1. Future prospects for NA61 heavy ions: rare observables Connecting to high-energy (RHIC) results M. van Leeuwen, Utrecht University and the NA61 collaboration Workshop: New Opportunities in the Physics Landscape at CERN 11-14 May 2009

2. 2 M. van Leeuwen, Future prospects for NA61: rare probes Motivation Heavy ion collisions: study strong interactions bulk matter –Identify phase transition to Quark-Gluon-Plasma Pure bulk = soft QCD, theoretically difficult Hard-soft interplay studied at RHIC shows many unexpected results – do these effects exist at SPS energies? –Can we ‘switch off’ some effects – transition ?

3. 3 M. van Leeuwen, Future prospects for NA61: rare probes Jet-like di-hadron correlations at RHIC At high p T > 4-6 GeV: Clear di-jet signature Away-side suppression due to energy loss associated  trigger 8 < p T trig < 15 GeV p T assoc > 3 GeV Use di-hadron correlations to probe the jet-structure in p+p, d+Au Near side Away side and Au+Au Combinatorial background STAR, PRL97, 162301 p+p event display

4. 4 M. van Leeuwen, Future prospects for NA61: rare probes Lowering p T : bulk response? 3.0 < p T trig < 4.0 GeV/c 1.3 < p T assoc < 1.8 GeV/c Near side Enhanced yield in Au+Au Away-side: Strong broadening in central Au+Au ‘Dip’ at  =  STAR, M. Horner, M. van Leeuwen, et al Au+Au 0-10% STAR preliminary Jet-like peak `Ridge’: associated yield at large  dN/d  approx. independent of  d+Au, 200 GeV Large modifications of di-hadron structure at intermediate p T Modified fragmentation? Bulk response? STAR, Putschke et al 3 < p t,trigger < 4 GeV p t,assoc. > 2 GeV

5. 5 M. van Leeuwen, Future prospects for NA61: rare probes Comparing SPS and RHIC SPS full energy: di-hadron structure similar to RHIC yields lower  lower ‘jet’ energy M. Szuba, Hot Quarks 2008

6. 6 M. van Leeuwen, Future prospects for NA61: rare probes Energy dependence of di-hadron correlations at SPS 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? M. Szuba, HQ08 New data needed to study , p T -dependence, above and below transition 40 AGeV20 AGeV

7. 7 M. van Leeuwen, Future prospects for NA61: rare probes Charm production at RHIC Low p T, R AA ~ 1 Total cross section scales with N coll as expected Suppression at high-p t : charm interacts with medium Does charm thermalise? Measure charm spectra at low p t, v 2 Will be measured at RHIC (STAR, PHENIX upgrades) and LHC (ALICE, others?) Can we measure this at SPS? Thermalised charm at SPS? STAR, PRL 98 (2007) 192301

8. 8 M. van Leeuwen, Future prospects for NA61: rare probes Charm with NA61? NA49: D 0  K  3.8M events Would need ~300M events (300 days running) for 1   Need vertex detector to measure D 0, p T spectra, v 2 Phys.Rev.C73:034910,2006 N(D 0 +D 0 ) = -0.36  0.74 per event N(D 0 +D 0 ) < 1.5 per event (C.L. 98%) NA61: c   +  - EPJ C59, 607 N(D 0 +D 0 ) expected: ~ 0.11 per central event e.g. 20M central events gives 80k D 0  K 

9. 9 M. van Leeuwen, Future prospects for NA61: rare probes Technology candidate: GOSSIP GridPix/InGrid GOSSIP Gas on Slimmed Silicon Pixels H. van der Graaf et al., NIKHEF Pixel size 55 x 55  m + time Use time-dependence to image track in gas layer Thin, precise and cheap ! Gas amplification + pixel readout

10. 10 M. van Leeuwen, Future prospects for NA61: rare probes Occupancy for vertex detector Central Pb+Pb at 158 AGeV Hits at z = 10 cm 2-track distance For y 0.3 cm, two-track distance ~ 300  m z = 10 cm safe choice for first plane y cms < 1

11. 11 M. van Leeuwen, Future prospects for NA61: rare probes Vertex resolution with vertex detector Decay distance along beamDecay length resolution 158 AGeV collisions Including Mult scatt ~600  m Si per plane Geometry: 6 planes, 10, 15 … 40 cm Lorentz boost: large decay lengths (mm scale) Looks promising: typical decay length >> resolution

12. 12 M. van Leeuwen, Future prospects for NA61: rare probes Summary of proposal 2 runs of NA61 ~10 weeks, 70M events (after baseline heavy ion program, 2014+) –Highest SPS energy: 158 AGeV –Low energy: 20/30 AGeV Measurement 1: jet-like di-hadron structure –Peak-dip transition, explore p T -dependence,  -  structure – connection to bulk response effects at RHIC Measurement 2: charm production –Need vertex detector –Measure yield, p T spectra (radial flow) and v 2 ?

13. 13 M. van Leeuwen, Future prospects for NA61: rare probes Towards a 4  detector? Qualitative step forward in hadron production experiments Goal: address unsolved issues from ISR era: –Cronin effect –Changeover/interplay soft-hard production –Baryon formation/transfer –Others? Concept: a large acceptance detector for ‘all’ particles (EM + charged hadrons + neutral hadrons) to perform exclusive measurements of hadron production at the SPS energy range. SPS has the potential to address many of these issues: wide energy range and choice of beams to narrow down the ‘model space’

14. 14 M. van Leeuwen, Future prospects for NA61: rare probes Extra slides

15. 15 M. van Leeuwen, Future prospects for NA61: rare probes Charm production at RHIC PHENIX, PRL 98 (2007) 172301 Total cross section scales with N coll -- as expected J. Dunlop, QM09 pQCD expectation p+p Au+Au  cc /N coll [mb] Remove!

16. 16 M. van Leeuwen, Future prospects for NA61: rare probes Lowering p T : gluon fragments/bulk response 3 < p t,trigger < 4 GeV p t,assoc. > 2 GeV Au+Au 0-10% STAR preliminary associated  trigger Jet-like peak `Ridge’: associated yield at large  dN/d  approx. independent of  Strong  -  asymmetry suggests effect of longitudinal flow or underlying event Long. flow J. Putschke, M. van Leeuwen, et al d+Au, 200 GeV

17. 17 M. van Leeuwen, Future prospects for NA61: rare probes Trigger particle More medium effects: away-side 3.0 < p T trig < 4.0 GeV/c 1.3 < p T assoc < 1.8 GeV/c Mach Cone/Shock wave T. Renk, J. Ruppert Stöcker, Casseldery-Solana et al A. Polosa, C. Salgado Gluon radiation +Sudakov Au+Au 0-10% d+Au Near side: Enhanced yield in Au+Au consistent with ridge-effect Away-side: Strong broadening in central Au+Au ‘Dip’ at  =  Medium response (shock wave) or gluon radiation with kinematic constraints? (other proposals exist as well: k T -type effect or Cherenkov radiation) M. Horner, M. van Leeuwen, et al Note also: not shown is large background – something non-trivial may be hiding there?

18. 18 M. van Leeuwen, Future prospects for NA61: rare probes  -correlations from NA49 M. Szuba, QM09

19. 19 M. van Leeuwen, Future prospects for NA61: rare probes Characterizing the shapes PHENIX M. Szuba, QM09

20. 20 M. van Leeuwen, Future prospects for NA61: rare probes Summary of correlation shapes Away-side shape: no (large) energy dependence Near-side shape: change from ‘dip’ to peak M. Szuba, QM09