phenomena**
**Jets**
**Non-linear dE/dx**
**Its detectors are **_**comprehensive**_
**~All final state species measured with a suite of detectors that nonetheless have significant overlap for comparisons**

- W.A. Zajc

- 29-Nov-01

## Fixing Initial Conditions

**Fixing Initial Conditions**

**Event characterization**
**Impact parameter b ****is *****well-defined***** in heavy ion collisions**
**Event multiplicity predominantly determined ****by *****collision geometry***
**Characterize this by global measures ****of ****multiplicity**** and/or ****transverse energy**** ****correlated with**
**            ****ZDC  ******** Zero Degree Calorimeter**
**Goals:**
**Uniform luminosity monitoring at all 4 intersections**
**Uniform event characterization by all 4 experiments**
**Process:**
**Correlated Forward-Backward Dissociation**
** ********tot**** = 11.0 Barns (+/- few %)**

- W.A. Zajc

- 29-Nov-01

## Run-1 Results

**All four experiments worked**
**All four experiments produced ****quality data within a few months ****of initial RHIC operation**
**Particle yields**
**Rapidity and p****T**** spectra**
**Flow**
**Source sizes**
**(Etc.)**
**This from a data set equivalent to ****1-3 days running of RHIC at design luminosity**

**RHIC worked ****(i.e, achieved its Year-1 goals):**
**Stable operation at 130 GeV**
**Delivery of 10% of design luminosity**

- W.A. Zajc

- 29-Nov-01

## RHIC’s Experiments

- W.A. Zajc

- 29-Nov-01

## Outline

**Outline**

**    ****Will present  *****sample ***** of results from various points of the collision process:**

- W.A. Zajc

- 29-Nov-01

## Kinematics 101

**Kinematics 101**

**Fundamental single-particle observable:**
**Momentum Spectrum**

- W.A. Zajc

- 29-Nov-01

## (PID) Acceptances

**(PID) Acceptances**

**STAR Acceptance**

**PHOBOS Acceptance**

- W.A. Zajc

- 29-Nov-01

## STAR Event

**Data Taken June 25, 2000.**
**Pictures from Level 3 online display**.

- W.A. Zajc

- 29-Nov-01

## STAR 

- W.A. Zajc

- 29-Nov-01

## Results on Particle Composition

**Results on Particle Composition**

**    ****Anti-particle/particle  ****ratios  from ****PHOBOS and BRAHMS**

**mid-rapidity**

**     ****Anti-particle, particle  ****spectra from ****PHENIX and STAR**

- W.A. Zajc

- 29-Nov-01

## Agreement between Experiments

**Overlaps in detector capabilities a feature of RHIC program**

**Excellent agreement in common observables provides confidence**

- W.A. Zajc

- 29-Nov-01

## BRAHMS

**An experiment with an emphasis:**
**Quality PID spectra over a broad range of rapidity and p****T **
**Special emphasis:**
**Where do the baryons go?**
**How is directed energy transferred to the reaction products?**
**Two magnetic dipole spectrometers in “classic” fixed-target configuration**

- W.A. Zajc

- 29-Nov-01

## Where do the Baryons Go?

**There is a ****(not-quite-perfect) correspondence between longitudinal momentum (rapidity) and the angle of emission in the ****center-of-mass**

- W.A. Zajc

- 29-Nov-01

## BRAHMS Results

**Anti-proton to proton yields as a function of rapidity:**

**                  ****(Two points are reflected about y=0)**
**Clear evidence for development of (nearly) baryon-free central region**

- W.A. Zajc

- 29-Nov-01

## Approaching the Early Universe

**Early Universe:**
**Anti-proton/proton = 0.999999999**

- E866
- Au+Au

- NA44
- Pb+Pb

-  pbar/p

- We’ve created “pure” matterapproaching this value

- For the first timein heavy ion collisions, more baryons are pair-produced than brought in from initial state

- W.A. Zajc

- 29-Nov-01

## Simple Chemistry

**Simple Chemistry**

**Assume **
**chemical description appropriate ******** (********,T)**
**Boltzmann approximation valid      ******** n(********,T) ~ e ********/ T**** **
**Feed down negligible                        ******** use “raw” ratios**
**Then **

- W.A. Zajc

- 29-Nov-01

## Locating RHIC on Phase Diagram

**Baryon ratios determine  ********/ T**
**K/******** ratio, momentum spectra determine T**
**T****CH**** = 190 ****± 20 ****MeV, ********B**** = 45 ****± 15 ****MeV ****(M. Kaneta and N. Xu, nucl-ex/0104021)**

- W.A. Zajc

- 29-Nov-01

## Dynamics 101

**Dynamics 101**

**Q. How to estimate initial energy density?**
**A. From rapidity density**
**“*****Highly relativistic nucleus-nucleus collisions: ******The central rapidity region*****”, J.D. Bjorken,**** Phys. Rev. **_**D27**_**, 140 (1983).**
**Assumes**
**~ 1-d hydrodynamic expansion**
**Invariance in y along “central rapidity plateau”****(I.e., flat rapidity distribution)**
**Then**
**    **
**    ****since boost-invariance of matter ********                     where ******** ~ 1 fm/c**

- W.A. Zajc

- 29-Nov-01

## Determining Energy Density

- For the most central events:

**PHENIX**

- EMCAL

- R2

**Determining Energy *****Density***

- Bjorken~ 4.6 GeV/fm3

-      ~30 times normal nuclear density     ~_1.5 to 2 times higher_ than         any previous experiments

- Bjorken formula for thermalized energy density

- time to thermalize the system (0 ~  1 fm/c)

- ~6.5 fm

**What is the energy density achieved?**
**How does it compare to the ****expected phase transition value ?**

- W.A. Zajc

- 29-Nov-01

## (Bose-Einstein) Condensates(?!?)

**Note that Bose condensation **
**Does *****not*****  require low temperature**
***Does***** require high phase space densities**

**Any realistic estimate of RHIC densities **
**Significantly (x10-100) in excess of these values**
**Quantum, condensate effects *****may*****  be important**
***But -- *****effects in highly dynamic, interacting system ****            difficult to quantify**

- W.A. Zajc

- 29-Nov-01

## Centrality Dependence of Elliptic Flow

**  ****( as per a hydrodynamic description)**

**Centrality Dependence of Elliptic Flow**

**    ****Parameterize azimuthal asymmetry of charged particles**** ****as**** **
**                                         ****1 + 2 ****v****2**** ****cos (2 ********)**

- W.A. Zajc

- 29-Nov-01

## PHOBOS

**An experiment with a philosophy:**
**Global phenomena **
**large spatial sizes **
**small momenta**
**Minimize the number of technologies:**
**All Si-strip tracking**
**Si multiplicity detection**
**PMT-based TOF**
**Unbiased global look at very large number of collisions (~10****9****)**

- W.A. Zajc

- 29-Nov-01

## PHOBOS Result on dNch/d

**PHOBOS Result on dN****ch****/d******

**Q. How many charged particles per nucleon-nucleon collision?**
**A: Express using**
**dN****ch****/d******** ~ “generic” dN****ch****/dy**
**N****part**
****** ****Number of participating nucleons**
**= 2 for p-p collision**
**~2A for central A-A collision**
**Plot multiplicity *****per N-N collision*****       ( dN****ch****/d******** )       /   ( N****part****/2  )**

**Does not (quite) ****distinguish between **
**“****Saturation” models, ****dominated by gg ********g**
**“****Cascade” models, ****dominated by ****gg ********gg, gg ********ggq**
**( X.N. Wang and M. Gyulassy, nucl-th/0008014 )**

- W.A. Zajc

- 29-Nov-01

## PHENIX 

- W.A. Zajc

- 29-Nov-01

## Excellent consistency between two analyses
Yields grow significantly faster than Nparticipants
Evidence for term ~ Ncollisions
Qualitatively consistent with HIJING
Inconsistent with some saturation models

**Excellent consistency between two analyses**
**Yields grow significantly faster than Nparticipants**
**Evidence for term ~ Ncollisions**
**Qualitatively consistent with HIJING**
**Inconsistent with some saturation models**

**PHENIX Results**

**      ****Evidence for highest energy densities yet achieved ****(~ 5 GeV/fm****3****)**

- W.A. Zajc

- 29-Nov-01

## Physics, Consistency between Experiments

**Trend **
**incompatible with final-state gluon ****saturation model**
**Good agreement with model ****based on *****initial-state***** saturation ****(Kharzeev and Nardi, nucl-th/0012025)**

**Excellent agreement between (non-trivial) PHENIX and PHOBOS analyses of this systematic variation with nuclear overlap.**

- W.A. Zajc

- 29-Nov-01

## Gluon saturation at RHIC

**Saturation condition  ******** ~ 1   ****Q****S****2**** ~ ********S**** A xG(x,Q****2****) ****/**** ********R****2**** ~ A****1/3**

**Gluon saturation at RHIC**

**When do the gluons overlap significantly?**

-  D. Kharzeev, nucl-th/0107033

**So for     ******** /mx  ~ 2R , ****~***** all***** constituents contribute****Parton density  ******** ~ A xG(x,Q****2****) ****/**** ********R****2**

**Parton cross section ****   ******** ~  ********S**** ******** ****2**** ****/**** Q****2**** **

- W.A. Zajc

- 29-Nov-01

## Initial State Partons?

**Procedure:**
**Determine scale Q****S****2**** as function of nuclear overlap**
**Q****S****2**** ~ A****1/3**** ~ N****part****1/3**
**Assume final-state multiplicities proportional to number of initial-state gluons in this saturated regime:**
**dN/d******** = c N****part**** xG(x, Q****S****2****)**
**Note that DGLAP requires evolution of xG(x, Q****S****2****) :**
**  ****xG(x, Q****S****2****) ~ ln (Q****S****2**** / ********QCD****2****)**
**Results:**
**“****Running” of the multiplicity yield****directly from  from xG(x, Q****2****)  +DGLAP**

- W.A. Zajc

- 29-Nov-01

## Extensions of Saturation Approach*

**Extensions of Saturation Approach*******

**Use HERA data, counting rules**
** ****x G(x,Q****2****) ~ x****-********(1-x)****4**
***Describe*****  rapidity dependence:**
**y ~ ln(1/x) **** ******** Q****S****2****(s,y) = Q****S****2****(s,y=0)e********y**

***Predict*****  energy dependence: **
**x = Q****S**** / ********s **** ******** Q****S****2****(s,y) = Q****S****2****(s****0****,y) (s/s****0****) ********/2 **
**Predict****10-14%****  increase between**** ********s = 130 and 200 GeV**
**Versus ****14********6%****  reported by ****PHOBOS**

** ********* D. Kharzeev and E. Levin, nucl-th/0108006**

- W.A. Zajc

- 29-Nov-01

## Energy Loss of Fast Partons

**Many approaches**
**1983: Bjorken  **
**1991: Thoma and Gyulassy (1991)**
**1993: Brodsky and Hoyer (1993)**
**1997: BDMPS- depends on path length(!)**
**1998: BDMS**
**Numerical values range from **
**        ****~ 0.1 GeV / fm (Bjorken, elastic scattering of partons)**
**~several GeV / fm (BDMPS, non-linear interactions of  gluons)**

- W.A. Zajc

- 29-Nov-01

## Rare processes at RHIC

**Both PHENIX and STAR have measured charged particle spectra out to “small” cross sections**

- W.A. Zajc

- 29-Nov-01

## Expectations

**Particle production via *****rare processes*****  should scale with ****N****coll****, the number of underlying binary nucleon-nucleon collisions**

**Assuming no “collective” effects**
**Test this on production at high transverse momentum**

- W.A. Zajc

- 29-Nov-01

## A*B scaling at RHIC?

**A*B scaling at RHIC?**

**NO!**
**Both STAR and PHENIX data see deficit of particles at high transverse momenta,*****relative to expected A*B scaling:***

**     ****Deficit ****opposite sign**** of ****enhancements**** previously seen in nuclear collisions ****(Cronin effect)**

- W.A. Zajc

- 29-Nov-01

## Additional Evidence

**Additional Evidence**

**PHENIX sees an equal or  larger  effect ****in the ********0**** spectrum**

**Consistent with crude estimates****of additional energy loss in a*****deconfined medium***

- W.A. Zajc

- 29-Nov-01

## Discovery of “Jet Quenching”?

**Some would (have) claimed just that**

**To be done ****before this can ****be experimentally ****established:**
**Improve p****T**** ****range (Run-2)**
**Measure p-p ****spectrum (Run-2)**
***Study in “cold nuclear matter” with p-A collisions***** (Run-2?)**
**Vary system size (Run-2??)**

- W.A. Zajc

- 29-Nov-01

## Summary of Results

**How many particles are produced?**
**More than ever produced previously**
**Have we made contact with the ****early universe?**
**Closer than all previous heavy ion experiments**
**Have we made sufficiently high energy densities for the phase transition?**
**Yes**
**Is there evidence that the dense matter behaves collectively?**
**Yes**
**Are there results consistent with the formation of a new state of matter?**
**Perhaps ??????!?**

****
****
********
****
****
**(1 ******** = 1 experiment )**

- W.A. Zajc

- 29-Nov-01

## What’s left?

***The all-important spin program***

- W.A. Zajc

- 29-Nov-01

## A polarized hadron collider is uniquely suited to some spin measurements:
G via
Direct photons
High pT pions
J/ production
                via
W+/W- production
Polarized Drell-Yan
RHIC has been equipped 
To provide polarized beams of protons
To make spin measurementsof same in (at least)PHENIX and STAR

**A polarized hadron collider is uniquely suited to some spin measurements:**
******G via**
**Direct photons**
**High p****T**** pions**
**J/******** production**
**                ****via**
**W****+****/W****-**** production**
**Polarized Drell-Yan**
**RHIC has been equipped **
**To provide polarized ****beams of protons**
**To make spin measurements****of same in (at least)****PHENIX and STAR**

**RHIC Spin Physics**

- W.A. Zajc

- 29-Nov-01

## What’s Left?

**Most of the program:**
**Energy scans**
**Species scans**
**All the systematic studies required before laying claim to new physics**
**Vital spin program**
***Example***** (A-A) program to do this:**
**Run-2: **
**Au+Au, crude p-p comparison run**
**First look at J/******** production, high p****T**
**d-Au run?**
**Run-3: **
**High luminosity Au+Au       (60%) of HI time**
**High luminosity light ions  (40%) of HI time**
**Detailed examination of A*B scaling of J/******** yield**
**Run-4: **
**p-d/p-p comparisons**
**Baseline data for rare processes**
**Run-5:**
**“****Complete” p-A program with p-Au**
**Energy scans**
**Systematic mapping of parameter space**

- W.A. Zajc

- 29-Nov-01

## Run-2 Goals

**Au-Au running**
**Achieve design values for**
**Energy (200 GeV)**
**Luminosity (2 x 10****26**** cm****-2**** s****-1****)**
**Interaction region (20 cm)**
**~ 12 week physics run **
**~ 100 x existing data sets from Run-1**
**p-p running**
**Commission **
**proton collisions at 200 GeV****(5 x 10****30**** cm****-2**** s****-1****)**
**Polarization for same ( ******** 50%)**
**~ 5 weeks physics run**
**(Additional ‘heavy ion’ running to be determined) **

- W.A. Zajc

- 29-Nov-01

## Run-2 (A-A) Results

**Significantly enhanced detectors**
**                                 ******
**Much greater integrated luminosity**
**Greatly extended reach in observables**
**p****T**** to 20 GeV/c                 (currently 5 GeV/c)**
***Spectra***** of ********’s  and ********’s  (currently mass peaks only)**

**J/********                                       (no current data)**
**Extended understanding of RHIC physics**
**Access truly perturbative regime**
**Understand detailed hadro-chemistry**
**Understand (Debye?) screening in hot system**

- W.A. Zajc

- 29-Nov-01

## Control (1)

**Q. How to establish the observed suppression at high p****T**** as a ****plasma effect?**
**Answers:**
**Study it out to highest possible transverse momenta**
**Study it as a function of flavor and/or color charge of probe**
***Control  *****initial state geometry**
***Control ***** initial state parton kinematics  ********  photon-tagged jets**

**RHIC:  one 15 GeV photon / hour**
**(Central Au-Au into ********y = 1)**

- W.A. Zajc

- 29-Nov-01

## Screening by the QGP

**                           ****In pictures:**

- W.A. Zajc

- 29-Nov-01

## Screening by the QGP

**Screening by the QGP**

**In first-order finger physics:**
**Follow usual derivation of Debye screening**
**Now put in QGP scales and assumptions:**
**Hadrons with radii greater than ****~ ********D**** will be dissolved**
**Study “onium” bound states**

- W.A. Zajc

- 29-Nov-01

## Control (2)

**Control (2)**

**A plasma should exhibit a thermal (Debye) screening length ******** ~ 1 /gT**
**Q. How to establish that the (to be observed) charmonium suppression pattern results from this mechanism?**
**Answers: **
**Study vs. p****T**
**Study vs. centrality**
**Study in lighter systems**
**Study vs. a *****control *****(a vector meson that should not be suppressed, the Upsilon)**

- W.A. Zajc

- 29-Nov-01

## Vector Meson Rates

**10 weeks of Au-Au running at design luminosity:**
**30K J/******** ‘s **
**Enough for rough **
**centrality dependence**
**p****T**** spectra**
**But modest ****with respect to 500K**** J/******** ‘s  in CERN Pb-Pb****data set**
**x 4 luminosity growth ****produces ‘CERN-like’ ****production rate**

**Upsilon rate ~ 10****-3**** J/******

**Major luminosity upgrade required to access this ****important physics**

- W.A. Zajc

- 29-Nov-01

## Summary

**Many  *****quantitative*****, *****verified***** ****results from RHIC Run-1**
**Striking agreement between the experiments******** many systematic effects are under control****    already in a very early stage of the program**
**Much more to come from Run-2 and beyond **
**Heavy ion physics**
**Spin physics**
**Proton-nucleus physics**

- W.A. Zajc

- 29-Nov-01

## RHIC Luminosity

**It’s high!**
**It’s an equal opportunity parton collider:**
**Can accelerate essentially ****all species**
**Designed for p-p to Au-Au**
**Asymmetric collisions ****(esp. p-A) allowed**
**Good news / bad news:**
**Permits many handles ****on systematics**
**Permits *****in situ***** ****measurements of ****“background” p-p and p-A physics**
***Detectors must handle unparalleled dynamic range in rates and ******track densities***

- W.A. Zajc

- 29-Nov-01

## An Interesting Technical Connection

**RHIC experiments are coping with data volumes at the leading edge of current HEP experience:**
**Run-1**
**~1 Tb per day (recording rate per experiment)**
**Data volumes ~ 10 Tb (per experiment, from last year)**
**Run-2 and beyond**
**Roughly same recording rate (up to x2 higher?)**
**Greatly increased volumes (multi-100 Tb)**
**RHIC Computing Facility is a real-world existence proof for data analysis on this scale:**
**HPSS capacity of ~1.5 petabytes**
**HPSS optimized file mover**
**Port of Objectivity to Linux**
**“****Grand Challenge” query processor**
**ROOT**
**Key members of development team ****(Brun, Rademakers, Buncic, Fine) ****have been supported by NP funds**
**NP supported contributions to ROOT**
**Multithreading**
**Port to SOLARIS**
**Objectivity encapsulation**
**StEvent**

- W.A. Zajc

- 29-Nov-01

## RHIC Computing Facility

|  | Last Year | Today | Near Future |
| --- | --- | --- | --- |
| HPSS robot | 1, 300 TB,
3 movers | 4, 1.2 PB,
6 movers | 6, 1.8 PB,
6 movers |
| Linux farms | 203 mach.
6,900 SI95 | 344 mach.
16,900 SI95 | 633 mach.
41,300 SI95 |
| RAID Disk | 14 TB | 36 TB | 61 TB |
| SUN Serv. | 3 rmineXX | 11 rmineX | 11 rmineX |

- W.A. Zajc

- 29-Nov-01

## “Old” Physics

**Example: Detection of low mass di-lepton pairs as probes of**
**Thermal radiation: ********* ******** e****+****e****-**
**Chiral restoration: ************ e****+****e****-**
**Deferred in initial design of RHIC experiments**
**Unknown backgrounds from mundane sources**
**(Conversion and Dalitz pairs)**
**Uncertain technical capabilities for ****“hadron blind” detectors**
**Now feasible ****(and remains compelling)**

- W.A. Zajc

- 29-Nov-01

## Physics Upgrades

**Significant portions of RHIC physics are luminosity limited**
**New physics opportunities have appeared since initial design of RHIC experiments**
**Initial survey of RHIC terrain now provides crucial information for pursuit of ****background-limited signals**
**New technologies have emerged since initial design of RHIC experiments**

- W.A. Zajc

- 29-Nov-01

## “New” Physics (1)

**Increased understanding of open charm significance**
**Saturation of  u,d,s  abundances important in establishing thermal properties of system**
**Chemical equilibrium  ******** no further information on *****dynamics***
**Charm (probably) does not chemically equilibrate**
**Important probe of early dynamics**
**Important complement to charmonium measurements**

**Major interest in pursuit of “open charm” as a plasma diagnostic**
**Currently only very modest capabilities via measurement of ****high p****T**** leptons**

**Important to extend with *****direct *****detection via displaced vertices**

- W.A. Zajc

- 29-Nov-01

## “New” Physics (2)

**Increased appreciation for role of proton-nucleus studies in calibrating plasma signals**
***Example:***** Strangeness enhancement in p-A, studied versus “centrality”**

****** ****FNAL E866**

******  ****MMS+MMN**

****** ****MMS**

****** ****Central**

**PHENIX**

**Increased appreciation for versatility of RHIC as hadron dynamics laboratory**
***Example:***** Study of Drell-Yan production in p-d vs. p-p ****(15 weeks each)**

- W.A. Zajc

- 29-Nov-01

## RHIC Spin Potential

**Wide range of measurements in ****many channels to address**
******G**
**Sea quark polarization**

- W.A. Zajc

- 29-Nov-01