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Meson spectroscopy - glueballs. Meike Door. Making a glueball Decay products Kaon detection Kinematic fitting Partial wave analysis Glueball candidates & spectra Further Research. Quantum Numbers are conserved. Making a glueball.

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meson spectroscopy glueballs
Meson spectroscopy - glueballs

Meike Door

  • Making a glueball
  • Decay products
  • Kaon detection
  • Kinematic fitting
  • Partial wave analysis
  • Glueball candidates & spectra
  • Further Research
making a glueball

Quantum

Numbers are

conserved

Making a glueball

J/ψ: meson, mass: 3097 MeV/c2 , lifetime ~10-20s, SpinParity (JP): 1-

Glueball: particleconsistingsolelyofgluons , JP=0+

Short lifetime: decayproductsareamongothers K+K- ,K0K0, π+π- , …

measure the decay products of a glueball
Measurethedecayproductsof a glueball
  • Let‘sfocus on K+K-, becausethisisthefavoreddecayprocess

(shownby M.S. Chanowitz, „chiralsuppressionofscalar-Glueballdecay“, Physicalreviewletters, 2005)

kaon detection 16 09 09
Kaondetection (16.09.09)

Drift chamberxyview

Chargedparticles: Usedriftchamber & TOF

B-field in thedriftchamber →

Kaonsfollow a curvedpath →

calculatethemomentumoftheKaon

4

slide5

Kaon detection (16.09.09)

dE/dx

EnergydepositiondE/dx in

thechamber → particleidentification

Kaonsare well distinguishable

fromotherparticles

TOF: mass & velocityofparticle

intermezzo kaons
Intermezzo: Kaons
  • Spin parity 0-, lifetime ~10-8s
  • K+ : K- : K0: :
  • due toweakinteractionthereis a couplingbetween K0K0 . → thephysicalKaonstatesare a mixure!

→ Discovery oftwokindsof neutral Kaons: Kl0 (long-lived, ~10-8s) and Ks0(short-lived, ~10-10s). SubjectofanotherSemimar!

  • But: Kaonsaredecayproductsofotherreactions, too… howcanyouprovethat a measuredKaoncamefrom a glueball?

0

_

conservation of energy momentum
Conservationofenergy & momentum

&

Glueball decays in e.g. Kaons: energy & momentum has to be conserved!

Remember last week:

(in natural units, c=1)

Decay into two Kaons:

Invariant massoftheglueball

Requirementforbeing a glueball !

slide8

Addtionally, must hold.

Advantage: The massof a kaonisvery well

known:

mK= 493,677±0,013 MeV

E andaremeasuredwith an uncertainty.

→ modify E and so thatmKisobtained

Thisiscalledkinematicfitting!

kinematic fitting 3 4

Kinematicfitting §3.4

Idea:useknownpropertiesof a given

processtoimprovethe

measurementsandresolution.

Mathematicalmethod…

until now we know
Untilnowweknow…

• whatarethedecayproductsof a glueball(Kaonsfavored)

• howKaonsaredetected

• underwhichconditionsKaonsare a decayproductofglueball

• Howtoimprovemeasurements & resolution

Kinematicfitting

Invariant massspectrum

we had a glueball
We had a glueball…

What was its mass, witdh, spin, parity?

Apply Partial Wave Analysis (PWA) (widely used in

high energy physics).

Use the fact that

Cross section is measureable.

How does the amplitude look like? Write it as

Legendre Polynomial * weighting factor

Cross section ~ Amplitude²

slide12
PWA

Legendre Polynomial x weighting factor

Partial wave amplitude

Spherical harmonic

Get Alm using the orthogonality relation:

*

Put in measured amplitude

→ Calculate partial wave amplitude Alm

(This is for spin=0. Spin ≠0 is more complicated)

glueball spin
Glueball spin

Θisthedecay

angle w.r.t. the

reconstructed

momentumof

theglueball

Spin 0: nofavoreddirection after decay

→ uniform angular distribution,

flat spectrum

Spin ≠ 0 : favoreddirection after decay

→ no uniform angular distribution,

noflat spectrum

Learnaboutthespinofyourglueball

Diagrams: „Physicsat BES-III“, Kuang-Ta Chao andYifang Wang, 2008, §3.5.5

what about parity
What about parity?
  • Glueballscanhave all statesindicated in themassspectrum
  • Kaons: 0-
  • Thereare JPCstates, whichsupressdecayinto KK

→ Can youimaginewhy?

Conservationofcharge/parityviolated

scalar glueball candidates
Scalar Glueball candidates
  • f0(1370)
  • f0(1500)
  • f0(1710)

Note:

There are also vector- and tensor- glueballs, and

pseudoscalar glueballs. Too much for today!

glueball f 0 1370
Glueball f0(1370)

f0(980)

3 particlesmeasured: φ, π+ , π-

f0(980) candidateformultiquark

ormoleculestates

(Chapter 11, Physicsof soft Pions)

f0(1790) discussedlater

f0(1370)

f0(1790)

glueball f 0 13701
Glueball f0(1370)

f0(980)

Figure: broadenhancementaround f0(1370)

BES II: strong f0(1370) signalfor J/ψ → π+π-

Nosignificant f0(1370) signalfor J/ψ → K+ K-

MassM=1350±50MeV

Width Γ = 265±40MeV

f0(1370)

f0(1790)

PWA: peakaround 1370MeV comesfrom

a dominant f0(1370) termthatinterferes

with an f2(1270) and a smaller f0(1500)

glueball f 0 1500
Glueball f0(1500)

f2(1270)

background

f0(1500) observed in many

experiments,

Interpreted as non- state

Strong f2(1270) signal

Shoulder at ~1.45 GeV

Enhancement at ~1.7GeV

Peak at ~2.1GeV

Shaded area: background

~1.7GeV

~1.45GeV

~2.1GeV

J/ψ→γπ+π-

glueball f 0 15001
Glueball f0(1500)

f2(1270),

  • PWA: background flat, peaksareleftover

Two 0+ states in the 1.45GeV & 1.75GeV

massregions

In contrastto f2(1270), the f0(1500) is not directlyobserved in certainproductionchannelsof J/ψhadronicdecays(f0(1500) has a larger branchingratiotoππ

than KK)

→ but existanceof a 0++ scalarat 1.5GeV issuggestedforotherproductionchannelswith a larger branchingratioto KK thantoππ

J/ψ→γπ+π-

f0(1500):

M = 1466±6±20 MeV

→ future: searchfor f0(1500) in moredecaymodes & studyingitsspin-parity

glueball f 0 1710
Glueball f0(1710)
  • f0(1710) main competitor of f0(1500) for the lightest 0+ glueball (large production rate, also in J/ψ decay)
  • Different experiments before BES gave different masses, widths and spin-parities
  • Most experiments give JP= 0+
  • BES-II: M=1738±30MeV; Γ=125±20MeV, JP= 0+
glueball f 0 17101
Glueball f0(1710)

f0(1710)

Pseuodoscalarglueball (not treated

in thislecture)

f2‘(1525)

_

J/ψ→γKK

M(K+K-) (GeV/c²)

Wheredoesthebackgroundcomefrom?

Spectrum: „Physics at BES-III“, Kuang-Ta Chao and Yifang Wang, 2008, §9.3.2

glueball f 0 17102
Glueball f0(1710)

PWA fit projection

Peak at 1765±13MeV

Thisstatemaybethe f0(1710) ,

the f0(1790) or a superposition!

f 0 1790 f 0 1710 1 or 2 states
f0(1790) & f0(1710): 1 or 2 states?

f0(1710)

_

J/ψ→γKK

f0(1790)

left: f0(1790) peak, right: f0(1710) peak. Masseslieclosetogether!

PWA showsthatthesestatesaredistinct

current further research
Current & Further Research
  • 1~2GeV: at least 3 scalarmesons (glueballcandidates) (f0(1370), f0(1500) & f0(1710)) whichareexplored
  • Behaviourhasunexpectedfeatures
  • Questionsariseabout

→ structure

→ decaymechanism

→ glueball (yesorno?)

→ Ifyes: istheglueball pure ormixed?

→ natureofthecandidatesremains a mystery

bes iii
BES-III
  • Large data sample & excellentdetectorperformance will increasethesensitivity
  • Searchforotherhadronstatesispossiblewith BES-III
  • Recently, two additional scalarmesoncandidates (f0(1790)& f0(1810)) werereportedby BES-II → confirmationrequiredbyBES-III
references
References
  • „Physicsat BES-III“, Kuang-Ta Chao andYifang Wang, 2008
  • M.S. Chanowitz, „chiralsuppressionofscalar-Glueballdecay“, Physicalreviewletters, 2005
  • BES-III detectorproperties, G.J. Tambave, lecture 16th sept. 2009