Physical Sciences and Mathematics Commons^™

The Design Of Primary Holding Magnet For The Lanl Neutron Electric Dipole Moment Experiment, Piya Amara Palamure

Theses and Dissertations--Physics and Astronomy

The measurement of the permanent electric dipole moment of the neutron (nEDM) plays a significant role in searching for sources of beyond standard model CP violating physics. The goal of the Los Alamos National Laboratory (LANL) nEDM experiment is to push the upper limit of the nEDM to < 3 × 10−27 e·cm (68 % CL). A highly uniform magnetic field is key to achieving this sensitivity for the nEDM measurement by reducing the systematic uncertainties associated with the magnetic field non-uniformity. The B0 coil was designed to achieve a field uniformity of < 0.3 nT·m−1 at a nominal holding field of 1 µT. This document will outline a novel technique employed in the construction of the B0 coil using printed circuit boards (PCBs) and will present preliminary field maps obtained with the B0 coil housed in a magnetically shielded room (MSR) at LANL.

As Ultra Cold Neutrons (UCNs) move from the source to the measurement cells, the UCNs experience a large magnetic field gradient in the region between the layers of the MSR. This large gradient would otherwise cause depolarization of the UCNs. To mitigate this, a double cos θ coil will serve as the …

Design Of The Highly Uniform Magnetic Field And Spin-Transport Magnetic Field Coils For The Los Alamos National Lab Neutron Electric Dipole Moment Experiment, Jared Brewington

Theses and Dissertations--Physics and Astronomy

Charge-Parity (CP) violation is one of Sakharov's three conditions which serve as guidelines for the generation of a matter-antimatter asymmetry in the early universe. The Standard Model (SM) of particle physics contains sources of CP violation which can be used to predict the baryon asymmetry. The observed baryon asymmetry is not predicted from SM calculations, meaning there must be additional sources of CP violation beyond the Standard Model (BSM) to generate the asymmetry. Permanent electric dipole moments (EDMs), which are inherently parity- and time reversal- violating, present a promising avenue for the discovery of new sources of CP violation to …

Elastic And Inelastic Compton Scattering From Deuterium At 61 Mev, Danula Godagama

Theses and Dissertations--Physics and Astronomy

A Compton scattering experiment using deuteron as target nuclei was carried out at the HIγS free electron laser facility at Durham, NC, with the goal of extracting the electromagnetic scalar polarizabilities of the neutron, α_n and β_n. A beam of 61~MeV gamma photons with a narrow energy spread was incident on a liquid deuterium target. The scattered gamma rays were detected at three scattering angles, 55^o, 115^o and 150^o. Backward-scattered gamma rays were detected using two large-volume NaI spectrometers with energy resolution (σ_E/E) better than 2%. The combined effect of …

Studies Of Time Variations Of The Magnetic Field In The Nedm@Sns Experiment, Mojtaba Behzadipour

Theses and Dissertations--Physics and Astronomy

It is thought that equal quantities of matter and antimatter were generated at the moment of the Big Bang. However, observations of the Universe show that there is a significant excess of matter over antimatter. The matter-antimatter asymmetry in the Universe (baryon to photon ratio) is observed to be of the order of 10^-10 [1]. Baryogenesis is a possible explanation for the matter-antimatter asymmetry of the universe. In 1967, Sakharov proposed three criteria necessary for Baryogenesis. The three conditions are: 1) baryon number violation, 2) C and CP violation and 3) departure from thermal equilibrium. However, the Standard Model's …

An Energy-Integrated Analysis For Measuring The Anomalous Precession Frequency For The Muon G − 2 Experiment At Fermilab, Laura Kelton

Theses and Dissertations--Physics and Astronomy

In the search for physics beyond the Standard Model, the Muon g − 2 Experiment at Fermilab (E989) will make the most precise measurement of the anomalous magnetic moment of the muon, a_μ. Improvements in precision come from both increased statistics and new techniques to significantly reduce previous systematic uncertainties. The muon a_μ is determined by extracting both the anomalous spin precession frequency, ω_a, and the average magnetic field sampled by the muons, B. Traditionally an energy threshold analysis method which requires reconstruction of decay positrons from the muon decay, μ⁺ → e^{+ …}

Cryogenic Magnetic Field Monitoring System In The Sns Neutron Edm Experiment, Umit Hasan Coskun

Theses and Dissertations--Physics and Astronomy

A permanent neutron electric dipole moment (nEDM), d_n, would violate charge-conjugation and parity (CP) symmetry. The neutron electric dipole moment currently has a global limit of d_n < 1.8 x 10^-26 e cm (90% CL). This limit is intended to be improved by two orders of magnitude by the nEDM experiment at the Spallation Neutron Source (SNS nEDM), d_n ~ 10^-28 e cm. The magnetic field non-uniformities within the experimental region must be precisely monitored and managed in order to suppress systematic effects in the experiment caused by magnetic field gradients. The estimation of magnetic field components within …

Extraction Of Deep Inelastic Cross Sections Using A 10.4 Gev Electron Beam And A Polarized Helium-3 Target, Murchhana Roy

Theses and Dissertations--Physics and Astronomy

Experiment E12-06-121 at Jefferson Lab aims to do a precision measurement of the neutron spin structure function g₂ using inclusive inelastic scattering of electrons over a large kinematic range of x and Q². The third moment of the linear combination of the spin structure functions g₁ and g₂, d₂, is one of the cleanest higher twist observables and contains information on quark-gluon correlations. It is connected to the "color polarizability" or "color Lorentz force" of the nucleon. The experimental data taking was successfully conducted in Hall C using a longitudinally polarized electron …

High Performance Data Acquisition And Analysis Routines For The Nab Experiment, David Mathews

Theses and Dissertations--Physics and Astronomy

Probes of the Standard Model of particle physics are pushing further and further into the so-called “precision frontier”. In order to reach the precision goals of these experiments, a combination of elegant experimental design and robust data acquisition and analysis is required. Two experiments that embody this philosophy are the Nab and Calcium-45 experiments. These experiments are probing the understanding of the weak interaction by examining the beta decay of the free neutron and Calcium-45 respectively. They both aim to measure correlation parameters in the neutron beta decay alphabet, a and b. The parameter a, the electron-neutrino correlation coefficient, is …

Enhancements To Uniformity Of Magnetic Fields At The Sns Nedm Experiment, Ahmad Saftah

Theses and Dissertations--Physics and Astronomy

The nEDM experiment at the Spallation Neutron Source (SNS) aims to increase
experimental sensitivity to hadronic CP violation by nearly two orders of magnitude.To do that the nEDMSNS experiment requires an extremely uniform magnetic field to maintain ³He polarization during transit to the measurement cell. The Magnetic Shield Enclosure (MSE) coil provides the required field. However, the superconducting shield distorts the MSE field.

This thesis discusses a magnetic cloak for the nEDM@SNS experiment that can restore the MSE field uniformity and cos theta coils designed to test the magnetic cloak in the first part. The second part of this …

Neutron Spectroscopy Of The Parity-Violating 0.734 Ev Neutron Resonance In Lanthanum-139 In Preparation For The Noptrex Time Reversal Violation Experiment, Danielle Schaper

Theses and Dissertations--Physics and Astronomy

One of the most outstanding questions in physics is the matter-antimatter asymmetry of the Universe, resulting from excess baryogenesis processes during the early moments of the formation of the Universe. At present, the types of processes needed to explain this matter excess, so-called `CP-violating processes' are known to exist within the present framework of the Standard Model of particle physics. However, decades of research has shown that our understanding of the origin of these processes is incomplete, as we do not presently know of enough sources of CP-violating processes to account for the large baryon asymmetry that we observe. The …

Energy Integrated Ratio Analysis Of The Anomalous Precession Frequency In The Fermilab Muon G-2 Experiment, Ritwika Chakraborty

Theses and Dissertations--Physics and Astronomy

The muon’s anomalous magnetic moment, a_μ, provides a unique way for probing physics beyond the standard model experimentally as it gathers contributions from all the known and unknown forces and particles in nature. The theoretical prediction of a_μ has been in greater than 3 σ tension with the experimental measurement since the results of the Muon g-2 Experiment at the Brookhaven National Laboratory (E-821) were published in the early 2000s with a precision of 540 ppb. To settle this tension, the new Fermilab Muon g - 2 Experiment (E-989) is currently taking data with the aim of …

Theoretical Study On Η′ → Π+Π−Π+(0)Π−(0), Ehsan Jafari, Bing An Li

Physics and Astronomy Faculty Publications

The η′ meson is associated with the U(1) anomaly. In this paper, a successful effective chiral theory of mesons has been applied to study the anomalous decays of η′ → π⁺π⁻π⁺⁽⁰⁾π⁻⁽⁰⁾. Contribution of triangle and box diagrams is calculated, which indicates that the box anomaly has a significant contribution to the decay amplitudes.

[Please download the article to see the rest of the abstract.]

Analyzing The Effect Of Second-Class Currents On Neutron Beta Decay Observables And The Effect Of Thomas Rotation On The Relativistic Transformations Of Electromagnetic Fields, Lakshya Malhotra

Theses and Dissertations--Physics and Astronomy

The next generation of neutron beta decay measurements will attempt to analyze various beta decay observables of up to O(10^-4) precision. At this level of experimental precision, the effects of second-class currents will contribute theoretical uncertainties to the interpretation of these measurements. Therefore, it is important to investigate the effects of these second-class currents on decay parameters, such as the Fierz interference term b which is linear in beyond standard model couplings. A maximum likelihood statistical framework and Rfit techniques are employed to study these second-class currents effects. Inputs to the Rfit technique are obtained through …

Effective Field Theory Applications: From Dark Matter To Neutrino Nucleon Scattering, Qing Chen

Theses and Dissertations--Physics and Astronomy

Weakly-interacting-massive-particles (WIMPs) are a large class of viable dark matter candidates. We compute cross sections for electroweak-doublet WIMPs scattering on atomic nuclei, at leading and subleading order using heavy WIMP effective field theory. Neutrino-nucleon charged current elastic scattering is an important process in the detectors of long baseline accelerator neutrino oscillation experiments. We compute QED radiative corrections to this process employing soft-collinear effective field theory.

The Pion Form Factor And Momentum And Angular Momentum Fractions Of The Proton In Lattice Qcd, Gen Wang

Theses and Dissertations--Physics and Astronomy

Lattice Quantum Chromodynamics (QCD) provides a way to have a precise calculation and a new way of understanding the hadrons from first principles. From this perspective, this dissertation focuses first on a precise calculation of the pion form factor using overlap fermions on six ensembles of 2+1-flavor domain-wall configurations generated by the RBC/UKQCD collaboration with pion masses varying from 137 to 339 MeV. Taking advantage of the fast Fourier transform, low-mode substitution (LMS) and the multi-mass algorithm to access many combinations of source and sink momenta, we have done a simulation with various valence quark masses and with a range …

Study Of Cell Charging Effects For The Neutron Electric Dipole Moment Experiment At Oak Ridge National Laboratory, Mark Broering

Theses and Dissertations--Physics and Astronomy

The neutron electric dipole moment (nEDM) collaboration at the Spallation Neutron Source plans to use ultra-cold neutrons in superfluid helium to improve the nEDM limit by about two orders of magnitude. In this apparatus, neutrons are stored in poly(methyl methacrylate), PMMA, cells located in a strong, stable electric field. This electric field is produced by high voltage electrodes located outside of the neutron cells. Several sources generate charged particles inside the neutron cells. The electric field pulls these charges farther apart, attracting each to the oppositely charged electrode. As the charges build up on the cells walls, they create an …

Sensitivity Of Electron-Proton Coincidence Asymmetries In Neutron Beta-Decay To Scalar And Tensor Interactions, Subash C. Nepal

Theses and Dissertations--Physics and Astronomy

We study the combined sensitivity of measurements of electron-proton coincidence asymmetries in polarized neutron beta-decay together with a measurement of the electron energy spectrum in unpolarized neutron beta-decay to beyond Standard Model (BSM) scalar and tensor interactions, via the appearance of such BSM physics in the Fierz interference terms b and b_v. Whereas measurements of the electron energy spectrum directly probe b, both the proton and neutrino asymmetries for which experimental results exist are not sensitive to b_v, but effectively to b - b_v. This results in reduced sensitivity to BSM scalar and …

Measurement Of Double-Polarization Asymmetries In The Quasi-Elastic 3He→(E→, E'P) Process, M. Mihovilovic, G. Jin, E. Long, Y. -W. Zhang, K. Allada, B. Anderson, J. R. M. Annand, T. Averett, W. Bertozzi, W. Boeglin, P. Bradshaw, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. P. Chen, E. Chudakov, R. De Leo, X. Deng, A. Deltuva, A. Deur, Chiranjib Dutta, L. El Fassi, D. Flay, S. Frullani, F. Garibaldi, H. Gao, S. Gilad, R. Gilman, O. Glamazdin, Wolfgang Korsch

Physics and Astronomy Faculty Publications

We report on a precise measurement of double-polarization asymmetries in electron-induced breakup of ³He proceeding to pd and ppn final states, performed in quasi-elastic kinematics at Q² = 0.25(GeV/c)² for missing momenta up to 250MeV/c. These observables represent highly sensitive tools to investigate the electromagnetic and spin structure of ³He and the relative importance of two- and three-body effects involved in the breakup reaction dynamics. The measured asymmetries cannot be satisfactorily reproduced by state-of-the-art calculations of ³He unless their three-body segment is adjusted, indicating that the spin-dependent part of the nuclear …

A Detection And Data Acquisition System For Precision Beta Decay Spectroscopy, Aaron P. Jezghani

Theses and Dissertations--Physics and Astronomy

Free neutron and nuclear beta decay spectroscopy serves as a robust laboratory for investigations of the Standard Model of Particle Physics. Observables such as decay product angular correlations and energy spectra overconstrain the Standard Model and serve as a sensitive probe for Beyond the Standard Model physics. Improved measurement of these quantities is necessary to complement the TeV scale physics being conducted at the Large Hadron Collider. The UCNB, ⁴⁵Ca, and Nab experiments aim to improve upon existing measurements of free neutron decay angular correlations and set new limits in the search for exotic couplings in beta decay. To …

Prompt Fission Neutron Energy Spectrum Of N+235U, Jason M. Mcginnis

Theses and Dissertations--Physics and Astronomy

Despite nuclear fission prominence in nuclear physics, there are still several fundamental open questions about this process. One uncertainty is the energy distribution of neutrons emitted immediately after fission. In particular the relative energy distribution of neutrons above 8~MeV has been difficult to measure. This experiment measured the prompt neutron energy spectrum of n+²³⁵U from 3-10~MeV. The measurement took place at Los Alamos National Laboratory (LANL) and used a double time-of-flight technique to measure both the beam and fission neutron kinetic energies. Fission event timing was measured with a parallel plate avalanche counter. The fission neutron time-of-flight was …

Magnetic Field Monitoring In The Sns Neutron Edm Experiment, Alina Aleksandrova

Theses and Dissertations--Physics and Astronomy

It is a well known fact that the visible universe is made almost entirely of baryonic matter. Yet, this is also one of the greatest puzzles that physicists are trying to solve: Where did all of this matter come from in the first place? The Standard Model (SM) of particle physics predicts a baryon asymmetry that is much smaller than what is observed in nature. In order to try and explain this discrepancy, Sakharov (1967) postulated three necessary conditions for baryogenesis in the early universe. One of these is the requirement that charge conjugation (C) and the product of C …

Improved Measurement Of The Longitudinal Spin Transfer To Λ And Λ¯ Hyperons In Polarized Proton-Proton Collisions At √S = 200 Gev, J. Adam, L. Adamczyk, J. R. Adams, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, F. Atetalla, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, K. Barish, A. J. Bassill, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. D. Brandenburg, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

The longitudinal spin transfer D_LL to Λ and Λ¯ hyperons produced in high-energy polarized proton-proton collisions is expected to be sensitive to the helicity distribution functions of strange quarks and antiquarks of the proton, and to longitudinally polarized fragmentation functions. We report an improved measurement of D_LL from data obtained at a center-of-mass energy of √s = 200  GeV with the STAR detector at RHIC. The data have an approximately twelve times larger figure of merit than prior results and cover |η| < 1.2 in pseudorapidity with transverse momenta p_T up to 6  GeV/c. In the forward scattering hemisphere …

Gluon Quasi-Parton-Distribution Functions From Lattice Qcd, Zhou-You Fan, Yi-Bo Yang, Adam Anthony, Huey-Wen Lin, Keh-Fei Liu

Physics and Astronomy Faculty Publications

We present the first attempt to access the x dependence of the gluon unpolarized parton-distribution function (PDF), based on lattice simulations using the large-momentum effective theory approach. The lattice calculation is carried out with pion masses of 340 and 678 MeV on a (2+1)-flavor domain-wall fermion configuration with lattice spacing a = 0.111  fm, for the gluon quasi-PDF matrix element with the nucleon momentum up to 0.93 GeV. Taking the normalization from similar matrix elements in the rest frame of the nucleon and pion, our results for these matrix elements are consistent with the Fourier transform of the global fit …

Proton Mass Decomposition From The Qcd Energy Momentum Tensor, Yi-Bo Yang, Jian Liang, Yu-Jiang Bi, Ying Chen, Terrence Draper, Keh-Fei Liu, Zhaofeng Liu

Physics and Astronomy Faculty Publications

We report results on the proton mass decomposition and also on related quark and glue momentum fractions. The results are based on overlap valence fermions on four ensembles of N_f = 2 + 1 domain wall fermion configurations with three lattice spacings and three volumes, and several pion masses including the physical pion mass. With fully nonperturbative renormalization (and universal normalization on both quark and gluon), we find that the quark energy and glue field energy contribute 32(4)(4)% and 36(5)(4)% respectively in the MS¯ (modified minimal substraction) scheme at μ = 2  GeV. A quarter of the trace anomaly …

Beam-Target Helicity Asymmetry E In K0Λ And K0Σ0 Photoproduction On The Neutron, D. H. Ho, R. A. Schumacher, A. D’Angelo, A. Deur, J. Fleming, C. Hanretty, T. Kageya, F. J. Klein, E. Klempt, M. M. Lowry, H. Lu, V. A. Nikonov, P. Peng, A. M. Sandorfi, A. V. Sarantsev, I. I. Strakovsky, N. K. Walford, X. Wei, R. L. Workman, K. P. Adhikari, S. Adhikari, D. Adikaram, Z. Akbar, J. Ball, L. Barion, M. Bashkanov, C. D. Bass, M. Battaglieri, I. Bedlinskiy, A. S. Biselli, Wesley P. Gohn

Physics and Astronomy Faculty Publications

We report the first measurements of the E beam-target helicity asymmetry for the γ^→ n^→ → K⁰Λ and K⁰Σ⁰ channels in the energy range 1.70 ≤ W ≤ 2.34 GeV. The CLAS system at Jefferson Lab uses a circularly polarized photon beam and a target consisting of longitudinally polarized solid molecular hydrogen deuteride with low background contamination for the measurements. The multivariate analysis method boosted decision trees is used to isolate the reactions of interest. Comparisons with predictions from the KaonMAID, SAID, and Bonn-Gatchina models are presented. These results will help separate the …

Nonperturbatively Renormalized Glue Momentum Fraction At The Physical Pion Mass From Lattice Qcd, Yi-Bo Yang, Ming Gong, Jian Liang, Huey-Wen Lin, Keh-Fei Liu, Dimitra Pefkou, Phiala Shanahan

Physics and Astronomy Faculty Publications

We present the first nonperturbatively renormalized determination of the glue momentum fraction ⟨x⟩_g in the nucleon, based on lattice-QCD simulations at the physical pion mass using the cluster-decomposition error reduction technique. We provide the first practical strategy to renormalize the gauge energy-momentum tensor nonperturbatively in the regularization-independent momentum-subtraction (RI/MOM) scheme and convert the results to the MS¯ scheme with one-loop matching. The simulation results show that the cluster-decomposition error reduction technique can reduce the statistical uncertainty of its renormalization constant by a factor of O(300) in calculations using a typical state-of-the-art lattice volume, and the nonperturbatively …

Quark Spins And Anomalous Ward Identity, Jian Liang, Yi-Bo Yang, Terrence Draper, Ming Gong, Keh-Fei Liu

Physics and Astronomy Faculty Publications

We calculate the intrinsic quark spin contribution to the total proton spin using overlap valence quarks on three ensembles of 2 + 1-flavor RBC/UKQCD domain-wall configurations with different lattice spacings. The lowest pion mass of the ensembles is around 171 MeV, which is close to the physical point. With overlap fermions and a topological charge derived from the overlap operator, we verify the anomalous Ward identity between nucleon states with momentum transfer. Both the connected and the disconnected insertions of the axial-vector current are calculated. For the disconnected-insertion part, the cluster-decomposition error reduction technique is utilized for the lattice with …

Measurement Of Unpolarized And Polarized Cross Sections For Deeply Virtual Compton Scattering On The Proton At Jefferson Laboratory With Clas, N. Hirlinger Saylor, B. Guegan, V. D. Burkert, L. Elouadrhiri, M. Garçon, F. X. Girod, M. Guidal, H. S. Jo, V. Kubarovsky, S. Niccolai, P. Stoler, K. P. Adhikari, S. Adhikari, Z. Akbar, M. J. Amaryan, S. Anefalos Pereira, J. Ball, I. Balossino, N. A. Baltzell, L. Barion, M. Battaglieri, V. Batourine, I. Bedlinskiy, A. S. Biselli, S. Boiarinov, W. J. Briscoe, W. K. Brooks, S. Bültmann, F. Cao, S. Carman, Wesley P. Gohn

Physics and Astronomy Faculty Publications

This paper reports the measurement of polarized and unpolarized cross sections for the ep → e′ p′ γ reaction, which is composed of deeply virtual Compton scattering (DVCS) and Bethe-Heitler (BH) processes, at an electron beam energy of 5.88 GeV at the Thomas Jefferson National Accelerator Facility using the Large Acceptance Spectrometer CLAS. The unpolarized cross sections and polarized cross section differences have been measured over broad kinematics, 0.10 < x_B < 0.58, 1.0 < Q² < 4.8GeV², and 0.09 < −t < 2.00GeV². The results are found to be consistent with previous CLAS data, and these new data are discussed in …

Harmonic Decomposition Of Three-Particle Azimuthal Correlations At Energies Available At The Bnl Relativistic Heavy Ion Collider, L. Adamczyk, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, A. V. Brandin, D. Brown, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

We present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from √s_NN = 7.7 to 200 GeV using the STAR detector. The quantity ⟨cos(mϕ₁ + nϕ₂ − (m + n)ϕ₃)⟩, with ϕ being the azimuthal angles of the particles is evaluated as a function of √s_NN, collision centrality, transverse momentum, p_T, pseudorapidity difference, Δη, and harmonics (m and n). These data provide detailed information on global event properties such as the three-dimensional structure of the initial …

Low-PT E+ E- Pair Production In Au + Au Collisions At √SNn = 193 Gev And U + U Collisions At √SNn = 193 Gev At Star, J. Adam, L. Adamczyk, J. R. Adams, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, F. Atetalla, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, K. Barish, A. J. Bassill, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, Renee H. Fatemi, Suvarna Ramachandran

Physics and Astronomy Faculty Publications

We report first measurements of e⁺e⁻ pair production in the mass region 0.4 < M_ee < 2.6  GeV/c² at low transverse momentum (p_T < 0.15  GeV/c) in noncentral Au+Au collisions at √s_NN = 200  GeV and U+U collisions at √s_NN = 193  GeV. Significant enhancement factors, expressed as ratios of data over known hadronic contributions, are observed in the 40%–80% centrality of these collisions. The excess yields peak distinctly at low p_T with a width (√⟨p²_T⟩) between 40 and 60  MeV/c. The absolute cross section of …