Compact Muon Solenoid
LHC, CERN
Visit us: CMS Public Website, CMS Physics ;
Contact us: CMS Publications Committee
| CMS-PAS-BPH-23-008 | ||
| Search for rare charm decays into two muons | ||
| CMS Collaboration | ||
| 28 July 2024 | ||
| Abstract: A search for the rare decay $ {\mathrm D}^0\to\mu^{+}\mu^{-} $ was conducted using $ \sqrt{s} = $ 13.6 TeV proton-proton collision data collected by the CMS experiment during the 2022-2023 operation of the CERN LHC, with an integrated luminosity of 64.5 fb$^{-1}$. The search exploits a new high-rate trigger that records events with two muons with transverse momenta as low as 4 and 3 GeV. Rare decays of the charm quark, which are less explored than rare bottom quark decays, offer a unique way to probe for new physics effects beyond the reach of modern colliders. No significant excess above the expected background was observed, leading to an upper limit of $ \mathcal{B}({\mathrm D}^0\to\mu^{+}\mu^{-}) < $ 2.6 $\times$ 10$^{-9} $ at the 95% confidence level. This is the most sensitive measurement to date, imposing additional constraints on new physics models. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
png pdf |
Figure 1:
Dipion invariant mass $ m_{\pi\pi} $ (left) and $ \mathrm{D}^{*} $-$ \mathrm{D^0} $ mass difference $ \Delta m $ (right) from the reconstructed candidates from zero bias samples after MVA$_{\mathrm{D}}$ selection. |
png pdf |
Figure 1-a:
Dipion invariant mass $ m_{\pi\pi} $ (left) and $ \mathrm{D}^{*} $-$ \mathrm{D^0} $ mass difference $ \Delta m $ (right) from the reconstructed candidates from zero bias samples after MVA$_{\mathrm{D}}$ selection. |
png pdf |
Figure 1-b:
Dipion invariant mass $ m_{\pi\pi} $ (left) and $ \mathrm{D}^{*} $-$ \mathrm{D^0} $ mass difference $ \Delta m $ (right) from the reconstructed candidates from zero bias samples after MVA$_{\mathrm{D}}$ selection. |
png pdf |
Figure 2:
The projection of $ m_{\mu\mu} $ (left) and $ \Delta m $ (right) of the fit in the full $ m_{\mu\mu} $ and $ \Delta m $ range. The bottom panel shows the data and the fit result after subtraction of the total background component. The grey error band represents the statistical and systematic uncertainties of the total background component. |
png pdf |
Figure 2-a:
The projection of $ m_{\mu\mu} $ (left) and $ \Delta m $ (right) of the fit in the full $ m_{\mu\mu} $ and $ \Delta m $ range. The bottom panel shows the data and the fit result after subtraction of the total background component. The grey error band represents the statistical and systematic uncertainties of the total background component. |
png pdf |
Figure 2-b:
The projection of $ m_{\mu\mu} $ (left) and $ \Delta m $ (right) of the fit in the full $ m_{\mu\mu} $ and $ \Delta m $ range. The bottom panel shows the data and the fit result after subtraction of the total background component. The grey error band represents the statistical and systematic uncertainties of the total background component. |
png pdf |
Figure 3:
The projection of $ m_{\mu\mu} $ (left) and $ \Delta m $ (right) of the fit with requirements 0.145 $ < \Delta m < $ 0.146 GeV and 1.84 $ < m_{\mu\mu} < $ 1.89 GeV, respectively. The bottom panel shows the data and the fit result after subtraction of the total background component. The grey error band represents the statistical and systematic uncertainties of the total background component. |
png pdf |
Figure 3-a:
The projection of $ m_{\mu\mu} $ (left) and $ \Delta m $ (right) of the fit with requirements 0.145 $ < \Delta m < $ 0.146 GeV and 1.84 $ < m_{\mu\mu} < $ 1.89 GeV, respectively. The bottom panel shows the data and the fit result after subtraction of the total background component. The grey error band represents the statistical and systematic uncertainties of the total background component. |
png pdf |
Figure 3-b:
The projection of $ m_{\mu\mu} $ (left) and $ \Delta m $ (right) of the fit with requirements 0.145 $ < \Delta m < $ 0.146 GeV and 1.84 $ < m_{\mu\mu} < $ 1.89 GeV, respectively. The bottom panel shows the data and the fit result after subtraction of the total background component. The grey error band represents the statistical and systematic uncertainties of the total background component. |
png pdf |
Figure 4:
The profile likelihood scan as a function of $ \mathrm{D^0}\to\mu^{+}\mu^{-} $ decay branching fraction. |
| Tables | |
png pdf |
Table 1:
Fitted yields with zero bias events after MVA$_{\mathrm{D}}$ selection. |
png pdf |
Table 2:
Summary of systematic uncertainties for the $ \mathrm{D^0}\to\mu^{+}\mu^{-} $ branching ratio measurement. |
png pdf |
Table 3:
The expected event yields for signal, the combinatorial background, the peaking background, and the semileptonic background are summarized (post-fit). The total expected and observed event yields are given in Total and Data column, respectively. The subrange is in one dimension with a full range in the other dimension. |
| Summary |
| The measurement of the branching fraction ($ \mathcal{B} $) of the $ \mathrm{D^0}\to\mu^{+}\mu^{-} $ decay, based on a data set of proton-proton collisions at $ \sqrt{s} = $ 13.6 TeV collected by the CMS experiment corresponding to an integrated luminosity of 64.5 fb$ ^{-1} $, has been presented. The branching fraction is measured using the cascade decay $ \mathrm{D}^{*+}\to\mathrm{D^0}\pi^{+} $, $ \mathrm{D^0}\to\mu^{+}\mu^{-} $ with the $ \mathrm{D^0}\to\pi^{+}\pi^{-} $ decay mode as the normalization channel, considering both prompt and non-prompt $ \mathrm{D^0} $ meson production. No significant excess above the background expectation was observed and an upper limit on the branching fraction has been set to be $ \mathcal{B} $($ \mathrm{D^0}\to\mu^{+}\mu^{-} $) < $ 2.6 $\times$ 10$^-9$ at 95% CL. The obtained value of $ \mathrm{D^0}\to\mu^{+}\mu^{-} $ branching fraction is found to be $ \mathcal{B}(\mathrm{D^0}\to\mu^{+}\mu^{-}) = $ (1.0 $ \pm $ 0.9) $\times$ 10$^{-9}$. The measurement is the most sensitive to date, representing a 35% improvement over the current best measurement [23]. This measurement provides the most stringent limit on flavor-changing neutral currents in the charm sector, setting additional constraints on new physics models that modify the decay branching fraction of $ \mathrm{D^0}\to\mu^{+}\mu^{-} $. The analysis is the first measurement at CMS using the newly developed low-mass double muon parking trigger [24]. It also marks the first publication on the $ \mathrm{D^0}\to\mu^{+}\mu^{-} $ branching fraction measurement at CMS, made possible by the enriched dimuon events collected by this innovative trigger. |
| References | ||||
| 1 | CMS Collaboration | Angular analysis of the decay $ {\mathrm{B}}^0 \to \mathrm{K}^{*0} \mu^+ \mu^- $ from pp collisions at $ \sqrt{s} = $ 8 TeV | PLB 753 (2016) 424 | CMS-BPH-13-010 1507.08126 |
| 2 | CMS Collaboration | Measurement of angular parameters from the decay $ {\mathrm{B}}^0 \to \mathrm{K}^{*0}\mu^{+}\mu^{-} $ in proton-proton collisions at $ \sqrt{s} = $ 8 TeV | PLB 781 (2018) 517 | CMS-BPH-15-008 1710.02846 |
| 3 | CMS Collaboration | Measurement of properties of $ \mathrm{B}_{s}^{0} \to\mu^{+}\mu^{-} $ decays and search for $ {\mathrm{B}^0} \to \mu^{+}\mu^{-} $ with the CMS experiment | JHEP 04 (2020) 188 | CMS-BPH-16-004 1910.12127 |
| 4 | ATLAS, CMS and LHCb Collaborations | Combination of the ATLAS, CMS and LHCb results on the $ \mathrm{B}_{s}^{0} \to \mu^{+}\mu^{-} $ decays | Physics Analysis Summary, LHCb-CONF-2020-002, ATLAS-CONF-2020-049, 2020 CMS-PAS-BPH-20-003 |
CMS-PAS-BPH-20-003 |
| 5 | CMS Collaboration | Measurement of the $ \mathrm{B}_{s}^{0} \to\mu^{+}\mu^{-} $ decay properties and search for the $ {\mathrm{B}^0} \to \mu^{+}\mu^{-} $ decay in proton-proton collisions at $ \sqrt{s} $ = 13 TeV | PLB 842 (2023) 137955 | CMS-BPH-21-006 2212.10311 |
| 6 | LHCb Collaboration | Angular analysis of the $ {\mathrm{B}}^{+} \to \mathrm{K}^{*+}\mu^{+}\mu^{-} $ Decay | PRL 126 (2021) 161802 | 2012.13241 |
| 7 | LHCb Collaboration | Measurement of $ CP $-Averaged observables in the $ {\mathrm{B}^0} \to \mathrm{K}^{*0}\mu^{+}\mu^{-} $ Decay | PRL 125 (2020) 011802 | 2003.04831 |
| 8 | LHCb Collaboration | Angular analysis of the rare decay $ \mathrm{B}_{s}^{0}\to\phi\mu^{+}\mu^{-} $ | JHEP 11 (2021) 043 | 2107.13428 |
| 9 | LHCb Collaboration | Branching Fraction Measurements of the Rare $ \mathrm{B}_{s}^{0} \to \phi\mu^{+}\mu^{-} $ and $ \mathrm{B}_{s}^{0} \to {f}_{2}^{'}(1525)\mu^{+}\mu^{-} $ Decays | PRL 127 (2021) 151801 | 2105.14007 |
| 10 | LHCb Collaboration | Measurement of the $ \mathrm{B}_{s}^{0} \to\mu^{+}\mu^{-} $ branching fraction and effective lifetime and search for $ {\mathrm{B}^0} \to \mu^{+}\mu^{-} $ decays | PRL 118 (2017) 191801 | 1703.05747 |
| 11 | LHCb Collaboration | Measurement of the $ \mathrm{B}_{s}^{0} \to\mu^{+}\mu^{-} $ decay properties and search for the $ {\mathrm{B}^0} \to \mu^{+}\mu^{-} $ and $ \mathrm{B}_{s}^{0}\to\mu^{+}\mu^{-}\gamma $ decays | PRD 105 (2022) 012010 | 2108.09283 |
| 12 | LHCb Collaboration | Analysis of neutral $ {\mathrm{B}} $-meson decays into two muons | PRL 128 (2022) 041801 | 2108.09284 |
| 13 | ATLAS Collaboration | Angular analysis of $ {\mathrm{B}^0} \to \mathrm{K}^*\mu^{+}\mu^{-} $ decays in pp collisions at $ \sqrt{s}= $ 8TeV with the ATLAS detector | JHEP 10 (2018) 47 | 1805.04000 |
| 14 | ATLAS Collaboration | Study of the rare decays of $ \mathrm{B}_{s}^{0} $ and $ {\mathrm{B}^0} $ mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector | JHEP 04 (2019) 098 | 1812.03017 |
| 15 | CMS and LHCb Collaboration | Observation of the rare $ \mathrm{B}_{s}^{0} \to\mu^{+}\mu^{-} $ decay from the combined analysis of CMS and LHCb data | Nature 522 (2015) 68 | CMS-BPH-13-007 1411.4413 |
| 16 | BABAR Collaboration | Measurement of angular asymmetries in the decays $ {\mathrm{B}} \to \mathrm{K}^{*}\ell^{+}\ell^{-} $ | PRD 93 (2016) 052015 | 1508.07960 |
| 17 | Belle Collaboration | Measurement of the Differential Branching Fraction and Forward-Backward Asymmetry for $ {\mathrm{B}} \to \mathrm{K}^{*}\ell^{+}\ell^{-} $ | PRL 103 (2009) 171801 | 0904.0770 |
| 18 | Belle Collaboration | Lepton-Flavor-Dependent Angular Analysis of $ {\mathrm{B}} \to \mathrm{K}^{*}\ell^{+}\ell^{-} $ | PRL 118 (2017) 111801 | 1612.05014 |
| 19 | CDF Collaboration | Measurements of the Angular Distributions in the Decays $ {\mathrm{B}} \to \mathrm{K}^{(*)}\mu^{+}\mu^{-} $ at CDF | PRL 108 (2012) 081807 | 1108.0695 |
| 20 | E. Golowich, J. Hewett, S. Pakvasa, and A. A. Petrov | Relating $ \mathrm{D^0}-\overline{\mathrm{D}}^{0} $ mixing and $ \mathrm{D^0}\to\mu^{+}\mu^{-} $ with new physics | PRD 79 (2009) 114030 | 0903.2830 |
| 21 | S. Fajfer and N. Košnik | Leptoquarks in flavor changing neutral current charm decays | PRD 79 (2009) 017502 | 0810.4858 |
| 22 | G. Burdman, E. Golowich, J. L. Hewett, and S. Pakvasa | Rare charm decays in the standard model and beyond | PRD 66 (2002) 014009 | hep-ph/0112235 |
| 23 | LHCb Collaboration | Search for rare decays of $ \mathrm{D^0} $ mesons into two muons | PRL 131 (2023) 041804 | 2212.11203 |
| 24 | CMS Collaboration | Enriching the physics program of the CMS experiment via data scouting and data parking | link | CMS-EXO-23-007 2403.16134 |
| 25 | LHCb Collaboration | Measurements of prompt charm production cross-sections in $ pp $ collisions at $ \sqrt{s}= $ 13 TeV | JHEP 03 (2016) 159 | 1510.01707 |
| 26 | CMS Collaboration | The CMS experiment at the CERN LHC | JINST 3 (2008) S08004 | |
| 27 | CMS Collaboration | Track impact parameter resolution for the full pseudorapidity coverage in the 2017 dataset with the CMS Phase-1 pixel detector | CMS Detector Performance Report CMS-DP-2020-049, 2020 CDS |
|
| 28 | CMS Collaboration | Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $ \sqrt{s} = $ 13 TeV | JINST 13 (2018) P06015 | CMS-MUO-16-001 1804.04528 |
| 29 | CMS Collaboration | Performance of the CMS Level-1 trigger in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | JINST 15 (2020) P10017 | CMS-TRG-17-001 2006.10165 |
| 30 | CMS Collaboration | The CMS trigger system | JINST 12 (2017) P01020 | CMS-TRG-12-001 1609.02366 |
| 31 | T. Sjöstrand et al. | An introduction to PYTHIA 8.2 | Comput. Phys. Commun. 191 (2015) 159 | 1410.3012 |
| 32 | CMS Collaboration | Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements | EPJC 80 (2020) 4 | CMS-GEN-17-001 1903.12179 |
| 33 | GEANT4 Collaboration | GEANT 4---a simulation toolkit | NIM A 506 (2003) 250 | |
| 34 | D. J. Lange | The EvtGen particle decay simulation package | NIM A 462 (2001) 152 | |
| 35 | N. Davidson, T. Przedzinski, and Z. Was | PHOTOS interface in C++: technical and physics documentation | Comput. Phys. Commun. 199 (2016) 86 | 1011.0937 |
| 36 | CMS Collaboration | Description and performance of track and primary-vertex reconstruction with the CMS tracker | JINST 9 (2014) P10009 | CMS-TRK-11-001 1405.6569 |
| 37 | K. Prokofiev and T. Speer | A kinematic and a decay chain reconstruction library | Prepared for Computing in High-Energy Physics (CHEP '04), Interlaken, Switzerland, 2004 | |
| 38 | T. Chen and C. Guestrin | XGBoost: A scalable tree boosting system | in Proceedings of the 22nd ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, KDD '16, New York, 2016 link |
|
| 39 | W. Verkerke and D. P. Kirkby | The RooFit toolkit for data modeling | eConf C0303241 (2003) MOLT007 | physics/0306116 |
| 40 | LHCb Collaboration | Search for the rare decay $ \mathrm{D^0}\to\mu^{+}\mu^{-} $ | PLB 725 (2013) 15 | 2106.03744 |
| 41 | CMS Collaboration | The CMS statistical analysis and combination tool: COMBINE | link | CMS-CAT-23-001 2404.06614 |
| 42 | P. D. Dauncey, M. Kenzie, N. Wardle, and G. J. Davies | Handling uncertainties in background shapes: the discrete profiling method | JINST 10 (2015) P04015 | 1408.6865 |
| 43 | CMS Collaboration | Tracking performances for charged pions with Run2 legacy data | CMS Detector Performance Report CMS-DP-2022-012, 2022 CDS |
|
|
|
Compact Muon Solenoid LHC, CERN |
|
|
|
|
|
|