Vitor Shen
Exploring hadrons.

ϕ(2170) feasibility at CBM

CBM (Compressed Baryonic Matter) is a fixed-target experiment at FAIR designed to explore strongly interacting matter at high baryon densities. At SIS100, its heavy-ion programme covers roughly 2–11 GeV per nucleon for the heaviest beams, with design interaction rates up to 10 MHz, depending on the measurement. SIS100 also provides proton beams up to 29 GeV kinetic energy.

My project investigates exclusive proton–proton (pp) reactions. The feasibility studies span centre-of-mass energies √s ≈ 4.05–7.61 GeV, with current full-detector simulations focused on a 29 GeV proton beam. High interaction rates offer opportunities to investigate rare hadronic channels, provided reconstruction and background suppression are effective.

Could CBM help us study strange counterparts of exotic XYZ states? This project explores how ϕ(2170) candidates could be reconstructed from their decay products in proton–proton collisions.

I study ϕπ⁺π⁻, ϕf₀(980), and K⁺K⁻π⁺π⁻ channels using Pluto generation, HepFastSim energy scans, and full CBMRoot simulation. Current work combines six-track reconstruction, TOF particle identification, kinematic fitting, and targeted and inclusive background studies to evaluate efficiency, mass resolution, and prospects for sensitivity.

Cascade hyperon reconstruction

MSc thesis: Realistic Track and Event Reconstruction of the Ξ Hyperons at PANDA

PANDA is designed to study the strong interaction using antiprotons with momenta of 1.5–15 GeV/c incident on a fixed target at FAIR. Antiproton–proton annihilation can produce hyperon–antihyperon pairs, providing access to the physics of baryons containing strange quarks. Sequential weak decays of Ξ hyperons create displaced decay vertices, making realistic track finding and event reconstruction essential.

My MSc thesis studied the full exclusive reaction p̄p → Ξ̄⁺Ξ⁻ → Λ̄π⁺Λπ⁻ → p̄π⁺π⁺pπ⁻π⁻ near its production threshold. I generated events with EvtGen in PandaRoot and evaluated realistic reconstruction in both PANDA’s target and forward spectrometers.

I compared Barrel, Cell, Hough, and Apollonius-triplet tracking approaches, including longitudinal-momentum reconstruction and forward tracking. The evaluation covered hit efficiency and purity, track-finding efficiency versus angle and momentum, and momentum resolution, with primary and secondary tracks examined separately.

At event level, I studied reconstruction efficiency versus antiproton beam momentum near threshold using full Monte Carlo truth matching. This isolated the tracking and decay-topology performance; subsequent event selection and physics analysis were left for future work.

Fast-neutron detector response & imaging

Neutrons carry no electric charge, so their detection relies on nuclear interactions that produce detectable secondary particles. Understanding how those interactions translate into detector signals is important for measuring neutrons in nuclear-physics experiments. This project used detector-response simulations to connect incident neutron energies with the response of individual detector units and arrays.

BSc thesis: Simulation of Detector Response for Neutron at High and Intermediate Energy. Using Geant4 and ROOT, I compared NE213 and NE230 liquid scintillators across four cylindrical detector geometries and seven neutron energies from 5 to 100 MeV. I analysed energy-deposition spectra, detection efficiency with a threshold, and the energy and angular distributions of escaping neutrons.

For neutron transmission imaging, I modelled a 40 × 40 array of NE213 detector units and simulated objects made of iron, lead, and aluminium. Small translations of the whole array enabled finer image sampling—from 40 × 40 to 200 × 200 pixels—and improved image definition in the simulations without reducing the physical detector-unit size.

Awarded Tsinghua OAPS and the Beijing Outstanding Undergraduate Thesis Award (2021).

Baryon spectroscopy at GlueX

Searches for N* and Y* resonances in the photoproduced K⁺π⁰Λ final state. Work included Python analysis pipelines, event selection, MC–reconstruction matching, and purity, efficiency, and resolution studies.

Symbolic amplitude models

With R. E. de Boer: Symbolic Amplitude Models with N* Resonances at GlueX. Prototypes using SymPy, QRules, and AmpForm automate decay-chain construction and visualization.

Amplitude Analysis 101

With R. E. de Boer: a tutorial-style technical report covering amplitude and decay-chain modelling, toy-data generation, and unbinned likelihood fitting with scientific Python.

Hyperon-pair event generator

Development of an event generator for antihyperon-hyperon pair production in antiproton-proton collisions.

A separate student project preceding my MSc thesis, focused on Monte Carlo event generation for hyperon physics. I developed a lightweight ROOT-based generator for antiproton–proton reactions, demonstrated with Λ̄Λ production and the subsequent decays into an antiproton–pion pair and a proton–pion pair.

The prototype supports quick tests of models and formalisms on simulated events. I benchmarked final-state angular distributions using four-momentum relations between the reference frames of parent and daughter particles.