CMS-PAS-EXO-16-044

CMS-PAS-EXO-16-044
Search for disappearing tracks in proton-proton collisions at $\sqrt{s} = $ 13 TeV
CMS Collaboration
February 2018

Abstract: A search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. A disappearing track is an isolated track with no associated hits in the muon detectors, little or no energy in associated calorimeter deposits, and missing hits in the outer layers of the silicon tracker. The search uses 38.4 fb$^{-1}$ of proton-proton collision data collected by the CMS detector in 2015 and 2016, at a center-of-mass energy of 13 TeV at the CERN LHC. The results of the search are interpreted in the context of anomaly-mediated supersymmetry breaking. The observation is consistent with the background-only hypothesis, and limits are set on the product of the cross section of direct chargino production and branching fraction to a neutralino and a pion in terms of the chargino mass and lifetime. At 95% confidence level, charginos with masses less than 715 GeV are excluded for a lifetime of 3 ns.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 08 (2018) 016. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Distributions of the maximum difference in azimuthal angle between any two jets (left) and the difference in azimuthal angle between the $ {\vec{p}_{\mathrm {T}}} $ of the leading jet and $ {\vec{p}_{\mathrm{T}}^{\text {miss} ,\, \text {no}\ \mu}} $ (right) for events from the basic control region before either of the angular requirements on the jets or $ {\vec{p}_{\mathrm{T}}^{\text {miss} ,\, \text {no}\ \mu}} $ are imposed. The blue lines show the distributions for simulated signal events with a chargino that has a lifetime of 100 cm/$c$ and mass of 300 GeV, with a corresponding production cross section of 0.58 pb. The gray shaded area indicates the statistical uncertainty in the SM background, and the leftmost bin of the left plot includes events with only one selected jet. The red dashed lines indicate the chosen value for the requirement on each variable, and the arrows indicate which events are selected.
png pdf	Figure 1-a: Distribution of the maximum difference in azimuthal angle between any two jets for events from the basic control region before either of the angular requirements on the jets or $ {\vec{p}_{\mathrm{T}}^{\text {miss} ,\, \text {no}\ \mu}} $ are imposed. The blue line shows the distribution for simulated signal events with a chargino that has a lifetime of 100 cm/$c$ and mass of 300 GeV, with a corresponding production cross section of 0.58 pb. The gray shaded area indicates the statistical uncertainty in the SM background. The leftmost bin includes events with only one selected jet. The red dashed line indicates the chosen value for the requirement on that variable, and the arrow indicates which events are selected.
png pdf	Figure 1-b: Distribution of the difference in azimuthal angle between the $ {\vec{p}_{\mathrm {T}}} $ of the leading jet and $ {\vec{p}_{\mathrm{T}}^{\text {miss} ,\, \text {no}\ \mu}} $ for events from the basic control region before either of the angular requirements on the jets or $ {\vec{p}_{\mathrm{T}}^{\text {miss} ,\, \text {no}\ \mu}} $ are imposed. The blue line shows the distribution for simulated signal events with a chargino that has a lifetime of 100 cm/$c$ and mass of 300 GeV, with a corresponding production cross section of 0.58 pb. The gray shaded area indicates the statistical uncertainty in the SM background. The red dashed line indicates the chosen value for the requirement on that variable, and the arrow indicates which events are selected.
png pdf	Figure 2: Distributions of $ {E_{\text {calo}}} $ (left) and number of missing outer hits (right) for tracks in simulation that pass the full selection except for the requirement on the variable being plotted. Each signal distribution and the sum of the SM background distributions are scaled to have unit area, and the rightmost bins include overflow entries. The gray shaded area indicates the statistical uncertainty in the SM background.
png pdf	Figure 2-a: Distribution of $ {E_{\text {calo}}} $ for tracks in simulation that pass the full selection except for the requirement on the variable being plotted. The signal distribution and the sum of the SM background distributions are scaled to have unit area, and the rightmost bin includes overflow entries. The gray shaded area indicates the statistical uncertainty in the SM background.
png pdf	Figure 2-b: Distribution of the number of missing outer hits for tracks in simulation that pass the full selection except for the requirement on the variable being plotted. The signal distribution and the sum of the SM background distributions are scaled to have unit area, and the rightmost bin includes overflow entries. The gray shaded area indicates the statistical uncertainty in the SM background.
png pdf	Figure 3: The expected and observed 95% CL upper limits on the product of the cross section of direct chargino production and branching fraction to $\tilde{\chi}_1^0 {\pi ^\mathrm {{\pm}}}$ as a function of chargino mass for various chargino lifetimes. The direct chargino production cross section includes both $\tilde{\chi}_1^0\tilde{\chi}_1^\pm $ and $\tilde{\chi}_1^\pm \tilde{\chi}_1^\mp $ production in roughly a 2:1 ratio across all chargino masses considered.
png pdf	Figure 3-a: The expected and observed 95% CL upper limits on the product of the cross section of direct chargino production and branching fraction to $\tilde{\chi}_1^0 {\pi ^\mathrm {{\pm}}}$ as a function of chargino mass for chargino lifetime 10 cm/$c$. The direct chargino production cross section includes both $\tilde{\chi}_1^0\tilde{\chi}_1^\pm $ and $\tilde{\chi}_1^\pm \tilde{\chi}_1^\mp $ production in roughly a 2:1 ratio across all chargino masses considered.
png pdf	Figure 3-b: The expected and observed 95% CL upper limits on the product of the cross section of direct chargino production and branching fraction to $\tilde{\chi}_1^0 {\pi ^\mathrm {{\pm}}}$ as a function of chargino mass for chargino lifetime 100 cm/$c$. The direct chargino production cross section includes both $\tilde{\chi}_1^0\tilde{\chi}_1^\pm $ and $\tilde{\chi}_1^\pm \tilde{\chi}_1^\mp $ production in roughly a 2:1 ratio across all chargino masses considered.
png pdf	Figure 3-c: The expected and observed 95% CL upper limits on the product of the cross section of direct chargino production and branching fraction to $\tilde{\chi}_1^0 {\pi ^\mathrm {{\pm}}}$ as a function of chargino mass for chargino lifetime 1000 cm/$c$. The direct chargino production cross section includes both $\tilde{\chi}_1^0\tilde{\chi}_1^\pm $ and $\tilde{\chi}_1^\pm \tilde{\chi}_1^\mp $ production in roughly a 2:1 ratio across all chargino masses considered.
png pdf	Figure 4: The expected and observed constraints on chargino lifetime and mass. The region to the left of the curve is excluded at 95% CL.
png pdf	Figure 5: The observed 95% CL upper limits on the product of the cross section of direct chargino production and branching fraction to $\tilde{\chi}_1^0 {\pi ^\mathrm {{\pm}}}$ as a function of chargino mass and lifetime. The direct chargino production cross section includes both $\tilde{\chi}_1^0\tilde{\chi}_1^\pm $ and $\tilde{\chi}_1^\pm \tilde{\chi}_1^\mp $ production in roughly a 2:1 ratio across all chargino masses considered.

Tables
png pdf	Table 1: Data-taking periods considered as independent data sets for this search and the respective integrated luminosities to which they correspond.
png pdf	Table 2: Definitions of the lepton vetoes used in the tag-and-probe studies to estimate $P_{\text {veto}}$ for each flavor of charged lepton. The criteria listed are chosen from the search criteria as the most efficient to reject each flavor.
png pdf	Table 3: Summary of the systematic uncertainties in the signal yields. The ranges represent either the variation with chargino mass and lifetime or with the data-taking period used to calculate the uncertainty, depending on the source of each uncertainty as described in the text.
png pdf	Table 4: Summary of numbers of events for the estimated backgrounds and the observed data. The uncertainties include those from statistical and systematic sources. In categories where the systematic uncertainty is negligibly small, it is not shown.

Summary

A search has been presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. In a sample of proton-proton data recorded at a center-of-mass energy of $\sqrt{s} = $ 13 TeV and corresponding to an integrated luminosity of 38.4 fb$^{-1}$, seven events are observed in the search sample, compared with the estimated background from standard model processes of 6.5 $\pm$ 0.9 (stat) $\pm$ 1.0 (syst) events. The observation is consistent with the background-only hypothesis, and we place constraints on the mass of charginos from direct electroweak production, for chargino mean proper lifetimes between 0.1 and 100 ns. Charginos with a mass up to 715 GeV for a lifetime of 3 ns are excluded at 95% confidence level. These constraints extend the limits set by a previous search performed by CMS [9]. For chargino lifetimes above ${\approx}$0.7 ns, the present search places the most stringent constraints on direct chargino production using the disappearing track signature.

References
1	G. F. Giudice, M. A. Luty, H. Murayama, and R. Rattazzi	Gaugino mass without singlets	JHEP 12 (1998) 027	hep-ph/9810442
2	L. Randall and R. Sundrum	Out of this world supersymmetry breaking	NPB 557 (1999) 79	hep-th/9810155
3	C. H. Chen, M. Drees, and J. F. Gunion	A nonstandard string / SUSY scenario and its phenomenological implications	PRD 55 (1997) 330	hep-ph/9607421
4	M. Ibe, S. Matsumoto, and T. T. Yanagida	Pure gravity mediation with $ m_{3/2} = $ 10 -- 100 TeV	PRD 85 (2012) 095011	1202.2253
5	L. J. Hall, Y. Nomura, and S. Shirai	Spread supersymmetry with wino LSP: gluino and dark matter signals	JHEP 01 (2013) 036	1210.2395
6	A. Arvanitaki, N. Craig, S. Dimopoulos, and G. Villadoro	Mini-split	JHEP 02 (2013) 126	1210.0555
7	N. Arkani-Hamed et al.	Simply unnatural supersymmetry		1212.6971
8	M. Citron et al.	End of the CMSSM coannihilation strip is nigh	PRD 87 (2013) 036012	1212.2886
9	CMS Collaboration	Search for disappearing tracks in proton-proton collisions at $ \sqrt{s}= $ 8 TeV	JHEP 01 (2015) 096	CMS-EXO-12-034 1411.6006
10	ATLAS Collaboration	Search for charginos nearly mass degenerate with the lightest neutralino based on a disappearing-track signature in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector	PRD 88 (2013) 112006	1310.3675
11	ATLAS Collaboration	Search for long-lived charginos based on a disappearing-track signature in pp collisions at $ \sqrt{s} = $ 13 TeV with the ATLAS detector	Submitted to JHEP	1712.02118
12	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
13	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
14	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
15	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
16	CMS Collaboration	CMS luminosity measurement for the 2015 data taking period	CMS-PAS-LUM-15-001	CMS-PAS-LUM-15-001
17	CMS Collaboration	CMS luminosity measurements for the 2016 data taking period	CMS-PAS-LUM-17-001	CMS-PAS-LUM-17-001
18	T. Sjostrand, S. Mrenna, and P. Z. Skands	PYTHIA 6.4 physics and manual	JHEP 05 (2006) 026	hep-ph/0603175
19	J. Pumplin et al.	New generation of parton distributions with uncertainties from global QCD analysis	JHEP 07 (2002) 012	hep-ph/0201195
20	F. E. Paige, S. D. Protopopescu, H. Baer, and X. Tata	ISAJET 7.69: A Monte Carlo event generator for pp, $ \overline{\mathrm{p}}\mathrm{p} $, and $ \mathrm{e}^+ \mathrm{e}^- $ reactions		hep-ph/0312045
21	B. Fuks, M. Klasen, D. R. Lamprea, and M. Rothering	Gaugino production in proton-proton collisions at a center-of-mass energy of 8 TeV	JHEP 10 (2012) 081	1207.2159
22	B. Fuks, M. Klasen, D. R. Lamprea, and M. Rothering	Precision predictions for electroweak superpartner production at hadron colliders with resummino	EPJC 73 (2013) 2480	1304.0790
23	P. M. Nadolsky et al.	Implications of CTEQ global analysis for collider observables	PRD 78 (2008) 013004	0802.0007
24	A. D. Martin, W. J. Stirling, R. S. Thorne, and G. Watt	Parton distributions for the LHC	EPJC 63 (2009) 189	0901.0002
25	J. Alwall et al.	MadGraph 5: going beyond	JHEP 06 (2011) 128	1106.0522
26	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
27	T. Sjostrand, S. Mrenna, and P. Z. Skands	A brief introduction to PYTHIA 8.1	CPC 178 (2008) 852	0710.3820
28	P. Nason	A new method for combining NLO QCD with shower Monte Carlo algorithms	JHEP 11 (2004) 040	hep-ph/0409146
29	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with parton shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
30	S. Alioli, P. Nason, C. Oleari, and E. Re	A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX	JHEP 06 (2010) 043	1002.2581
31	T. Melia, P. Nason, R. Rontsch, and G. Zanderighi	$ \text{W}^{+}\text{W}^{-} $, WZ and ZZ production in the POWHEG BOX	JHEP 11 (2011) 078	1107.5051
32	P. Nason and G. Zanderighi	W$ ^+ $W$ ^- $, WZ and ZZ production in the POWHEG-BOX-V2	EPJC 74 (2014) 2702	1311.1365
33	NNPDF Collaboration	Parton distributions for the LHC Run II	JHEP 04 (2015) 040	1410.8849
34	P. Skands, S. Carrazza, and J. Rojo	Tuning PYTHIA 8.1: the Monash 2013 tune	EPJC 74 (2014) 3024	1404.5630
35	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
36	GEANT4 Collaboration	GEANT4 --- a simulation toolkit	NIMA 506 (2003) 250
37	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
38	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ k_t $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
39	CMS Collaboration	Jet algorithms performance in 13 TeV data	CMS-PAS-JME-16-003	CMS-PAS-JME-16-003
40	Particle Data Group Collaboration	Review of particle physics	CPC 40 (2016) 100001
41	R. D. Cousins and V. L. Highland	Incorporating systematic uncertainties into an upper limit	NIMA 320 (1992) 331
42	The ATLAS Collaboration, The CMS Collaboration, The LHC Higgs Combination Group	Procedure for the LHC Higgs boson search combination in summer 2011	CMS-NOTE-2011-005
43	A. L. Read	Presentation of search results: The CL$ _{\text{s}} $ technique	JPG 28 (2002) 2693
44	T. Junk	Confidence level computation for combining searches with small statistics	NIMA 434 (1999) 435	hep-ex/9902006
45	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727