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

Outline

      Analysis motivations Previous publication and results Experimental setup and observation principle Data sample selection and K distribution K   0 s K 0 s 0 s mass spectra with interference fits Non-interference function Interference function Summary and conclusion C. Zhou (McGill Univ.) ECT *– Trento, February 25-29, 2008 2

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 C. Zhou (McGill Univ.) ECT *– Trento, February 25-29, 2008 Examples of glueballs 3

Motivations (Cont.)

 The K K 0 s 0 s K 0 s system is expected to couple to scalar and tensor glueballs : has S=0, P=-1, C=+1 K 0 s K 0 s : 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 4

Motivations (Cont.)

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



Previous Publication

“K0sK0s Final State in two photon collisions and implications for glueballs” (L3)

Published in

Phys.Lett.B501:173-182,2001 ( hep-ex/0010037)

~4 σ for f J (1710) C. Zhou (McGill Univ.) ECT *– Trento, February 25-29, 2008 6

HERA

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

HERA and ZEUS

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

Tracking Detector

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

K

0 s

K

0 s

states observation principles

IP Pri. Vtx p π + π + K 0 s Collinearity Angle K 0 s Sec. Vtx π + π p π + p π p k1 π p π p k2 Two V0 candidates

DATA Sample and Event Selection

HERAI

121.6 pb -1 Luminosity

HERAII

401.68 pb -1

Total

Tracking Quality Cuts

P т(pion) (GeV) > 0.14

η(pion) (-1.75,1.75)

K 0 s Selection Cuts

P т(kaon) (GeV) η(kaon) Decay Length (cm) Collinearity(2D) Inv_ ππ (GeV) > 0.25

(-1.6,1.6) (0,30) < 0.12

(0.4806,0.515) C. Zhou (McGill Univ.) ECT *– Trento, February 25-29, 2008 The data sample is dominated by 90% photoproduction, while 10% is Deep Inelastic Scattering 11

K

0 s

mass distribution

Full sample contains: 1300509 K 0 s  672418 K 0 s K 0 s C. Zhou (McGill Univ.) ECT *– Trento, February 25-29, 2008 12

Fitting functions

 Modified Relativistic Breit-Wigner (MRBW) function:  Background function: • • • • C i is the amplitude of the resonance m *,i Г d,i is the mass of resonance is the effective resonance width M is the K 0 s K 0 s invariant mass C. Zhou (McGill Univ.) • A, B, C are free parameters • m K0s is the K 0 s mass from PDG ECT *– Trento, February 25-29, 2008 13

Fitting using Breit-Wigner with no interference

J PC = 0 ++ J PC = 2 ++ 2 ++ 2 ++

The structure around 1270 region is due to the destructive interference between f 2 (1270) and a 2 (1320) The dip between f 2 (1270)/a 2 (1320) and f 2 (1525) is due to the constructive interference between the states. C. Zhou (McGill Univ.) ECT *– Trento, February 25-29, 2008 14

Fitting using Breit-Wigner with interference

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

Fitting using Breit-Wigner with interference

Isospin I = Quark Content Charge Factor Amplitude ratio f 2 (1270) 0 (

u u



d d

) / ( 2 3  2 3  1 3  1 3 ) 1 2 2 5 BW

Coherent States

a 2 (1320) 1 (

u u



d d

) / 2 ( 2 3  2 3  1 3  1 3 ) 1 2

-

3 BW f 2 (1525) 0

s s

1 3  1 3 2 BW Function = a {5 * BW_f 2 (1270)

–

+ b {BW_f 0 (1710)} 2 + c Background U(M) 3 * BW_a 2 (1320) + 2 * BW_f 2 (1525)} 2 a b c are free parameters BW is Relativistic Breit-Wigner function: C. Zhou (McGill Univ.) ECT *– Trento, February 25-29, 2008 16

Fitting using Breit-Wigner with interference

Destructive interference C. Zhou (McGill Univ.) ECT *– Trento, February 25-29, 2008 Х 2 /ndf = 86/110 Improved fitting in 1270 and 1420 region, where destructive and constructive interference are well described.

17

Summary

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

Conclusion

   Inclusive

ep → K 0 s K 0 s X

decay production was studied with all ZEUS statistics (0.5 fb -1 ) Clear evidence for f’ 2 (1525) and f 0 (1710) resonance state with large statistical significance Very competitive measurements on peak position and width for f’ 2 (1525) and f 0 (1710) are done with interference fit and compared well with the PDG values C. Zhou (McGill Univ.) ECT *– Trento, February 25-29, 2008 19