1. Cascade Physics and Meson Decays in GlueX
Aleksandr Starostin
Bernard Nefkens
UCLA

2. A.Starostin, New GlueX Proposals
Outline
Cascades in GlueX
Motivation
Cascade Photoproduction
Detector Requirements
Physics of Meson Decays
Summary
January 29, 2009
A.Starostin, New GlueX Proposals

3. Cascades: Physics Motivation
Review of Cascade physics:
Workshop “Cascade Physics: A New Window on Baryon Spectroscopy”, December 1-3, 2005, JLab
Presentations available at
January 29, 2009
A.Starostin, New GlueX Proposals

4. Summary of Physics with Cascades
Spectroscopy of cascade exited states including search for parity doubles (requires JP)
d-u quark mass difference (m(Ξ-)-m(Ξ0) ~ 6.5 MeV, requires good energy resolution)
Search for exotic states: Ξ+ and Ξ--
January 29, 2009
A.Starostin, New GlueX Proposals

5. What is known about cascades?
Ξ0 = uss, Ξ-= dss
Only 11 Ξ*; 6 “well-established”
Those we know aren't known well: only have JP for three states and a guess of a fourth
SU(3) symmetry requires one Ξ I=1/2 per octet and per decuplet:
n(Ξ*)=n(N*) +n(Δ*)
Adamovich et al., EPJ C5, 621
Hemingway et al., PLB 68, 197
January 29, 2009
A.Starostin, New GlueX Proposals

6. A.Starostin, New GlueX Proposals
Cascades in the Constituent Quark Model
S.Capstick and N.Isgur
Most of the exited Ξ* states are narrow ( MeV): the decay mode Ξ*->Ξπ is suppressed (relative to N*->Nπ and Δ*->Δπ)
Phase-space factor
Flavor overlap factor
January 29, 2009
A.Starostin, New GlueX Proposals

7. A.Starostin, New GlueX Proposals
Width of the Cascades
N* and Δ* resonances overlap, because of that spectroscopy N* and Δ* requires complicated and ambiguous phase-sift analysis
Cascades are expected to be narrow, parameters of the cascades can be extracted directly from the mass spectra
January 29, 2009
A.Starostin, New GlueX Proposals

8. Search for parity doublets
1/2
3/2
5/2
7/2
9/2 - + N*
1650
( )
1710
( )
1700
( )
1720
( )
1675
( )
1680
( )
2250
( )
2220
( )
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A.Starostin, New GlueX Proposals

9. Search for parity doublets
The high-mass light baryon spectrum exhibits occurrence of parity doublets. Glozman suggested to explain the mass degeneracy by assuming that chiral symmetry is restored in highly excited hadronic states.
L.Y. Glozman, PL B 475, 329 (2000)
T.D. Cohen and L.Y. Glozman PR D 65, (2001)
R.L. Jaffe et al. Phys. Rep. 435, 157 (2006)
M. Shifman and A. Vainshtein PR D 77, (2008)
“Evidence for a Parity Doublet Δ(1920)P33 and Δ(1940)D33
from γp->pπ0η”
I.Horn et al., PRL 101, (2008)
January 29, 2009
A.Starostin, New GlueX Proposals

10. A.Starostin, New GlueX Proposals
Quark mass difference
Quark masses are parameters of the Standard Model
Cascades may provide d-u mass difference
The difference can be determined for all for exited of Ξ- and Ξ0 states
January 29, 2009
A.Starostin, New GlueX Proposals

11. Search for exotic Ξ+ and Ξ--
Finding Ξ+ and/or Ξ-- would be a unique signature for a five-quark state, member of the antidecupled
Evidences for existance of Ξ–- were found by CERN NA49 (PRL, 92, (2004))
Search was also conducted by CLAS
January 29, 2009
A.Starostin, New GlueX Proposals

12. Photoproduction of cascades
Cascades in CLAS g11 run
Number of events for the ground state – 7678, for the first exited state – 658
for most of the run the maximum energy of tagged photons 3.8 GeV, some data with 4.8 GeV (the threshold is about 2.85 GeV)
Estimates for the γp -> 2K+Ξ- total cross section by Denis Weygand – between 3.5 GeV and 4.8 GeV cross section is flat, order of 10 nb.
L. Guo et al. PRC 76, (2008)
January 29, 2009
A.Starostin, New GlueX Proposals

13. Detector requirements
Very good K/π separation
There are two detached vertices – high resolution tracking device is essential
For neutral cascades – high acceptance EM calorimeter
Hall-D: tagged photons with energies close to 12 GeV
GlueX: coverage close to 4π in particular for EM
January 29, 2009
A.Starostin, New GlueX Proposals

14. Decays of Light Mesons

15. Physics of Meson Decays
JP = 0- : π0, η, η’(958)
Jp = 1- : ρ(770), ω(782), ψ(1020)
Tests of Chiral perturbation theory and other theories of strong interactions
Measurements of electromagnetic form factors
Search for violation of discrete symmetries: C, P, CP, and T
Search for leptoquark and violation of lepton family number,
Most of the decays do not require a dedicated experiment
January 29, 2009
A.Starostin, New GlueX Proposals

16. A.Starostin, New GlueX Proposals
Tests of ChPT
η->π0π0π0
η->π+π-π0
η’->ηπ0π0
η’->ηπ+π-
Dalitz plot allows to study ππ and ηπ interactions, slop parameters of the Dalitz plot,
“cusp” at the opening of π0π0->π+π- (carries information on the a0-a2 ππ scattering length)
January 29, 2009
A.Starostin, New GlueX Proposals

17. Dalitz and double Dalitz decays
η->l+l-γ
η->l+l-l+l-
ω->l+l-π0
η’->l+l-γ
η’->l+l-l+l-
Spectrum of the l+l- mass in the Dalitz carries information on the EM form-factor of the decay vertex
January 29, 2009
A.Starostin, New GlueX Proposals

18. A.Starostin, New GlueX Proposals
Tests of C
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A.Starostin, New GlueX Proposals

19. A.Starostin, New GlueX Proposals
More decays
Tests of P invariance: η->2π, η’->2π, η->4π, η’->4π
Search for leptoquaks: η->μ+μ-, η->e+e-
Search for violation of Lepton Family number: η->μe, η’->μe, etc
Tests of T invariance: absence of the transverse polarization of μ in η->γμ+μ-
January 29, 2009
A.Starostin, New GlueX Proposals

20. Branching Ratio of η->e+e- and existence of the leptoquark
Leptoquark – a hypothetical particle suggested by A. Salam, carries interaction between quarks and leptons, encountered in various extensions of the Standard Model, such as technicolor theories or GUTs
η->e+e-
The single-photon exchange mechanism is forbidden because of conservation of angular momentum
The decay is dominated by a two-photon intermediate state which is suppressed
Provides lower limits of the masses of leptoquarks and axions.
D.Wyler, in proc. inter. workshop. “Rare decays of light mesons”, Gif-sur-Yvatte, France March 29-30, 1990.
January 29, 2009
A.Starostin, New GlueX Proposals

21. A.Starostin, New GlueX Proposals
Summary
Universality and resolution of the GlueX detector combined with 12GeV tagged photon beam makes cascade program in Hall-D feasible. Both, charged and neutral cascades will be detected using missing mass and invariant mass
The objectives of the cascade program will be to establish spectrum of the exited states and their spin-parity. These data can be used to establish the existence of the cascade parity doublets, calculate d-u quark mass difference and search for the exotic cascade states
Both neutral and charged decays of light mesons can be detected in GlueX. This data sample will be used to test Chiral Perturbation Theory and other theories of strong interactions, search for violation discrete symmetries, and more.
January 29, 2009
A.Starostin, New GlueX Proposals

22. A.Starostin, New GlueX Proposals
January 29, 2009
A.Starostin, New GlueX Proposals

23. Predictions of the Cascade spectrum
Many quark models, 1/Nc expansions of QCD, etc. predict spectrum of exited baryon states
Predicted is a rich spectrum of exited states (the constituent quark model by S.Capstick and N.Isgur predicts 45 states below 2.3 GeV, the algebraic model by F.Iachello predicts 32 states)
The constituent quark model and the algebraic model predict the most of the cascade states to be narrow
Lattice QCD calculations?
January 29, 2009
A.Starostin, New GlueX Proposals

24. A.Starostin, New GlueX Proposals
Tests P
January 29, 2009
A.Starostin, New GlueX Proposals

25. What is known about cascades?
Ξ0 = uss, Ξ+= dss
SU(3) symmetry requires one Ξ I=1/2 per octet and per decuplet
Gell-Mann-Okubo mass relation
in octet:
Equal spacing mass relation in
decuplet:
January 29, 2009
A.Starostin, New GlueX Proposals

26. Dalitz and double Dalitz decays
Invariant mass of l+l- in the Dalitz and double Dalitz decays: η->l+l-γ, η->l+l-l+l-, ω->l+l-π0, η’->l+l-γ, η’->l+l-l+l- carries information on the EM form-factor of the decay vertex
January 29, 2009
A.Starostin, New GlueX Proposals

27. Cascades in 1/Nc expansion
70-plet:
7 masses in range MeV
Two pairs of same J states nearly degenerate
L=2 56-plet:
6 masses in range MeV
Same J states separated by >140 MeV
Larger errors in predictions than in 70-plet
Parameter free mass relations rather well tested.
Presented by J L Goity
January 29, 2009
A.Starostin, New GlueX Proposals

28. Search for “Cascaderium”
NN scattering length a =-17.3 fm.
If ΞΞ 1S0 potential is same as for NN:
predicted a BOUND STATE:
dibaryon S=-4
decays weakly to ΞΛπ->NN4π
ΞΞ binding predicted by many potential models
γd -> 2K+ 2K0 [Ξ0 Ξ-]
γα -> 2K+ 2K0 [Ξ0 Ξ-] n p
Neutral cascades are preferred to avoid repulsion
(J.Miller, Cascade workshop)
Figure by R.Jones
January 29, 2009
A.Starostin, New GlueX Proposals

29. Test of Time reversal invariance
January 29, 2009
A.Starostin, New GlueX Proposals

30. Search for exotic Ξ+ and Ξ--
Ξ+ and Ξ–- are unique signatures for a five-quark state, member of the antidecupled
Evidences for existance of Ξ–- were found by CERN NA49 (PRL, 92, (2004))
Search was also conducted by CLAS (run g12?)
January 29, 2009
A.Starostin, New GlueX Proposals

31. Cascades in quark models
45 cascades states with masses below 2.3 GeV
S.Capstick and N. Isgur PRD (1986)
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A.Starostin, New GlueX Proposals

32. Cascades in agebraic model
A.R. Bijker, F.Iachello, and A. Leviatan
Ann. Phys (2000)
January 29, 2009
A.Starostin, New GlueX Proposals