baryon spectroscopy at clas and clas12 baryons’10, dec 2010, osaka, japan ken livingston,...

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 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

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

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

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

ry Σ

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).

PREL

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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

.

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

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

Prelim

inarybutanol 12C CH2

Prelim

inary

, also

in p

rogr

ess

for K

Y.

• 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


• 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


• G13b. Linearly polarized photons on n (Deuterium)• Measurement of for γ n → - p Daria Sokhan, Edinburgh


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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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

G13 n (p)s pn (p)

s pNeil Hassall, Glasgow



PREL

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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)

+

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

• 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%

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 bin

340 (20E, 17) kinematic bins

Almost full angular coverage



Results compared with previous results from GRAAL7, 50MeV Energy bins

1175 -> 1475MeV

Good agreement with previous results

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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

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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

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

baryon spectroscopy at clas and clas12 baryons’10, dec 2010, osaka, japan ken livingston,...

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