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\title{Chung-Yao Fellowship 2016}

\author{Sho Uemura}
\institute{SLAC}
\date[May 8, 2016]

\begin{document}

\begin{frame}
	\titlepage
\end{frame}

\begin{frame}{Summary of CV}
	\begin{itemize}
		\item 2006--2010: S.B., Massachusetts Institute of Technology (Physics, Mathematics)
			\begin{itemize}
				\item Thesis: \emph{Differential Cross Section Measurement for the d(n,np) Reaction}, with Prof. June Matthews
			\end{itemize}
		\item 2010--2016: Ph.D., Stanford University (Physics)
			\begin{itemize}
				\item Degree expected September 2016
				\item Thesis: \emph{Searching for Heavy Photons with Separated Decay Vertices in the HPS Experiment}, with Prof. John Jaros
			\end{itemize}
	\end{itemize}
\end{frame}

%\begin{frame}{Current research: Heavy Photon Search (HPS)}
	%\begin{itemize}
		%\item Tracker assembly and survey
		%\item Hit time reconstruction
		%\item MC production
		%\item Vertexing analysis
	%\end{itemize}
%\end{frame}

\begin{frame}{Current research: dark forces and the heavy photon}
	\begin{columns}
		\column{0.6\textwidth}
		\begin{itemize}
			\item ``Dark sector'' emerging as a picture of dark matter that allows for self-scattering, collisional excitation, annihilation
			\begin{itemize}
				\item Standard Model forces don't couple to the dark sector
				\item Dark forces don't couple to Standard Model matter
				\item ``Portals'' create weak effective couplings between the sectors
			\end{itemize}
			\item Vector portal: dark force is a massive $U(1)$ boson (heavy photon)
			\begin{itemize}
				\item Kinetic mixing with the photon $\to$ weak coupling to electric charge
			\end{itemize}
			\item Two relevant parameters: mass $m_{A'}$, relative coupling strength $\epsilon^2=\alpha'/\alpha$
		\end{itemize}
		\column{0.4\textwidth}
		\begin{center}
			\includegraphics[width=\textwidth]{sm_dark}

			\includegraphics[width=\textwidth]{kinetic_mixing}
		\end{center}
	\end{columns}
\end{frame}

\begin{frame}{The Heavy Photon Search}
	\begin{columns}
		\column{0.65\textwidth}
		\begin{itemize}
			\item HPS is a dedicated experiment looking for heavy photons
			\item Production: virtual bremsstrahlung from $e^-$ on a fixed target
			\item Signature: $e^+e^-$ mass resonance or displaced vertex
			\item Apparatus: silicon microstrips in dipole (measurement), PbWO$_4$ calorimeter (trigger)
			\item Facility: CEBAF linac at Jefferson Lab, Hall B beamline
		\end{itemize}
		\column{0.35\textwidth}
		\includegraphics[width=\textwidth]{A-visible-HPS-official-6-2015}
	\end{columns}
	\begin{center}
		\includegraphics[width=0.6\textwidth]{HPS-pic.jpg}
	\end{center}
\end{frame}

\begin{frame}{Assembly and survey of SVT}
	\begin{columns}
		\column{0.65\textwidth}
	\begin{itemize}
		\item Pair half-modules onto support structure at 50/100 mrad stereo angle
		\item Survey assembled modules using optical/touch-probe CMM: get sensor positions and curvature
		\item Modules (in sets of 3) mount onto U-channels; survey U-channels to relate sensors to each other and beamline survey
	\end{itemize}
		\column{0.35\textwidth}
		\includegraphics[angle=270,width=\textwidth]{uch_survey.jpg}
	\end{columns}
	\begin{center}
		\includegraphics[width=0.28\textwidth]{support_proto.jpg}
		\includegraphics[width=0.22\textwidth]{pairing_l456.jpg}
		\includegraphics[width=0.28\textwidth]{l123_front.PNG}
	\end{center}
\end{frame}

\begin{frame}{SVT hit time reconstruction}
	\begin{columns}
		\column{0.6\textwidth}
		\begin{itemize}
			\item SVT hit occupancies are very high; reject hits outside a time window defined by the ECal event time
			\item HPS is designed for a maximum occupancy of 1\% (L1 next to the beam gap) in 8 ns window; to run at planned current with good tracking efficiency, hit time recon must be good within 8 ns
			\item Use APV25 readout chip to take 6 samples at 24 ns spacing; fit the pulse coming out of the preamp to get hit time resolution $\sim$2 ns
				\begin{itemize}
					\item Minimize effect of pulse pileup on the time fit
				\end{itemize}
			\item Use fitted hit times in track finding
		\end{itemize}
		\column{0.4\textwidth}
		\includegraphics[width=\textwidth]{t0}

		\includegraphics[width=\textwidth]{nakahama_pileup.pdf}
	\end{columns}
\end{frame}

\begin{frame}{Monte Carlo}
	\begin{itemize}
		\item Full simulation of pileup, time evolution, triggers and readout
		\item Mock data challenge: 1 week equivalent of simulated data with secret A' signals mixed in
		\item Set up and exercise all our MC, data handling and recon tools on Jefferson Lab compute farm
	\end{itemize}
	\begin{center}
		\includegraphics[width=0.6\textwidth]{flowchart.png}
	\end{center}
\end{frame}

\begin{frame}{Vertexing search}
	\begin{columns}
		\column{0.55\textwidth}
		\begin{itemize}
			\item Looking for a tail in $+Z$ at a single mass
			\item Multiple scattering distribution leads to Gaussian core and non-Gaussian tail: fit the tail and do a cut-and-count analysis
			\item Blinded analysis; currently using 10\% of the data
			\item Pushing for publication this year
			%\item Tails of the vertex distribution agree between data (black) and MC (red)
			%\item Work continues to use both data and MC to characterize tails
		\end{itemize}
%		\begin{center}
%			\includegraphics[width=\textwidth]{rad-bh-diagrams}
%		\end{center}
		\column{0.45\textwidth}
		\includegraphics[width=\textwidth]{golden-mgraham-zvsmass}

		\includegraphics[width=\textwidth]{golden-mgraham-norm-36}
	\end{columns}
\end{frame}

\begin{frame}{Research plan}
	\begin{itemize}
		\item 50\% ATLAS, 50\% CEPC
		\item ATLAS: Higgs analysis, Phase II inner tracker
		\item CEPC: tracker studies and development
	\end{itemize}
\end{frame}

%\begin{frame}{Producing heavy photons}
%\begin{columns}
%\column{0.65\textwidth}
%\begin{itemize}
%\item Similar to bremsstrahlung: $e^-$ (1.1, 2.2 and 6.6 GeV) on high-Z fixed target
%\end{itemize}
%\column{0.35\textwidth}
%\includegraphics[width=0.8\textwidth]{prod_diagram}
%\end{columns}
%\begin{center}
%\includegraphics[width=0.65\textwidth]{production}
%\end{center}
%\begin{itemize}
%\item $A'$ carries most of incident $e^-$ energy (unlike $\gamma$ bremsstrahlung)
%\item Pairs from $A'$ decay are produced along beam with some decay length and small opening angle
%% \begin{itemize}
%% 	\item Track pairs, find vertex and invariant mass
%% \end{itemize}
%\end{itemize}
%\end{frame}
%
%\begin{frame}{Reach}
%\begin{columns}
%\column{0.5\textwidth}
%\begin{itemize}
%\item Bump hunt: look for a peak in pair invariant mass
%\item Vertexing (my thesis topic): look for pairs originating downstream of the target
%\begin{itemize}
%\item Requires a tracker close to the target for $\sim$mm vertex resolution
%\end{itemize}
%\item HPS probes a large unexplored region of the parameter space
%\begin{itemize}
%\item Bump-hunt region is under pressure (Babar result not shown in plot); vertexing is our strength
%\end{itemize}
%\end{itemize}
%\column{0.5\textwidth}
%\includegraphics[width=\textwidth]{reach.pdf}
%\end{columns}
%\end{frame}
%
%\begin{frame}{The HPS detector}
%\begin{center}
%\includegraphics[width=0.8\textwidth]{svt.pdf}
%\end{center}
%\begin{columns}
%\column{0.5\textwidth}
%\begin{itemize}
%\item Thin (0.125\% or 0.25\% $X_0$) tungsten target
%\item Silicon microstrip tracker in dipole magnet for measurement
%\item PbWO$_4$ calorimeter for trigger
%\end{itemize}
%\column{0.5\textwidth}
%\includegraphics[width=\textwidth]{hps_setup.pdf}
%\end{columns}
%\end{frame}
%
%\begin{frame}{HPS schedule}
%\begin{itemize}
%\item Schedule has been controlled by CEBAF schedule:
%\begin{itemize}
%\item Test run in May 2012 before shutdown for 12 GeV upgrade: photon beam only, good for testing detector performance but no physics
%\item Commissioning November-December 2014, physics running in spring 2015
%\item Further running planned, but thesis will be written on 2015 data
%\end{itemize}
%\item We are pushing to publish a result within a year after we get data
%\end{itemize}
%\end{frame}
%
%\begin{frame}{My role in HPS}
%\begin{itemize}
%\item SVT mechanics
%\begin{itemize}
%\item Testing, disassembly and re-QA of test run SVT
%\item Assembly and survey of new SVT
%\end{itemize}
%\item Software
%\begin{itemize}
%\item Readout simulation for ECal and SVT
%\item Trigger studies and simulation
%\item Hit time reconstruction in SVT
%\item Bulk production of MC for mock data challenge
%\end{itemize}
%\item Taking shifts
%\end{itemize}
%\end{frame}
%
%\begin{frame}{Work with test run SVT}
%\begin{columns}
%\column{0.6\textwidth}
%\begin{itemize}
%\item Developed calibrations for test run SVT
%\item Helped set up power/cooling/dry air for DAQ tests of the SVT last year
%\item Disassembled SVT; repeating QA for all half-modules
%\end{itemize}
%\column{0.4\textwidth}
%\includegraphics[width=\textwidth]{svt_tim.jpg}
%
%\includegraphics[width=\textwidth]{disassembled.jpg}
%\end{columns}
%\end{frame}


%\begin{frame}{Reconstruction, in brief (SVT only)}
%\begin{itemize}
%\item Hit time reconstruction of individual strip hits
%\item Clustering to form strip clusters
%\item Track finding to form tracks with 5 or 6 stereo hits
%\item Track refit using GBL
%\item Vertexing using Billoir algorithm
%\item Result: $e^+e^-$ pairs with 2-track vertex and invariant mass
%\end{itemize}
%\end{frame}
%
%\begin{frame}{Vertex search}
%\begin{itemize}
%\item Signal: small number of events with detached vertices and a single mass
%\begin{itemize}
%\item Parameters: mass, production cross-section, lifetime
%\item In minimal model (100\% branching ratio to $e^+e^-$), cross-section and lifetime are both determined by $\alpha'/\alpha$
%\end{itemize}
%\item Background: QED tridents with finite vertex resolution (with non-Gaussian tails) and smooth mass distribution
%\begin{itemize}
%\item Mix of Bethe-Heitler and radiative tridents
%\item Beam-gas interactions possible but expected to be rare
%\end{itemize}
%\end{itemize}
%\end{frame}
%
%\begin{frame}{Resolutions and tails}
%\begin{itemize}
%\item We care about mass resolution and vertex resolution
%\item Mass resolution depends on angular and momentum resolution
%\begin{itemize}
%\item Position resolution at target tells us about angular resolution
%\item e-W elastic scattering gives momentum resolution near beam energy
%\item M\o ller scattering gives angular and momentum resolution across momentum range
%\end{itemize}
%\item Vertex resolution depends on angular resolution, but non-Gaussian tails of the distribution are a big deal
%\begin{itemize}
%\item Mishits: wrong L1 hit is added to the track (MS makes the ```bad'' hit a better fit than the ``good'' one), pulls track
%\item Kinks: large-angle scatter in early layer
%\end{itemize}
%\end{itemize}
%\end{frame}
%
%\begin{frame}{Event cuts}
%\begin{itemize}
%\item Basic event cuts:
%\begin{itemize}
%\item Track quality (track fit and time $\chi^2$, ECal track match)
%\item Pair quality: (vertex fit $\chi^2$, $E_++E_-\approx E_{beam}$)
%\item Kinematic cuts to reduce Bethe-Heitler tridents
%\end{itemize}
%\item Important to reduce vertex tails (may or may not be useful for other analyses):
%\begin{itemize}
%\item Track quality: layer 1 isolation cut (mishits), kink cut (large-angle scatters)
%\end{itemize}
%\end{itemize}
%\end{frame}
%
%\begin{frame}{Blinding}
%\begin{itemize}
%\item Hidden signal box: cut out events with vertex Z above some limit
%\begin{itemize}
%\item Box should be looser than expected signal region, but tight enough that background and resolutions can be characterized before unblinding
%\item Must be able to kill most backgrounds without looking in the box
%\end{itemize}
%\item Subsample: develop analysis on a fraction of the data
%\begin{itemize}
%\item Bump hunt will probably use this approach
%\end{itemize}
%\end{itemize}
%\end{frame}
%
%\begin{frame}{Analysis}
%\begin{center}
%\includegraphics[width=0.5\textwidth]{toy}
%\end{center}
%\begin{itemize}
%\item Moving mass window
%\item Profile likelihood
%\item Discovery/setting limits
%\end{itemize}
%\end{frame}
%
%
%\begin{frame}{Fitting the signal}
%\begin{itemize}
%\item A complete fit of the background is hard and unnecessary; use a scanning window
%\item Scan through the signal parameters (mass, lifetime); only fit data within a mass window and above some cutoff Z
%\item Signal shape is completely determined by mass, lifetime, and the known mass resolution; background distribution can be fit with an ansatz
%\item Use a mass window larger than mass resolution (to capture all signal events), but small enough that background (i.e. trident rate and vertex resolution as function of mass) can be fit well
%\item Use unbinned likelihood fit to use full event-by-event vertex resolution information
%\end{itemize}
%\end{frame}
%
%\begin{frame}{Profile likelihood}
%$$\lambda(\mu)=\frac{L(\mu,\hat{\hat{\theta}})}{L(\hat{\mu},\hat{\theta})}$$
%\begin{itemize}
%\item Do a likelihood fit to the data in the scanning window, optimizing the background parameters $\theta$ as a function of the signal strength (production rate) parameter $\mu$
%\item Profile likelihood ratio: ratio of the likelihood at each $\mu$ to the likelihood at the best fit $\hat{\mu}$
%\item $\lambda(0)$ gives the local p-value for discovery (correct for look-elsewhere effect to get global p-value)
%\item Setting limits: we can calculate the p-value for the $\mu$ corresponding to 100\% branching ratio
%\end{itemize}
%\end{frame}

\end{document}

