hypernuclear physics the electromagnetic approach recent results motivation

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The Angular Dependence of16 ( ,O e ′ eK+) Λ16 ( ,N and H e ′ eK+)Λ

- hypernuclear physics

- the electromagnetic approach

- recent results

- motivation

- the elementary reaction

- angular distribution

- the apparatus

- kinematics and counting rates

- beam time request

- summary and conclusion

proposal for PAC 31 (F. Garibaldi January 0507 - Hall A Collaboration meeting - Jlab)

HYPERNUCLEAR PHYSICS

Hypernuclei are bound states of nucleons with a strange baryon (Λ hyperon).

Extension of physics on N-N interaction to system with S#0

Internal nuclear shell are not Pauli-blocked for hyperons

Spectroscopy

Unique aspects of strangeness many body problems

Λ - N interaction

A hypernucleus is a “laboratory” to study nucleon-

hyperon interaction (Λ-N interaction)

Importance for astrophysics

Experimental evidence for single particle orbits deep in nucleus

They cannot be seen by nucleons

Only hyperons (Λ) which are free from Pauli blocking make it possible.

Hotchi et al., Phys.Rev.C 64 (2001) 044302

What do we find from Λ hypernuclear data?

Λ feels a weaker potential than nucleons UΛ = -30 MeV (c.f. UN = -50 MeV)

-> Attraction : Λ-N < N-N

Mass of hypernucleus BΛ (MeV)

Better energy resolution is necessary for more studies on ΛN interaction :

ΛN spin-dependent forces, ΛN-N force, ..

SKS at KEK-PS

Unified understanding of B-B interactionsin the quark (+meson) picture

together with and hypernuclear data

Present Status of Λ Hypernuclear Spectroscopy

O. Hashimoto and H. Tamura, Prog. Part. Nucl. Phys, in press.

(e,e’K+)

(-,K+)

16ΛN

ΛN interaction

most of information is carried out by the spin dependent part doublet splitting determined by , sΛ, T

(r)

Hall A

High resolution,

high yield, and systematic study is essential

Improving energy

resolution

using electromagnet

ic probe

and635 KeV

BNL 3 MeV(FWHM)

KEK336 2 MeV(FWHM)

≤ 500 KeV

1.45 MeV(FWHM)

€

611BΛ

C126

12C(e,e’K)11B

KINEMATICSKINEMATICS

EEbeambeam = 4.016 — 3.777 — 3.656 GeV = 4.016 — 3.777 — 3.656 GeV

Pe= 1.80 — 1.56 — 1.44 GeV/c

PPkk= 1.96 GeV/c= 1.96 GeV/c

ee = = KK = 6° = 6°

= E ~ 2.2 GeV – Q2 = 0.079 (GeV/c)2Beam current : 100 ATarget thickness : ~100 mg/cm2

Counting Rates ~ 0.1 – 10 counts/peak/hourCounting Rates ~ 0.1 – 10 counts/peak/hour

the proposal: studying, using waterfall target, different processes

1. electroproduction of hypernucleus as function of scattering angle (momentum transfer)

2. elementary process on proton

- systematic study of reaction as function of A and neutron rich nuclei- better understanding of the elementary reaction

- cross section as funtion of angle (momentum transfer (w. function))

what is missing ?

- energy resolution ~ 635 KeV, the best achieved in hypernuclear production experiments

- work is in progress to further improve the resolution

- first clear evidence of excited core states at ~2.5 and 6.5 MeV with high statistical significance

- the width of the strong pΛ 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)

1/2

1-

3/2

2-

(3+,2+)

2+admixture

sp= 4.47 nb/(GeV sr2

th= 4.68 nb/(GeV sr2 )

good agreement with theory 1/2

1-

3/2

2-

admixture

(3+,2+)

2+

Red line: Fit to the dataBlue line: Theoretical curve: Sagay Saclay-Lyon (SLA) used for the elementary K-Λ electroproduction on proton.Hypernuclear wave function obtained by M.Sotona and J.Millener

Red line: Fit to the dataBlue line: Theoretical curve: Sagay Saclay-Lyon (SLA) used for the elementary K-Λ electroproduction on proton.Hypernuclear wave function obtained by M.Sotona and J.Millener

E94-107

1H (e,e’K)Λ1H (e,e’K)Λ

16O(e,e’K)16NΛ16O(e,e’K)16NΛ

Low counting levels above Ethr.

16O(e,e’K)16NΛ

16O(e,e’K)16NΛ

16O(e,e’K)16NΛ16O(e,e’K)16NΛ

E-94107: Preliminary spectra of missing energy

16O(e,e’K)16NΛ16O(e,e’K)16NΛ 16O(,K+)16OΛ

16O(,K+)16OΛ16O(K-, ) 16OΛ16O(K-, ) 16OΛ

~ 800 KeV

elementary reaction: similar discrepancy

this has to be understood !

E-94107: Very Preliminary Results on 9Be target

Can we get info also about 9B angular distribution?

how

lack of relevant information about the elementary process makes an interpretation of obtained hypernuclear spectra difficult

contains direct information on the target and hypernuclear structure, production mechanisms

Hall A experimental setup (septum magnets, waterfall target, excellent energy resolution and PID) give unique opportunity to measure, at the same time, elementary process and hypernuclear process

in this kinematical region models for the K+- Λ electromagnetic production on protons differ drastically

the ratio of the hypernuclear and elementary cross section measured at the same kinematics should be almost model independent at very forward kaon scattering angles

why

dependence of hypernuclear cross section on angle

determined mainly by the following factors

- transition operator, which is given by the model used to describe the elementary production on individual 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

elementary process

elementary process

- in principle, the amplitude can be calculated in QCD, in practice semifenomenological description Quantum HadronDynamics(QHD), degrees of freedom, nucleon, kaon, resonances.

- parameters of the Lagrangian taken from other processes or from fit to data taking into account general principles (SU(2), SU(3))

- elm. structure of hadrons by f.f.(important at Eg>1.5 GeV for suppression of X-section)

- non pointilike structure of hadrons in the strong vertex, only recently in some models

two group of models according to the assumption for h.f.f.

- KMAID, Jansen, H2

- Saclay-Lyon, WiJiCo

description very bad in the kinematical region relevant for hypernuclear calculations

elementary process; angular distribution

electroproduction on 16O; angular distribution

- the slope depends on the spin of hypernuclear state

- excitation of hypernuclear states brings in a different combinations of the elementary amplitudes for different final states

- the nuclear structure for a specific final state can emphasize either spin-flip or non-spin flip amplitudes, as well as combinations of them with different phases.

- deviations from an exponential decreases of cross sections with q could be caused by interference between the different amplitudes

Simultaneously measuring the electroproduction cross section on hydrogen and oxygen targets at a few kaon scattering angles can therefore not only discriminate between two groups of elementary models but it can shed new light also on some problems of hypernuclear physics

kinematics and counting rates

Waterfall Target thicknes = 130 mg/cm2

Beam current = 100 A

beam time request

SNR = 5 - 6

Hall A - Two High Resolution SpectrometersHall A - Two High Resolution SpectrometersQDQ - Momentum Range: 0.3 –4 GeV/c p/p : 1 x 10-4 – p = =-5% - –6 mr

1 (+1) Cherenkov threshold aerogels

+ RICH in the hadron

spectrometer + septum magnet

QuickTime™ and aMotion JPEG OpenDML decompressor

are needed to see this picture.

PID

electron arm:gas Cherenkov + shower counter

--> 105 pion rejection hadron arm

2 aerogel detectors (n=1.015 and n=1.025)

RICH detector

pion rejection ~ 10.000 !!

RICH upgrade

this proposal

Summary and conclusionsthe proposed experiment will answer the following the proposed experiment will answer the following

questionsquestions

• does the cross section for the photo-production continue in rising as the kaon angle goes to zero or is there a plateau or even a dip like for the high-energy data?(relationship with CLASS data)

• is the concept of the hadronic form factors as it is used in the isobaric models still correct? What is the angular dependence of the hypernuclear form factor at forward angle?

. is the hypernuclear angular dependence the same as the hypernuclear process?

• which of the models describes better the reality at forward angles and can be therefore used in analysis of hypernuclear data without introducing an additional uncertainty?

. the success of the previous experiment (very “clean” (background free) data) guarantees for the experimental equipment (optics, PID), analysis, rates (beam time) evaluation to be under control. (extrapolations “easy”).

“unique possibility” for this experiment in Hall A with waterfall target, septa and PID

these questions arethese questions are very important for our very important for our understanding of dynamicsunderstanding of dynamics of of the process and the process and vitalvital for the hypernuclear calculations and for the hypernuclear calculations and interpretation of the data, interpretation of the data, they urgethey urge to be answered also for “building” to be answered also for “building” the the hypernuclear program at Jlab in the futurehypernuclear program at Jlab in the future

The scientific case for these measurements is well made. The elementaryproduction reaction may help shed light on striking discrepanciesbetween current models of this reaction at small angles. At this time,the small-angle behavior of the p(e,e'K+)Lambda cross-section isessentially unknown and difficult to access experimentally. The study ofthe angular dependence would be of great use to distinguish between theseveral competing models available to-date. Hence, JLab can make asignificant contribution to basic hyperon physics. In addition, thesmall-angle regime of the elementary cross section is essential inputfor hypernuclear production calculations. Comparison of elementary andhypernuclear production data at the same kinematics may allowconclusions about the hypernuclear reaction dynamics. The simultaneousacquisition of data for each of these two types of reaction with a watertarget is particularly appealing.

While the scientific case is compelling, the discussion raises a few concerns.

Furthermore, the experimental part of the proposal appears somewhat thin.

The proposal would clearly gain from some clarificationsand a more thorough experimental discussion.

The two main concerns I have are

-Extraction of the photoproduction cross section from the electroproduction- data may not be unambiguous;

- The signal-to-noise ratio in the hypernuclear channel may become too poor to obtain a clear signal at the proposed angles

Given the scarcity of hypernuclear data, there is significant discovery potential.

The status of the "already measured" (p. 14) E94-107 data point attheta_CM = 5.4 degrees is only briefly discussed on pp. 7-9, and adiscrepancy of a factor of 2 with the SLA model is noted. It remainssomewhat vague how final these results are. Even so, it would beillustrative to add these (presumably preliminary) data to Figs. 7 and9. A discussion of the current uncertainty and main source of errorwould likewise help.

On p. 13/Fig. 6: "Moreover, the CLAS and SAPHIR data are not fullyconsistent at the forward angles...". This should be "... the LEPS andSAPHIR data..." (red triangles and blue squares). Interestingly, thesedata _are_ consistent in Fig 7, which shows different kinematics.

On p. 10 and 16, the authors discuss the possibility of extracting thephotoproduction cross-section from electroproduction data. On p. 10,they claim that longitudinal and interference terms "should benegligible". On p. 16, they state that "LT and TT interference terms cancontribute significantly". This is confusing.

In same line of discussion, on p. 16, a claim is made that "we believethat [by] utilizing the data distribution in the azimuthal angle ... itwill be possible to estimate the contribution of the interferenceterms". This is highly unconvincing. The acceptance of the HRS in theout-of-plane direction in these kinematics is very small (a fewdegrees). It appears nearly impossible to obtain data as a function ofazimuth, especially with sufficient statistics and coverage to perform aFourier decomposition.

Since contributions from interference terms increase with angle, it isnot unlikely that the proposed measurements will only yield meaningfulelectroproduction results. Best suited for extracting a photoproductioncross section are the already existing data from E94-107. Should it notbe possible to extract photoproduction data reliably, how useful is themeasurement of the elementary process then?

On p. 21, Table 5, there is an estimate of rates. There is no word as to how these estimates were obtained. Since calculations differ in theircross section predictions by up to an order of magnitude, it would be very useful to provide somewhat more detail.

For instance, If the SLA model was used, which E94-107 already suggests to be over-predicting cross sections, these estimates might be significantly too optimistic.

Since the signal-to-noise ratio in the hypernuclear channel is poor, it is essential to convince the PAC that this is not a potential show-stopper.

In the same vein, a discussion of expected statistics and systematics in the 16N-Lambda channel is missing.

Also completely missing is a discussion of how the two reaction channels can be separated in the analysis.

On p. 22, it would help to elaborate what property of the RICH will improve with the upgrade.

Is it just a larger pad area and so a widergeometric acceptance? How, then, the better resolution?

Comparison with BB interaction models SΛ SN T (MeV)

ND -0.048 -0.131 -0.264 0.018 NF 0.072 -0.175 -0.266 0.033 NSC89 1.052 -0.173 -0.292 0.036 NSC97f 0.754 -0.140 -0.257 0.054

( “Quark” 0.0 -0.4 )

Exp. 0.4 -0.01 -0.4 0.03

Tensor forces (T) is well explained by meson-exchange models.

Strength equivalent to quark-model LS force by Fujiwara et al.

G-matrix calc.

by Yamamoto

Spin-orbit forces (SΛ , SN) cannot be explained by meson models.

Data seems to favor quark models.

Consistent with Hiyama et al.

--but 9ΛBe calculation by Fujiwara et al. (quark+meson) cannot reproduce it.

PRL 85 (2000) 270

Revised

9Be (K-, - ) 9ΛBe

Study of ΛN interaction from spectorscopyBNL E930 (AGS D6 line + Hyperball)

ΛN tensor force: T = 0.03 MeV=> agree with meson-exchange model predictions

ΛN spin-orbit force: SΛ = -0.01 MeV

=> agree with quark-model predictions

43±5 keV 26.1±2.0 keV

16O (K-, - ) 16ΛO

E (keV)E (keV)

Ukai et al.,PRL 93 (2004) 232501

Akikawa et al., PRL 88 (2002) 082501

MeV

MeV

Discovery of “Hypernuclear Fine Structure”

HYPERNUCLEI and ASTROPHYSICS Strange baryons may appear in

neutral b-stable matter through process like:

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n + e− → Σ− + ν e

The presence of strange baryons in neutron stars strongly affect their properties. Example: mass-central density relation for a non-rotating (left) and a rotating (right) star The effect strongly depends upon

the poorly known interactions of strange baryons

More data needed to constrain theoretical models.

- both potential sets are fitted equally well to hyperon-nucleon data

- large evident differences in their predictions for neutron star structure

- the onset density and concentration of the lambda are quite different with both models

- need for more experimental constraints on these potentials evident

Hypernuclear investigation (1)• Few-body aspects and YN, YY interaction

– Flavor SU(3) extended nuclear interaction• BB interaction

– Spin dependent interactions • Spin-orbit interaction, …….

– Λ mixing or the three-body interaction• Mean field aspects of nuclear matter

– A baryon deep inside a nucleus distinguishable as a baryon ?

– Medium effect ?– Tensor interaction in normal nuclei and hypernuclei

• Astrophysical aspect– Role of strangeness in compact stars– Hyperon-matter, SU(3) quark-matter, …– YN, YY interaction information

1953 1970 : hypernuclear identification with visualizing techniquesemulsions, bubble chambers

1970 Now : Spectrometers at accelerators:

CERN (up to 1980) BNL : (K-, p-)

and (p+,K+), production

methods KEK (K-, p-) and (p+, K+),

production methods

> 2000 : Stopped kaons at DANE (FINUDA) : (K-stop,

p-)

> 2000 : The new electromagnetic

way :

HYPERNUCLEAR production with

ELECTRON BEAM at JLAB

Elementary reactionon neutron :

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K− + n → π − + Λ

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+ + n → K + + Λ

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12C → 12CΛ

e.g.

Elementary reactionon proton :

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e + p → ′ e + K + + Λ

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12C → 12BΛ

e.g.

Hypernuclei: historical background - experimental techniques

Production of MIRROR hypernuclei

Λ: I=0, q=0 Λn = ΛpSpectroscopy of mirror hypernuclei reveal Λn ≠ Λp Λ0 mixing and ΛN-N coupling