E94-107: Hypernuclei Status Report

Francesco Cusanno

Hall A collaboration meeting, May 17-18, 2004

E94-107: high resolution hypernuclei spectroscopy program on 1p-shell nuclei

Main goal: N interaction

Septum magnets commissioned on December

RICH added to the hadron PID system

Data taking: January 13 – 28 and April 17 – May 17

Collected charge: 49.6 Coulomb on 12C and 56.1 Coulomb on 9Be, one day on Hydrogen

e + AZ -> e’ + K+ + A(Z -1)

Hypernuclear High Resolution Spectroscopy E-94-107

F. Garibaldi, S. Frullani, J. LeRose, P. Markowitz, T. Saito

VN = V( r ) + V( r ) S.SN + V(r ) SN.lN + VT( r) S12

Sezioni d'urto sull'O

0,00001

0,0001

0,001

0,01

0,1

1

10

5 2010 15

nb/s

r2 /G

eV

Electron scattering angle

Cross section

The targets

12C: comparison with present data, better understanding of the data with hadronic probes and Hall C E89-009 (additional peak(s) found respect to predictions)

9Be: spin doublets, s-s potential parameter clarification.

The next goals:

7Li: large neutron excess

16O: ground state doublet investigation, ‘original’ target

The kinematics

Ei = 4.016 GeV, 3.777 (3.775) GeVPk= 1.98 GeV/c, 1.96 GeV/cPe= 1.80 GeV/c, 1.56 GeV/c

On-line ‘observations’

Cross sections on nuclei are smaller than expected

The background is smaller than expected and it is very strongly reduced by the PID system.The resulting contamination on the missing energy spectrum is very small.The absence of contamination and the good resolution allow a good spectroscopy also with the real counting rate.

The missing energy spectrum could be strongly improved by a ‘event-by-event’ evaluation of the beam central energy

Main Results 12C

Run Time:January 9 – 27 and April 18 – 25

Number of Runs Analyzed 198 (January) + 214 (April, runs from 2524 up to 2777)

Total Charge:Accumulated 49.6 Coulomb; different sets of data: RICH, kinematics,

beam energy

1 Coulomb @ 100 A are 2.8 hours = 5.79 effective days (2.71 + 3.08)

Total Counts700 Total ground-state counts, background subtracted;

Background counts = 1.1 counts / MeV x Coulomb (RICH);

700 Counts in the g. s. peak = 14.1 counts / Coulomb;

Not all of the data here!

background

Performance• The ground state and the p-shell state are identified with a good statistics• Indication of core-excited states and p-shell state (confirmation of Hall C E89009 data?). • The reduction factor with respect to the expected counting rate is 7.0 – 7.5. • The energy resolution is ‘under investigations’

1.5 MeV800 keV

Much better?MeV

MeV MeV

MeVRun #

Main Results 9BeRun Time:

Started on 26 April Owl shift;

Runs Analyzed on 11 April 8.00 am, 16 Days.

Number of Runs Analyzed 435 from 2779 up to 3445.

Total Charge:Accumulated 56.1 Coulomb;

1 Coulomb @ 100 A are 2.8 hours = 6.54 effective days;

Beam Efficiency 41%;

Total Counts1050 Total Counts no background subtracted;

400 Background counts = 7.1 counts / Coulomb;

650 Counts in the peak = 11.6 counts / Coulomb;

Performance• The reduction factor with respect to the expected counting rate is 6.5 (a bit better than C?) . • The resolution is improved 0.8 MeV (FWHM) with respect to the C data but is still poor for a

correct identification of the peaks.

Present and Future Work

Beam energy correction with EPICS variables (thanks Ole)

Optimized Coincidence Time calculation (thanks Rob)

Data normalization (thanks Bob)

Fine tuning of the RICH code

optics database (thanks Doug and Yi)

Beam incident angle, raster

Conclusions

We have just completed the data taking (yesterday)

On-line results are promising. The 12C data seem confirm the data from Hall C, The 9Be data show a interesting structure that would confirm the expected spectrum

Optics database optimized for missing mass reconstruction, the obtained resolution on optics data is excellent

We are presently working on the missing mass calculation, very probably the present resolution is affected by a not optimized correction on the beam energy value

The analysis is continuously going forward, to obtain ‘publishable’ results ASAP (at least for my theses :-D).

THANKS

The experiment was proposed in 1994!Now we have just ended the data taking and we start to see nice results.

Many people have done a strong effort to realize it.

THANK YOU VERY MUCH !!!