University of Hawaii Colloquium Discovery of the Z c (3900)

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1 University of Hawaii Colloquium Discovery of the Z c (3900) Frederick A. Harris May 9, /11/2014 1

2 OUTLINE Introduction to charmonium Original era of discovery From discovery to precision: Charmonium states at BESIII η c (1S) η c (2S) h c A new era of discovery beyond the quark model XYZ states Y(4260) Z c (3900) Summary With thanks to Ryan Mitchell IHEP 4/11/2014 2

3 Standard Model Standard Model particles are made of quarks, leptons, and the force carriers. Visible matter. p = uud n = udd π + = ud BEPCII operates in the GeV energy region so it can study the lighter quarks (u, d, c, and s) and the leptons. τ charm factory 4/11/2014 3

4 Introduction to charmonium 4/11/2014 4

5 Introduction to Charmonium Charmonium is one of the simplest bound states in QCD. Like positronium in QED. Classify using J PC. Match to n 2S+1 L J quark model states: J = L + S P = (-1) L+1 C = (-1) L+S J P = ½ + 4/11/2014 5

6 How to predict? Potential Models Introduction to Charmonium 4/11/2014 6

7 Introduction to Charmonium A more fundamental approach: Lattice QCD 4/11/2014 7

8 Original era of discovery 4/11/2014 8

Original Era of Discovery The charm quark was predicted by Glashow, Iliopolis, and Maiani in 1970 in order to explain why there were flavor changing charged currents (K + μ + ν) but no flavor

9 Original Era of Discovery The charm quark was predicted by Glashow, Iliopolis, and Maiani in 1970 in order to explain why there were flavor changing charged currents (K + μ + ν) but no flavor changing neutral currents (K 0 L μ + μ - ). Known as the GIM mechanism. J/ψ Discovery On Nov. 11, 1974, Burt Richter (SLAC) announced the discovery of the ψ and Sam Ting (Brookhaven) announced the discovery of the J. The November Revolution Sam Ting with few hundred J/ s 4/11/2014 9

10 The November Revolution: J/ψ Discovery They received the Nobel Prize in 1976 for their discovery. The J/ψ with a mass of GeV was soon interpreted as being made up of a c and a c-bar quark. The discovery led physicists to finally take quarks seriously. Phys. Rev. Lett. 33, 1406 (1974). 4/11/

11 Original Era of Discovery The Mark I detector at SLAC 4/11/

12 Original Era of Discovery Discovery at SLAC of the Ψ, Ψ(2S), or the Ψ(3668) PRL 33, 1453 (1974). 4/11/

13 Original Era of Discovery Discovery at SLAC of the biggest Ψ(3668) decay mode. PRL 34, 1181 (1975). 4/11/

14 Original Era of Discovery Discovery generated many, many theory papers. 4/11/

15 Original Era of Discovery And many more states discovered: 4/11/

16 From Discovery to Precision Charmonium states at BESIII 4/11/

17 From Discovery to Precision Beijing Electron Positron Collider (BEPCII) 4/11/

18 BEPCII: a high luminosity double ring collider SC RF CM Energy: GeV Luminosity: 1 x cm -2 s 1.89 GeV Beam magnets Uses 93 bunches and SC mini-beta. 4/11/

19 BESIII Detector Muon Counter SC magnet TOF Be beam pipe Drift Chamber CsI(Tl) calorimeter 4/11/

20 4/11/

21 BESIII Hawaii members: Jeong-Wan Park: Inclusive gamma studies at Y(4260) Mihajlo Kornicer: studies Χ c1 ηππ, η ππ and τ mass Tao Luo: τ mass studies Jianbin Jiao J/Ψ and Ψ decays to hyperons Gary Varner Data sets (started from 2008): 1.25 B J/Ψ events 125 M Ψ(3668) events 2.9 fb -1 at Ψ(3770) for D physics 500 pb -1 at GeV XYZ 2 fb -1 4/11/

22 BESIII A few results from 2012: Measurements of the mass and width of the η c (1S) using the decay Ψ(2S) γη(1s). PRL 108, (2012) First observations of the M1 transition Ψ(2S) γη(2s). PRL 109, (2012) Study of Ψ(2S) π 0 h c (1P), h c (1P) γη c (1S) via η c (1S) exclusive decays. PRD 86, (2012). 4/11/

23 Charmonium spectrum below open charm Only J/ and produced directly in e + e - collisions, but states below produced through radiative and hadronic transitions. 4/11/

24 c 4/11/

25 c (1s) S wave spin singlet ground state of charmonium. Known for long time. Precise measurement of c mass provides information on the hyperfine (ΔM(1S)) splitting of c and J/. Also important to check lattice QCD calculations. 25

26 c (1s) But: mass and width poorly determined. PDG12 M( c ) status PDG12 Γ tot ( c ) even worse! For Ψ(1S, 2S) c, average = ± 1.3 MeV/c 2. For or pp production, average = ± 1.0 MeV/c 2. 3 σ difference. Discrepancy pointed out by CLEOc. 4/11/

27 c (1s) BESIII: Studied Ψ(3686) c, c exclusive decays using 106 M Ψ(3686) decays. Did simultaneous fit taking into consideration distorted line shape (hindered M1) with significant interference (15 ) between c and non- c decays. BESIII KsK K + K KsK3 2K2 4/11/

28 Mass and Width of c mass = ± 0.6 stat ± 0.6 syst MeV/c 2 BESIII, PRL 108, (2012); arxiv: width = 32.0 ± 1.2 stat ± 1.0 syst MeV Now consistent with γγ and p-pbar production. Currently BESIII is the most precise measurement M hf (1S) cc-bar = M(J/Ψ) M(η c ) = ± 0.8 MeV/c 2. In good agreement with recent LQCD calculations: M hf (1S) cc-bar MeV/c2. BESIII LQCD theorists much happier. T. Burch et al., PRD 81, (2010) T. Kawanai and S. Sasaki, PRD 85, (2012) D. Mohler, arxiv: (2012) C. Davies et al., arxiv: (2013) 4/11/

29 c (2S) First observation by Crystal Ball in 1982 (M=3.592GeV, from ' X) never confirmed. First observed by Belle in B ± K ± η c (2S), η c (2S) K S K ± π Ŧ. Published results (PDG2012): All B-factory/CLEO! 4/11/

30 c (2S) PDG2012 UL BESIII PRD 84, (2011) UL BESIII UL BESIII 4/11/

31 First observation of c (2S) BESIII studies: ' c (2S) K s K, K + K - 0. Difficult since E = 48 MeV. Detailed analysis of backgrounds necessary. BESIII K o SK ± π Ŧ K + K - π o Simultaneous fit of c (2S) and cj N(h c (2S)) = 127 ± 18 statistical significance 11s 4/11/

32 ' c (2S) KK M(η C (2S)) = ± 2.9 ± 1.6 MeV/c 2 Γ(η C (2S)) = 16.9 ± 6.4 ± 4.8 MeV B( ' c (2S)) x B( c (2S) KKπ) = 1.30 ± 0.20 ± 0.30)x10-5 Using Br( c (2S) KK )=(1.9±0.4±1.1)% from BaBar BESIII Br( ' c (2S)) = (6.8 ± 1.1 stat ± stat 4.5 sys ) CLEO-c: 10-4 < (PRD81,052002(2010)) Predictions for B( ' c (2S)): ( ) x 10-4 [see compilation in arxiv: ]. BESIII discovers this transition after 18 years of searching. BESIII, PRL 109, (2012). 4/11/

c (2S) BESIII BESIII also studies: ' c (2S) K s K ± Ŧ PRD 87, 052005 (2013). N(η C (2S)) = 57 ± 17 significance 4.2 σ M(η C (2S)) = 3646.9 ± 1.6 ± 3.6 MeV/c 2 Γ(η C (2S)) = 9.9 ± 4.8 ± 2.

33 c (2S) BESIII BESIII also studies: ' c (2S) K s K ± Ŧ PRD 87, (2013). N(η C (2S)) = 57 ± 17 significance 4.2 σ M(η C (2S)) = ± 1.6 ± 3.6 MeV/c 2 Γ(η C (2S)) = 9.9 ± 4.8 ± 2.9 MeV B( ' c (2S)) x B( c (2S) K S K ± π Ŧ π + π - ) = 7.03 ± 2.10 ± 0.70)x10-6 M hf (2S) = M(Ψ(3686)) M(η C (2S)) = 47.2 ± 1.3 MeV/c 2 [PDG2012] LQCD calculation: M hf (1S) cc-bar 57.9 ± 2.0 MeV/c 2. D. Mohler, CHARM2012, arxiv: (2012). 4/11/

34 c (2S) η c (2S) mass PDG2012 compilation values η c (2S) width BESIII BaBar M(η c (2S)) BESIII BESIII BaBar BaBar Belle Belle CLEO BESIII BaBar Belle CLEO BESIII Γ(η c (2S)) 4/11/

35 h c 4/11/

h c ( 1 P 1 ) Not in PDG summary table until 2008. CLEOc used ' π o h c, h c c and obtained: M(h C ) AVG = 3525.20 0.18 0.

36 M(h C ) important to learn about hyperfine interaction of P wave states. Hyperfine or triplet-singlet splitting determined by spin-spin term in QCD potential models. Expected to be ~ 0 for P wave states. h c ( 1 P 1 ) Not in PDG summary table until CLEOc used ' π o h c, h c c and obtained: M(h C ) AVG = MeV/c 2 CLEO (B 1 x B 2 ) AVG = (4.16 ± 0.30 ± 0.37) x 10-4 PRL 101, (2008). M hf (1P) = <M( 3 P J )> - M( 1 P 1 ) = ± 0.18 ± 0.12 MeV, where <M( 3 P J )> = spin weighted centroid of 3 P J states = [M( cj )+ 3*M( cj ) + 5*M( cj )]/9 Consistent with lowest order expectation of 0. 4/11/

37 Methods to study h c Only detect π 0 : inclusive. Rate ~ B( π o h c ) BESIII, PRL 104, (2010) Detect π 0 and : E 1 tagged. Rate ~ B( π o h c ) x B(h c c ) BESIII, PRL 104, (2010) Detect π 0,, and c decay: exclusive. Rate ~ B( π o h c ) x B(h c c ) x B( c X) Exclusive c decays 4/11/

0 h c,h c c, c exclusive decays BESIII Summed distribution 832±35 evts. mass recoiling from π 0 (GeV/c 2 ) mass recoiling from π 0 (GeV/c 2 ) Mass = 3525.31±0.11±0.14 MeV/c 2 Width = 0.70±0.28±0.

38 0 h c,h c c, c exclusive decays BESIII Summed distribution 832±35 evts. mass recoiling from π 0 (GeV/c 2 ) mass recoiling from π 0 (GeV/c 2 ) Mass = ±0.11±0.14 MeV/c 2 Width = 0.70±0.28±0.22 MeV M hf (1P) [MeV/c 2 ] = ± 0.11 ± 0.15 MeV/c 2 Consistent with BESIII inclusive and CLEOc BESIII Collaboration, PRD 86, (2012) Currently the most precise measurements 4/11/

39 c lineshape from 0 h c,h c c BESIII Sum of 16 η c decay modes Background subtracted From simultaneous fit to hadronic mass spectra M(η c ) = ± 1.16 ± 0.52 MeV/c 2 Γ(η c ) = 36.4 ± 3.2 ± 1.7 MeV Lineshape is much less distorted than for J/, c ; the non-resonant interfering background is small. This channel much better for determining the c resonance parameters. BESIII Collaboration, PRD 86, (2012) 4/11/

40 The New Era of Discovery XYZ States and Y(4260) 4/11/2014 ICHEP

41 XYZ States Many charmonium states predicted by potential models and LQCD. Many have been found. 4/11/

42 XYZ States (EPJ C71, 1534 (2011)) 4/11/

43 Important Processes e + e - annihilation e + c B decay ISR e + e - radiate one or more photons. Measure σ over range of energies. B b q e - e + e - W c c c c s q K (*) 2 photon even spin mesons anti glueball filter. High luminosities at B factories allow use of ISR and 2 photon processes. 4/11/ e - c

44 Belle ( ) Experiments BESII ( ) e + e - CLEOc ( ) ( ) 4/11/

45 Experiments BESIII ( ) e + e - Belle II (2016? - ) Others: D0 CDF SND CMD3 LHCb ATLAS CMS Panda 4/11/

46 Y(4260) BaBar, PRL 95, (2005) BaBar, PRD 86, (2012) Not only does Y(4260) not fit in normal quark model, it decays to π + π - J/Ψ even though it is above DD-bar threshold. Belle, PRL 99, (2007) Belle 4/11/

Y(4260) New XYZ era has generated many, many theoretical papers. Some theoretical ideas for Y(4260): DD * bound state [NPA815, 53 (2009)]. J/Ψ f 0 bound state (with KK ππ) [PRD80, 094012 (2009)].

47 Y(4260) New XYZ era has generated many, many theoretical papers. Some theoretical ideas for Y(4260): DD * bound state [NPA815, 53 (2009)]. J/Ψ f 0 bound state (with KK ππ) [PRD80, (2009)]. Tetraquarks (or two diquarks) [PRD72, (2005)]. Hadrocharmonium [PLB666, 215 (2008)]. Hybrid charmonium [PLB628, 215 (2005), PRD78, (2008), PLB625, 212 (2005)]. On Dec. 14, 2012, BESIII began running with a CM energy of 4260 MeV. Also took data at 4360 MeV. 4/11/

48 Y(4260) Select e + e - π + π - J/Ψ, J/Ψ l + l - events. BESIII 1477 events found. Born cross section, (62.9 ± 1.9 ± 3.7) pb, consistent with production of Y(4260). 4/11/

49 Y(4260) A structure around 3.9 GeV/c is observed in the π ± J/Ψ mass spectrum. If interpreted as a particle, it carries charge and couples to charmonium. BESIII MC: σ, f(980), NR 4/11/

Z c (3900) Plot maximimum of M(π + J/Ψ) and M(π - J/Ψ) for each event. Fit with BW convolved with Gaussian resolution function; neglect interference with background.

50 Z c (3900) Plot maximimum of M(π + J/Ψ) and M(π - J/Ψ) for each event. Fit with BW convolved with Gaussian resolution function; neglect interference with background. BESIII N(Z c (3900)) = 307 ± 48 M(Zc(3900)) = ( ± 3.6 ± 4.9) MeV/c 2 Γ(Z c (3900)) = (46 ± 10 ± 20) MeV accepted by PRL arxiv: Structure has charge and couples to charmonium. Suggestive of a state containing more than just a C and C-bar quark. 4/11/

Z c (3900) Studies at B factories found unconfirmed/controversial structures in π ± Ψ(3686), Z ± (4430), [Belle, PRL 100, 142001 (2008);

systems. π ± J/Ψ Luckily, the Z c (3900) has already been confirmed by Belle [arxiv:1304.

51 Z c (3900) Studies at B factories found unconfirmed/controversial structures in π ± Ψ(3686), Z ± (4430), [Belle, PRL 100, (2008); BaBar, PRD 79, (2009)] and π ± Χ c1, Z 1 ± (4050) and Z 2 ± (4250), [Belle, PRD 78, (2008); BaBar, PRD 85, (2012)] systems. π ± J/Ψ Luckily, the Z c (3900) has already been confirmed by Belle [arxiv: ] in ISR Y(4260) production and by Kam Seth [arxiv: ] using 586 pb -1 of CLEO data taken at a CM energy of 4170 MeV [Ψ(4170)]. Seth also sees a peak in π 0 J/Ψ. π 0 J/Ψ 4/11/

52 Z c (3900) s (GeV) σ(ee ππ J/Ψ), pb N(Z c ) M(Z c ) Γ(Z c ) MeV/c 2 MeV R % BESIII π + π ± ± 6 46 ± ± 3 Belle π + π ± 8 63 ± ± 9 Seth π + π ± ± 5 34 ± ± 11 Seth π 0 π ± ± ± ± 15 R=B(Y(e + e - Z c π) B(Z c πj/ψ)/b(e + e - ππj/ψ) Measurements agree well. Seth not at peak of Y(4260), but at peak of 2 3 D 1 state of charmonium, E CM = 4170 MeV. Do not need to attribute unusual properties to initial state of Y(4260). 4/11/

53 Z c (3900) Belle also measures cross section in latest work. Belle has claimed two resonances in this region: Y(4260) and Y(4008); Belle, PRL99, (2007). However BaBar uses a different background description and does not confirm the Y(4008); BaBar, PRD86, (2012). Therefore situation at E CM = 4170 GeV unclear. BESIII will be able to clarify and study many more decay modes of the Y(4260). Accumulating more data. Belle Belle 4/11/

54 4/11/

55 Summary Charmonium physics has entered the precision era. BESIII making major contributions. Present XYZ discovery era like original charm discovery era. BESIII has begun XYZ physics with the discovery of the Z C (3900). By analyzing many other decay modes, it will help illuminate the nature of these particles. Tau-charm energy region will continue to be interesting due to large variety of physics possible. Very rich and interesting energy region. 4/11/

56 Thank you 4/11/

BESIII data taking status & plan Previous data BESIII present & future Goal J/ BESII 58M 1.2 B 20*BESII 10 B CLEO:28 M 0.5 B 20*CLEOc 3B CLEO:0.8 /fb 2.9/fb 3.5*CLEOc 20 /fb Above open charm CLEO:0.

57 BESIII data taking status & plan Previous data BESIII present & future Goal J/ BESII 58M 1.2 B 20*BESII 10 B CLEO:28 M 0.5 B 20*CLEOc 3B CLEO:0.8 /fb 2.9/fb 3.5*CLEOc 20 /fb Above open charm 4160) 2011: 4040) 2013:1/fb@4260, 4360 Rscan & Tau BESII 2012: 12/pb@2.23,2.4,2.8,3.4 25/pb, scan 2013, R scan, 5-10 /fb J/ : 20 * BESII ; : 20* CLEO ; : 3.5 * CLEO 4/11/

Charmonium Spectroscopy at BESIII

Charmonium Spectroscopy at BESIII Hu Liu (on behalf of the BESIII Collaboration) Institute of High Energy Physics, Beijing, China 8 th QWG @GSI 05-10-2011 Slide 1 Outline Brief Introduction of BEPCII &