New Physics At The Large Hadron Collider - Proceedings Of The Conference

Proceedings of the Conference

Harald Fritzsch

• Publisher: WSPC
• Year: 2016
• eBook ISBN:
  9789813145511
• Topic: Physical Sciences
• Subtopic: Mathematical & Computational Physics

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The Standard Theory of Particle Physics describes successfully the observed strong and electroweak interactions, but it is not a final theory of physics, since many aspects are not understood: (1) How can gravity be introduced in the Standard Theory? (2) How can we understand the observed masses of the leptons and quarks as well as the flavor mixing angles? (3) Why are the masses of the neutrinos much smaller than the masses of the charged leptons? (4) Is the new boson, discovered at CERN, the Higgs boson of the Standard Theory or an excited weak boson? (5) Are there new symmetries at very high energy, e.g. a broken supersymmetry? (6) Are the leptons and quarks point-like or composite particles? (7) Are the leptons and quarks at very small distances one-dimensional objects, e.g. superstrings?

This proceedings volume comprises papers written by the invited speakers discussing the many important issues of the new physics to be discovered at the Large Hadron Collider.

-->0 Readership: Graduates and researchers in high energy physics. -->
New Physics, Physics Beyond the Standard Model, Supersymmetry, LHC0

Accelerator Considerations of Large Circular Colliders

Alex Chao

SLAC National Accelerator Laboratory, Stanford, CA, USA
[email protected]

As we consider the tremendous physics reaches of the big future circular electron–positron and proton–proton colliders, it might be advisable to keep a close track of what accelerator challenges they face. Good progresses are being made, and yet it is reported here that substantial investments in funding, manpower, as well as a long sustained time to the R&D efforts will be required in preparation to realize these dream colliders.

1.Introduction

Several collider options are presently being considered today as potential candidates to provide the energy frontier facilities beyond the LHC. With a widely varying degrees of maturity, one quickly comes up with a list that at least include:

•e⁺e⁻ linear collider: (a) superconducting, (b) normal conducting, (c) plasma-laser.

•e⁺e⁻ circular collider.

•pp circular collider.

•μ+ μ⁻ circular collider.

•γγ collider.

It is too early to discuss which options should prevail at this point. For now, to limit the scope, let us consider only two of the options above, namely the circular e⁺e⁻ and pp colliders. Furthermore, let us for now focus on their technical challenges — some of them are not simple extrapolations from what we have today or even tomorrow. As we consider the tremendous physics reaches of these powerful colliders, their induced technical challenges, and therefore the required R&D investments to make them realities are something we want to keep a close track of.

For this purpose, I will try to mention some of the main technical challenges for the big circular e⁺e⁻ and pp colliders as presently envisioned, particularly the CEPC effort in China¹ and the FCC effort at CERN.² Clearly only the few high level challenges can be mentioned here. For discussion purposes, I choose to use the pre-CDR CEPC parameters when discussing the e⁺e⁻ collider, and the FCC-hh parameters when discussing the pp collider. No programmatic or budgetary discussions are intended.

2.e⁺e⁻ Circular Collider Issues in a Nutshell

The pre-CDR design of CEPC is a single purpose Higgs factory with a circumference of 54 km. As such, its center-of-mass energy E_cm = 240 GeV is considered given. In contrast, the FCC-ee aims for a wider physics goals with a higher energy and a larger ~100 km circumference. As their technical issues are similar, we choose to apply the CEPC parameters for our discussions.

At this high energy, synchrotron radiation becomes an immediate challenge. To put it under control, we must have large circumference C. However, the synchrotron radiation power P

E⁴/C, so we are using the first power of C to fight the fourth power of the beam energy E.

Let us try to scale from LEP on how to optimize the choice of C. There are two ways to do this:

(1)The first way is to minimize the total cost. The total cost contains two terms, one is proportional to the circumference, the other is proportional to the total synchrotron radiation power, i.e. we have $ = C + E⁴/C. It follows from this expression that the total cost is minimum when C = E², and the minimum cost is $_min = 2E². Since LEP-I was designed to minimize the total cost, we can use this result to scale from LEP-I (E_cm = 110 GeV, C = 27 km) to obtain the Higgs factory parameters. By this scaling, we obtain C = 128 km when E_cm = 240 GeV. We can also scale the total cost this way, but as promised, I will not venture in that direction.

(2)If minimum total cost is not the issue but the total synchrotron radiation power is, then we should scale by holding the total synchrotron radiation power fixed, i.e. the scaling is C

E⁴. Since LEP-II was designed with synchrotron radiation power as the limit, we now scale from LEP-II (E_cm = 209 GeV, C = 27 km). The result is for the Higgs factory, E_cm = 240 GeV, C = 47 km.

The pre-CDR CEPC design C = 54 km is closer to case (2). Cost optimization was understandably not yet a consideration.

After choosing a large circumference, strong synchrotron radiation still severely limits the beam current:

The beam current I must be kept low compared with colliders without synchrotron radiation power limit. To illustrate this point, one can compare the KEKB beam current of 2.6 A with the 18 mA beam current envisioned for CEPC.

Now with a limited total beam current, the only way to push up the luminosity is to lump more particles into fewer bunches and to have very small bunch size. This consideration leads to the following comparison:

It then follows that in a Higgs factory, each beam-beam collision is necessarily very violent and the beam-beam perturbation to the particle motion is very strong. The conventional beam-beam limit (Coulomb force between the colliding beam bunches) becomes substantially more severe.

But the beam-beam limit due to the conventional Coulomb interaction is not yet the main problem. What becomes critical is another effect called beamstrahlung (synchrotron radiation induced at the beam-beam collisions),³ which has never been a problem before but becomes serious at 240 GeV. Beamstrahlung pushes the beam collision optimization and the interaction region design to unprecedented level of sophistication.

In a nutshell, the issues for the big e⁺e⁻ collider are synchrotron radiation in the bending arcs, plus synchrotron radiation at the beam-beam collisions.

3.pp Circular Collider Issues in a Nutshell

By far the biggest technical challenge is superconducting magnets. This is a well-recognized issue but let me restate the obvious here:

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Table of contents

• Cover
• Halftitle
• Title
• Copyright
• Preface
• Contents
• 1. Accelerator Considerations of Large Circular Colliders
• 2. Physics Potential and Motivations for a Muon Collider
• 3. Pentaquarks and Possible Anomalies at LHCb
• 4. Neutrino Masses and SO10 Unification
• 5. Neutrino Experiments: Hierarchy, CP, CPT
• 6. Constraining the Texture Mass Matrices
• 7. Rare B-Meson Decays at the Crossroads
• 8. Exploring the Standard Model at the LHC
• 9. Meson/Baryon/Tetraquark Supersymmetry from Superconformal Algebra and Light-Front Holography
• 10. The Spin-Charge-Family Theory
• 11. Search for Direct CP Violation in Baryonic b-Hadron Decays
• 12. New Physics and Astrophysical Neutrinos in IceCube
• 13. The 750 GeV Diphoton Excess and SUSY
• 14. Constraints on the wn Form Factor from Analyticity and Unitarity
• 15. Dynamical Tuning of the Initial Condition in Small Field Inflations — Can We Testify the CW Mechanism in the Universe
• 16. Physics of Higgs Boson Family
• 17. On the Breaking of
• 18. Neutrino Mass Ordering in Future Neutrinoless Double Beta Decay Experiments
• 19. Predicting the CP-Phase for Neutrinos
• 20. Sum Rules for Leptons
• 21. Composite Weak Bosons at the Large Hadron Collider
• 22. Searching for Composite Higgs Models at the LHC
• 23. Gauge-Higgs EW and Grand Unification
• 24. Colour Octet Extension of 2HDM
• 25. New Physics/Resonances in Vector Boson Scattering at the LHC
• 26. Dimensional Regularization is Generic
• 27. A De-gauging Approach to Physics Beyond the Standard Model
• 28. Extension of Standard Model in Multi-spinor Field Formalism — Visible and Dark Sectors
• 29. Aspects of String Phenomenology and New Physics
• 30. Cosmological Constant vis-à-vis Dynamical Vacuum: Bold Challenging the ΛCDM