A high-density pellet target for antiproton physics with

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A high-density pellet target for antiproton
physics with
ÖRJAN NORDHAGE GSI/Uppsala University Germany/Swed
en
6th International Conference on Nuclear Physics
at Storage Rings 23-26 May 2005, Jülich - Bonn,
Germany
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Contents

• PANDA Motivation
• Pellet Target Principle, WASA, Target
  Thickness, Requirements, RD, Pellet Tracking
• Implementation into PANDA
• Conclusion

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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
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Target thickness at or HESR
Number of antiprotons 11011 Momentum range 1.5
15 GeV/c (ß 0.848 0.998) HESR circumference
574 m Design luminosity 21032 cm-2s-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
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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)
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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
To be printed, NIM A (2005)
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WASA Pellet Target Dimensions
Vac. inj. cap. exit 0 m Skimmer (F0.59mm)
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 F) alone define Sip
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Target thickness and pellets
Pellets are discrete and locally very thick
1019 atoms/cm2 Thus, the effective thickness
needs an associated area
Pellet beam
N.B. Not in scale beam (mm) gtgt pellet (30µm)
Maximum luminosity if beam area and target area
are matched
l
Antiproton beam
Sip
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Pellet requirements at or HESR
With
we need pellets of a certain size, and how often?
Last H2 run (Dec. 2003) f9000/s, 33µm, 95m/s
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RD 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

1. Improved survival ratio
2. 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)
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RD of Pellet Parameters Location
Pellet Test Station (PTS) at The Svedberg
Laboratory (TSL)
Upper floor
Lower floor
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RD PTS vacuum measurement
Technical Progress Report for PANDA (2005)

• Input to VAKLOOP SLAC-PUB-5962
• PTS Geometry
• Corresponding conductance
• Pellet outgassing To be printed, NIM A (2005)
• Pumping speed

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RD 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
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Pellet Target in the -detector
(Corresponding distance for WASA 3.3m)
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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
N.B. 12.5m in z-direction
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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, Matthias Schult,
Ulrich Wiedner
Funding EU, GSI, Swedish Research Council
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Conclusion

• To reach the design luminosity in PANDA, a Pellet
  Target might be the only possible 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 is going to be used for
  further tests
• The vacuum condition has been experimentally
  tested agrees with calculations
• A Pellet Tracking System is an excellent approach
  to the (close to perfect) vertex determination

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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. Plot is independent of pellet speed