Meson Spectroscopy Overview What is the role of

Meson Spectroscopy Overview: What is the role of Glue. X in the global spectroscopy program? Curtis A. Meyer Carnegie Mellon University

Outline What are light-quark exotic mesons? How should we look for these mesons? What is the experimental evidence? What are the experimental programs? What is special about Glue. X? May 2010 Glue. X Graduate Student Day 2

Spectroscopy and QCD Quarkonium Mesons i ad r q al q Consider the three lightest quarks 4++ ++ L=3 3 ++ 2 3+- 9 Combinations 3 -2 -L=2 1 -2 -+ L=1 2++ 1++ 0++ 1+- L=0 1 -0 -+ May 2010 S=1 S=0 Glue. X Graduate Student Day 3

Spectroscopy an QCD Quarkonium Mesons q 4++ ++ L=3 3 ++ 2 3+- , K*, , 3 -2 -L=2 1 -2 -+ L=1 L=0 , K, , ’ May 2010 Mesons come in nonets of the same JPC Quantum Numbers a, K, f, f’ 2++ 1++ 0++ 1+1 -0 -+ q b, K, h, h’ SU(3) is broken last two members mix , K*, , S=1 S=0 , K, , ’ Glue. X Graduate Student Day 4

Spectroscopy an QCD Quarkonium Mesons q Nothing to do with Glue! 4++ ++ L=3 3 ++ 2 3+- Allowed JPC Quantum numbers: 0 -1– 2 -3 -4 -5 -- 3 -2 -L=2 1 -2 -+ L=1 2++ 1++ 0++ 1+- L=0 1 -0 -+ May 2010 q S=1 S=0 0++ 0 -+ 1++ 1 -+ 2++ 2 -+ 3++ 3 -+ 4++ 4 -+ 5++ 5 -+ 0+1+2+3+4+5+- Exotic Quantum Numbers non quark-antiquark description Glue. X Graduate Student Day 5

QCD Potential Lattice QCD ground-state flux-tube m=0 linear potential The normal mesons are built up from a “quark-antiquark pair” with and a “ground-state” flux tube. (π, K, η, η’) JPC=0 -+ May 2010 (ρ, K*, ω, Φ) JPC=1 -- (b 1, K 1, h 1’) JPC=1+- ( ) 0++, 1++, 2 --, 2 -+, 3++, 3 - -, 3+ - Glue. X Graduate Student Day 6

QCD Potential Lattice QCD ground-state excited flux-tube m=1 m=0 S=0, L=0, m=1 S=1, L=0, m=1 J=1 CP=+ J=1 CP=JPC=0 -+, 0+- JPC=1++, 1 -(not exotic) linear potential 1 -+, 1+- -+, 2+2 exotic Gluonic Excitations provide an experimental measurement of the excited QCD potential. Many of the hybrid nonets have exotic quantum numbers. May 2010 Glue. X Graduate Student Day 7

Hybrid Predictions Flux-tube model: 8 degenerate nonets 1++, 1 -- 0 -+, 0+-, 1 -+, 1+-, 2 -+, 2+- ~1. 9 Ge. V/c 2 Lattice QCD Calculations S=0 S=1 Lattice QCD Calculations 1 -+ 2+0+- ~1. 9 ~2. 2 At the physical pion mass? In the charmonium sector: 1 -+ 4. 39 0. 08 0+4. 61 0. 11 May 2010 Glue. X Graduate Student Day 8

QCD Exotics We expect 3 nonets of exotic-quantum-number mesons: 0+-, 1 -+, 2+ 1 IG(JPC)=1 -(1 -+) K 1 IG(JPC)= b 0, h 0’, K 0 b 2, h 2’, K 2 May 2010 - ’ 1 IG(JPC)=0+(1 -+) π , η’ , K → π1 , η’ 1, K 1 ½ (1 ) 1 -+ 0+2+- Glue. X Graduate Student Day 9

QCD Exotics We expect 3 nonets of exotic-quantum-number mesons: 0+-, 1 -+, 2+ 1 IG(JPC)=1 -(1 -+) K 1 IG(JPC)= b 0, h 0’, K 0 b 2, h 2’, K 2 May 2010 - ’ 1 IG(JPC)=0+(1 -+) π , η’ , K → π1 , η’ 1, K 1 ½ (1 ) 1 -+ 0+2+- What are the mixing angles Between the isoscalar states? Glue. X Graduate Student Day 10

Hybrid Decays The angular momentum in the flux tube stays in one of the daughter mesons (an (L=1) and (L=0) meson). L flux Lflux Exotic Quantum Number Hybrids 1 b 1 , f 1 , , a 1 1 (1300) , a 1 b 2 a 1 , h 1 , a 2 h 2 b 1 , Mass and model dependent predictions Populate final states with π±, π0, K±, K 0, η, (photons) b 0 (1300) , h 1 h 0 b 1 , h 1 May 2010 Glue. X Graduate Student Day 11

Hybrid Decays The angular momentum in the flux tube stays in one of the daughter mesons (an (L=1) and (L=0) meson). L flux Lflux Exotic Quantum Number Hybrids 1 b 1 , f 1 , , a 1 1 (1300) , a 1 b 2 a 1 , h 1 , a 2 h 2 b 1 , b 0 (1300) , h 1 h 0 b 1 , h 1 May 2010 Mass and model dependent predictions Populate final states with π±, π0, K±, K 0, η, (photons) The channels we are looking at for PWA. Glue. X Graduate Student Day 12

Hybrid Decays The angular momentum in the flux tube stays in one of the daughter mesons (an (L=1) and (L=0) meson). L flux Lflux Exotic Quantum Number Hybrids 1 b 1 , f 1 , , a 1 1 (1300) , a 1 b 2 a 1 , h 1 , a 2 h 2 b 1 , b 0 (1300) , h 1 h 0 b 1 , h 1 May 2010 Mass and model dependent predictions Populate final states with π±, π0, K±, K 0, η, (photons) The channels we are looking at for PWA. Other interesting channels for PWA. Glue. X Graduate Student Day 13

Experimental Evidence for Hybrids The most extensive data sets to date are from the BNL E 852 experiment. There is also data from the VES experiment at Protvino and some results from the Crystal Barrel experiment at LEAR. Finally, there is a CLAS (Jefferson Lab) result. We have Also just started to see results from the COMPASS experiment at CERN. May 2010 Glue. X Graduate Student Day 14

E 852 Experiment -p→ - p Mass = 1370 +-16+50 -30 Me. V/c 2 1(1400) Width= 385 +- 40+65 -105 Me. V/c 2 The a 2(1320) is the dominant signal. There is a small (few %) exotic wave. (1997) a 2 1 Interference effects show a resonant structure in 1 -+. (Assumption of flat background phase as shown as 3. ) Seen by Crystal Barrel in ηπ- and ηπ0 May 2010 Glue. X Graduate Student Day 15

Crystal Barrel Experiment CBAR Exotic Same strength as the a 2. 1(1400) Mass = 1400 +- 20 Me. V/c 2 Width= 310+-50+50 -30 Me. V/c 2 Produced from states with one unit of angular momentum. Without 1 c 2/ndf = 3, with = 1. 29 0 - May 2010 Glue. X Graduate Student Day 16

E 852 Experiment -p → hp 0 p Dzierba (et. al) PRD 67 (2003) (~45000 Events) Adams (et. al) PLB 657 (2007) Problematic Resonant Description (~23000 Events) Confirms the ηπ- results May 2010 Glue. X Graduate Student Day 17

E 852 Experiment -p →π +π - - p (~250, 000 Events) Suggestive of a 1, a 2, π2 →ρπ π2→f 2π (1998) Partial Wave Analysis π1(1600) →ρπ M = 1598 ± 8+29 -47 Me. V/c 2 Γ = 168± 20+150 -12 Me. V/c 2 May 2010 Glue. X Graduate Student Day 18

E 852 Experiment Natural-parity exchange: 0+, 1 -, 2+, … Unnatural-parity exchange: 0 -, 1+, 2 -, … π1(1600) Unnatural exchange Natural exchange π1(1600) M = 1598 ± 8+29 -47 Me. V/c 2 Γ = 168± 20+150 -12 Me. V/c 2 Leakage from other partial waves. Only quote results from the 1+ (natural parity) exchange. May 2010 Glue. X Graduate Student Day 19

E 852 Experiment Data are dominated by 1 -+, 2++ and 4++ partial waves. Data are dominated by natural parity exchange. -p ’ -p (~6000 Events) (2001) π1(1600) M = 1597± 10+45 -10 Me. V/c 2 Γ = 340± 50 Me. V/c 2 The exotic wave is the dominant wave in this channel. May 2010 Glue. X Graduate Student Day 20

E 852 Experiment π- p→ωπ0π-p (~145, 000 Events) (2004) π1(1600)→b 1π M = 1664± 8± 10 Me. V/c 2 Γ = 185± 25± 38 Me. V/c 2 mε=01 -+b 1π mε=1+ 1 -+b 1π Seen in both natural and unnatural parity exchange. The unnatural dominates 2++ωρ 4++ωρ π1(2000)→b 1π M = 2014± 20± 16 Me. V/c 2 Γ = 230± 32± 73 Me. V/c 2 Δφ(1 -+ - 2++) Seen primarily in natural parity exchange. The natural dominates Δφ(1 -+ - 4++) Δφ(2++ - 4++) Solid curves are a two-pole 1 -+ solution. Dashed curves are a one-pole 1 -+ solution. May 2010 Glue. X Graduate Student Day 21

E 852 Experiment (2004) π- p→ηπ+π-π-p (~69000 Events) 1++f 1πΔΦ(1 -+ - 2 -+) π1(1600)→f 1π M = 1709± 24± 41 Me. V/c 2 Γ = 403± 80± 115 Me. V/c 2 Natural parity exchange 2 -+f 1πΔΦ(1 -+ - 1++) 1 -+f 1πΔΦ(1++ - 2 -+) π1(2000)→f 1π M = 2001± 30± 92 Me. V/c 2 Γ = 333± 52± 49 Me. V/c 2 Natural parity exchange Black curves are a two-pole 1 -+ solution. Red curves are a one-pole 1 -+ solution. May 2010 Glue. X Graduate Student Day 22

New Analysis Dzierba et. al. PRD 73 (2006) 10 times statistics in each of two channels. π-p→pπ-π0π0 (3000000 Events) π-p→pπ-π-π+ (2600000 Events) Get a better description of the data via moments comparison. Intensity for the exotic 1 -+ wave goes away. Phase motion between the 1 -+ and the 2++ wave is not affected. No Evidence for the 1(1600) May 2010 Glue. X Graduate Student Day 23

New Analysis Where does the intensity go? Always Include: (0+)π2(1670)→f 2π(L=0) (1 -)π2(1670)→f 2π(L=0) (0+)π2(1670)→f 2π(L=2) (1+)π2(1670)→f 2π(L=2) PDG: π2(1670) Decays 3π 96% f 2π 56% ρπ 31% Modified wave set: Leave out (1+)π2(1670)→ρπ(L=1) (1+)π2(1670)→ρπ(L=3) (0+)π2(1670)→ρπ(L=3) Most of the strength in the exotic π1(1600) is better described by known decays of the π2(1670). May 2010 Glue. X Graduate Student Day 24

COMPASS Experiment (420, 000 Events) 1 -+ Exotic Wave (180 Ge. V pions) π1(1600) m=1660 Γ=269 π2(1670) m=1658 Γ=271 42 Partial waves included, exotic is dominantly 1+ production. ar. Xiv: 0910. 5842 May 2010 Glue. X Graduate Student Day 25

CLAS Experiment γp→nπ+π+π- Eγ = 4. 8 – 5. 4 Ge. V 83000 Events after all cuts Overall Acceptance < 5% Baryons “removed” by hard kinematic cuts. PWA No evidence of π1(1600)→ρπ, (13. 5 nb upper limit). May 2010 Glue. X Graduate Student Day 26

Summary of the π1(1400) Mode Mass ηπ- 1370± 15+50 -30 ηπ0 1257± 20± 25 ηπ 1400 Width Production 385± 40+65 -105 1+ 354± 60 1+ (controversial) 310 seen in proton-antiproton annihilation Mode 3π η’π b 1 π f 1 π Width 168± 20+150 -12 340± 50 185± 25± 38 403± 80± 115 Summary of the π1(1600) 3π Mass 1598 ± 8+29 -47 1597± 10+45 -10 1664± 8± 10 1709± 24± 41 1660 ± 10+64 -0 269± 21+42 -64 Production 1+, 0 -, 1(controversial) 1+ 3π not seen in 0 - , 1+ Photoproduction 1+ 1+ COMPASS Summary of the π1(2000) Mode Mass b 1π 2014± 20± 16 f 1π 2001± 30± 92 May 2010 Width 230± 32± 73 332± 52± 49 Glue. X Graduate Student Day Production 1+ 1+ 27

Exotic Signals 1 IG(JPC)=1 -(1 -+) K 1 IG(JPC)= - ’ 1 IG(JPC)=0+(1 -+) 1(1400) Width ~ 0. 3 Ge. V, Decays: only weak signal in p production (scattering? ? ) strong signal in antiproton-deuterium. 1(1600) Width ~ 0. 30 Ge. V, Decays , ’ , (b 1 ) Only seen in p production, (E 852 + VES) Production mechanisms not consistent. COMPASS sees a state with the same mass & width as the π2(1670). 1(2000) Weak evidence in preferred hybrid modes f 1 and b 1 natural parity exchange May 2010 ½ (1 ) Glue. X Graduate Student Day NOT A HYBRID What is going on? The right place. Needs confirmation. 28

The Glue. X Experiment Future May 2010 Glue. X Graduate Student Day 29

COMPASS Currently running at CERN Detect charged particles and photons. Good PID 190 Ge. V/c beam. Diffractive production: Partial wave analysis reported on three-pion final state. repeat E 852 studies, but at much higher energy. Central production: Mass and width of the exotic exactly match the repeat studies done by WA 102 at CERN (glueballs). May 2010 With large wave set, they see the Glue. X Graduate Student Day 30

BES III Currently running in Beijing Tagged decays of Ψ-states to look for glueballs and hybrids. Possible to look for charmed hybrids, but rates may be a limiting factor. Can also look for exotic hybrids in the decay of these states. I am not certain What the expected rates are. Radiative J/Ψ decays are supposed to be glue-rich, oddly a prime candidate is not seen --- f 0(1500). May 2010 Glue. X Graduate Student Day 31

PANDA Proton-antiproton annihilation at new facility in Germany (GSI). Time scale is similar to Glue. X (probably later). Main program is in the charm sector with emphasis on charmed hybrid mesons. Some hints that it is easier to produce exotic hybrids in these reactions. Also search for glueballs. There should also be a light exotic meson program here. May 2010 Glue. X Graduate Student Day 32

More likely to find exotic hybrid mesons using beams of photons Photoproduction Simple (0++) natural parity exchange with L=1: 0+-, 1+-, 2+J. Dudek et. al, PRD 79 (2009) Compute radiative decays in charmonium to normal and hybrid mesons. Rates are comparable. Work currently underway to compute the same for light quarks. 8. 4 -9 Ge. V tagged, linearly polarized photon beam, up to 108/s May 2010 Glue. X Graduate Student Day 33

Jlab 0+- and 2+In photoproduction, couple to , or ? b 0 IG(JPC)=1+(0+-) h 0 IG(JPC)=0 -(0+-) a 1, f 0, f 1, a 1 h’ 0 IG(JPC)=0 -(0+-) f 0, f 1, a 1 g N X e N K 0 I(JP)=½(0+) , a 1, f 0, f 1 “Similar to 1 ” f 0, f 1, a 1 h 2 IG(JPC)=0 -(2+-) f 0, f 1, a 1 Kaons do not have exotic QN’s May 2010 b 2 IG(JPC)=1+(2+-) Glue. X Graduate Student Day h’ 2 IG(JPC)=0 -(2+-) K 2 I(JP)= ½(2+) 34

Glue. X vs E 852 Acceptance π0η final state Glue. X High, and reasonably uniform Acceptance up to 2. 5 Ge. V/c 2. Sensitive to charged particles And photons. Some particle ID in the initial phases, plans to upgrade this. Able to fully reconstruct the 4 -12 Particle final states. May 2010 Glue. X Graduate Student Day 35

Exotics and QCD In order to establish the existence of gluonic excitations, We need to establish the existence and nonet nature of the 1 -+ state. We need to establish at other exotic QN nonets – the 0+- and 2+-. Decay Patterns are Crucial Coupled Channel PWA Needed. Very Large Data Sets Expected From Glue. X The challenge is carrying out a PWA with huge statistics and good theoretical underpinnings to the method. May 2010 Glue. X Graduate Student Day 36

Summary QCD predicts several nonets of exotic-quantum-number mesons. Evidence hints at some exotic-quantum-number states, and two are consistent with a π1 state. Where are the other states? The first searches in photoproduction have come up negative, but the acceptance is poor, and the lower energy regime may not have been optimal. Phenomenology was very poor first photoproduction search. The Glue. X experiment at Jefferson Lab is now under construction with first beam in the hall expected in 2014. The Glue. X experiment has high acceptance for multi-particle final states, sensitivity to photons, and a linearly polarize photon beam. May 2010 Glue. X Graduate Student Day 37