The requirement of electroweak naturalness in simple supersymmetric models implies the existence ... more The requirement of electroweak naturalness in simple supersymmetric models implies the existence of a cluster of four light Higgsinos with a mass ∼100-300 GeV, the lighter the better. While such light compressed spectra may be challenging to observe at the LHC, the International Linear e þ e -Collider (ILC) with ffiffi ffi s p > 2m Higgsino would serve as both a SUSY discovery machine and a precision microscope. We study Higgsino pair production signatures at the ILC based on a full, GEANT4-based simulation of the ILD detector concept. We examine several benchmark scenarios that may be challenging for discovery at the HL-LHC due to mass differences between the Higgsino states between 20 and 4 GeV. Assuming ffiffi ffi s p ¼ 500 GeV and 1000 fb -1 of integrated luminosity, the individual Higgsino masses can be measured to 1%-2% precision in the case of the larger mass differences, and at the level of 5% for the smallest mass difference case. The Higgsino mass splittings are sensitive to the electroweak gaugino masses and allow extraction of gaugino masses to ∼3%-20% (depending on the model). Extrapolation of gaugino masses via renormalization group running can test the hypothesis of gaugino mass unification. We also examine a case with natural generalized mirage mediation, where the unification of gaugino masses at an intermediate scale apparently gives rise to a natural SUSY spectrum somewhat beyond the reach of HL-LHC.
We give explicit formulas for the decays of the neutralinos and charginos of the minimal model of... more We give explicit formulas for the decays of the neutralinos and charginos of the minimal model of supersymmetry into other neutralinos and charginos plus a W, Z, or Higgs boson. The important features of these decays are illustrated and their phenomenological implications discussed. In general, this class of two-body decays is dominant for the heaviest charginos and neutralinos.
The work contained herein constitutes a report of the “Beyond the Standard Model” working group f... more The work contained herein constitutes a report of the “Beyond the Standard Model” working group for the Workshop “Physics at TeV Colliders”, Les Houches, France, 26 May–6 June, 2003. The research presented is original, and was performed specifically for the workshop. Tools for calculations in the minimal supersymmetric standard model are presented, including a comparison of the dark matter relic density predicted by public codes. Reconstruction of supersymmetric particle masses at the LHC and a future linear collider facility is examined. Less orthodox supersymmetric signals such as non-pointing photons and Rparity violating signals are studied. Features of extra dimensional models are examined next, includingmeasurement strategies for radions and Higgs’, as well as the virtual effects of Kaluza Klein modes of gluons. An LHC search strategy for a heavy top found in many little Higgs model is presented and finally, there is an update on LHC Z? studies
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Oct 6, 2022
We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for ... more We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for Snowmass 2021, focusing mainly on several whitepaper contributions to BSM model building (TF08) and closely related areas.
The International Linear Collider (ILC) is on the table now as a new global energyfrontier accele... more The International Linear Collider (ILC) is on the table now as a new global energyfrontier accelerator laboratory taking data in the 2030's. The ILC addresses key questions for our current understanding of particle physics. It is based on a proven accelerator technology. Its experiments will challenge the Standard Model of particle physics and will provide a new window to look beyond it. This document brings the story of the ILC up to date, emphasizing its strong physics motivation, its readiness for construction, and the opportunity it presents to the US and the global particle physics community.
program containing both leading-logarithm and next-to-leading-logarithm contributions has been de... more program containing both leading-logarithm and next-to-leading-logarithm contributions has been developed and used to study the photoproduction of large-transverse-momentum hadronic jets. Predictions are presented and discussed for a variety of observables including singlejet invariant cross sections, dijet cross sections, and angular distributions. For some observables the inclusion of the next-to-leading-logarithm terms dramatically lessens the dependency on the choice of the renormalization and factorization scales entering the calculation, thereby increasing the precision of the calculation. The flexibility of the Monte Carlo technique allows predictions for additional observables to be generated easily.
The top group studied discovery issues as well as measurements to be made at the Tevatron, the LH... more The top group studied discovery issues as well as measurements to be made at the Tevatron, the LHC and the SSC.
We present the activities of the "New Physics" working group for the "Physics at TeV Colliders" w... more We present the activities of the "New Physics" working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 30 May-17 June, 2011). Our report includes new agreements on formats for interfaces between computational tools, new tool developments, important signatures for searches at the LHC, recommendations for presentation of LHC search results, as well as additional phenomenological studies.
We take a critical view of the treatment of threshold effects in SUSY spectrum computations from ... more We take a critical view of the treatment of threshold effects in SUSY spectrum computations from high-scale input. We discuss the two principal methods of (a) renormalization at a common SUSY scale versus (b) integrating out sparticles at their own mass scales. We point out problems in the implementations in public spectrum codes, together with suggestions for improvements. In concrete examples, we compare results of Isajet 7.72 and SPheno 2.2.3, and present the improvements done in Isajet 7.73. We also comment on theoretical uncertainties. Last but not least, we outline how a consistent multiscale approach may be achieved.
The supersymmetrized DFSZ axion model is especially compelling in that it contains 1. the SUSY so... more The supersymmetrized DFSZ axion model is especially compelling in that it contains 1. the SUSY solution to the gauge hierarchy problem, 2. the Peccei-Quinn (PQ) solution to the strong CP problem and 3. the Kim-Nilles solution to the SUSY μ problem. In a string setting, where a discrete R-symmetry ($$ {\textbf{Z}}_{24}^R $$ Z 24 R for example) may emerge from the compactification process, a high-quality accidental axion (accion) can emerge from the accidental, approximate remnant global U(1)PQ symmetry where the decay constant fa is linked to the SUSY breaking scale, and is within the cosmological sweet zone. In this setup, one also expects the presence of stringy remnant moduli fields ϕi. Here, we consider the situation of a single light modulus ϕ coupled to the PQMSSM in the early universe, with mixed axion plus higgsino-like WIMP dark matter. We evaluate dark matter and dark radiation production via nine coupled Boltzmann equations and assess the severity of the cosmological modul...
We continue our examination of prospects for the discovery of heavy Higgs bosons of natural SUSY ... more We continue our examination of prospects for the discovery of heavy Higgs bosons of natural SUSY (natSUSY) models at the high luminosity LHC (HL-LHC), this time focusing on charged Higgs bosons. In natSUSY, higgsinos are expected at the few hundred GeV scale whilst electroweak gauginos inhabit the TeV scale and the heavy Higgs bosons, H, A and H± could range up tens of TeV without jeopardizing naturalness. For TeV-scale heavy SUSY Higgs bosons H, A and H±, as currently required by LHC searches, SUSY decays into gaugino plus higgsino can dominate H± decays provided these decays are kinematically accessible. The visible decay products of higgsinos are soft making them largely invisible, whilst the gauginos decay to W, Z or h plus missing transverse energy (ET). Charged Higgs bosons are dominantly produced at LHC14 via the parton subprocess, gb→H±t. In this paper, we examine the viability of observing signatures from H±→τν, H±→tb and H±→W,Z,h+ET events produced in association with a to...
Naturalness arguments imply the existence of higgsinos lighter than 200-300 GeV. However, because... more Naturalness arguments imply the existence of higgsinos lighter than 200-300 GeV. However, because these higgsinos are nearly mass degenerate, they release very little visible energy in their decays, and (even putting aside triggering issues) signals from electroweak higgsino pair production typically remain buried under Standard Model backgrounds. Prospects for detecting higgsino pair production via events with monojets or monophotons from initial state radiation are also bleak because of signal-to-background rates typically at the 1% level. Here, we consider the possibility of reducing backgrounds by requiring the presence of soft daughter leptons from higgsino decays in monojet events. We find that LHC14 experiments with an integrated luminosity of 300 fb −1 should be sensitive to light higgsinos at the 5σ level for µ < 170 GeV with a S/B ∼ 8.5%. For an integrated luminosity of 1000 fb −1 (which should be possible at a high luminosity LHC) the corresponding sensitivity to µ extends to over 200 GeV though the systematic uncertainty would have to be controlled to considerably better than 5%. The corresponding reach from measurements of the rate asymmetry between monojet events with same flavour vs. opposite flavour dileptons is ∼10-15 GeV smaller, but does not suffer the systematic uncertainty from the normalization of the background.
We revisit the various measures of practical naturalness for models of weak-scale supersymmetry (... more We revisit the various measures of practical naturalness for models of weak-scale supersymmetry (SUSY) including: 1. electroweak (EW) naturalness; 2. naturalness via sensitivity to high-scale (HS) parameters [Ellis-Enquist-Nanopoulos-Zwirner/Barbieri-Giudice (EENZ/BG)]; 3. sensitivity of Higgs soft terms due to high-scale radiative corrections; and 4. stringy naturalness (SN) from the landscape. The EW measure is most conservative and seems unavoidable. We debut a new numerical routine for calculating the EENZ/BG measure from any SUSY Les Houches Accord file. We implement a careful analysis and comparison of these measures in the mSUGRA/CMSSM and NUHMi model parameter spaces and via parameter-space scans. We demonstrate the reasoning behind why-and the extent to which-the EENZ/ BG and HS measures overestimate the degree of fine-tuning. We find the overestimation can range up to a factor of over 1000. While EENZ/BG and HS have ambiguities when applied to models such as anomalyand mirage-mediation, the EW measure has no such ambiguity and so we display the natural parameter space regions of these models. SN depends on the landscape distribution of soft terms, but is closely related to EW naturalness via the atomic principle.
Supersymmetric models with low electroweak fine-tuning contain light higgsinos with mass not too ... more Supersymmetric models with low electroweak fine-tuning contain light higgsinos with mass not too far from m_h\simeq 125 GeV, while other sparticles can be much heavier. In the R-parity conserving MSSM, the lightest neutralino is then a higgsino-like WIMP (albeit with non-negligible gaugino components), with thermal relic density well below measured values. This leaves room for axions (or other, perhaps not as well motivated, stable particles) to function as co-dark matter particles. The local WIMP abundance is then expected to be below standard estimates, and direct and indirect detection rates must be accordingly rescaled. We calculate rescaled direct and indirect higgsino-like WIMP detection rates in SUSY models that fulfil the electroweak naturalness condition. In spite of the rescaling, we find that ton-scale noble liquid detectors can probe the entire higgsino-like WIMP parameter space, so that these experiments should either discover WIMPs or exclude the concept of electroweak...
If the squark mass mq is 0(40) GeV, as suggested by one interpretation of the CERN pp collider da... more If the squark mass mq is 0(40) GeV, as suggested by one interpretation of the CERN pp collider data, then one expects slepton masses m?-0(20-30) GeV in a wide class of models. Sleptons with such masses would be produced copiously in W ~ t~ and Z ° ~ ~Z-decays. We present rates and distributions for these processes, incorporating detector resolutions and experimental cuts. We show how the supersymmetric signals (especially for Z ° ~ ~-t r-) can easily be distinguished from the standard model backgrounds.
The requirement of electroweak naturalness in simple supersymmetric models implies the existence ... more The requirement of electroweak naturalness in simple supersymmetric models implies the existence of a cluster of four light Higgsinos with a mass ∼100-300 GeV, the lighter the better. While such light compressed spectra may be challenging to observe at the LHC, the International Linear e þ e -Collider (ILC) with ffiffi ffi s p > 2m Higgsino would serve as both a SUSY discovery machine and a precision microscope. We study Higgsino pair production signatures at the ILC based on a full, GEANT4-based simulation of the ILD detector concept. We examine several benchmark scenarios that may be challenging for discovery at the HL-LHC due to mass differences between the Higgsino states between 20 and 4 GeV. Assuming ffiffi ffi s p ¼ 500 GeV and 1000 fb -1 of integrated luminosity, the individual Higgsino masses can be measured to 1%-2% precision in the case of the larger mass differences, and at the level of 5% for the smallest mass difference case. The Higgsino mass splittings are sensitive to the electroweak gaugino masses and allow extraction of gaugino masses to ∼3%-20% (depending on the model). Extrapolation of gaugino masses via renormalization group running can test the hypothesis of gaugino mass unification. We also examine a case with natural generalized mirage mediation, where the unification of gaugino masses at an intermediate scale apparently gives rise to a natural SUSY spectrum somewhat beyond the reach of HL-LHC.
We give explicit formulas for the decays of the neutralinos and charginos of the minimal model of... more We give explicit formulas for the decays of the neutralinos and charginos of the minimal model of supersymmetry into other neutralinos and charginos plus a W, Z, or Higgs boson. The important features of these decays are illustrated and their phenomenological implications discussed. In general, this class of two-body decays is dominant for the heaviest charginos and neutralinos.
The work contained herein constitutes a report of the “Beyond the Standard Model” working group f... more The work contained herein constitutes a report of the “Beyond the Standard Model” working group for the Workshop “Physics at TeV Colliders”, Les Houches, France, 26 May–6 June, 2003. The research presented is original, and was performed specifically for the workshop. Tools for calculations in the minimal supersymmetric standard model are presented, including a comparison of the dark matter relic density predicted by public codes. Reconstruction of supersymmetric particle masses at the LHC and a future linear collider facility is examined. Less orthodox supersymmetric signals such as non-pointing photons and Rparity violating signals are studied. Features of extra dimensional models are examined next, includingmeasurement strategies for radions and Higgs’, as well as the virtual effects of Kaluza Klein modes of gluons. An LHC search strategy for a heavy top found in many little Higgs model is presented and finally, there is an update on LHC Z? studies
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Oct 6, 2022
We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for ... more We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for Snowmass 2021, focusing mainly on several whitepaper contributions to BSM model building (TF08) and closely related areas.
The International Linear Collider (ILC) is on the table now as a new global energyfrontier accele... more The International Linear Collider (ILC) is on the table now as a new global energyfrontier accelerator laboratory taking data in the 2030's. The ILC addresses key questions for our current understanding of particle physics. It is based on a proven accelerator technology. Its experiments will challenge the Standard Model of particle physics and will provide a new window to look beyond it. This document brings the story of the ILC up to date, emphasizing its strong physics motivation, its readiness for construction, and the opportunity it presents to the US and the global particle physics community.
program containing both leading-logarithm and next-to-leading-logarithm contributions has been de... more program containing both leading-logarithm and next-to-leading-logarithm contributions has been developed and used to study the photoproduction of large-transverse-momentum hadronic jets. Predictions are presented and discussed for a variety of observables including singlejet invariant cross sections, dijet cross sections, and angular distributions. For some observables the inclusion of the next-to-leading-logarithm terms dramatically lessens the dependency on the choice of the renormalization and factorization scales entering the calculation, thereby increasing the precision of the calculation. The flexibility of the Monte Carlo technique allows predictions for additional observables to be generated easily.
The top group studied discovery issues as well as measurements to be made at the Tevatron, the LH... more The top group studied discovery issues as well as measurements to be made at the Tevatron, the LHC and the SSC.
We present the activities of the "New Physics" working group for the "Physics at TeV Colliders" w... more We present the activities of the "New Physics" working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 30 May-17 June, 2011). Our report includes new agreements on formats for interfaces between computational tools, new tool developments, important signatures for searches at the LHC, recommendations for presentation of LHC search results, as well as additional phenomenological studies.
We take a critical view of the treatment of threshold effects in SUSY spectrum computations from ... more We take a critical view of the treatment of threshold effects in SUSY spectrum computations from high-scale input. We discuss the two principal methods of (a) renormalization at a common SUSY scale versus (b) integrating out sparticles at their own mass scales. We point out problems in the implementations in public spectrum codes, together with suggestions for improvements. In concrete examples, we compare results of Isajet 7.72 and SPheno 2.2.3, and present the improvements done in Isajet 7.73. We also comment on theoretical uncertainties. Last but not least, we outline how a consistent multiscale approach may be achieved.
The supersymmetrized DFSZ axion model is especially compelling in that it contains 1. the SUSY so... more The supersymmetrized DFSZ axion model is especially compelling in that it contains 1. the SUSY solution to the gauge hierarchy problem, 2. the Peccei-Quinn (PQ) solution to the strong CP problem and 3. the Kim-Nilles solution to the SUSY μ problem. In a string setting, where a discrete R-symmetry ($$ {\textbf{Z}}_{24}^R $$ Z 24 R for example) may emerge from the compactification process, a high-quality accidental axion (accion) can emerge from the accidental, approximate remnant global U(1)PQ symmetry where the decay constant fa is linked to the SUSY breaking scale, and is within the cosmological sweet zone. In this setup, one also expects the presence of stringy remnant moduli fields ϕi. Here, we consider the situation of a single light modulus ϕ coupled to the PQMSSM in the early universe, with mixed axion plus higgsino-like WIMP dark matter. We evaluate dark matter and dark radiation production via nine coupled Boltzmann equations and assess the severity of the cosmological modul...
We continue our examination of prospects for the discovery of heavy Higgs bosons of natural SUSY ... more We continue our examination of prospects for the discovery of heavy Higgs bosons of natural SUSY (natSUSY) models at the high luminosity LHC (HL-LHC), this time focusing on charged Higgs bosons. In natSUSY, higgsinos are expected at the few hundred GeV scale whilst electroweak gauginos inhabit the TeV scale and the heavy Higgs bosons, H, A and H± could range up tens of TeV without jeopardizing naturalness. For TeV-scale heavy SUSY Higgs bosons H, A and H±, as currently required by LHC searches, SUSY decays into gaugino plus higgsino can dominate H± decays provided these decays are kinematically accessible. The visible decay products of higgsinos are soft making them largely invisible, whilst the gauginos decay to W, Z or h plus missing transverse energy (ET). Charged Higgs bosons are dominantly produced at LHC14 via the parton subprocess, gb→H±t. In this paper, we examine the viability of observing signatures from H±→τν, H±→tb and H±→W,Z,h+ET events produced in association with a to...
Naturalness arguments imply the existence of higgsinos lighter than 200-300 GeV. However, because... more Naturalness arguments imply the existence of higgsinos lighter than 200-300 GeV. However, because these higgsinos are nearly mass degenerate, they release very little visible energy in their decays, and (even putting aside triggering issues) signals from electroweak higgsino pair production typically remain buried under Standard Model backgrounds. Prospects for detecting higgsino pair production via events with monojets or monophotons from initial state radiation are also bleak because of signal-to-background rates typically at the 1% level. Here, we consider the possibility of reducing backgrounds by requiring the presence of soft daughter leptons from higgsino decays in monojet events. We find that LHC14 experiments with an integrated luminosity of 300 fb −1 should be sensitive to light higgsinos at the 5σ level for µ < 170 GeV with a S/B ∼ 8.5%. For an integrated luminosity of 1000 fb −1 (which should be possible at a high luminosity LHC) the corresponding sensitivity to µ extends to over 200 GeV though the systematic uncertainty would have to be controlled to considerably better than 5%. The corresponding reach from measurements of the rate asymmetry between monojet events with same flavour vs. opposite flavour dileptons is ∼10-15 GeV smaller, but does not suffer the systematic uncertainty from the normalization of the background.
We revisit the various measures of practical naturalness for models of weak-scale supersymmetry (... more We revisit the various measures of practical naturalness for models of weak-scale supersymmetry (SUSY) including: 1. electroweak (EW) naturalness; 2. naturalness via sensitivity to high-scale (HS) parameters [Ellis-Enquist-Nanopoulos-Zwirner/Barbieri-Giudice (EENZ/BG)]; 3. sensitivity of Higgs soft terms due to high-scale radiative corrections; and 4. stringy naturalness (SN) from the landscape. The EW measure is most conservative and seems unavoidable. We debut a new numerical routine for calculating the EENZ/BG measure from any SUSY Les Houches Accord file. We implement a careful analysis and comparison of these measures in the mSUGRA/CMSSM and NUHMi model parameter spaces and via parameter-space scans. We demonstrate the reasoning behind why-and the extent to which-the EENZ/ BG and HS measures overestimate the degree of fine-tuning. We find the overestimation can range up to a factor of over 1000. While EENZ/BG and HS have ambiguities when applied to models such as anomalyand mirage-mediation, the EW measure has no such ambiguity and so we display the natural parameter space regions of these models. SN depends on the landscape distribution of soft terms, but is closely related to EW naturalness via the atomic principle.
Supersymmetric models with low electroweak fine-tuning contain light higgsinos with mass not too ... more Supersymmetric models with low electroweak fine-tuning contain light higgsinos with mass not too far from m_h\simeq 125 GeV, while other sparticles can be much heavier. In the R-parity conserving MSSM, the lightest neutralino is then a higgsino-like WIMP (albeit with non-negligible gaugino components), with thermal relic density well below measured values. This leaves room for axions (or other, perhaps not as well motivated, stable particles) to function as co-dark matter particles. The local WIMP abundance is then expected to be below standard estimates, and direct and indirect detection rates must be accordingly rescaled. We calculate rescaled direct and indirect higgsino-like WIMP detection rates in SUSY models that fulfil the electroweak naturalness condition. In spite of the rescaling, we find that ton-scale noble liquid detectors can probe the entire higgsino-like WIMP parameter space, so that these experiments should either discover WIMPs or exclude the concept of electroweak...
If the squark mass mq is 0(40) GeV, as suggested by one interpretation of the CERN pp collider da... more If the squark mass mq is 0(40) GeV, as suggested by one interpretation of the CERN pp collider data, then one expects slepton masses m?-0(20-30) GeV in a wide class of models. Sleptons with such masses would be produced copiously in W ~ t~ and Z ° ~ ~Z-decays. We present rates and distributions for these processes, incorporating detector resolutions and experimental cuts. We show how the supersymmetric signals (especially for Z ° ~ ~-t r-) can easily be distinguished from the standard model backgrounds.
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Papers by Howard Baer