Precision Microwave Spectroscopy of the Positronium n=2 Fine Structure

by David Cassidy (UCL)

Thursday 20 May 2021, 16:00 → 17:30 Europe/Zurich

CERN

Since positronium (Ps) atoms are composed only of leptons they are, for all practical purposes, pure QED systems, unaffected by nuclear structure effects. Also, being composed of a particle-antiparticle pair, Ps atoms are metastable, and may decay via self-annihilation, as well as through the usual radiative decay channels seen in regular atoms. The energy levels of Ps can be calculated to arbitrary precision (in principle), and precision spectroscopy of Ps can therefore be used to perform rigorous tests of bound-state QED theory.

In this talk I will discuss the current state of the art in experimental Ps optical and microwave spectroscopy. In particular, I will describe some recent measurements of the Ps n = 2 fine structure, specifically 2 3S1 à 2 3PJ (J = 0,1,2) transitions.  The experiments were performed using intense ns positron pulses generated using a Surko-type buffer gas positron trap. These were converted into a dilute gas of (ground state) Ps atoms in vacuum; UV laser light was used to produce atoms in the long-lived 23S1 level, and microwave radiation was then used to drive transitions to the short-lived 23PJ levels, which decay radiatively to the ground state before annihilating. The microwave transitions were observed via the time spectrum of the resulting Ps annihilation radiation.

We found that the measured J = 1 and J = 2 lineshapes exhibited significant asymmetries, whereas a symmetric lineshape was observed for the J = 0 transition. The observed asymmetries are not consistent with the most obvious quantum interference or line-pulling phenomena arising from nearby (off-resonant) transitions, and in the absence of a complete lineshape model we are therefore unable to precisely determine the intervals for these transitions. Since the J = 0 lineshape did not exhibit any significant asymmetry it was possible to extract a value for the transition frequency: however, the obtained interval was found to disagree with theory by 2.77 MHz, which amounts to 4.2 standard deviations: this discrepancy has not yet been explained.  

 

To participate in this seminar, check this link

https://us04web.zoom.us/j/932734874

---

In case of questions contact Stefan Ulmer (stefan.ulmer@cern.ch)

Since positronium (Ps) atoms are composed only of leptons they are, for all practical purposes, pure QED systems, unaffected by nuclear structure effects. Also, being composed of a particle-antiparticle pair, Ps atoms are metastable, and may decay via self-annihilation, as well as through the usual radiative decay channels seen in regular atoms. The energy levels of Ps can be calculated to arbitrary precision (in principle), and precision spectroscopy of Ps can therefore be used to perform rigorous tests of bound-state QED theory.

In this talk I will discuss the current state of the art in experimental Ps optical and microwave spectroscopy. In particular, I will describe some recent measurements of the Ps n = 2 fine structure, specifically 2 3S1 à 2 3PJ (J = 0,1,2) transitions.  The experiments were performed using intense ns positron pulses generated using a Surko-type buffer gas positron trap. These were converted into a dilute gas of (ground state) Ps atoms in vacuum; UV laser light was used to produce atoms in the long-lived 23S1 level, and microwave radiation was then used to drive transitions to the short-lived 23PJ levels, which decay radiatively to the ground state before annihilating. The microwave transitions were observed via the time spectrum of the resulting Ps annihilation radiation.

We found that the measured J = 1 and J = 2 lineshapes exhibited significant asymmetries, whereas a symmetric lineshape was observed for the J = 0 transition. The observed asymmetries are not consistent with the most obvious quantum interference or line-pulling phenomena arising from nearby (off-resonant) transitions, and in the absence of a complete lineshape model we are therefore unable to precisely determine the intervals for these transitions. Since the J = 0 lineshape did not exhibit any significant asymmetry it was possible to extract a value for the transition frequency: however, the obtained interval was found to disagree with theory by 2.77 MHz, which amounts to 4.2 standard deviations: this discrepancy has not yet been explained.  

 

To participate in this seminar, check this link

https://us04web.zoom.us/j/932734874

---

In case of questions contact Stefan Ulmer (stefan.ulmer@cern.ch)

Since positronium (Ps) atoms are composed only of leptons they are, for all practical purposes, pure QED systems, unaffected by nuclear structure effects. Also, being composed of a particle-antiparticle pair, Ps atoms are metastable, and may decay via self-annihilation, as well as through the usual radiative decay channels seen in regular atoms. The energy levels of Ps can be calculated to arbitrary precision (in principle), and precision spectroscopy of Ps can therefore be used to perform rigorous tests of bound-state QED theory.

In this talk I will discuss the current state of the art in experimental Ps optical and microwave spectroscopy. In particular, I will describe some recent measurements of the Ps n = 2 fine structure, specifically 2 3S1 à 2 3PJ (J = 0,1,2) transitions.  The experiments were performed using intense ns positron pulses generated using a Surko-type buffer gas positron trap. These were converted into a dilute gas of (ground state) Ps atoms in vacuum; UV laser light was used to produce atoms in the long-lived 23S1 level, and microwave radiation was then used to drive transitions to the short-lived 23PJ levels, which decay radiatively to the ground state before annihilating. The microwave transitions were observed via the time spectrum of the resulting Ps annihilation radiation.

We found that the measured J = 1 and J = 2 lineshapes exhibited significant asymmetries, whereas a symmetric lineshape was observed for the J = 0 transition. The observed asymmetries are not consistent with the most obvious quantum interference or line-pulling phenomena arising from nearby (off-resonant) transitions, and in the absence of a complete lineshape model we are therefore unable to precisely determine the intervals for these transitions. Since the J = 0 lineshape did not exhibit any significant asymmetry it was possible to extract a value for the transition frequency: however, the obtained interval was found to disagree with theory by 2.77 MHz, which amounts to 4.2 standard deviations: this discrepancy has not yet been explained.  

 

To participate in this seminar, check this link

https://us04web.zoom.us/j/932734874

---

Since positronium (Ps) atoms are composed only of leptons they are, for all practical purposes, pure QED systems, unaffected by nuclear structure effects. Also, being composed of a particle-antiparticle pair, Ps atoms are metastable, and may decay via self-annihilation, as well as through the usual radiative decay channels seen in regular atoms. The energy levels of Ps can be calculated to arbitrary precision (in principle), and precision spectroscopy of Ps can therefore be used to perform rigorous tests of bound-state QED theory.

In this talk I will discuss the current state of the art in experimental Ps optical and microwave spectroscopy. In particular, I will describe some recent measurements of the Ps n = 2 fine structure, specifically 2 3S1 à 2 3PJ (J = 0,1,2) transitions.  The experiments were performed using intense ns positron pulses generated using a Surko-type buffer gas positron trap. These were converted into a dilute gas of (ground state) Ps atoms in vacuum; UV laser light was used to produce atoms in the long-lived 23S1 level, and microwave radiation was then used to drive transitions to the short-lived 23PJ levels, which decay radiatively to the ground state before annihilating. The microwave transitions were observed via the time spectrum of the resulting Ps annihilation radiation.

We found that the measured J = 1 and J = 2 lineshapes exhibited significant asymmetries, whereas a symmetric lineshape was observed for the J = 0 transition. The observed asymmetries are not consistent with the most obvious quantum interference or line-pulling phenomena arising from nearby (off-resonant) transitions, and in the absence of a complete lineshape model we are therefore unable to precisely determine the intervals for these transitions. Since the J = 0 lineshape did not exhibit any significant asymmetry it was possible to extract a value for the transition frequency: however, the obtained interval was found to disagree with theory by 2.77 MHz, which amounts to 4.2 standard deviations: this discrepancy has not yet been explained.  

 

To participate in this seminar, check this link

https://us04web.zoom.us/j/932734874

---

Since positronium (Ps) atoms are composed only of leptons they are, for all practical purposes, pure QED systems, unaffected by nuclear structure effects. Also, being composed of a particle-antiparticle pair, Ps atoms are metastable, and may decay via self-annihilation, as well as through the usual radiative decay channels seen in regular atoms. The energy levels of Ps can be calculated to arbitrary precision (in principle), and precision spectroscopy of Ps can therefore be used to perform rigorous tests of bound-state QED theory.

In this talk I will discuss the current state of the art in experimental Ps optical and microwave spectroscopy. In particular, I will describe some recent measurements of the Ps n = 2 fine structure, specifically 2 3S1 à 2 3PJ (J = 0,1,2) transitions.  The experiments were performed using intense ns positron pulses generated using a Surko-type buffer gas positron trap. These were converted into a dilute gas of (ground state) Ps atoms in vacuum; UV laser light was used to produce atoms in the long-lived 23S1 level, and microwave radiation was then used to drive transitions to the short-lived 23PJ levels, which decay radiatively to the ground state before annihilating. The microwave transitions were observed via the time spectrum of the resulting Ps annihilation radiation.

We found that the measured J = 1 and J = 2 lineshapes exhibited significant asymmetries, whereas a symmetric lineshape was observed for the J = 0 transition. The observed asymmetries are not consistent with the most obvious quantum interference or line-pulling phenomena arising from nearby (off-resonant) transitions, and in the absence of a complete lineshape model we are therefore unable to precisely determine the intervals for these transitions. Since the J = 0 lineshape did not exhibit any significant asymmetry it was possible to extract a value for the transition frequency: however, the obtained interval was found to disagree with theory by 2.77 MHz, which amounts to 4.2 standard deviations: this discrepancy has not yet been explained.  

 

To participate in this seminar, check this link

https://us04web.zoom.us/j/932734874

---

Since positronium (Ps) atoms are composed only of leptons they are, for all practical purposes, pure QED systems, unaffected by nuclear structure effects. Also, being composed of a particle-antiparticle pair, Ps atoms are metastable, and may decay via self-annihilation, as well as through the usual radiative decay channels seen in regular atoms. The energy levels of Ps can be calculated to arbitrary precision (in principle), and precision spectroscopy of Ps can therefore be used to perform rigorous tests of bound-state QED theory.

In this talk I will discuss the current state of the art in experimental Ps optical and microwave spectroscopy. In particular, I will describe some recent measurements of the Ps n = 2 fine structure, specifically 2 3S1 à 2 3PJ (J = 0,1,2) transitions.  The experiments were performed using intense ns positron pulses generated using a Surko-type buffer gas positron trap. These were converted into a dilute gas of (ground state) Ps atoms in vacuum; UV laser light was used to produce atoms in the long-lived 23S1 level, and microwave radiation was then used to drive transitions to the short-lived 23PJ levels, which decay radiatively to the ground state before annihilating. The microwave transitions were observed via the time spectrum of the resulting Ps annihilation radiation.

We found that the measured J = 1 and J = 2 lineshapes exhibited significant asymmetries, whereas a symmetric lineshape was observed for the J = 0 transition. The observed asymmetries are not consistent with the most obvious quantum interference or line-pulling phenomena arising from nearby (off-resonant) transitions, and in the absence of a complete lineshape model we are therefore unable to precisely determine the intervals for these transitions. Since the J = 0 lineshape did not exhibit any significant asymmetry it was possible to extract a value for the transition frequency: however, the obtained interval was found to disagree with theory by 2.77 MHz, which amounts to 4.2 standard deviations: this discrepancy has not yet been explained.  

 

To participate in this seminar, check this link

https://us04web.zoom.us/j/932734874

---