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Title: Searching for Heavy Photons with Detached Verices in the Heavy Photon Search Experiment

Abstract

The Jefferson Lab Heavy Photon Search (HPS) experiment is searching for a hypothetical massive particle called the heavy photon which could mediate a dark electromagnetic-type force. If heavy photons kinetically mix with Standard Model photons, they may be radiated by electrons scattering from a heavy nucleus and then decay to e+e- pairs. HPS uniquely searches for heavy photons that either decay at the target or a measurable distance after. The experiment utilizes a silicon vertex tracker (SVT) for momentum and vertex reconstruction, together with an electromagnetic calorimeter for measuring particle energies and triggering events. The HPS experiment took its first data during the spring 2015 engineering run using a 1 GeV electron beam incident on a tungsten target and its second data in the spring of 2016 at a beam energy of 2.3 GeV. The 2015 run obtained two days of production data that was used for the first physics results. The analysis of the data was conducted as a blinded analysis by tuning cuts on 10% of the data. This dissertation discusses the displaced vertex search for heavy photons in the 2015 engineering run. It describes the theoretical motivation for looking for heavy photons and provides an overview ofmore » the HPS experimental design and performance. The performance details of the experiment are primarily derived from the 2015 engineering run with some discussion from the higher energy running in 2016. This dissertation further discusses the cuts used to optimize the displaced vertex search and the results of the search. The displaced vertex search did not set a limit on the heavy photon but did validate the methodology for conducting the search. Finally, we used the full data set to make projections and guide future analyses.« less

Authors:
 [1]
+ Show Author Affiliations
  1. Old Dominion Univ., Norfolk, VA (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
OSTI Identifier:
1409025
Report Number(s):
JLAB-PHY-17-2592; DOE/OR/23177-4268
DOE Contract Number:
AC05-06OR23177
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Szumila-Vance, Holly. Searching for Heavy Photons with Detached Verices in the Heavy Photon Search Experiment. United States: N. p., 2017. Web. doi:10.2172/1409025.
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Szumila-Vance, Holly. Searching for Heavy Photons with Detached Verices in the Heavy Photon Search Experiment. United States. doi:10.2172/1409025.
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Szumila-Vance, Holly. Tue . "Searching for Heavy Photons with Detached Verices in the Heavy Photon Search Experiment". United States. doi:10.2172/1409025. https://www.osti.gov/servlets/purl/1409025.
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@article{osti_1409025,
title = {Searching for Heavy Photons with Detached Verices in the Heavy Photon Search Experiment},
author = {Szumila-Vance, Holly},
abstractNote = {The Jefferson Lab Heavy Photon Search (HPS) experiment is searching for a hypothetical massive particle called the heavy photon which could mediate a dark electromagnetic-type force. If heavy photons kinetically mix with Standard Model photons, they may be radiated by electrons scattering from a heavy nucleus and then decay to e+e- pairs. HPS uniquely searches for heavy photons that either decay at the target or a measurable distance after. The experiment utilizes a silicon vertex tracker (SVT) for momentum and vertex reconstruction, together with an electromagnetic calorimeter for measuring particle energies and triggering events. The HPS experiment took its first data during the spring 2015 engineering run using a 1 GeV electron beam incident on a tungsten target and its second data in the spring of 2016 at a beam energy of 2.3 GeV. The 2015 run obtained two days of production data that was used for the first physics results. The analysis of the data was conducted as a blinded analysis by tuning cuts on 10% of the data. This dissertation discusses the displaced vertex search for heavy photons in the 2015 engineering run. It describes the theoretical motivation for looking for heavy photons and provides an overview of the HPS experimental design and performance. The performance details of the experiment are primarily derived from the 2015 engineering run with some discussion from the higher energy running in 2016. This dissertation further discusses the cuts used to optimize the displaced vertex search and the results of the search. The displaced vertex search did not set a limit on the heavy photon but did validate the methodology for conducting the search. Finally, we used the full data set to make projections and guide future analyses.},
doi = {10.2172/1409025},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Aug 01 00:00:00 EDT 2017},
month = {Tue Aug 01 00:00:00 EDT 2017}
}
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Thesis/Dissertation:
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DOI:  10.2172/1409025
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  • The Heavy Photon Search (HPS) is a new experiment at Jefferson Lab that searches for a massive U(1) vector boson (known as a heavy photon or A′) in the MeV-GeV mass range and coupling weakly to ordinary matter through a kinetic mixing interaction. The HPS experiment seeks to produce heavy photons by electron bremsstrahlung on a fixed target, is sensitive to heavy photon decays to e+e-, and targets the range in heavy photon mass m_A' ~ 20 - 600 MeV, and kinetic mixing strength epsilon^2 ~ 10^-5 - 10^−10. HPS searches for heavy photons using two signatures: a narrow massmore » resonance and displaced vertices. This dissertation presents the theoretical and experimental motivations for a heavy photon, the design and operation of the HPS experiment, and the displaced vertex search. The data used in this dissertation is the unblinded fraction of the 2015 HPS run, for the period of operation where the HPS silicon vertex tracker (SVT) was operated at its nominal position. This data was recorded from May 13 to May 18, 2015, at a beam energy of 1.056 GeV and a nominal beam current of 50 nA. The integrated luminosity is 119 nb^-1, which is equivalent to 0.172 days of ideal running at the nominal beam current. This dissertation presents results (signal significance and upper limits) from the displaced vertex search in the mass range m_A' ~ 20 - 60 MeV, and kinetic mixing strength epsilon^2 ~ 2 × 10^-8 - 10^-10. This search does not have sufficient sensitivity to exclude a canonical heavy photon at any combination of m_A' and epsilon^2. The strictest limit achieved in this analysis on the production of a particle that decays like a heavy photon is 115 times the expected production cross-section for a heavy photon. Factors limiting the sensitivity of this analysis are discussed. Projections of HPSperformance with the full 2015 data set, and with planned improvements to theanalysis, are presented. Comparisons are also made to earlier reach estimates.« less

  • The Heavy Photon Search Experiment (HPS) seeks to detect a hypothesised hidden sector boson, the A', predicted to be produced in dark matter decay or annihilation. Theories suggest that the A' couples weakly to electric charge through kinetic mixing, allowing it, as a result, to decay to Standard Matter (SM) lepton pair, which may explain the electron and positron excess recently observed in cosmic rays. Measuring the lepton pair decay of the A' could lead to indirect detection of dark matter. The HPS experiment is a fixed target experiment that will utilize the electron beam produced at the Thomas Jeffersonmore » National Accelerator Facility (Jefferson Lab). The detector set-up includes a silicon vertex tracker (SVT) and an Electromagnetic Calorimeter (ECal). The ECal will provide the trigger and detect e+e- pairs and its construction and testing forms the focus of this thesis. The ECal consists of 442 PbWO 4- tapered crystals with a length 16cm and a 1.6x1.6cm 2 cross-section, stacked into a rectangular array and are coupled to Large Area APDs and corresponding pre-amplifiers. Supplementary to the ECal is a Light Monitoring System (LMS) consisting of bi-coloured LEDs that will monitor changes in APD gain and crystal transparency due to radiation damage. Before construction of the ECal each of the components were required to be individually tested to determine a number of different characteristics. Irradiation tests were performed on PbWO 4 ECal crystals and, as a comparison, one grown by a different manufacturer to determine their radiation hardness. A technique for annealing the radiation damage by optical bleaching, which involves injecting light of various wavelengths into the crystal, was tested using the blue LED from the LMS as a potential candidate. The light yield dependence on temperature was also measured for one of the PbWO 4 crystal types. Each APD was individually tested to determine if they functioned correctly and within the requirements of the experiment, then arranged into groups of similar gain at chosen applied voltages, for connection to High Voltage (HV) supplies. Each bi-coloured LED was also tested to determine if they functioned within the specifications of the experiment; including their signal quality at high frequency and their radiation hardness. The HPS crystals were recycled from a previous Jefferson Lab detector, the Inner Calorimeter from CLAS, which needed to be dismantled and reconditioned using various removal and cleaning techniques. The HPS ECal was then constructed in a new formation using a combination of different gluing and construction techniques, and initial functionality tests were performed.« less

  • This dissertation presents the results of the first search for heavy, neutral, longlived particles that decay to photons at a hadron collider. We use a sample of +jet+missing transverse energy events inmore » $$p \bar{p}$$ collisions at √s = 1.96 TeV taken with the Collider Detector at Fermilab. Candidate events are selected based on the arrival time of a high-energy photon at the electromagnetic calorimeter as measured with a timing system that was recently installed. The final result is that we find 2 events, using 570±34 pb -1 of data collected during 2004-2005 at the Fermilab Tevatron, consistent with the background estimate of 1.3±0.7 events. While our search strategy does not rely on model-specific dynamics, we interpret this result in terms of cross section limits in a supersymmetric model with $$\vec{X}$$$0\atop{1}$$ eG and set a world-best e 01 mass reach of 101 GeV/c 2 at e = 5 ns. We can exclude any γ+jet+missing transverse energy signal that would produce more than 5.5 events.« less

  • This paper consists of two studies: the results of a search for heavy Majorana neutrinos (N) using an event signature defined by two like-sign charged muons and two jets, and the results from studies of a prototype quartz plate calorimeter. The data in the Majorana search correspond to an integrated luminosity of 5.0 fbmore » $$^{−1}$$ of pp collisions at a centre-of-mass energy of 7 TeV collected with the CMS detector at the Large Hadron Collider. No excess of events are observed beyond the expected standard model background and therefore upper limits are set on the square of the mixing element, $$|V_{\mu N} |$$as a function of Majorana neutrino mass. These are the first direct upper limits on the heavy Majorana-neutrino mixing for m$$_N$$ > 90 GeV . The second part of this thesis is the results of performance tests of a 20-layer quartz plate calorimeter prototype. The calorimeter prototype was tested at the CERN H2 area in hadronic and electromagnetic configurations, at various en ergies of pion and electron beams. The beam test and simulation results of this prototype are reported.« less

  • Pair production of stable weakly interacting neutral particles in e/sup +/e/sup -/ annihilation can be tagged by the observation of a single radiative photon in an otherwise invisible final state. The first such search for single unaccompanied photons is described, analyzed, and used to set limits on neutrinos and super-symmetric particles. The search was performed with the MAC detector at the PEP e/sup +/e/sup -/ storage ring at SLAC. The single-photon tagging technique exploits unique features of the general-purpose MAC detector, including total absorption calorimetry which provides highly efficient particle detection over nearly the full solid angle. The upper limitmore » on the single-photon signal excludes with 90% confidence the existence of 17 or more light-neutrinos. The upper limit on single-photons beyond those expected from radiative production of the three known neutrinos is interpreted as a lower limit on the masses of the selectrons that are exchanged in photino pair production and the charginos that are exchanged in neutrino pair production. Degenerate selectrons that have mass less than 47 GeV/c/sup 2/ are excluded with 90% confidence if photinos are light. The MAC search, when combined with all other reported single-photon searches excludes with 90% confidence the existence of more than 4.8 light-neutrinos, and degenerate selectrons with mass less than 65 GeV/c/sup 2/ if photinos are light.« less