The history of LHCb

I. Belyaev, G. Carboni, N. Harnew, C. Matteuzzi. F. Teubert
In this paper we describe the history of the LHCb experiment over the last three decades, and its remarkable successes and achievements. LHCb was conceived primarily as a b-physics experiment, dedicated to CP violation studies and measurements of very rare b decays, however the tremendous potential for c-physics was also clear. At first data taking, the versatility of the experiment as a general-purpose detector in the forward region also became evident, with measurements achievable such as electroweak physics, jets and new particle searches in open states. These were facilitated by the excellent capability of the detector to identify muons and to reconstruct decay vertices close to the primary pp interaction region. By the end of the LHC Run 2 in 2018, before the accelerator paused for its second long shut down, LHCb had measured the CKM quark mixing matrix elements and CP violation parameters to world-leading precision in the heavy-quark systems. The experiment had also measured many rare decays of b and c quark mesons and baryons to below their Standard Model expectations, some down to branching ratios of order 10-9. In addition, world knowledge of b and c spectroscopy had improved significantly through discoveries of many new resonances already anticipated in the quark model, and also adding new exotic four and five quark states.

Click to access 2101.05331.pdf

The EFT-Hedron

Nima Arkani-Hamed, Tzu-Chen Huang, Yu-tin Huang
We re-examine the constraints imposed by causality and unitarity on the low-energy effective field theory expansion of four-particle scattering amplitudes, exposing a hidden “totally positive” structure strikingly similar to the positive geometries associated with grassmannians and amplituhedra. This forces the infinite tower of higher-dimension operators to lie inside a new geometry we call the “EFThedron”. We initiate a systematic investigation of the boundary structure of the EFThedron, giving infinitely many linear and non-linear inequalities that must be satisfied by the EFT expansion in any theory. We illustrate the EFThedron geometry and constraints in a wide variety of examples, including new consistency conditions on the scattering amplitudes of photons and gravitons in the real world.

Click to access 2012.15849.pdf

Reflections on a Revolution

John Iliopoulos, reply by Sheldon Lee Glashow
In response to “The Yang–Mills Model” (Vol. 5, No. 2).

To the editors:

It is an honor and a pleasure to comment on Sheldon Lee Glashow’s magisterial essay on the Yang–Mills model. His essay is all the more special for describing one of the greatest chapters in the history of physics, the story of a beautiful mathematical concept transformed into a theory for all seasons, the Standard Model of particle physics. It was of course Glashow who played a central role in the electroweak part of the story by coming up with his masterpiece, the SU(2) × U(1) gauge theory. And with the added masterstroke from Steven Weinberg, his high-school buddy, as he reminds us, we now have not just a theory of all relevant particle interactions at today’s energies, but also a theory of the origin of the masses of elementary particles. Simply, mass turned into a dynamical variable, the knowledge of which enables us to unambiguously predict the associated Higgs boson decay into the relevant particles. And we know with certainty that the W and Z bosons, predicted by Glashow, and the third-generation fermions receive their masses from the Higgs mechanism….

Dark Matter Capture by Atomic Nuclei

Bartosz Fornal, Benjamin Grinstein, Yue Zhao
We propose a new strategy to search for a particular type of dark matter via nuclear capture. If the dark matter particle carries baryon number, as motivated by a class of theoretical explanations of the matter-antimatter asymmetry of the universe, it can mix with the neutron and be captured by an atomic nucleus. The resulting state de-excites by emitting a single photon or a cascade of photons with a total energy of up to several MeV. The exact value of this energy depends on the dark matter mass. We investigate the prospects for detecting dark matter capture signals in current and future neutrino and dark matter direct detection experiments.

Click to access 2005.04240v1.pdf

Comments on magnetic black holes

Juan Maldacena
We discuss aspects of magnetically charged black holes in the Standard Model. For a range of charges, we argue that the electroweak symmetry is restored in the near horizon region. The extent of this phase can be macroscopic. If Q is the integer magnetic charge, the fermions lead to order Q massless two dimensional fermions moving along the magnetic field lines. These greatly enhance Hawking radiation effects.


Click to access 2004.06084.pdf

Natural Philosophy versus Philosophy of Naturalness

Goran Senjanovic
I reflect on some of the basic aspects of present day Beyond the Standard Model particle physics, focusing mostly on the issues of naturalness, in particular on the so-called hierarchy problem. To all of us, physics as natural science emerged with Galileo and Newton, and led to centuries of unparalleled success in explaining and often predicting new phenomena of nature. I argue here that the long standing obsession with the hierarchy problem as a guiding principle for the future of our field has had the tragic consequence of deviating high energy physics from its origins as natural philosophy, and turning it into a philosophy of naturalness.