Energy Loss Fluctuations Research Articles

Renormalization of radiobiological response functions by energy loss fluctuations and complexities in chromosome aberration induction: deactivation theory for proton therapy from cells to tumor control.

We employ a multi-scale mechanistic approach built upon our recent phenomenological/computational methodologies [R. Abolfath et al., Sci. Rep. 7, 8340 (2017)] to investigate radiation induced cell toxicities and deactivation mechanisms as a function of linear energy transfer in hadron therapy. Our theoretical model consists of a system of Markov chains in microscopic and macroscopic spatio-temporal landscapes, i.e., stochastic birth-death processes of cells in millimeter-scale colonies that incorporates a coarse-grained driving force to account for microscopic radiation induced damage. The coupling, hence the driving force in this process, stems from a nano-meter scale radiation induced DNA damage that incorporates the enzymatic end-joining repair and mis-repair mechanisms. We use this model for global fitting of the high-throughput and high accuracy clonogenic cell-survival data acquired under exposure of the therapeutic scanned proton beams, the experimental design that considers γ-H2AX as the biological endpoint and exhibits maximum observed achievable dose and LET, beyond which the majority of the cells undergo collective biological deactivation processes. An estimate to optimal dose and LET calculated from tumor control probability by extension to ~106 cells per mm-size voxels is presented. We attribute the increase in degree of complexity in chromosome aberration to variabilities in the observed biological responses as the beam linear energy transfer (LET) increases, and verify consistency of the predicted cell death probability with the in vitro cell survival assay of approximately 100 non-small cell lung cancer (NSCLC) cells. The present model provides an interesting interpretation to variabilities in α and β indices via perturbative expansion of the cell survival fraction (SF) in terms of specific and lineal energies, z and y, corresponding to continuous transitions in pair-wise to ternary, quaternary and more complex recombination of broken chromosomes from the entrance to the end of the range of proton beam.

Estimating the effect of electron beam interactions with biological tissues

The stopping power and range for electrons in matter are the most important parameters in predicting the consequences of the electrons interacting with matter. In this work, we used our previously developed method to calculate these parameters. In our calculation method, the main parameter is the velocity-dependent electronic charge density of the target, which we obtained by using Roothaan–Hartree–Fock (RHF) wave functions. For range calculations, we used the continuous slowdown approach (CSDA), which neglects the energy-loss fluctuations so the incident particle loses its energy in a medium continuously at a rate equal to the total stopping power. The stopping power and CSDA range values have been calculated for electrons incident on brain, breast, and eye tissues. Obtained results have been compared with the available data.

The impact of incorporating shell-corrections to energy loss in silicon

Modern silicon tracking detectors based on hybrid or fully integrated CMOS technology are continuing to push to thinner sensors. The ionization energy loss fluctuations in very thin silicon sensors significantly deviates from the Landau distribution. Therefore, we have developed a charge deposition setup that implements the Bichsel straggling function, which accounts for shell-effects. This enhanced simulation is important for comparing with testbeam or collision data with thin sensors as demonstrated by reproducing more realistically the degraded position resolution compared with naïve ionization models based on simple Landau-like fluctuation. Our implementation of the Bichsel model agrees well with the multipurpose photo absorption ionization (PAI) model in Geant4 and is significantly faster. The code is made publicly available as part of the Allpix software package in order to facilitate predictions for new detector designs and comparisons with testbeam data.

Studying the characteristics of scintillation counters in a beam of relativistic particles

In this work, the results of the measurements of characteristics of 40-cm and 2-m scintillation counters irradiated by a particle beam with a momentum of 7 GeV/c from the accelerator of the Institute for High Energy Physics are presented. The scintillators used in counters are BC-404 and BC-408 scintillators. The counters are viewed from both ends by R1828-01 photomultiplier tubes. The PMT signal spectra are well described by a convolution of the Landau and Gaussian distributions. Their width is determined mainly by fluctuations of ionization energy losses. The time distributions of the signals obey the Gaussian law. For the 40-cm counter, the time resolution is σ(T) = 88 ps; for the 2-m counter, it varies from 120–160 ps in its center to ~100 ps near the end.

Origins of the di-jet asymmetry in heavy-ion collisions

The di-jet asymmetry—the measure of the momentum imbalance in a di-jet system—is a key jet quenching observable. Using the event generator Jewel we show that the di-jet asymmetry is dominated by fluctuations both in proton–proton and in heavy-ion collisions. We discuss how in proton–proton collisions the asymmetry is generated through recoil and out-of-cone radiation. In heavy-ion collisions two additional sources can contribute to the asymmetry, namely energy loss fluctuations and differences in path length. The latter is shown to be a sub-leading effect. We discuss the implications of our results for the interpretation of this observable.

Fluctuations in Strong-Coupling Heavy Quark Energy Loss

We present recent and new results for observables related to heavy quarks from a strong-coupling energy loss model that includes fluctuations in the energy loss. We find that the inclusion of these next-to-leading order fluctuations yields results consistent with all measured data. Correlation measurements and bottom decays to electrons are potential future measurements that can distinguish between weak- and strong-coupling energy loss models.

Progress in Geant4 Electromagnetic Physics Modelling and Validation

In this work we report on recent improvements in the electromagnetic (EM) physics models of Geant4 and new validations of EM physics. Improvements have been made in models of the photoelectric effect, Compton scattering, gamma conversion to electron and muon pairs, fluctuations of energy loss, multiple scattering, synchrotron radiation, and high energy positron annihilation. The results of these developments are included in the new Geant4 version 10.1 and in patches to previous versions 9.6 and 10.0 that are planned to be used for production for run-2 at LHC. The Geant4 validation suite for EM physics has been extended and new validation results are shown in this work. In particular, the effect of gamma-nuclear interactions on EM shower shape at LHC energies is discussed.

Simulation of ion beam scattering in a gas stripper

Ion beam scattering in the gas stripper of an accelerator mass spectrometer (AMS) enlarges the beam phase space and broadens its energy distribution. As the size of the injected beam depends on the acceleration voltage through phase space compression, the stripper becomes a limiting factor of the overall system transmission especially for low energy AMS system in the sub MV region. The spatial beam broadening and collisions with the accelerator tube walls are a possible source for machine background and energy loss fluctuations influence the mass resolution and thus isotope separation. To investigate the physical processes responsible for these effects, a computer simulation approach was chosen. Monte Carlo simulation methods are applied to simulate elastic two body scattering processes in screened Coulomb potentials in a (gas) stripper and formulas are derived to correctly determine random collision parameters and free path lengths for arbitrary (and non-homogeneous) gas densities. A simple parametric form for the underlying scattering cross sections is discussed which features important scaling behaviors. An implementation of the simulation was able to correctly model the data gained with the TANDY AMS system at ETH Zurich. The experiment covered transmission measurements of uranium ions in helium and beam profile measurements after the ion beam passed through the He-stripper. Beam profiles measured up to very high stripper densities could be understood in full system simulations including the relevant ion optics. The presented model therefore simulates the fundamental physics of the interaction between an ion beam and a gas stripper reliably. It provides a powerful and flexible tool for optimizing existing AMS stripper geometries and for designing new, state of the art low energy AMS systems.

Fluctuating heavy quark energy loss in a strongly coupled quark-gluon plasma

Results from an energy loss model that includes thermal fluctuations in the energy loss for heavy quarks in a strongly-coupled plasma are shown to be qualitatively consistent with single particle data from both RHIC and LHC. The model used is the first to properly include the fluctuations in heavy quark energy loss as derived in string theory and that do not obey the usual fluctuation-dissipation relations. These fluctuations are crucial for simultaneously describing both RHIC and LHC data; leading order drag results without fluctuations are falsified by current data. Including the fluctuations is non-trivial and relies on the Wong-Zakai theorem to fix the numerical Langevin implementation. The fluctuations lead to surprising results: B meson anisotropy is similar to that for D mesons at LHC, and the double ratio of D to B meson nuclear modification factors approaches unity more rapidly than even predictions from perturbative energy loss models. It is clear that future work in improving heavy quark energy loss calculations in AdS/CFT to include all energy loss channels is needed and warranted.

Azimuthal jet tomography at RHIC and LHC

Results based on a generic jet-energy loss model that interpolates between running coupling pQCD-based and AdS/CFT-inspired holographic prescriptions are compared to recent data on the high-p_T pion nuclear modification factor and the high-p_T elliptic flow in nuclear collisions at RHIC and LHC. The jet-energy loss model is coupled to various (2+1)d (viscous hydrodynamic) fields. The impact of energy-loss fluctuations is discussed. While a previously proposed AdS/CFT jet-energy loss model with a temperature-independent jet-medium coupling is shown to be inconsistent with the LHC data, we find a rather broad class of jet-energy independent energy-loss models $dE/dx= \kappa(T) x^z T^{2+z}$ that can account for the current data with different temperature-dependent jet-medium couplings $\kappa(T)$ and path-length dependence exponents of $0\le z \le 2$.

Fluctuations of energy losses of charged particles colliding with an oscillator

Fluctuations of energy losses of fast charged particles colliding with an oscillator have been considered in the dipole approximation. In this approximation, the problem has been solved exactly, and fluctuations of energy losses of the oscillator from the initial state |m〉 = |0〉 have been found in the form of the sum of single integrals. It has been shown that the Bohr formulas for fluctuations can be obtained in the passage to the classical limit, whereas analogs of the Fano formula in perturbation theory and the Titeica formula in the nonperturbative case can be obtained when the velocities of an ion are much higher than atomic velocities.

Erratum: Constraints on the path-length dependence of jet quenching in nuclear collisions at RHIC and LHC

Recent data on the high-p T pion nuclear modification factor, R AA (p T ), and its elliptic azimuthal asymmetry, v 2(p T ), from RHIC/BNL and LHC/CERN are analyzed in terms of a wide class of jet-energy loss models coupled to different (2+1)d transverse plus Bjorken expanding hydrodynamic fields. We test the consistency of each model by demanding a simultaneous account of the azimuthal, the transverse momentum, and the centrality dependence of the data at both 0.2 and 2.76 ATeV energies. We find a rather broad class of jet-energy independent energy-loss models dE/dx = κ(T)x z T 2+z ζ q that, when coupled to bulk constrained temperature fields T(x, t), can account for the current data at the χ 2 /d.o.f. < 2 level with different temperature-dependent jet-medium couplings, κ(T), and path-length dependence exponents 0 ≤ z ≤ 2. We extend previous studies by including a generic term, 0 < ζ q < 2 + q, to test different scenarios of energy-loss fluctuations. While a previously proposed AdS/CFT jet-energy loss model with a temperature-independent jet-medium coupling as well as a near-T c dominated, pQCD-inspired energy-loss scenario are shown to be inconsistent with the LHC data, once the parameters are constrained by fitting to RHIC results, we find several new solutions with a temperature-dependent κ(T). We conclude that the current level of statistical and systematic uncertainties of the measured data does not allow a constraint on the path-length exponent z to a range narrower than [0 − 2].

Azimuthal jet tomography at RHIC and LHC

Abstract Results based on a generic jet-energy loss model that interpolates between running coupling pQCD-based and AdS/CFT-inspired holographic prescriptions are compared to recent data on the high- p T pion nuclear modification factor and the high- p T elliptic flow in nuclear collisions at RHIC and LHC. The jet-energy loss model is coupled to various ( 2 + 1 ) d (viscous hydrodynamic) fields. The impact of energy-loss fluctuations is discussed. While a previously proposed AdS/CFT jet-energy loss model with a temperature-independent jet-medium coupling is shown to be inconsistent with the LHC data, we find a rather broad class of jet-energy independent energy-loss models d E / d x = κ ( T ) x z T 2 + z that can account for the current data with different temperature-dependent jet-medium couplings κ ( T ) and path-length dependence exponents of 0 ≤ z ≤ 2 .

Constraints on the path-length dependence of jet quenching in nuclear collisions at RHIC and LHC

Recent data on the high-p T pion nuclear modification factor, R AA (p T ), and its elliptic azimuthal asymmetry, v 2(p T ), from RHIC/BNL and LHC/CERN are analyzed in terms of a wide class of jet-energy loss models coupled to different (2+1)d transverse plus Bjorken expanding hydrodynamic fields. We test the consistency of each model by demanding a simultaneous account of the azimuthal, the transverse momentum, and the centrality dependence of the data at both 0.2 and 2.76 ATeV energies. We find a rather broad class of jet-energy independent energy-loss models dE/dx = κ(T)x z T 2+z ζ q that, when coupled to bulk constrained temperature fields T(x, t), can account for the current data at the χ 2 /d.o.f. < 2 level with different temperature-dependent jet-medium couplings, κ(T), and path-length dependence exponents 0 ≤ z ≤ 2. We extend previous studies by including a generic term, 0 < ζ q < 2 + q, to test different scenarios of energy-loss fluctuations. While a previously proposed AdS/CFT jet-energy loss model with a temperature-independent jet-medium coupling as well as a near-T c dominated, pQCD-inspired energy-loss scenario are shown to be inconsistent with the LHC data, once the parameters are constrained by fitting to RHIC results, we find several new solutions with a temperature-dependent κ(T). We conclude that the current level of statistical and systematic uncertainties of the measured data does not allow a constraint on the path-length exponent z to a range narrower than [0 − 2].

Realistic medium-averaging in radiative energy loss

Abstract We present results from a jet energy loss calculation using the Gyulassy-Levai-Vitev (GLV) formalism and bulk medium evolution from the covariant transport MPC. At both RHIC and LHC energies we find that realistic transverse expansion strongly reduces elliptic flow at high p T compared to calculations with transversely “frozen” profiles. We argue that this is a generic feature of GLV energy loss. Transverse expansion also leads to stronger high- p T suppression, while fluctuations in energy loss with the location of scattering centers weaken the suppression. But, unlike the reduction of v 2 , these effects nearly disappear once α s is adjusted to reproduce R A A in central collisions.

고온가스 및 액체 바이패스 적용 용량가변 히트펌프의 성능특성에 관한 실험적 연구

A small air-conditioner or chiller for a constant temperature bath normally uses a constant speed compressor. The constant speed compressor is relatively inexpensive, but it uses on/off control for capacity modulation. The on/off control has several disadvantages, specifically energy loss and large temperature fluctuation. Continuous operation with a bypass system can be an alternative to on/off control, for capacity modulation. In this study, a heat pump system having a hot-gas bypass and a liquid bypass was adopted. The performance of the bypass-type heat pump was measured, by varying the bypass valve opening. The differences of the COP between the hot-gas bypass and the liquid bypass, in the cooling and heating operations, were within 2% and 1%, respectively. The liquid bypass showed a wider range of capacity control in the cooling operation but the hot-gas bypass showed a wider range of capacity control in the heating operation.

Holographic lessons for quark dynamics

We give a brief overview of recent results obtained through the gauge/gravity correspondence, concerning the propagation of a heavy quark in strongly coupled conformal field theories (such as super-Yang–Mills), both at zero and finite temperature. In the vacuum, we discuss energy loss, radiation damping, signal propagation and radiation-induced fluctuations. In the presence of a thermal plasma, our emphasis is on early-time energy loss, screening and quark–antiquark evolution after pair creation. Throughout, quark dynamics is seen to be efficiently encapsulated in the usual string worldsheet dynamics.

Calculation of integral characteristics of electron radiation in substance

A method is proposed for calculating energy release and other characteristics of a fast electron beam in a substance, based on a numerical solution to the conjunctive equation. This method allows one to take into account both the fluctuations of energy losses and the formation of secondary electrons. The proposed method was compared to calculations using the Monte Carlo method and, in the case of propagation of a sheet beam in a uniform absorber, to the experimental data.

Statistical fluctuations in energy loss for swift heavy ions in thick polymeric foils

The statistical fluctuations in energy loss have been measured for O, Si, and S ions, in varying thicknesses of polyethylene naphthalate [PEN, or $({\text{C}}_{7}{\text{H}}_{5}{\text{O}}_{2})$] polymeric foils. The measurements have been performed in the fractional energy-loss limits $\ensuremath{\Delta}E/E\ensuremath{\sim}5--90\text{ }%$. These fluctuations have been found to be enhanced with an increase in $\ensuremath{\Delta}E/E$. Such a behavior has been reproduced by Bethe-Livingston formulation after modifying it suitably.

SU‐GG‐T‐338: Recent Improvements in the Geant4 Monte Carlo Simulation Toolkit for Medical Physics Applications

Purpose: Rapid growth of the medical user base for the Geant4 Monte Carlo Simulation Toolkit over the past few years has led to major improvements in the code addressing specific needs of the medical physics community. Problems in applying the toolkit to the energy domain of medical physics have been indicated by users (e.g. by the paper by Poon et al. [1]) and subsequently addressed by the code developers. Consequently, many recent papers show greatly improved results for simulations [2,3]. The purpose of this presentation is to update the medical physics community about key improvements in the Geant4 toolkit for radiotherapy physics applications. Method and Materials: A recent Technical Note published by the SLAC (Stanford Linear Accelerator) Geant4 team has provided the first and most useful summary of code improvements in the energy regions of interest to radiation therapy. We have analyzed this information and assessed the impact on simulations in electron and photon therapy. Further, we have expanded the information to issues affecting proton and ion therapy as well as imaging applications. Results: The original multiple scattering model in Geant4 was based on the Lewis formalism. Results from Poon et al. and others showed that the approach was insufficiently precise. In response to these findings, modifications were made to the model based on ideas from Penelope and EGSnrc including: limit the particle step size near geometry boundaries, use correlations between lateral displacement and scattering angle and add options to use single or plural scattering near boundaries (instead of multiple scattering). Single Scattering processes were added which can be used to entirely replace multiple scattering if desired. Models for energy loss fluctuations were substantially revised. Conclusion: This presentation summarizes significant recent improvements in Geant4, which may lead to an even more widespread acceptance of this toolkit in radiation therapy.