Decay pion spectroscopy of electro-produced light Lambda hypernuclei at MAMI
ORAL · Invited
Abstract
The hypertriton 3ΛH, the lightest hypernucleus, consists of a proton, a neutron, and a Lambda. This simplest Lambda hypernucleus has been used as an essential benchmark of hypernuclear physics, including understanding Λ-N interaction. Its Lambda-binding energy (BΛ) is approximately 130 ± 50 keV based on emulsion data summarized by Jurič et al. The shallow binding energy suggests a 3ΛH lifetime similar to that of a Lambda particle in free space(τΛ = 263 ps). However, recent heavy ion collision experiments have observed lifetimes and binding energies of hypernuclei, sparking significant interest.
After 2010, the STAR and ALICE collaborations reported a 20-30% shorter lifetime for 3ΛH. These groups also reported binding energies of BΛ = 406 ± 120(stat.) ± 110(syst.) keV and preliminarily BΛ = 102 ± 63(stat.) ± 67(syst.) keV, respectively. For understanding the correlation between hypertriton's lifetime and binding energy, accurate measurement of these values is crucial.
In October 2022, we conducted decay-pion spectroscopy experiments on s-shell hypernuclei (3ΛH and 4ΛH) at Mainz Microtron (MAMI). Some electro-produced hypernuclei form bound states and decay via two-body weak decay, emitting pions with monochromatic momentum. By measuring this momentum with high-resolution magnetic spectrometers (Δp/p ~ 10-4) and combining it with a Kaon spectrometer to tag strangeness production and suppress background events, we successfully measured the 4ΛH mass with an accuracy of 80 keV in 2014.
In 2022, to enhance the yield of 3ΛH and reduce background events, we changed the target from 9Be to 7Li in this experiment. The 7Li target was positioned at a 90-degree angle to increase luminosity and mitigate the effects of the pion energy struggle. Additionally, we introduced a new technology for beam energy measurement to achieve hypernuclear mass determination with 10-20 keV accuracy.
In this presentation, I will discuss this experimental method and provide an update on the latest analysis.
After 2010, the STAR and ALICE collaborations reported a 20-30% shorter lifetime for 3ΛH. These groups also reported binding energies of BΛ = 406 ± 120(stat.) ± 110(syst.) keV and preliminarily BΛ = 102 ± 63(stat.) ± 67(syst.) keV, respectively. For understanding the correlation between hypertriton's lifetime and binding energy, accurate measurement of these values is crucial.
In October 2022, we conducted decay-pion spectroscopy experiments on s-shell hypernuclei (3ΛH and 4ΛH) at Mainz Microtron (MAMI). Some electro-produced hypernuclei form bound states and decay via two-body weak decay, emitting pions with monochromatic momentum. By measuring this momentum with high-resolution magnetic spectrometers (Δp/p ~ 10-4) and combining it with a Kaon spectrometer to tag strangeness production and suppress background events, we successfully measured the 4ΛH mass with an accuracy of 80 keV in 2014.
In 2022, to enhance the yield of 3ΛH and reduce background events, we changed the target from 9Be to 7Li in this experiment. The 7Li target was positioned at a 90-degree angle to increase luminosity and mitigate the effects of the pion energy struggle. Additionally, we introduced a new technology for beam energy measurement to achieve hypernuclear mass determination with 10-20 keV accuracy.
In this presentation, I will discuss this experimental method and provide an update on the latest analysis.
*This work is supported by JSPS KAKENHI (Grant No. JP18H05459, 20H01926, 23KJ0180), GP-PU Tohoku University, the DFG (Grant No. PO256/7-1), and the EU Horizon 2020 R&I program No. 824093. Two of the authors (R. Kino and K. Okuyama) are JSPS research fellowships.
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Presenters
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Ryoko Kino
- Tohoku University