Future prospects for NA61 heavy ions: rare observables Connecting to high-energy results M. van Leeuwen, Utrecht University And the NA61 collaboration

Motivation Heavy ion collisions: study strong interactions bulk matter Pure bulk = soft QCD, theoretically difficult Hard-soft interplay studied at RHIC shows many unexpected results – do these effects exist at SPS energies?

Jet-like di-hadron correlations at RHIC 8 < pTtrig < 15 GeV Combinatorial background associated pTassoc > 3 GeV  trigger Near side Away side Use di-hadron correlations to probe the jet-structure in p+p, d+Au and Au+Au At high pT > 4-6 GeV: Clear di-jet signature Away-side suppression due to energy loss

Lowering pT: bulk response? d+Au, 200 GeV 3.0 < pTtrig < 4.0 GeV/c Jet-like peak 1.3 < pTassoc < 1.8 GeV/c Au+Au 0-10% STAR preliminary M. Horner, M. van Leeuwen, et al Near side Enhanced yield in Au+Au `Ridge’: associated yield at large  Away-side: Strong broadening in central Au+Au ‘Dip’ at  =  dN/d approx. independent of  Large modifications of di-hadron structure at intermediate pT Modified fragmentation? Bulk response?

Comparing SPS and RHIC M. Szuba SPS full energy: di-hadron structure similar to RHIC, yields lower  lower jet energy

Energy dependence of di-hadron correlations at SPS M. Szuba Qualitative change from low to high energy: from near-side dip to near-side peak Clear turn-on as a function of energy. What is the mechanism?

Charm production at RHIC STAR, PRL 98 (2007) 192301 J. Dunlop, QM09 pQCD expectation Suppression at high-pt: charm interacts with medium Total cross section scales with Ncoll Q: does charm thermalise? Measure charm spectra at low pt, v2 Requires upgrades ~10M$ for STAR and PHENIX at RHIC

Charm with NA61? NA49: D0 K p N(D0+D0) = -0.36  0.74 per event N(D0+D0) < 1.5 per event (C.L. 98%) 3.8M events Phys.Rev.C73:034910,2006 Expected yields: 1 year running of NA61 ~300M events would give 3s  Need vertex detector

Technology candidate: GOSSIP H. van der Graaf et al., NIKHEF GOSSIP GridPix Gas on Slimmed Silicon Pixels Pixel readout 55x55 mm + time Use time-dependence to image track in gas layer

Occupancy for vertex detector 2-track distance Hits at z = 10 cm Central Pb+Pb at 158 AGeV For y < 4 ~ R > 0.3 cm, two-track distance ~ 300 mm z = 10 cm safe choice for first plane

Vertex resolution with vertex detector Decay distance along beam Resolution 158 AGeV collisions Including Mult scatt ~600 mm Si per plane Geometry: 6 planes, 10, 15 … 40 cm Lorentz boost: large decay lengths (mm scale) Looks promising: typical decay length >> resolution

Summary of proposal 2 runs of NA61 ~8 weeks, 200-300M events Highest SPS energy: 158 AGeV Low energy: 20/30 AGeV Measurement 1: jet-like di-hadron structure Peak-dip transition, explore pT-dependence, h-j structure – connection to bulk response effects at RHIC Measurement 2: charm production Need vertex detector Measure yield, pT spectra (radial flow) and v2?

Extra slides

PHENIX, PRL 98 (2007) 172301

Lowering pT: gluon fragments/bulk response d+Au, 200 GeV  trigger Au+Au 0-10% STAR preliminary Jet-like peak associated 3 < pt,trigger < 4 GeV pt,assoc. > 2 GeV Long. flow J. Putschke, M. van Leeuwen, et al `Ridge’: associated yield at large  dN/d approx. independent of  Strong - asymmetry suggests effect of longitudinal flow or underlying event

More medium effects: away-side Mach Cone/Shock wave T. Renk, J. Ruppert Stöcker, Casseldery-Solana et al 3.0 < pTtrig < 4.0 GeV/c 1.3 < pTassoc < 1.8 GeV/c Trigger particle Au+Au 0-10% A. Polosa, C. Salgado Gluon radiation +Sudakov d+Au M. Horner, M. van Leeuwen, et al Medium response (shock wave) or gluon radiation with kinematic constraints? Near side: Enhanced yield in Au+Au consistent with ridge-effect (other proposals exist as well: kT-type effect or Cherenkov radiation) Away-side: Strong broadening in central Au+Au ‘Dip’ at  =  Note also: not shown is large background – something non-trivial may be hiding there?

Dj-correlations from NA49 M. Szuba, QM09

Characterizing the shapes PHENIX M. Szuba, QM09

Summary of correlation shapes M. Szuba, QM09 Away-side shape: no (large) energy dependence Near-side shape: change from ‘dip’ to peak