Search for Exotic Hadrons at Jefferson Lab Elton S. Smith, Jefferson Lab Q+ X+ X−− S5 N5 Strong interactions quark model Latest on Pentaquarks Gluonic excitations JLab 12-GeV upgrade

Families within families of matter DNA 10-7 m Molecule 10-9 m Atom 10-10 m Nucleus 10-14 m Proton 10-15 m Quark <10-18 m

Interactions understood in terms of quarks Very high energy BUT… free quarks have been not found, only particles that contain quarks

Electromagnetic and color forces ±1 charge O(a) ~ 0.01 g ±3 “color” charges O(as) ~ 1 Color force in Quantum Chromo Dynamics (QCD)

Quarks are confined inside colorless hadrons Quarks combine to “neutralize” color force q q q q q mesons baryons glueball meson hybrid meson Configurations outside the standard quark model q pentaquark molecules

Families of quarks S=+1 S= 0 I3 = Q ─ ½ (B+S) −½ +½ S=−1

Baryons built from meson-baryon, or qqqqq Hadron multiplets K p Mesons qq Baryons qqq N S X W─ Baryons built from meson-baryon, or qqqqq Q+ X+ X−−

Quarks and QCD G~15 MeV s (ud) (uds) (ud) Spin ½+ antidecuplet L=1 L=1 Quantum Chromo Dynamics allows hadronic states with different quark configurations (e.g. 4q+q pentaquarks). When the antiquark has a different flavor than the other 4 quarks, the pentaquark has “exotic” quantum numbers. G~15 MeV Rotational excitations of the soliton [rigid core surrounded by chiral (meson) fields] Diakonov, Z.Phys. A359, 305 (1997) L=1 (ud) s JW hep-ph/0307341 JM hep-ph/0308286 SZ hep-ph/0310270 L=1 (ud) (uds) I=1,S=0 I=0,S=1/2 Karliner, Lipkin, hep-ph/0307243 Spin ½+ antidecuplet

Initial evidence for pentaquark states Spring8 DIANA JLab-d ELSA ITEP SVD/IHEP JLab-p HERMES ZEUS pp  S+Q+. COSY-TOF CERN/NA49 Q0c H1 X--

The Q+ width Measured width dominated by experimental resolution U. Meissner Measured width dominated by experimental resolution Analysis of K+A data give limit of few MeV. K+D -> X K+D , K+Xe → X Sibirtsev et al.: GQ < 1 MeV In most cases the observed width of the state is dominated by experimental resolution. Estimates of the natural width have to rely on estimates using the elastic K+n -> K+ n or K+-deuteron total cross section measurements. Several estimates show that the Q+ width cannot be more than about 1 MeV. The analysis of K+D total cross section data gives a width of 0.9 +/- 0.3 MeV. The data and fits are shown in here. Very narrow for a hadronically decaying particle with mass ~100 MeV above threshold: Q+(1540) -> nK+, pK0 From selected data sample What can we say about event rates? K+n → Q+ => G~1 MeV, K-p → L* => G~16 MeV. => s(Q+)/s(L*) ~ 1.4% for formation. GQ = 0.9 +/-0.3 MeV W. Gibbs, Phys.Rev.C70, 054208 (2004)

Null Results

Pentaquark Scorecard (April 2005) Negative Results Positive Results Experiment  (1520)  Lc ____________________________________ E690 5000 ALEPH 2800 CDF 3300 16000 BaBar 10000000 100000 HERA-B 5000 3000 50000 SPHINX 5500 23700 12000 HYPERCP COMPASS BELLE 15520 SELEX 2,800,000  (1530) D D* ________________________________________________________ E690 15000 ALEPH 3350 200 25000 CDF 36000 1000 3000000 536000 BaBar 258000 17000 HERA-B 18000 ZEUS 2600 160 WA89 676000 FOCUS 84000 36000 Experiment signal backgrd  (1520)  Spring 8 19 17 25 Spring 8 56 162 180 SAPHIR 55 56 530 CLAS(d) 43 54 212 126 CLAS(p) 41 35 DIANA 29 44 1152  19 8 HERMES 51 150 850 COSY 57 95 ZEUS 230 1080 5700* 193 SVD 35 93 260 NOMAD 33 59 ________________________________________ signal backgrd  D* NA49 38 43 1640 H1 50 52 3000 * Estimate from cross section

Experimental evidence for Q+ Many experiments New results from dedicated experiments Examples from CLAS detector only No attempt at completeness

Search for Pentaquarks at CLAS A comprehensive program to search for pentaquarks in photoproduction experiments at Jeffeson Lab were approved in 2003- 2004 with the goal of confirming previous results and explore new kinematics with at least a factor 10 increase in statistics. CLAS(d) g2 2003 Phys. Rev. Lett. 91, 252001-1 SAPHIR 2003 Phys. Lett. B572, 127 NA49 2004 Phys. Rev. Lett. 92, 042003-1 CLAS(p) g6 2004 Phys. Rev. Lett. 92, 032001-1 Relevant Publication g10 deuteron Eg ~ 1.0-3.5 GeV preliminary results g11 proton Eg ~ 1.6-3.8 GeV hep-ex/0510061, accepted by PRL eg3 deuteron Eg ~ 4.0-5.4 GeV data taken, analysis in progress Super-g proton Eg ~ 3.8 – 5.7 GeV planned for 2006

JLab accelerator CEBAF Continuous Electron Beam Energy 0.8 ─ 5.7 GeV 200 mA, polarization 75% 1499 MHz operation Simultaneous delivery 3 halls

CEBAF Large Acceptance Spectrometer Torus magnet 6 superconducting coils Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers Liquid D2 (H2)target + g start counter; e minitorus Drift chambers argon/CO2 gas, 35,000 cells Gas Cherenkov counters e/p separation, 256 PMTs Time-of-flight counters plastic scintillators, 684 photomultipliers

Quark lines for production of Q+ g K− us us K+ Q+ n ddu ddu n Q+ is composed of (uudds) quarks

gd → p K─K+ (n) in CLAS K+ p K- Sectors 3 & 6 Sectors 1 & 4

CLAS Cross Section Checks gp  p w g10 preliminary (3375A) World data CLAS g11 preliminary SAPHIR np- 1.05 < Eg < 1.15 GeV ds/dWCM (mb/sr) Different final states are measured simultaneously in the CLAS detector Cross section for known reactions have been extracted to test the accuracy of the analysis procedure 1% of statistics gp  K+L s(mb) CLAS g11 preliminary SAPHIR cosqCM(p-) Eg(GeV)

CLAS published data on gd → p K─K+ (n) Q+ p K– Re-scattering Events/10 MeV MM(K-p) (GeV/c2)

New high Statistics CLAS(d) result The statistical significance in the published data is an unlucky coincidence of a statistical fluctuation and an underestimate of the background in the mass region of 1.54 GeV/c2. preliminary M(nK+)(GeV) Model-independent uppper limit 95% CL for Q+ is < 20nb. With assumptions about the spectator, we can set a model- dependent upper limit to the cross section of < 4-5 nb.

Search for the Q+ (1540) on proton target K0 K+ p+ g p Q+ p− Counts KS M (p+p-)(GeV) The K0 is detected via its KS component decaying into p+ p- Final state neutron is identified using the missing mass technique Strangeness is tagged detecting the K+ Using the full statistics (70 pb-1) a total of ~120000 events are selected Counts n Mx(p+p-K+ X)(GeV)

Upper Limit on the Q+ Yield Counts/4 MeV Counts/4 MeV -0.8 < cosqCM < -0.6 Q+(1540) ? no structure is observed at a mass of ~1540 MeV the nK+ mass spectrum is smooth M(nK+)(GeV) Counts/4 MeV 0.6 < cosqCM < 0.8 M(nK+)(GeV) M(nK+)(GeV)

Upper limit to the cross section gp→Q+K0 Absolute cross section Detection efficiency computed for several Q+ production models Br(Q+→nK+) = 50% s < 1.3 nb

Pentaquark Status publ. Comments s/ b+s Group Signal Backgr. Significance publ. Comments ---------------------------------------------------------------------- SPring8 19 17 4.6s 3.2s SPring8 90 260 4.8s SAPHIR 55 56 4.8s 5.2s DIANA 29 44 4.4s 3.4s CLAS(d) 43 54 5.2s 4.4s CLAS(p) 41 35 7.8s 4.7s  18 9 6.7 3.5s HERMES 51 150 4.3-6.2 3.6s ZEUS 230 1080 4.6 6.4s COSY 57 95 4-6 4.7s SVD 41 87 5.6 3.6s SVD-2 370 2000 7.5s Improved analysis NA49 38 43 4.2 4.2s H1 50.6 51.7 5-6 5.0s SPring8 80 200 4.8s L*(K+n) STAR 2,250 150,000 3.5-5s Q++ candidate s/ b+s G11 CLAS-p G10 CLAS-d ? BELLE Q+ This slide summarizes the remaining evidence for any pentaquark. The new CLAS results eliminated two signals one on hydrogen and one on deuterium. The two non-Theta+ signals at H1 and NA49 are highly questionable and contradict later results from ZEUS and HERA-B with higher sensitivity. Finally, the very new CLAS data on deuterium, presented here for the first time, should be confronted with the LEPS deuterium results from SPring8 which have lower statistics. On the side favoring pentaquark signal is some positive news: The SVD-2 improved analysis gives many more events with high significance. SprinG8 claims a signal in L*(K+n) with 5s, and there is a signal of a doubly charged Q++ from STAR at RHIC. ? BABAR X5 HERA-B, CDF, COMPASS ZEUS, FOCUS, BABAR Q0c From V. Burkert EINN 2005, Milos Greece

Remarks on Pentaquarks - theory All models have difficulty understanding the very narrow widths of the Q+ (~ 1 MeV). Quark models do not naturally generate positive parity multiplets (s-wave configuration leads to negative parity). Most calculations on the lattice do not predict bound states Role and importance of diquark configurations has been highlighted during these investigations u d d

Remarks on Pentaquarks - experiment Beware of statistics - Naïve estimates tend to overestimate significance of signal. Empirical (smooth) background shapes do not always represent reality and need to be treated with special care. Jefferson Lab has dedicated significant resources and priority to check initial results by running dedicated experiments proposed and analyzed in record times. Summary: Pentaquark is not dead, but it is on live support

Gluonic Excitations hybrid meson q hybrid meson High mass requires higher energy beams Predicted for heavy quarks by lattice QCD Exotic JPC combinations do not mix with conventional mesons Goal is to probe the dynamical role of glue in mesons

Normal Mesons – qq color singlet bound states Spin/angular momentum configurations & radial excitations generate our known spectrum of light quark mesons. Starting with u - d - s we expect to find mesons grouped in nonets - each characterized by a given J, P and C. Spin 0 Spin 1 K0 K+ K* r w f p0 h’ p− p+ h K− K0 JPC = 0– + 0++ 1– – 1+ – 2++ … Allowed combinations JPC = 0– – 0+ – 1– + 2+ – … Not-allowed: exotic

Quark binding and configuration of gluons Confinement arises from flux tubes and their excitation leads to a new spectrum of mesons From G. Bali

Hybrid Mesons Hybrid mesons 1 GeV mass difference (p/r) Normal mesons

Quantum Numbers of Hybrid Mesons Excited Flux Tube Quarks Hybrid Meson like Exotic Flux tube excitation (and parallel quark spins) lead to exotic JPC like

exotic nonets 2 + – 2 + + 2 – + 1 – – 1– + 1 + – 1 + + 0 + – 0 – + Radial excitations Meson Map 1.0 1.5 2.0 2.5 qq Mesons L = 0 1 2 3 4 Each box corresponds to 4 nonets (2 for L=0) Mass (GeV) exotic nonets 0 – + 0 + – 1 + + 1 + – 1– + 1 – – 2 – + 2 + – 2 + + 0 + + Glueballs Hybrids (L = qq angular momentum)

Reports of JPC exotics p1(1400) and p1(1600) are likely four-quark (qqqq) mesons or generated by meson-meson interactions. p1(2000) mass and decays are consistent with theoretical expectations, but need confirmation. No families of exotics have been reported.

understood acceptance Exotic signal in E852 Correlation of Phase & Intensity Exotic signal 1(1600) Leakage From Non-exotic Wave due to imperfectly understood acceptance Result has also been challenged using a larger statistics data sample with both p−p−p+ and p−p0p0 hep-ex/0502022

Families of Exotics g  ,, 1-+ nonet K1 IG(JPC)= ½ (1-) h’1 IG(JPC)=0+(1-+) h1 IG(JPC)=0+(1-+) K1 IG(JPC)= ½ (1-) 1-+ nonet p1 IG(JPC)=1-(1-+) N g e X Couple to vector meson + exchanged particle p1  rp h1  rb1 , wf g  ,, h’1  fw

Strategy for Exotic Meson Search Use 8 – 9 GeV polarized photons (12 GeV electron beam) Expect production of hybrids to be comparable to normal mesons Dearth of experimental data Use hermetic detector with large acceptance Decay modes expected to have multiple particles hermetic coverage for charged and neutral particles high data acquisition rate to enable amplitude analysis Perform partial-wave analysis identify quantum numbers as a function of mass check consistency of results in different decay modes

Upgrade magnets and power supplies CHL-2 Upgrade magnets and power supplies 12 6 GeV CEBAF add Hall D (and beam line) Enhance equipment in existing halls

GlueX collaboration

Architect’s rendering of Hall D complex Service Buildings Hall D Cryo Plant Counting House

Coherent Bremsstrahlung 12 GeV electrons Incoherent & coherent spectrum flux This technique provides requisite energy, flux and polarization tagged 0.1% resolution 40% polarization in peak photons out collimated electrons in spectrometer diamond crystal Hadronic Backgrounds photon energy (GeV)

Coherent Bremsstrahlung GlueX / Hall D Detector Lead Glass Detector Solenoid Coherent Bremsstrahlung Photon Beam Tracking Target Cerenkov Counter Time of Flight Barrel Calorimeter Note that tagger is 80 m upstream of detector Detector Review Oct 20-22, 2004 Electron Beam from CEBAF

Acceptance: high and uniform over PWA angles  ~ 0.98 Acceptance  ~ 0.99 cosGJ GJ

Finding an Exotic Wave An exotic wave (JPC = 1-+) was generated at level of 2.5 % with 7 other waves. Events were smeared, accepted, passed to PWA fitter. Mass Input: 1600 MeV Width Input: 170 MeV Output: 1598 +/- 3 MeV Output: 173 +/- 11 MeV Double-blind M. C. exercise Statistics shown here correspond to a few days of running.

JLab 12 GeV Upgrade Project Status Highlight in the 20-year plan of the Office of Science (2003) What’s New: “New supercomputing studies indicate that force fields called “flux-tubes” may be responsible [for the mechanism that confines quarks], and that exciting these should lead to the creation of never-before-seen particles.” Determination of “Mission Need” CD-0 (Apr 2004) Review of Science program for the 12-GeV Upgrade (Apr 2005) From the Executive Summary: “After a decade of research, we should know whether the formation of flux tubes by the gluon fields is the mechanism of confinement…” Successful Project Review (Jul 2005), CD-1 expected soon Four-year construction project planned to start in FY08

Summary of GlueX program Mapping the spectrum of hybrid mesons provides essential experimental data on the physics of the strong interactions at low energies in the region of confinement. This unique experimental program is possible now due to to high quality electron beam at the 12-GeV CEBAF Upgrade increases in computational power new developments in detector readout technology technology to produce thin diamond crystals GlueX will establish the existence of exotic hybrids if they are present at the level of a few % of conventional mesons.

Conclusions The spectrum of hadrons provides a means of probing QCD in the region of strong coupling. The detailed study of pentaquarks has caused our field to reexamine our understanding of strongly interacting QCD and clarified the strengths and weaknesses of the quark model. Mapping out the spectrum of hybrid mesons will confirm predictions of lattice QCD… or provide new insights into the dynamics of the complete theory. models lattice experiment