High-Density Pellet Target for Antiproton Physics

1. A high-density pellet target for antiproton physics with ÖRJAN NORDHAGE GSI/Uppsala University Germany/Sweden 2nd Swedish Workshop on FAIR Physics, Lund, September 12-13, 2005

2. Contents (For details, please see the proceedings of STORI’05) • PANDA – Motivation • Pellet Target – Principle, WASA, Target Thickness, Requirements, R&D, Pellet Tracking • Implementation into PANDA • Conclusion Örjan Nordhage, 2nd SFAIR meeting

3. Motivation for • Physics program: • Charmonium spectroscopy (mass, width, decay branches) • Gluonic excitations (charmed hybrids, glueballs) • Properties of charmed mesons in nuclei • Single and double hypernuclei spectroscopy • … Very rare events together with a limited number of antiprotons, put high demands on the target and its thickness Örjan Nordhage, 2nd SFAIR meeting

4. Target thickness at or HESR Number of antiprotons: 1×1011 Momentum range: 1.5 – 15 GeV/c (β: 0.848 – 0.998) HESR circumference: 574 m Design luminosity: 2×1032 cm-2s-1 The reaction pp meansa pure hydrogen target and currently, pellets (frozen micro-spheres) are the only proven working solution, which provides such an effective target thickness Örjan Nordhage, 2nd SFAIR meeting

5. Pellet Target – Principle • Pellet generation: • Cooling of gas to liquid • Jet break-up into droplets • Vacuum injection • Skimmer to collimate the pellet beam [B. Trostell, NIM A 362 (1995) and/or C. Ekström et al., NIM A 371 (1996)] Örjan Nordhage, 2nd SFAIR meeting

6. WASA Pellet Target – Principle 70-100 kHz Freeze either in v.i.c. or within some cm after What gets through is very close to homogenously distributed Completely frozen: bounce like billiard balls 5-10,000 /s [Ö.N. et al., NIM A 546 (2005)] Örjan Nordhage, 2nd SFAIR meeting

7. WASA Pellet Target – Dimensions Vac. inj. cap. exit: 0 m Skimmer (Φ=0.59mm): 0.7 m Interaction point: 2.4 m Dump: 3.6 m Bounce at skimmer Get through skimmer Define pellet spread at i.p., we get N.B. Target geometry (skimmer position and diameter Φ) alone define Sip Örjan Nordhage, 2nd SFAIR meeting

8. Target thickness and pellets Pellets are discrete and locally very thick ~ 1020 atoms/cm2 Thus, the effective thickness needs an associated area Pellet beam N.B. Not in scale: beam (~mm) >> pellet (~30μm) Maximum luminosity if beam area and target area are matched ‹l› Antiproton beam Sip Örjan Nordhage, 2nd SFAIR meeting

9. A factor less than 2 off from is already achieved R&D Pellet requirements at or HESR With we need pellets of a certain size, and how often? Last H2 run (Dec. 2003): f~9000/s, 33μm, 95m/s Örjan Nordhage, 2nd SFAIR meeting

10. R&D of Pellet Parameters – How To Goal: smaller pellets much more often Size reduction by: • Decreased nozzle outlet • Increased transducer frequency • Decreased driving pressure • Improved survival ratio • Decreased angular spread Rate increase by: Spread due to transverse velocity component of gas after the v.i.c.? If so, simulations by FEMLAB might give us the ideal geometry (of the exit) Örjan Nordhage, 2nd SFAIR meeting

11. Pellet pipes ”antiproton beam pipe” Vacuum gauges R&D of Pellet Parameters – Location Pellet Test Station (PTS) at The Svedberg Laboratory (TSL) in Uppsala: Lower floor Upper floor Örjan Nordhage, 2nd SFAIR meeting

12. R&D: PTS vacuum measurement [Technical Progress Report for PANDA (2005)] • Input to V. Ziemann’s VAKLOOP [SLAC-PUB-5962] • PTS Geometry • Corresponding conductance • Pellet outgassing [Ö.N. et al., NIM A 546 (2005)] • Pumping speed Örjan Nordhage, 2nd SFAIR meeting

13. CELSIUS/WASA interaction region: Pellets Gauge 48 MeV protons R&D: Beam-caused pellet heating • The mass loss of pellets is temperature dependent • The beam will deposit energy to the pellets • Thus: an increase in pellet temperature and mass loss Question: Vacuum effect? Answer from (!?!): ”Dedicated Spring’05 experiment at CELSIUS” Örjan Nordhage, 2nd SFAIR meeting

14. Measured beam size: Ultimately, the goal is to evaluate this additional effect for PANDA – just wait until later this Autumn R&D: Beam-caused pellet heating Current in green [0,2] mA, pressure in red [1.3,2.5]×10-7 mbar Time [s] Örjan Nordhage, 2nd SFAIR meeting

15. Sofar existing (1D): LineScanCam, 512 pixels, readout 98 kHz (+laser, framegrabber) R&D: Pellet Tracking/Profile System Pellets’ discrete nature is an advantage – allows for a localized target and a well-defined vertex Goal: combined pellet counter and profile system – online Basic idea: Örjan Nordhage, 2nd SFAIR meeting

16. 3.7m Pellet Target in the -detector (Corresponding distance for WASA: 3.3m) Örjan Nordhage, 2nd SFAIR meeting

17. N.B. 12.5m in z-direction Pellet Target in the -detector HESR-vacuum distribution for two different pellet sizes, but the same target thickness Define: ’background due to gas to signal from pellet’-ratio Örjan Nordhage, 2nd SFAIR meeting

18. Thanks to… Present and recent pellet collaborators: TSL: Hans Calén, Curt Ekström, Carl-Johan Fridén, Zhankui Li, Gunnar Norman Uppsala (ISV): Florian Lang, Inti Lehmann, Jonas Lith, Matthias Schult, Ulrich Wiedner Funding: EU, GSI, Swedish Research Council Örjan Nordhage, 2nd SFAIR meeting

19. Conclusion • To reach the design luminosity in PANDA, a Pellet Target is a very promising option due to the high target thickness it provides • The existing WASA Pellet Target is almost suitable as it is – and we know how to improve it further • The Pellet Test Station at TSL is going to be used for further tests • The vacuum condition has been experimentally tested – agrees with calculations (results on beam-pellet interaction is being analyzed now…) • A Pellet Tracking System is an excellent approach to the (close to perfect) vertex determination Thanks for your attention! Örjan Nordhage, 2nd SFAIR meeting

20. Pellet requirements at or HESR The pellet size goal is determined by the inter-pellet distance that could be matched by the antiproton beam N.B. The plot is independent of pellet speed Örjan Nordhage, 2nd SFAIR meeting