Gary Westfall1 The Rare Isotope Accelerator Program at MSU Gary Westfall Michigan State University With contributions from Konrad Gelbke Presentation to Rare Ion Science Assessment Committee Brad Sherrill Hendrik Schatz

Gary Westfall2 From the 2002 NSAC Long Range Plan 2. The Rare Isotope Accelerator (RIA) is our highest priority for major new construction. RIA will be the world-leading facility for research in nuclear structure and nuclear astrophysics. The exciting new scientific opportunities offered by research with rare isotopes are compelling. RIA is required to exploit these opportunities and to ensure world leadership in these areas of nuclear science. RIA will require significant funding above the nuclear physics base. This is essential so that our international leadership positions at CEBAF and at RHIC be maintained.

Gary Westfall3 Questions from Nuclear Physics What are the heaviest nuclei that can exist? –How many neutrons can a nucleus hold? –What is the heaviest element? –Are there very long-lived super-heavy elements? How do protons and neutrons make stable nuclei and rare isotopes? –Is there a path to understand nuclei in terms of their fundamental constituents and their interactions? –What are the relevant degrees of freedom and effective interactions in nuclei? –What is the nature paring phenomena (superconducting phases) in nuclei? What is the origin of simple patterns in complex nuclei? –Where does the angular momentum of a nucleus come from? –What is the origin of the dynamical symmetries found in nuclei? –How do we understand the transition between various symmetry phases? What is the equation of state of matter made of nucleons?

Gary Westfall4 What is the nature of matter at extreme conditions ? (for example in neutron stars ?) Questions from Astrophysics What is the origin of the heavy elements from iron to uranium ? (one of 11 science questions for the “new” century – NAS report “Connecting Quarks with the Cosmos”) Why do stars explode ?

Gary Westfall5 International Solutions

Gary Westfall6 The Rare Isotope Accelerator - RIA High power heavy-ion driver (400 kW, 400 MeV/nucleon) Wide range of research capabilities All four experimental areas are needed!

Gary Westfall7 What Science is Addressed by Each Technique? Experiments with fast beams cover most of the science effectively, and the techniques are well established

Gary Westfall8 Reduced-Cost Options Studied at MSU The NSCL group has studied options for rare isotope research Option 1: MSU-SCF (MSU South Campus Facility) –Build a new high-power heavy-ion driver plus reaccelerator on a green-field site, allowing staged upgrades to full RIA capability Option 2: NSCL Upgrade –Add a kW driver and reaccelerator to the existing NSCL site For both options the technologies for the driver linac and the fast beam capabilities are essentially developed and present no performance risk

Gary Westfall9 Option 1: MSU-SCF Fast beams, gas stopping, ISOL, reacceleration –Energy/nucleon: 180 MeV 238 U, 227 MeV 129 Xe, 300 MeV 3 He, 340 MeV 1 H –Power: 100 kW TPC $540 M (FY2005-$)

Gary Westfall10 MSU-SCF Cost Elements All cost estimates are in FY05 dollars and based upon NSCL labor rates Total Estimated Cost (TEC) $376 M (excluding contingency) Contingency$94 M Preoperations$57 M R&D$10 M Total Project Cost (TPC)$537 M

Gary Westfall11 MSU-SCF Upgrade Elements Multi-user capability, flexible selection of upgrade elements –Energy/nucleon: 400 MeV 238 U, 539 MeV 129 Xe, 864 MeV 3 He, 1122 MeV 1 H –Power 400 kW Upgrade TPC: $355 M (FY2005-$)

Gary Westfall12 Option 2: NSCL Upgrade TPC: $302 M (FY2005-$) Fast beams, gas stopping, reaccelerated beams – no ISOL –180 MeV/u kW, 215 MeV/u kW

Gary Westfall13 MSU-SCF Scientific Reach: Beam intensities (pps) Scientific reach of NSCL upgrade is very similar to MSU-SCF when in-flight production and separation are used

Gary Westfall14 MSU-SCF Intensity Gains over NSCL (MSU-SCF/NSCL) Gain factors

Gary Westfall15 Intensity Gains from 400 AMeV Upgrade of MSU-SCF Gain factors

Gary Westfall16 Summary - RIA Program at MSU There are sound scientific reasons to include the fast beam capability for any reaccelerated exotic beams facility that makes use of in-flight production techniques  Much larger scientific reach  Proven technology with no risk Several options exist to build a world-class reaccelerated beams facility  The NSCL upgrade is a particularly cost-effective option – but it offers limited possibilities for additional on-site upgrades  The MSU-SCF is an attractive alternative that allows flexible upgrade options to full RIA capability without major disruption of the ongoing research and education program

Gary Westfall17 Balance Functions at RHIC Previous Results Au+Au at 130 GeV J. Adams et al., PRL 90, (2003) New Results (long PRC paper being prepared by STAR) Au+Au, p+p, d+Au at 200 GeV 100 times more Au+Au events B(  ) and B(  ) for all charged particles B(  y) for pions and kaons B(q inv ) for pions and kaons B(q long ), B(q out ), and B(q side ) for pions Widths of the Balance Function Comparison with HIJING and Blast Wave Models Gary Westfall Michigan State University for the STAR Collaboration

Gary Westfall18 Balance Functions and Delayed Hadronization Bass, Danielewicz, and Pratt [Phys. Rev. Lett. 85, 2689 (2000)] proposed the balance function The basic premise is that charge/anti-charge pairs are created close together in space-time If these pairs are created early in the collision, they will be pulled apart in rapidity by longitudinal expansion and will suffer scattering for the duration of the collision, losing their correlation in rapidity If instead, the system exists in a deconfined phase for a time long compared with 1 fm/c, and then the pairs are created at hadronization, they will experience less expansion and fewer collisions, retaining more of their correlation in rapidity Previous measurements for Au+Au at 130 GeV published by STAR, PRL 90, (2003)

Gary Westfall19 Definition of the Balance Function To quantify the correlation of charge/anti-charge pairs, Bass, Danielewicz, and Pratt proposed the balance function that counts correlated charge/anti-charge pairs as a function of relative rapidity,  y  |y 2 -y 1 | N +- (  y) is calculated by histogramming  y for all negative particles correlated with all positive particles in a given event and the resulting histogram is summed over all events, similarly for N ++ (  y), N -+ (  y), and N -- (  y) N +(-) is the total number of positive(negative) particles summed over all events

Gary Westfall20 Understanding the Balance Function Theoretical expectations for B(  y) –PYTHIA representing p+p collisions shows a characteristic width of about 1 unit of  y –Bjorken thermal model representing delayed hadronization shows narrower balance function width Nucleon-nucleon  –Wide Delayed hadronization  –Narrow Use the width of the balance function as an observable No STAR acceptance

Gary Westfall21 Balance Function for All Charged Pairs, Au+Au at 200 GeV no electrons Central Peripheral Real Shuffled Mixed

Gary Westfall22 Balance Function Widths, All Charged Particles p+p, d+Au, and Au+Au

Gary Westfall23 Conclusions The balance function B(  ) for all charged particles from Au+Au collisions at 200 GeV is much narrower in central collisions than in peripheral collisions –Consistent with models incorporating delayed hadronization The width of balance functions from p+p, d+Au, and Au+Au scale with N part The width of the balance functions predicted by HIJING for Au+Au shows no centrality dependence and is similar to p+p

Gary Westfall24 Balance Function for Pion Pairs, Au+Au at 200 GeV p < 0.7 GeV, no electrons Central Peripheral Identified charged pion pairs (  +,  - )

Gary Westfall25 Balance Function for Kaon Pairs, Au+Au at 200 GeV p < 0.7 GeV, no electrons Central Peripheral Identified charged kaon pairs (K +,K - )

Gary Westfall26 Balance Function Widths for Pions and Kaons p+p and Au+Au

Gary Westfall27 Comparison to Blast Wave Model Blast wave model by Pratt et al. Pion gas including emission of charge pairs close together in time and space, radial expansion, resonances, HBT, Coulomb, strong interactions, and STAR acceptance filter Predicted width of balance function is narrowest possible Agrees with balance function observed in most central bin More peripheral bins are clearly wider Cheng, Petriconi, Pratt and Skoby, PRC 69, (2004)

Gary Westfall28 Balance Function for Pions using q inv Peripheral p < 0.7 GeV, no electrons Identified charged pion pairs (  +,  - ) Central HBT/Coulomb Effects

Gary Westfall29 Conclusions - Balance Function Au+Au results for balance function widths using all charged particles scale smoothly to the p+p and d+Au results as a function of N part –Consistent with models incorporating delayed hadronization B(  y) for kaons is narrower than B(  y) for pions and shows no centrality dependence –B(  y) for pions in central Au+Au collisions is explained by a complete blast wave model –B(  y) for kaons represents not only a charge balance but a strangeness balance May indicate that kaons are created early in the collision

Gary Westfall30 Backup Slides

Gary Westfall31 Wait…. But wait, we still have some questions… –Do different particles have the same balance function widths? Look at balance function for identified particles Look at detailed model predictions –What about radial flow effects? Look at B(q inv ) that should be insensitive to flow effects –Does the balance function narrow only in the longitudinal direction? 3D balance functions

Gary Westfall32 MSU-SCF Intensity Gains over FAIR at GSI (MSU-SCF/FAIR) Gain factors