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| CMS-PAS-EXO-21-007 | ||
| Search for high-mass exclusive diphoton production with tagged protons | ||
| CMS Collaboration | ||
| June 2022 | ||
| Abstract: A search for high-mass exclusive diphoton production via photon-photon fusion with tagged protons is presented. The analysis utilizes 102.7 fb$^{-1}$ of data collected by the CMS and TOTEM Precision Proton Spectrometer in the 2016, 2017, and 2018 LHC runs. Events are selected that have two photons with high transverse momenta that are back-to-back in azimuth and with a large diphoton invariant mass. To remove the dominant backgrounds, tagged final state protons from the event are required to match the kinematics of the final state photons. Only events having opposite-side protons within an asymmetric fractional momentum loss between 0.035 and 0.15 (0.18) for the detectors on the negative (positive) side of CMS are considered. One exclusive diphoton candidate is observed for an expected background of 1.1 events. Limits at 95% confidence level are derived on the four-photon anomalous coupling parameters for $|\zeta_1|$ < 7.3 $\times$ 10$^{-14}$ GeV$^{-4}$, $|\zeta_2|$ < 1.5 $\times$ 10$^{-13}$ GeV$^{-4}$ using an effective field theory. Additionally, axion-like particles are excluded in the mass range of 500 to 2000 GeV. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to PRD. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
The process for diphoton production via photon exchange with intact protons in the final state. Several couplings may enter the four-photon shaded area such as a loop (box) of charged fermions or bosons. The model can be extended with intermediate interactions of new physics objects, such as a loop of a heavy charged particle or an $s$-channel process producing a scalar axion-like resonance that decays into two photons. |
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Figure 2:
A schematic of one side of the PPS detector with respect to the central CMS detector. The 210 and 220 m stations are identified that house the Roman Pot detectors. Timing detector stations are also noted, but they are not used in this analysis. A symmetric set of detectors exists on the other side of CMS as well. |
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Figure 3:
Anomalous Quartic Gauge Coupling (AQGC) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for an AQGC signal using $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$, $\zeta _2 = $ 0 GeV$^{-4}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 3-a:
Anomalous Quartic Gauge Coupling (AQGC) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for an AQGC signal using $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$, $\zeta _2 = $ 0 GeV$^{-4}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 3-b:
Anomalous Quartic Gauge Coupling (AQGC) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for an AQGC signal using $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$, $\zeta _2 = $ 0 GeV$^{-4}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 3-c:
Anomalous Quartic Gauge Coupling (AQGC) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for an AQGC signal using $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$, $\zeta _2 = $ 0 GeV$^{-4}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 3-d:
Anomalous Quartic Gauge Coupling (AQGC) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for an AQGC signal using $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$, $\zeta _2 = $ 0 GeV$^{-4}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 4:
Axion-like particle (ALP) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for ALP signals using $f^{-1} = $ 10$^{-1}$ TeV$ ^{-1}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 4-a:
Axion-like particle (ALP) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for ALP signals using $f^{-1} = $ 10$^{-1}$ TeV$ ^{-1}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 4-b:
Axion-like particle (ALP) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for ALP signals using $f^{-1} = $ 10$^{-1}$ TeV$ ^{-1}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 4-c:
Axion-like particle (ALP) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for ALP signals using $f^{-1} = $ 10$^{-1}$ TeV$ ^{-1}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 4-d:
Axion-like particle (ALP) signal kinematics for the single photon $\eta $ (top left), single photon ${p_{\mathrm {T}}}$ (top right), diphoton acoplanarity (bottom left), diphoton mass (bottom right). The signal simulation shown here is generated with FPMC for ALP signals using $f^{-1} = $ 10$^{-1}$ TeV$ ^{-1}$. The distributions represent the signal sample after undergoing the full CMS detector response. A preselection is applied to these events as described in Section 5. |
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Figure 5:
Kinematic distributions for events passing the $\xi ^{\gamma \gamma} \in $ PPS signal selection. From top to bottom and left to right shows the single photon $\eta $, single photon ${p_{\mathrm {T}}}$, diphoton acoplanarity, diphoton mass, diphoton $\xi ^-$, and diphoton $\xi ^+$. The black dots represent the data, filled histograms represent the SM backgrounds, and the lined histogram represents an AQGC signal having $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\zeta _2 = $ 0 $\times$ 10$^{-13}$ GeV$^{-4}$ multiplied by a factor of 100 for reference. The bottom of each plot shows the ratio of the number of data events to SM background events. |
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Figure 5-a:
Kinematic distributions for events passing the $\xi ^{\gamma \gamma} \in $ PPS signal selection. From top to bottom and left to right shows the single photon $\eta $, single photon ${p_{\mathrm {T}}}$, diphoton acoplanarity, diphoton mass, diphoton $\xi ^-$, and diphoton $\xi ^+$. The black dots represent the data, filled histograms represent the SM backgrounds, and the lined histogram represents an AQGC signal having $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\zeta _2 = $ 0 $\times$ 10$^{-13}$ GeV$^{-4}$ multiplied by a factor of 100 for reference. The bottom of each plot shows the ratio of the number of data events to SM background events. |
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Figure 5-b:
Kinematic distributions for events passing the $\xi ^{\gamma \gamma} \in $ PPS signal selection. From top to bottom and left to right shows the single photon $\eta $, single photon ${p_{\mathrm {T}}}$, diphoton acoplanarity, diphoton mass, diphoton $\xi ^-$, and diphoton $\xi ^+$. The black dots represent the data, filled histograms represent the SM backgrounds, and the lined histogram represents an AQGC signal having $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\zeta _2 = $ 0 $\times$ 10$^{-13}$ GeV$^{-4}$ multiplied by a factor of 100 for reference. The bottom of each plot shows the ratio of the number of data events to SM background events. |
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Figure 5-c:
Kinematic distributions for events passing the $\xi ^{\gamma \gamma} \in $ PPS signal selection. From top to bottom and left to right shows the single photon $\eta $, single photon ${p_{\mathrm {T}}}$, diphoton acoplanarity, diphoton mass, diphoton $\xi ^-$, and diphoton $\xi ^+$. The black dots represent the data, filled histograms represent the SM backgrounds, and the lined histogram represents an AQGC signal having $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\zeta _2 = $ 0 $\times$ 10$^{-13}$ GeV$^{-4}$ multiplied by a factor of 100 for reference. The bottom of each plot shows the ratio of the number of data events to SM background events. |
png pdf |
Figure 5-d:
Kinematic distributions for events passing the $\xi ^{\gamma \gamma} \in $ PPS signal selection. From top to bottom and left to right shows the single photon $\eta $, single photon ${p_{\mathrm {T}}}$, diphoton acoplanarity, diphoton mass, diphoton $\xi ^-$, and diphoton $\xi ^+$. The black dots represent the data, filled histograms represent the SM backgrounds, and the lined histogram represents an AQGC signal having $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\zeta _2 = $ 0 $\times$ 10$^{-13}$ GeV$^{-4}$ multiplied by a factor of 100 for reference. The bottom of each plot shows the ratio of the number of data events to SM background events. |
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Figure 5-e:
Kinematic distributions for events passing the $\xi ^{\gamma \gamma} \in $ PPS signal selection. From top to bottom and left to right shows the single photon $\eta $, single photon ${p_{\mathrm {T}}}$, diphoton acoplanarity, diphoton mass, diphoton $\xi ^-$, and diphoton $\xi ^+$. The black dots represent the data, filled histograms represent the SM backgrounds, and the lined histogram represents an AQGC signal having $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\zeta _2 = $ 0 $\times$ 10$^{-13}$ GeV$^{-4}$ multiplied by a factor of 100 for reference. The bottom of each plot shows the ratio of the number of data events to SM background events. |
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Figure 5-f:
Kinematic distributions for events passing the $\xi ^{\gamma \gamma} \in $ PPS signal selection. From top to bottom and left to right shows the single photon $\eta $, single photon ${p_{\mathrm {T}}}$, diphoton acoplanarity, diphoton mass, diphoton $\xi ^-$, and diphoton $\xi ^+$. The black dots represent the data, filled histograms represent the SM backgrounds, and the lined histogram represents an AQGC signal having $\zeta _1 = $ 5 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\zeta _2 = $ 0 $\times$ 10$^{-13}$ GeV$^{-4}$ multiplied by a factor of 100 for reference. The bottom of each plot shows the ratio of the number of data events to SM background events. |
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Figure 6:
The number of data and simulated background events are shown for three sequential selection regions. The first bin is the preselection region, the second bin uses the acoplanarity selection defined in the text, and the third bin uses the diphoton $\xi $ selection defined in the text. |
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Figure 7:
Mass and rapidity matching for events passing the CMS diphoton selection and two reconstructed protons passing the asymmetric proton $\xi $ selection. Events matching at 2$\sigma $ are enclosed within a green rectangle. |
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Figure 8:
Both efficiency and acceptance effects parameterized as function of the proton $\xi $ for all years. Differences in the reconstruction percentage can be attributed to differences in detector location, configuration, and design. |
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Figure 8-a:
Both efficiency and acceptance effects parameterized as function of the proton $\xi $ for all years. Differences in the reconstruction percentage can be attributed to differences in detector location, configuration, and design. |
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Figure 8-b:
Both efficiency and acceptance effects parameterized as function of the proton $\xi $ for all years. Differences in the reconstruction percentage can be attributed to differences in detector location, configuration, and design. |
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Figure 9:
The observed and expected exclusion limits on the anomalous coupling parameters $\zeta _1$ and $\zeta _2$. |
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Figure 10:
ALP signal efficiency times acceptance ($\epsilon \times A$) for samples generated with $f^{-1}= $ 10$^{-1}$ TeV$^{-1}$ within the fiducial volume of this search. Values are shown for the PPS $\epsilon \times A$ and the same value convolved with the CMS $\epsilon \times A$. The CMS $\epsilon \times A$ remains mostly constant as a function of ALP mass and the nominal values are 85%, 80% and 81% for 2016, 2017, and 2018, respectively. |
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Figure 11:
Limits on axion-like particle (ALP) production in the plane of the ALP mass and the coupling strength. The shape of the limit curve follows the PPS acceptance times efficiency curve. |
| Tables | |
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Table 1:
Selection criteria for various training samples used to train the BDT to identify photons. $H/E$ is defined as the ratio between the energy deposits in the hadronic and electromagnetic calorimeters. |
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Table 2:
Summary of the predicted number of events for each Standard Model background contributing to the $\xi \in $ PPS selection region. The uncertainties quoted are statistical only. |
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Table 3:
A summary of the selection regions defined in the text. |
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Table 4:
Systematic uncertainties corresponding to each year of data used in the analysis. |
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Table 5:
Anomalous coupling signal efficiency for each year of the Run II period. The left column is the CMS only efficiency, the middle column is the PPS efficiency, and the right column is the multiplicative combination of the previous columns. |
| Summary |
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A search has been performed for physics beyond the standard model in high-mass exclusive diphoton events with two intact protons. The data used correspond to 102.7 fb$^{-1}$ in pp collisions collected by the CMS and PPS detectors in 2016, 2017, and 2018. Signal diphoton events are selected using a criteria developed for exclusive two-photon production and the final signal region is defined by having two opposite-side protons with corresponding kinematics to the diphoton system. The data are found to be in agreement with the predicted background with 1 event observed and 1.103 $\pm$ 0.003 (statistical) $\pm$ 0.238 (systematic) events expected. The best current limits are placed on 4$\gamma$ anomalous couplings within the fiducial range of the analysis defined as ${p_{\mathrm{T}}}^{\gamma} > $ 100 GeV and 0.035 $ < \xi < $ 0.15 (0.18) for the positive-z (negative-z) arm of PPS. Additionally, the strongest limits to data are placed on ALP production between the mass ranges of 500 - 2000 GeV within the fiducial volume of the analysis. |
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Compact Muon Solenoid LHC, CERN |
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