News

Nuclear and Particle Physics Colloquium

FALL 2009

Every Monday
@4:15 pm
Room 26-414, Kolker Room

Refreshments @ 4:00pm

(Titles and abstracts will be added as each is received)

"Bringing our Galaxy's Supermassive Black Hole and its Environs into Focus with Laser Guide Star Adaptive Optics"

Collisions at the Relativistic Heavy Ion Collider are believed to produce a strongly coupled quark-gluon plasma which behaves as a nearly ideal liquid. Understanding the dynamics responsible for plasma production and the rapid relaxation to local equilibrium is a challenging task. Therefore, it is useful to have a toy model where one can study similar problems in a controlled setting. One such class of toy models is provided by gauge/gravity duality, which maps the dynamics of many interesting strongly coupled quantum field theories onto classical gravitational dynamics in a higher dimensional spacetime. In particular, the relaxation of a plasma towards a hydrodynamic description is mapped onto the relaxation of a black hole geometry towards a quasi-static configuration. Therefore, by studying the creation of a black hole and its subsequent relaxation, one can learn about the creation of a strongly coupled plasma and its relaxation to local equilibrium. I will describe several processes which can create plasmas and dual black holes and present recent numerical work for systems with a high degree of spacetime symmetry.

Abstract:
Now that the launch date is set, a short history of the AMS project is given with past and present challenges for NASA and the MIT based AMS collaboration formed by Prof. S.C.C.Ting. Scientific surprises from the engineering flight in 1998 are described, as well as expectations for the AMS-02 data to come. AMS-02 is a large aperture magnetic spectrometer in space detecting all charged particles to TeV energies, including isotopes up to Fe. The conditions in space, the technology and function of super-conducting magnet,and detection components are presented. Assembly of the experiment at Geneva may be viewed online outside the LNS headquarters.

For Paul Dirac, the idea that mathematical beauty is the lodestar for
theoretical physicists was 'almost a religion'. He first described 'the
principle of mathematical beauty' in his 1939 Scott Lecture, which marked the beginning of his role as a philosopher-scientist. In this talk, I shall look at the origin of Dirac's aesthetic beliefs - in his school and college education - and in his own work, during his great creative streak from 1925-1933. Finally, I look at how his views led him to lose faith in quantum electrodynamics, a theory he co-invented, and also at how his views are partly responsible for his reputation as 'the first modern theorist'.

The Large Area Telescope (LAT), one of two instruments on the Fermi
Gamma-Ray Space Telescope (formerly GLAST, launched June 11, 2008) is a pair conversion detector designed to study the gamma-ray sky in the energy range 20 MeV to >300 GeV. The greatly improved sensitivity of the LAT compared with its predecessor experiment, EGRET on the Compton Gamma-Ray Observatory, coupled with the uniform and deep sky coverage, and lack of consumables, provides a unique capability for studying the gamma-ray Universe. A menagerie of gamma-ray sources exists: within our own Galaxy pulsars, X-ray binaries, supernova remnants, and molecular clouds are a few examples. The propagation of cosmic rays in the Galaxy produces diffuse gamma-ray emission through interactions with the interstellar gas and radiation fields, and is the bright background against which the sources are detected. Diffuse gamma-ray emission is also expected from similar processes in the solar system and nearby galaxies, such as the Large Magellanic Cloud (which was detected by EGRET). The extragalactic gamma-ray sky is dominated by emission from blazar active galactic nuclei which are highly variable, and gamma-ray bursts, and perhaps exotic processes that may contribute the to extragalactic gamma-ray background. The LAT has detected many gamma-ray sources and the diffuse emissions of the Milky Way with unprecedented sensitivity and resolution. I will give an overview of the instrument and status, and results obtained on some of these topics for the first year of the Fermi/LAT mission.

The initial conditions in high energy nucleus-nucleus collisions are determined by the small momentum fraction part of the nuclear wavefunction. This is the regime of gluon saturation caused by nonlinear interactions in QCD at high energies. The most direct way to experimentally study QCD at the high energy limit would be deep inelastic scattering at a future high energy electron ion collider (EIC). We have learned much about QCD at high energy from measurements of relativistic heavy ion collisions at RHIC and soon will at the LHC, but the EIC would be necessary to interpret these results better. This talk describes some of the connections between these experimental programs.

I discuss calculable particle physics models with low-energy supersymmetry where the flavor hierarchy is generated by quark and lepton compositeness, and where the composites emerge from the same sector that dynamically breaks supersymmetry. These models give rise to a spectrum of soft supersymmetry breaking masses which is quite different from what is commonly found in models of gauge or gravity mediation of supersymmetry breaking.

The G0 experiment measures the parity-violating electron scattering from hydrogen and deuterium targets. By combining forward and backward angle measurements, the strange quark contributions to the elastic charge and magnetic nucleon form factors can be determined; in addition we determine the effective axial vector nucleon form factor. Status reports on N-Delta transition, photo-pion production and transverse beam polarization asymmetries will also be presented.

Although primarily motivated as an experiment to study the longitudinal spin structure of the nucleon, the HERMES experiment has yielded results touching a much broader range of physics. In particular, first measurements of significantly non-zero azimuthal spin asymmetries immediately led to renewed interest in the role of the transverse momenta of partons in deep inelastic scattering distributions. After reviewing the phenomenology of these distributions, the latest results from the HERMES experiment will be presented.

"Factorization of Gauge Theory Amplitudes and Radiative Corrections at LHC energies"

Gauge theory amplitudes at high energies factor into universal collinear and soft functions. This allows one to compute radiative corrections to all hard scattering amplitudes in the standard model to next-to-leading-log order, including QCD and electroweak radiative corrections, mass effects, and Higgs exchange corrections. The radiative corrections can be very large --- for example the purely electroweak corrections to WW production are about
40% at 2 TeV.

Nearly all issues related to risks to future generations arising from long-term disposal of such spent nuclear fuel is primarily attributable to the transuranic elements and long-lived fission products, approximately 2% of its content. The transuranic elements of concern are plutonium, neptunium, americium, and curium, which are produced by neutron captures in uranium fuel. Long-lived (>100,000-year half-life) isotopes of iodine and technetium are also created by nuclear fission of uranium. If we can reduce or otherwise securely handle this 2% of the spent fuel, the toxic nature of the remaining spent fuel after a few centuries of cooling is below that of the natural uranium ore that was originally mined for nuclear fuel. One long term solution is to use fast-spectrum reactors to close the fuel cycle. The multiple passes allow extraction of most of the available energy in the fuel, the "problem wastes" are burnt in a fast-neutron spectrum, and the very small amount of remaining long-lived waste could then be safely stored in a small geologic repository. The problem for the next 100 years is the implementation plan for licensing and industry constructing a sufficient number of fast reactors to burn their own waste and the LWR waste from existing and new reactors. Until the long term solution can be implemented, we propose an interim solution called Subcritical Minor Actinide Reduction through Transmutation (SMART). Our proposed interim solution is to dispose spent fuel using a combination of approaches depending on the lifetime of the radioactive isotope. Long-lived fissile isotopes like Pu239 and U235 can be stored with U238 and Np237 for fabrication into nuclear fuel at a future date. The short-lived fission products can be stored in man-made containers until they safely decay to low radiotoxicity levels. The long-lived fission products can either be vitrified and buried or transmuted. That leaves addressing the intermediate-lived isotopes, mainly americium. The Am can be transmuted using an accelerator. Since it is envisioned that the government would be responsible for constructing the accelerator burners, the number of accelerator systems must be kept to an absolute minimum. This approach results in a design having only an Am feedstock to the transmuter.



		Nuclear and Particle Physics Colloquium FALL 2009 Every Monday @4:15 pm Room 26-414, Kolker Room Refreshments @ 4:00pm (Titles and abstracts will be added as each is received) *September 14 No talk, because of talk on Tuesday (see below) TUESDAY, September 15 The 2009 Bruno Rossi Lecture in Astrophysics "Bringing our Galaxy's Supermassive Black Hole and its Environs into Focus with Laser Guide Star Adaptive Optics" Andrea Ghez, University of California, Los Angeles Title and abstract at: http://web.mit.edu/astrophysics/colloq.html 4pm (refreshments at 3:45pm) The Pappalardo Room, 4-349 September 21 Paul Chesler, MIT "Creating strongly coupled liquids and dual black holes" Collisions at the Relativistic Heavy Ion Collider are believed to produce a strongly coupled quark-gluon plasma which behaves as a nearly ideal liquid. Understanding the dynamics responsible for plasma production and the rapid relaxation to local equilibrium is a challenging task. Therefore, it is useful to have a toy model where one can study similar problems in a controlled setting. One such class of toy models is provided by gauge/gravity duality, which maps the dynamics of many interesting strongly coupled quantum field theories onto classical gravitational dynamics in a higher dimensional spacetime. In particular, the relaxation of a plasma towards a hydrodynamic description is mapped onto the relaxation of a black hole geometry towards a quasi-static configuration. Therefore, by studying the creation of a black hole and its subsequent relaxation, one can learn about the creation of a strongly coupled plasma and its relaxation to local equilibrium. I will describe several processes which can create plasmas and dual black holes and present recent numerical work for systems with a high degree of spacetime symmetry. September 28 Ulrich Becker, MIT "The Alpha Magnetic Spectrometer Launch 7/29/2010 for > 3 years" Abstract: Now that the launch date is set, a short history of the AMS project is given with past and present challenges for NASA and the MIT based AMS collaboration formed by Prof. S.C.C.Ting. Scientific surprises from the engineering flight in 1998 are described, as well as expectations for the AMS-02 data to come. AMS-02 is a large aperture magnetic spectrometer in space detecting all charged particles to TeV energies, including isotopes up to Fe. The conditions in space, the technology and function of super-conducting magnet,and detection components are presented. Assembly of the experiment at Geneva may be viewed online outside the LNS headquarters. October 5 Graham Farmelo, IAS "Paul Dirac and the religion of mathematical beauty" For Paul Dirac, the idea that mathematical beauty is the lodestar for theoretical physicists was 'almost a religion'. He first described 'the principle of mathematical beauty' in his 1939 Scott Lecture, which marked the beginning of his role as a philosopher-scientist. In this talk, I shall look at the origin of Dirac's aesthetic beliefs - in his school and college education - and in his own work, during his great creative streak from 1925-1933. Finally, I look at how his views led him to lose faith in quantum electrodynamics, a theory he co-invented, and also at how his views are partly responsible for his reputation as 'the first modern theorist'. October 12 Columbus Day, no talk October 19 Troy Porter, UC Santa Cruz "Results from the first year of the Fermi/LAT mission" The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-Ray Space Telescope (formerly GLAST, launched June 11, 2008) is a pair conversion detector designed to study the gamma-ray sky in the energy range 20 MeV to >300 GeV. The greatly improved sensitivity of the LAT compared with its predecessor experiment, EGRET on the Compton Gamma-Ray Observatory, coupled with the uniform and deep sky coverage, and lack of consumables, provides a unique capability for studying the gamma-ray Universe. A menagerie of gamma-ray sources exists: within our own Galaxy pulsars, X-ray binaries, supernova remnants, and molecular clouds are a few examples. The propagation of cosmic rays in the Galaxy produces diffuse gamma-ray emission through interactions with the interstellar gas and radiation fields, and is the bright background against which the sources are detected. Diffuse gamma-ray emission is also expected from similar processes in the solar system and nearby galaxies, such as the Large Magellanic Cloud (which was detected by EGRET). The extragalactic gamma-ray sky is dominated by emission from blazar active galactic nuclei which are highly variable, and gamma-ray bursts, and perhaps exotic processes that may contribute the to extragalactic gamma-ray background. The LAT has detected many gamma-ray sources and the diffuse emissions of the Milky Way with unprecedented sensitivity and resolution. I will give an overview of the instrument and status, and results obtained on some of these topics for the first year of the Fermi/LAT mission. October 26 Tuomas Lappi, Saclay "Understanding saturation and AA collisions with an eA collider" The initial conditions in high energy nucleus-nucleus collisions are determined by the small momentum fraction part of the nuclear wavefunction. This is the regime of gluon saturation caused by nonlinear interactions in QCD at high energies. The most direct way to experimentally study QCD at the high energy limit would be deep inelastic scattering at a future high energy electron ion collider (EIC). We have learned much about QCD at high energy from measurements of relativistic heavy ion collisions at RHIC and soon will at the LHC, but the EIC would be necessary to interpret these results better. This talk describes some of the connections between these experimental programs. November 2 Shamit Kachru, UCSB "Dynamical Supersymmetry Breaking, with Taste" I discuss calculable particle physics models with low-energy supersymmetry where the flavor hierarchy is generated by quark and lepton compositeness, and where the composites emerge from the same sector that dynamically breaks supersymmetry. These models give rise to a spectrum of soft supersymmetry breaking masses which is quite different from what is commonly found in models of gauge or gravity mediation of supersymmetry breaking. November 9 Douglas Beck, University of Illinois "Results from the Backward Angle G0 Experiment" The G0 experiment measures the parity-violating electron scattering from hydrogen and deuterium targets. By combining forward and backward angle measurements, the strange quark contributions to the elastic charge and magnetic nucleon form factors can be determined; in addition we determine the effective axial vector nucleon form factor. Status reports on N-Delta transition, photo-pion production and transverse beam polarization asymmetries will also be presented. November 16 Edward R. Kinney, University of Colorado HERMES and the Renaissance of Transverse Momenta in Deep Inelastic Scattering Although primarily motivated as an experiment to study the longitudinal spin structure of the nucleon, the HERMES experiment has yielded results touching a much broader range of physics. In particular, first measurements of significantly non-zero azimuthal spin asymmetries immediately led to renewed interest in the role of the transverse momenta of partons in deep inelastic scattering distributions. After reviewing the phenomenology of these distributions, the latest results from the HERMES experiment will be presented. November 23 Sacha Kopp, University of Texas "Results from the MINOS Experiment at Fermilab" Abstract November 30 Aneesh Manohar, UC San Diego "Factorization of Gauge Theory Amplitudes and Radiative Corrections at LHC energies" Gauge theory amplitudes at high energies factor into universal collinear and soft functions. This allows one to compute radiative corrections to all hard scattering amplitudes in the standard model to next-to-leading-log order, including QCD and electroweak radiative corrections, mass effects, and Higgs exchange corrections. The radiative corrections can be very large --- for example the purely electroweak corrections to WW production are about 40% at 2 TeV. December 7 Richard Sheffield, Los Alamos SUBCRITICAL MINOR ACTINIDE REDUCTION THROUGH TRANSMUTATION Nearly all issues related to risks to future generations arising from long-term disposal of such spent nuclear fuel is primarily attributable to the transuranic elements and long-lived fission products, approximately 2% of its content. The transuranic elements of concern are plutonium, neptunium, americium, and curium, which are produced by neutron captures in uranium fuel. Long-lived (>100,000-year half-life) isotopes of iodine and technetium are also created by nuclear fission of uranium. If we can reduce or otherwise securely handle this 2% of the spent fuel, the toxic nature of the remaining spent fuel after a few centuries of cooling is below that of the natural uranium ore that was originally mined for nuclear fuel. One long term solution is to use fast-spectrum reactors to close the fuel cycle. The multiple passes allow extraction of most of the available energy in the fuel, the "problem wastes" are burnt in a fast-neutron spectrum, and the very small amount of remaining long-lived waste could then be safely stored in a small geologic repository. The problem for the next 100 years is the implementation plan for licensing and industry constructing a sufficient number of fast reactors to burn their own waste and the LWR waste from existing and new reactors. Until the long term solution can be implemented, we propose an interim solution called Subcritical Minor Actinide Reduction through Transmutation (SMART). Our proposed interim solution is to dispose spent fuel using a combination of approaches depending on the lifetime of the radioactive isotope. Long-lived fissile isotopes like Pu239 and U235 can be stored with U238 and Np237 for fabrication into nuclear fuel at a future date. The short-lived fission products can be stored in man-made containers until they safely decay to low radiotoxicity levels. The long-lived fission products can either be vitrified and buried or transmuted. That leaves addressing the intermediate-lived isotopes, mainly americium. The Am can be transmuted using an accelerator. Since it is envisioned that the government would be responsible for constructing the accelerator burners, the number of accelerator systems must be kept to an absolute minimum. This approach results in a design having only an Am feedstock to the transmuter. December 14 No Talk
updated 11/17/09