Antiproton Physics at GSI

• Introduction• The antiproton facility• The physics program

- Charmonium spectroscopy- Hybrids and glueballs- Interaction of charm particles with nuclei- Strange baryons in nuclear fields- Further options (CP, inverted DVCS, low energy p )

• Detector concept• Selected simulation results• Conclusions

J.Ritman, Uni-Gießen for the NUPECC committee visit to GSI 12-13.07.2001

The GSI p Facility

p production similar to CERN, HESR = High Energy Storage Ring

• Production rate 107/sec• Pbeam = 1.5 - 15 GeV/c• Nstored = 1010 p• Lumin. = 2x1032 cm-2s-1 • p/p~10-5 (el. cooling < 8 GeV/c)• p/p~10-4 (stochastic cooling)

Charmonium SpectroscopyThe charmonium system is the positronium of QCD. It provides a unique window to study the interplay of perturbative and non-perturbative effects.

Energy levels / widths Details of QQ interaction

Exclusive decays Mixing of perturb. and non-pert. effects

Comparison e+e- versus pp

e+e- interactions: Only 1-- states are formed Other states only by secondary decays (moderate mass resolution)

pp reactions: All states directly formed (very good mass resolution)

Severe limitations to existing experiments (no B-field, beamtime, beam momentum reproducibility,…)Many open questions: ’c, states above DD threshold,…

Charmed HybridsPredictions for charmed hybrids (ccg)

Mass: lowest state 3.9-4.5 GeV/c2

Quantum numbers: many allowed values, ground state JPC = 1-+ (exotic)

Width: Could be narrow (~MeV) for some states since DD suppressed O+- DD,D*D*,DsDs (CP-Inv.) (QQg) (Qq)L=0+(Qq)L=0 (Dynamic Selection Rule)If DD forbidden, then the preferred decay is

(ccg) (cc) + X , e.g. 1-+ J/

Search for Charmed Hybrids

Mixing with QQ states: - Excluded for spin exotic hybrids - Possible for non-exotic states, but less probable than the light quark sector, since there are fewer states with smaller width.

Example of state with exotic q.-n. (1-+) pd X(1-+)++p, X CB@LEARStrength similar to qq states

Partial Wave Analysis as important toolExpectations at HESR: 104 non-exotic q.-n. & 102 exotic /dayA signal in production but not in formation is interesting!

Charmed Hadrons in Nuclear Matter

Investigating the properties of hadrons in matter is a main research topic at GSI. Partial restoration of chiral symmetry should take place in nuclear matter. Light quarks are sensitive to quark condensate Evidence for mass changes of pions and kaons has been deduced previously: - deeply bound pionic atoms - (anti)kaon yield and phase space distribution

D mesons are the QCD analog of the H atom. They allow chiral symmetry to be studied on a single light quark

±

The expected signal for a changing mass scenario would be a strong enhancement of the D meson cross section, and relative D+ D- yields, in the near/sub-threshold region.

This probes ground state nuclear matter density and T~0 (complementary to heavy ion collisions)

Open Charm in Nuclei

cc Production on Nuclei

A lowering of the DD mass would allow charmonium states to decay into this channel, thus resulting in a dramatic increase of width.

Thus one will study relative changes to the yield and width of the charmonium states.

J/ – Nucleon Absorbtion

The J/ suppression observed at SPS is believed to be related the generation of the QGP. Such suppression can also be generated by purely hadronic interactions, so it is very important to know the N-J/ cross section in nuclear matter.

p + A J/ + (A-1)

Proton Form Factors at large Q2

At high values of momentum transfer |Q2| the system should be describable by perturbative QCD. Due to dimensional scaling, the FF should vary as Q4.

222 lns

s

CG

p

M

q2>0

q2<0

The time like FF remains about a factor 2 above the space like. These differences should vanish in pQCD, thus the asymptotic behavior has not yet been reached at these large values of |q2|. (HESR up to s ~ 25 GeV2)

Strange Baryons in Nuclear FieldsHypernuclei open a 3rd dimension (strangeness) in the nuclear chart

-

3 GeV/c

K+KTrigger

_

secondary target

p

• New Era: high resolution -spectroscopy

• Double-hypernuclei: very little data

• Baryon-baryon interactions: -N only short ranged (no 1 exchange due to isospin) - impossible in scattering reactions

-(dss) p(uud) (uds) (uds)

Experiments with Open Charm

HESR will produce about 2.5x109 DD/year (~1% reconstr.)

• Leptonic decays: structure of D mesons(/tot D)

• D0/D0 mixing: should be small <10

• CP: direct is dominantNeed about 108 decays

Direct CP in hyperon decays (self analyzing decay)

Production of charmed baryons:excitation function, differential cross sections,

spin observables

Inverted DVCS„Deeply Virtual Compton Scattering“ (DVCS) allows the „Skewed Parton Distributions“ to be measured using the Handbag-Diagram Dynamics of quarks and gluons in hadrons

Measurements of the inverted process less stringent requirements on the detector resolution.(however the connection of DVCS to the SPDs needs to be theoretically analyzed in this kinematic region)

General Purpose DetectorDetector requests:• nearly 4 solid angle• high rate capability• good PID (,e,,,K,p)• efficient trigger (e,,K,D,)

J/+-

‘+-

pp ‘ pp (s=3.6 GeV)4K

Detector

Target• A fiber/wire target will be needed for D physics,• A pellet target is conceived:

1016 Atom/cm2 20-40 m

Central Tracking Detectors

• Micro Vertex Detector: (Si) 5 layers• Straw-Tubes: 15 skewed double-layers• Mini-Drift-Chambers • RICH: DIRC and aerogel

PbWO4 Calorimeter

Length = 17 X0

APD readout (in field)

pp J/

dE

p

e/-Separation in EM-Calorimeter

e/ Separation 10-3

Summary

• HESR will deliver cooled antiprotons up to 15 GeV/c• The physics program

- Charmonium spectroscopy- Hybrids and glueballs- Interaction of charm particles with nuclei- Strange baryons in nuclear fields- Further options

• Detector concept• Selected simulation results

HESR Detector

• Pellet-Target: 1016 Atoms/cm2 20-40 m• MicroVertexDetektor: (Si) 5 layers• Straw-Tubes: 15 skewed double layers• RICH: DIRC and Aerogel (Proximityfocussing)•Straw-Tubes + Mini-Drift-Chambers

• PbWO4-calorimeter 17X0

• 2T-Solenoid & 2Tm-Dipole• Muon filter• EM- & H-cal. near 0°