Detection prospects of long-lived quirk pairs at the LHC far detectors

We examine the sensitivity reaches of several LHC far detectors, such as FASER2, MATHUSLA, ANUBIS, SND@LHC, and FACET, to five simplified quirk scenarios. We include the next-to-leading order QCD corrections in our simulation of quirk events, which enhance the total production rate and increase the fraction of events in the forward direction for most cases. We calculate the timescales for the quirk pair to lose energy through radiations and for the quirk pair annihilation. Our results show that these far detectors can offer promising probes to the quirk scenario, complementing the searches at the main detectors. Especially, FACET and FASER2 detectors can surpass the majority of searches conducted at the LHC main detector, with the exception of the HSCP search, for the color-neutral quirk $\mathcal{E}$.

Figure 1

Left panel: the LO and NLO total production cross sections for different quirk scenarios. We take $\kappa =1$ and $m_{W_R}=2\mathrm{TeV}$ for the $W_R$ scenario. The middle and right panels show the fraction of events that have $\theta (\mathcal{Q}\overline{\mathcal{Q}})<0.002$ and $\theta (\mathcal{Q}\overline{\mathcal{Q}})\in [0.3,0.9]$ for varying quirk mass in all scenarios.

Figure 2

Normalized distributions of the boost factor for events in FASER2 detector (left) and the distribution of the velocity for events in the MATHUSLA detector (right). For the $W_R$ scenario, we have chosen $m_{W_R}=2000\mathrm{GeV}$.

Figure 3

Ground state wave function at origin.

Figure 4

Timescale for the energy loss through radiation and for the decay of each channel. Relevant parameters are set as $m_{\mathcal{Q}}=100\mathrm{GeV}$, $\epsilon =0.1$, and ${\epsilon }^{\prime }=0$.

Figure 5

Lifetime of the $\tilde{\mathcal{V}}-\tilde{\mathcal{E}}$ bound state in the $W_R$ scenario. The $\kappa =1$ has been set.

Figure 6

The schematic diagram illustrates the locations and effective volumes of the detectors. The SND@LHC and FASER2 detectors are enlarged by a factor of 25 for better visibility. For the FACET detector, only the radius is scaled up by the same factor.

Figure 7

The panels show the fractions of quirk events, as a function of quirk mass and confinement scale, that have different signatures at MATHUSLA and FASER2. The upper panels show the results for $\mathcal{E}$, while the lower panels show the results for $\mathcal{D}$. From left to right: the fraction of events that travel through the MATHUSLA, decay inside MATHUSLA, travel through the FASER2, and decay inside FASER2. Relevant parameters are set as $\epsilon =0.1$ and ${\epsilon }^{\prime }=0$.

Figure 8

The panels show the fraction of quirk events in the $W_R$ scenario, as a function of quirk mass and confinement scale, that can travel through the FASER2. The $W_R$ mass has been chosen as 2 TeV. From left to right: $\kappa =0.08$ and considering time for annihilation, $\kappa =0.08$ and assuming annihilation is prompt, $\kappa =0.12$ and considering time for annihilation, $\kappa =0.12$ and assuming annihilation is prompt, respectively.

Figure 9

Three-event contours for various quirk scenarios that have quirk going through different detectors ($300{\mathrm{fb}}^{-1}$ luminosity). Uncolored quirks ($\mathcal{E}$, $\tilde{\mathcal{E}}$): Solid curves represent contours based on $\epsilon =0.1$, with colors indicating detectors. Dark shaded areas show $\epsilon$ variability from $0.1/3$ to $3\times 0.1$ (larger $\epsilon$ implies smaller $\mathrm{\Lambda }$), while light shaded areas indicate $\epsilon$ fluctuations from $0.1/10$ to $10\times 0.1$. Colored quirks ($\mathcal{D}$, $\tilde{\mathcal{D}}$): Solid curves (with QCD radiation, ${\epsilon }^{\prime }=0.01$) and dashed curves (without QCD radiation, ${\epsilon }^{\prime }=0$) outline contours, with colors indicating detectors. Shaded areas around solid curves reflect ${\epsilon }^{\prime }$ variability from $0.01/2$ to $2\times 0.01$ (larger ${\epsilon }^{\prime }$ implies smaller $\mathrm{\Lambda }$). For two fermionic quirks ($\mathcal{E}$ and $\mathcal{D}$), the projected bounds from HSCP search [8], mono-jet search [8], coplanar search [20], and out-of-time decay search [17] are shown by orange shaded region, gray shaded region, pink shaded region, and blue shaded region, respectively.

Figure 10

Three-event contours for various quirk scenarios that have quirk decaying inside different detectors ($3000{\mathrm{fb}}^{-1}$ luminosity). Uncolored quirks ($\mathcal{E}$, $\tilde{\mathcal{E}}$): Solid curves represent contours based on $\epsilon =0.1$, with colors indicating detectors. Colored quirks ($\mathcal{D}$, $\tilde{\mathcal{D}}$): Solid curves (with QCD radiation, ${\epsilon }^{\prime }=0.01$) and dashed curves (without QCD radiation, ${\epsilon }^{\prime }=0$) outline contours, with colors indicating detectors.

Figure 11

Three-event contours of the $W_R$ quirk scenarios that have quirk going through different detectors. Solid curves show results including quirk pair annihilation time, while dashed curves exclude it, both at $\epsilon =0.1$. Shaded areas around solid curves reflect $\epsilon$ variability from $0.1/3$ to $3\times 0.1$ (larger $\epsilon$ implies smaller $\mathrm{\Lambda }$). The $W_R$ mass and $\kappa$ are given in the title of each plot.