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Study of the Glueball Candidate Fj(2220) at CLEO

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Study of the Glueball Candidate Fj(2220) at CLEO PROCEEDINGS SUPPLEMENTS ELSEVIER Nuclear Physics B (Proc. Suppl.) 82 (2000) 33%343 www.dsevier.ni/locate/npe Study of the glueball candidate fJ(2220) at CLEO Hans P. Paar a aPhysics Department 0319, University of California San Diego, 9500 Gilman Drive, La Jolla CA 92093-0319. (e-mail address: [email protected]) The CLEO detector at the Cornell e+e - storage ring CESR was used to search for the two-photon production of the glueball candidate fJ(2220) in its decay to K~K~ and 7r+Tr-. I present restrictive upper limits on the product of the two-photon width and the respective branching fraction [F77BK~K~]fj(2220 ) < 1.3 eV, 95% CL and [FT~BTr+Tr-]fj(2220) < 2.beV, 95% CL. When these two limits are combined to calculate a lower limit on the Stickiness, a measure of the two-gluon coupling relative to the two-photon coupling, a lower limit SFJ(2220) > 102, 95% CL is found. A new measure of this ratio of couplings is the Gluiness; a combined lower limit of Gfj(2220) > 66, 95% CL is found. These limits on the Stickiness and the Gluiness indicate that the fJ(2220) is likely to have substantial neutral patton or glueball content. 1. INTRODUCTION while spin 0 is unlikely [7]. QCD predicts (using lattice calculations) that a tensor glueball exists The unequivocal demonstration that glueballs and that it should have a mass near 2.2 GeV [8]. exist would prove the existence of a new form A pure glueball will couple to photons only of matter. In this report I describe investiga- through its sea quarks. Therefore its two-photon tions [1-3] into the nature of the glueball candi- coupling is expected to be weak. The absence of date fj (2220). two-photon production of the fj (2220) would thus The fj (2220) was discovered in radiative J/¢ be a strong indication of a glueball nature of the decay [4] by the Mark III Collaboration at PEP fj (2220). A search for the two-photon production in the early 80's. Although the fJ(2220) has since of the fj (2220), decaying into K~K~ or 7r+Tr- was been observed in hadronic collisions[5], its pro- performed using the CLEO detector at the Cot- duction in radiative J/g, decay has only recently nell e+e - storage ring CESR. Below I describe been confirmed by the BES Collaboration who the detector and event simulation in Sec. 2, the have observed [6] the fJ(2220) in radiative J/¢ analysis procedures and results for the K~K~ and decay in four decay channels Qr+Tr-, p~, K+K -, 7r+Tr- final states in Sec. 3 and Sec. 4 respectively, and K~K~). The production in glue-rich radiative and the interpretation in Sec. 5. J/¢ decay, its narrow total width, and its flavor independent coupling (as evidenced by its simi- lar branching fraction for final states that con- 2. DETECTOR AND tain non-strange or strange particles [6]) make the EVENT SIMULATION fj (2220) a promising candidate for a glueball. Be- cause the fj (2220) is not near a q~ meson and is The CLEO detector[9] is a general pur- narrow, it is not expected to mix with q~ states pose detector that provides charged particle and might therefore even be a candidate for a tracking, precision electromagnetic calorimetry, pure glueball (a hadron in which a/l valence par- charged particle identification, and muon detec- tons are gluons). The experiments favor a spin 2 tion. Charged particle detection over 95% of the assignment to the fj (2220) but spin 4 is possible solid angle is provided by three concentric wire chambers in a magnetic field of 1.5 T giving a mo- 0920-5632/00/$ - see front matter © 2000 Elsevier Science B.'V: All rights reserved. PII S0920-5632(00)00175-4 338 H.P Paar/Nuclear Physics B (Proc. Suppl.) 82 (2000) 337-343 mentum resolution ap/p = 0.5% at p = 1 GeV. and 2. There is a strong enhancement near the The driftchambers are surrounded by a time of ( m Kso,m Kso ) point. The m~r+7r_ mass resolution flight system and a CsI based electromagnetic near the K so mass is 3.3MeV. KsKo so events are calorimeter giving an energy resolution aE/E = selected by requiring both pion-pair masses to be 4% for 100 MeV electromagnetic showers. A su- within a circle of radius 10 MeV centered on the perconducting coil and muon detectors surround ( m~co"~s , mvo,,s) point and their K~K~ pair mass is the calorimeter. Three redundant triggers pro- formed. Fig. 2 shows the K~K~ pair mass distri- vide efficient registration of two- and four-prong bution. It has a significant f'2(1525) signal but no events. The CESR ring operates at a center-of- visible fj (2220) signal. mass energy of approximately 10.6 GeV. The re- The mass region near the fj (2220) is shown in sults in this paper are based upon 3.0 fb -1 of data detail in Fig. 3. In the absence of a signal, an up- for the K~K~ final state and 4.8fb -1 of data for per limit is set as follows. The background is fit- the 7r+Tr- final state. ted with a linear function from 2.05 to 2.35 GeV, The event simulation uses uses the BGMS [10] excluding a safely large +40 MeV region centered formalism for the event generation and GEANT on 2234 MeV. This gives an average background for the detector simulation down to the detec- of 1.8 ± 0.3 events per 10MeV. The signal re- tor component level. The trigger simulation and gion is determined by maximizing the ratio c 2/B the event reconstruction use this information to where ~ is the fraction of the signal and B the ex- determine the detector response. Photon form- pected number of background events within that factors based upon vector-meson dominance with region. This leads to a signal region of ±18 MeV a mass my = 768.5 MeV are used. The spin of the (centered on 2234 MeV) with c = 70%. fj (2220) is taken to be 2. Mass and width of the There are four events within the signal re- fj (2220) were obtained by averaging MarkIII [4] gion while the background is estimated to be 6.5 and BES [6] results: mfj (2220) = 2234 ± 6 MeV events. The standard PDG technique [7] for ex- and Ffj(2220) = 19 ± llMeV. A Breit-Wigner tracting an upper limit gives 4.9 events, 95% CL. line shape was used. The simulated data are pro- The curve in Fig. 3 is the sum of the background cessed through the same event reconstruction and and a signal of 4.9 events. From the simulation, analysis procedures as the real data. The trigger the detection efficiency is found to be 7.0% for simulation uses the raw data to determine which spin 2, helicity 0 and 15% for spin 2, helicity 2. triggers, if any, fired for a given event. With the ratio F~.r 2'2 : F.r.r 2'0 = 6 : 1 [11] an up- per limit 3. THE KsKo so FINAL STATE [F~.r BK~K~]fj(2220 ) < 1.3eV, 95%CL (1) The event selection required events to have ex- results. The upper limit can be specified without actly four tracks whose sum of charges is zero, to the assumption of a 6:1 ratio for helicity 2 and 0 have an event energy less than 6.0 GeV, to have as (0.52r~.r 2,° + 1.08F~.r2'2)BK~K~ < 1.3eV at the transverse component of the vector sum of 95% CL. the tracks to be less than 0.2 GeV, and to sat- When the mass and the width of the f3 (2220) isfy at least one of the three triggers. Events axe varied by 6 and llMeV respectively (one are required to have 7r+Tr- pairs whose vertices standard deviation), the upper limit ranges from have a separation in the plane perpendicular to 1.2 to 1.8 eV. The upper limit includes the effects the beam of at least 5 mm. The momenta of the of systematic uncertainties in the trigger (8%), four tracks at their respective vertices are used the tracking (7%), the event selection (7%), and to calculate two pion-pair masses [m~r+~r-]l and the background subtraction (16%). Other sources [m~r+~r- L. A legoplot of the pion-pair masses of systematic uncertainties, such as the photon is shown in Fig. 1. There are two entries per form-factor used in the simulation, are negligi- event corresponding to the exchange of labels 1 ble. Because of its similarity to the fJ(2220), the H.P Paar/Nuclear Physics B (Proc. Suppl,) 82 (2000) 337-343 339 3010'2sr/-00t .... J .... I .... ] .... E .... 40 > :i OT- 30 .... " ...... ! ¢ :>O LU 20 .... 10- """ ...... " o 2.1o 2.15 2.20 2.25 2.30 2.35 O" InKs KS (GeV) o' 'tS-' llUm .... o.5o~'~ • 0.523 + - 0.493 m ('n'+Tr-)2 0"49~.4'03~ • 493 5 0.473 rn (~-+,~-), Figure 3. K~K~ pair mass distribution near the mass of the fJ(2220). The arrows indicate the signal region. The solid line is the sum of a fit to the background and a signal that corresponds to Figure 1. [mTr+~r-], versus [m +7i_]2. Each the 95% CL upper-limit of 4.9 events• event has two entries corresponding to ex- change of the labels 1 and 2.
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