CMS-EXO-17-002

CMS-EXO-17-002 ; CERN-EP-2017-271
Search for excited quarks of light and heavy flavor in $ \gamma $+jet final states in proton-proton collisions at $\sqrt{s} = $ 13 TeV
CMS Collaboration
13 November 2017
Phys. Lett. B 781 (2018) 390
Abstract: A search is presented for excited quarks of light and heavy flavor that decay to $ \gamma $+jet final states. The analysis is based on data corresponding to an integrated luminosity of 35.9 fb$^{-1}$ collected by the CMS experiment in proton-proton collisions at $\sqrt{s} = $ 13 TeV at the LHC. A signal would appear as a resonant contribution to the invariant mass spectrum of the $ \gamma $+jet system, above the background expected from standard model processes. No resonant excess is found, and upper limits are set on the product of the excited quark cross section and its branching fraction as a function of its mass. These are the most stringent limits to date in the $ \gamma $+jet final state, and exclude excited light quarks with masses below 5.5 TeV and excited b quarks with masses below 1.8 TeV, assuming standard model couplings.
Links: e-print arXiv:1711.04652 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The product of acceptance and efficiency for ${{\mathrm{q} }}$ and ${{\mathrm{b} }}$ signals as a function of generated $m_{{{\mathrm{q} }}}$ or $m_{{{\mathrm{b} }}}$ mass, calculated using MC simulation.
png pdf	Figure 2: The $ {\gamma + \text {jet}}$ invariant mass distribution in data (black points) for the inclusive category used for the ${{\mathrm{q} *}}$ analysis, after final selection. The result of the fit to the data using the parametrization defined in Eq. xxxxx) is shown by the blue dashed curve with associated bands indicating the uncertainty. The bin-by-bin pull, (Data-Fit)/(stat. unc.), where the denominator refers to the statistical uncertainty in data, is also presented. The green and yellow bands corresponds to 1 and 2 standard deviations, respectively from the mean value. Simulations of excited quark signals representing the expected excess of signal events over the background are shown for the mass values of 1.0 and 5.0 TeV for $f = 1.0$, and 2.0 TeV for $f = 0.5$.
png pdf	Figure 3: The $ \gamma $+b-jet invariant mass distribution in data (black points) used for the ${{\mathrm{b} *}}$ analysis, after final selection for (left) 1b tag category and (right) 0b tag category. The result of the fit to the data using the parametrization defined in Eq. xxxxx) is shown by the blue dashed curve with associated bands indicating the uncertainty. The bin-by-bin pull, (Data-Fit)/(stat. unc.), where the denominator refers to the statistical uncertainty in data, is also presented. The green and yellow bands corresponds to 1 and 2 standard deviations, respectively from the mean value. Simulations of excited b quark signals representing the expected excess of signal events over the background are shown for the 1b and 0b tag categories for the mass values of 1.0 and 2.0 TeV for $f = 1.0$.
png pdf	Figure 3-a: The $ \gamma $+b-jet invariant mass distribution in data (black points) used for the ${{\mathrm{b} *}}$ analysis, after final selection for (left) 1b tag category and (right) 0b tag category. The result of the fit to the data using the parametrization defined in Eq. xxxxx) is shown by the blue dashed curve with associated bands indicating the uncertainty. The bin-by-bin pull, (Data-Fit)/(stat. unc.), where the denominator refers to the statistical uncertainty in data, is also presented. The green and yellow bands corresponds to 1 and 2 standard deviations, respectively from the mean value. Simulations of excited b quark signals representing the expected excess of signal events over the background are shown for the 1b and 0b tag categories for the mass values of 1.0 and 2.0 TeV for $f = 1.0$.
png pdf	Figure 3-b: The $ \gamma $+b-jet invariant mass distribution in data (black points) used for the ${{\mathrm{b} *}}$ analysis, after final selection for (left) 1b tag category and (right) 0b tag category. The result of the fit to the data using the parametrization defined in Eq. xxxxx) is shown by the blue dashed curve with associated bands indicating the uncertainty. The bin-by-bin pull, (Data-Fit)/(stat. unc.), where the denominator refers to the statistical uncertainty in data, is also presented. The green and yellow bands corresponds to 1 and 2 standard deviations, respectively from the mean value. Simulations of excited b quark signals representing the expected excess of signal events over the background are shown for the 1b and 0b tag categories for the mass values of 1.0 and 2.0 TeV for $f = 1.0$.
png pdf	Figure 4: The observed and expected upper limits at 95% CL on $\sigma \mathcal {B}$ as a function of the mass of the excited quark, for $f = 1.0$. The limits are compared with theoretical predictions for excited quark production for three couplings. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the mean limits under the background-only hypothesis.
png pdf	Figure 5: The observed and expected upper limits at 95% CL on $\sigma \mathcal {B}$ as a function of the mass of the excited b quark, for $f = 1.0$. The limits are compared with theoretical predictions for excited b quark production for three couplings. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the mean limits under the background-only hypothesis.
png pdf	Figure 6: The observed and expected regions excluded at 95% CL for ${{\mathrm{q} }}$ and ${{\mathrm{b} }}$ production and decay, as a function of $m_{{{\mathrm{q} }}}$, $m_{{{\mathrm{b} }}}$ and $f$.

Tables
png pdf	Table 1: Summary of the dominant sources of uncertainties and their effect on the signal yield.

Summary

A search has been presented for excited states of light and b quarks in $ \gamma $+jet final states, using data corresponding to an integrated luminosity of 35.9 fb$^{-1}$, collected at $\sqrt{s} = $ 13 TeV. Upper limits at the 95% confidence level are placed on the product of production cross section and decay branching fraction for the presence of ${\mathrm{q}*}$ and ${\mathrm{b}*}$ excited quarks in $ \gamma $+jet final states. Comparing these upper limits with theoretical predictions, excited light quarks within the mass range 1.0 $ < m_{\mathrm{q}*} < $ 5.5 TeV and excited b quarks within the mass range 1.0 $ < m_{\mathrm{b}*} < $ 1.8 TeV are excluded at 95% confidence level, assuming standard model couplings. These are the most sensitive limits for ${\mathrm{q}*}$ and ${\mathrm{b}*}$ searches in the $ \gamma $+jet final states. In addition, the search for excited b quarks is the first to be presented in any final state at $\sqrt{s} = $ 13 TeV.

References
1	W. Buchmuller	Composite quarks and leptons	Acta Phys. Austriaca Suppl. 27 (1985) 517
2	U. Baur, I. Hinchliffe, and D. Zeppenfeld	Excited quark production at hadron colliders	Int. J. Mod. Phys. A 2 (1987) 1285
3	U. Baur, M. Spira, and P. M. Zerwas	Excited quark and lepton production at hadron colliders	PRD 42 (1990) 815
4	S. Bhattacharya, S. S. Chauhan, B. C. Choudhary, and D. Choudhury	Quark excitations through the prism of direct photon plus jet at the LHC	PRD 80 (2009) 015014	0901.3927
5	CDF Collaboration	Search for excited quarks in $ \text{p}\bar{\text{p}} $ collisions at $ \sqrt{s} = $ 1.8 TeV	PRL 72 (1994) 3004
6	CDF Collaboration	Search for new particles decaying to dijets at CDF	PRD 55 (1997) 5263	hep-ex/9702004
7	CDF Collaboration	Search for new particles decaying into dijets in proton-antiproton collisions at $ \sqrt{s} = $ 1.96 TeV	PRD 79 (2009) 112002	0812.4036
8	CMS Collaboration	Search for excited quarks in the $ \gamma + $jet final state in proton-proton collisions at $ \sqrt{s}= $ 8 TeV	PLB 738 (2014) 274	CMS-EXO-13-003 1406.5171
9	CMS Collaboration	Search for resonances and quantum black holes using dijet mass spectra in proton-proton collisions at $ \sqrt{s} = $ 8 TeV	PRD 91 (2015) 052009	CMS-EXO-12-059 1501.04198
10	CMS Collaboration	Search for narrow resonances decaying to dijets in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	PRL 116 (2016) 071801	CMS-EXO-15-001 1512.01224
11	ATLAS Collaboration	Search for new phenomena with photon+jet events in proton-proton collisions at $ \sqrt{s}= $ 13 TeV with the ATLAS detector	JHEP 03 (2016) 041	1512.05910
12	CMS Collaboration	Performance of photon reconstruction and identification with the CMS detector in proton-proton collisions at $ \sqrt{s} = $ 8 TeV	JINST 10 (2015) P08010	CMS-EGM-14-001 1502.02702
13	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
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	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ k_t $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
16	CMS Collaboration	Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV	JINST 12 (2017) P02014	CMS-JME-13-004 1607.03663
17	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
18	CMS Collaboration	Jet algorithms performance in 13 TeV data	CMS-PAS-JME-16-003	CMS-PAS-JME-16-003
19	CMS Collaboration	Identification of b quark jets at the CMS Experiment in the LHC Run 2	CMS-PAS-BTV-15-001	CMS-PAS-BTV-15-001
20	CMS Collaboration	Identification of b-quark jets with the CMS experiment	JINST 8 (2013) P04013	CMS-BTV-12-001 1211.4462
21	T. Sj$\ddot\texto$strand et al.	An introduction to PYTHIA 8.2	CPC 191 (2015) 159	1410.3012
22	GEANT4 Collaboration	GEANT4 --- a simulation toolkit	NIMA 506 (2003) 250
23	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
24	P. Skands, S. Carrazza, and J. Rojo	Tuning PYTHIA 8.1: the Monash 2013 Tune	EPJC 74 (2014) 3024	1404.5630
25	NNPDF Collaboration	Parton distributions with LHC data	NPB 867 (2013) 244	1207.1303
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	J. Alwall et al.	Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions	EPJC 53 (2008) 473	0706.2569
28	R. A. Fisher	On the interpretation of $ \chi^{2} $ from contingency tables, and the calculation of p	J. Roy. Stat. Soc. 85 (1922) 87
29	J. Butterworth et al.	PDF4LHC recommendations for LHC Run II	JPG 43 (2016) 023001	1510.03865
30	CMS Collaboration	CMS luminosity measurement for the 2016 data taking period	CMS-PAS-LUM-17-001	CMS-PAS-LUM-17-001
31	T. Junk	Confidence level computation for combining searches with small statistics	NIMA 434 (1999) 435	hep-ex/9902006
32	A. L. Read	Presentation of search results: The CLs technique	JPG 28 (2002) 2693
33	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727