arXiv subjects

Shanzhen Chen

Publications and source records attributed to Shanzhen Chen.

12 recordsLinked to original sources

arXiv2026

A Telescope System for Charge and Position Measurement of High Energy Nuclei

A high-granularity telescope system with a large sensitive area and low material budget has been developed for high-energy heavy ion beam tests. The telescope consists of nine layers of silicon microstrip detectors (SSDs), whose performance was validated through a heavy ion beam test at the CERN SPS. A hybrid machine learning algorithm is proposed to address the challenges of nuclear charge measurement with SSDs. The system achieves a spatial resolution of $\mathcal{O}(1) \,$\SI{}{\micro\metre} and a charge resolution better than 0.16 charge units for nuclei from $Z = 1$ to $Z = 29$, with a sensitive area of $8 \times 8 \, \mathrm{cm}^2$. To the best of our knowledge, this represents the most precise charge and spatial resolution simultaneously achieved by a silicon telescope to date.

physics.ins-det↗

arXiv2026

Beam Test Characterization of Silicon Microstrip Detector Flight-Model Ladders for the AMS-02 Upgrade

The AMS-02 experiment plans to install a new silicon microstrip tracker layer (Layer-0) on top of the existing detector, increasing the cosmic-ray acceptance by a factor of 3. Layer-0 employs a design in which multiple silicon microstrip detectors (SSDs) are connected in series to form long detector ladders. We present a detailed performance study of the flight-model ladders using a 350~GeV mixed hadron beam at the CERN SPS. The study focuses on the following aspects: (i) the performance of ladders with different numbers of SSDs, for which the intrinsic spatial resolution at normal incidence varies from $9.5~\mu\mathrm{m}$ to $11.4~\mu\mathrm{m}$ for ladders composed of 8 to 12 SSDs; (ii) the response consistency for particles impacting on the \emph{Head} and \emph{Tail} regions of the ladder; and (iii) the dependence of the detector performance on the particle incidence angle.

physics.ins-det↗

arXiv2025

Prospect for measurement of CP-violating parameters of $B_s^0 \to \phi\gamma$ at the Tera Z factory

$b \to s\gamma$ transition is a critical flavor-changing neutral current (FCNC) process that could be used to probe CP violation (CPV) and new physics (NP). We quantify the anticipated precision for measuring $B_s^0 \to \phi\gamma$ at the CEPC Z pole operation, showing that the relative statistical uncertainty could be as low as 0.16\%, improved by approximately two orders of magnitude compared to existing measurements. Additionally, we perform a time-dependent analysis of the $B_s^0 \to \phi\gamma$ decay, accounting for $B_s^0/\bar{B}_s^0$ mixing extract the mixing-induced and CP-violating parameters $\boldsymbol{\mathcal{A}_{\phi\gamma}^\Delta}$, $\boldsymbol{C_{\phi\gamma}}$ and $\boldsymbol{S_{\phi\gamma}}$. Using central value from LHCb measurement as input, we evaluate the anticipated accuracy of measurements of these parameters. The projected statistical uncertainties are $\sigma_{A_{\phi\gamma}^{\Delta}{}^{\text{stat}}} = 0.021$, $\sigma_C^{\text{stat}} = 0.0092$ and $\sigma_S^{\text{stat}} = 0.0096$, and the systematic uncertainties are $\sigma_{A_{\phi\gamma}^{\Delta}{}^{\text{syst}}} = 0.035$, $\sigma_C^{\text{syst}} = 0.0027$ and $\sigma_S^{\text{syst}} = 0.0064$. Furthermore, the 1$\sigma$ sensitivity boundaries for NP in this study are found to be $\mathcal{A}_{\phi\gamma}^\Delta < -0.05$ or $\mathcal{A}_{\phi\gamma}^\Delta > 0.15$, $\mathcal{C}_{\phi\gamma} < -0.02$ or $\mathcal{C}_{\phi\gamma} > 0.04$, and $\mathcal{S}_{\phi\gamma} < -0.04$ or $\mathcal{S}_{\phi\gamma} > 0.04$. We also conduct a relevant detector optimization study by establishing the correlation between the anticipated precision and the intrinsic resolution of the ECAL, as well as the performance of the PID system.

hep-ex↗

arXiv2025

New Physics Search at the CEPC: a General Perspective

The Circular Electron-Positron Collider (CEPC), a proposed next-generation Higgs factory, provides new opportunities to explore physics beyond the Standard Model (SM). With its clean electron-positron collision environment and the ability to collect large samples of Higgs, W, and Z bosons, the CEPC enables precision measurements and searches for new physics. This white paper outlines the CEPC's discovery potential, including studies of exotic decays of the Higgs, Z, and top quarks, dark matter and dark sector phenomena, long-lived particles, supersymmetry, and neutrino-related signatures. Advanced detector technologies and reconstruction techniques, such as one-to-one correspondence reconstruction and jet origin identification, significantly improve sensitivity to rare and weakly interacting processes. The CEPC is particularly well suited to probe the electroweak phase transition and test models of electroweak baryogenesis and dark sector interactions. In addition, global fit analyses highlight the CEPC's complementary role in constraining a wide range of new physics scenarios. These features position the CEPC as a powerful tool for exploring the next frontier in fundamental particle physics in the post-Higgs discovery era.

hep-ex↗

arXiv2025

Prospect for measurement of $C\!P$-violating observables in $B_s^0 \to D_s^{\mp} K^{\pm}$ decays at a future ${Z}$ factory

A precise determination of the CKM angle $\gamma$ from $B_s^0$ oscillations in $B_s^0 \to D_s^\mp K^\pm$ decays offers a critical test of the Standard Model and probes for new physics. We present a comprehensive study on the prospects of measuring $\gamma$ at a future Tera-$Z$ factory, utilizing the baseline detector concept of the Circular Electron Positron Collider (CEPC). A two-dimensional simultaneous fit framework, incorporating flavor tagging, decay time resolution modeling, and acceptance corrections, is developed using full Monte Carlo simulations of $B_s^0 \to D_s^\mp \left(\to K^\mp K^\pm \pi^\mp\right) K^\pm$ decays and inclusive background processes. The effective flavor tagging power reaches $23.6\%$, while the decay time resolution is determined to be $26\mathrm{\,fs}$. Projecting to full statistics of signal events across three dominant $D_s^-$ decay channels, we estimate a statistical precision of $\sigma(\gamma) = 0.69^\circ$, which corresponds to $4.1$ Tera-$Z$ boson equivalent data. This study establishes the feasibility of sub-degree level $\gamma$ measurements at a $Z$-factory, highlighting its unique advantages in time-dependent $C\!P$ violation studies through ultra-precise vertexing and background suppression capabilities.

hep-ex↗

arXiv2024

Flavor Physics at the CEPC: a General Perspective

We discuss the landscape of flavor physics at the Circular Electron-Positron Collider (CEPC), based on the nominal luminosity outlined in its Technical Design Report. The CEPC is designed to operate in multiple modes to address a variety of tasks. At the $Z$ pole, the expected production of 4 Tera $Z$ bosons will provide unique and highly precise measurements of $Z$ boson couplings, while the substantial number of boosted heavy-flavored quarks and leptons produced in clean $Z$ decays will facilitate investigations into their flavor physics with unprecedented precision. We investigate the prospects of measuring various physics benchmarks and discuss their implications for particle theories and phenomenological models. Our studies indicate that, with its highlighted advantages and anticipated excellent detector performance, the CEPC can explore beauty and $\tau$ physics in ways that are superior to or complementary with the Belle II and Large-Hadron-Collider-beauty experiments, potentially enabling the detection of new physics at energy scales of 10 TeV and above. This potential also extends to the observation of yet-to-be-discovered rare and exotic processes, as well as testing fundamental principles such as lepton flavor universality, lepton and baryon number conservation, etc., making the CEPC a vibrant platform for flavor physics research. The $WW$ threshold scan, Higgs-factory operation and top-pair productions of the CEPC further enhance its merits in this regard, especially for measuring the Cabibbo-Kobayashi-Maskawa matrix elements, and Flavor-Changing-Neutral-Current physics of Higgs boson and top quarks. We outline the requirements for detector performance and considerations for future development to achieve the anticipated scientific goals.

hep-ex↗

arXiv2023

Heavy Flavour Physics and CP Violation at LHCb: a Ten-Year Review

Heavy flavour physics provides excellent opportunities to indirectly search for new physics at very high energy scales and to study hadron properties for deep understanding of the strong interaction. The LHCb experiment has been playing a leading role in the study of heavy flavour physics since the start of the LHC operations about ten years ago, and made a range of high-precision measurements and unexpected discoveries, which may have far-reaching implications on the field of particle physics. This review highlights a selection of the most influential physics results on CP violation, rare decays, and heavy flavour production and spectroscopy obtained by LHCb using the data collected during the first two operation periods of the LHC. The upgrade plan of LHCb and the physics prospects are also briefly discussed.

hep-ex↗

arXiv2022

Prospects for $B^0_{(s)}\toπ^0π^0$ and $B^0_{(s)}\toηη$ modes and corresponding $CP$ asymmetries at Tera-$Z$

The physics potential of measuring $B^0_{(s)}\toπ^0π^0$ and $B^0_{(s)}\toηη$ decays via four-photon final states at Tera-$Z$ phase of CEPC or FCC-ee is investigated in this paper. We propose an electromagnetic calorimeter (ECAL) with both high energy resolution and excellent separation power to efficiently reconstruct $π^0$ and $η$ from hadronic final states with high photon multiplicity. The resulting $B$-meson mass resolution is approximately 30 MeV, allowing 3 $σ$ separation between $B^0$ and $B_s^0$. With the assistance of the $b$-jet tagging, the relative sensitivities to $B^0\toπ^0π^0$, $B^0_s\toπ^0π^0$, $B^0\toηη$, and $B^0_s\toηη$ signal strengths at Tera-$Z$ are projected as 0.45%, 4.5%, 18%, and 0.95%, respectively. Their dependence on various detector performances is also discussed. In addition, $B^0\toπ^0π^0$ and its two isospin-related modes are paid special attention due to their roles in the determination of the CKM angle $α$ ($ϕ_2$). The anticipated precisions of their branching-ratio and $CP$-asymmetry measurements at Tera-$Z$ are evaluated. We show that the measurement of the time-integrated $B^0\toπ^0π^0$ $CP$ asymmetry at Tera-$Z$ is complementary to $B$-factory ones. The precision on $α$ combining $Z$- and $B$-factory results reaches $0.4^\circ$, lower than the systematic uncertainties attached to isospin breaking.

hep-ph↗

arXiv2022

Requirement analysis for dE/dx measurement and PID performance at the CEPC baseline detector

The Circular Electron-Positron Collider (CEPC) can be operated not only as a Higgs factory but also as a Z-boson factory, offering great opportunities for flavor physics studies where Particle Identification (PID) is critical. The baseline detector of the CEPC could record TOF and dE/dx information that can be used to distinguish particles of different species. We quantify the physics requirements and detector performance using physics benchmark analyzes with full simulation. We conclude that at the benchmark TOF performance of $50\,$ps, the dE/dx resolution should be better than 3% for incident particles in the barrel region with a relevant energy larger than $2\, $GeV/c. This performance leads to an efficiency/purity of $K^{\pm}$ identification 97%/96%, $D^0\to π^+K^-$ reconstruction 68.19%/89.05%, and $ϕ\to K^+K^-$ reconstruction 82.26%/77.70%, providing solid support for relevant CEPC flavor physics measurements.

physics.ins-det↗

arXiv2017

On model-independent searches for direct CP violation in multi-body decays

Techniques for performing model-independent searches for direct CP violation in three and four-body decays are discussed. Comments on the performance and the optimisation of a binned chisquare approach and an unbinned approach, known as the energy test, are made. The use of the energy test in the presence of background is also studied. The selection and treatment of the coordinates used to describe the phase-space of the decay are discussed. The conventional model-independent techniques, which test for P-even CP violation, are modified to create a new approach for testing for P-odd CP violation. An implementation of the energy test using GPUs is described.

hep-ex↗

arXiv2015

Search for $CP$ violation in $D^0\rightarrow π^-π^+π^0$ decays at LHCb

The LHCb experiment has recorded the world's largest sample of charmed meson decays. This paper presents a study of a $D^0$ meson decaying into a final state containing a neutral pion in LHCb. The search for $CP$ violation exploits a novel model-independent unbinned technique to assign a $p$-value for the no $CP$ violation hypothesis. With a data sample size exceeding that of previous measurements by almost an order of magnitude the world's best sensitivity is obtained. The $p$-value of no CP violation hypothesis given data of $D^0\rightarrow π^-π^+π^0$ decay analysed is found to be $(2.6 \pm 0.5)\times 10^-2$.

hep-ex↗

arXiv2013

Can LHCb Study Three Body Decays with Neutrals?

We present the first attempt to use a new method to measure CP violation in Dalitz plots. This method is unbinned, model independent and has a greater sensitivity to CP violating effects than binned methods. Preliminary studies have been made using the three-body decays $D^0 \rightarrow K_\mathrm{S}^0 h^+ h^-$ and $D^0 \rightarrow h^+ h^- π^0$, which are especially challenging since there is one neutral particle in each of the final states. An attempt to visualise where CP violation occurs in Dalitz plots is also presented.

hep-ex↗