1. Valentina Santoro European Spallation Spurce ESS XYZ states: experimental overview XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Kandinsky Untitled

2. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Outline A little Bit of History … Charmonium-like states The X(3872) The Y(4360) and Y(4660) The Search for tetraquark 2 Once upon a time there was a resonance…. Valentina Santoro

3. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Charmonium Spectrum before the B-factories 3  Charmonium properties were well understood up to  (3770) (i.e. about the DD threshold) with some missing pieces (like the  c (2S) )  No new cc states were discovered between 1980 to 2002  cc states above open charm threshold are expected to have significant width values and to decay mainly to open charm channels (E835 experiment - year 2000) in the same year -B factories started to take data Crystal Ball  c (2S) candidate Valentina Santoro

4. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Charmonium spectrum In a few years the situation changed rapidly There were discoveries of new charmonium states like the h c (1P),  c (2S) and  c2 (2P) And several new “charmonium –like” states 4 ( September 2015) Eur. Phys.J.C71, 1534 (2011) Z(3930)

5. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 All in all X(3872) Z(4430) + Z 1 + and Z 2 + Y(4140) Y(4260) Y(4350) Y(4008) Y(4660) X(3940) Y(3940) PRL 91, 262001 (2003) PRL 98, 082001 (2007) PRL 94, 182002 (2005) PRL 96, 082003 (2006) PRL 100, 142001 (2008) PRL 95, 142001 (2005) PRL 98, 212001 (2007) PRD 78, 072004 (2008) PRL 99, 182004 (2007) PRL 99, 142002 (2007) ? X(3915) 5  c2 (2P) PRL 102, PRL 102,242002 (2009) X(4160) PRL 100, PRL 100,202001 (2008) X(4630) PRL 101, PRL 101, 172001 (2008) PRL 104, PRL 104, 092001 (2010) Z c (3900) + Z 0 (3900) PRL 110, 252001 (2013) Valentina Santoro

6. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Exotic charmonium-like states interpretation 6 Molecular state: loosely bound state of a pair of mesons. The dominant binding mechanism should be pion exchange. Being weakly bound, mesons tend to decay as if they were free. NA Tornqvist PLB 590, 209 (2004) ES Swanson PLB 598,197 (2004) E Braaten & T Kusunoki PRD 69 074005 (2004) CY Wong PRC 69, 055202 (2004) MB Voloshin PLB 579, 316 (2004) F Close & P Page PLB 578,119 (2004) ….. Tetraquark: Bound state of four quarks, i.e. diquark-antidiquark Strong decays proceed via rearrangement processes. L Maiani et al PRD 71,014028 (2005) T-W Chiu & TH Hsieh PRD 73, 111503 (2006) D Ebert et al PLB 634, 214 (2006) … Distinctive features of multi-quark picture with respect to charmonium: - prediction of many new states - possible existence of states with non-zero charge, strangeness or both. Charmonium hybrids States with an excited gluonic degree of freedom Lattice and model predictions for the lowest lying hybrid: m ~4200 MeV P Lacock et al (UKQCD) PLB 401, 308 (1997) SL Zhu PLB 625, 212 (2005) FE Close, PR Page PLB 628, 215 (2005) E Kou, O Pene PLB 631, 164 (2005) … Conventional charmonium C Meng & KT Chao PRD 75, 114002 (2007) W Dunwoodie & V Ziegler PRL 100 062006 (2008) O Zhang, C Meng & HQ Zheng arXiv:0901.1553 … Valentina Santoro

7. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Experiments (3.1 GeV) (9.0 GeV ) Cherenkov Detector Drift Chamber Electromagnetic Calorimeter Solenoid (1.5T) Instrumented Flux Return Silicon Vertex Tracker 7 Valentina Santoro

8. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 The X(3872) 8 Valentina Santoro Butterfly Windmill Salvador Dali’

9. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 The Discovery Discovered by Belle in B → J/      K; confirmed by CDF, D0 and BaBar Narrow (Γ<2.3MeV) particle with mass m(X)=3871.4±0.6 MeV/c 2 PRD 71, 071103 (2005) PRD 73, 011101 (2006) PRL 93, 072001 (2004) PRL 93, 162002 (2004) “Inclusive Production” CDF & D0 BELLE & BaBar “Exclusive Production (B decay)” 9 PRL 91, 262001 (2003) Valentina Santoro

10. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 The X(3872) 10 X(3872) Properties Narrow (  ≤2.3 MeV) with mass m(X)=3871.69±0.17 MeV/c 2 (PDG 2014) Observed in X(3872) J/      dipion mass is “  -like” Also seen in decays X(3872) → D 0 D *0, X(3872) → J/  X(3872) → J/ , X(3872) →  (2S)  seen by BaBar and LHCb but not by Belle C is positive, spin-parity identified as J PC = 1 ++ ; Possible Interpretations Conventional Charmonium χ c1 (2 3 P 1 ) (1 ++ ), D 0 D *0 Molecule Charmonium- hadronic Molecular hybrid state ….. Valentina Santoro Successful predictions vary by model

11. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 The X(3872) Quantum numbers For several years until 2013 its quantum number were controversial between 1 ++ and the assignment 2 -+. In 2013 LHCb study the decay B + → X(3872)K + with the X(3872) → J/     The quantum, numbers of X(3872) → J/  have been determined to be J PC =1 + + PRL 110, 222001 (2013) t is a test statistic to discriminate between the two J PC hypotheses H owever it was assumed that the decay is dominated by the lowest values of angular momentum between the X(3872) decay products Valentina Santoro 11

12. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 New Results from LHCb(1) 12 PRD 92, 011102 (RC) (2015) 3.0 fb -1 The analysis is repeated here using 3-times the statistics and without any assumption on L min B + → X(3872)K +, X(3872) → J/  0,  0 →      and J/  →     Crystall-Ball +linear function for the background N( B + → X(3872)K + )=1011 ±38 with 80% signal purity Valentina Santoro

13. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 New Results from LHCb(2) 13 Distribution of the test statistic t=-2ln(L(J x alt ))/L(1 ++ )] for the simulated experiments under the J PC =J x alt (alt=alternative)hypothesis and under the J PC =1 ++ hypothesis J PC = 1 ++ gives the highest Likelihood value with an upper limit of D-wave contribution of 4% at 95% C.L. Valentina Santoro PRD 92, 011102 (RC) (2015)

14. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Observation of e + e - →  X(3872) 14 PRL 112, 092001 (2014) J/     invariant mass for √s=4.009 GeV+√s=4.229GeV+√s=4.260 GeV+√s=4.360GeV Evidence of decay X(3872) → J/     6.3  Suggestive of Y(4260) →  X(3872) Valentina Santoro σ B [e + e − → γX.3872]× B[X(3872) → π + π − J/ψ] vs E cm

15. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 The Y(4360) and Y(4660) 15 Memories After Death (1938) Osvaldo Licini Valentina Santoro

16. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Y (4350) and Y(4660)      (2S) (Brief story(1)) Y (4260) discovered in ISR    − J/ . How about    −  (2S) in ISR? In  (2S)     BaBar observed the Y(4350) Single resonance fit => m=(4324±24) MeV/c 2, Γ=(172±33) MeV Incompatible with ψ(4415); Poorly described by Y(4260) PRL 98 212001 (2007) 298 fb -1 Confirms the BaBar result Report a new enhancement 16 PRL 99, 142002 (2007) 673 fb -1 Valentina Santoro

17. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 BaBar update using the full dataset, including the Y(2S) and Y(3S) data  (2S) → J/     17 520 fb -1 Confirm the BELLE enhancement ~ 4.6 GeV/c 2 The obtained parameters for the Y(4360) and Y(4660) are consistent with the Belle results Y (4350) and Y(4660)      (2S) (Brief story(2)) PRD 89, 111103 (2014)

18. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 18 New results from Belle (1) 980fb -1 PRD91, 112007 (2015) Unbinned simultaneous maximum likelihood fit for the Y(4360) and Y(4660): Amp=BW 1 +BW 2 × e i  Consistent with previous measurements Valentina Santoro

19. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 19 New results from Belle (2) 980fb -1 Unbinned simultaneous maximum likelihood fit adding the Y(4260 ) : Amp=BW 1 +BW 2 × e i  +BW 3 × e i  Valentina Santoro Significance of Y(4260) is 2.4  very low, but affects Y(4360) and Y(4660) masses and widths.

20. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Invariant mass distribution of  +  - from Y(4360) and Y(4660)  in the J/  +  - mode 20 New Results from Belle(3) PRD91, 112007 (2015) 4.0< M(  +  -  2S))<5.5 GeV/c 2 Y(4360): 4.0< M(  +  -  2S))<4.5 GeV/c 2 Y(4660): 4.5< M(  +  -  2S))<4.9 GeV/c 2 MC simulation with an incoherent sum of the f 0 (500) and f o (980) seems to describe the data reasonably well Dots:Data Shaded Histogram: MC simulation Green Histogram:  2S)  sidebands Valentina Santoro 980fb -1

21. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Summary on the Y-states Valentina Santoro 21 The Y(4260) is the most notorious of these 3 states (seen in J/  +  -, in J/  0    J/  +    and recently in  X(3872)) Its nature is still unclear The Y(4360) and Y(4660) have been found only in  (2S)  +  - the  +  - mass spectra seem to have interesting features

22. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 The Search for tetraquark 22 In the original paper in which he proposed the quark model, Gell-Mann stated that ``Baryons can now be constructed from quarks using the combination ( qqq ), ( qqqqq ) etc., while mesons are made out of ( qq), ( qqqq) etc..” He chose the lowest configuration to create the representations describing the know meson and baryon states. However, the higher configurations were not a priori excluded, and experimentalists and theorists have been seeking evidence supporting the existence of such states every since. PRD 79, 112001 (2009) Valentina Santoro

23. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 The Z(4430) + In 2008 Belle observed broad, charged charmonium-like states in ( cc )K  analysis : Z(4430) + in B →  (2S)    23 PRL 100, 142001 (2008) Maiani: arXiv: 0708.3997 Karliner & Lipkin arXiv: 0802.0649 Not confirmed by BaBar experiment that studied also the J/   K + and the J/   K S 0 channel Belle performed a Dalitz reanalysis and confirmed the Z PRD 79, 112001 (2009) Z(4430) + →  2S)  + Quark content at least ccud : not simple qq mesons PRD 80, 031104 (2009) Valentina Santoro

24. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 24 In 2013 Belle reanalysis using full amplitude fit m=4485 ±22 +28 -11 GeV/c 2  =200 +41 -46 +26 -35 MeV The Z(4430) + from BELLE PRD 88, 074026 (2013) 6.4  The Z(4430) + was reconfirmed with 6.4  Valentina Santoro

25. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 Valentina Santoro 25 PRL 112, 222002 (2014) In 2014 LHCb uses a sample of >25k B 0 → ψ(2S)K - π +, ψ(2S) →      factor 10 more than BaBar and Belle As Belle LHCb uses a full amplitude fit 4D (m 2 K+π−, m 2  (2S)π−, cosθ ψ(2S),  The Z(4430) + from LHCb(1) 3.0 fb -1 The data are described well only if we add an additional resonance (Z(4430) + ) m=4475 ±7 +15 -25 GeV/c 2  =172±13 +37 -34 MeV 13.9 

26. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 26 PRL 112, 222002 (2014) To establish the nature of the Z(4430) + the B-W amplitude has been replaced by 6 different amplitudes in m  ’  2 bins in the peak region Argand plot shows a clear and large phase change confirming the resonance behaviour The Z(4430) + from LHCb(2) Black points: Data Red curve: predictions from the B-W formula Valentina Santoro Spin parity also studied by LHCb confirming Belle claim => Z(4430) + is J P =1 + 18  using a conservative approach

27. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 27 The Z(4430) + from LHCb(3) Valentina Santoro A Model indipendent approach has been used to see if reflection of the structure in m(K  ) and cos  reproduce the m(  (2s)  ) distribution: Explanation of the data with plausible K* contributions is ruled at high significance without assuming anything about K* resonance shapes or their interference patterns For more details see Thomas Britton talk yesterday NEW from LHCb

28. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 The Z c (3900) from BES III BESIII reported a study of the process e + e - → J/    - at √s=4.260 GeV And they observed a charged structure in the J/    mass. M(Z c (3900))=3899±3.6±4.9 MeV/c 2  (Z c (3900))=46±10±20 MeV L=(525 pb -1 ) The distrubution is fitted with an S-wave Breit-wigner; p*q phase space factor and efficiency correction applied Background PRL 110, 252001 (2013) 28 Valentina Santoro

29. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 The Z c (3900) from BELLE After ~ 1 week from the BESIII result BELLE reported a study of the process e + e - → J/    - And they observed the same charged state. m(Z c (3900))=3894.5±6.6±4.5 MeV/c 2  (Z c (3900))=63±24±26 MeV L=(967 pb -1 ) The distrubution is fitted with an S-wave Breit-wigner; p*q phase space factor and efficiency correction applied Background PRL 110, 252002 (2013) 29 Valentina Santoro

30. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 30 PRD 86, 010001 (2012) m: (3894.8 ± 2.3 ± 2.7) MeV/c 2  : (29.6 ± 8.2 ± 8.2) MeV Significance = 10  Neutral partner for the Z c (3900)? Study of e + e - → J/     Structure in J/   mass spectrum Valentina Santoro

31. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 31 Summary of the tetraquark searches Z c (3900) + Z(4430) + Valentina Santoro

32. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 32 Conclusions(1) Valentina Santoro

33. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 33 Conclusions(2) Valentina Santoro

34. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 34 Thanks for your attention Valentina Santoro

35. XVI International Conference on Hadron Spectroscopy, September 13-18, 2015 35 Soon after its discovery there were several theoretical interpretation about the nature of this state PRL 102, 242002 (2009) CDF reported the study of the decay mode B + → J/    →      J/  →     2009 M Y4143 = 4143 ± 2.9 ± 1.2 MeV/c 2  Y4143 = 11.7 +8.3 -5 ± 3.7 MeV They observe a narrow peak near the threshold in the J/  mass spectrum 2.7 fb -1 Some months after the CDF result BELLE shows its J/  mass spectrum using 772 x10 6 BB pairs They did not observe the Y(4140) in B decays or in two-photon production NEVER PUBLISHED arXiv: 0903:3107, 0903:2529 ecc… Valentina Santoro