A Flavor of BESIII Physics

Transcription

1 A Flavor of BESIII Physics Roy A. Briere Wichita State University 12 Mar 2014

2 Nick invited me sometime ago. My cover story for waiting so long concerned waiting for more BESIII results, being busy with teaching, etc. Now I can reveal my real reason: I could sense the historic basketball season of 2014! Go Shockers!!!

3 Outline Introduction: Weak Interactions BESIII & BEPCII Open Charm Physics The Z c (3900) & Friends The Future Conclusion Mar 2014 Wichita State 3

4 Particles of the Standard Model Note 3 copies, or generations (only masses differ) Each force has some unique features Spin-1/2 Matter Particles ( Fermions ) Spin-1 Force Carriers ( Gauge Bosons ) Mar 2014 Wichita State 4

5 Ordinary Matter Only First Generation : u,d,e, υ e Nucleus of u,d; plus e υ e : beta decay, fusion, n d u d neutron beta decay: W e υ e u u d p Brown Muck = strong force (quarks always bound!) Mar 2014 Wichita State 5

6 Particle Physics Phenomenology Interactions = vertices in Feynman diagrams We can spin around vertices in space-time Vertices are the building blocks of diagrams γ γ e e e e emission pair creation e e + All are same basic vertex Note: fermions lines never end inside diagram Mar 2014 Wichita State 6 γ e + e absorption γ pair annihilation due to 1/2-integral spin

7 Standard Model Vertex Gallery f Z f γ u, d, l u, d, l All Fermions: Charged Fermions: Only Quarks: u, d, l, ν u, d, l u, d q all but the Higgs Boson g q W + W u d d u ν l l ν All Fermions, in matched pairs ( to conserve electric charge! ) Only W changes particle type Only this W interaction can (sometimes) change the fermion generation There are also All-Gauge vertices: ggg gggg WWγ WWZ WWγγ WWγZ WWZZ WWWW ggg is shorthand for: g g others are analogous Mar 2014 Wichita State 7 g

8 Vertices for all Gauge Bosons u d u d e υ e γ, g,z 0 W ± W ± γ, g,z 0 Toy model: One generation of fermions Neutral: --fermion unaltered if γ, g,z 0 emitted e υ e γ, Z 0 W ± W ± Z 0 Charged: -- fermion changes -- W connects pairs of fermions Empty boxes are an Mar 2014 Wichita State interesting story 8

9 Generations of Fermions Think of with successive approximations: 1) Ordinary matter: one generation u d e υ (our previous chart) 2) 3 generations, with no inter-gen. transitions So, just three independent copies 3) Three generations, interconnected by weak interactions! t b τ υ τ c s µ υ µ u d e υ e Mar 2014 Wichita State 9

10 Strengths of all W ± couplings CKM Mixing Matrix: 9 elements Ampl (q i q j W) ~ V ij ( V ij also appear in meson mixing ) q i V ij q j W Weak Decays: d,c,t decay: normal s u W : slow b c W : very slow just a rotation matrix u c t d s b Mar 2014 Wichita State 10

11 The Higgs Boson The Higgs gives elementary particles mass It s actually designed to give W,Z bosons mass It probably also gives matter fermions mass So does it give ME mass? Not much! ( A common error in popularized Higgs articles ) We re mostly NOT elementary particles: our mass is mostly protons and neutrons Interaction energy of QCD gives them 99+% mass of their mass ( maybe the Higss gives Dark Matter mass?!? We don t know! ) What the Higgs also does: Adds most of the arbitrary parameters to the Standard Model ( fermion masses, CKM quark mixing, ) Pizza, Chicago-style? Origin of my mass? Mar 2014 Wichita State 11

12 Quarks vs. Neutrinos Both quarks & neutrinos allow studies of weak interactions Neutrinos are naively similar We now know they mix and have mass, like quarks But not so fast They are unusually light: hints at something new Also, they could be their own antiparticles ( Majorana vs. Dirac * ) Experimentally different Neutrinos interact only weakly Con: small rates, need huge detectors Pro: no strong-interaction pollution I chose quarks: easier to do, harder to interpret * Our condensed matter colleagues also discuss Majorana & Dirac behavior in special materials Mar 2014 Wichita State 12

13 The Three Interactions* E-M is described by Quantum Electrodynamics Predictions for e, µ magnetic moments ( g-2 ) are most precise of any physical theory! Strong Force: QCD ( Chromodynamics ) Details of bound states: baryons, mesons ( exotics? More later ) Binding effects confuse our quark-based studies of weak interactions Also, hadronization: how high-energy quarks form hadrons ( ignore today ) Weak Force Cause of all non-trivial decays ( particle type change ) That s WHY we can use quarks, despite their binding inside hadrons: Flavor-change = quark-type change implies a weak process BUT: Also source of need for Higgs mechanism Violates discrete symmetries C, P, CP * No gravity in particle physics, except to hold experiments down Mar 2014 Wichita State 13

14 BESIII & BEPCII* BEPCII Accelerator BESIII Detector Our Datasets Physics Overview * Note that with CLEO-c & CESR-c, we did similar physics Threshold) with data taken from Mar 2014 Wichita State 14

15 IHEP, Beijing ~13 km due west of Tiananmen Square Offices L i n a c T.D. Lee s Sculpture Main Gate Ring Mar 2014 Wichita State 15

16 BEPCII Two-ring, large crossing angle, multi-bunch, high-current RF SR IP RF Zoom into the IP - Design - Beam energy: GeV Luminosity: 1 x cm -2 s -1 Optimum energy: 1.89 GeV Energy spread: 5.16 x 10-4 No. of bunches: 93 Bunch length: 1.5 cm Total current: 0.91 A Synch. Rad n mode: 2.5 GeV Mar 2014 Wichita State 16

17 BESIII Non-destructive measurements first! 53 institutions total 22 outside China Wire tracker (no Si); TOF + de/dx for PID; CsI Ecal ; RPC muon Mar 2014 Wichita State 17

18 e + e - & Charmonium Direct, high-statistics production of J PC = 1 -- charmonium J/ψ ψ [ 2s+1 L J = 3 S 1 states ] also: ψ(3770)* Y(4260) σ eff ~ 2500 nb for J/ψ Depends on beam energy spread ( BEPCII a bit narrower than CESR-c ) Radiative ( γ, π 0, π π, η ) transitions give access to other states: χ cj h c η c 3 P 0,1,2 1 P 1 1 S 0 Mar 2014 Wichita State 18

19 e + e - & D Meson Pairs Rich Spectroscopy: Main point for us: ψ(3770) is a good source of D mesons. ψ(3770) J/ ψ (3770) decays: -- mostly to D pairs -- analogous to ϒ(4S) & B pairs Q Q ψ (2S), J/ψ decays: -- ggg+ggγ ; other charmonia; dileptons ; radiative Q q q Q Mar 2014 Wichita State 19 Q Q

20 Physics Runs July 2008: First collisions w/ detector in place New BEPCII accelerator & New BESIII detector 2009: First physics data Many machine studies, brief physics runs 2010: First publications 3 papers in 2010 ; increased to 25 in : Standard physics runs About 6 months, starting ~Dec. of previous year Peak Luminosity: 0.7 x /cm 2 /s (70% design) run with lower currents than design Mar 2014 Wichita State 20

21 Data Sets 1.3 x 10 9 J/ψ [ 2009 only: x 10 9 ] 0.4 x 10 9 ψ [ 2009 only: x 10 9 ] 2.9 fb ψ(3770) D pairs 0.48 fb 4009 MeV 2011 D s pairs & 1.92 fb 4230, 4260 MeV fb 4360 MeV fb -1 9 other energies fb high E ( incl MeV ) Also, τ threshold mass scan 2014: end of talk Mar 2014 Wichita State 21

22 61 published / accepted papers, + 6 advanced drafts ( My personal classification ) 8 new low-energy resonances ( incl. one null search ) 8 η, η (a 0 -f 0 ) decays (mixing) 5 XYZ states 3 ψ(3770), ψ(4040) decays 19 J/ψ, ψ, χ cj hadronic decays 11 J/ψ, ψ, χ cj radiative / 2-photon / rare decays 6 h c, η c, η c decays & parameters 2 ψ J/ψ hadronic transition 2 D physics Breadth of Physics 3 Luminosity, # J/ψ, ψ ( engineering numbers ) Mar 2014 Wichita State 22

23 Low-E Resonance Gallery No time to discuss today! 1) 2) 3) 4) 5) 6) 1) p p bar in J/ψ γ p p bar CPC 34, 421 (2010); PRL 108, (2012) 2) π + π η in J/ψ γ π + π η PRL 106, (2011) 3) η π + π in J/ψ ω η π + π PRL 107, (2011) NOTE: 4) p π 0 in ψ p p bar π 0 PRL 110, (2013) There are many resonance and PWA papers 5) ω φ in J/ψ γ ω φ PRD , (2013) from BESIII! My goal here was to highlight 6) 3(π + π ) in J/ψ γ 3(π + π ) PRD 88, (R) (2013) the new, unexpected peaks only Mar 2014 Wichita State 23

24 Open Charm Physics Overview of D tags & Key Topics D + µν D 0 πeν, Keν Strong Phase δ Kπ D + K S π + π 0 ( in backups ) Mar 2014 Wichita State 24

25 D ψ(3770) ψ(3770): σ DD ~ 6.6 nb Only D pairs: no phase space for even one extra pion Reconstruct one D in a set of hadronic tag modes: Reduces backgrounds Find the other D s direction ( produce a tagged D beam! ) can now solve for a neutrino 4-vector, if needed Familiar tag variables (also used in B physics) Conservation of momentum & energy M bc = (E 2 beam - p cand2 ) 1/2 ΔE = E cand - E beam ( cand is the candidate D: a sum over decay daughters ) Measure (# tags & signal) / (# tags) : tag-side efficiency mostly cancels; tag systematics cancel Mar 2014 Wichita State 25

26 u c t B Physics & Small CKM Elements 1 -λ Aλ 3 (1-ρ-iη) d s b Measure from B 0 -B 0 mixing Usefulness is limited by theory λ 1 -Aλ 2 Aλ 3 (ρ-iη) Aλ 2 1 Measure from B decays t b d,s B 0 B 0 d,s b t Mar 2014 Wichita State 26 b q B υ e e + c,u q D,π Note the QCD fog (Isgur s brown muck )

27 D c d,s Leptonic D Decays µ + υ µ f D is the decay constant : Chance that quarks overlap ψ(0) 2 : square of wavefunction at origin b t d,s B 0 B d,s 0 b t Decay constants also in Box Diagram ( W exchange : really ~point-like four-fermi ) c D q Semileptonic D Decays υ e e + s,d q K,π Physics is all in the form factor : Chance c,qbar quarks bind into final state K,π Similar form factors in semileptonic B decay Mar 2014 Wichita State 27

28 D + µν Uses 9 tag modes ( for reference, CLEO-c used 6 ) Even includes Cabibbo-suppressed modes! BESIII 2.9 fb -1 arxiv: Subm. To PRD K π + π + K S π K S K K + K π K + π π π 0 π + π π Signal side: ONE track! Veto on extra tracks, and un-matched showers with E > 300 MeV K S π π 0 K + 3π π + K S π π π + Reconstruct MM 2 = (missing-mass) 2 (invariant mass) 2 of missing energy-mom. four-vector Presumably just a neutrino: signal peaks at 0 Mar 2014 Wichita State 28

29 Clean Signal ( log plot! ) D + µν missing K L peak BESIII 2.9 fb -1 arxiv: Subm. To PRD Result: ± 20.6 ± 2.6 events above background B( D + µν ) = ( 3.71 ± 0.19 ± 0.06 ) x 10-4 Combining with V cd, G F, τ D, m D : f D = ( ± 5.3 ± 1.8 ) MeV ( ± 2.6 ± 0.9 )% most precise! previous best: (207.6 ± 9.3 ± 2.5) MeV ( CLEO-c, τν floating) (205.8 ± 8.5 ± 2.5) MeV ( CLEO-c, including τν fixed to SM ratio ) Mar 2014 Wichita State 29

30 Lattice QCD Results From FLAG : Flavor Lattice Averaging Group N f = 2+1: ( 2 results; 1 dominates ) f D = ± 3.3 N f = 2+1+1: ( 1 result ) f D = ± 3.0 ± 3.6 Good agreement with exp t N f : # of dynamical (virtual) quark flavors; m u = m d m s -or- m u = m d m s m c Mar 2014 Wichita State 30

31 D + µν vs. D s + µν D s and f Ds Cabibbo-allowed : CKM V cs 2 ~ 1 Can do near threshold at charm factory BUT can also do with high-mom. Charm at B factories Currently, the best result is from Belle (a B factory ) BESIII hasn t taken data for this yet D and f D : Cabibbo-suppressed : CKM V cd 2 ~ 0.05 Can ONLY do near threshold at charm factory Mar 2014 Wichita State 31

32 Pre-CLEO-c Semileptonic Results D 0 K e + ν D 0 π e + ν PRL 94, (2005) kaons pions pions kaons 10.6 GeV World s best when done But note Kaons under pion peak! ( even w/rich PID ) Decays with K are 10x more common than those with a π : Separate via particle ID techniques (hard) BUT: CLEO-c & BESIII have excellent kinematic separation!!! Mar 2014 Wichita State 32

33 Use 4 hadronic tag modes D 0 Keν, πeν BESIII 0.9 fb -1 CHARM2012 arxiv: Signal side: two tracks, e & K/π K π + K π + π 0 Signal variable: U = E miss - p miss zero, similar to MM 2 ) Keυ K π + π 0 π 0 πeυ K π + π + π Mar 2014 Wichita State 33

34 D 0 Keν, πeν BESIII 0.9 fb -1 CHARM2012 arxiv: Slide directly from CHARM2012, for illustration No attempt to update Lattice QCD Form Factors f(q 2 ) Mar 2014 Wichita State 34

35 q 2 in D 0 Keν ( πeν acts the same ) q 2 = M(eυ) 2 c quark turns into s quark + eυ u Highest q 2 : e s υ s at rest: easier to stay bound to u u Lowest q 2 : s eυ s moves with high momentum, needs to take u with it That s why the form factor is larget at large q 2 Mar 2014 Wichita State 35

36 Quantum Correlations At threshold, i.e. ψ(3770), we make D 0 D 0 pairs These neutral mesons: are quantum-mechanically entangled ( like EPR photon pairs ) and can exist in superpositions States [ D± D bar ] / 2 are CP+ and CP-, respectively If one D is CP-, then the other is CP+ Reconstruct one D in a CP-eigenstate; watch other one decay When the D and Dbar components decay to common final states, there is interference: we can measure relative phases! We can even reverse the sign of the interference term: Tag = CP+ Decay rate A - A bar 2 Tag = CP- Decay rate A +A bar 2 Mar 2014 Wichita State 36

37 Strong Phase δ Kπ BESIII 2.9 fb -1 Preliminary ( simple = no mixing ) CF ± DCSD Mar 2014 Wichita State 37

38 Strong Phase δ Kπ BESIII 2.9 fb -1 Preliminary Mar 2014 Wichita State 38

39 Strong Phase δ Kπ BESIII 2.9 fb -1 Preliminary All δ Kπ slides courtesy of Yangheng Zheng, CHARM2013 Mar 2014 Wichita State 39

40 X, Y, Z Physics Recall the Y(4260) Z c (3900) ± J/ψ π ± Z c (3885) ± (D*D) ± ( in backups ) Z c (4020) ± h c π ± Z c (4025) ± (D*D*) ± ( in backups ) Y(4260) γ X(3872) Tetraquarks? Hybrids? Molecules? no matter : FUN!!! Mar 2014 Wichita State 40

41 Hadronica Exotica Mesons: Baryons: q q q q q Conventional hadrons Tetraquarks: q q q q Pentaquarks: q q q q q Molecules: q q q q q q q q q Exotics Hybrids: Glueballs: q q g g g Smoking gun for exotics: quantum numbers not possible for conventional states Next best signature: too many states for quark model, or unusual decay pattern Why is the Z c exotic? Seems to contain a cc pair, but is NOT neutral ( actually, if exotic, we generically expect neutral partners ) Mar 2014 Wichita State 41

42 2013: Large dataset at Y(4260) Y(4260) dip in σ tot! E(GeV) Total charm ~4.3 nb ( CLEO-c scan ) e + e J/ψ π π ~ 70 pb ( BaBar/Belle ) PDG Y(4260) data: Γ = (95 ± 14) MeV Γ J/ψππ Γ ee / Γ = ev Mar 2014 Wichita State 42

43 Y(4260) π π J/ψ BESIII 525 pb -1 PRL 110, (2013) Study 525 pb -1 collected at E cm = 4260 MeV ; look at well-known J/ψ π π decay of Y(4260) J/ψ di-lepton peaks: µµ ee Pair-wise invariant masses: ( of π π J/ψ ) Mar 2014 Wichita State 43

44 Shift focus! Z c+ (3900) BESIII 525 pb -1 PRL 110, (2013) Peak(s) in J/ψ π masses: really only one (next page) in both π charges not due to π π structure (not even if D-wave π π) Structure in di-pion mass: well-modeled via f 0 (980) + σ(500) + non-res. Now, red curve is MC w/ π π structure Mar 2014 Wichita State 44

45 Z c+ (3900) BESIII 525 pb -1 PRL 110, (2013) Dalitz Plots Two stripes in J/ψ π mass one is a reflection of the other: correlation in two J/ψ π axes Fold over Dalitz plot! [ plot M max ( J/ψ π) ] high in one low in other Mar 2014 Wichita State 45

46 Fit To: S-wave BW + MC resolution + empirical background function (4 parameters) Z c+ (3900) BESIII 525 pb -1 PRL 110, (2013) Total rate: e + e π π J/ψ Born-level cross-section = (62.9 ± 1.9 ± 3.7) pb Consistent with Y(4260) Z c+ (3900) peak in π + J/ψ : M = ( ± 3.6 ± 4.9) MeV Γ = (46 ± 10 ± 20) MeV Fractional rate of Z c+ (3900) peak : (21.5 ± 3.3 ± 7.5) % Mar 2014 Wichita State 46

47 BESIII, Belle, NWU We present : the ( Z c ) 3 BESIII Z c + (3900) PRL 110, (2013) Belle Z c + (3895) PRL 110, (2013) Northwestern U. Z c + (3900) PLB 727, 366 (2013) Note horizontal range differences! BESIII: 525 pb -1 at E cm = 4260 MeV BelleII: ISR from ~10 GeV, cut on 4.15 < M(J/ψππ) < 4.45 GeV (hence, higher upper endpoint on mass above ) NWU: 586 pb -1 at E cm = 4170 MeV ( CLEO-c legacy data ) Mar 2014 Wichita State 47

48 Z c (4020) in π + π - h c Use h c η c γ Select events with : π + π - recoil mass near h c π + π - γ recoil mass near η c Then use 16 η c decay modes Inset: scatter plot of 2 recoil masses 1-D Projection: h c peak in mass( γ η c ) from η c band ( h c : first seen in CLEO ) 3.4 fb 13 E cm points ( ~87% in 4 points ) h c π + π - Dalitz Plot: BESIII 3.4 fb -1 PRL 111, (2013) m 2 hc π m 2 π π Mar 2014 Wichita State 48

49 Z c (4020) in π + π - h c BESIII 3.4 fb -1 PRL 111, (2013) Large, narrow peak in π ± h c mass! Zoom in on a fit to peak m(π ± h c ) m(π ± h c ) Inset shows insignificant Z c (3900) Parameters of new Peak: M = ( ± 0.8 ± 2.7) MeV Γ = (7.9 ± 2.7 ± 2.6) MeV Mar 2014 Wichita State 49

50 Y(4260) γ X(3872) BESIII 2.9 fb -1 PRL 112, (2014) Analysis: Observe e + e γ X(3872) at several energies Fit extracted σ(e) to resonance: does it look like Y(4260)? GeV GeV Summed over E cm ; zoomed in X(3872) Peak GeV GeV 6.3 σ X signal: M(X) = ( ± 0.7 ± 0.2) MeV Γ(X) < 2.4 MeV (90% CL) Mar 2014 Wichita State 50

51 Y(4260) γ X(3872) BESIII 2.9 fb -1 PRL 112, (2014) Study of γππ structure : γ angle consistent with E1 ππ consistent with ρ (as with CDF data) 4 th point Fit to cross-sections to : Y(4260) Resonance linear rise E1 phase space ( E γ3 ) no 4260 Y(4260) clearly best: CL s in order: 92%, 6%, 3% Mar 2014 Wichita State 51

52 The Future Mar 2014 Wichita State 52

53 Running: Now & Later Start of this run: >100 points for an R had scan : GeV Mix of 5 & 10 MeV steps ~ 6-8 pb -1 per point Input to precision QED theory to describe the chance a photon fluctuates into a quark-antiquark pair Just finished: working on 500 pb MeV ( not optimal for Λ c pairs, but we can do Absolute BF ) Future Runs: ( no particular order ) lower-energy R scan D s *D s 4170 MeV More ψ(3770), J/ψ, ψ More XYZ Easy to fill MANY years! Mar 2014 Wichita State 53

54 Our Logo Now I can explain it Tail on E turns it into a ψ : Red in honor of China Tail coverts B into a D D pair Three colors represent our QCD work Mar 2014 Wichita State 54

55 Conclusions Precision D Physics is Underway (semi)leptonic: world s best; D + µν unique to threshold Quantum Correlations also unique to threshold Spectroscopy Very Active Much XYZ work discussed also many other analyses completed on new low-energy hadronic resonances Many other facets to our program Charmonium states & transitions More low-energy hadron physics R had scans ( & charm decomposition! ) Tau threshold (?Koide formula? ) Mar 2014 Wichita State 55

56 Backups Mar 2014 Wichita State 56

57 Flavor Physics Connections D 0, D +, D s + golden mode Branching Fractions Hadronic: Help normalize heavy flavor physics ( base of unitarity triangle ) e.g., HQET-based V cb involves D BF s [ Systematics limited after CLEO-c; lower priority to check but working on D* BF s ] Tests of Lattice QCD (or V cd, V cs using LQCD ) Leptonic: D +, D s µν, τν decay constants B 0, B 0 s decay constants enter in BBbar mixing Semileptonic: D K l ν, π l ν form factors Exclusive B π l ν also involves form factors Strong Phases Quantum Correlations: allow access Improve & control systematics on CKM γ / φ 3 extraction Interactions with all four small CKM elements accessed with B s Plus, two more which are directly available in charm decays Mar 2014 Wichita State 57

58 Other Quantum Correlation Work Coherence factors: feed into CKM γ/φ 3 B analyses ( the alphabet techniques : GLW, ADS, GGSZ, ) K S π + π most advanced: binned analysis ( CLEO-style ) K π + π 0 π + π π 0 likely to pursue both model-ind t analyses, and also detailed Dalitz analyses + other modes ( e.g., K π + π + π & K S K + π have been done by CLEO-c ) Mixing analyses: statistics-limited at ψ(3770) ( Too bad: neat ψ(3770) where DCSD cancels for conjugate final states ) Luminosity x cross-section much B factories, LHCb But We do have a y CP analysis in the works Mar 2014 Wichita State 58

59 D 0 Keν, πeν Numerical results Only 1/3 of current data! BESIII 0.9 fb -1 CHARM2012 arxiv: Mar 2014 Wichita State 59

60 Signal via Recoil Mass : Constrain K S π + π 0 to m D 4 vector of e + e - and D give recoil mass D + K S π + π 0 Dalitz BESIII 2.9 fb -1 arxiv Good channel for K S π 0 S-wave studies Resulting Dalitz Plot : To appear in PRD ρ resonance is dominant >85% signal Other projections are dominated by cos 2 shadow of ρ Mar 2014 Wichita State 60

61 D + K S π + π 0 Dalitz BESIII 2.9 fb -1 arxiv To appear in PRD Model D Fit : Try many resonances Drop insignificant one Contains κ π ( kappa ) and non-resonant Mar 2014 Wichita State 61

62 D + K S π + π 0 Dalitz BESIII 2.9 fb -1 arxiv To appear in PRD We also perform a Model-Independent Partial-Wave Analysis (MIPWA) for the S-wave Kπ components : non-res. + κ + K * 0 (1430) ) Reduces model-dependence ( always a problem ) Extract amplitude & phase of S-wave Kπ in mass bins Conclusion: Inclusion / omission of the K * 0 (1430) resonance affects high-mass shape, but always significant phase motion at low masses ( i.e., the κ region ) Mar 2014 Wichita State 62

63 Z c (3885) (DD*) ± BESIII 525 pb -1 PRL 112, e + e D D* bar 4260 MeV Two channels: (a) D 0 D* π + (b) D + D* 0bar π (2014) Reconstruct: bachelor π and one of D + or D 0 D π recoil mass: clear peak at D* masses; cut on Mar 2014 Wichita State 63

64 Z c (3885) (DD*) ± BESIII 525 pb -1 PRL 112, (2014) Plot DD*masses: Clear excesses over phase-space near threshold Peak parameters: M = ( ± 1.5 ± 4.2) MeV Γ = ( 24.8 ± 3.3 ± 11) MeV about 2σ & 1σ lower than Z c (3900) Curves: Also determine J P via π angle Mar 2014 Wichita State 64

65 Z c (4025) (D*D*) ± e + e D* D* bar 4260 MeV BESIII 827 pb -1 arxiv: D + K π π + D + recoil mass Keep high recoil mass Recon. - nominal Improves resolution D* + D* 0 π with D* + D + π 0 D* 0bar D 0bar π 0 Reconstruct: D +, π -, one π 0 cut on D + mass, & recoil mass Vertical Band: π 0 from D* + Horizontal Band: π 0 from D* 0bar Mar 2014 Wichita State 65

66 Z c (4025) (D*D*) ± BESIII 827 pb -1 arxiv: Peaks near sum of D* 0bar & π 0 masses π - recoil mass: D* + D* 0bar mass Inconsistent with phase-space Parameters of new Peak: (65 ± 9)% of all D* + D* 0 π - M = ( ± 2.6) MeV Γ = (24.8 ± 5.6) MeV Same peak as previous h c result??? More work is needed Mar 2014 Wichita State 66