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Baryon spectroscopy at CLAS and CLAS12
Baryons’10, Dec 2010, Osaka, Japan
Ken Livingston, University of Glasgow, ScotlandFor the CLAS collaboration
• Hadron spectroscopy at CLAS
• The N* programme
• CLAS 12
• Summary
• Hadron spectroscopy at CLAS
• The N* programme
• CLAS 12
• Summary
• Study of nucleon resonances:• Measurement of the transition form factors• Search for missing states
• Strangeness production• and production• Cascade spectroscopy
• Search for “unconventional states”• high statistics search of pentaquark states• search for hybrid mesons
• Study of nucleon resonances:• Measurement of the transition form factors• Search for missing states
• Strangeness production• and production• Cascade spectroscopy
• Search for “unconventional states”• high statistics search of pentaquark states• search for hybrid mesons
> 100 analyses in progress
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Missing baryon resonances
• Clear indication of resonances in γp cross section for many channels
• Constituent quark models predict many resonances, but several missing
• Mostly from πN scattering and single π photoproduction
• Eg. Cross sections show some hints of new D13.
• Better to look at angular distributions and polarization observables.
•Really missing or undetected since weak coupling to these channels
• Try other channels. Eg. K photoproduction
With D13
Without D13
Mart & Benhold, Phys. Rev. C 61 012201(R) (1999)
After Cx, Cy from CLAS, revised as most likely P13. Eur Phys J A34 (07) 243
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Polarization observables in pseudoscalar meson production
4 Complex amplitudes: 16 real polarization observables.
Complete measurement from 8 carefully chosen observables.
πN has high statistics but in KY recoil is self-analysing
I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B95 347 (1975).I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B95 347 (1975).
πN KY
recoil targ γ
γ targ recoil
☻☻☻
☻
linearly polarized photons
☻☻☻☻☻☻
longitudinally polarized target
☻☻☻☻☻☻
☻☻☻☻☻☻
transversely polarized target
circ polarized photons
☻☻☻☻☻☻
Complete, andover-determined
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A B C
Continuous Electron Beam Accelerator Facility
E: 0.75 –6 GeV Imax: 200A RF: 1499 MHz Duty Cycle: 100% (E)/E: 2.5x10-5
Polarization: 80% Simultaneous
distribution to 3 experimental Halls
Injector
LIN
AC L
INA
CExperimental Halls
Jefferson Lab
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CEBAF Large Acceptance Spectrometer
Cherenkov Counter e/ separation, 256 PMTsTime of Flight
Plastic Scintillator, 684 PMTs
Drift Chamber35,000 cells
Target + start counter e mini-torus
Electromagnetic Calorimeterlead/plastic scintillator, 1296 PMTs
Torus Magnet6 Superconductive Coils
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Tagged photons at CLAS
• Tagged bremsstrahlung photons up to 6GeV.
• Timing resolution < 1 beam bucket.
• Circularly polarized
• up to ~80% now standard
• Linearly polarized
• coherent bremsstrahlung up to >90%.
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Polarization observables at CLAS
+ N → m
Linear Polarisation
Circular polarisation
Nucleon recoil polarimiter x →
Y
Hyperons are “self analysing”
Transverse polarized nucleon targets p n 2011
Longitudinally polarized nucleon targets p n 2011
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Polarization observables - a simple example,
• Systematics of detector acceptance cancel out.
• “Only” need to know Plin, the degree of linear polarization.
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1st pol. observables in K photoproduction on p at CLAS.
P, Cx and Cz
2 2 2x zR P C C
→ fully polarised
R. Bradford et al., Phys. Rev. C 75, 035205 (2007).
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g8b, July 2005Lin. polarized photon energy range: 1.3 – 2.1 GeV
preliminary results:p, Mike Dugger, ASU
CLAS data SAID
• Very high statistics. Good agreement with previous measurement. • We have P well determined – expect <5% systematic error in P.• ~10MeV Eg bins, and will extend up to 2.1GeV• Similar for np, ’p
Bea
m A
sym
met
ry Σ
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g8b preliminary results - and
Craig Paterson, Glasgow
pppp
Single polarization observablesPhoton asymmetryP Recoil polarization (induced pol. along y)T Target asymmetry
Double polarization observablesOx Polarization transfer along xOz Polarization transfer along z
figure by R.Schumacher, CMU
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g8b preliminary results -
• Results compared with previous results from LEPS
• 6, 100MeV Energy bins
• 1550 -> 2050MeV
• More bins for our data
Increase the angular coverage to backward angles
LEPS also recently have some consistent, new points at backward angles.Hicks et al., PRC 76, 042201(R) (2007).
PREL
IMIN
A
RY
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g8b preliminary results -
Ox/O
z extracted from fit to 2d asymmetry
T Target asymmetry from 2d asymmetry (not shown)
P Recoil pol. from acceptance corrected proton dist.
g8bGRAALCLAS J.W.C. McNabb, et al. (CLAS) Phys. Rev. C 69, 042201(R) (2004).
P R
ecoi
l pol
.
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G8b Summary
• Single (P,T,) and double (Ox,O
z) polarization observables
• High stats, wide coverage, some 1st measurements
• Prelim results already being used as input to models
Several analyses at advanced stage:
pnp, ’p
• Photon asymmetry ()
• Very high statistics
pp
• Photon asymmetry ()
• 1st measurement
…. several publications expected next year
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Meson photoproduction with linearly and circularly polarized photons on polarized target
E02-112: γp→KY (K+Λ, K+Σ0, K0Σ+)E03-105/E04-102: γp→π0p, π+n E05-012: γp→ηpE06-013: γp→π+π-p
g9a running conditionsNovember 3, 2007– February 12, 2008Longitudianally polarized targetCircularly and linearly polarized photon beam 0.5-2.4 GeVTrigger: at least one charged particle in CLASTarget Pol > 80%, Relaxation time > 1600hrs – better that design goals
g9 FROST – FROzen Spin Target (butanol = C4H9OH)
g9b March – July 2010 Transversely polarized target
Racetrack coils for transverse polarization
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butanol 12C CH2
g9aFROST sample analysis of gp+n Eugene Pasyuk, ASU. Jo McAndrew, Edinburgh
•Select + applying cut on vs. p•Vertex cuts•Select missing neutron
Based on ~2% of statistics
Helicity asymmetry E Raw asymmetry
Prelim
inarybutanol 12C CH2
Prelim
inary
, also
in p
rogr
ess
for K
Y.
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• G10. Unpolarized photons on Deuterium• 1st measurement of σ for the γ n → K+ Σ-
Measurements on n (Deuterium) target
• Detect - n, K+
• Σ from - n inv. mass
• Circularly and linearly polarized photons on n (g13, Deuterium target)• γ n → K+ Σ- analysis for polarization observables underway. Edwin Munevar, GWU
Sergio Anefalos Pereira, INFN. Phys. Lett. B 688 (2010) 289-293
• CLAS Data ▲ LEPS _____ Gent RPR model
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PREL
IMIN
A
RY
G13 1st measurement of Beam Asymmetry n (p)s p
Neil Hassall, Glasgow
Single, and double polarization observables in progress
Measurements on n (Deuterium) target
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• Alspector, PRL 28, 1403 (1972).• Abrahamian,SJNP 32, 69 (1980).• Adamyan, JPG 15, 1797 (1989).
Existing data:
Assumed polarisation P = 1
VERY PRELIMINARY!
Only statistical error is shown!
~ 30 % of the data
Measurements on n (Deuterium) target
• G13b. Linearly polarized photons on n (Deuterium)• Measurement of for γ n → - p Daria Sokhan, Edinburgh
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Measurements on n (Deuterium) target
HDIce slide still to be added here.
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CHL-2CHL-2
Upgrade of the arc magnets
12 GeV CEBAF Construction of the new Hall D
Beam Power: 1MWBeam Current: 90 µAMax Pass energy: 2.2 GeVMax Enery Hall A-C: 10.9 GeVMax Energy Hall D: 12 GeV
Upgrade of the instrumentation of the existing Halls
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< 6 GeV
Spectroscopy with CLAS12
The construction of Low Q Tagging Facility or Forward Tagger has been proposed to continue the spectroscopy program with CLAS12 using quasi-real photoproduction
• electron scattering at “0” degrees (LowQ, post-target tagging): low-Q2 virtual photon real photon
• photons tagged by detecting the scattered electron
• quasi-real photons are linearly polarized and the polarization can be determined event by event
• high luminosity on thin (gas)- targets
• can exploit CLAS12 PiD for final states with strangeness
• Complementary to GLUEX Coh. Brem. photon beam
• Parasitic running
A new physics programme•Meson spectroscopy
– Spectroscopy on H target and search for exotics– Spectroscopy on 4He and other gas targets
•Hadron spectroscopy– Heavy mass baryon resonances (Cascades and -)
•Compton scattering•Meson polarizabilities•Large -t physics•T-GPDs
Meson Spectroscopy at CLAS and CLAS12, Carlos Salgado SP2, Wed 14.00
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Summary to be improved
CLAS has large hadron spectroscopy programme
Focus here was on N* with Kaon and Pion channels
Very high stats single pol measurements for pi, eta
Data for complete measurement KL, SL on p already taken
Analysis underway
Data for complete measurement KL, SL n next year (HDIce)
Many results close to publication from g8
Much awaited input for models
Could definitive N* answers be only a few years away?
CLAS 12
A forward tagger offers a whole new hardon spectrosopy programme
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p (n)nRussell Johnstone, Glasgow
K production on n. Deuterium target
PREL
IMIN
ARY
pho
ton
asy
mm
etry
How good a “free” neutron target is Deuterium ?
G13. Compare photon asymmetry of p (n)nwithp (free and bound p)
× Free
● Quasi free
Free and quasi-free protonQuasi free neutron good approx. to free, here.
Coscm (-1.0 - +1.0)Each plot is 200MeV photon energy bin1100-2150MeV
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G13 n (p)s pn (p)
s pNeil Hassall, Glasgow
K production on n. Deuterium target
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K production on n. Deuterium target
PREL
IMIN
A
RY
G13 1st measurement of Beam Asymmetry n (p)s
pNeil Hassall, Glasgow
Single, and double polarization observables in progress
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Recoil polarimetry possibilities ?
g8b data+ p → + n with (n,p) scatter (detect +p)
Mx(p→++X)
+
n
p
Start counter
K.LivingstonAngle between Pn
calc and Ppmeasured
x and y (transverse) components of nucleon polarisation
n() =no(){1+A()[Pycos()–Pxsin()] - How to do this for 4 detector
Nucleon polarimeter for CB@MAMI, D. Watts, Edinburgh
Graphite
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• Tagging spectrometer with high rate, good energy and timing resolution
• High precision goniometer (GWU)
• High quality, thin diamond (Glasgow)
• Tight photon beam collimation (ISU)
• Polarimetry
“A device called a goniometer tilts the diamond, much like a lady turning her hand to admire the sparkle of a new ring.” - JLAB On Target Magazine
Peak > 90% pol.
CLAS coherent bremsstrahlung facility
Photo
n
ener
gy
P > 90%
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Measurements with photon beam profile detectorD. Glazier, Glasgow
1st Measurement of 2D photon enhancement for coherent bremsstrahlung (MAMI,Mainz) paper in preparation
• Good agreement with coherent bremstrahlung calculations
• Improvements in incoherent component, collimation + multiple scattering.
• No evidence of high energy photons from quasi channeling.
• Investigation of 2D strip detector for polarimetry
Coherent peak at 300Mev, MAMI electron beam energy 855MeV
below peak coherent peak above peak
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Photon Asymmetry, , extracted from cos(2) fit to azimuthal kaon distribution
Fits shown for 1 energy bin
340 (20E, 17) kinematic bins
Almost full angular coverage
g8b preliminary results -
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g8b preliminary results -
Results compared with previous results from GRAAL7, 50MeV Energy bins
1175 -> 1475MeV
Good agreement with previous results
PREL
IMIN
A
RY
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Results compared with previous results from LEPS6, 100MeV Energy bins
1550 -> 2050MeV
More bins for our data!!!
Increase the angular coverage to backward angles
PREL
IMIN
A
RY
g8b preliminary results -
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• Pair production simulations by Kharkov group
• Polarimeter built and tested at Sping8, recently tested at Jlab
e+
e-
• Polarimeter to be based on Jlab design
• Microstrip detectors, or pixel detectors (Atlas group)
• Bonn student completed 10 months exchange in Glasgow now to be full time in Bonn.
Polarimetry: from pair (e+,e-) productionH.Schmieden, Bonn
• Well described by QED, but experimentally difficult – small opening angle
PRELIMINARY
J.Santoro, CUA
Peak > 90% pol.
K.Livingston, Glasgow
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Use reaction with a known photon asymmetry
• Can be high statistics
• Very good relative monitor of polarization
• Combined beam, target polarization.
• Non-indpendent – depends on specific expt
• Need very good systematics or calibration
• Awaiting MAMI polarized target and polarised photon beam in 2nd half of 2007
Polarimetry: from hadronic reactionR. Beck, Mainz -> Bonn
Recent preliminary results from JLab (g8b)
• Proton target
• Back to back charge particles in Start Counter
• Atomic or hardonic ?
• Asymmetry from ~20mins DAQ data
• Constant with E from 1.3GeV – 1.9GeV