Meson Spectroscopy and Partial Wave Analysis at CLAS
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Transcript of Meson Spectroscopy and Partial Wave Analysis at CLAS
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Meson Spectroscopy and Partial Wave Analysis at CLAS
Raffaella De VitaINFN – Genova
for the CLAS Collaboration
Workshop on Amplitude Analysis in Hadron Spectroscopy
ECT* Trento, ItalyJanuary 24-28 2011
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Meson Production at CLASStudy of meson properties and production represents a large fraction of the physics program at CLAS
• vector meson production at large momentum transfer
• vector meson modification in the nuclear medium
• meson spectroscopy and search for exotics
• …
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
The first CLAS result
Study of photoproduction at large momentum transfer
• POMERON 2- gluons • Nucleon wave function• Correlations between quarks• u-exchange around -tmax
g p p p K+ K-
E.Anciant et al. PRL 85 4682 (2000)
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Meson Production at CLASStudy of meson properties and production represents a large fraction of the physics program at CLAS
• vector meson production at large momentum transfer
• vector meson modification in the nuclear medium
• meson spectroscopy and search for exotics
• … • Search for exotic mesons• Study of scalar mesons• Study of strangeonia• …
• Reveal the nature of the mass of hadrons• Identify the relevant degrees of freedom• Understand the origin of confinement and the
role of gluons• …
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R. De Vita Meson Spectroscopy at CLAS and CLAS12: the present and the future MENU2010, Williamsburg, 2 June 2010
Jefferson Lab
A B C
Continuous Electron Beam Accelerator Facility
E: 0.75 –6 GeV Imax: 200mA RF: 1499 MHz Duty Cycle: 100% s(E)/E: 2.5x10-5
Polarization: 80% Simultaneous
distribution to 3 experimental Halls
Injector
LIN
AC LINAC
Experimental Halls
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R. De Vita Meson Spectroscopy at CLAS and CLAS12: the present and the future MENU2010, Williamsburg, 2 June 2010
The CLAS detector at JLab
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
CEBAF Large Acceptance Spectrometer
Cherenkov Counter e/ separation, 256 PMTs
Time of FlightPlastic Scintillator, 684 PMTs
Drift Chamber35,000 cells
Target + g start counter e mini-torus
Electromagnetic Calorimeterlead/plastic scintillator, 1296 PMTs
Torus Magnet6 Superconductive Coils
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Hall-B Photon Tagger• Photon beam produced from the
primary electron beam via Bremsstrahlung
• Gold and diamond radiator for In/Coherent Bremsstrahlung
• Energy coverage: 0.2-0.95 E0• Efficiency ~ 80%• Energy Resolution ~ 10-3
• Timing Resolution ~100 ps
Maximum photon energy of 5.7 GeV- Wmax 3.4 GeV
Beam intensity 107 g/s
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Search for the Exotic π1(1600)• Candidate for an exotic hybrid
meson• Should belong to JPC=1-+ multiplet• Observed in pion beam
experiments and pp annihilation but with controversial results
• Observed by VES initially in ηπ and then in other decays
• Strongest signal observed by E852 in ρπ, f2π, and others
• E852 results not confirmed by a later analysis of a larger data sample
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Search for the Exotic π1(1600)• Candidate for an exotic hybrid
meson• Should belong to JPC=1-+ multiplet• Observed in pion beam
experiments and pp annihilation but with controversial results
• Observed by VES initially in ηπ and then in other decays
• Strongest signal observed by E852 in ρπ, f2π, and others
• E852 results not confirmed by a later analysis of a larger data sample
• Recently positive results reported by COMPASS
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Search for the π1(1600) at CLASFirst results from a photoproduction experiment:
• Bremsstrahlung photon beam produced from 5.744 GeV electrons
• Photon flux of 5×107 γ/s• Liquid-hydrogen target
• Search in the γpnπ+π+π-
• Final state selected detecting the 3 pions and using the missing mass technique
• Selection of low –t region and forward-going pions to reduce baryon-resonance background
M. Nozar et al. (CLAS Collaboration),PRL 102, 102002 (2009)
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
PWA for the 3π channel• Full PWA of selected 83000 events
from G6C data set• PWA based on isobar model
developed from E852 tools• Choice of waves based on observed
dominance of ρ and f2 in the ππ invariant mass
• Different sets of waves used for low mass an high mass portion of the 3 π spectrum
• Spin-density matrix reduced to Rank-2 matrix because of limited statistics
• Unbinned log-likelihood fit with different sets of waves
Final wave set:
13 waves
31 waves
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Results from the 3π channel
CLAS-g6C
Possible distortion/leakages because of limited wave set forced by low statistics
Results are consistent with expectations from previous measurements
Demonstrate that PWAs in CLAS are feasible Higher statistics data samples are necessary
for thorough study
Dominance of the 2++ state a2(1320): clear signal at correct mass and width
a2(1320) cross section (0.81±0.25) μb in agreement with previous measurements
No-evidence of exotic 1-+ state π1(1600), upper limit on c.s. of 13.5 nb (95%CL)
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Photoproduction of Pion Pairs Study of π+π- production on the
proton and study of scalar mesons
• Bremsstrahlung photon beam: 1.6-3.8 GeV
• 40 cm long liquid hydrogen target• ~7∙109 triggers• Integrated Luminosity ~ 80 pb-1
• Proton and π+ detected in CLAS• Reactionπ γppπ+π- isolated via
missing mass• Analysis focused on high energy (3.0-
3.8 GeV) and low –t (0.4-1.0 GeV2) region
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Photoproduction of Pion Pairs1) Extraction of Moments of the Di-Pion Angular Distribution
• Moments can be expressed as bilinear combination of partial wave amplitudes
+…
• Partial Waves are parameterized using Dispersion Relations in term of known phase shifts and unknown coefficients and fitted to the experimental moments
• Partial Wave cross sections are derived and can be compared with models
Short range (QCD) production
Meson formation
e.g. 2 system
2) Evaluation of Partial Waves from Experimental Moments
• Moments are expanded on a set of basis function and weighted with Monte Carlo events to account for detector acceptance and efficiency
• Moments are fitted to the data using an unbinned likelihood procedure
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Moments of the Di-Pion Angular Distribution
3.2 GeV < Eg < 3.4 GeV 0.5 GeV2 < -t < 0.6 GeV2
M. Battaglieri et al. (CLAS Collaboration), PRD 80, 072005
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Partial Wave Amplitudes M(+-) spectrum below 1.5 GeV:
• P-wave: r meson• D-wave: f2(1270)• S-wave: s, f0(980) and f0(1370)
Moments of the 2-pion angular distribution extracted via likelihood fit of data
Partial Wave fitted to experimental moments
gpp+-
Known states well reproduced, e.g. r(770)
P wave
D wave
S wave
r(770)
f0(980)
f2(1270)
First observation of f0(980) in photoproduction
3.4 GeV < Eg < 3.6 GeV0.5 GeV2 < -t < 0.6 GeV2
M. Battaglieri et al. (CLAS Collaboration), PRL 102, 102001
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
New High Statistics Photon run: g12Search for new forms of hadronic matter in photoproduction on the proton:
• Data taking completed in 2008• Photon Energy up to 5.5 GeV• More than 26 billion triggers (2-prong + 3-prong)• Total Luminosity: 68 pb-1 (~50 pb-1 for E> 4.4 GeV) • 10 times more statistics than previous CLAS run in this energy range• Data processing completed and physics analysis in progress
Several exclusive channels are being analyzed:γp π+π+π-(n)γp pπ+π-ηγp pK+K- (η/π)γp K+K+ X*- (1530)γp π+K+K-(n)γp e+e-p...
Meson Spectroscopy• Search for exotic mesons• Study of Strangeonia• …
Baryon Spectroscopy• Cascades• …
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
G12: search for the π1(1400)D. Schott (Florida International U.)
g
p Δ++
X
p
η
π-
π+π
γp➝Δ++ηπ-• All particles detected• By requiring a Δ++ exchanged particles is
constrained to be a pion:➝ X resonance is constrained to be m=1 state➝ From VMD π:ρ exchanges are 9:1
• Structure corresponding to known states are clearly visible in πη mass spectrum
• PWA started !!
PRELIMINARY
PRELIMINARY
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
G12: search for the π1(1600)C. Bookwalter (Florida State U.)
g
p
X
n
π+
π-
π+
π,ρ
γp➝nπ+π+π-
• 3 pions detected and neutron reconstructed via missing mass
• Low –t region and forward-going pions selected to suppress baryons-resonance background
• ∼850 000 events after all selection cuts
PRELIMINARY
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
G12: search for the π1(1600)C. Bookwalter (Florida State U.)
g
p
X
n
π+
π-
π+
π,ρ
γp➝nπ+π+π-
• 3 pions detected and neutron reconstructed via missing mass
• Low –t region and forward-going pions selected to suppress baryons-resonance background
• ∼850 000 events after all selection cuts
PWA in progress..
PRELIMINARY
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Study of strangeonia• Mesons containing ss pairs• Can be regular states in the quark model or hybrids with/without
exotic quantum numbers• Experimental data still quite sparse, only 7 of the 22 states expected
below 2.2 GeV are widely accepted • Model prediction for width and decays available• Experimental search would require measurement of many different
final states
State Γtot Γi
KK KK* ηφ K*K*, KK1,(2)η'φ, …
φ(1019) Γth=2.5 MeVΓexp=4.26 MeV
φ(1680) Γth=378 MeVΓexp=150 MeV
Γth=89 MeV Γth=245 MeV Γth=44 MeV
φ(2050) Γth=378 MeV Γth=20 MeV Γth=21 MeV Γth=337 MeV
3P0 model, Barnes, Black and Page (2002)
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
G12: study of strangeoniaM. Saini (Florida State U.)
• Several different final states are being investigated:KK, KK*, ηφ ,…
γp p➝ φη ➝pK+K-η
PRELIMINARYPWA started
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Coherent Meson Production on 4He
Strongest evidence of JPC=1-+ 1(1400) exotic meson -p nh0 in E852-Brookhaven
Search for a resonance in P-wave in 0h and 0h’ Known (non-exotic) resonances can be used as a
benchmark (e.g. JPC=2++ a2(1232))
Eliminate s-channel resonance background
Simper PWA: S=I=0 target acts as spin and parity filter for final state mesons Production cross section expected ~ e-bt |A FA(t)|2 low -t kinematic
Meson spectroscopy on 4Heg4He 4He0 h g4He 4He0 h’
gp p+-
r D++
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Coherent Production of π0η, π0η’ on 4He
➔ Only C=-1 ω-exchanges is allowed, Natural Parity Exchange (NPE)
➔ The helicity of the produced state will be that of the incoming photon, λ=λγ, production of π0η (π0η’) in S-wave is forbidden
220 +- ++
AAA
dd
C
s
),(Im212 0
2/1max
0 1
+ +
+ LL
L
L
DLLA
;0;00 -AA
),(Im212 101
2/1max
1
+ +
+ LL
L
DLLA
• Resonances decaying to π0η (π0η’) in a P wave is exotic (JPC = 1-+) because of the quantum numbers of the final state (I=1, C=+1, G=-1, and P=(-1)L )
• Scattering off a spin and isospin zero target works as a spin and parity filter
s 22
2
2111 sinsin)1cos5(
27
21cos53 --+
+++ FDPdd
C
Test for above assumptions
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
EG6: Meson spectroscopy in coherent production on 4He
• search for exotics in h, h’ final states• 6 GeV electron beam on target on high pressure gas target• scattered electron at “0” degrees quasi-real photo-production• recoiling nucleus detected in Radial TPC• hadronic final state detected in CLAS• data taking completed in fall 2009• analysis in progress
Analysis of existing CLAS data shows clear peaks associated to known mesons in
ep(e’)p00
ep(e’)p0h
The Technique works!!
a0(980)f2(1270)f0(980)
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
EG6: Meson spectroscopy in coherent production on 4He
• search for exotics in h, h’ final states• 6 GeV electron beam on target on high pressure gas target• scattered electron at “0” degrees quasi-real photo-production• recoiling nucleus detected in Radial TPC• hadronic final state detected in CLAS• data taking completed in fall 2009• analysis in progress
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
EG6: Meson spectroscopy in coherent production on 4He
• search for exotics in h, h’ final states• 6 GeV electron beam on target on high pressure gas target• scattered electron at “0” degrees quasi-real photo-production• recoiling nucleus detected in Radial TPC• hadronic final state detected in CLAS• data taking completed in fall 2009• analysis in progress
Radial TPC with 7atm. He4 Target
Solenoid for forward-focusing of Moeller electrons and bending of recoil nucleus in the TPC
PbWO4 calorimeter for improved photon acceptance at forward angles
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
EG6: Meson spectroscopy in coherent production on 4He
• search for exotics in h, h’ final states• 6 GeV electron beam on target on high pressure gas target• scattered electron at “0” degrees quasi-real photo-production• recoiling nucleus detected in Radial TPC• hadronic final state detected in CLAS• data taking completed in fall 2009• analysis in progress
RTPC calibration using elastic events on 4He
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
SummaryRich physics program in meson spectroscopy with CLAS:• Meson spectrum investigated in photoproduction to determine properties of
regular states and search for unconventional configurations• Large statistics data sets are now available• Several decay modes have been/are being investigated• Different PWA frameworks have been developed:
• Isobar model• Moments + Dispersion relations
• First results published, several new analyses in progress...• Present program will be extended with CLAS12 using quasi-real
photoproduction
Better understanding of hadrons structure Progress in understanding confinement in QCD and the role of constituent
quarks and gluons in the description of the non-perturbative regime
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Hybrids and Exotics
Normal meson:qq state
m=0, PC=(-1)S+1
Hybrid meson:qqg
gluonic field contribute to quantum numbers
PC≠(-1)S+1
Excitation of the flux tube leads to a new spectrum of hadrons that can have exotic quantum numbers JPC = 0+- , 1-+ , 2+- ...
Lattice QCD calculations predict masses around 2 GeV, a range that can be explored at JLab
Hybrids (qqg) are the ideal system to study qq interaction and the role of gluonsThe existence is not prohibited by QCD but not yet firmly established. A possibility to identify unambiguously a meson as an hybrid state is to look for exotic quantum numbers
Normal mesons (qq) are classified according to their JPC where P=(-1)L+1 C=(-1)L+S
JPC= 0-+ (π,K,η,η’)1-- (ρ,K*,ω,Φ)1+- (b1,K1,h1,h1’)...
S1
S2
L
Some combinations of JPC are not allowed for conventional qq systems but can exist for “unconventional” states as hybrids
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R. De Vita Meson Spectroscopy and Partial Wave Analysis at CLAS ECT* Trento, January 27 th 2011
Search for Exotics in Photoproduction
Pion BeamQuark spins anti-alignedJPC = 1-- , 1++
Quark spinsalready alignedJPC = 0+- , 1-+ , 2+-
Photon Beam
regular mesons @ Eg = 5GeVX = a2
Exotic meson @ Eg = 8GeVX = 1(1600)
Photoproduction: exotic JPC are more likely produced by S=1 probe
Few data (so far) but expected similar production rate as regular mesons
Production rate for exotics is expected to be comparable to regular mesons
A. Szczepaniak and M. Swat, Phys. Lett. B516 (2001) 72
Signals for exotic hybrids have been reported by various experiments but evidence is not yet fully convincing: more data are needed and experiments with different production modes (different probes) are crucial