New Exclusion Limits on Dark Gauge Forces from Proton Bremsstrahlung in Beam-Dump Data (1311.3870v1)

Abstract: We re-analyze published proton beam dump data taken at the U70 accelerator at IHEP Serpukhov with the $\nu$-calorimeter I experiment in 1989 to set mass-coupling limits for dark gauge forces. The corresponding data have been used for axion and light Higgs particle searches in Refs. \cite{Blumlein:1990ay,Blumlein:1991xh} before. More recently, limits on dark gauge forces have been derived from this data set, considering a dark photon production from $\pi^0$-decay \cite{Blumlein:2011mv}. Here we determine extended mass and coupling exclusion bounds for dark gauge bosons ranging to masses $m_{\gamma'}$ of 624 MeV at admixture parameters $\varepsilon \simeq 10^{-6}$ considering high-energy Bremsstrahlung of the $U$-boson off the initial proton beam and different detection mechanisms.

• The paper presents a detailed analysis using the ν-CAL I beam dump dataset to set exclusion limits on dark gauge bosons.
• It utilizes the Fermi-Williams-Weizsäcker method to derive production cross-sections for U-bosons, extending bounds up to 624 MeV.
• The study refines detection strategies for dark gauge forces and provides a foundation for future explorations beyond the Standard Model.

New Exclusion Limits on Dark Gauge Forces from Proton Bremsstrahlung in Beam-Dump Data

The research paper titled "New Exclusion Limits on Dark Gauge Forces from Proton Bremsstrahlung in Beam-Dump Data," authored by Johannes Blümlein and Jürgen Brunner, explores the parameters affecting dark gauge forces, specifically through the lens of proton beam dump experiments conducted at the U70 accelerator at IHEP Serpukhov. This paper utilizes the dataset from the $\nu$-calorimeter I experiment from 1989, previously employed for searches involving axions and light Higgs particles.

Analytical Framework

The investigation focuses on setting exclusion limits for dark gauge bosons generated by high-energy Bremsstrahlung of $U$-bosons from an initial proton beam. The paper extends mass and coupling exclusion bounds for dark gauge bosons up to masses $m_{\gamma'}$ of 624 MeV at mixing parameters $\varepsilon \simeq 10^{-6}$, thereby offering a more comprehensive parameter space. The re-analysis employs a meticulous approach to re-examine experimental conditions and constraints, leveraging existing theoretical frameworks and experimental data.

Methods and Findings

The production of dark gauge bosons (referred to as $\gamma'$) is primarily investigated through the process of Bremsstrahlung, wherein a $U_1'$-boson, $\gamma'$, is emitted off the incoming proton. The cross-section for the production of $\gamma'$ in the high-energy proton beam dump is derived, utilizing parameterizations of measured distributions and the Fermi-Williams-Weizsacker method for detailed computations.

Significant attention is given to the theoretical formulation of the production cross-section, which is constrained and validated through specific energy and momentum transfer conditions that ensure the appropriateness of the Fermi-Williams-Weizsacker approximation in this experimental setting. The paper comprehensively revamps the understanding of production cross-sections by considering arbitrary boson masses and polarization effects.

Detection and Experimental Setup

The detection strategy for the $\gamma'$ particles focuses on their decay channels into $e^+ e^-$ and $\mu^+ \mu^-$. The paper outlines the branching ratios and decay probabilities within the experimental detector's fiducial volume. The types of particles generated from these decays are categorized and analyzed, providing insight into both direct and indirect detection scenarios.

The experimental setup of the $\nu$-CAL I detector is revisited, highlighting its modular structure that aids in detecting decay events and electromagnetic showers. The constraints derived from experimental data, such as the number of protons on target and detection efficiencies, are integrated into predictive models to establish exclusion limits on $\epsilon$ within specified mass ranges of $\gamma'$.

Numerical Analysis and Exclusion Limits

The numerical results, expressed in terms of expected signal events, are presented across various scenarios of $\epsilon$ and $m_{\gamma'}$. These results are crucial as they help delineate the regions in the parameter space that can be excluded based on the confidence interval approaches. The exclusion regions thus established extend the boundaries set by previous experimental constraints—proposing significant implications for further experimental searches and theoretical models, contributing to the broader understanding of dark photon interactions and the hidden sector in particle physics.

Implications and Future Work

The paper emphasizes the importance of using beam dump data in identifying the dark photon parameter space. Moreover, despite being slightly dated, the methods and findings serve as a foundation for future experiments and theoretical models aiming to explore dark sectors, thereby enriching our understanding of possible new forces beyond the Standard Model.

In conclusion, this research piece not only refines existing methodologies and exclusion limits but also offers a powerful framework for future explorations in dark matter physics, potentially guiding experimental strategies in upcoming particle physics investigations.