A highdensity pellet target for antiproton physics with

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

Contents (For details, please see the proceedings of STORI’ 05) 1. PANDA – Motivation 2. Pellet Target – Principle, WASA, Target Thickness, Requirements, R&D, Pellet Tracking 3. Implementation into PANDA 4. Conclusion Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 2

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 Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 3

Target thickness at or HESR Number of antiprotons: 1× 1011 Momentum range: 1. 5 – 15 Ge. V/c (β: 0. 848 – 0. 998) HESR circumference: 574 m Design luminosity: 2× 1032 cm-2 s-1 The reaction pp means a pure hydrogen target and currently, pellets (frozen micro-spheres) are the only proven working solution, which provides such an effective target thickness Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 4

Pellet Target – Principle Pellet generation: 1) Cooling of gas to liquid 2) Jet break-up into droplets 3) Vacuum injection 4) Skimmer to collimate the pellet beam [B. Trostell, NIM A 362 (1995) and/or C. Ekström et al. , NIM A 371 (1996)] Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 5

WASA Pellet Target – Principle 70 -100 k. Hz Freeze either in v. i. c. or within some cm after Completely frozen: bounce like 5 -10, 000 /s billiard balls Sept. 12, 2005 What gets through is very close to homogenously distributed [Ö. N. et al. , NIM A 546 (2005)] Örjan Nordhage, 2 nd SFAIR meeting 6

WASA Pellet Target – Dimensions Vac. inj. cap. exit: 0 m Bounce at skimmer Skimmer (Φ=0. 59 mm): 0. 7 m Interaction point: 2. 4 m Dump: 3. 6 m Get through skimmer Define pellet spread at i. p. , we get N. B. Target geometry (skimmer position and diameter Φ) alone define Sip Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 7

Target thickness and pellets Pellets are discrete and locally very thick ~ 1020 atoms/cm 2 Maximum luminosity if beam area and target area are matched Sept. 12, 2005 N. B in t o N. : e l a sc > > ) 0 3 ~ t( ) m μ e ll e p m m ~ ‹l › ( m a be Antiproton beam Örjan Nordhage, 2 nd SFAIR meeting Pellet beam Thus, the effective thickness needs an associated area Sip 8

Pellet requirements at or HESR With we need pellets of a certain size, and how often? A factor less than 2 off from is already achieved Last H 2 run (Dec. 2003): f~9000/s, 33μm, 95 m/s Sept. 12, 2005 R& D Örjan Nordhage, 2 nd SFAIR meeting 9

R&D of Pellet Parameters – How To Goal: smaller pellets much more often Size reduction by: 1) Decreased nozzle outlet 2) Increased transducer frequency 3) Decreased driving pressure Rate increase by: 1) Improved survival ratio 2) Decreased angular spread 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) Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 10

R&D of Pellet Parameters – Location Pellet Test Station (PTS) at The Svedberg Laboratory (TSL) in Uppsala: Pellet pipes ”antiproton beam pipe” Upper floor Sept. 12, 2005 Vacuum gauges Lower floor Örjan Nordhage, 2 nd SFAIR meeting 11

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 Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 12

R&D: Beam-caused pellet heating CELSIUS/WASA interaction region: • 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? Pellets Gauge 48 Me. V protons Answer from (!? !): ”Dedicated Spring’ 05 experiment at CELSIUS” Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 13

R&D: Beam-caused pellet heating Current in green [0, 2] m. A, pressure in red [1. 3, 2. 5]× 10 -7 mbar Measured beam size: Ultimately, the goal is to evaluate this additional effect for PANDA – just wait until later this Autumn Sept. 12, 2005 Time [s] Örjan Nordhage, 2 nd SFAIR meeting 14

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: Sofar existing (1 D): Line. Scan. Cam, 512 pixels, readout 98 k. Hz (+laser, framegrabber) Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 15

Pellet Target in the -detector (Corresponding distance for WASA: 3. 3 m) 3. 7 m Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 16

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 Sept. 12, 2005 N. B. 12. 5 m in z-direction Örjan Nordhage, 2 nd SFAIR meeting 17

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 Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 18

Conclusion q To reach the design luminosity in PANDA, a Pellet Target is a very promising option due to the high target thickness it provides ! q q q n o i t The existing WASA Pellet Target is almost suitable n e t t as it is – and we know how to improve a it further r u o y is going to be used The Pellet Test Stationoat TSL r f s for further tests k n a Thcondition has been experimentally The vacuum tested – agrees with calculations (results on beampellet interaction is being analyzed now…) q A Pellet Tracking System is an excellent approach to the (close to perfect) vertex determination Sept. 12, 2005 Örjan Nordhage, 2 nd SFAIR meeting 19

Pellet requirements at The pellet size goal is determined by the interpellet distance that could be matched by the antiproton beam Sept. 12, 2005 or HESR N. B. The plot is independent of pellet speed Örjan Nordhage, 2 nd SFAIR meeting 20