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Author: Bishnu PandeyAdvisor: Dr. Liguang Tang

Department of Physics, Hampton University, Hampton, Virginia 23668

Abstract :

Approach to Access Λ-n Interactionn Interaction:

CSV parameterization: δuu

v = −δdδud

v = k(1 −δd x)4 x −δd0.5 (x −δd 0.0909)

Summary:

Acknowledgements:

A Possible Observation of Λnn Continuum Structure and a Bound ΣNN State using the (e e’K+ ) Reaction

The E12-n Interaction17-n Interaction003 experiment was carried out at Jefferson Lab in November 2018 by using the Hall A high resolution spectrometers and the tritium target. By using the (e e’K+ ) reaction, two possible Λnn resonance states and a ΣNN bound state were observed for the first time with an energy resolution of better than 1.6 MeV (FWHM). However, greater statistics are needed to solidly conform the observed states. The experimentally observed Λnn state should provide constraint in describing the Λn interaction for which no scattering data exist. The result is drafted in a paper and the first draft of which is distributed to the collaborators for review.

Charge Symmetry Breaking Puzzle:

Introduction:

Tritium Gas Used as Production Target:

Momentum Optimization and Missing Mass:

● The momentum calibration is the two dimensional correlation.

● There are only three correlation lines (2 blue and 1 pink line) to calibrate the momentum matrices and in between there is large gap where the matrix quality may not be uniform.

● One additional data point that is included in matrix tune. ● After optimization the Λ and landed at their known masses

with a separation of 76.94 . ● The peak width for Λ and is achieved less than 1.5 MeV (σ).).

Z Vertex Reconstruction: Hydrogen Contamination Test:

Coincidence Time:

● For A = 3 non-n Interactionstrange mirror pair of nuclei, ignoring the Columb interaction between the protons, the binding energy difference is ~ 80 KeV.

● For A = 4 isospin mirror pair of hypernuclei, the charge symmetry breaking (CSB) is more than 3 times larger than that observed in A = 3 mirror pair of nuclei.

● The significant CSB in A = 4 mirror pair suggests that Λn interaction need to be measured experimentally to understand the charge symmetry puzzle.

C. Rappold et al., Phys. Rev. C 88, 041001(R) (2013)

6Li (2A GeV) on 12C target and study the invariant mass of final state particles

It was claimed to be a bound state. All theoretical studies ruled it out. However, some theoretical studies indicated that Λnn

resonance may likely exist and by measuring the binding energy and the natural width of such state, it is possible to extract the Λ-n Interactionn interaction.

Hall A was not Optimized for the Experiment:

● An electron beam with energy E = 4.326 GeV was used to produce the (e e’K+ ) reaction by hitting a tritium target.

● Coincidence K+ were detected in the right spectrometer with central momentum of 1.823 GeV/c.

● The scattered electrons were detected in the the left spectrometer with central momentum of 2.218 GeV/c.

● The two high peaks centered at ± 12.5 cm were formed by the events from the entrance and exit aluminum end caps.

● A z vertex resolution of ~ 4.5 mm in (σ).) is achieved which is satisfied by the experimental requirements.

● A z -n Interactionvertex gate ranging from -n Interaction10 cm to 10 cm was applied to select the events from the gas region.

● Two low index aerogel detectors A1 and A2 were used to separate K+ from rest of hadrons.

● The time resolution of about ps was achieved with the CEBAF's beam bunch separation of 2 ns.

● About 2 % of H contamination is observed in the tritium gas which is consistent with other tritium experiments.

Mass Spectroscopy of :

This project is supported by DE-FG02-97ER41047.

I would like to acknowledge my advisor and spokesperson of the experiment Dr. Liguang Tang for his continuous support and excellent guidance.

● The experiment demonstrated that by using the tritium target and the (e e’K+ ) reaction, it is possible to observe the 3 body final state Λnn and ΣNN interaction. However, Hall A system need to be optimized for higher statistics.

● From this experiment two resonance states of and one bound state of were observed. However, to make a definite identification, higher statistics are required.

● A simulation predicted the intrinsic missing mass resolution of A = 3 resonance to be σ). = 0.66 MeV. Thus, the natural width is about 0.55 MeV.

● However, due to low statistics the precision does not permit sufficient constrain in determination of the Λ-n Interactionn Interaction.

● The first draft of the paper is under review.

● The Hyperions (Y) have long history but we don’t have sufficient data to explain YN interaction.

● Limited data exist for the Λp interaction and beyond this point data doesn’t exist.

● Λn interaction is the missing piece.● The Λp and Λn interactions are considered identical and

in reality which may not be true.

Kinematics space for ee’K+

● Hall A with tritium target aimed to search for the Λnn resonance or the bound state as indicated by HypHI experiment. However, the system was not optimized for this experiment.

● The electron arm was at very large angle , produces large which results low production yield.

● The path length for the hadron arm is too large (~ 26 m) which limits the K+ survival rate ~ 10 %.

● The is too high ~ 400 MeV/c which gives very small value of .

The Mass Spectroscopy with Higher Bins:

● Two Λnn resonance states and a bound ΣNN state is observed, however, greater statistics is needed to make definite identification.

● The red line shows simulated Λ and Σ quasi-n Interactionfree distributions.

● The vertical black dash lines indicate the locations of the and thresholds.