CHARMONIUM AT

CHARMONIUM ATAgnes LundborgQWG workshopBrookhaven June 2006

CHARMONIUM AT

Agnes LundborgUppsala University

Sweden

Background

• We thought that we understood charmonium quite well. Positronium of QCD, medium heavy quarks, potential model, narrow states. Perfect laboratory!

• In the last few years the B-factories and CLEO-c have been making unexpected discoveries. BESIII is coming up. E835 and Crystal Barrel are done.

• PANDA as next generation (2011)• What, why and how can PANDA

do better?


Charmonium spectrumpotential models vs.datadashed: nonrel (left), Godfrey-Isgur (right)


--1 in cc

+ -e e ψ cc + X

pp cc

FormationThe two particles fuse intothe intermediate state.

Proton-antiproton versus electron-positron

ProductionThe state is reached through decaysor nonresonant production.

3500 3520 MeV3510

CB

all

ev./

2 M

eV

100

ECM

CBall

1000

E 8

35 e

v./

pb

c1

E835

CBall, Edwards et al. PRL 48 (1982) 70

E835, Ambrogiani et al., PRD 62 (2000) 052002


Typical resolution in production

Crystall Ball e+e- Resolution of nonvector charmoniumdepends on the detector.B-factories and other currente+e- experiments (BES, CLEO-c)

Typical resolution information

Proton-antiproton E835Energy spread in beam

1c Γ < 8MeV

c1χ

s 0.4MeV

PDG Γ 0.91MeV

ECM


Discovery in production and precision measurement in scanning.

Important for: cross section shape measurementsPrecision measurements on mass and widths both at

resonance-energies and two-meson thresholds.

Resonance shape(Breit Wigner?)

Beam momentumprofile

Measured cross section

Scanning mode


Storage ring for p

High density targetpellet ,cluster jet, wire

High luminosity modestochastic cooling

High precision modeElectron cooling to 8 GeV

10pN = 5×10 beamp = 1.5 -15GeV c

-4 32 -2 -1Δp 10 L = 2×10 cm sp

5 1 - 3 -2 -1Δp 10 L 10 cm sp

15 210 atoms/cm

HESR at FAIRHigh Energy Storage Ring

5 5 5 -Δp 10 gives Δp = 0 keVatp = GeV!!!p


Glueball gg

Calculation flux-tubemodel, latticeQCD, bag-model, constituent gluonmodel.

Observations in the light quark sector:

•Exotic qn. 1-+Hybrid?

•Difficult to identify in the light quark sector, many overlapping states which mix.

Charmonium energy region•Light quark form a structureless continuum with few heavier states on top.

•A spin exotic can be seen in production but not formation and would then immediately be identified as interesting.Model independently! Without a complicated formalism!

QCD conceptually allows for states wheregluons contribute to the quantum numbers

Hybrid qqg

Meson qq

1

1

π (1400) E852(πp) Crystal Barrel(pp)

π (1600) E852(πp) Crystal Barrel(pp)

-+ +- +-Spin - exotichybrids 1 ,0 ,2

Nonrelativistic decay: charmquarks stay as they are. Gluonic excitation goes into a light scalar.

Production mode JPC=1-+p p /g

1( )c s

J

e e


Lowest energy charmonium hybrid

(spin-exotic)

[C.Bernard, Phys.Rev. D56 (1997) 7039][F.E. Close, Phys. Rev. 1998][P.R. Page, Acta Phys. Polon. 1998][P. Page, Phys Lett.B402(1997)][UKQCD, McNeile, Phys. Rev. D56(2002)]

1 4.1 4.4

(20)

PCJ M GeV

MeV

Good experimentaltag!

Final state:7 photons! 1 lepton pair!We need:1 Excellent calorimeterwith full angular range coverage.

A possible exotic charmonium hybrid channel:


We need an excellent:Electromagnetic Calorimeter (EMC)

Almost -acceptance barrel plus endcaps

Compact material (PWO, BGO)

Granularity (Molière radius)

Low threshold tens of MeVReadout inside magnetic field: APD

Also high energy photons GeV22 radiation lengths of crystal

Timing 1 ns – triggeringAnd high count rate (10 annihilations per s)

Radiation hardness (less radiation than CMS)

Last thing to solve: High resolution requires a large light output!

4π

7

p


Cooperation with manufacturersin Bogoroditsk and Shanghaiworking with doping and crystal growthprocesses has produced better crystals.

Third generation PWO with much larger light yields and thereforebetter resolution.

But that is not enough!Cooling

gives overall good performance.Already at acceptable resolutions!-25°C

Panda becomes

a Polarbear

0

[ 835]

( ) 100

3.5

Claudia Patrigniani E

pp J pb

at GeV off resonance

0 0, , , , , ...pp cc m m Complicated QCD process!Only theoretical guideline PCACfor only one channel.

0J p

p


Charmonium production

Use experimental data

cc pp m known amplitude A

extrapolate A to pp cc m

We know this decay width…

It’s a kinematical extrapolation, not very far..

[A.Lundborg, T.Barnes, U. WiednerPRD73 (2006) 096003.]

Integrate

Width proportional to Dalitz area

We want to know this crosssection.


Constant amplitude?First estimates.Cross section in the order between10 pb to 1 nb 200 to 20 000 events per day.Background 10 000 000 events per second.


Results, '

?

Isoscalar

enhanced

Technical Progress Report simulations

All neutral channel

No significant structures or regions of poor efficiency for the calorimetersetup.

0 0pp ηπ π 6γ

Charmed hybrid – red curve

•7 photons, 2 oppositely charged tracks•Mass window cuts on the intermediate particles.

Gives 12% detection efficiency.Any possible background would includes a and many photons.


J

0 0, ( ) ,g g c s wave c J pp


Signal

Background

[E835, PLB 566 (2003) 45-50]

cpp Measured at E835 about 50 pb in the region | cosθ |< 0.25

Major background sources 0 0pp π π 0pp π γ

[E835, PRD 56, 5 (1997) 2509(23)]

Event selection•Exactly two neutral tracks.•No charged tracks.•No pion candidates

•Invariant mass energy window

•Momentum of candidate <0.4 GeV/c•Opening angle >178.5•Momentum angle

0γγ π|m -m |< 25MeV

γγ pp CM| E -E | < 0.4 GeV

o

| cosθ |< 0.25

cη efficiency 10.3%

#Signal= 5.1

#Background


± 0 ± 0 ± 0 ± ±D , D , K , K , π , π , μ , e , γ

p,p, Λ, Σ, Ξ

PANDA Identification and tracking of:

MVD

Cherenkovs and TOF

Muon chamberTrackers andB-fields

EMC

Micro vertex detector

Displaced vertices of open charm and strangeness

Build on ALICE, ATLAS and CMS experience with hybrid detectors.Silicon pixel (3 layers) and strips (2 layers)7.2 million barrel pixels, 2 millionforward pixels

R&D:Requirements on pixel size and orientation.Investigate photon conversions(cooling system, electronics, detector).


±± 0s

0s

D ,D ,D cτ order of 100μm

K , Λ, Σ cτ order of 1-10 cm

14cm


Time projection chamber+Low material budget. +dEdx particle ID.High rates events per second->Ungated TPC-Space charge from ions-Overlaying events requires very good resolution for disentangling+GEM-foils (Gas electron multiplier)

Central tracking – two alternatives2 T axial B-field, same space, forward direction MWPCs.

Straw tube tracker10000 strawsZ-coordinate from either:-Skew angle 7-15 mm -Charge sharing 3 mm-Maximum material+Handles rates and has no space chargeproblem

710

210000 holes/cm

03%X/X

74 cm

TPC prototype in Munich


To conclude:

Panda will provide the next generation of charmonium knowledge!Precision – state of the art detectors, formation versus production.Rates – pellet target, beam. Proton-antiproton.Scope - detection of charged and neutral particles over (almost) full phase space

Charmonium energy region •Charmonium•Charmonium hybrids •Glueballs•DD-thresholds•Meson molecules•Other topics: hypernuclei, drell-Yan,charm in nuclei, di-baryons, crossed channel compton scattering.

Hardware R&D, software optimization andcivil construction on-going.Beam-on in: (Maybe) 2011


PANDA 2006: 300 people, 15 countries, 46 institutesTechnical Progress Report in february 2005 timelines, plans, simulations, technical solutions and R&D-work.

[PANDA technical progress reporthttp://www-panda.gsi.de]


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