Compact Muon Solenoid
LHC, CERN

Visit us: CMS Public Website, CMS Physics ; Contact us: CMS Publications Committee

CMS-PAS-EXO-19-006

Search for fractionally charged particles in pp collisions at $ \sqrt{s}= $ 13 TeV

CMS Collaboration

29 November 2022

Abstract: Every known charged particle has an electric charge that is a multiple of 1/3e. In the absence of a mechanism to explain this quantization, particles with other charges may exist as well. In particular, only weak constraints have been set on the existence of free-propagating particles with charge below 1e and mass accessible at the LHC. A search is presented for fractionally charged particles using energy loss in the tracking detector as a key variable to suppress backgrounds. Using a data set corresponding to an integrated luminosity of 138 fb$^{-1}$ of proton-proton collisions collected at a center-of-mass energy of 13 TeV by the CMS experiment, masses up to 636 GeV and charges as low as 1/2e are excluded at 95% confidence level.

Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PRL. The superseded preliminary plots can be found here.

Figures
png pdf	Figure 1: The $ \mathrm{d}E/\mathrm{d}x $ distribution for hits on candidate tracks in the control and search regions in 2018 data.
png pdf	Figure 2: Distribution of $ N_{\text{hits}}^{\text{low dE/dx}} $ in the search and control regions for the early 2016 (top left), late 2016 (top right), 2017 (bottom left) and 2018 (bottom right) data sets. The vertical bars and the shaded area correspond to the statistical uncertainty in the search and the control region, respectively. The p-values of the fits $ \chi^{2} $ are 6% (early 2016), 78% (late 2016), 65% (2017) and 9% (2018). The top (bottom) lower panels show the ratio of the number of tracks observed in the control (search) region and the fit function. The vertical bars correspond to the uncertainty from statistical sources, while the shaded area gives the systematic uncertainty in the fit from the difference with the alternative function and the binomial fit starting at $ N_{\text{hits}}^{\text{low dE/dx}} = $ 1.
png pdf	Figure 2-a: Distribution of $ N_{\text{hits}}^{\text{low dE/dx}} $ in the search and control regions for the early 2016 data set. The vertical bars and the shaded area correspond to the statistical uncertainty in the search and the control region, respectively. The p-value of the fit $ \chi^{2} $ is 6%. The top (bottom) lower panels show the ratio of the number of tracks observed in the control (search) region and the fit function. The vertical bars correspond to the uncertainty from statistical sources, while the shaded area gives the systematic uncertainty in the fit from the difference with the alternative function and the binomial fit starting at $ N_{\text{hits}}^{\text{low dE/dx}} = $ 1.
png pdf	Figure 2-b: Distribution of $ N_{\text{hits}}^{\text{low dE/dx}} $ in the search and control regions for the late 2016 data set. The vertical bars and the shaded area correspond to the statistical uncertainty in the search and the control region, respectively. The p-value of the fit $ \chi^{2} $ is 78%. The top (bottom) lower panels show the ratio of the number of tracks observed in the control (search) region and the fit function. The vertical bars correspond to the uncertainty from statistical sources, while the shaded area gives the systematic uncertainty in the fit from the difference with the alternative function and the binomial fit starting at $ N_{\text{hits}}^{\text{low dE/dx}} = $ 1.
png pdf	Figure 2-c: Distribution of $ N_{\text{hits}}^{\text{low dE/dx}} $ in the search and control regions for the 2017 data set. The vertical bars and the shaded area correspond to the statistical uncertainty in the search and the control region, respectively. The p-value of the fit $ \chi^{2} $ is 65%. The top (bottom) lower panels show the ratio of the number of tracks observed in the control (search) region and the fit function. The vertical bars correspond to the uncertainty from statistical sources, while the shaded area gives the systematic uncertainty in the fit from the difference with the alternative function and the binomial fit starting at $ N_{\text{hits}}^{\text{low dE/dx}} = $ 1.
png pdf	Figure 2-d: Distribution of $ N_{\text{hits}}^{\text{low dE/dx}} $ in the search and control regions for the 2018 data set. The vertical bars and the shaded area correspond to the statistical uncertainty in the search and the control region, respectively. The p-value of the fit $ \chi^{2} $ is 9%. The top (bottom) lower panels show the ratio of the number of tracks observed in the control (search) region and the fit function. The vertical bars correspond to the uncertainty from statistical sources, while the shaded area gives the systematic uncertainty in the fit from the difference with the alternative function and the binomial fit starting at $ N_{\text{hits}}^{\text{low dE/dx}} = $ 1.
png pdf	Figure 3: Exclusion region (hatched) at 95% CL in the FCP charge-mass plane for the considered signal model. The exclusion region extends down to a mass of 50 GeV, above which the background control region is free from signal. Previous exclusion from OPAL [10] is given for comparison.

Tables
png pdf	Table 1: Number of tracks observed, expected for background events, and expected for signal events, in the highest $ N_{\text{hits}}^{\text{low dE/dx}} $ bin, for each data set. The corresponding systematic uncertainties are also listed. The results for an FCP scenario at a mass of 100 GeV and a charge of 2/3e (i.e. the most sensitive scenario) is also shown.

Summary

In summary, we presented a search for fractionally charged particles using an integrated luminosity of 138 fb$^{-1}$ of pp collisions collected at $ \sqrt{s}= $ 13 TeV with the CMS detector. The key feature of low ionization energy in the CMS tracker detector is used to isolate a potential signal from the background. No significant deviation is observed in data with respect to the expected background. The existence of fractionally charged particles is excluded up to a mass of 636 GeV for a signal of charge $ Q = $ 2/3e. These are the best limits on this particular new-physics signature in the considered phase space.

Additional Figures

png pdf

Additional Figure 1: Exclusion region (hatched) at 95% CL in the FCP charge-mass plane for the considered signal model. Signal points at electric charges 0.9, 0.8, 2/3, 0.5 and 1/3$e$ are connected by straight lines to guide the eye. The existence of FCPs as described by the considered model is excluded in the mass range between 50 and 635 GeV (65 GeV) for a signal of electric charge $ Q = $ 2/3$e$ (1/3$e$). Previous exclusions from CMS [5,6] as well as OPAL [10] are given for comparison.

References
1	B. Holdom	Two U(1)'s and Epsilon Charge Shifts	PLB 166 (1986) 196
2	S. A. Abel et al.	Kinetic Mixing of the Photon with Hidden U(1)s in String Phenomenology	JHEP 07 (2008) 124	0803.1449
3	P. Langacker	The Physics of Heavy $ Z^\prime $ Gauge Bosons	Rev. Mod. Phys. 81 (2009) 1199	0801.1345
4	D. E. Morrissey, D. Poland, and K. M. Zurek	Abelian Hidden Sectors at a GeV	JHEP 07 (2009) 050	0904.2567
5	CMS Collaboration	Search for fractionally charged particles in pp collisions at $ \sqrt{s}= $ 7 TeV	PRD 87 (2013) 092008	CMS-EXO-11-074 1210.2311
6	CMS Collaboration	Searches for Long-Lived Charged Particles in pp Collisions at $ \sqrt{s} $ = 7 and 8 TeV	JHEP 07 (2013) 122	CMS-EXO-12-026 1305.0491
7	S. L. Dubovsky, D. S. Gorbunov, and G. I. Rubtsov	Narrowing the window for millicharged particles by CMB anisotropy	[Pisma Zh. Eksp. Teor. Fiz.79, 3] JETP Lett. 79 (2004) 1	hep-ph/0311189
8	N. Vinyoles and H. Vogel	Minicharged Particles from the Sun: A Cutting-Edge Bound	JCAP 03 (2016) 002	1511.01122
9	S. Davidson, S. Hannestad, and G. Raffelt	Updated bounds on millicharged particles	JHEP 05 (2000) 003	hep-ph/0001179
10	OPAL Collaboration	Search for heavy charged particles and for particles with anomalous charge in $ e^{+} e^{-} $ collisions at LEP	Z. Phys. C 67 (1995) 203
11	M. Staelens	Recent Results and Future Plans of the MoEDAL Experiment	MoEDAL Collaboration, in Meeting of the Division of Particles and Fields of the American Physical Society (DPF) Boston, 2019	1910.05772
12	A. Haas, C. S. Hill, E. Izaguirre, and I. Yavin	Looking for milli-charged particles with a new experiment at the LHC	PLB 746 (2015) 117	1410.6816
13	A. Ball et al.	A Letter of Intent to Install a milli-charged Particle Detector at LHC P5		1607.04669
14	A. Ball et al.	Search for millicharged particles in proton-proton collisions at $ \sqrt{s} = $ 13 TeV		2005.06518
15	P.-K. Hu, A. Kusenko, and V. Takhistov	Dark Cosmic Rays	PLB 768 (2017) 18	1611.04599
16	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004
17	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
18	T. Sjöstrand et al.	An Introduction to PYTHIA 8.2	Comput. Phys. Commun. 191 (2015) 159	1410.3012
19	J. Alwall et al.	The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations	JHEP 07 (2014) 079	1405.0301
20	NNPDF Collaboration	Parton distributions for the LHC Run II	JHEP 04 (2015) 040	1410.8849
21	NNPDF Collaboration	Parton distributions from high-precision collider data	EPJC 77 (2017) 663	1706.00428
22	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
23	CMS Collaboration	Investigations of the impact of the parton shower tuning in Pythia 8 in the modelling of $ \mathrm{t} \overline{\mathrm{t}} $ at $ \sqrt{s}= $ 8 and 13 TeV	CMS Physics Analysis Summary, 2016 CMS-PAS-TOP-16-021	CMS-PAS-TOP-16-021
24	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
25	GEANT4 Collaboration	GEANT 4---a simulation toolkit	NIM A 506 (2003) 250
26	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
27	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
28	CMS Collaboration	The CMS Phase-1 Pixel Detector	in preparation, 2020
29	CMS Collaboration	Precision luminosity measurement in proton-proton collisions at $ \sqrt{s} = $ 13 TeV in 2015 and 2016 at CMS	EPJC 81 (2021)	CMS-LUM-17-003 2104.01927
30	CMS Collaboration	CMS luminosity measurement for the 2017 data-taking period at $ \sqrt{s} = $ 13 TeV	CMS Physics Analysis Summary, 2018 CMS-PAS-LUM-17-004	CMS-PAS-LUM-17-004
31	CMS Collaboration	CMS Luminosity Measurements for the 2018 Data Taking Period at $ \sqrt{s} = $ 13 TeV	CMS Physics Analysis Summary, 2018 CMS-PAS-LUM-18-002	CMS-PAS-LUM-18-002
32	T. Junk	Confidence level computation for combining searches with small statistics	NIM A 434 (1999) 435	hep-ex/9902006
33	A. L. Read	Presentation of search results: The CL(s) technique	JPG 28 (2002) 2693

Compact Muon Solenoid LHC, CERN

© Copyright CERN for the benefit of the CMS Collaboration