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New Particles in the Strange Charm System.

New Particles in the Strange Charm System. Brian Meadows University of Cincinnati. Outline. Introduction to Particle Physics Forces of nature Quarks How are new particles found ? The B A B AR Experiment The discovery of an new kind of particle? D ’ sJ ! D s  0

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New Particles in the Strange Charm System.

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  1. New Particlesin the Strange Charm System. Brian Meadows University of Cincinnati Brian Meadows, U. Cincinnati.

  2. Outline • Introduction to Particle Physics • Forces of nature • Quarks • How are new particles found ? • The BABAR Experiment • The discovery of an new kind of particle? D’sJ ! Ds0 • What is Interesting about this? • Other new particles Brian Meadows, U. Cincinnati

  3. Forces of Nature Particle physics is all about fundamental forces: • Electromagnetic force • Holds atoms together (and apart!) • Stops us falling through the floor. ! Long range / 1/r2 • Gravity • Dominates on astrophysical scales. • Holds our feet ON the floor! ! Long range / 1/r2 Brian Meadows, U. Cincinnati

  4. Forces of Nature • Strong force • Holds protons (p) and neutrons (n) together in nuclei. • Holds quarks together inside neutrons, protons and all “hadrons”. • Contributes to “hadron” decays, e.g. r!p+p- ! Short range (nuclear diameter » 10-15 m) • Weak force • Causes radioactive decay e.g. n!p+ + e- + ne • Not really “weak” but just “rare”. ! Very short range (» 10-18 m). Brian Meadows, U. Cincinnati

  5. The Force Scales • Particles that leave “tracks” either • are stable OR • decay by weak interaction Brian Meadows, U. Cincinnati

  6. Quarks and Flavors • Just 6 quarks are building blocks for all strongly interacting particles (hadrons) • They come in two charges u c t - charge +2/3 e d s b - charge -1/3 e • Each has a unique “flavor”: “Isospin” : u (I = ½ ,I3 = + ½ ); d (I = ½ ,I3 = + ½ ) “Strangeness” : s (S = -1) “Charm” : c (C = +1) “Beauty” : b (B = +1) “Top” : t (T = +1) • “Baryon number” (B#) of each is 1/3. • Antiquarks have opposite charges, flavors and B#. Brian Meadows, U. Cincinnati

  7. Quarks and Hadrons • Hadrons are particles that feel the Strong Force. Baryons -p, n, , , , , c, … • Basic composition - 3 quarks p = uud, n = udd, + = uus, p = uud, … etc. Mesons -, K, D, Ds, B, , , , f, a, … • Basic composition - quark-antiquark pairs + = ud, - = ud, K- = su, D+ = cd Ds+ = cs , B0 = bd, … etc. • Additional quark-antiquark pairs are not excluded. Brian Meadows, U. Cincinnati

  8. d d d Quarks and Decay Diagrams • Strong decay D*+!D0 + + • Weak decay Ds+!K0 + K+ c D0 c u All flavors conserved D*+ u + s K0 c Flavors NOT Conserved (c!s) Ds+ W u s K+ s Brian Meadows, U. Cincinnati

  9. How to Find a New Particle • IFa) It is stable OR b) It decays by weak interaction: can observe it directly as a track in a set of detectors. • Its mass is the “effective mass M” of the decay products. For example Ds+!K-+K+++ of the indicated decay products. (Note – units are such that c=1!) Brian Meadows, U. Cincinnati

  10. How to Find a New Particle • IF it decays by Strong or EM forces: • Its lifetime  is too short for a track of visible length. • BUT its decay products (usually) do leave tracks. • Measure 4-momenta of decay products and compute their effective mass M as before to determine particle’s mass. • “Uncertainty Principle” relates lifetime () and the precision (M) to which the particle’s mass can be determined. M£¼h (6 £ 10-27 J¢sec) • We expect a peak in the M distribution with width: • M ~ 100 MeV (Strong), ~10 eV (EM), ~0.01 eV for Weak decays. Brian Meadows, U. Cincinnati

  11. The BaBar Detector At Stanford Linear Accelerator Center (SLAC) Brian Meadows, U. Cincinnati.

  12. The BaBar Detector at SLAC (PEP2) • Asymmetric e+e- collisions at (4S). •  = 0.56 (3.1 GeV e+, 9.0 GeV e-) • Principal purpose – study CPV in B decays 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

  13. Electromagnetic Calorimeter • CsI (doped with Tl) crystals • Arranged in 48()£120() • » 2.5% gaps in . • Forward endcap with 8 more  rings (820 crystals). g g  BABAR  0!gg 0!gg Brian Meadows, U. Cincinnati

  14. 144 quartz bars Particle ID - DIRC • Measures Cherenkov angle in 144 quartz bars arranged as a “barrel”. • Photons transported by internal reflection • Along the bars themselves. • Detected at end by ~ 10,000 PMT’s Detector of Internally Reflected Cherenkov light PMT’s Brian Meadows, U. Cincinnati

  15. Particle ID - DIRC It Works Beautifully! 10 8 6 4 2 0 BABAR K/ separation () Provides excellent K/ separation over the whole kinematic range • 2.5 3 3.5 4 • Momentum (GeV/c) Brian Meadows, U. Cincinnati

  16. 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

  17. 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

  18. “A Typical Event”  clusters Brian Meadows, U. Cincinnati

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  21. Surprising Discovery of New Particle Brian Meadows, U. Cincinnati.

  22. Data Selection • We looked for decays of well known particles: Ds! K-K++ and: 0! • The Ds decays are weak • So it leaves a track. • The 0 decays are EM • So there is no track. • 0’s could come from either end of the Ds track. Brian Meadows, U. Cincinnati

  23. K+K-+ Effective Mass Spectrum • Effective mass for Ds+!K-K++ • Can also see another well known particle D+!K-K++ • Define signal and background(sideband) regions Brian Meadows, U. Cincinnati

  24. The Ds+0 Effective Mass !!see PRL 90, 242001 (2003) • 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§ Ds*(2112) (known) Ds*(2112) (known) 0 Brian Meadows, U. Cincinnati

  25. 400 300 200 100 0 Events / 5 MeV/c2 2.1 2.2 2.3 2.4 2.5 m(Ds+0) GeV/c2 The Signal is Very Narrow Ds*(2112) Fit to polynomial and a single Gaussian. N = 1267 § 53 Events m = 2316.8 § 0.4 GeV/c2 = 8.6 § 0.4 MeV/c2 (errors statistical only). Measurement Resolution curve.  is compatible with detector resolution. Brian Meadows, U. Cincinnati

  26. It Also Behaves Like a Particle Should:CMS Momentum (p*) Dependence • Signal seen in all p* ranges. • Background less significant at higher p* values • Yield maximum at ~3.9 GeV/c • Excitation curve appears to be compatible with charm fragmentation process. Brian Meadows, U. Cincinnati

  27. 250 200 150 100 50 0  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 Multiple Ds+ Modes • Separate Ds+!K-K++ into + and K¤0K+ subsamples: • Ds*+(2112) and signal at 2.317 GeV/c2 present in both channels with roughly equal strength. p* > 3.5 GeV/c Brian Meadows, U. Cincinnati

  28. Search for Other DsJ+(2317) Decay Modes • We also looked at effective mass spectra for • Ds+0 0 • Ds+ • Ds+  • Ds*+(2112) • Ds+0  • In all cases, we required that: • The ’s are not part of any 0 candidate. • The combination has p* > 3.5 GeV/c. None of these found Brian Meadows, U. Cincinnati

  29. Ds+, Ds+, Ds*(2112) • No evidence for DsJ(2317) in any of these decays. • Absence of Ds+ weakly suggests J = 0 • However other two modes would be expected for a JP = 0+. Brian Meadows, U. Cincinnati

  30. Ds+0, Ds*(2112)0- Other Possibilities • No evidence for D*sJ(2317)+ either of these modes • BUT … • There seems to be a second state at ~ 2460 MeV/c2 ! Events / 7 MeV/c2 Ds*(2112)0 A second, newstate: Ds’(2460) ! Ds*(2112)p0 m(Ds+0) Brian Meadows, U. Cincinnati

  31. What is Interesting About New Ds’s? Ds mesons hitherto thought of as cs states. Two problems for the new states: a) cs states have no isospin (I = 0) The p meson has I=1 (triplet of charges). p+, p0, p- So where does the isospin come from in the decay Ds*(2317) !Ds + p0?? b) Other problem has to do with the fact that this new state does not fit in with models of quark-antiquark mesons. Some physicists think it may have an additional q-qbar pair! Brian Meadows, U. Cincinnati

  32. SQ L Sq Heavy-Light Quark Systems areLike the Hydrogen Atom • c quark (Q) much heavier than s quark (q) • When mQ ! 1, sQ is fixed. • So jq = L­sq is separately conserved • Total spin J = jq­sQ • Ground state (L=0) is doublet with jq=1/2 • Orbital excitations (L>0) – two doublets (jq=l+1/2 and jq=l-1/2). • Energy levels can be computed – correctly predicts where at least 27 Qq and QQ particles are found to within 10 MeV. • The new Ds states have masses too low by ~140 MeV ! Brian Meadows, U. Cincinnati

  33. Heavy-Light Systems (2) 2jqLJ Width JP • Narrow statesare easy to find. • Two wide states are harder. • Since charm quark is not infinitely heavy, some jq=1/2, 3/2 mixing can occur for the JP=1+ states. jq = 3/2 2+ small 3P2 large 1+ 1P1 L = 1 1+ 3P1 small jq = 1/2 1P0 0+ large tensor spin-orbit jq = 1/2 1- small 1S1 L = 0 small 0- 1S0 Brian Meadows, U. Cincinnati

  34. Charmed Meson Spectroscopy c. 1995 Brian Meadows, U. Cincinnati

  35. Charmed Meson Spectroscopy pre 2003 D*0K+threshold D0K+threshold BABAR may have found these – but below threshold. Brian Meadows, U. Cincinnati

  36. We Seem to have Started Something! • Our competitor – the BELLE experiment in Japan – has seen a new, massive state X(3872) !J/+- • Again, its mass profile is narrow (width comparable to resolution). • Its existence has been confirmed in the CDF experiment at FNAL in proton-antiproton collisions at 1 TeV. • It is also seen in the BaBar experiment. • What is interesting: • This lies just 100 MeV below D*(2112) D threshold. • Ds* (2317) lies just 40 MeV below DK threshold • Ds’ (2460) lies just 40 MeV below D*(2112) K threshold Brian Meadows, U. Cincinnati

  37. Yet Another New Narrow State! BELLE’s “X” CDF Confirms “X” BELLE : m = 3872.0 § 0.6 § 0.5 MeV/c2 CDF : m = 3871.4 § 0.7 (stat.) MeV/c2  compatible with resolution. Brian Meadows, U. Cincinnati

  38. Unusual Baryons Also Being Seen • Various peaks have been reported in effective mass spectra of exotic systems such as strangeness S = +1 baryons (Cannot be three quark systems because s quark has strangeness S = -1). • If confirmed, these signals could be regarded as “pentaquarks” – three quark baryons with an additional quark-antiquark pair. Brian Meadows, U. Cincinnati

  39. New, Narrow S = +1 Baryon! CLAS hep-ex/0307018 DIANA hep-ex/0304040 Spring-8 hep-ex/0301020 PRL 91: 012002 (2003) d!K+K-pn K+Xe!K0pXe'  n!K+K-n MM(K+) CLAS : m = 1542 § 5 MeV/c2; DIANA : m = 1539 § 2 MeV/c2 Spring-8 : m = 1.54 § .01 GeV/c2 ¼ resolution Brian Meadows, U. Cincinnati

  40. Conclusions • New, narrow (ie width consistent with mass resolution) states are being found after the discovery by BaBar of DsJ*(2317) !Ds + p0 • The D_s states have masses inconsistent with spectroscopic models. • There is conjecture that mesons (and baryons) with additional quark-antiquark pairs may finally be seen. Brian Meadows, U. Cincinnati

  41. Particle ID - DIRC D0 D0 Brian Meadows, U. Cincinnati

  42. The Ds(2317) Appears !!see PRL 90, 242001 (2003) • When Antimo Palano plotted Ds+0 effective masses he found a huge, unexpected peak. A new particle!! There is no signal from Ds+sidebands. The (well known) Ds*(2112)!Ds+0 signal is clear too. How did CLEO miss it?! CLEO discarded All these events. Brian Meadows, U. Cincinnati

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