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Meson and Baryon Spectroscopy at HERA

Lake Louise Winter Institute 2004 Alberta, Canada 15 – 21 February. Meson and Baryon Spectroscopy at HERA. McGill University DESY. Mauricio Barbi. Introduction Neutral Meson Spectroscopy K s K s resonances in DIS K s p resonances in DIS Summary. for. Collaborations.

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Meson and Baryon Spectroscopy at HERA

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  1. Lake Louise Winter Institute 2004 Alberta, Canada 15 – 21 February Meson and Baryon Spectroscopy at HERA McGill University DESY Mauricio Barbi • Introduction • Neutral Meson Spectroscopy • Ks Ks resonances in DIS • Ks p resonances in DIS • Summary for Collaborations

  2. mesons baryons q q q q q Introduction • Constituent quark model • QCD allows multiquark (> 3q), hybrid (quarks + gluons) and gluonic states “exotics” in the constituent quark model. • Hadron spectroscopy QCD in the non-perturbative regime. How does confinement works? Insight on the degrees of freedom which determine the spectrum of hadrons. • Powerful tool for testing the QCD bases. Lake Louise, Alberta, CA.

  3. central rapidities Inclusive Photoproduction of , 0, f0(980) and f2(1270) -- H1 • Insight on long-lived hadron production. Hadronic collisions particle production at central values of rapidity governed only by the properties of the QCD vacuum. • Production at HERA at similar energy as at RHIC, but in light hadron collisions. • H1 data, 38.7 pb-1, luminosity at an average photon-proton CM energy of 210 GeV Lake Louise, Alberta, CA.

  4.   (LAr Calorimeter) H1 preliminary 3<pT<8 GeV, |y|<1 dN/dM [1/GeV] η Fit with 1 gaussian + polynomial bkg M [GeV] æ ö G m m ( m ) 3 å ç ÷ 0 , i i = + F ( m ) A ç ÷ 2 - + G 2 2 2 2 ( m m ) m ( m ) è ø Mγγ[GeV] = 1 i 0 , 0 , i i i ( ) å 2 - - a - + a m a m a m 2 m e (Re f ( m )) 2 3 4 p 1 Invariant Mass Distribution Rapidity limited to |y|<1 H1 preliminary 0, f0, f2+- (Central Jet Chamber) ρ0 |y|<1 Comb bg Fit with 3 relativistic BWs, a bkg function and reflection contribution mainly from  and K*.  K* f0 f2 Lake Louise, Alberta, CA.

  5. ρ0 f0 f2 η Differential cross section as a function of rapidity (y) and PT Differential cross sections • Flat in rapidity. • Power law in pT compatible with thermodynamic- based approach. H1 preliminary H1 preliminary d/dy [nb] d /(dydpT2) [nb/GeV2] y pT [GeV] Lake Louise, Alberta, CA.

  6. H1 preliminary 1/(2j+1)d/(dydpT2) [nb/GeV2] ρ0 f0 f2 η + (published) m + pT [GeV] Differential cross sections as a function of ( mass + PT ) • Cross sections follow similar power law as for pions at same gp collision energy. • Dependence mainly on the hadron’s mass and pT support universality of long-lived hadron production. Lake Louise, Alberta, CA.

  7. f0(1) 0 s Scalar JPC=0++Nonet K0(1430) K0(1430) 0 + f0(8) 0 f0(1370) ~ uu+dd f0(1500) ~ ?? f0(1710) ~ ?? f0(8) 0 s s f0(1) a0(????) - a0(????) a0(????) + 0 3 candidates for 2 spots f0(1710)is a glueball candidate K0(1430) K0(1430) - 0 K SK S resonances in Deep Inelastic Scattering (DIS) at HERA -- ZEUS • Scalar meson nonet not well understood; a state yet to be confirmed, and an excess of candidates for the available positions in the nonet; • Lattice QCD predicts lightestglueball with JPC=0++ and mass between 1.4-1.8 GeV; • ep collisions at HERA as a new environment for resonance studies; gluon rich initial state in ep deep inelastic scattering (DIS); • K studied at HERA before; clean sample; • K K couples to meson states with JPC=(even)++. Lake Louise, Alberta, CA.

  8. 0 0 s s SVTX 0 K s VTX p Event Selection Kinematical region limited by event selection requirements and limit for HERA running with 920 GeV protons. Integrated luminosity of 121 pb-1 (1996-2000 data); Use the ZEUS Central Tracker Detector Q2= photon virtuality x = Bjorken scaling variable y = fraction of the lepton energy transferred to the proton in the proton rest frame Take only K in the region of 10 MeV around the fitted K mass; Lake Louise, Alberta, CA.

  9. Results / Discussions Fit with 3 modified relativistic Breit-Wigners and a background function. • First observation of JPC=(even)++ in DIS: • - a state consistent withf2’(1525), • with peak at MeV, width • of MeV and candidates • - X(1726)( is this the f0(1710) ?) • with peak at MeV, width • of MeV and candidates • A third state is observed in the 1300 MeV mass region, consistent with the interference. Lake Louise, Alberta, CA.

  10. 0 s Current 93% of the KsKs pairs are in the target region Target 0 s Results / Discussions 93% of the K K production is in a region where sizeable initial state gluon radiation may be expected. Lake Louise, Alberta, CA.

  11. mass width mass width PDG 2002 values (MeV) f0(1710) : f2’(1525) : L3 Phys. Lett. B501 (2001) 173-182 BELLE hep-ex/0104024 BES hep-ex/0307058 Results / Discussions Confronting L3, BELLE, BES and ZEUS ZEUS Accepted by Phys. Lett. B Hep-ex/0308006 1700 MeV mass region L3: mass 1767±14 MeV; width 187±60 MeV BELLE: mass 1768±9.6 MeV; width 323±29 MeV BES: mass 1722±17 MeV; width 167 MeV ZEUS: mass 1726±7 MeV; width 38 MeV Lake Louise, Alberta, CA.

  12. Evidence for exotic baryons in K S p final state in DIS at HERA -- ZEUS • Recent calculations based on chiral soliton model (Diakonov et al) predict the existence of a narrow S=+1 state Q+ with mass around 1530 MeV • Some experiments have reported the observation of a narrow resonance around 1530 MeV Anti-decuplet 1530 MeV 1710 MeV 1890 MeV 2070 MeV Lake Louise, Alberta, CA.

  13. Selection • Q+ can decay to K0p or K+n • Search for resonances in inclusive DIS, using 121 pb-1 of ZEUS data. • DIS event selection and K0 reconstruction similar to those in KsKs analysis. • Use Central Tracker Detector dE/dX to select (anti)proton. Preliminary p K± p± Lake Louise, Alberta, CA.

  14. Combined fit • Ks in the mass region 480-510 MeV. • (Anti)protons in the dE/dX proton band and with p < 1.3 GeV • Remove K*(892) reflection • Resolution of 5 MeV in the 1530 MeV region Preliminary 372±75 candidates Peak at 1527±2(stat) MeV Width of 10±2(stat) MeV Significance of ~5s Fit: Gaussian + P3 (free parameters) Lake Louise, Alberta, CA.

  15. S(1480)??? S(1480)??? Fitting (K s p) and (K s anti-proton) separately 126±50 candidates Peak at 1529±3(stat) MeV Width of 7±3(stat) MeV Preliminary Preliminary 393±86 candidates Peak at 1523±3(stat) MeV Width of 16±3(stat) MeV Lake Louise, Alberta, CA.

  16. Confronting with other measurements Experiment M (MeV) Significance G (MeV) SPring8 1540  10  5 < 25 (4.6s) DIANA 1539  2  “few” < 9 (4.4s) CLAS (d) 1542  2  5 21 (5.3s)SAPHIR 1540  4  2 < 25 (4.8s) ITEP (v’s) 1533  5 < 20 (6.7s) CLAS (p) 1555  1  10 26  7 (4.3s) HERMES 1528  2.6  2.1 19  5  2 (5.6s) ZEUS (Prel.) 1527±2 10±2 (5.0s) Lake Louise, Alberta, CA.

  17. Summary Three results were reported in hadron spectroscopy: • Neutral meson spectroscopy • First measurement of cross section for inclusive photoproduction of • , 0, f0(980) and f2(1270) at gpaverage energy of 210 GeV; • Differential spectra similar to those of light, long-lived hadrons. • KsKs resonances in DIS • First observation of resonances in KsKsfinal state in DIS was reported; • A state is observed at MeV, consistent with the f2’(1525); • Another state X(1726) is observed at MeV, probably the f0(1710)(glueball candidate). More stat. is needed to establish its width; • States are in a region where sizeable initial state gluon rad. is expected. • Ksp resonances in DIS • was studied in inclusive DIS sample at HERA; • A signal is observed at 1527±3 MeV with width of 10±2(stat) MeV, consistent with the predicted Q+ pentaquark; • First evidence for pentaquark in HEP colliding experiment; • Evidence for anti-pentaquark ( ). Lake Louise, Alberta, CA.

  18. Extras….. KsKs final state Lake Louise, Alberta, CA.

  19. Summary • First measurement of cross section for inclusive photoproduction of , 0, f0(980) and f2(1270) at gpaverage energy of 210 GeV. • Differential spectra similar to those of light, long-lived hadrons. Lake Louise, Alberta, CA.

  20. 0 s 0 s Summary • First observation of resonances in KKfinal state in DIS was reported; • An enhancement is observed in the 1300 MeV mass region, but its measurement is affected by the cut to eliminate the presence of the f0(980)/a0(980) at threshold; • A state is observed in the 1500 MeV mass region consistent with the f2’(1525); • Another state X(1726) is observed, probably the f0(1710)(a glueball candidate), but more statistics is needed to establish its width; • The states are produced in a region where sizeable initial state gluon radiation is expected. Lake Louise, Alberta, CA.

  21. Summary • was studied in inclusive DIS sample at HERA. • A signal is observed at 1527±3 MeV with width of 10±2(stat) MeV, consistent with the predicted Q+ pentaquark • Separate and spectra also show enhancement at this mass. The shapes are slightly different due to the different CTD response to positive and negative tracks. • First evidence for pentaquark in HEP colliding experiment • First evidence for anti-pentaquark ( ) • Improvements ongoing! Lake Louise, Alberta, CA.

  22. 0 s 0 0 s s K SK S resonances in Deep Inelastic Scattering (DIS) at HERA -- ZEUS • ep collisions at HERA as a new environment for resonance studies; gluon rich initial state in ep deep inelastic scattering (DIS); • K studied at HERA before; clean sample; • K K couples to meson states with JPC=(even)++. Some production processes at HERA Quark jets Odderon exchange Radiative VM decay Gluon ladder Lake Louise, Alberta, CA.

  23. Event Selection • Integrated luminosity of 120 pb-1 (1996-2000 data); • Events with scattered e- (e+) in Rear Calorimeter (RCAL); • Use only good tracks measured with the Central Tracking Detectors (CTD). ZEUS Detector RCAL CTD Lake Louise, Alberta, CA.

  24. Q2= photon virtuality x = Bjorken scaling variable y = fraction of the lepton energy transferred to the proton in the proton rest frame p Event Selection DIS variables Lake Louise, Alberta, CA.

  25. 0 0 s s SVTX 0 K s VTX Event Selection • Take only K in the region of 10 MeV around the fitted K mass; Lake Louise, Alberta, CA.

  26. 0 0 s s K K 0 0 0 0 0 0 0 0 s s s s s s s s K K system does not open at threshold meson fJ Event Selection Remove enhancement at K K invariant mass threshold due to the presence of the f0(980)/a0(980) state. 2553 K K candidates found in the range 0.995 < M(K K ) < 2.795 GeV Lake Louise, Alberta, CA.

  27. Current region in DIS is equivalent to an e+e- hemisphere Breit Frame Current 93% of the KsKs pairs are in the target region Target 0 0 s Pz(KsKs)<0 s 93% of the K K production is in a region where sizeable initial state gluon radiation may be expected. Pz(KsKs)>0 Results / Discussions Lake Louise, Alberta, CA.

  28. PDG 2002 values (MeV) mass width mass width Results / Discussions ZEUS fit values (MeV) 2/N width events mass width events mass • Correlations between the parameters are accounted; • Sensitivity of the data to the widths of the resonances is checked. Lake Louise, Alberta, CA.

  29. central values of rapidity H1 • How do quarks and gluons convert to colourless hadrons? • pQCD does not apply • phenomenological models of hadronisation H1prel. Data vs MC (selected events) Inclusive photoproduction of neutral hadronic resonances: , 0, f0(980) and f2(1270) Ntrack θtrack Ecluster [GeV] Rtransv [cm] Dtrack-cluster [cm] |cos α| Test universality of hadroproduction Lake Louise, Alberta, CA. good agreement

  30. ρ0 ρ0 f0 f0 f2 η f2 + η H1 Differential photoproduction cross sections H1 preliminary 1/(2j+1)d/(dydpT2) [nb/GeV2] d/dy [nb] d /(dydpT2) [nb/GeV2] (published) y pT [GeV] meson mass + pT [GeV] 2000 data: 39 pb-1 |ylab| < 1 <Wp> = 210 GeV Same behaviour as for light, long-lived hadrons Lake Louise, Alberta, CA.

  31. Quark Model (u,d,s) Scalars JPC = 0++ S=1 I=0 S q q L=1 JPC = 2++ I Tensors P = (-1)x(+1)x(-1)L = (-1)L+1 C = (-1)L+S J = 0 or 2 Masses 1-2 GeV, scalar and tensor mesons much heavier than the pseudoscalars Scalar and Tensor Mesons Lake Louise, Alberta, CA.

  32. QCD: richer than Quark Model, predicts gluon states with JPC = 0++,2++, I=0 Is this a qq state? mix g f0(1370) f0(1500) f0(1710) Observed States Ks: has S=L=0, P=-1, C=+1 KsKs: has P=+1, C=+1 g J=even KsKs final state couples only to JPC=(even)++ and it is CLEAN. This is the golden channel (given statistics) to look for scalar and tensor meson resonances Lake Louise, Alberta, CA.

  33. TensorJPC=2++ Nonet f2(1270) ~ uu+dd f2(1525) ~ ss f2(8) K2(1430) K2(1430) 0 + f2(1) f2(8) f2(1) a2(1320) - a2(1320) a2(1320) + 0 K2(1430) K2(1430) - 0 Lake Louise, Alberta, CA.

  34. Production mechanisms in DIS Odderon Exchange Gluon poor processes VM Radiative decays Gluon rich processes In quark Jets In gluon jets Lake Louise, Alberta, CA.

  35. Armenteros-Podolanski variables Photon conversion Event Selection • Armenteros-Podolanski variable • to remove photon conversions • and ; Lake Louise, Alberta, CA.

  36. Results / Discussions 2/N width width events mass width events mass widh events mass events mass PDG 2002 values (MeV) • Correlations between the parameters are accounted; • Sensitivity of the data to the widths of the resonances is checked. Lake Louise, Alberta, CA.

  37. Current region in DIS is equivalent to an e+e- hemisphere Results / Discussions Breit Frame 78% of the KsKs pairs have xp>1 Increasing xp More gluons Pz(KsKs)<0 (7%) Pz(KsKs)>0 (93%) High xpcorresponds to production in a region where sizeable initial state gluon radiation may be expected. Lake Louise, Alberta, CA.

  38. KS0KS0 final state in DIS • First observation of JCP=(even)++ in DIS. Two states are observed: • a state consistent with f2’(1525) • X(1726) (is this the f0(1710) ?) Several states have been observed in the 2GeV region (see PDG02) f0(980)/a0(980) gives Ks pair with very small opening angle in the lab. We would like to remove collinear Ks pairs and then fit the spectrum. Threshold Enhancement due to f0(980)/a0(980) Fit 3 Breit-Wigner and a backg. function: Problematic region Lake Louise, Alberta, CA.

  39. Observation of J=even meson resonances in ep cosKK < 0.92 cut Lake Louise, Alberta, CA.

  40. KS0KS0 final state in DIS Fit with 4 Breit-Wigner Þ Attempt to include the 1980 MeV mass region Lake Louise, Alberta, CA.

  41. How well a smooth background describes the data: It is less than 1% likely that a smooth distribution describes the data. Lake Louise, Alberta, CA.

  42. e+e-ggggKsKs If f(1710) is a glueball it should have small coupling to gg Lake Louise, Alberta, CA.

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