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Probing Extreme Electromagnetic Fields with the Breit-Wheeler Process

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Probing Extreme Electromagnetic Fields with the Breit-Wheeler Process Daniel Brandenburg, for the STAR Collaboration (Shandong University & BNL/CFNS) March 3, 2020 36th Winter Workshop on Nuclear Dynamics Puerto Vallarta, Mexico Outline of this Talk 1. Intro: What is the Breit-Wheeler Process? 2. Results from STAR Collaboration 3. Vacuum Birefringence in Extreme Magnetic Fields 4. The Magnetic Field in Heavy Ion Collisions 1. Measuring the “Initial” (� = 0) Magnetic Field 2. Evidence for Long-lived Magnetic Field or Medium Effects? 5. Conclusions 3/3/20 Daniel Brandenburg 2 Fundamental Interactions : Light & Matter � �⋆ �% Photo Electric Effect Bremsstrahlung Compton Scattering 1887 Hertz, Ann Phys 1895 Röntgen, Ann Phys 1906 Thomson, Conduction of (Leipzig) 31, 983 (Leipzig) 300, 1 Electricity through Gases Bethe-Heitler Pair Single Photon Dirac Annihilation Breit-Wheeler Production Annihilation 1934, Klemperer, pair production 1932, Anderson, 1933, Blackett & Proc Camb Phil Predicted 1934 Science 76,238 Occhialini, Proc R Soc 30, 347 Soc Lond A 139, 699 February 5, 2020 Daniel Brandenburg Based on slide by O. Pike 3 The Breit-Wheeler Process : �� → �)�% �- �/ o Breit-Wheeler process is by definition the lowest-order, tree level process o Two diagrams contribute at the lowest-order o t-channel process, specifically note: �+ = �-+ + �/+ February 5, 2020 Daniel Brandenburg 4 Ultra-Peripheral Heavy-Ion Collisions Ultra-relativistic charged nuclei produce highly Lorentz- contracted electromagnetic field Weizäcker-Williams Equivalent Photon Approximation (EPA): � ≈ � → In a specific phase space, transverse EM fields can be quantized as a flux of real photons Weizsacker̈ , C. F. v. Zeitschrift fur̈ Physik 88 (1934): 612 - / / � ∝ �⃗ = �×� ≈ � ≈ � � CD �� ≈ 1 → High photon density Ultra-strong electric and magnetic fields: � ≈ � → Expected magnetic field strength � ≈ ���� − ���� T Skokov, V., et. al. Int. J. Mod. Phys. A 24 (2009): 5925–32 � � Test QED under extreme conditions 3/3/20 Daniel Brandenburg 5 �� → �)�% Process in UPCs ´103 Zero Degree Calorimeter 60 Au+Au UPC Data 1 neutron 50 2 neutrons 40 3 neutrons 4 neutrons 30 Total Fit 20 dN/d(ADC Sum West ZDC) 10 0 200 400 600 800 1000 1200 ADC Sum West ZDC Breit-Wheeler �� → �)�% Mutual Coulomb excitation and pair production process nuclear dissociation • Provides efficient trigger condition →Provides high statistics sample (>6,000 �)�% pairs from data collected in 2010) → Allows for multidifferential analysis February 5, 2020 Daniel Brandenburg 6 Total �� → �)�% cross-section in the STAR Acceptance A Pure QED 2 → 2 scattering : )) 1 arXiv : 1910.12400 %M %M 2 STAR ��⁄�� ∝ � ≈ � Au+Au UPC gg® e+e- (QED) No vector meson production gg® e+e- (gEPA) → Forbidden for real photons with -1 10 gg® e+e- (STARLight) helicity ±1 (i.e. 0 is forbidden) Scale Uncertainty : ± 13% (mb/(GeV/c ) - e ) % + � �� → � � in the STAR Acceptance: -2 e 10 Data : 0.261±0.004 (stat.) ± 0.013 e ® P > 0.2 GeV/c & |he| < 1.0 dM (sys.) ± 0.034 (scale) mb g ee g |y | < 1.0 & P < 0.1 GeV/c STARLight gEPA QED ( s -3 0.22 mb 0.26 mb 0.29 mb d 10 0.5 1 1.5 2 2.5 M (GeV/c2) Measurement of total cross ee section agrees with theory STARLight: S. R. Klein, et. al. Comput. Phys. Commun. 212 (2017) 258 gEPA & QED : W. Zha, J.D.B., Z. Tang, Z. Xu arXiv:1812.02820 [nucl-th] calculations at ±�� level February 5, 2020 Daniel Brandenburg 7 Toy MC setup ØIn e+e- pair rest frame, the . is defined as the angle between positron momentum and the beam line • The . distribution for the --->e+e- has e+e- pair mass dependence �� �� → �)�%• The ⁄�cos���. distribution for the hadronic �S two-body decay is flat C 1 �� → �)�% : Individual �)/�% preferentially arXiv : 1910.12400 STAR 2 aligned along beam axis [1]: Mee = 2 GeV/c 0.4 Au+Au2 UPC 0.8 (mb) Mee = 1.2 GeV/c - gg2® e+e (XnXn)´0.88 ) / / - Mee = 0.4 GeV/c 4� 4� e 2 + - / / + Isotropic e e / 1 − / sin � cos � + / Mee = 0.01 GeV/c 4� � � ')| 0.3 e � � = 2 + 4 1 − 0.6 q / / / � ® 4� / → 1 − 1 − / cos � NOTE: for virtual photons � g g 0.2 isotropic (flat) distribution 0.4( d|cos( s o Highly virtual photon interactions should d have an isotropic distribution 0.1 0.2 2 0.4 < Mee < 0.76 GeV/c o Measure �S, the angle between the �) and the beam axis in the pair rest frame. 0 0 0 0.2 0.4 0.6 0.8 0 0.5 1 1.5 2 2.5 3 12/6/17 |cos(q')| 3 q for gg->e+e- process [1] S. Brodsky, T. Kinoshita and H. Terazawa, Phys. Rev. D4, 1532 (1971) STARLight: S. R. Klein, et. al. Comput. Phys. Commun. 212 (2017) 258 February 5, 2020 Daniel Brandenburg 8 �� �� → �)�% ⁄���� �S C �� → �)�% : Individual �)/�% preferentially arXiv : 1910.12400 STAR aligned along beam axis [1]: 0.4 Au+Au UPC (mb) gg® e+e- (XnXn)´0.88 ) / / - 4� 4� e + - / / + Isotropic e e / 1 − / sin � cos � + / 4� � � ')| 0.3 e � � = 2 + 4 1 − q / / / � ® 4� / 1 − 1 − / cos � � g g 0.2 ( d|cos( s o Highly virtual photon interactions should d 0.1 have an isotropic distribution 2 0.4 < Mee < 0.76 GeV/c o Measure �S, the angle between the �) and the 0 beam axis in the pair rest frame. 0 0.2 0.4 0.6 0.8 |cos(q')| ⇒Data are fully consistent with �(�) distribution expected for �� → �)�% [1] S. Brodsky, T. Kinoshita and H. Terazawa, Phys. Rev. D4, 1532 (1971) ⇒Measurably distinct from isotropic STARLight: S. R. Klein, et. al. Comput. Phys. Commun. 212 (2017) 258 distribution February 5, 2020 Daniel Brandenburg 9 ) % �� �� → � � ⁄��+ B arXiv : 1910.12400 o High precision data – test theory 5 STAR predictions Au+Au UPC o STARLight predicts significantly 4 gg® e+e- (STARLight) lower ⟨�+⟩ than seen in data 3 arXiv : 1910.12400 (mb/(GeV/c)) ) - e + 2 e ® dP g 1 g 2 0.4 < Mee < 0.76 GeV/c ( s d 0 0 0.02 0.04 0.06 0.08 0.1 P (GeV/c) QED and STARLight are scaled to match measured �(�� → �)�%) STARLight: S. R. Klein, et. al. Comput. Phys. Commun. 212 (2017) 258 QED : W. Zha, J.D.B., Z. Tang, Z. Xu arXiv:1812.02820 [nucl-th] February 5, 2020 Daniel Brandenburg 10 ) % �� �� → � � ⁄��+ B arXiv : 1910.12400 o Data are well described by 5 STAR leading order QED ) % Au+Au UPC calculation (�� → � � ) with + - 4 gg® e e (QED) quasi-real photons + - gg® e e (STARLight) o STARLight predicts significantly 3 arXiv : 1910.12400 (mb/(GeV/c)) lower ⟨�+⟩ than seen in data ) - STARLight calculations do not have e o + 2 centrality-dependent �+ e distribution ® dP g 1 g 2 0.4 < Mee < 0.76 GeV/c ( s o Experimentally investigate d 0 0 0.02 0.04 0.06 0.08 0.1 impact parameter dependence : P (GeV/c) Compare UPC to peripheral ) % → QED and STARLight are scaled to match measured �(�� → � � ) collisions (come back to later) STARLight: S. R. Klein, et. al. Comput. Phys. Commun. 212 (2017) 258 QED : W. Zha, J.D.B., Z. Tang, Z. Xu arXiv:1812.02820 [nucl-th] 11/05/19 Daniel Brandenburg 11 Classical Electromagnetism • Maxwell’s equations are linear ØSuperposition principle holds 1 �/ �ℒfghiijfhg ℒ = − �/ � = � = �l� fghiijfhg / �� 2�l � 1 �ℒfghiijfhg � = � � = − �l �� → Unique speed of light in vacuum: - � = = 299792458 m/s qDCD February 5, 2020 Daniel Brandenburg 12 Quantum Electrodynamics Three important discoveries that alter the classical picture: o Einstein’s energy-mass equivalence: � = ��/ o Uncertainty principle: Δ�Δ� ≥ ℏ/2 Einstein o Existence of positron : Dirac predicts negative electron energy states (1928), Anderson discovered positron in 1932 Anderson February 5, 2020 Daniel Brandenburg 13 Quantum Electrodynamics Three important discoveries that alter the classical picture: o Einstein’s energy-mass equivalence: � = ��/ o Uncertainty principle: Δ�Δ� ≥ ℏ/2 Einstein o Existence of positron : Dirac predicts negative electron energy states (1928), Anderson discovered positron in 1932 → Vacuum fluctuations o 1936: Euler & Heisenberg present modified Lagrangian | | / - z / }~ z / z ℒz{ = | − � + | − � + 7 ⋅ � + ⋯ /CD f CD f f Anderson oNon-linear → Superposition principle is broken! NB: in 1951 Shwinger derived the Lagrangian within QED formalism February 5, 2020 Daniel Brandenburg 14 Vacuum Magnetic Birefringence - � = BUT � ≠ � and � ≠ � qC ∥ + ∥ + Light behaves as if it is traveling through a medium with an index of refraction �ƒhf ≠ 1 Guido Zavattini ICNFP2019 February 5, 2020 Daniel Brandenburg 15 wikipedia Optical Birefringence Birefringent material: Different index of refraction for light polarized parallel (�∥) vs. perpendicular (�+) to material’s ordinary axis → splitting of wave function when �� = �∥ − �+ ≠ � Birefringent Material Linearly polarized (vertical) Ordinary ray Extra-ordinary ray Linearly polarized (horizontal) February 5, 2020 Daniel Brandenburg 16 Vacuum Birefringence Vacuum birefringence : Predicted in 1936 by Heisenberg & Euler. Index of refraction for � interaction with �-field depends on relative polarization angle i.e. �� = �∥ − �+ ≠ � Empty space + R. P. Mignani, et al., Mon. Not. Roy. Astron. Soc. 465 (2017), 492 Ultra-strong Magnetic Field Linearly polarized (vertical) Linearly polarized (horizontal) February 5, 2020 Daniel Brandenburg 17 Birefringence of the QED Vacuum Vacuum birefringence : Index of refraction Feynman Diagram for Vacuum Birefringence for � interaction with �-field depends on relative polarization angle i.e. �� = �∥ − �+ ≠ � � from � Lorentz contraction of EM fields → Quasi-real photons should be linearly polarized (� ⊥ � ⊥ �) Recently realized that a consequence of Probe � Observed � ) % �∥ − �+ ≠ � in �� → � � collisions is a ��� ��� modulation [3] between the pair momentum and the daughter momentum. ����(�) = transmission process �� → �� ����(�) = absorption process �� → �)�% (diagram cut) Can we observe vacuum birefringence [1]S. Bragin, et. al., Phys. Rev. Lett. 119 (2017), 250403 [2]R. P. Mignani, et al., Mon. Not. Roy. Astron. Soc. 465 (2017), 492 in ultra-peripheral collisions? [3] C. Li, J. Zhou, Y.-j. Zhou, Phys. Lett. B 795, 576 (2019) February 5, 2020 Daniel Brandenburg 18 [1] C.
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    + THE NEWSLEITER I VOLUME IV NO. 1 1981 THE OLIVER CHALLENGE T he Monterey I nstitute for Research in Ast ronomy will soon become an important center for stellar astronorny due in large part to the determination of its staff and the generous st^pport of many individuals and companies. Thanks to donations of equipment, f oundation grants, and personal contributions, M IRA now possesses a telescope and instrumentat ion. With a use permit for Chews Ridge in the Los Padres National Forest, MIRA has access to one of the finest sites for optical astronorny in North America. But, one component of MIRA's observatory is still missing: the observatory building. ln December 1980, Dr. Bbrnard M. Oliver, recently retired Vice-President for Research and Development at Hewlett- Packard, pledged a personal challenge grant of $200,000 for the construction of M IRA's observatory building. For every dollar contributed to the building fund between now and the end of the year, Dr. oliver will donate a matching dollar. The matching of ttre Oliver Challenge by MIRA's Friends will be a maior step toward the construction of the observatory building on Chews Ridge. A native Californian educated at Stanford and the California lnstitute of Technology, Dr. oliver's interest in M IRA dates back several years. tast June, he visited Monterey to give a lecture m the 'Search for Extraterrestrial I ntelligence' to the Friends of MIRA. At that time, he visited the MIRA shop to assess the staf f 's work on the Ret icon Spect rophotqmeter and related instrumentation.
  • PREFACE Symposium 177 of the International Astronomical Union

    PREFACE Symposium 177 of the International Astronomical Union

    PREFACE Symposium 177 of the International Astronomical Union was held in late May of 1996 in the coastal city of Antalya, Turkey. It was attended by 142 scientists from 32 countries. The purpose of the symposium was to discuss the causes and effects of the composition changes that often occur in the atmospheres of cool, evolved stars such as the carbon stars in the course of their evolution. This volume includes the full texts of papers presented orally and one-page abstracts of the poster contributions. The chemical composition of a star's observable surface layers depends not only upon the composition of the interstellar medium from which it formed, but in many cases also upon the star's own history. Consequently, spectroscopic studies of starlight can tell us much about a star's origin, the path it followed as it evolved, and the physical processes of the interior which brought about the composition changes and made them visible on the surface. Furthermore, evolved stars are often surrounded by detectable shells of their own making, and the compositions of these shells provide additional clues concerning the star's evolutionary history. It was Henry Norris Russell who showed in 1934 that the gross spectro- scopic differences between the molecular spectra of carbon stars and M stars could be explained as due to a simple reversal of the abundances of oxygen and carbon. It was also realized early on that the interstellar medium is nowhere carbon-rich, and that changes in chemical composition must be the result of nuclear reactions that take place in the hot interiors of stars, not in their atmospheres.