Search for new physics in final states with a lepton and missing transverse energy in pp collisions at the LHC

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Search for new physics in final states with a lepton and missing transverse energy in pp collisions at the LHC

S. Chatrchyan et al.*

(CMS Collaboration)

(Received 12 February 2013; published 8 April 2013)

This Letter describes the search for an enhanced production rate of events with a charged lepton and a neutrino in high-energypp collisions at the LHC. The analysis uses data collected with the CMS detector, with an integrated luminosity of5:0 fb¹ at ffiffiffi

ps

¼ 7 TeV, and a further 3:7 fb¹ at ffiffiffi ps

¼ 8 TeV. No evidence is found for an excess. The results are interpreted in terms of limits on a heavy charged gauge boson (W⁰) in the sequential standard model, a split universal extra dimension model, and contact interactions in the helicity-nonconserving model. For the last, values of the binding energy below 10.5 (8.8) TeV in the electron (muon) channel are excluded at a 95% confidence level. Interpreting the‘ final state in terms of a heavyW⁰with standard model couplings, masses below 2.90 TeV are excluded.

DOI:10.1103/PhysRevD.87.072005 PACS numbers: 12.60.Cn, 13.85.Rm, 14.70.Pw

I. INTRODUCTION

New heavy gauge bosons are predicted by various ex- tensions of the standard model (SM). The sequential standard model (SSM) [1] postulates the existence of a W⁰ boson, a heavy analogue of theW. In such a theory, the W⁰ is expected to appear as a narrow resonance with decay modes and branching fractions similar to those of theW.

ForW⁰masses above 180 GeV, where thet b decay channel opens up, the predicted branching fraction is about 8.5%

for each of the leptonic final states. Previous searches [2,3]

with pp collision data at ffiffiffi ps

¼ 7 TeV by the Compact Muon Solenoid (CMS) and ATLAS experiments at the Large Hadron Collider (LHC), based on an integrated luminosity of up to5 fb¹, have excluded SSMW⁰bosons with masses up to 2.6 TeV.

Other models for new physics predict the same final state, such as those with universal extra dimensions (UED) and bulk fermions, or split UED [4,5]. Such models of extended space-time assume one additional compact dimension of radius R. The split-UED parameter space is defined by 1=R and , with being the bulk mass parameter of the fermion field in five dimensions.

For suitable nonzero values of , as assumed by split- UED models, the cross sections are sufficiently large to allow observation by LHC experiments. All SM particles have corresponding Kaluza-Klein (KK) partners, for in- stanceW_KKⁿ , wheren denotes the nth KK excitation mode.

Only KK-even modes of W_KKⁿ couple to SM fermions, owing to KK-parity conservation [6]. Modes withn 4 have a smaller cross section and are not expected to be

accessible at ffiffiffi ps

¼ 8 TeV, hence the only mode considered isn ¼ 2.

Motivated by the observation of mass hierarchies in the fermion sector, theories have been developed where leptons and quarks are composite objects [7]. At energies much lower than the binding energy of these fundamental constituents, typically called, quark and lepton compositeness would manifest itself as a four-fermion contact interaction (CI). One of the possible contact interactions between two quarks, a neutrino, and a charged lepton, is described by the helicity-nonconserving (HNC) model [8].

The corresponding cross section is proportional to the square of the partonic center-of-mass energy and to ⁴. While CDF has set a limit on > 2:81 TeV [9] based on a final state with an electron and a neutrino, no limit in the HNC model has yet been set in the muon channel.

In this Letter, a search is presented for an excess of events with an isolated charged lepton (an electron or muon) and a neutrino in the final state, using the CMS detector. The data sample corresponds to an integrated luminosity of5:0 fb¹ at ffiffiffi

ps

¼ 7 TeV collected in 2011, and3:7 fb¹at ffiffiffi

ps

¼ 8 TeV collected in 2012. The CMS 2011 result has been published in Ref. [2].

II. THE CMS DETECTOR

The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. Within the superconducting solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter, and a brass and scintillator hadron calorimeter. Muons are measured in gas-ionization detectors embedded in the steel return yoke.

Extensive forward calorimetry complements the coverage provided by the barrel and end cap detectors. A more detailed description of the CMS detector can be found in Ref. [10]. CMS uses a right-handed coordinate system, with the origin at the nominal interaction point, the x

*Full author list given at the end of the article.

Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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axis pointing to the center of the LHC, they axis pointing up (perpendicular to the LHC plane), and thez axis along the anticlockwise-beam direction. The polar angle is measured from the positivez axis and the azimuthal angle

is measured in the x-y plane.

III. THE SEARCH STRATEGY

Candidate events with at least one high transverse momentum (pT) electron or muon are selected using single- lepton triggers. Isolated high-pTleptons are reconstructed

using very stringent quality criteria while the neutrino gives rise to experimentally observed missing transverse energy (E^miss_T ). The details on lepton identification and E^miss_T reconstruction, as optimized for the 2011 analysis, can be found in Ref. [2]. The discriminating variable of this analysis is the transverse mass MT of the lepton-E^miss_T system, calculated as

MT¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 p^‘_T E^miss_T ð1 cos ‘;Þ

q ; (1)

where _‘;is the azimuthal angle between the charged lepton’s transverse momentump^‘_Tand theE^miss_T direction.

InW⁰decays, as well as for the other models considered, the lepton andE^miss_T are expected to be almost back to back in the transverse plane, and balanced in transverse energy.

Additional kinematic criteria therefore select events with a ratio of the leptonp^‘_Tand theE^miss_T ,0:4 < p^‘_T=E^miss_T < 1:5, along with the requirement of the angular difference, j‘; j < 0:2. For simulated SSM W⁰ events with masses between 0.5 and 2.5 TeV passing these selection criteria, the signal efficiency (including 90% geometrical acceptance) is found to be 70%–75% with 2% uncertainty in the electron channel and 67%–72% with 1% uncertainty in the muon channel. For the HNC contact-interaction model the signal efficiency is independent of the interaction scale and has been determined from simulation to be 80% with 1% uncertainty for the electron channel and 77%

with 4% uncertainty for the muon channel. The transverse mass distributions for accepted SM events in the electron and muon channels are shown in Fig. 1, along with two example W⁰ signals. The observed event with the highest transverse mass in the electron channel hasMT¼ 2:38 0:05 TeV based on E_T¼ 1:2 TeV with 1% uncertainty. In the muon channel the maximum transverse mass isM_T¼ 1:33 0:03 TeV with a measured p^‘_T of 690 22 GeV.

The two types of processes,W⁰production and compositeness, can be distinguished by examining the shape of the lepton-E^miss_T transverse mass spectrum. Both processes manifest themselves through an excess of events at the

FIG. 1 (color online). Observed lepton-E^miss_T transverse mass distributions in the electron (top) and the muon (bottom) channel. The dashed lines show the parametrization of the background as described in the text (labeled as BG parametrization in the legend). Simulated signal distributions for a SSM W⁰ are also shown, including detector resolution effects. The simulated background labeled as ‘‘diboson’’ includesWW, ZZ, andWZ contributions. The last bin contains the contributions of all bins above the displayed range.

) V e G

T ( M 1500

Events / 40 GeV

10-2

10-1

1 10

102 _{W + HNC} _{= 4 TeV}

= 7 TeV W + HNC

= 9 TeV W + HNC W only

CMS Simulation, 3.7 fb^-1, 2012, s = 8 TeV

1000 2000 2500 3000

FIG. 2 (color online). Simulated transverse mass distribution shown for contact interaction (HNC model), in the muonþ E^miss_T channel at generator level for CI signals with ¼ 4, 7, and 9 TeV, and the SM background (W ! ).

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high end of the spectrum. The W⁰ signal events are expected to concentrate in a Jacobian peak around the W⁰ mass, as shown in Fig. 1. Compositeness would rather yield an unstructured excess, with the excess relative to the standard model contribution increasing as a function of M_T, as shown in Fig.2.

IV. SIGNAL AND BACKGROUNDS

The W⁰ (this also includes W_KK^n¼2) and CI signals are generated at leading order (LO) withPYTHIA 6.4.26 [11]

using the CTEQ6L1 [12] parton distribution functions.

They are scaled to the next-to-next-to-leading order (NNLO) cross section calculated with FEWZ [13,14] for eachW⁰(W_KK^n¼2) mass point. In the absence of higher-order calculations, LO cross sections are used for the CI model.

The primary source of background is the off-peak, high-M_T tail of the standard model W ! ‘ decays.

Other important backgrounds arise from tt, Drell-Yan, and diboson (WW, WZ, ZZ) events. An important background also comes from QCD multijet processes, but this is largely removed by the analysis selections and therefore cannot be readily distinguished in Fig. 1. Contributions from decays with leptons in the final state that subse- quently decay to an electron or muon and neutrinos are considered as well, but found to be negligible. ThePYTHIA

6 generator is used for all background processes except for tt, which is generated with^MADGRAPH4 [15] in combination withPYTHIA. The numbers of Monte Carlo events are normalized using the integrated luminosity of the recorded data and with NNLO cross sections, except diboson and multijet samples, for which the next-to-leading order and LO cross sections are used, respectively. In all event samples, additional minimum bias interactions are super- imposed onto the main background processes to match the luminosity profile of the analyzed data set.

The background prediction is based on the transverse mass distributions of these simulations, as seen in Fig.1.

The summed background distribution is parametrized with a function of form fðM_TÞ ¼_ðM_T^a_þbÞc to avoid event

TABLE I. Data, background, and signal event yields for different transverse mass thresholds.

M_T> 1:0 TeV M_T> 1:5 TeV M_T> 2:0 TeV

Electron channel

Data 3 1 1

SM background 6:8 0:4 0:69^þ0:05_0:04 0:13 0:02

M_W⁰¼ 2:5 TeV 9:7 0:3 7:5 0:2 4:7 0:2

M_W⁰¼ 3 TeV 1:98 0:06 1:5 0:05 1:15^þ0:05_0:04

CI, ¼ 4 TeV 220 5 72 3 21 1

CI, ¼ 9 TeV 8:6 0:2 2:8 0:1 0:81^þ0:05_0:04

Muon channel

Data 9 0 0

SM background 6:5^þ1:9_1:5 0:92^þ0:49_0:32 0:20^þ0:14_0:08

M_W⁰¼ 2:5 TeV 9:4 0:3 7:0 0:5 4:1^þ0:8_0:7

M_W⁰¼ 3 TeV 1:9 0:1 1:4 0:1 0:94^þ0:12_0:10

CI, ¼ 4 TeV 240 20 80^þ15₁₃ 28^þ8₆

CI, ¼ 9 TeV 34 3 12^þ3₂ 3:5^þ1:2_0:9

(GeV) MW'

500 1000 1500 2000 2500 3000 3500 4000

B (fb)×σ

1 10 102

103

104

105 Observed 95% CL limit

ν

→ e Observed 95% CL limit W'

ν µ

→ Observed 95% CL limit W' Expected 95% CL limit

σ

± 1 Expected 95% CL limit

σ

± 2 Expected 95% CL limit SSM W' NNLO PDF uncertainty

= 10 TeV NNLO µ

with WKK

= 0.05 TeV NNLO µ

with WKK

= 8 TeV s , 2012, CMS, 3.7 fb-1

miss

+ ET

µ

miss, e + ET

FIG. 3 (color online). Limits on the cross section times the single channel branching fraction ( B) for heavy bosons based on the 2012 data for the electron and the muon channels.

For the individual channels, only the observed limits are shown.

For the combination, the observed limit, the expected limit, the 1, and the 2 bands are displayed. The model assumes equal branching fractions for the electron and the muon channel, hence the combination corresponds to doubling the number of events.

All limits are displayed for the single channel branching fraction.

The W⁰ mass limits are derived with a Bayesian method for the models of a SSMW⁰andW_KK^n¼2in split UED. TheW_KK^n¼2is the lowest mass state that can couple to SM fermions and has the same final state as the SM-like W⁰. Because it has even KK parity, it can be produced singly.

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fluctuations due to the limited size of the Monte Carlo event sample, also shown in Fig.1. In the low mass control region, e.g. forMT> 500 GeV, the background prediction in the electron channel is 169 events from a direct count and155 16 events from the parametrization. The corresponding event numbers in the muon channel are 162 and 138 12, from the direct count and the parametrization, respectively. The number of observed events in each channel is 153. The expected background due to SM processes drops significantly with increasing M_T. The number of events observed and the number expected from the parametrization, above three characteristic high M_T thresholds, are shown in TableIfor the electron and the muon channels. Also summarized are the expected numbers of W⁰ and CI signal events, as evaluated from simulation, including systematic uncertainties due to imperfections in the description of the detector performance.

V. RESULTS AND EXCLUSION LIMITS For determining the exclusion limits, systematic uncertainties on the signal and background yields are included via nuisance parameters with a log-normal

prior distribution in the same way as in our previous analysis from Ref. [2]. The lepton-energy calibration and resolution distort the transverse mass spectrum.

Uncertainties in the energy scale and the energy resolution make comparable contributions to the overall uncertainty in the electron channel: the energy scale has an uncertainty of 1(3)% in the barrel (end caps) and the resolution has an uncertainty of 1.4(3)% for the barrel (end caps) [16]. For muons, the dominant uncertainty stems from the momentum scale, which is taken to be 5% p_T=TeV [17] and results in larger errors on the background and signal event yields in the muon channel, as can be seen in Table I. The muon p_T resolution has been determined with cosmic ray muons to be 10% at high p_Twith an uncertainty of 0.6% [17].

Similarly, the impact of theE^miss_T energy scale is mod- eled by shifting the hadronic component event by event by 10%, while the resolution is taken into account by a 10%

smearing. In all cases, the impact on the expected number of signal events is around 1% for each source of uncertainty. The background parametrization procedure is re- peated using the distorted distributions. Additionally, an uncertainty is derived by fitting the undistorted background with two different functions. The estimates shown in Table I include a systematic uncertainty that covers the range of results from these fits, with the statistical uncertainty coming from the fit to the original distribution.

Additionally, an uncertainty of 4.4% is considered on the integrated luminosity [18].

The number of data events above a transverse mass threshold M^min_T is compared to the expected number of signal and background events, with the M_T^min threshold being optimized for the best expected exclusion limit, using steps of 50 GeV. Very similar results are achieved TABLE II. Exclusion limits in TeV on the SSMW⁰mass for

the electron and muon channel as well as their combinations based on5:0 fb¹of 2011 data at ffiffiffi

ps

¼ 7 TeV and 3:7 fb¹ of 2012 data at ffiffiffi

ps

¼ 8 TeV.

Obs. Exp. Obs. Exp. Obs. Exp.

Channel 2011 2011 2012 2012 2011 þ 2012 2011 þ 2012

e 2.40 2.45 2.60 2.70 2.70 2.75

2.40 2.45 2.75 2.65 2.75 2.70

e þ 2.50 2.60 2.85 2.80 2.90 2.90

(GeV) MW'

1000 1500 2000 2500 3000 SSM W'σ / excl.σ

10-3

10-2

10-1

1 10

Observed 95% CL limit Expected 95% CL limit

σ

= 7 / 8 TeV s , 2011 / 2012, CMS, 5.0 / 3.7 fb-1

miss

e + ET

(GeV) MW'

1000 1500 2000 2500 3000 SSM W'σ / excl.σ

10-3

10-2

10-1

1 10

σ

= 7 / 8 TeV s , 2011 / 2012, CMS, 5.0 / 3.7 fb-1

miss

+ ET

µ

(GeV) MW'

1000 1500 2000 2500 3000 SSM W'σ / excl.σ

10-3

10-2

10-1

1 10

σ

= 7 / 8 TeV s , 2011 / 2012, CMS, 5.0 / 3.7 fb-1

miss

+ ET

µ

miss, e + ET

FIG. 4 (color online). Combination of 2011 and 2012 data for the electron and the muon channels using5:0 fb¹of data at ffiffiffi ps 7 TeV from 2011 and 3:7 fb¹of data at ffiffiffi ¼

ps

¼ 8 TeV from 2012. The left and middle plots show the individual combinations for the electron (left) and muon channel (right). To the right the combination of both is displayed. The limits are derived with a Bayesian method. Plotted is the signal strength modifier_excl=_{SSM W}⁰as a function of theW⁰mass, where_exclis the cross section excluded at a 95% C.L. and_{SSM W}⁰is the cross section predicted by the SSM. AllW⁰mass points below the ratio_excl=_{SSM W}⁰ ¼ 1, shown as a red dashed line, are excluded in the sequential standard model.

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when optimizing for discovery. The same optimization procedure is applied for the W⁰ and CI searches but the optimizedMTthresholds are specific to each analysis. For aW⁰mass of up to 2.5 TeV the optimization tends to select a value forM_T^min a little below the peak of the Jacobian, retaining most of the events in the peak. To keep a significant signal contribution for higher masses, the M_T^min threshold is shifted to lower values owing to the increasing off-shell fraction. For CI no such effect exists and the optimized M_T^min threshold is roughly constant around 1 TeV.

No significant excess has been observed in the data, and upper limits are set on the production cross section times the branching fraction BðW⁰ ! ‘Þ, with ‘ ¼ e or , using a Bayesian method with the assumption of a flat prior for the parameter of interest. The expected and observed upper cross section limits on a SSMW⁰, at 95% confidence level (C.L.), for ffiffiffi

ps

¼ 8 TeV data, are shown in Fig.3for both channels and their combination. Using the central value of the theoretical NNLO SSMW⁰cross section times branching fraction, which is assumed to be identical in the two channels, we exclude masses less than 2.60 TeV in the electron and 2.75 TeV in the muon channel. The expected limits are 2.70 TeV and 2.65 TeV, respectively. The observed limit forW⁰ ! e is slightly lower than the expectation because of one event with a transverse mass of 2.3 TeV (Fig. 1). Combining both channels, the limit increases to 2.85 TeV (Table II). To further enhance the sensitivity, the new results can be combined with the published [2] ffiffiffi

ps

¼ 7 TeV results, based on an integrated

luminosity of5 fb¹, thus extending the limit to 2.90 TeV as shown in Fig.4and TableII.

The limit can be reinterpreted in terms of the W_KK^n¼2 mass, as shown in Fig. 3, for values of the Dirac mass term ¼ 0:05 TeV and ¼ 10 TeV and directly trans- lated to bounds on the split-UED parameter space, ð1=R; Þ (Fig.5). The four-fermion contact interaction of the HNC model is excluded for values of < 10:5 TeV in the electron channel and < 8:8 TeV in the muon channel (Fig. 6). While the expected sensitivity is comparable in both search channels, the exclusion limit in the electron FIG. 5 (color online). The 95% C.L. limits on the split-UED

parameters and 1=R derived from the W⁰ mass limits taking into account the corresponding width of the W_KK^n¼2. For the 3:7 fb¹ of 2012 data, the individual limits for the electron and muon channels are shown together with their combination, improving the excluded parameter space based on the 2011 data shown in yellow.

(TeV) Λ

6 8 10 12 14

B (fb)×σ

1 10 102

103

104

σ

± 2 Expected 95% CL limit HNC contact interaction LO PDF uncertainty

= 8 TeV s , 2012, CMS, 3.7 fb-1

miss CI e + ET

(TeV) Λ

6 8 10 12 14

B (fb)×σ

1 10 102

103

104

σ

± 2 Expected 95% CL limit HNC contact interaction LO PDF uncertainty

= 8 TeV s , 2012, CMS, 3.7 fb-1

miss CI + ET

µ

FIG. 6 (color online). Bayesian limits on the cross section times the single channel branching fraction ( B) for contact interactions (HNC model) in the electronþ E^miss_T (top) and the muonþ E^miss_T channel (bottom) based on an integrated luminosity of3:7 fb¹of ffiffiffi

ps

¼ 8 TeV data. The expected limit in either channel excludes values of the new interaction scale < 9 TeV.

The observed limit, driven by the data, excludes < 10:5 TeV (8.8) in the electron (muon) channel. The signal efficiency is independent of.

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channel is higher because of a downward fluctuation of data (see Table I) in the search region of MT> 1 TeV.

These limits are summarized in TableIII.

VI. SUMMARY

A search for new physics has been carried out usingpp collisions recorded with the CMS detector at center-of- mass energies of ffiffiffi

ps

¼ 7 and 8 TeV. The transverse mass spectrum of either electrons or muons and missing transverse energy has been measured. The observed spectra are consistent with the standard model expectation, and mass limits on sequential standard model W⁰ and W_KK^n¼2 have been set at the 95% C.L. These are the most stringent limits to date. For the first time, a limit on the compositeness scale has been set for contact interactions in the HNC model based on the final state with a muon andE^miss_T . The corresponding exclusion limit in the electron channel significantly improves the existing one.

ACKNOWLEDGMENTS

We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC and thank the technical and administrative staffs at CERN and at other CMS institutes for their contributions to the success of the CMS effort. In addition, we gratefully

acknowledge the computing centers and personnel of the Worldwide LHC Computing Grid for delivering so effectively the computing infrastructure essential to our analyses. Finally, we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies:

BMWF and FWF (Austria); FNRS and FWO (Belgium);

CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MEYS (Bulgaria); CERN; CAS, MoST, and NSFC (China);

COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); MoER, SF0690030s09, and ERDF (Estonia);

Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Republic of Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand);

PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MON, RosAtom, RAS, and RFBR (Russia);

MSTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); ThEPCenter, IPST and NSTDA (Thailand); TUBITAK and TAEK (Turkey);

NASU (Ukraine); STFC (United Kingdom); DOE and NSF (USA).

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TABLE III. Exclusion limits for other model interpretations for the electron and muon channel or their combination based on3:7 fb¹ of 2012 data at ffiffiffi

ps

¼ 8 TeV.

Model Channel Observed limit Expected limit

W^n¼2_KK ¼ 0:05 TeV e þ m_W^n¼2_KK < 1:5 TeV m_W^n¼2_KK < 1:4 TeV W^n¼2_KK ¼ 10:0 TeV e þ m_W^n¼2_KK < 3:3 TeV m_W^n¼2_KK < 3:2 TeV

HNC CI e < 10:5 TeV < 9:0 TeV

HNC CI < 8:8 TeV < 9:0 TeV

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S. Chatrchyan,¹V. Khachatryan,¹A. M. Sirunyan,¹A. Tumasyan,¹W. Adam,²E. Aguilo,²T. Bergauer,² M. Dragicevic,²J. Ero¨,²C. Fabjan,^2,bM. Friedl,²R. Fru¨hwirth,^2,bV. M. Ghete,²N. Ho¨rmann,²J. Hrubec,² M. Jeitler,^2,bW. Kiesenhofer,²V. Knu¨nz,²M. Krammer,^2,bI. Kra¨tschmer,²D. Liko,²I. Mikulec,²M. Pernicka,^2,a D. Rabady,^2,cB. Rahbaran,²C. Rohringer,²H. Rohringer,²R. Scho¨fbeck,²J. Strauss,²A. Taurok,²W. Waltenberger,²

C.-E. Wulz,^2,bV. Mossolov,³N. Shumeiko,³J. Suarez Gonzalez,³S. Alderweireldt,⁴M. Bansal,⁴S. Bansal,⁴ T. Cornelis,⁴E. A. De Wolf,⁴X. Janssen,⁴S. Luyckx,⁴L. Mucibello,⁴S. Ochesanu,⁴B. Roland,⁴R. Rougny,⁴

M. Selvaggi,⁴H. Van Haevermaet,⁴P. Van Mechelen,⁴N. Van Remortel,⁴A. Van Spilbeeck,⁴F. Blekman,⁵ S. Blyweert,⁵J. D’Hondt,⁵R. Gonzalez Suarez,⁵A. Kalogeropoulos,⁵M. Maes,⁵A. Olbrechts,⁵S. Tavernier,⁵ W. Van Doninck,⁵P. Van Mulders,⁵G. P. Van Onsem,⁵I. Villella,⁵B. Clerbaux,⁶G. De Lentdecker,⁶V. Dero,⁶ A. P. R. Gay,⁶T. Hreus,⁶A. Le´onard,⁶P. E. Marage,⁶A. Mohammadi,⁶T. Reis,⁶L. Thomas,⁶C. Vander Velde,⁶ P. Vanlaer,⁶J. Wang,⁶V. Adler,⁷K. Beernaert,⁷A. Cimmino,⁷S. Costantini,⁷G. Garcia,⁷M. Grunewald,⁷B. Klein,⁷

J. Lellouch,⁷A. Marinov,⁷J. Mccartin,⁷A. A. Ocampo Rios,⁷D. Ryckbosch,⁷M. Sigamani,⁷N. Strobbe,⁷ F. Thyssen,⁷M. Tytgat,⁷S. Walsh,⁷E. Yazgan,⁷N. Zaganidis,⁷S. Basegmez,⁸G. Bruno,⁸R. Castello,⁸L. Ceard,⁸

C. Delaere,⁸T. du Pree,⁸D. Favart,⁸L. Forthomme,⁸A. Giammanco,^8,dJ. Hollar,⁸V. Lemaitre,⁸J. Liao,⁸ O. Militaru,⁸C. Nuttens,⁸D. Pagano,⁸A. Pin,⁸K. Piotrzkowski,⁸J. M. Vizan Garcia,⁸N. Beliy,⁹T. Caebergs,⁹ E. Daubie,⁹G. H. Hammad,⁹G. A. Alves,¹⁰M. Correa Martins Junior,¹⁰T. Martins,¹⁰M. E. Pol,¹⁰M. H. G. Souza,¹⁰

W. L. Alda´ Ju´nior,¹¹W. Carvalho,¹¹J. Chinellato,¹¹A. Custo´dio,¹¹E. M. Da Costa,¹¹D. De Jesus Damiao,¹¹ C. De Oliveira Martins,¹¹S. Fonseca De Souza,¹¹H. Malbouisson,¹¹M. Malek,¹¹D. Matos Figueiredo,¹¹

L. Mundim,¹¹H. Nogima,¹¹W. L. Prado Da Silva,¹¹A. Santoro,¹¹L. Soares Jorge,¹¹A. Sznajder,¹¹ E. J. Tonelli Manganote,¹¹A. Vilela Pereira,¹¹T. S. Anjos,^12bC. A. Bernardes,^12bF. A. Dias,^12a,e T. R. Fernandez Perez Tomei,^12aE. M. Gregores,^12bC. Lagana,^12aF. Marinho,^12aP. G. Mercadante,^12b S. F. Novaes,^12aSandra S. Padula,^12aV. Genchev,^13,cP. Iaydjiev,^13,cS. Piperov,¹³M. Rodozov,¹³S. Stoykova,¹³

G. Sultanov,¹³V. Tcholakov,¹³R. Trayanov,¹³M. Vutova,¹³A. Dimitrov,¹⁴R. Hadjiiska,¹⁴V. Kozhuharov,¹⁴ L. Litov,¹⁴B. Pavlov,¹⁴P. Petkov,¹⁴J. G. Bian,¹⁵G. M. Chen,¹⁵H. S. Chen,¹⁵C. H. Jiang,¹⁵D. Liang,¹⁵S. Liang,¹⁵

X. Meng,¹⁵J. Tao,¹⁵J. Wang,¹⁵X. Wang,¹⁵Z. Wang,¹⁵H. Xiao,¹⁵M. Xu,¹⁵J. Zang,¹⁵Z. Zhang,¹⁵ C. Asawatangtrakuldee,¹⁶Y. Ban,¹⁶Y. Guo,¹⁶W. Li,¹⁶S. Liu,¹⁶Y. Mao,¹⁶S. J. Qian,¹⁶H. Teng,¹⁶D. Wang,¹⁶

L. Zhang,¹⁶W. Zou,¹⁶C. Avila,¹⁷C. A. Carrillo Montoya,¹⁷J. P. Gomez,¹⁷B. Gomez Moreno,¹⁷ A. F. Osorio Oliveros,¹⁷J. C. Sanabria,¹⁷N. Godinovic,¹⁸D. Lelas,¹⁸R. Plestina,^18,fD. Polic,¹⁸I. Puljak,^18,c Z. Antunovic,¹⁹M. Kovac,¹⁹V. Brigljevic,²⁰S. Duric,²⁰K. Kadija,²⁰J. Luetic,²⁰D. Mekterovic,²⁰S. Morovic,²⁰ L. Tikvica,²⁰A. Attikis,²¹M. Galanti,²¹G. Mavromanolakis,²¹J. Mousa,²¹C. Nicolaou,²¹F. Ptochos,²¹P. A. Razis,²¹

M. Finger,²²M. Finger, Jr.,²²Y. Assran,^23,gS. Elgammal,^23,hA. Ellithi Kamel,^23,iA. M. Kuotb Awad,^23,j M. A. Mahmoud,^23,jA. Radi,^23,k,lM. Kadastik,²⁴M. Mu¨ntel,²⁴M. Murumaa,²⁴M. Raidal,²⁴L. Rebane,²⁴A. Tiko,²⁴

P. Eerola,²⁵G. Fedi,²⁵M. Voutilainen,²⁵J. Ha¨rko¨nen,²⁶A. Heikkinen,²⁶V. Karima¨ki,²⁶R. Kinnunen,²⁶ M. J. Kortelainen,²⁶T. Lampeń,²⁶K. Lassila-Perini,²⁶S. Lehti,²⁶T. Lindeń,²⁶P. Luukka,²⁶T. Maënpaä¨,²⁶ T. Peltola,²⁶E. Tuominen,²⁶J. Tuominiemi,²⁶E. Tuovinen,²⁶D. Ungaro,²⁶L. Wendland,²⁶A. Korpela,²⁷T. Tuuva,²⁷

M. Besancon,²⁸S. Choudhury,²⁸F. Couderc,²⁸M. Dejardin,²⁸D. Denegri,²⁸B. Fabbro,²⁸J. L. Faure,²⁸F. Ferri,²⁸ S. Ganjour,²⁸A. Givernaud,²⁸P. Gras,²⁸G. Hamel de Monchenault,²⁸P. Jarry,²⁸E. Locci,²⁸J. Malcles,²⁸ L. Millischer,²⁸A. Nayak,²⁸J. Rander,²⁸A. Rosowsky,²⁸M. Titov,²⁸S. Baffioni,²⁹F. Beaudette,²⁹L. Benhabib,²⁹

L. Bianchini,²⁹M. Bluj,^29,mP. Busson,²⁹C. Charlot,²⁹N. Daci,²⁹T. Dahms,²⁹M. Dalchenko,²⁹L. Dobrzynski,²⁹ A. Florent,²⁹R. Granier de Cassagnac,²⁹M. Haguenauer,²⁹P. Mine´,²⁹C. Mironov,²⁹I. N. Naranjo,²⁹M. Nguyen,²⁹

C. Ochando,²⁹P. Paganini,²⁹D. Sabes,²⁹R. Salerno,²⁹Y. Sirois,²⁹C. Veelken,²⁹A. Zabi,²⁹J.-L. Agram,^30,n J. Andrea,³⁰D. Bloch,³⁰D. Bodin,³⁰J.-M. Brom,³⁰M. Cardaci,³⁰E. C. Chabert,³⁰C. Collard,³⁰E. Conte,^30,n

F. Drouhin,^30,nJ.-C. Fontaine,^30,nD. Gele´,³⁰U. Goerlach,³⁰P. Juillot,³⁰A.-C. Le Bihan,³⁰P. Van Hove,³⁰ S. Beauceron,³¹N. Beaupere,³¹O. Bondu,³¹G. Boudoul,³¹S. Brochet,³¹J. Chasserat,³¹R. Chierici,^31,c D. Contardo,³¹P. Depasse,³¹H. El Mamouni,³¹J. Fay,³¹S. Gascon,³¹M. Gouzevitch,³¹B. Ille,³¹T. Kurca,³¹ M. Lethuillier,³¹L. Mirabito,³¹S. Perries,³¹L. Sgandurra,³¹V. Sordini,³¹Y. Tschudi,³¹P. Verdier,³¹S. Viret,³¹

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Z. Tsamalaidze,^32,oC. Autermann,³³S. Beranek,³³B. Calpas,³³M. Edelhoff,³³L. Feld,³³N. Heracleous,³³ O. Hindrichs,³³R. Jussen,³³K. Klein,³³J. Merz,³³A. Ostapchuk,³³A. Perieanu,³³F. Raupach,³³J. Sammet,³³ S. Schael,³³D. Sprenger,³³H. Weber,³³B. Wittmer,³³V. Zhukov,^33,pM. Ata,³⁴J. Caudron,³⁴E. Dietz-Laursonn,³⁴

D. Duchardt,³⁴M. Erdmann,³⁴R. Fischer,³⁴A. Gu¨th,³⁴T. Hebbeker,³⁴C. Heidemann,³⁴K. Hoepfner,³⁴ D. Klingebiel,³⁴S. Knutzen,³⁴P. Kreuzer,³⁴M. Merschmeyer,³⁴A. Meyer,³⁴P. Millet,³⁴M. Olschewski,³⁴

K. Padeken,³⁴P. Papacz,³⁴H. Pieta,³⁴H. Reithler,³⁴S. A. Schmitz,³⁴F. Schneider,³⁴L. Sonnenschein,³⁴ J. Steggemann,³⁴D. Teyssier,³⁴S. Thu¨er,³⁴M. Weber,³⁴M. Bontenackels,³⁵V. Cherepanov,³⁵Y. Erdogan,³⁵ G. Flu¨gge,³⁵H. Geenen,³⁵M. Geisler,³⁵W. Haj Ahmad,³⁵F. Hoehle,³⁵B. Kargoll,³⁵T. Kress,³⁵Y. Kuessel,³⁵

J. Lingemann,^35,cA. Nowack,³⁵I. M. Nugent,³⁵L. Perchalla,³⁵O. Pooth,³⁵P. Sauerland,³⁵A. Stahl,³⁵ M. Aldaya Martin,³⁶I. Asin,³⁶N. Bartosik,³⁶J. Behr,³⁶W. Behrenhoff,³⁶U. Behrens,³⁶M. Bergholz,^36,q A. Bethani,³⁶K. Borras,³⁶A. Burgmeier,³⁶A. Cakir,³⁶L. Calligaris,³⁶A. Campbell,³⁶E. Castro,³⁶F. Costanza,³⁶ D. Dammann,³⁶C. Diez Pardos,³⁶T. Dorland,³⁶G. Eckerlin,³⁶D. Eckstein,³⁶G. Flucke,³⁶A. Geiser,³⁶I. Glushkov,³⁶

P. Gunnellini,³⁶S. Habib,³⁶J. Hauk,³⁶G. Hellwig,³⁶H. Jung,³⁶M. Kasemann,³⁶P. Katsas,³⁶C. Kleinwort,³⁶ H. Kluge,³⁶A. Knutsson,³⁶M. Kra¨mer,³⁶D. Kru¨cker,³⁶E. Kuznetsova,³⁶W. Lange,³⁶J. Leonard,³⁶W. Lohmann,^36,q

B. Lutz,³⁶R. Mankel,³⁶I. Marfin,³⁶M. Marienfeld,³⁶I.-A. Melzer-Pellmann,³⁶A. B. Meyer,³⁶J. Mnich,³⁶ A. Mussgiller,³⁶S. Naumann-Emme,³⁶O. Novgorodova,³⁶F. Nowak,³⁶J. Olzem,³⁶H. Perrey,³⁶A. Petrukhin,³⁶

D. Pitzl,³⁶A. Raspereza,³⁶P. M. Ribeiro Cipriano,³⁶C. Riedl,³⁶E. Ron,³⁶M. Rosin,³⁶J. Salfeld-Nebgen,³⁶ R. Schmidt,^36,qT. Schoerner-Sadenius,³⁶N. Sen,³⁶A. Spiridonov,³⁶M. Stein,³⁶R. Walsh,³⁶C. Wissing,³⁶ V. Blobel,³⁷H. Enderle,³⁷J. Erfle,³⁷U. Gebbert,³⁷M. Go¨rner,³⁷M. Gosselink,³⁷J. Haller,³⁷T. Hermanns,³⁷ R. S. Ho¨ing,³⁷K. Kaschube,³⁷G. Kaussen,³⁷H. Kirschenmann,³⁷R. Klanner,³⁷J. Lange,³⁷T. Peiffer,³⁷N. Pietsch,³⁷ D. Rathjens,³⁷C. Sander,³⁷H. Schettler,³⁷P. Schleper,³⁷E. Schlieckau,³⁷A. Schmidt,³⁷M. Schro¨der,³⁷T. Schum,³⁷

M. Seidel,³⁷J. Sibille,^37,rV. Sola,³⁷H. Stadie,³⁷G. Steinbru¨ck,³⁷J. Thomsen,³⁷L. Vanelderen,³⁷C. Barth,³⁸ C. Baus,³⁸J. Berger,³⁸C. Bo¨ser,³⁸T. Chwalek,³⁸W. De Boer,³⁸A. Descroix,³⁸A. Dierlamm,³⁸M. Feindt,³⁸ M. Guthoff,^38,cC. Hackstein,³⁸F. Hartmann,^38,cT. Hauth,^38,cM. Heinrich,³⁸H. Held,³⁸K. H. Hoffmann,³⁸ U. Husemann,³⁸I. Katkov,^38,pJ. R. Komaragiri,³⁸P. Lobelle Pardo,³⁸D. Martschei,³⁸S. Mueller,³⁸Th. Mu¨ller,³⁸

M. Niegel,³⁸A. Nu¨rnberg,³⁸O. Oberst,³⁸A. Oehler,³⁸J. Ott,³⁸G. Quast,³⁸K. Rabbertz,³⁸F. Ratnikov,³⁸ N. Ratnikova,³⁸S. Ro¨cker,³⁸F.-P. Schilling,³⁸G. Schott,³⁸H. J. Simonis,³⁸F. M. Stober,³⁸D. Troendle,³⁸R. Ulrich,³⁸

J. Wagner-Kuhr,³⁸S. Wayand,³⁸T. Weiler,³⁸M. Zeise,³⁸G. Anagnostou,³⁹G. Daskalakis,³⁹T. Geralis,³⁹ S. Kesisoglou,³⁹A. Kyriakis,³⁹D. Loukas,³⁹I. Manolakos,³⁹A. Markou,³⁹C. Markou,³⁹E. Ntomari,³⁹ L. Gouskos,⁴⁰T. J. Mertzimekis,⁴⁰A. Panagiotou,⁴⁰N. Saoulidou,⁴⁰I. Evangelou,⁴¹C. Foudas,⁴¹P. Kokkas,⁴¹ N. Manthos,⁴¹I. Papadopoulos,⁴¹G. Bencze,⁴²C. Hajdu,⁴²P. Hidas,⁴²D. Horvath,^42,sF. Sikler,⁴²V. Veszpremi,⁴² G. Vesztergombi,^42,tA. J. Zsigmond,⁴²N. Beni,⁴³S. Czellar,⁴³J. Molnar,⁴³J. Palinkas,⁴³Z. Szillasi,⁴³J. Karancsi,⁴⁴

P. Raics,⁴⁴Z. L. Trocsanyi,⁴⁴B. Ujvari,⁴⁴S. B. Beri,⁴⁵V. Bhatnagar,⁴⁵N. Dhingra,⁴⁵R. Gupta,⁴⁵M. Kaur,⁴⁵ M. Z. Mehta,⁴⁵M. Mittal,⁴⁵N. Nishu,⁴⁵L. K. Saini,⁴⁵A. Sharma,⁴⁵J. B. Singh,⁴⁵Ashok Kumar,⁴⁶Arun Kumar,⁴⁶

S. Ahuja,⁴⁶A. Bhardwaj,⁴⁶B. C. Choudhary,⁴⁶S. Malhotra,⁴⁶M. Naimuddin,⁴⁶K. Ranjan,⁴⁶P. Saxena,⁴⁶ V. Sharma,⁴⁶R. K. Shivpuri,⁴⁶S. Banerjee,⁴⁷S. Bhattacharya,⁴⁷K. Chatterjee,⁴⁷S. Dutta,⁴⁷B. Gomber,⁴⁷Sa. Jain,⁴⁷

Sh. Jain,⁴⁷R. Khurana,⁴⁷A. Modak,⁴⁷S. Mukherjee,⁴⁷D. Roy,⁴⁷S. Sarkar,⁴⁷M. Sharan,⁴⁷A. Abdulsalam,⁴⁸ D. Dutta,⁴⁸S. Kailas,⁴⁸V. Kumar,⁴⁸A. K. Mohanty,^48,cL. M. Pant,⁴⁸P. Shukla,⁴⁸T. Aziz,⁴⁹R. M. Chatterjee,⁴⁹

S. Ganguly,⁴⁹M. Guchait,^49,uA. Gurtu,^49,vM. Maity,^49,wG. Majumder,⁴⁹K. Mazumdar,⁴⁹G. B. Mohanty,⁴⁹ B. Parida,⁴⁹K. Sudhakar,⁴⁹N. Wickramage,⁴⁹S. Banerjee,⁵⁰S. Dugad,⁵⁰H. Arfaei,^51,xH. Bakhshiansohi,⁵¹

S. M. Etesami,^51,yA. Fahim,^51,xM. Hashemi,^51,zH. Hesari,⁵¹A. Jafari,⁵¹M. Khakzad,⁵¹

M. Mohammadi Najafabadi,⁵¹S. Paktinat Mehdiabadi,⁵¹B. Safarzadeh,^51,aaM. Zeinali,⁵¹M. Abbrescia,^52a,52b L. Barbone,^52a,52bC. Calabria,^52a,52b,cS. S. Chhibra,^52a,52bA. Colaleo,^52aD. Creanza,^52a,52cN. De Filippis,^52a,52c,c

M. De Palma,^52a,52bL. Fiore,^52aG. Iaselli,^52a,52cG. Maggi,^52a,52cM. Maggi,^52aB. Marangelli,^52a,52bS. My,^52a,52c S. Nuzzo,^52a,52bN. Pacifico,^52aA. Pompili,^52a,52bG. Pugliese,^52a,52cG. Selvaggi,^52a,52bL. Silvestris,^52a

G. Singh,^52a,52bR. Venditti,^52a,52bP. Verwilligen,^52aG. Zito,^52aG. Abbiendi,^53aA. C. Benvenuti,^53a D. Bonacorsi,^53a,53bS. Braibant-Giacomelli,^53a,53bL. Brigliadori,^53a,53bP. Capiluppi,^53a,53bA. Castro,^53a,53b

F. R. Cavallo,^53aM. Cuffiani,^53a,53bG. M. Dallavalle,^53aF. Fabbri,^53aA. Fanfani,^53a,53bD. Fasanella,^53a,53b P. Giacomelli,^53aC. Grandi,^53aL. Guiducci,^53a,53bS. Marcellini,^53aG. Masetti,^53aM. Meneghelli,^53a,53b,c A. Montanari,^53aF. L. Navarria,^53a,53bF. Odorici,^53aA. Perrotta,^53aF. Primavera,^53a,53bA. M. Rossi,^53a,53b

T. Rovelli,^53a,53bG. P. Siroli,^53a,53bN. Tosi,^53aR. Travaglini,^53a,53bS. Albergo,^54a,54bG. Cappello,^54a,54b