1. Changyi Zhou (McGill University )
on behalf of
ZEUS Collaboration
February 26, 2008

2. ECT *– Trento, February 25-29, 2008
Outline
Analysis motivations
Previous publication and results
Experimental setup and observation principle
Data sample selection and K0s mass distribution
K0sK0s spectra with interference fits
Non-interference function
Interference function
Summary and conclusion
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

3. ECT *– Trento, February 25-29, 2008
Motivations
The Standard Model explains the existence of hadrons well.
The Standard Model allows for the existence of particles made by gluons.
A gluon carries both a color and an anti-color.
Either two or three gluons may confine together as color singlet GLUEBALLs
Examples of glueballs
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

4. ECT *– Trento, February 25-29, 2008
Motivations (Cont.)
The K0sK0s system is expected to couple to scalar and tensor glueballs
K0s: has S=0, P=-1, C=+1
K0sK0s : has P=+1, C=+1  J = even
Question: What is the mixing fraction
of mesons and glueballs?
Hybrid? Tetraquarks? Flavor octet states?
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

5. ECT *– Trento, February 25-29, 2008
Motivations (Cont.)
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

6. ECT *– Trento, February 25-29, 2008
Previous Publication
“K0sK0s Final State in two photon collisions and implications for glueballs” (L3) Published in Phys.Lett.B501: ,2001 (hep-ex/ )
~4σ for fJ(1710)
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

7. ECT *– Trento, February 25-29, 2008
HERA
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

8. ECT *– Trento, February 25-29, 2008
HERA and ZEUS
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

9. ECT *– Trento, February 25-29, 2008
Tracking Detector
Central Tracking Detector (CTD)
official coordinate resolution ~160 m e p
Micro-Vertex Detector (MVD)
25-35 m resolution for vertical incidence
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

10. K0sK0s states observation principles
pk1 π+
Collinearity Angle
pπ-
Pri. Vtx
K0s π-
Sec. Vtx IP
pπ+ π+
K0s
Decay Length
pk2
pπ-
Two V0 candidates π-

11. DATA Sample and Event Selection
Luminosity
HERAI
HERAII
Total
121.6 pb-1
pb-1
≈ 0.5 fb-1
Tracking Quality Cuts
Pт(pion) (GeV)
> 0.14
η(pion)
(-1.75,1.75)
K0s Selection Cuts
Pт(kaon) (GeV)
> 0.25
η(kaon)
(-1.6,1.6)
Decay Length (cm)
(0,30)
Collinearity(2D)
< 0.12
Inv_ππ (GeV)
(0.4806,0.515)
The data sample is dominated by 90% photoproduction, while 10% is Deep Inelastic Scattering
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

12. ECT *– Trento, February 25-29, 2008
K0s mass distribution
Full sample contains:
K0s  K0sK0s
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

13. ECT *– Trento, February 25-29, 2008
Fitting functions
Modified Relativistic Breit-Wigner (MRBW) function:
Ci is the amplitude of the resonance
m*,i is the mass of resonance
Гd,i is the effective resonance width
M is the K0sK0s invariant mass
Background function:
A, B, C are free parameters
mK0s is the K0s mass from PDG
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

14. Fitting using Breit-Wigner with no interference
The structure around 1270 region is due to the destructive interference between f2(1270) and a2(1320)
JPC= 0++
JPC=
The dip between f2(1270)/a2(1320) and f2(1525) is due to the constructive interference between the states.
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

15. Fitting using Breit-Wigner with interference
No interference fit
Interference fit
WA102
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

16. Fitting using Breit-Wigner with interference
Coherent States
f2(1270)
a2(1320)
f2(1525)
Isospin I = 1
Quark Content
Charge Factor
Amplitude ratio
5 BW
-3 BW
2 BW
Function = a {5 * BW_f2(1270) – 3 * BW_a2(1320) + 2 * BW_f2(1525)}2
+ b {BW_f0(1710)}2
+ c Background U(M)
a b c are free parameters
BW is Relativistic Breit-Wigner function:
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

17. Fitting using Breit-Wigner with interference
Destructive interference
Х2/ndf = 86/110
Improved fitting in 1270 and 1420 region, where destructive and constructive interference are well described.
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

18. ECT *– Trento, February 25-29, 2008
Summary
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008

19. ECT *– Trento, February 25-29, 2008
Conclusion
Inclusive ep → K0s K0sX decay production was studied with all ZEUS statistics (0.5 fb-1)
Clear evidence for f’2(1525) and f0(1710) resonance state with large statistical significance
Very competitive measurements on peak position and width for f’2(1525) and f0(1710) are done with interference fit and compared well with the PDG values
End
C. Zhou (McGill Univ.)
ECT *– Trento, February 25-29, 2008