High Resolution Hypernuclear Spectroscopy in Hall A E94107E07012

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High Resolution Hypernuclear Spectroscopy in Hall
A (E94-107/E07-012) F. Garibaldi Hall A
Collaboration meeting June 12 2009

• Electroproduction of hypernuclei
• Experimental challenges
• The experimental Program at Jefferson Lab
• E-94-107
• 12C(e,eK)12??
• 16O(e,eK)16?
• ?Be(e,eK)9?Li
• H(e,eK)???0
• E07-012 (angular distribution)
• Conclusions

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HYPERNUCLEAR PHYSICS

• Hypernuclei are bound states of nucleons with a
  strange baryon (Lambda hyperon).
• Extension of physics on N-N interaction to
  system with S0
• Internal nuclear shell
• are not Pauli-blocked
• for hyperons
• Spectroscopy

A hypernucleus is a laboratory to study
nucleon-hyperon interaction (?-N interaction)
??- N interaction
Unique aspects of strangeness many body problems
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and
using electromagnetic probe
High resolution, high yield, and systematic study
is essential
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LN interaction
V
D
SL
SN
T
Each of the 5 radial integral (V, D, SL , SN, T)
can be phenomenologically determined from the
low lying level structure of p-shell hypernuclei
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reasonable counting rates
forward angle
septum magnets
good energy resolution
do not degrade HRS
minimize beam energy instability
background free spectrum
unambiguous K identification
High Pk/high Ein (Kaon survival)
RICH detector
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JLAB Hall A Experiment E94-107
E94107 COLLABORATION
A.Acha, H.Breuer, C.C.Chang, E.Cisbani,
F.Cusanno, C.J.DeJager, R. De Leo, R.Feuerbach,
S.Frullani, F.Garibaldi, D.Higinbotham,
M.Iodice, L.Lagamba, J.LeRose, P.Markowitz,
S.Marrone, R.Michaels, Y.Qiang, B.Reitz,
G.M.Urciuoli, B.Wojtsekhowski, and the Hall A
Collaboration

• Ebeam 4.016, 3.777, 3.656 GeV
• Pe 1.80, 1.57, 1.44 GeV/c Pk 1.96
  GeV/c
• qe qK 6
• W ? 2.2 GeV Q2 0.07 (GeV/c)2
• Beam current lt100 mA Target thickness 100
  mg/cm2
• Counting Rates 0.1 10 counts/peak/hour

16O(e,eK)16?N 12C(e,eK)12?? ?Be(e,eK)9?Li H(
e,eK)???0
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To be added to do the experiment
aerogel first generation
aerogel second generation
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Septum Magnets
Accurate monitoring of many parameters over a
long period of data taking Beam energy spread
and absolute calibration, spectrometers settings
and stability,
Excellent energy resolution
600 KeV ? 500 KeV Best performance for beam
and HRSSepta with accurate optics calibrations
Electrons scattered at 6 deg sent to the HRS at
12.5 deg.
1. DEbeam/E 2.5 x 10-5 2. DP/P (HRS septum)
10-4 3. Straggling, energy loss
1. It was delivered for the first time for 12C
experiment
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RICH detector C6F14/CsI proximity focusing RICH
MIP
Cherenkov angle resolution
Separation Power
Performances - Np.e. of detected
photons(p.e.) - and ?? (angular resolution)
maximize
minimize
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The RICH detector at Jefferson Lab
RICH flying to hunt kaons into the detector hut
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RICH PID Effect of Kaon selection
Coincidence Time selecting kaons on Aerogels and
on RICH
AERO K
AERO K RICH K
p
P
K
Pion rejection factor 1000
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?sp 4.47 nb/(GeV sr2 ??th 4.68 nb/(GeV sr2
) good agreement with theory
Red line Fit to the data
Blue line Theoretical curve Sagay Saclay-Lyon
(SLA) used for the elementary K-?
electroproduction on proton. (Hypernuclear wave
function obtained by M.Sotona and J.Millener)
E94-107 12C(e,eK)11LB
(3,2)
(3,2)
1/2 1-
3/2 2-
1/2 1-
2
2
3/2 2-
admixture
admixture
The energies of the 1/2- and 3/2- levels of the
core are raised primarily by the SN term because
the interaction lN. SN changes the spacing of the
core levels (the magnitude can be changed by
changing SN or changing the p-shell w.f. of the
core)

• energy resolution 635 KeV, the best achieved in
  hypernuclear production experiments
• first clear evidence of excited core states at
  2.5 and 6.5 MeV with high statistical
  significance
• -the width of the strong p??peak and the
  distribution of strength within several MeV on
  either side of this peak can put constraints on
  the hypernuclear structure calculations
• -hint for a peak at 9.65 MeV excitation energy
  (admixture)

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the WATERFALL target provides 16O and H targets
H2O foil
Be windows
H2O foil
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Results on the WATERFALL target - 16O and H
spectra
1H (e,eK)L
1H (e,eK)L,S
L
Energy Calibration Run
S
16O(e,eK)16NL
Nb/sr2 GeV MeV
Excitation Energy (MeV)

• Water thickness from elastic cross section on H
• Fine determination of the particle momenta and
  beam energy
• using the Lambda peak reconstruction (resolution
  vs position)

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Results on 16O target Hypernuclear Spectrum of
16NL
Binding Energy BL13.760.16 MeV Measured for the
first time with this level of accuracy (very
important!) (ambiguous interpretation from
emulsion data interaction involving L production
on n more difficult to normalize) Within errors,
the binding energy and the excited levels of the
mirror hypernuclei 16O? and 16N? (this
experiment) are in agreement, giving no strong
evidence of charge-dependent effects
Fit 4 regions with 4 Voigt functions c2/ndf 1.19

• Theoretical model based on
• SLA p(e,eK)??(elementary process)
• ?N interaction fixed parameters from KEK and
• BNL 16?O spectra
• Four peaks reproduced by theory
• The fourth peak (? in p state) position disagrees
  with theory. This might be an indication of a
  large spin-orbit term S? (under investigation)

0.0/13.76?0.16
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Results on 16O target Hypernuclear Spectrum of
16NL
Evidences of a fifth peak in the quasi-free
regions (already observed in KEK data) is now
investigated. Results from new fits are VERY
PRELIMINARY.Theoretical effort is ongoing to
investigate s1/2? coupling to core excited states
CoreExcitedStates?s1/2?
PRELIMINARY
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Results from9Be(e,eK) 9LiL
Eanergy resolution 500 KeV
Theoretical cross sections based on Saclay-Lyon A
model. Core nucleus 8Li has 3 low lying states
to which lambda in s-state can couple generating
3 doublets of hypernuclear states
Preliminary!
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Results on H target The elementary process
1H(e,eK)L
In all Jlab hypernuclear electroproduction
experiments the K mesons are detected at very
small (few degrees) laboratory scattering angles,
at very low Q2 (close to the photon-point). This
region of kaon scattering angles is not covered,
unfortunately, even by recent very precise photo-
and electroproduction data on the elementary
production process from CLAS, SAPHIR, and LEPS
Collaborations.
In this kinematic region different models for the
K- L electromagnetic production on protons
differ drastically. This lack of relevant
information about the elementary process makes an
interpretation of obtained hypernuclear spectra
difficult.
Lack of data at forward angle
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what is missing ?
- Systematic study of reaction as function of A
and neutron rich nuclei (E05-015)
The interpretation of the hypernuclear spectra is
difficult because of the lack of relevant
information about the elementary process.
- Angular distribution (momentum transfer) at
forward angles
In this kinematical region models for the K-
??electromagnetic production on protons differ
drastically
The Proposal studying, using waterfall target,
different processes
The ratio of the hypernuclear and elementary
cross section measured at the same kinematics is
almost model independent at very forward kaon
scattering angles . Contains direct information
on the target and hypernuclear structure,
production mechanisms
Hall A experimental setup (septum magnets,
waterfall target, excellent energy resolution AND
Particle Identification ) give unique opportunity
to measure, simultaneously, hypernuclear
process AND elementary process
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Results on H target The p(e,eK)L Cross
Section
p(e,e'K)L on Waterfall Production run
p(e,e'K)L on LH2 Cryo Target Calibration run
Expected data from the Proposal E07-012 to study
the angular dependence of p(e,eK)L and
16O(e,eK)16NL at Low Q2 approved PAC January,
2007
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Proposal E07-012 to study the angular dependence
of p(e,eK)? and 16O(e,eK)16? N at Low
Q2 http//www.jlab.org/exp_prog/proposals/07/PR-07
-012.pdf Approved PAC January, 2007 Scheduled to
run April 19-May 14, 2012 The last 6 GeV era
experiment in Hall A
Approved for 12 days
SNR 6
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Good News / Bad News

• ? Qweak will run
• ? Qweak wants all the cryogens it can get
• Must build a room temperature septum pair à la
  PREX

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Re Room Temperature Septa

• Two not quite identical RT septa will work
• Same iron but different coils
• RTlight for 6 electron side (B0.737 T)
• Reduced coil allows close proximity to the beam
  line
• RTstd for 8.5 11 Kaons (B1.215 1.51 T)
• Beefier coil, but doesnt have to get as close to
  the beam line
• Benefits from the PREX experience
• But theres work to do.

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Angular Distribution
None of the models is able to describe the data
over the entire range. New data is
electroproduction could longitudinal amplitudes
dominate?
E98-108 data
?
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L/T Ratio
Data is at different W Estimate L/T lt 0.5 at Q2?0
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Transverse Angular Estimate
Estimate of purely transverse amplitudes Still
greater than models can predict
?
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Q2 Binning
? drops with increasing Q2, S0 essentially flat
with Q2 Extracting the slope with respect to Q2
underway
?
?0
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TCM Binning
? slight rise with increasing TCM ? S0
essentially flat with TCM Extracting the slope
with respect to TCM underway
?
?0
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W Binning
?, S0 essentially flat with W at forward angles,
as expected from photoproduction
?
?0
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S0/? Ratio Binning
S0/? ratio essentially flat with Q2 (between
0.05 and 1.0) at forward angles, 0.5
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Conclusions

• Experiment E94-107 systematic study of p
  shell light hypernuclei
• The experiment required important modifications
  on the Hall A apparatus
• Good quality data on 12C, 9Be and 16O targets
  (12B? , 9Li? and 16N? hypernuclei)
• New experimental equipment showed excellent
  performance
• Data on 12C show new information. For the first
  time significant strength and energy resolution
  on the core excited part of the spectrum
• The width of the strong p? peak and the
  distribution of strength within several MeV on
  either side of this peak can put constraints on
  the hypernuclear structure calculations (hint for
  an unexpected peak at 9.65 MeV excitation
  energy)
• very good data on 16N? hyp. spectr. (and
  p(e,eK)? X-Sect measurement) precise
  determinaton of the L binding energy
• interesting preliminary results on 9Be (final
  results coming soon)
• new experiment (angular distribution) is expeted
  to bring new information on elementary process
  and hypernuclear structure

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Summary H(e,eK)?S0

• - E94-107 calibration data provide low Q2
  measurement of ?? ratio
• - None of the existing models is able to
  reproduce the angular distribution
• - ?0/? Ratio (greater than QHD prediction) falls
  with Q2
• - At Q2 0, ratio .75
• - At Q2 .07 ratio ß .5
• Final results in progress (Armando is writing his
  thesis)

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The cross section of (e,eK) on a nuclear target
and its angular dependence determined by

• - Transition operator, which is given by the
  model used to describe the elem. prod. on protons
• - Structure (that is the many particle wave
  function) of the target nucleus and hypernuclear
  state
• Momentum transferred to the nucleus, q p? - pK
• Angular dependence determined mainly by the
  momentum transferred to the nucleus (q) via the
• nucleus - hypernucleus transition form factor
  (q is a rapidly increasing function of the kaon
• scattering angle)

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The PID Challenge

• Very forward angle ---gt high background of p
  and p
• TOF and 2 aerogel in not sufficient for
  unambiguous K identification !

Kaon Identification through Aerogels
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Rich Performances key parameters
Npe for ? and p
Cherenkov angle for p
Nclusters
Npe p/p ratio
Cherenkov average angle (rad)
Angular resolution
pK 2 GeV/c
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