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

J. Blümlein, J. Brunner

TL;DR

This work reanalyzes 1989 proton beam-dump data from the ν-calorimeter I at IHEP Serpukhov to constrain dark U(1)' gauge bosons (γ') via γ'-Bremsstrahlung from the proton beam. It develops a production framework using a generalized WW approximation, accounts for γ' decays into e^+e^−, μ^+μ^−, and hadrons, and includes pair-production detection channels for m_{γ'}<2m_e, within a carefully modeled detector geometry. By applying the CLs formalism to the observed electron and muon signatures and backgrounds, the study derives exclusion regions in the m_{γ'}–ε plane extending up to m_{γ'} ≈ 0.63 GeV at ε ~ 10^{-6}, complementing π^0-decay based limits. The results broaden the landscape of viable dark-photon parameter space and demonstrate the continued value of archival beam-dump data for new beyond-Standard-Model searches.

Abstract

We re-analyze published proton beam dump data taken at the U70 accelerator at IHEP Serpukhov with the $ν$-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 $π^0$-decay \cite{Blumlein:2011mv}. Here we determine extended mass and coupling exclusion bounds for dark gauge bosons ranging to masses $m_{γ'}$ 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.

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

TL;DR

This work reanalyzes 1989 proton beam-dump data from the ν-calorimeter I at IHEP Serpukhov to constrain dark U(1)' gauge bosons (γ') via γ'-Bremsstrahlung from the proton beam. It develops a production framework using a generalized WW approximation, accounts for γ' decays into e^+e^−, μ^+μ^−, and hadrons, and includes pair-production detection channels for m_{γ'}<2m_e, within a carefully modeled detector geometry. By applying the CLs formalism to the observed electron and muon signatures and backgrounds, the study derives exclusion regions in the m_{γ'}–ε plane extending up to m_{γ'} ≈ 0.63 GeV at ε ~ 10^{-6}, complementing π^0-decay based limits. The results broaden the landscape of viable dark-photon parameter space and demonstrate the continued value of archival beam-dump data for new beyond-Standard-Model searches.

Abstract

We re-analyze published proton beam dump data taken at the U70 accelerator at IHEP Serpukhov with the -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 -decay \cite{Blumlein:2011mv}. Here we determine extended mass and coupling exclusion bounds for dark gauge bosons ranging to masses of 624 MeV at admixture parameters considering high-energy Bremsstrahlung of the -boson off the initial proton beam and different detection mechanisms.

Paper Structure

This paper contains 6 sections, 28 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Production Cross Section
  3. The Detection Processes
  4. The Experimental Setup and Data Taking
  5. Results
  6. Conclusions

Figures (5)

  • Figure 1: Flux of produced $\gamma'$-particles within the angular acceptance of the detector per beam proton as function of their energy in the laboratory frame. The black, red, green, blue and magenta lines correspond to $\gamma'$ with masses between 0 and 800 MeV in steps of 200 MeV for $\epsilon = 1$.
  • Figure 2: Branching ratio of $\gamma'$ into $e^+e^-$ (red), $\mu^+\mu^-$ (blue) and hadrons (black).
  • Figure 3: Expected $\gamma'$-events in the electron channel (left) and muon channel (right). Color bands (left) per decade from $10^7$ events (yellow) to one event (dark blue) and (right) per semi-decade from 30 events (green) to one event (dark blue).
  • Figure 4: Expected $\gamma'$ events from pair production. Color scale in $\log_{10}$ from $10^9$ events (red) to one event (dark blue).
  • Figure 5: Comparison of the present exclusion bounds (red area and lines) with other exclusion limits (grey area and lines) derived from data on the anomalous magnetic moments of the electron and muon Pospelov:2008xx, $\Upsilon(3S)$ decays UPS, Belle BELLE, $J/\psi$-decays JPSI, $K$-decays Beranek:2012ey, KLOE-2 Babusci:2012cr, A1 Merkel:2011ze, APEX Abrahamyan:2011gv, HADES Agakishiev:2013jla, E774 E774, E141 E141, E137 E137Essig:2010xa, Orsay Davier:1989wz, KEK Konaka:1986cb, NOMAD and PS191 Gninenko:2011uv, CHARM Gninenko:2012eq, SINDRUM Gninenko:2013sr, WASA Adlarson:2013eza and $\nu$-CAL I for $\pi_0$-decay Blumlein:2011mv (blue line).${}^1$