CMS-PAS-EXO-17-002

CMS-PAS-EXO-17-002
Search for excited states of light and heavy flavor quarks in the $\gamma$+jets final state in proton-proton collisions at $\sqrt{s}= $ 13 TeV
CMS Collaboration
July 2017

Abstract: A search for excited states of light and heavy flavor quarks decaying into the $\gamma$+jets final state is presented. 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 in 2016 at the LHC. Events containing at least one photon and one jet with high transverse momenta are selected and the $\gamma$+jets invariant mass distribution is searched for a resonance peak. The upper limits on the cross section times branching fraction are evaluated as a function of the excited quark masses. At 95% confidence level, the most stringent limits are presented in $\gamma$+jets final state to exclude the excited light quarks with masses below 5.5 TeV and the excited b quarks with masses below 1.8 TeV for coupling multiplier $f = 1.0$.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 781 (2018) 390. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Acceptance times efficiency for ${ {\mathrm {q}^\star } }$ and ${ {\mathrm {b}^\star } }$ signal for coupling $f = 1.0$ as a function of generated M$_{{ {\mathrm {q}^\star } }}$ or M$_{{ {\mathrm {b}^\star } }}$ mass using MC simulation.
png pdf	Figure 2: The $\gamma$+jets invariant mass distribution in data (black points) for the inclusive category used for the ${ {\mathrm {q}^\star } }$ analysis, after final selection. The result of the fit to the data using the parametrization defined in Eq. 2 is shown with the blue dashed curve. The bin-by-bin pull, (Data-Fit)/stat. unc., where stat. unc. refers to the statistical uncertainty in data, is also presented. Simulations of excited quark signals are shown for mass points 1.0 and 5.0 TeV for $f = 1.0$ and for mass point 2.0 TeV for $f = 0.5$.
png pdf	Figure 3: The $\gamma$+b-jets invariant mass distribution in data (black points) used for the ${ {\mathrm {b}^\star } }$ analysis, after final selection for (a) 1 b tag category and (b) 0 b tag category. The result of the fit to the data using the parametrization defined in Eq. 2 is shown with the blue dashed curve. The bin-by-bin pull, (Data-Fit)/stat. unc., where stat. unc. refers to the statistical uncertainty in data, is also presented. Simulations of excited b quark signals are shown under 1 and 0 b tag category for masses 1.0 and 2.0 TeV for $f = 1.0$.
png pdf	Figure 3-a: The $\gamma$+b-jets invariant mass distribution in data (black points) used for the ${ {\mathrm {b}^\star } }$ analysis, after final selection for 1 b tag category. The result of the fit to the data using the parametrization defined in Eq. 2 is shown with the blue dashed curve. The bin-by-bin pull, (Data-Fit)/stat. unc., where stat. unc. refers to the statistical uncertainty in data, is also presented. Simulations of excited b quark signals are shown under 1 and 0 b tag category for masses 1.0 and 2.0 TeV for $f = 1.0$.
png pdf	Figure 3-b: The $\gamma$+b-jets invariant mass distribution in data (black points) used for the ${ {\mathrm {b}^\star } }$ analysis, after final selection for 0 b tag category. The result of the fit to the data using the parametrization defined in Eq. 2 is shown with the blue dashed curve. The bin-by-bin pull, (Data-Fit)/stat. unc., where stat. unc. refers to the statistical uncertainty in data, is also presented. Simulations of excited b quark signals are shown under 1 and 0 b tag category for masses 1.0 and 2.0 TeV for $f = 1.0$.
png pdf	Figure 4: The expected and observed 95% CL upper limits on $\sigma \times \text {B}$ for excited quark search in $\gamma$+jets final state corresponding to coupling $f = 1.0$. The limits are compared with the theoretical predictions for excited quark production. The uncertainties at 1 and 2 standard deviations (s.d.) levels are shown as green and yellow shaded bands around expected limit.
png pdf	Figure 5: The expected and observed 95% CL upper limits on $\sigma \times \text {B}$ for excited b quark search in $\gamma$+b-jets final state corresponding to coupling $f = 1.0$. The limits are compared with the theoretical predictions for excited b quark production. The uncertainties at 1 and 2 standard deviations (s.d.) levels are shown as green and yellow shaded bands around expected limit.
png pdf	Figure 6: The observed and expected excluded regions for ${ {\mathrm {q}^\star } }$ and ${ {\mathrm {b}^\star } }$ at 95% CL as a function of M$_{{ {\mathrm {q}^\star } }}$, M$_{{ {\mathrm {b}^\star } }}$ and the coupling strength $f$.

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

Summary

We have presented a search for excited states of light and heavy flavor quarks in the $\gamma$+jets and $\gamma$+b-jets final states, respectively. The search is performed with data collected at $\sqrt{s} =$ 13 TeV in 2016, which corresponds to an integrated luminosity of 35.9 fb$^{-1}$.

The 95% CL upper limits are placed on $\sigma\times\text{B}$ for $ {\mathrm{q}^\star} $ and $ {\mathrm{b}^\star} $ production in $\gamma$+jets and $\gamma$+b-jets final states, respectively. Comparing these cross section upper limits with theoretical predictions, an excited quark within mass range 1.0 $ < \text{M}_{ {\mathrm{q}^\star} } < $ 5.5 TeV and an excited b quark within mass range 1.0 $ < \text{M}_{ {\mathrm{b}^\star} } < $ 1.8 TeV are excluded at 95% CL for coupling multipliers $f = 1.0$. We present the first result on the search of excited b quark at $\sqrt{s} = $ 13 TeV at the LHC. These are best results to date for $ {\mathrm{q}^\star} $ and $ {\mathrm{b}^\star} $ searches in $\gamma$+jets final state at the LHC.

References
1	U. Baur, I. Hinchliffe, and D. Zeppenfeld	Excited Quark Production at Hadron Colliders	Int. J. Mod. Phys. A 2 (1987) 1285
2	W. Buchmuller	Composite Quarks and Leptons	Acta Phys. Austriaca Suppl. 27 (1985) 517
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 $ p\bar{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	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
8	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
9	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
10	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
11	CMS Collaboration	Search for excited quarks in the $ \gamma + $jet final state in proton proton collisions at $ \sqrt{s} = $ 13 TeV
12	CMS Collaboration	Searches for dijet resonances in pp collisions at $ \sqrt{s} = $ 13 TeV using data collected in 2016
13	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
14	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
15	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	Submitted to JINST	CMS-PRF-14-001 1706.04965
16	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ k_t $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
17	CMS Collaboration	Determination of Jet Energy Calibration and Transverse Momentum Resolution in CMS	JINST 6 (2011) P11002	CMS-JME-10-011 1107.4277
18	M. Cacciari, G. P. Salam, and G. Soyez	FastJet User Manual	EPJC 72 (2012) 1896	1111.6097
19	CMS Collaboration	Jet Performance in pp Collisions at 7 TeV
20	CMS Collaboration	Identification of b quark jets at the CMS Experiment in the LHC Run 2
21	CMS Collaboration	Identification of b-quark jets with the CMS experiment	JINST 8 (2013) P04013	CMS-BTV-12-001 1211.4462
22	T. Sjostrand et al.	An Introduction to PYTHIA 8.2	CPC 191 (2015) 159	1410.3012
23	GEANT4 Collaboration	GEANT4: A Simulation toolkit	NIMA 506 (2003) 250
24	CMS Collaboration	Underlying Event Tunes and Double Parton Scattering
25	P. Skands, S. Carrazza, and J. Rojo	Tuning PYTHIA 8.1: the Monash 2013 Tune	EPJC 74 (2014) 3024	1404.5630
26	R. D. Ball et al.	Parton distributions with LHC data	Nucl. Phys. B 867 (2013) 244	1207.1303
27	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
28	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
29	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
30	R. A. Fisher		Genesis Publishing Pvt Ltd
31	CMS Collaboration	CMS Luminosity Measurement for the 2016 Data Taking Period
32	T. Junk	Confidence level computation for combining searches with small statistics	NIMA 434 (1999) 435	hep-ex/9902006
33	A. L. Read	Presentation of search results: The CL(s) technique	JPG 28 (2002) 2693