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Baryon Spectroscopy at Jlab and J-PARC
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Transcript of Baryon Spectroscopy at Jlab and J-PARC
Baryon Spectroscopy at Jlab and J-PARCK. Hicks (Ohio U.)
Baryons2013 Conference24 June 2013
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Physics of broad & overlapping resonances
Δ (1232)
Width: a few hundred MeV. Resonances are highly overlapped in energy except D(1232).
→Complex PWA is necessary
Width: ~10 keV to ~10 MeV Each resonance peak is clearly separated.
N* : 1440, 1520, 1535, 1650, 1675, 1680, ...D : 1600, 1620, 1700, 1750, 1900, …
From: H. Kamano, JAEA seminar
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Decuplet Assignments (PDG)
From p-scatt. database: all **** rated.
Lots of missing states! Lack of K-scatt. data or photoproduction data.
L=0
L=1
L=2
L=4
S
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Octet Assignments (PDG)
L=0
L=0
L=1
L=2
Here, there are more assignments, but many have few-star ratings.
Mass hierarchy problem with L=1, S=3/2 !! 6/24/2013
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Capstick & Roberts (1993)
Even 20 years ago, this problem was known! (Note: just Np PWA.)6/24/2013
Experiment vs. Quark Model
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Goals of this Physics• Understanding the spectrum of excited
states of the nucleon leads to a deeper understanding of non-perturbative QCD.• Similarly, the spectrum of excited states of the
hydrogen atom led to advances in QM.• My working hypothesis:
• The constituent quark model is a failure for excited states of the nucleon.
• Perhaps the reason is that the CQM does not include effects of the meson-baryon cloud.
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L(1405) Photoproduction at CLAS
If the L(1405) were a single 3-quark resonance, then all three decays should be symmetric.
However, if the resonance is dynamically generated, interference of poles with different isospin can occur
R. Schumacher, Thursday 9:00 talk
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Drell-Yan: nucleon has pion cloud
From: P. Reimer, arXiv:0704.3621.
The Drell-Yan process measures the antiquark sea in the nucleon.
The results show that there is an asymmetry to the u* and d* sea in the proton.The nucleon has an admixture of qqq(qqbar).
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NΔ Transition Form Factor (GM) from EBAC
In the relativistic QM framework, the bare-core contribution is well described by the three-quark component of the wavefunction at high Q2.
One third of G*M at low Q2 is due to contributions from meson–baryon (MB) dressing:
bare quark core
Meson-BaryonCloudEffect
The area of Q2<7.0 GeV2 is far from pQCD domain
B.Julia-Diaz et al., PRC 69, 035212 (2004)
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Dynamical Coupled-Channels modelMB channels
pN->ppNReactionAmplitude
Resonance core
meson cloud
meson
baryon
Physical N*s will be a “mixture” of the two pictures:
bare resonancecore (from QM)
B*
ppN
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Recent Lattice CalculationsN
ote:
Not
real
mas
s!
Reference: J. Dudek et al.,, arXiv:1201.2349
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Projection of N* to SLJ
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A Tale of Two Labs
• Jefferson Lab and J-PARC share a common interest: to understand QCD.• The combination of high-quality hadronic data
with double-polarization photoproduction data is more powerful than either one alone.
• Of course, other labs also share this interest.• It is becoming clear that both hadronic and
photoproduction data are needed due to coupled-channels effects that naturally link them together.
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P11(1440) couplings from CLAS
Npp
Np
Light front models:I. Aznauryan
S. Capstick hybrid P11(1440)
Mesoncloudeffect
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CLAS: e p → e' p p+ p-
The BLUE dotted curve uses only the known resonances from the Particle Data Group.
The RED solid curve includes an extra resonance not seen from the PWA of pN data alone.
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CLAS: Partial Wave Analysis
A new P13 resonance, much lower in mass than the quark model prediction, is necessary to fit the data.6/24/2013
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Importance of Npp Decay
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What data do we need?
• For almost 40 years, there have been no new measurements on (p,2p) in the nucleon resonance region.• For many years, elastic pN was good enough
• With precise new data on gN pN, ppN at Jefferson Lab, Bonn and elsewhere, along with theory advances, it becomes clear that hadronic-beam data is also needed to properly interpret the photoproduction data.
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p-N Total Cross Sections
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ppN Total Cross Sections
Kamano et al., PRC 79, 025206 (2009).
Dashed line: no channel coupling.
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The Primary Source of (p,2p)
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Complete (p,2p) DatabaseM. Manley, Phys. Rev. D 30, 904 (1984).
Total number of events!6/24/201323
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Mass Projections
Note: the normalization of these data is not known. The total cross sections were used to set the vertical scale.
The solid curves are the full calculation using only pN elastic data. The other curves do not include some coupled-channels effects.
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S31F37
F35
P31
P33D33
D35
S31F37
F35
P31
P33
D33
D35
PRELIMINARY PRELIMINARY
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TCS
M(π+ n)
M(π+ π+)
TCS
M(π0 p) M(π+ p)
M(π+ π0)
Current model
Refit F37 PWAkeeping N* πΔ off
PRELIMINARY
W W
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J-PARC Experiment
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K1.8 beamline with TPC
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Experimental SetupHyp-TPC Spectrometer
Hyp-TPC
p- beamSuperconducting HelmholtzDipole magnet
Measure (p,2p) in large acceptance TPC p-p→p+p-n, p0p-p p+p→p0p+p, p+p+n
p+- beam ~ 1M/spill (p=0.6-2.0 GeV/c)Liquid-proton targetTrigger: Two charged particles in hodoscope
Hodoscope
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Hyp-TPC– P-10 gas – H-target in TPC– Gating grid wires– 3-layer GEM
• Good performance at high beam rates
– Pad size • 2.5 x 9~13 mm : 30 layers• 5045 pads in total• p/K/p PID with dE/dx
vs p
p- beam
~600
Gating GridGEMPad plane
Target holder
500φ50φ
B=1Tp-
p+E=180V/cm
n
P-10 gas
Liquid H target
ionization
Electrondrift
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TPC prototype test results• Beam test at RCNP (Nov.2011)
Position resolution (B=0)sx=0.40mm sy= 0.55mm
Hit position distortion <0.1mm
Field wires
Drift field
Chargedparticle
e20cm
ExpectedDp/p=1-3% (p,p)
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Expected statisticsTotal (p,2p) cross section : ~2 mbPion beam rate : ~106 (per 6 second spill)5cm thick Liquid Hydrogen targetTPC acceptance of 50%Result: 200 events / spill
Energy coverage: W=1.50 – 2.15 GeV26 energy bins(DW=0.025)20 angle bins10K events / binResult: 24M events in 45 shifts (2 months)
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Status of R&D• TPC development
– 1st prototype successful to confirm basic performance at high beam rate
– Design for real size 2nd prototype going on with electronics development
Other R&D specially for P45• Liquid hydrogen target
– to fit TPC target hole of ~ 5cm cylinder• Trigger hodoscopes
– Optimize segmentation6/24/2013 33
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General Summary
The N* spectrum is a long-standing problem.Today, we know that dynamical coupled-
channels calculations are needed.→ Coupled channels requires hadronic data.→ Many N* states couple to 2p decay. My opinion: without quality (p,2p) data, it is
difficult to see how the N* spectrum can be extracted with PWA techniques.
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Backup slides
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Additional final state: KY data
• Data for KL and KS come for free• Cross sections are smaller, but the final state
is two-body, so less data are needed.• These final states have two charged particles
and hence will be part of the trigger.• Data on p+p K+S+ are especially useful
• Only isospin 3/2 contributes: D resonances.• Is the D(1600) the I=3/2 partner of the Roper?
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