1 / 19

Probing the Dense Fireball: Charm Production and Detection at Threshold Beam Energies

Probing the Dense Fireball: Charm Production and Detection at Threshold Beam Energies. Volker Friese Gesellschaft f ür Schwerionenforschung Darmstadt, Germany v.friese@gsi.de. JINR Particpiation in the Experimental Programme on the Future GSI facility

mara-peters
Download Presentation

Probing the Dense Fireball: Charm Production and Detection at Threshold Beam Energies

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Probing the Dense Fireball:Charm Production and Detectionat Threshold Beam Energies Volker Friese Gesellschaft für Schwerionenforschung Darmstadt, Germany v.friese@gsi.de JINR Particpiation in the Experimental Programme on the Future GSI facility International Workshop, JINR Dubna, November 2003

  2. charm is produced, not put into the collisions : a heavy strange quark charm is heavy! mc 1 GeV >> T  170 MeVperturbative treatment possible (?)calculable from QCD principles Why charm is interesting JINR International Workshop, Dubna, November 2003 2 V. Friese

  3. Charm in heavy-ion collisions Common picture: Production of charm in the initial hard parton-parton interactions (before possible QGP formation) Charmonium: Absorption by comoving participants: “normal suppression” In deconfined matter: Additional dissociation due to free colour charges (Debye screening): “anomalous suppression” QGP signature! JINR International Workshop, Dubna, November 2003 3 V. Friese

  4. But: If scaled to h-, J/ is independent of Np In fact: anomalous J/ suppression observed in Pb+Pb at SPS (158 AGeV) Gazdzicki & Gorenstein, Phys. Rev. Lett. 83 (1999) 4009 hard to understand with hard production and subsequent suppression  soft production of charmed hadrons? NA50, QM 2001 Charm production : hard or soft? JINR International Workshop, Dubna, November 2003 4 V. Friese

  5. 5 x 10-2 2 x 10-1 for central Pb+Pb @ 158 AGeV p+N data allow estimate of open charm yield in elementary collisions • predictions for A+A differ dramatically! Compilation by Gazdicki andMarkert Acta Phys. Pol. B 31(2000) 965 Open charm can tell! Soft A dependence : <D> ~ <h-> ~ Np pQCD : <D> ~ A2 ~ Np4/3 JINR International Workshop, Dubna, November 2003 5 V. Friese

  6. Predictions of open charm yield differ by orders of magnitude for different production scenarios, especially at low energies Gorenstein et al J. Phys. G 28 (2002) 2151 More scenarios… Hadron gas in chemical equilibrium Canonical suppression analoguous to strangeness Equilibrated QGP + statistical coalescence JINR International Workshop, Dubna, November 2003 6 V. Friese

  7. Open charm in dense matter Various QCD inspired models predict a change of D mass in hadronic medium Mishra et al, nucl-th/0308082 Substantial change (several 100 MeV) already at =0 In analogy to kaon mass modification, but drop for both D+ and D- Effect for charmonium is substantially smaller JINR International Workshop, Dubna, November 2003 7 V. Friese

  8. Reduced D meson mass : consequences If the D mass is reduced in the medium: DD threshold drops below charmonium states Mishra et al, nucl-th/0308082 • Decay channels into DD open for ’, c, J/ • broadening of charmonium states • suppression of J/ • enhancement of D mesons Hayashigaki, PLB 487 (2000) 96 JINR International Workshop, Dubna, November 2003 8 V. Friese

  9. Transport models : reduced D mass has dramatic consequences for the production cross section in p+N and secondary +N, especially near N+N threshold Cassing et al, Nucl. Phys. A 691 (2001) 753 HSD : D yield enhanced by a factor of 7 at 25 AGeV! Reduced D meson mass : consequences contd. JINR International Workshop, Dubna, November 2003 9 V. Friese

  10. First evidence ? Enhancement of open charm (3 x pQCD) could explain the excess of intermediate mass dimuons observed at SPS peripheral central Abreu (NA50), Eur. Phys. J. C 145 (2000) 443 JINR International Workshop, Dubna, November 2003 10 V. Friese

  11. A short summary • Experimental data on open charm production in nucleus nucleus collisions will give insight into exciting physics questions related to both QGP and dense baryonic matter. But: No measurement available so far. • Effects of in-medium modification increase with baryon density and are best studied near threshold. • Open charm measurement will be one of the major tasks of CBM. • Improvement in theory is surely needed to disentangle various (maybe competing) effects and make strong predictions. JINR International Workshop, Dubna, November 2003 11 V. Friese

  12. Challenges in open charm measurement Detection by charged hadronic decay, e.g. D0 +K- Near threshold means: extremely low yield (~10-3) Heavy ion collision means: high charged multiplicity (~1000) Without cuts: S/B = 1.3 x 10-5 Background suppression of 105 needed Au + Au @ 25 AGeV, UrQMD + GEANT JINR International Workshop, Dubna, November 2003 12 V. Friese

  13. Tracking in the CBM detector JINR International Workshop, Dubna, November 2003 13 V. Friese

  14. Background reduction for D0 combinatorial +K- background • Cut variables: • decay angle • decay vertex position • pair impact parameter • pointing angle vz + + bK * p + pK D0 b K- K- CMpair Lab JINR International Workshop, Dubna, November 2003 14 V. Friese

  15. Secondary vertex resolution The most effective cut for background reduction is on the two-track vertex position resolution depends on: thickness of tracking stations single hit resolution JINR International Workshop, Dubna, November 2003 15 V. Friese

  16. Requirements on the tracking detector First station must be close (5cm) to the target: radiation hardness MHz event rate: fast readout few materials good hit position resolution Hybrid MAPS JINR International Workshop, Dubna, November 2003 16 V. Friese

  17. Estimate of D0 detection capability based on GEANT simulation, no magnetic field, perfect PID, background from UrQMD Signal efficiency 48 % Background reduction 2 x 105 S/B  2 Significance at 107 events: 7.5 Similar study for D+ ++K- : S/B  3 Improvements towards reality: include magnetic field ready include track finding available include hadron PID under work JINR International Workshop, Dubna, November 2003 17 V. Friese

  18. K- from D0 decay Decay + PID efficiency Daughter identification Time-of-flight measurement 10m from target Resolution 80 ps assumed The majority of the daughters accepted by the tracking system can be identified JINR International Workshop, Dubna, November 2003 18 V. Friese

  19. Summary • The measurement of open charm in heavy ion collisions gives access to a wide range of yet unsolved physical questions. • D mesons are expected to be quite sensitive to the dense baryonic environment created in nucleus collisions at SIS300 energies. • Measurement near production threshold will give insight into the medium modification of the D meson mass and will hopefully serve to constrain the various model calculations. • Compared to experiments at RHIC or LHC, CBM will have to deal with extremely low open charm rates. • We will have to cope for that with excellent secondary vertex resolution and high event rates. • If CBM will be able to handle the interaction rates promised to us by the accelerator, the open charm measurement will most probably be possible. JINR International Workshop, Dubna, November 2003 19 V. Friese

More Related