We present new results on charmonium and charmonium-like states from the
BaBar experiment located at the PEP-II asymmetric energy $e^+e^-$ storage ring
at the SLAC National Accelerator Laboratory.Comment: 4 pages, 4 figures, Contributed to the Proceedings of XX
  International Workshop on Deep Inelastic Scattering and related
  Subjects,26-30 March 2012, University of Bon

Fioravanti, Elisa

English

arXiv

We present new results on charmonium and charmonium-like states from the BaBar experiment located at the PEP-II asymmetric energy e+e− collider at the SLAC National Accelerator Laboratory

Fioravanti, E.

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2013-11438-1Colloquia: IFAE 2012IL NUOVO CIMENTO Vol. 36 C, N. 1 Gennaio-Febbraio 2013Charmonium and charmonium-like results from BaBarE. FioravantiINFN, Sezione di Ferrara - Via Saragat 1, 44122 Ferrara, Italyricevuto il 31 Agosto 2012Summary. — We present new results on charmonium and charmonium-like statesfrom the BaBar experiment located at the PEP-II asymmetric energy e+e− colliderat the SLAC National Accelerator Laboratory.PACS 13.66.Bc – Hadron production in e−e+ interactions.PACS 14.40.Lb – Charmed mesons.PACS 14.40.Pq – Heavy quarkonia.PACS 13.25.Gv – Decays of J/ψ, Υ, and other quarkonia.1. – Charmonium spectroscopyThe charmonium spectrum consists of eight narrow states below the open charmthreshold (3.73GeV) and several tens of states above the threshold. Below the thresholdalmost all states are well established. On the other hand, very little is known abovethe threshold, there are several new “Charmonium-like” states that are very difficult toaccommodate in the charmonium spectrum.The B-factories are an ideal place to study charmonium since charmonium states areproduced in four different processes:– B decays, charmonium states of any quantum numbers can be produced– Two photon production: in this process two virtual photons are emitted by thecolliding e+e− pair (e+e− → e+e−γ∗γ∗ → e+e−(cc¯)), charmonium states withJPC = 0±+, 2±+, 4±+, . . . , 3++, 5++ . . . can be produced.– Initial State Radiation (ISR): where a photon is emitted by the incoming electronor positron (e+e− → γcc¯), only states with JPC = 1−− are formed– Double charmonium production: in this process a J/ψ or a ψ(2S) is producedtogether with another charmonium state.c© Societa` Italiana di Fisica 199200 E. FIORAVANTIFig. 1. – The efficiency-corrected invariant-mass distribution for the J/ψω final state. Thevertical dashed line is at the X(3872) mass.2. – Study of the process γγ → J/ψωThe charmonium-like state Y(3940) was first seen by Belle [1] and then confirmed byBaBar [2] in the same B meson decay mode, but with lower mass and smaller widthcompared to the Belle results.In a re-analysis [3] of the BaBar data which used the complete Υ(4S) data sample,the precision of the Y(3940) measurements was improved and evidence for the decayX(3872)→ J/ψω was reported. This confirmed an earlier unpublished Belle claim for theexistence of this decay mode [4]. The latter was based on the behaviour of the invariantπ+π−π0 mass distribution near the X(3872), whereas the BaBar result is obtaineddirectly from a fit the the J/ψω mass distribution.A subsequent paper from Belle [5] reports the observation in γγ → J/ψω of a state,the X(3915), with mass and width values similar to those obtained for the Y(3940) inthe BaBar analysis [2].The BaBar analysis of the process γγ → J/ψω has been performed in order to searchfor the X(3915) and the X(3872) resonances via the decay to J/ψω, using a data sampleof 519 fb−1. Figure 1 presents the reconstructed J/ψω invariant-mass distribution afterall the selection criteria have been applied. We perform an extended maximum-likelihoodfit to the efficiency-corrected spectrum. A large peak at near 3915MeV/c2 is observedwith a significance of 7.6 σ. The measured resonance parameters are m[X(3915)] =(3919.4± 2.2± 1.6)MeV/c2, Γ[X(3915)] = (13± 6± 3)MeV. The measured value of thetwo-photon width times the branching fraction, Γγγ [X(3915)]× B(X(3915)→ J/ψω) is(52 ± 10 ± 3) eV and (10.5 ± 1.9 ± 0.6) eV for the spin hypotheses J = 0 and J = 2,respectively, where the first error is statistical and the second is systematic. In addition,a Bayesian upper limit (UL) at 90% confidence level (CL) is obtained for the X(3872),Γγγ [X(3872)]× B(X(3872)→ J/ψω) < 1.7 eV, assuming J = 2.3. – Study of the process γγ → ηcπ+π−This analysis has been studied for the first time and is performed to search for reso-nances decaying into ηcπ+π−, using a data sample of 474 fb−1. The ηc was reconstructedvia its decay to K0SK+π−, with K0S → π+π−. The signal yield for each X resonance isextracted from a two-dimensional fit to m(K0SK+π−) and m(K0SK+π−π+π−). Figure 2presents the two-dimensional fits around each of the resonances. No significant signal isCHARMONIUM AND CHARMONIUM-LIKE RESULTS FROM BABAR 201Fig. 2. – Distributions of (a,c,e) m(K0SK+π−) and (b,d,f) m(K0SK+π−π+π−) with the fit func-tion overlaid for the fit regions of the (a,b) χc2(1P ), (c,d) ηc(2S), and (e,f) X(3872), X(3915)and χc2(2P ). The vertical dashed lines in (f) indicate the peak mass positions of the X(3872),X(3915) and χc2(2P ).Table I. – Results of the γγ → ηcπ+π− fits. For each resonance X, we show the peak massand width used in the fit; the product of the two-photon partial width Γγγ and the X → ηcππbranching fraction, and the 90% CL upper limits on this product.Resonances MX (MeV/c2) ΓX (MeV) ΓγγB (eV) ULCentral Valueχc2(1P ) 3556.20± 0.09 1.97± 0.11 7.2+5.5−4.4 ± 2.9 15.7ηc(2S) 3638.5± 1.7 13.4± 5.6 65+47−44 ± 18 133X(3872) 3871.57± 0.25 3.0± 2.1 −4.5+7.7−6.7 ± 2.9 11.1X(3915) 3915.0± 3.6 17.0± 10.4 −13+12−12 ± 8 16χc2(2P ) 3927.2± 2.6 24± 6 −16+15−14 ± 6 19observed in any of the fits. Table I summarizes these results. ULs are obtained on thebranching fractions B(ηc(2S)→ ηcπ+π−) < 7.4% and B(χc2(1P )→ ηcπ+π−) < 2.2% at90% CL.4. – Search for the Z1(4050)+ and Z2(4250)+Belle reported the observation of two resonance-like structures, Z1(4050)+ andZ2(4250)+ in the study of B¯0 → χc1K−π+, both decaying to χc1π+ [6].BaBar studied the same final states [7] to search for the Z1(4050)+ and Z2(4250)+decay into χc1π+ in B¯0 → χc1K−π+ and B+ → K0Sχc1π+ (this mode is analyzedfor the first time) where χc1 → J/ψγ, using a data sample of 429 fb−1. The χc1π+mass distribution, background-subtracted and efficiency-corrected, was modeled using202 E. FIORAVANTIFig. 3. – Fit to the background-subtracted and efficiency-corrected χc1π mass distributions. Seetext for more details.the Kπ mass distribution and the corresponding normalized Kπ Legendre polynomialmoments. Figure 3 shows the results of the fits to the χc1π+ mass spectrum. Thefit shown in fig. 3(a) includes both Z1(4050)+ and Z2(4250)+ resonances and the fitshown in fig. 3(b) includes a single broad Z(4150)+ resonance. Figures 3(c,d) showthe χc1π mass spectrum fitted in the Dalitz plot region 1.0 ≤ m2(Kπ) < 1.75GeV2/c4in order to make a direct comparison to the Belle results [6] (this region is labeled as“window” in table II). The results of the fits are summarized in table II and in everycase the yield significance does not exceed 2σ. The ULs on the 90% CL on the branchingfractions are: B(B¯0 → Z1(4050)+K−)× B(Z1(4050)+ → χc1π+) < 1.8× 10−5; B(B¯0 →Z2(4250)+K−)×B(Z2(4250)+ → χc1π+) < 4.0× 10−5 and B(B¯0 → Z+K−)×B(Z+ →χc1π+) < 4.7× 10−5.Table II. – Results of the χc1π fits. Nσ and Fraction give, for each fit, the significance and thefractional contribution of the Z resonances.Data Resonances Nσ Fraction (%) χ2/NDFa) Total Z1(4050)+ 1.1 1.6± 1.4 57/57Z2(4250)+ 2.0 4.8± 2.4b) Total Z(4150)+ 1.1 4.0± 3.8 61/58a) Window Z1(4050)+ 1.2 3.5± 3.0 53/46Z2(4250)+ 1.3 6.7± 5.1b) Window Z(4150)+ 1.7 1.37± 8.0 53/47CHARMONIUM AND CHARMONIUM-LIKE RESULTS FROM BABAR 203Fig. 4. – (a) The fit to the J/ψπ+π− invariant-mass distribution. (b) The fit to the dipioninvariant-mass distribution from the Y(4260) signal region.5. – Study of the J/ψπ+π− system via initial state radiation (ISR)The Y(4260) charmonium-like resonance was discovered by BaBar [8] in ISR pro-duction of J/ψπ+π−. A subsequent Belle analysis [9] of the same final state suggestedalso the existence of an additional resonance around 4.1GeV/c2 that they dubbed theY(4008).The BaBar analysis of the J/ψπ+π− system produced in ISR has been repeatedusing a data sample of 454 fb−1 [10].The J/ψπ+π− mass region below ∼ 4GeV/c2 is investigated for the first time. Inthat region an excess of events has been observed and the conclusion, after a detailedstudy of the ψ(2S) lineshape (to estimate the ψ(2S) tail contribution to that region),is that it is not possible to discount the possibility of a contribution from a J/ψπ+π−continuum cross section in this region. From this study we obtain the cross sectionvalue 14.05 ± 0.26 (stat) pb for radiative return to the ψ(2S) and a measurement ofthe width Γ(ψ(2S) → e+e−) = 2.31 ± 0.05(stat) keV. Figure 4(a) shows the fit tothe J/ψπ+π− distribution. A clear signal of the Y(4260) is observed for which thevalues obtained are m[Y (4260)] = 4244 ± 5 ± 4MeV/c2, Γ[Y (4260)] = 114+16−15 ± 7MeVand Γee × B(J/ψπ+π−) = 9.2 ± 0.8(stat) ± 0.7(syst) eV. No evidence for the stateat ∼ 4GeV/c2 reported by Belle [9] was seen. A study of the π+π− system from theY (4260) decay to J/ψπ+π− has been performed. The dipion system is in a predominantlyS-wave state. The mass distribution exhibits an f0(980) signal, for which a simple modelindicates a branching ratio with respect to J/ψπ+π− of 0.17± 0.13(stat). The fit to thedipion invariant-mass distribution is shown in fig. 4(b).REFERENCES[1] Choi S.-K. et al. (Belle Collaboration), Phys. Rev. Lett., 94 (2005) 182002.[2] Aubert B. et al. (BaBar Collaboration), Phys. Rev. Lett., 101 (2008) 082001.[3] del Amo Sanchez P. et al. (BaBar Collaboration), Phys. Rev. D., 82 (2010)011101(R).[4] Belle Collaboration, hep-ex/0505037.[5] Uehara S. et al. (Belle Collaboration), Phys. Rev. Lett., 104 (2010) 092001.[6] Mizuk R. et al. (Belle Collaboration), Phys. Rev. D, 78 (2008) 072004.[7] Lees J. P. et al. (BaBar Collaboration), Phys. Rev. D, 85 (2012) 052003.[8] Aubert B. et al. (BaBar Collaboration), Phys. Rev. Lett., 95 (2005) 142001.[9] Yuan C. Z. et al. (Belle Collaboration), Phys. Rev. Lett., 99 (2007) 182004.[10] BaBar Collaboration, hep-ex/1204.2158v1.

Charmonium and charmonium-like results from BaBar

Charmonium and charmonium-like states are a unique system for studying QCD and possibly exotic bound states. We present new results on such states, which are created in two-photon fusion or in electron-positron collisions and decaying into a variety of final states, including psi pi pi, eta_c pi pi, and J/psi omega

FIORAVANTI, Elisa

Archivio istituzionale della ricerca - Università di Ferrara

http://eprints.bice.rm.cnr.it/18094/1/ncc10396.pdf

Charmonium and charmonium-like results from Babar

Abstract

Similar works

Full text

Available Versions

Scientific Open-access Literature Archive and Repository

Archivio istituzionale della ricerca - Università di Ferrara

Archivio istituzionale della ricerca - Università di Ferrara