News and Views (5&6)

1 A Revolution in the Standard Model of Particle Physics? The “Overweight” W Gauge Boson from CDF II by Lei Wu

The Standard Model (SM) of particle physics is one of the most fundamental theories of physics. It describes the fundamental particles that make up our world and the three fundamental interactions between them: the electromagnetic force, the weak force, and the strong force. In the Standard Model, all interactions are mediated by exchanging gauge bosons.

Discovered in 1983, the W boson is an electrically charged fundamental particle in the SM. Together with its neutral partner, the Z boson, they mediate the weak force, one of the Universe’s four fundamental forces, which governs certain types of radioactive decay and plays an important role in the nuclear reactions that power the Sun. However, the W boson mass is “notoriously” difficult to measure, because the W boson decays into an invisible neutrino plus a charged lepton in collider experiments.

After over ten years of careful work, the Collider Detector at Fermilab (CDF) experimental collaboration at the Fermi National Accelerator Laboratory announced that they have achieved the most precise measurement to date of the W boson mass in the world, Mw=80,433.5 +/− 9.4 MeV/c². The experimental results were published as a cover article in the April 7 issue of Science [1].

The new CDF result shows a seven-sigma deviation from the prediction of the Standard Model Mw= 80,357 +/− 6 MeV/c2, as shown in Fig. 1. A seven-sigma discrepancy is significantly higher than the five-sigma level that physicists normally claim as a definitive discovery. However, due to its inconsistency with other experimental measurements, including those from ATLAS and LHCb, the CDF result is in the process of being further investigated.

Fig. 1

Tension with the value expected based on the SM. The horizontal bars denote the uncertainty of the various measurements [1]

Furthermore, the mass of the W boson can also be determined by internal symmetries and other SM parameters. Changing the W boson mass would affect the theoretical predictions, such as top quark mass and Z boson mass, from the consistency test of the SM. Therefore, a global electroweak precision fit is now essential to uncover any secrets that may be behind the new data.

If the new CDF measurement holds, it may lead to a revolution in particle physics, and require new physics beyond the SM. One possible explanation is related to the “God Particle” Higgs boson, which was discovered at the Large Hadron Collider in 2012 [2,3]. If the Higgs sector is larger than the SM (i.e., if there are multi-Higgs bosons), it would bring new contributions to the W boson mass. Another possibility is that the new CDF result might indicate the existence of a supersymmetry theory, which is a space-time symmetry between two basic classes of particles: bosons and fermions. The supersymmetric particles would correct the W boson via the quantum effect, making the W boson heavier.

With the Sagan standard in mind, we still need to wait for confirmation from other existing experiments or future high energy lepton colliders [4,5] before we claim this is a major discovery.

[1] https://www.science.org/doi/10.1126/science.abk1781

[2] https://doi.org/10.1016/j.physletb.2012.08.020

[3] https://doi.org/10.1016/j.physletb.2012.08.021

[4] AAPPS Bulletin. Aug2020, Vol. 30 Issue 4, p56-78. 23p.

[5] AAPPS Bulletin. Dec2017, Vol. 27 Issue 6, p21-25. 5p.

2 The Physical Society of Japan Announces the Recipients of the 27th Outstanding Paper Award by JPS

In recognition of important achievements toward progress in physics, the Physical Society of Japan (JPS) annually selects outstanding papers from among original research articles published in the Journal of the Physical Society of Japan, Progress of Theoretical Physics, Progress of Theoretical and Experimental Physics, and JPS Conference Proceedings. The selection committee has chosen four papers for the 2022 award based on 16 nominations (for 15 papers) made by the editors of the JPS journals and representatives of the 16 divisions of the JPS.

The 2022 award ceremony was held at noon on March 17, 2022.

The titles of the four selected papers, together with their citations, follow below.

2.1 Evolution toward Quantum Critical End Point in UGe ₂

2.1.1 J. Phys. Soc. Jpn. 80, 083703 (2011)

Hisashi Kotegawa , Valentin Taufour, Dai Aoki, Georg Knebel, and Jacques Flouquet

It has been a new trend to explore novel physical properties around a quantum critical point (QCP) at which an order is tuned to zero by an external parameter. In contrast to the case of antiferromagnetic order, where both theoretical and experimental studies have been devoted, experimental studies of ferromagnetic order are still rare although there are many theoretical approaches. For an itinerant ferromagnetic order, it is known that a second-order phase transition will be taken over by a first-order phase transition, resulting in a new critical end point (CEP) under a magnetic field.

This paper deals with the phase transition in the ferromagnet UGe2 where CEP was not determined, and neither is known for the field- and pressure-dependence of the transition temperature toward CEP. The authors measured the Hall effect and electrical resistivity under various magnetic fields and pressures and subsequently constructed a complete temperature-field-pressure phase diagram. In addition to having exactly determined the CEP, the authors also found that the field- and pressure-dependence of the transition temperature (T_CEP) is not explained by existing theories. They proposed that the details of band structure should be taken into account in theoretical modeling.

The work has become a milestone in the research field and stimulated many later theoretical studies. Therefore, this paper deserves the Outstanding Paper Award from the Physical Society of Japan.

2.2 Three-Dimensional Dirac Electrons at the Fermi Energy in Cubic Inverse Perovskites: Ca ₃ PbO and Its Family

2.2.1 J. Phys. Soc. Jpn. 80, 083704 (2011)

Toshikaze Kariyado and Masao Ogata

In topological insulators, Dirac electrons with linear dispersion appear only on the surface. In contrast, Dirac semimetals have Dirac points in the bulk electronic state have attracted attention as topologically related materials. This paper is the first paper, from the early days of topological semimetal research, to show through first-principles calculations that the cubic antiperovskite oxide Ca₃PbO is a Dirac semimetal. Antiperovskite oxide is an oxide where oxygen is coordinated at the position corresponding to copper in a perovskite structure, and alkali metal (Ca, Sr, etc.) resides at the position of oxygen. Pb (or Sn) takes a rare negative ion valence of −4.

The authors found that in this material system, Dirac electrons appear near the Fermi surface at six symmetric positions around the gamma point due to the band inversion intersection of the d-electron of the alkali metal and the p-electron of Pb (Sn). In addition, the mechanism of the suppression of band repulsion leading to the stable Dirac points without opening a gap due to crystal symmetry is derived from a model for low energy states. In addition, the authors discussed the extent of band inversion among a series of antiperovskite oxides.

Following this pioneering work, another group theoretically proposed that some antiperovskite oxides may even become topological crystal insulators. This paper also motivated a number of experimental investigations, including the discovery of superconductivity. In the active research field of topological materials, this paper is considered as a pioneering and highly original paper that triggered progress in international research on Dirac semimetals. For this reason, this paper deserves the Outstanding Paper Award from the Physical Society of Japan.

2.3 Microscopic Description of Electric and Magnetic Toroidal Multipoles in Hybrid Orbitals

2.3.1 J. Phys. Soc. Jpn. 87, 033709 (2018)

Satoru Hayami and Hiroaki Kusunose

In this paper, the authors derived the quantum-mechanical operator expressions of new multipoles, i.e., magnetic and electric toroidal multipoles. Electric toroidal multipoles do not appear in the classical electromagnetism framework, but through their understanding of the correspondence between electricity and magnetism, the authors introduced the concept of magnetic toroidal multipoles.

The authors of the paper also showed that these toroidal moments can be expressed by considering the hybridization between orbitals with different orbital angular momentum, such as p- and d-electrons, and d- and f-electrons. This is an original paper that proposes a microscopic framework for equally treating the magnetic and electric properties of materials and provides a unified basis for arguing physical properties created by multiple degrees of freedom of electrons.

In a later work by the authors [S. Hayami, M. Yatsushiro, Y. Yanagi, and H. Kusunose, Phys. Rev. B 98, 165110 (2018)], together with those by other groups published at the same time, the group-theory based classifications for general multipole ordered phases were provided. The frameworks given in these works are applicable to a variety of realistic materials and emergent cross-correlation responses and led to understanding many important experimental results. This paper played an integral role in the advancement of this discipline and is highly esteemed throughout the community. For these reasons, we determined that this paper deserves the Outstanding Paper Award of the Physical Society of Japan.

2.4 TeV Scale B-L Model with a Flat Higgs Potential at the Planck Scale: In View of the Hierarchy Problem

2.4.1 Prog. Theor. Exp. Phys. 2013, 023B08 (2013)

Satoshi Iso and Yuta Orikasa

This paper, which is an extension of previous research that realized the electroweak symmetry breaking in the classically conformal model with B-L symmetry, introduces a gauge field for B-L symmetry. The model itself is very simple but contains rich structure. The newly added particles determine the dynamics with the SU (3)_c x SU (2)_L x U (1)_Y singlet scalar field Φ and the U (1)_B-L gauge field in the Standard Model. Since there are only two parameters, the model has a high predictive power. In this theory, B-L symmetry breaking and electroweak symmetry breaking by the Coleman-Weinberg mechanism simultaneously take place while solving the gauge hierarchy, and new U (1) gauge bosons and right-handed neutrinos appear in the TeV scale region. Although there are other classically conformal models, this work distinguishes itself in that it is the culmination of the authors’ previous research, while being also a pioneering and yet simple and essential model in this field. Another interesting point is that this works provides a new perspective for diverse areas of study, such as neutrino oscillations, inflation, and leptogenesis.

This paper has been cited in many references and has had a significant influence on the development of this field as it is one of the fundamental works in this field. Therefore, we determined that this paper deserves the Outstanding Paper Award of the Physical Society of Japan.

3 The Physical Society of Japan: 3rd (2022) Fumiko Yonezawa Memorial Prize by JPS

The late Fumiko Yonezawa, emeritus professor of Keio University, made major contributions to physics, such as the development of the coherent potential approximation, and the theory of the metal-insulator transition in liquid selenium. Prof. Yonezawa served as the first female president of the Physical Society of Japan (JPS) and as the president of the Society for Women Scientists for a Bright Future, she also promoted female scientists.

In 2020, JPS established the “Fumiko Yonezawa Memorial Prize” to celebrate the achievements of Prof. Yonezawa and to honor and encourage the activities of the women who are members of JPS.

Prize winners are selected once a year, with a maximum of about five recipients. The prize ceremony is held during the annual meeting of JPS. The prize recipients are expected to present commemorative lectures at JPS meetings within a period of one year after receiving the prize. Winners receive items such as certificates and honorary shields, as well as additional prizes, namely: (1) paid attendance fees for JPS meetings for the next 3 years; and (2) an exemption, of up to 200,000 JPY (yen), from publication fees and open access fees for the Journal of the Physical Society of Japan, and from the article processing charges for the journal, Progress of Theoretical and Experimental Physics (valid for three years for submissions after the prize is received).

The citations of the winners of the 3rd (2022) Fumiko Yonezawa Memorial Prize are listed below.

Natsumi Iwata

Associate Professor, Institute for Advanced Co-Creation Studies, Osaka University

Theoretical study of high energy density plasma dynamics driven by intense light

Irradiating high-power lasers in the relativistic intensity level ionizes materials, thereby creating a high-energy density plasma. In such situations, the strong laser radiation at the gigabar pressure level pushes the irradiated plasma surface, where electron acceleration by lasers in the relativistic regime and heating of the high-temperature plasma occur simultaneously. It is an important issue in plasma physics to explore phenomena in such extreme conditions.

Dr. Natsumi Iwata has been theoretically studying the dynamics of high-energy density plasma driven by high-power lasers. She proposed that the plasma induces a strong electric field in the picosecond regime at the irradiated plasma surface and thus stops pushing the surface due to the laser radiation pressure. Dr. Iwata also clarified that continuous irradiation of lasers gives rise to the blowout of the heated plasma, resulting in a strong acceleration of plasma particles. Furthermore, highlighting the fact that there is a transition in plasma behavior, under continuous laser irradiation, to a statistical regime where random scatterings due to fluctuating electromagnetic fields become dominant, Dr. Iwata conducted simulations for time evolution of the electron energy under statistical scatterings and presented the corresponding plasma expansion theory. In particular, she elucidated that a coupling to fluctuating electromagnetic fields changes the electron dynamics from ballistic to diffusive and thus suppresses the scattering of electrons, leading to a confinement of the high-energy density plasma. In a more recent study, she proposed a statistical approach to the multivariate analysis of experimental data using Bayesian inference and obtained, for example, a scaling law in ion acceleration driven by strong laser light, thereby contributing to the development of data-analysis methods.

We have concluded that Dr. Iwata's scientific achievements deserve the Fumiko Yonezawa Memorial Prize of the Physical Society of Japan.

Keiko Takase

NTT Basic Research Laboratories, Senior Research Scientist

Research on quantum transport and control of spin-orbit interaction in novel semiconductor materials

Dr. Takase has been both experimentally and theoretically studying the quantum properties of quantum effect devices in semiconductor materials such as graphene and III-V semiconductor nanowires. In graphene research, she succeeded in fabricating wafer-scale epitaxial graphene on a silicon carbide (SiC) substrate. Transport spectroscopy of the fabricated graphene field effect transistor (FET) on SiC and the theoretical model elucidated the quantum properties of epitaxial graphene. Furthermore, Dr. Takase succeeded in fabricating FETs using III-V semiconductor nanowires such as InAs and InSb, in collaboration with a materials scientist specializing in nanowire growth, using MOVPE (metalorganic vapor phase epitaxy). Due to their large spin-orbit interaction, these semiconductors are expected to have potential applications in the field of spintronics. Measurements in extreme environments, such as low temperatures and strong magnetic fields, and theoretical calculations revealed that the FET fabricated by Takase et al. can efficiently control a large spin-orbit interaction at a low gate voltage. It is expected to lead to energy savings of FET in the future.

Dr. Takase's continuous research activities, evident in publications and various awards, as well as her outreach activities make her a role model for young female researchers. Dr Takase thus deserves to receive the Fumiko Yonezawa Memorial Prize of the Physical Society of Japan.

4 Formation of the Arab Physical Society by Sameen Ahmed Khan

The Arab Physical Society was formally launched with a day-long online event on April 7, 2022. The event was headlined with presentations by eminent physicists including Nobel laureates (Gerard ‘t Hooft, 1999, Takaaki Kajita, 2015 and Roger Penrose, 2020), Dirac medallists (Edward Witten, 1985, John Ellis, 2005 and Charles Kane, 2012) and a Fields medallist (Edward Witten, 1990). The presentations covered important physics research topics of contemporary interest. The inaugural address was given by Prince Hassan Ben Talal of Jordan, a strong advocate of science for several decades [1]. The event was attended by over 1700 participants.

On June 7, 2021, the Arab Physical Society (ArPS) was registered as a non-profit membership organization. To date, over four hundred persons have registered as members. The mission of the ArPS is to promote excellence and creativity in the field of physics for the benefit of the Arab region and humanity, and specifically, to encourage scientific and research collaboration among researchers and students in the Arab region. Its objectives are as follows:

1. To organize scientific and educational activities;

2. To join other physical societies and relevant international scientific institutions to reduce the knowledge gap in physics between the Arab world and developed countries;

3. To spread physics education and knowledge through conferences, seminars, workshops, and summer and winter schools in the fields of physics, in addition to delivering specialized and public lectures;

4. To establish a peer-review journal in fundamental physics and applications;

5. To promote interactions among individuals, institutions, and organizations with an interest in physics, especially among members of the Arab Physical Society; and

6. To address ethical issues arising from scientific topics.

The Arab Physical Society has established an organizational structure through its governing council, advisory committee, and focal point. Each of these governing bodies has seven members of which three are women. The advisory committee consists of physicists from institutions in Egypt, Jordan, Libya, Morocco, Palestine, Qatar, and Syria. Shaaban Khalil, a high-energy physicist, is the founding president of ArPS. He is the director at the Fundamental Physics Center at the Zewail City of Science and Technology in Egypt [2-3]. A membership drive is underway in several categories including (1) honorary membership (to distinguished Arab physicists living inside or outside the Arab world); (2) regular membership; (3) student and early career membership; (4) associate membership (to physicists with distinguished research profile without conditions on their citizenship); and (5) organizations/foundations membership. ArPS is scheduled to have an Annual General Assembly and a series of events throughout the year. The upcoming major events sponsored by the ArPS include the International Conference on Neutrinos and Dark Matter, which will be held from September 25–28, 2022, at Sharm El-Sheikh, Egypt [1]. ArPS membership is open to any person working or interested in physics, related science, and engineering irrespective of nationality or place of residence. There is a nominal annual membership fee of fifty euros [1].

The organizers, distinguished speakers, and the numerous participants are very enthusiastic that the Arab Physical Society will go a long way in fostering physics research and education in the Arab world. John Ellis summarized their aspirations, “The establishment of the Arab Physical Society and this inaugural event will help physics in the region gain international visibility and consolidate links between physicists across the region.” The ArPS is, according to its website, also keen to foster diversity “to ensure that everyone has the same opportunities, regardless of gender, ethnicity, religion and culture.” Physics has progressed in the Middle East in recent decades. Apart from the university-level areas of progress, there have been joint international initiatives such as the initiative with SESAME: Synchrotron-Light for Experimental Science and Applications in the Middle East in Jordan [4-5]. There has been participation in the activities at CERN: European Organization for Nuclear Research, Geneva Switzerland [6]. In passing, we note that an organization by the same name, the Arab Physical Society (ARPS) was formed in 1974 by Antoine Benjamin Zahlan, who was a physics professor at the American University of Beirut, Beirut, Lebanon. The objective of ARPS was “the advancement and progress of science, especially physics, in the Arab world.” Little is documented about this attempt from 1974 [7].

References

1. Arab Physical Society, https://www.arabphysicalsociety.org/.

2. S. A. Khan, Ahmed Hassan Zewail (1946–2016), Current Science, 111 (05), 936-937 (2016); http://www.currentscience.ac.in/Volumes/111/05/0936.pdf.

3. M. Chergui, Ahmed Hassan Zewail, Physics Today, 69 (12), 69 (2016); https://doi.org/10.1063/PT.3.3406.

4. S. A. Khan, SESAME: The First Synchrotron Facility in the Middle East, AAPPS Bulletin, 10 (2), 36-39 (2000); Association of Asia Pacific Physical Societies.

5. T. Feder, Middle East synchrotron light source is set to start up, Physics Today, 69 (12), 32 (2016); https://dx.doi.org/10.1063/PT.3.3392.

6. S. A. Khan, Joint visits to CERN with SESAME, CERN Courier, 44 (10), 34 (December 2004).

7. Editors, Arab Physical Society holds first meeting, Physics Today, 28 (6), 71 (1975); https://dx.doi.org/10.1063/1.3069026.