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A New Narrow Resonance in the D s + 0 System. Brian Meadows University of Cincinnati. Outline. Introduction The BaBar Experiment Observation of D sJ (2317) ! D s 0 Search for other Modes ! D s , D s , D s1 (2112), D s 0 0 , D s 0 Corroboration by CLEO
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A New Narrow Resonance in the Ds+0 System. Brian Meadows University of Cincinnati Brian Meadows, U. Cincinnati.
Outline • Introduction • The BaBar Experiment • Observation of DsJ (2317)! Ds0 • Search for other Modes !Ds, Ds, Ds1(2112), Ds00, Ds0 • Corroboration by CLEO • Interpretations • Summary Brian Meadows, U. Cincinnati
Introduction The spectrum of Ds (cs) states has gaps. • The scalar state predicted could decay to DK so it would be broad (» 270-990 MeV/c2). Observed Predicted Ds2 Ds1 D*K Mass GeV D0K D*s DsJ(2317) Ds New State JP This would make it difficult to observe …BUT If it were below DK threshold, it could be narrow. Brian Meadows, U. Cincinnati
The BaBar Detector at SLAC (PEP2) • Asymmetric e+e- collisions at (4S). • = 0.56 (3.1 GeV e+, 9.0 GeV e-) 1.5 T superconducting field. Instrumented Flux Return (IFR) Resistive Plate Chambers (RPC’s): Barrel: 19 layers in 65 cm steel Endcap: 18 “ “ 60 cm “ Brian Meadows, U. Cincinnati
Particle ID - DIRC Detector of Internally Reflected Cherenkov light • Measures Cherenkov angle in quartz • Photons transported by internal refl. • Detected at end by » 10,000 PMT’s 144 quartz bars Brian Meadows, U. Cincinnati
Particle ID - DIRC It Works Beautifully! Provides excellent K/ separation over the whole kinematic range Brian Meadows, U. Cincinnati
Electromagnetic Calorimeter • CsI (doped with Tl) crystals • Arranged in 48()£120() • » 2.5% gaps in . • Forward endcap with 8 more rings (820 crystals). Brian Meadows, U. Cincinnati
PEP-II performances Peak Luminosity 4.9 £ 1033 cm-2¢ s-1 • 24 fb-1 in run 1 • 70 fb-1 in run2 • 10 fb-1 so far in run3 run3 This analysis uses runs 1 and 2 » 110 M cc pairs run2 (~12% off peak) run1 Brian Meadows, U. Cincinnati
Off • On Charm at the BABARB Factory? • Cross section is large Can use off peak data • Also • Relatively small combinatorial backgrounds in e+e- interactions. • Good particle ID. • Detection of all possible final states including neutrals. • Good tracking and vertexing • Very high statistics. Brian Meadows, U. Cincinnati
Charm at the BABARB Factory? • Present sample of 91 fb-1 sample contains • Compare with earlier charm experiments: • E791 - 35,400 1 • FOCUS - 120,000 2 • CDF - 56,320 • Approximately 1.12 £ 106 untagged D0!K-+ events 1. E791 Collaboration, Phys.Rev.Lett. 83 (1999) 32. 2. Focus Collaboration, Phys.Lett. B485 (2000) 62. Brian Meadows, U. Cincinnati
Data Selection • All pairs of ’s, each having energy > 100 MeV, are fitted to a 0 with mass constraint. • Each 0 is fitted twice: • To the production vertex to investigate the Ds+0 mass. • To the K+K-+ vertex so that we can also use the Ds! K+K-+0 mode. D’s from B decays were removed: - each event was required to have p*D > 2.5 GeV/c Brian Meadows, U. Cincinnati
K+K-+ Mass Spectrum Approx. 131,000 Ds+ events above large background. Small bump at 2010 MeV/c2 from Brian Meadows, U. Cincinnati
The Ds+ Dalitz Plot • Events in the Ds+ mass band: • K* and bands do not cross (no double counting). • cos2 distributions evident in vector bands. Brian Meadows, U. Cincinnati
Selection of Ds+!+ and K¤0K+ • Select mass band: |m(K+K-) – 1.019| · 0.01 GeV/c2; • Select K¤0 mass band: |m(+K-) – 0.896| · 0.05 GeV/c2; • Require |cos| > 0.5 to enhance proper helicities of each vector. • Each resulting sample has about same size. Brian Meadows, U. Cincinnati
Total K+K-+ Mass Spectrum • Sum of + and K¤0K+ contributions is » 80,000 Ds+ above background. • We define • signal region: 1.954 < m(K+K-+) < 1.980 GeV/c2 • and two sideband regions: 1.912 < m(K+K-+) < 1.934 GeV/c2 1.998 < m(K+K-+) < 2.020 GeV/c2 Brian Meadows, U. Cincinnati
Ds+0 Mass Spectrum • A striking signal observed in the Ds+0 system. • Signal clearly associated with both Ds+ and 0 • Is not a reflection of any other known state (MC) D § Ds§ 0 Brian Meadows, U. Cincinnati
200 150 100 50 0 K* Events / 5 MeV/c2 2.1 2.3 2.5 2.1 2.3 2.5 m(Ds+0)GeV/c2 Ds+0 Mass Spectra • Separate + and K¤0K+ subsamples: • Require p¤ > 3.5 GeV/c • Ds*+(2112) and signal at 2.32 GeV/c2 present in both channels with roughly equal strength. Brian Meadows, U. Cincinnati
Study Ds+0 mass spectrum behavior in p* intervals Present in all intervals Better signal to background at higher p* values Study dependence in Monte Carlo Ds0 CMS Momentum (p*) Dependence • A p* > 3.5 GeV/c cut • Improves signal-to-background • Slightly improves resolution Brian Meadows, U. Cincinnati
400 300 200 100 0 Events / 5 MeV/c2 2.1 2.2 2.3 2.4 2.5 m(Ds+0) GeV/c2 Fit to the Signal • Require p* > 3.5 GeV/c. Fit to polynomial and a single Gaussian. m = 2316.8 § 0.4 GeV/c2 = 8.6 § 0.4 MeV/c2 (errors statistical only). Brian Meadows, U. Cincinnati
Experimental Resolution • Fit Ds*+(2112) width in Monte Carlo and Data: Data: = 6.6 § 0.1 MeV/c2 MC: = 5.7 § 0.1 MeV/c2 • So MC is too optimistic by factor 1.16. • Generate Monte Carlo events for DsJ+(2317) with = 0: = 7.7 § 0.2 MeV/c2 • Scale by factor 1.16 ! expect = 8.9 MeV/c2. • ForDsJ+(2317) with p* > 3.0 GeV/c we find: = 9.0 § 0.4 MeV/c2 So width is consistent with mass resolution. Brian Meadows, U. Cincinnati
Data from Ds+!K+K-+0 X 103 Use other vertex for 0 Require at least one vector meson in two body subsystem. No from a 0 candidate can be part of any other 0. Require p* > 3.5 GeV/c. Require laboratory momentum of each be > 300 MeV/c. 25 20 15 10 5 0 Ds+ D+ 1.75 2.0 m(K+K-+0) GeV/c2 Brian Meadows, U. Cincinnati
Over 1500 events in the signal. The resonance has width comparable with the mass resolution in these systems. It is evident in two different topologies a)D§s!K§ K¨ § (two modes) b) D§s!K§ K¨ §0 Masses consistent in all channels – width » resolution. New Narrow Resonance “DsJ(2317)” “Ds(2317)” Ds1(2112) p* > 3.5 GeV/c p* > 3.5 GeV/c Ds1(2112) Brian Meadows, U. Cincinnati
DsJ+(2317) Decay Angular Distribution • Helicity angle distribution could provide spin information. • The Ds+0 mass spectrum is fitted in 10 slices of cos . • The corrected distribution in cos is consistent with being flat (43 % probability). uncorrected Acceptance corrected cos cos cos Brian Meadows, U. Cincinnati
Search for Other DsJ+(2317) Decay Modes • We have studied the mass spectra for • Ds+00 • Ds+ • Ds+ • Ds*+(2112) • Ds+0 • In all cases, we require that: • The ’s are not part of any 0 candidate. • The combination has p* > 3.5 GeV/c. Brian Meadows, U. Cincinnati
DsJ (2317)? Events / 12 MeV/c2 m(Ds00) GeV/c2 Ds00 System Limited statistics in this system. No prominent structure at the mass of DsJ+(2317) Brian Meadows, U. Cincinnati
Ds+, Ds+, Ds1(2112) • No evidence for any of these decays. • Suggests JP = 0+ Brian Meadows, U. Cincinnati
DsJ(2317) Other Possibilities -Ds+0, Ds1(2112)0 • No evidence for DsJ(2317) • Enhancement at 2460 MeV/c2 mostly due to kinematic overlap between DsJ(2317) and Ds1(2112) bands. • Great care required to extract any signal from the region. Ds1(2112)0 Brian Meadows, U. Cincinnati
CLEO Sees it Too Not in Ds+- • They use 13.5 fb-1 • Signal seen in Ds0 • Not seen in Ds+-, • Ds, Ds1(2112) Signal has events (» same yield / fb as BABAR). Brian Meadows, U. Cincinnati
Physics Summary • We observe a state at 2.32 GeV/c2 whose measured width is consistent with the mass resolution ( < 10 MeV/c2). • So far, this is only seen in the Ds0 decay mode. • The mass is about 40 MeV/c2 below the DK threshold. • The decay to Ds0 implies natural parity (0+, 1-, 2+, etc.) • JP=0+ suggested by absence of a signal in Ds+ and Ds00. • If this is so, decay to Ds1(2112) is allowed, but not yet seen. Brian Meadows, U. Cincinnati
So What is this State? • If this state is a cs meson, then the decay observed violates isospin conservation • This is not unusual. Ds1(2112) also decays to Ds0 about 5% of the time. Cho and Wise have predicted this rate using 0- mixing. • A multi quark state (conjectured by N. Isgur and H. Lipkin). • First heavy quark recurrence of a0(980) or even f0(980)? a0(980) ! / KK (I=1) f0(980) ! / KK (I=0) • Work is in progress to search for Ds+§ decay modes. Brian Meadows, U. Cincinnati
If it is a cs Meson … R. Cahn and J.D. Jackson, hep-ph/0305012. • It could be the missing P wave cs state with JP = 0+. • Our result disagrees with current expectations. Mass and decay modes are quite different from those expected. • Use Ds(2317) mass as one of three inputs – predict mass of fourth p wave state. pwave states Drawing: R Cahn, J. Jackson Brian Meadows, U. Cincinnati
Summary • New charmed, strange, narrow resonance at 2.32 GeV/c. • Poses possible problems for the quark potential model. • May be a four quark or DK bound state. • Much speculation is being generated: R. Cahn, J.D. Jackson, hep-ph/0305012 T. Barnes, F. E. Close, H. J. Lipkin, hep-ph/0305025 E. Van Beveran, G. Rupp, hep-ph/0305035 H-Y Cheng, W-S Hou, hep-ph 0305038 W. A. Bardeen, E. J. Eichten, C. T. Hill, hep-ph 0305049 P. Szczepaniak, hep-ph 0305060 S. Godfrey, hep-ph/0305122 P. Colangelo, F. De Fazio, hep-ph/0305140 Brian Meadows, U. Cincinnati
Back up Slides Brian Meadows, U. Cincinnati
Silicon Vertex Tracker (SVT) • 5 Layers double sided AC-coupled Silicon • Rad-hard readout IC (2 MRad – replace ~2005) • Low mass design • Stand alone tracking for slow particles • Point resolution z » 20 m • Radius 32-140 mm Brian Meadows, U. Cincinnati
Drift Chamber 40 layer small cell design 7104 cells He-Isobutane for low multiple scattering dE/dx Resolution »7.5% Mean position Resolution 125 m Brian Meadows, U. Cincinnati
Particle ID - DIRC D0 D0 Brian Meadows, U. Cincinnati
An Example: Ds Production spectrum • Below 2.4 GeV/c Ds can come from B decay • Use off peak data there to reduce combinatorial background Off peak (normalized for p*>2.4 GeV/c) On peak Brian Meadows, U. Cincinnati
Data Selection • In this study we look for resonances decaying to: Ds0 • Ds+ mesons are selected with +,K¤0K+ and K+K-+0 decay modes, so we select events in final state: K+K-+ (+ charged conjugate) • To do this we: • Select all combinations of three charged tracks with total charge § 1, an identified K+K- pair and a third track which is not a K§. • Require Ds+ candidate fit well to a common vertex. • Fit the Ds+ composite momentum to a primary vertex Brian Meadows, U. Cincinnati
Resolution Improvement a) Constrain Ds mass b) Remove duplicated ’s Brian Meadows, U. Cincinnati
Another Topology Ds+!K+K-+0 Rational: • Mode has same topology as Ds+0 when Ds+!K+K-+. • Width of Ds+!K+K-+0 gives further, direct information on the Ds+0 mass resolution. • Can provide corroborative evidence for Ds+0(2317) signal. Strategy: • Use other vertex fit. • Select cleaner sample using K*0, K*§, +, resonant sub channel selections. Brian Meadows, U. Cincinnati
Test Using Monte Carlo Simulation • We simulate the reaction e+e-!cc using GEANT4. • Events generated contain all that is presently known about charm spectroscopy. • Approximately 80 x 106 events are processed exactly the same way as the data. Brian Meadows, U. Cincinnati
Test Using Monte Carlo Simulation • Sum of + and K¤0K+ and Ds+0 mass spectra. • We observe the known decay: Ds¤+(2112)!Ds+0. • The Ds+0 mass spectrum shows no sign of 2.32 GeV/c2 signal. We would expect » 1,400 events. We conclude that the 2.32 GeV/c2 structure is not due to reflections from known charm states. Brian Meadows, U. Cincinnati
2.32 GeV/c2 Is 2.32 GeV/c2 Structure due to Ds¤+(2112)? • We use the ’s from the 0 candidate to compute the two masses Ds+1,2. • The 2.32 GeV/c2 signal survives when events with a Ds+1,2 mass in the Ds¤+(2112) are removed. Ds¤+(2112) removed Ds¤+(2112) selected We conclude that the signal at 2.32 GeV/c2 is not a Ds¤+ reflection Brian Meadows, U. Cincinnati
Mass and Width Ds+!K-K++0: M = 2317.6 § 1.3 MeV/c2 = 8.8 § 1.1 MeV/c2 Ds+!K*0K+, +: M = 2316.8 § 0.4 MeV/c2 = 8.6 § 0.4 MeV/c2 Brian Meadows, U. Cincinnati
DK Molecule? T. Barnes, F.E. Close, H.J. Lipkin, hep-ph/0305025 • I=0 csnn or a DK bound state? • If DK bound state, then some I=0 component to explain narrow width. Brian Meadows, U. Cincinnati
A qqcs Four Quark State? From H. Cheng and W. Hou, hep-ph/0305038. Brian Meadows, U. Cincinnati
Quasi Bound cs State? E. van Beveren, G. Rupp, hep-ph/0305035 • Charmed cousin of a0(980), f0(980), (600), (800) nonet. • Predicts D0(2030) – broad because above DK threshold • Also predicts D0(2640), D0(2790) to go with K0(1430), etc. Brian Meadows, U. Cincinnati