Baryon spectroscopy at CLAS and CLAS12
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Transcript of Baryon spectroscopy at CLAS and CLAS12
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
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 D13Without 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
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
☻☻☻
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linearly polarized photons
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longitudinally polarized target
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transversely polarized target
circ polarized photons
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Complete, andover-determined
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 LINAC
Experimental Halls
Jefferson Lab
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
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%.
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
Polarization observables - a simple example,
• Systematics of detector acceptance cancel out.
• “Only” need to know Plin, the degree of linear polarization.
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).
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
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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
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).
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g8b preliminary results -
Ox/Oz 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,Oz) 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
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
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
Preliminary
butanol 12C CH2
Prelim
inary,
also
in pr
ogres
s
for KY.
• 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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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
• 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
Measurements on n (Deuterium) target
HDIce slide still to be added here.
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
< 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
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
p (n)nRussell Johnstone, Glasgow
K production on n. Deuterium target
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p
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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
G13 n (p)s pn (p)
s pNeil Hassall, Glasgow
K production on n. Deuterium target
K production on n. Deuterium target
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G13 1st measurement of Beam Asymmetry n (p)s
pNeil Hassall, Glasgow
Single, and double polarization observables in progress
Recoil polarimetry possibilities ?
g8b data+ p → + n with (n,p) scatter (detect +p)
Mx(p→++X)
+
np
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
• 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
Photon
energ
y
P > 90%
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
Photon Asymmetry, , extracted from cos(2) fit to azimuthal kaon distribution
Fits shown for 1 energy bin340 (20E, 17) kinematic binsAlmost full angular coverage
g8b preliminary results -
g8b preliminary results -
Results compared with previous results from GRAAL7, 50MeV Energy bins1175 -> 1475MeVGood agreement with previous results
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Results compared with previous results from LEPS6, 100MeV Energy bins1550 -> 2050MeVMore bins for our data!!!
Increase the angular coverage to backward angles
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g8b preliminary results -
• 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
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