√s = 7 TeV with the ATLAS detector

arXiv:1208.1447v1 [hep-ex] 7 Aug 2012

CERN-PH-EP-2012-201

Submitted to: Physical Review Letters

Search for a supersymmetric partner to the top quark in final states with jets and missing transverse momentum

at √s = 7 TeV with the ATLAS detector

The ATLAS Collaboration

Abstract

A search for direct pair production of supersymmetric top squarks (˜t1) is presented, assuming the ˜t1decays into a top quark and the lightest supersymmetric particle, ˜χ⁰₁, and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted Standard Model background of 13.5^{+ 3.7}_{− 3.6} (4.4^{+ 1.7}_{− 1.3}) events in two signal regions based on RL dt = 4.7 fb⁻¹ of pp collision data taken at √

s = 7 TeV with the ATLAS detector at the LHC. An exclusion region in the ˜t1 versus ˜χ⁰₁ mass plane is evaluated:

370 < mt˜1 < 465 GeV is excluded for m_χ˜⁰₁∼ 0 GeV while m^˜t1= 445 GeV is excluded for m_χ˜⁰₁ ≤ 50 GeV.

jets and missing transverse momentum at √s = 7 TeV with the ATLAS detector

The ATLAS Collaboration (Dated: August 7, 2012)

A search for direct pair production of supersymmetric top squarks (˜t1) is presented, assuming the ˜t1 decays into a top quark and the lightest supersymmetric particle, ˜χ⁰1, and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted Standard Model background of 13.5^{+ 3.7}

− 3.6(4.4^{+ 1.7}

− 1.3) events in two signal regions based on RL dt = 4.7 fb⁻¹ of pp collision data taken at√s = 7 TeV with the ATLAS detector at the LHC.

An exclusion region in the ˜t1 versus ˜χ⁰1 mass plane is evaluated: 370 < m˜t1< 465 GeV is excluded for m_χ˜⁰

1 ∼ 0 GeV while m^˜t1 = 445 GeV is excluded for m_χ˜⁰

1≤ 50 GeV.

PACS numbers: 12.60.Jv,13.85.Rm,14.80.Ly

The Standard Model (SM) is a successful but incom- plete model of particle interactions. Supersymmetry (SUSY) [1–9] provides an elegant solution to cancel the quadratic mass divergences that would accompany a SM Higgs boson by introducing supersymmetric partners of all SM particles, such as a scalar partner of the top quark (˜t). Like t¯t, direct ˜t˜t^⋆ is produced primarily through gluon fusion at the Large Hadron Collider (LHC). The production cross section depends mostly on the mass of the top partner and has minimal dependence on other SUSY parameters [10–12]. The LHC enables searches for direct ˜t˜t^⋆production at higher mass scales than previous accelerators [13–27]. The viability of SUSY as a scenario to stabilize the Higgs potential and to be consistent with electroweak naturalness [28, 29] is tested by the search for ˜t below the TeV scale.

In this Letter, we present a search for direct ˜t˜t^⋆produc- tion assuming ˜t1→ t ˜χ⁰₁→ bW ˜χ⁰₁where ˜t1is the lightest ˜t eigenstate and ˜χ⁰₁represents the lightest supersymmetric particle (LSP) in R-parity conserving models [30–34]. We consider events where both W bosons decay hadronically, yielding a final state with six high transverse momentum (pT) jets from the all-hadronic t¯t final state and large missing transverse momentum (E_T^miss) from the LSPs.

The kinematics of both top quarks are therefore fully specified by the visible decay products. Additionally, SM backgrounds from all-hadronic t¯t are suppressed as there is no intrinsic E_T^miss except from semi-leptonic c- and b- quark decays. The dominant background consists of t¯t events that contain a W → ℓν decay where the lepton (ℓ), often of τ flavor, is either lost or mis-identified as a jet and which have large E_T^missfrom the neutrino.

The data sample was acquired during 2011 in LHC pp collisions at a center-of-mass energy of 7 TeV with the ATLAS detector [35], which consists of tracking detectors surrounded by a 2 T superconducting solenoid, calorime- ters, and a muon spectrometer in a toroidal magnetic field. The high-granularity calorimeter system, with ac- ceptance covering |η| < 4.9 [36], is composed of liquid argon with lead, copper, or tungsten absorbers and scin-

tillator tiles with steel absorbers. This data set, com- posed of events with a high-pT jet and large E_T^miss as selected by the trigger system, corresponds to an inte- grated luminosity of 4.7 fb⁻¹ with a relative uncertainty of 3.9% [37, 38].

Jets are constructed from three-dimensional clusters of calorimeter cells using the anti-kt algorithm with a distance parameter of 0.4 [39, 40]. Jet energies are cor- rected [41] for losses in material in front of the active calorimeter layers, detector inhomogeneities, the non- compensating nature of the calorimeter, and the impact of multiple overlapping pp interactions. These correc- tions are derived from test beam, cosmic ray, and pp collision data, and from a detailed Geant4 [42] detector simulation [43]. Jets containing a b-hadron are identified with an algorithm exploiting both the impact parame- ter and secondary vertex information [44, 45]. A factor correcting for the slight differences in the b-tagging effi- ciency between data and the Geant4 simulation is applied to each jet in the simulation. The b-jets are restricted to the fiducial region of the tracker, |η| < 2.5. Non-t¯t backgrounds are minimized by requiring either ≥ 1 b-jets with a selection corresponding to a 60% efficiency with a low < 0.2% mis-identification rate (tight), or ≥ 2 b- jets each with 75% efficiency but a higher ≈ 1.7% mis- identification rate per b-jet (loose).

The E_T^missis the magnitude of p^miss_T , the negative vec- tor sum of the pTof the clusters of calorimeter cells, cal- ibrated according to their associated reconstructed ob- ject (e.g., jets and electrons), and of the pT of muons above 10 GeV within |η| < 2.4. Events containing fake E_T^miss induced by jets associated with calorimeter noise or non-collision backgrounds [46], or by cosmic- ray muons or poorly reconstructed muons [47, 48], are removed from consideration. Large p^miss_T colinear with a high-pT jet could indicate a significant fluctuation in the reconstructed jet energy or the presence of a semi- leptonic c- or b-quark decay. Therefore, the difference in azimuthal angle (∆φ) between the p^miss_T and any of the three highest-pT jets in the event, ∆φ(p^miss_T , jet), is re-

quired to be > π/5 radians. Fake E_T^missis also suppressed by requiring that the ∆φ between the above computed p^miss_T and one calculated with the tracking system, using tracks having pT> 0.5 GeV, is < π/3 radians.

Events are required to have at least one jet with pT > 130 GeV in |η| < 2.8 and ET^miss > 150 GeV to ensure full efficiency of the trigger. At least five other jets having pT> 30 GeV and |η| < 2.8 must be present.

In addition to the jet and E_T^miss requirements, events containing “loose” electrons [49, 50] with pT > 20 GeV and |η| < 2.47 that do not overlap with any jet within

∆R < 0.4, where ∆R =p(∆η)²+ (∆φ)², are rejected.

Similarly, events with muons [47, 51] having pT> 10 GeV and |η| < 2.4 that are separated by ∆R > 0.4 from the nearest jet are rejected. A jet with 1–4 tracks and

∆φ(p^miss_T , jet) < π/5 indicates a likely W → τν decay.

Events with such τ -like jets that have transverse mass mT=p2pTE^miss_T (1 − cos ∆φ) < 100 GeV are rejected.

The presence of high-pTtop quarks that decay through t → bW → bjj in the ˜t¹t˜^⋆₁ final state is exploited to further reduce SM backgrounds by only considering events with reconstructed three-jet invariant masses con- sistent with the top-quark mass (mt). A clustering tech- nique resolves the combinatorics associated with high- multiplicity jet events. The three closest jets in the η − φ plane are combined to form one triplet; a sec- ond triplet is formed from the remaining jets by repeat- ing the procedure. The resulting three-jet mass (mjjj) spectrum is shown in Fig. 1 for the control region con- structed from ℓ+jets events (defined below). There is a clear peak associated with the hadronically-decaying top quarks above a small non-t¯t background. A requirement of 80 < mjjj < 270 GeV is placed on each reconstructed triplet in the event. The kinematics of the t → bW → bℓν decay is also exploited to further reduce the dominant ℓ+jets t¯t background, as the mTdistribution of the p^miss_T and b-jet (m^jet_T) has an endpoint at mt. When there are

≥ 2 loose b-jets, the m^jetT for the b-jet closest to the p^miss_T is required to be > 175 GeV. The largest m^jet_T , calcu- lated for each of the four highest-pT jets, is required to be > 175 GeV in the case of only one tight b-jet.

Two signal regions (SR) are defined including the above kinematic and mass requirements. The first, which requires E_T^miss > 150 GeV (SRA), is optimized for low m˜t1, while the second, requiring E_T^miss > 260 GeV (SRB), is used for higher mt˜1. Using these signal re- gions, the search is most sensitive to ˜t1t˜^⋆₁ production with 350 . m˜t1 . 500 GeV and m_χ˜⁰₁ ≪ m^˜t1. Sig- nal events are simulated using Herwig++ [52] with the MRST2007LO* [53] parton distribution functions (PDF) generated with the ˜t1 and ˜χ⁰₁ masses at fixed values in a grid with 50 GeV spacing. The mixing parameters are chosen such that the lightest scalar top is mostly the partner of the right-handed top quark. The branch- ing fraction of ˜t1 → t ˜χ⁰₁ is set to 100% [54]. Signal

[GeV]

m

0 200 400 600

Events / 20 GeV

20 40 60 80 100

ATLAS

=7 TeV s

-1, L dt = 4.7 fb

∫

t t Single Top V (V) + jets

+ V t t

MC Stat Error ) = (400,1) GeV

1

χ∼0

,m

~t

(m Data 2011

FIG. 1. Three-jet invariant mass distribution of the hadronic top-quark candidate in the control region constructed from ℓ+jets events. Data are indicated by points; shaded his- tograms represent contributions from several SM sources (with t¯t scaled by 0.66). The hatched error bars indicate the total statistical uncertainty on the expected background.

The distribution for the m˜t1= 400 GeV, m_χ˜⁰

1 = 1 GeV signal expectation in this control region is overlaid.

cross sections are calculated to next-to-leading order in the strong coupling constant, including the resummation of soft gluon emission at next-to-leading-logarithmic ac- curacy (NLO+NLL) [10–12]. The nominal production cross section and associated uncertainty are taken from an envelope of cross section predictions using different PDF sets and factorization and renormalization scales, as described in Ref. [55]. The ˜t1˜t^⋆₁ cross section for m˜t1 = 400 GeV is σ˜t1˜t^⋆1 = 0.21 ± 0.03 pb.

In the signal region, the dominant source of SM back- ground is t¯t → τ+jets events where the τ lepton is re- constructed as a jet. Additional, smaller, backgrounds include other t¯t → ℓ+jets final states, t¯t + V where V represents a W or Z boson, single top quark produc- tion, V +jets, and V V +jets. The t¯t events are produced with ALPGEN [56] using the CTEQ6L1 PDF [57] and interfaced to HERWIG [58, 59] for particle production and JIMMY [60] for the underlying event model. Addi- tional t¯t samples generated with MC@NLO [61, 62] and AcerMC [63], interfaced to HERWIG and JIMMY, are used to estimate event generator systematic uncertain- ties. Samples of t¯t+ V are produced with MadGraph [64]

interfaced to PYTHIA [59, 65, 66]. Single top events are generated with MC@NLO [67, 68] and AcerMC. The as- sociated production of W and Z bosons and light and heavy-flavor jets is simulated using ALPGEN; diboson

) [GeV]

miss

p

candidate, τ

T

( m

0 20 40 60 80 100

Events / 10 GeV

5 10 15 20 25

30

=7 TeV s

-1, L dt = 4.7 fb

∫

t t Single Top V (V) + jets

+ V t t

Bkg Syst Error ) = (400,1) GeV

1

χ∼0

,m

~t

(m Data 2011

FIG. 2. The mTdistribution for τ -like jets with the selection described in the text. Data are indicated by points; shaded histograms represent contributions from several SM sources (with t¯t scaled by 0.66). The hatched error bar indicates the systematic uncertainty on the total expected background.

The expected signal distribution for m˜t1 = 400 GeV, m_χ˜⁰

1 = 1 GeV is overlaid.

production is simulated with SHERPA [69].

All samples are passed through the Geant4 simula- tion of the ATLAS detector, and are reconstructed in the same manner as the data. The simulation includes the effect of multiple pp interactions and is weighted to reproduce the observed distribution of the number of in- teractions per bunch crossing. SM event samples are nor- malized to the results of higher-order calculations using the cross sections cited in Ref. [70] except for the ℓ+jets t¯t background. This sample is renormalized by a factor that scales the t¯t expectation to agree with the observed data in a control region (CR) kinematically close to the signal region but with little expected signal. The CR is con- structed from events containing one muon or one “tight”

electron [49] with pT> 30 GeV consistent with originat- ing from a W -boson decay (40 < m^ℓ_T< 120 GeV) and ≥ 5 jets, where m^ℓ_T is the transverse mass of the electron or muon and p^miss_T . The lepton must be isolated such that the scalar pTsum of tracks in a cone of ∆R < 0.2 around the lepton, excluding the track of the lepton, is < 1.8 GeV for the muon or is < 10% of the electron pT, respectively.

The jet, b-jet, and E_T^missrequirements remain the same as the standard signal selection; however, some topological constraints are relaxed (∆φ(p^miss_T , jet) > π/10 radians and mjjj < 600 GeV) and others removed (m^jet_T ) to gain statistics. The t¯t purity in the control region is > 80%;

the expected signal contamination is < 3%. The lepton is

[GeV]

miss

E

100 200 300 400 500 600

Events / 50 GeV

2 4 6 8 10

ATLAS

=7 TeV s

-1, L dt = 4.7 fb

∫

t t Single Top V (V) + jets

+ V t t

Bkg Syst Error ) = (400,1) GeV

1

χ∼0

,m

~t

(m Data 2011

FIG. 3. The ET^miss distribution in data compared to the SM expectation for signal region A. The hatched error bar indicates the systematic uncertainty on the total expected background. The expected signal distribution for m˜t1 = 400 GeV, m_χ˜⁰

1 = 1 GeV is overlaid. The SM background dis- tributions do not include the 0.2 ± 0.2 events of all-hadronic t¯t and QCD multi-jets estimated from data.

treated as a jet of the same energy and momentum, mim- icking the effect of the τ lepton. Effects of the additional E^miss_T from the τ neutrino are smaller than the statisti- cal uncertainties. The scale factor needed to bring the

≥ 6 jet ℓ+jets ALPGEN t¯t events into agreement with the data after recalculating all quantities except E_T^miss is 0.66 ± 0.05; the uncertainty quoted here is statistical only. This scale factor is used in Figs. 1−3. The nor- malization is validated with an orthogonal t¯t-dominated sample created from SRA by selecting events with τ -like jets; the requirement on m^jet_T is removed to increase the sample size. The mT of τ -like jets is shown in Fig. 2, where the t¯t sample has been normalized as described above. Expectations from the simulation agree with the data within uncertainties. Contributions to the signal re- gion from QCD multi-jet and all-hadronic t¯t production are estimated with a data-driven technique [71]. Jets are smeared in a low-E_T^missdata sample using response func- tions derived from control regions dominated by multi-jet events. Only 0.2 ± 0.2 such events remain in SRA after the full event selection.

The E_T^miss distribution in SRA is shown in Fig. 3 for data, for the SM backgrounds, and for expectations of

˜t1˜t^⋆₁production with mt˜1 = 400 and m_χ˜⁰

1= 1 GeV. Num- bers of events and combined statistical and systematic uncertainties, for both SRA and SRB, are tabulated in Table I. Uncertainties in the event generators, including

TABLE I. The numbers of expected events for the SM back- grounds and an example SUSY signal point, and the observed number of events in data. The 95% CLs upper limit on the observed (expected) visible cross section is appended below.

SRA SRB

ET^miss > 150 GeV > 260 GeV

t¯t 9.2 ± 2.7 2.3 ± 0.6

t¯t + W/Z 0.8 ± 0.2 0.4 ± 0.1

Single top 0.7 ± 0.4 0.2 ^{+ 0.3}

− 0.2

Z+jets 1.3^{+ 1.1}

− 1.0 0.9 ^{+ 0.8}

− 0.7

W +jets 1.2^{+ 1.4}

− 1.0 0.5 ± 0.4

Diboson 0.1^{+ 0.2}

− 0.1 0.1 ^{+ 0.2}

− 0.1

Multi-jets 0.2 ± 0.2 0.02 ± 0.02

Total SM 13.5^{+ 3.7}

− 3.6 4.4 ^{+ 1.7}

− 1.3

SUSY (m˜t1, m_χ˜⁰

1) = (400, 1) GeV 14.8 ± 4.0 8.9 ± 3.1

Data (observed) 16 4

Visible cross section [fb] 2.9 (2.5) 1.3 (1.3)

the impact of initial- and final-state radiation, are the dominant source of systematic uncertainty of 28% (23%) in SRA (SRB). Other major sources of uncertainty in- clude 22% (32%) for the jet energy calibration, 6.5%

(6.8%) for jet energy resolution, 5.9% (6.2%) for b-jet identification, and 1.4% (1.5%) for E_T^miss in SRA (SRB).

The number of observed events in the data is well matched by the SM background. These results are in- terpreted as exclusion limits for m˜t1 and m_χ˜⁰

1 using a CLs likelihood ratio combining Poisson probabilities for signal and background [72]. Systematic uncertainties are treated as nuisance parameters assuming Gaussian distri- butions. Uncertainties associated with jets, b-jets, E_T^miss, and luminosity are fully correlated between signal and background; the others are assumed to be uncorrelated.

The expected limits for the signal regions are evaluated for each (m˜t1, m_χ˜⁰₁) point; the SR with the better ex- pected sensitivity is used for that point. The expected and observed 95% C.L. exclusion limits are displayed in Fig. 4. Top squark masses between 370 and 465 GeV are excluded for m_χ˜⁰₁ ∼ 0 GeV while mt^˜1 = 445 GeV is ex- cluded for mχ_˜⁰₁ ≤ 50 GeV. These values are derived from the −1σ observed limit contour to account for theoreti- cal uncertainties on the SUSY cross sections. The 95%

CLsupper limit on the number of events beyond the SM in each signal region, divided by the integrated luminos- ity, yields limits on the observed (expected) visible cross sections of 2.9 (2.5) fb in SRA and 1.3 (1.3) fb in SRB.

In conclusion, we have presented a search for the direct production of ˜t1˜t^⋆₁ in the all-hadronic t ˜χ⁰₁¯t ˜χ⁰₁decay chan- nel, assuming B(˜t1 → t ˜χ⁰₁) = 100%. A total of 16 (4) events are observed compared to a predicted Standard Model background of 13.5^{+ 3.7}_{− 3.6} (4.4^{+ 1.7}_{− 1.3}) events in two signal regions based on RL dt = 4.7 fb⁻¹ of pp collision

[GeV]

t1

m~

200 300 400 500 600

[GeV] 1 0 χ∼m

0 100 200 300

0

χ∼1

→ t+

t1

production, ~ t1

~ t1

~

= 7 TeV s

-1, L dt = 4.7 fb

∫

ATLAS

t

< m

1 0χ

∼

- mt

m~

All Hadronic

t

< m

1 0χ

∼

- mt

m~

exp) σ

±1 Expected limit (

Theory) σSUSY

±1 Observed Limit (

FIG. 4. Expected and observed 95% CLs exclusion limits in the plane of m_χ˜⁰

1 vs. m˜t1, assuming B(˜t¹ → t ˜χ⁰1) = 100%.

The dashed line shows the expected limit at 95% C.L. with the shaded region indicating the ±1σ exclusions due to exper- imental uncertainties. Observed limits are indicated by the solid contour (nominal) and the dotted contours (obtained by varying the SUSY cross section by the theoretical uncertain- ties). The inner dotted contour indicates the excluded region.

data taken at√

s = 7 TeV with the ATLAS detector at the LHC. No evidence for ˜t1˜t^⋆₁ is observed in data and 95% C.L. limits are set on ˜t1˜t^⋆₁ production as a function of m˜t1 and m_χ˜⁰

1.

We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently.

We acknowledge the support of ANPCyT, Argentina;

YerPhI, Armenia; ARC, Australia; BMWF, Austria;

ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONI- CYT, Chile; CAS, MOST and NSFC, China; COLCIEN- CIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Founda- tion, Denmark; EPLANET and ERC, European Union;

IN2P3-CNRS, CEA-DSM/IRFU, France; GNAS, Geor- gia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands;

RCN, Norway; MNiSW, Poland; GRICES and FCT, Portugal; MERYS (MECTS), Romania; MES of Rus- sia and ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slovakia; ARRS and MVZT, Slovenia;

DST/NRF, South Africa; MICINN, Spain; SRC and

Wallenberg Foundation, Sweden; SER, SNSF and Can- tons of Bern and Geneva, Switzerland; NSC, Taiwan;

TAEK, Turkey; STFC, the Royal Society and Lever- hulme Trust, United Kingdom; DOE and NSF, United States of America.

The crucial computing support from all WLCG part- ners is acknowledged gratefully, in particular from CERN and the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC- IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Tai- wan), RAL (UK) and BNL (USA) and in the Tier-2 fa- cilities worldwide.

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The ATLAS Collaboration

G. Aad⁴⁸, T. Abajyan²¹, B. Abbott¹¹¹, J. Abdallah¹², S. Abdel Khalek¹¹⁵, A.A. Abdelalim⁴⁹, O. Abdinov¹¹, R. Aben¹⁰⁵, B. Abi¹¹², M. Abolins⁸⁸, O.S. AbouZeid¹⁵⁸, H. Abramowicz¹⁵³, H. Abreu¹³⁶, B.S. Acharya^164a,164b, L. Adamczyk³⁸, D.L. Adams²⁵, T.N. Addy⁵⁶, J. Adelman¹⁷⁶, S. Adomeit⁹⁸, P. Adragna⁷⁵, T. Adye¹²⁹, S. Aefsky²³, J.A. Aguilar-Saavedra^124b,a, M. Agustoni¹⁷, M. Aharrouche⁸¹, S.P. Ahlen²², F. Ahles⁴⁸, A. Ahmad¹⁴⁸, M. Ahsan⁴¹, G. Aielli^133a,133b, T. Akdogan^19a, T.P.A. ˚Akesson⁷⁹, G. Akimoto¹⁵⁵, A.V. Akimov⁹⁴, M.S. Alam², M.A. Alam⁷⁶, J. Albert¹⁶⁹, S. Albrand⁵⁵, M. Aleksa³⁰, I.N. Aleksandrov⁶⁴, F. Alessandria^89a, C. Alexa^26a, G. Alexander¹⁵³, G. Alexandre⁴⁹, T. Alexopoulos¹⁰, M. Alhroob^164a,164c, M. Aliev¹⁶, G. Alimonti^89a, J. Alison¹²⁰,

B.M.M. Allbrooke¹⁸, P.P. Allport⁷³, S.E. Allwood-Spiers⁵³, J. Almond⁸², A. Aloisio^102a,102b, R. Alon¹⁷²,

A. Alonso⁷⁹, F. Alonso⁷⁰, A. Altheimer³⁵, B. Alvarez Gonzalez⁸⁸, M.G. Alviggi^102a,102b, K. Amako⁶⁵, C. Amelung²³, V.V. Ammosov^128,∗, S.P. Amor Dos Santos^124a, A. Amorim^124a,b, N. Amram¹⁵³, C. Anastopoulos³⁰, L.S. Ancu¹⁷, N. Andari¹¹⁵, T. Andeen³⁵, C.F. Anders^58b, G. Anders^58a, K.J. Anderson³¹, A. Andreazza^89a,89b, V. Andrei^58a, X.S. Anduaga⁷⁰, P. Anger⁴⁴, A. Angerami³⁵, F. Anghinolfi³⁰, A. Anisenkov¹⁰⁷, N. Anjos^124a, A. Annovi⁴⁷, A. Antonaki⁹, M. Antonelli⁴⁷, A. Antonov⁹⁶, J. Antos^144b, F. Anulli^132a, M. Aoki¹⁰¹, S. Aoun⁸³, L. Aperio Bella⁵, R. Apolle^118,c, G. Arabidze⁸⁸, I. Aracena¹⁴³, Y. Arai⁶⁵, A.T.H. Arce⁴⁵, S. Arfaoui¹⁴⁸, J-F. Arguin¹⁵, E. Arik^19a,∗, M. Arik^19a, A.J. Armbruster⁸⁷, O. Arnaez⁸¹, V. Arnal⁸⁰, C. Arnault¹¹⁵, A. Artamonov⁹⁵, G. Artoni^132a,132b, D. Arutinov²¹, S. Asai¹⁵⁵, R. Asfandiyarov¹⁷³, S. Ask²⁸, B. ˚Asman^146a,146b, L. Asquith⁶, K. Assamagan²⁵, A. Astbury¹⁶⁹, M. Atkinson¹⁶⁵, B. Aubert⁵, E. Auge¹¹⁵, K. Augsten¹²⁷, M. Aurousseau^145a, G. Avolio¹⁶³, R. Avramidou¹⁰, D. Axen¹⁶⁸, G. Azuelos^93,d, Y. Azuma¹⁵⁵, M.A. Baak³⁰, G. Baccaglioni^89a, C. Bacci^134a,134b, A.M. Bach¹⁵, H. Bachacou¹³⁶, K. Bachas³⁰, M. Backes⁴⁹, M. Backhaus²¹, E. Badescu^26a, P. Bagnaia^132a,132b, S. Bahinipati³, Y. Bai^33a, D.C. Bailey¹⁵⁸, T. Bain¹⁵⁸, J.T. Baines¹²⁹, O.K. Baker¹⁷⁶, M.D. Baker²⁵, S. Baker⁷⁷, E. Banas³⁹, P. Banerjee⁹³, Sw. Banerjee¹⁷³, D. Banfi³⁰, A. Bangert¹⁵⁰, V. Bansal¹⁶⁹, H.S. Bansil¹⁸, L. Barak¹⁷², S.P. Baranov⁹⁴, A. Barbaro Galtieri¹⁵, T. Barber⁴⁸, E.L. Barberio⁸⁶, D. Barberis^50a,50b, M. Barbero²¹,

D.Y. Bardin⁶⁴, T. Barillari⁹⁹, M. Barisonzi¹⁷⁵, T. Barklow¹⁴³, N. Barlow²⁸, B.M. Barnett¹²⁹, R.M. Barnett¹⁵, A. Baroncelli^134a, G. Barone⁴⁹, A.J. Barr¹¹⁸, F. Barreiro⁸⁰, J. Barreiro Guimar˜aes da Costa⁵⁷, P. Barrillon¹¹⁵, R. Bartoldus¹⁴³, A.E. Barton⁷¹, V. Bartsch¹⁴⁹, A. Basye¹⁶⁵, R.L. Bates⁵³, L. Batkova^144a, J.R. Batley²⁸, A. Battaglia¹⁷, M. Battistin³⁰, F. Bauer¹³⁶, H.S. Bawa^143,e, S. Beale⁹⁸, T. Beau⁷⁸, P.H. Beauchemin¹⁶¹, R. Beccherle^50a, P. Bechtle²¹, H.P. Beck¹⁷, A.K. Becker¹⁷⁵, S. Becker⁹⁸, M. Beckingham¹³⁸, K.H. Becks¹⁷⁵, A.J. Beddall^19c, A. Beddall^19c, S. Bedikian¹⁷⁶, V.A. Bednyakov⁶⁴, C.P. Bee⁸³, L.J. Beemster¹⁰⁵, M. Begel²⁵, S. Behar Harpaz¹⁵², M. Beimforde⁹⁹, C. Belanger-Champagne⁸⁵, P.J. Bell⁴⁹, W.H. Bell⁴⁹, G. Bella¹⁵³,

L. Bellagamba^20a, F. Bellina³⁰, M. Bellomo³⁰, A. Belloni⁵⁷, O. Beloborodova^107,f, K. Belotskiy⁹⁶, O. Beltramello³⁰, O. Benary¹⁵³, D. Benchekroun^135a, K. Bendtz^146a,146b, N. Benekos¹⁶⁵, Y. Benhammou¹⁵³, E. Benhar Noccioli⁴⁹, J.A. Benitez Garcia^159b, D.P. Benjamin⁴⁵, M. Benoit¹¹⁵, J.R. Bensinger²³, K. Benslama¹³⁰, S. Bentvelsen¹⁰⁵, D. Berge³⁰, E. Bergeaas Kuutmann⁴², N. Berger⁵, F. Berghaus¹⁶⁹, E. Berglund¹⁰⁵, J. Beringer¹⁵, P. Bernat⁷⁷, R. Bernhard⁴⁸, C. Bernius²⁵, T. Berry⁷⁶, C. Bertella⁸³, A. Bertin^20a,20b, F. Bertolucci^122a,122b, M.I. Besana^89a,89b, G.J. Besjes¹⁰⁴, N. Besson¹³⁶, S. Bethke⁹⁹, W. Bhimji⁴⁶, R.M. Bianchi³⁰, M. Bianco^72a,72b, O. Biebel⁹⁸,

S.P. Bieniek⁷⁷, K. Bierwagen⁵⁴, J. Biesiada¹⁵, M. Biglietti^134a, H. Bilokon⁴⁷, M. Bindi^20a,20b, S. Binet¹¹⁵, A. Bingul^19c, C. Bini^132a,132b, C. Biscarat¹⁷⁸, B. Bittner⁹⁹, K.M. Black²², R.E. Blair⁶, J.-B. Blanchard¹³⁶, G. Blanchot³⁰, T. Blazek^144a, I. Bloch⁴², C. Blocker²³, J. Blocki³⁹, A. Blondel⁴⁹, W. Blum⁸¹, U. Blumenschein⁵⁴, G.J. Bobbink¹⁰⁵, V.B. Bobrovnikov¹⁰⁷, S.S. Bocchetta⁷⁹, A. Bocci⁴⁵, C.R. Boddy¹¹⁸, M. Boehler⁴⁸, J. Boek¹⁷⁵, N. Boelaert³⁶, J.A. Bogaerts³⁰, A. Bogdanchikov¹⁰⁷, A. Bogouch^90,∗, C. Bohm^146a, J. Bohm¹²⁵, V. Boisvert⁷⁶, T. Bold³⁸, V. Boldea^26a, N.M. Bolnet¹³⁶, M. Bomben⁷⁸, M. Bona⁷⁵, M. Boonekamp¹³⁶, S. Bordoni⁷⁸, C. Borer¹⁷, A. Borisov¹²⁸, G. Borissov⁷¹, I. Borjanovic^13a, M. Borri⁸², S. Borroni⁸⁷, V. Bortolotto^134a,134b, K. Bos¹⁰⁵,

D. Boscherini^20a, M. Bosman¹², H. Boterenbrood¹⁰⁵, J. Bouchami⁹³, J. Boudreau¹²³, E.V. Bouhova-Thacker⁷¹, D. Boumediene³⁴, C. Bourdarios¹¹⁵, N. Bousson⁸³, A. Boveia³¹, J. Boyd³⁰, I.R. Boyko⁶⁴, I. Bozovic-Jelisavcic^13b, J. Bracinik¹⁸, P. Branchini^134a, A. Brandt⁸, G. Brandt¹¹⁸, O. Brandt⁵⁴, U. Bratzler¹⁵⁶, B. Brau⁸⁴, J.E. Brau¹¹⁴, H.M. Braun^175,∗, S.F. Brazzale^164a,164c, B. Brelier¹⁵⁸, J. Bremer³⁰, K. Brendlinger¹²⁰, R. Brenner¹⁶⁶, S. Bressler¹⁷², D. Britton⁵³, F.M. Brochu²⁸, I. Brock²¹, R. Brock⁸⁸, F. Broggi^89a, C. Bromberg⁸⁸, J. Bronner⁹⁹, G. Brooijmans³⁵, T. Brooks⁷⁶, W.K. Brooks^32b, G. Brown⁸², H. Brown⁸, P.A. Bruckman de Renstrom³⁹, D. Bruncko^144b,

R. Bruneliere⁴⁸, S. Brunet⁶⁰, A. Bruni^20a, G. Bruni^20a, M. Bruschi^20a, T. Buanes¹⁴, Q. Buat⁵⁵, F. Bucci⁴⁹,

J. Buchanan¹¹⁸, P. Buchholz¹⁴¹, R.M. Buckingham¹¹⁸, A.G. Buckley⁴⁶, S.I. Buda^26a, I.A. Budagov⁶⁴, B. Budick¹⁰⁸, V. B¨uscher⁸¹, L. Bugge¹¹⁷, O. Bulekov⁹⁶, A.C. Bundock⁷³, M. Bunse⁴³, T. Buran¹¹⁷, H. Burckhart³⁰, S. Burdin⁷³, T. Burgess¹⁴, S. Burke¹²⁹, E. Busato³⁴, P. Bussey⁵³, C.P. Buszello¹⁶⁶, B. Butler¹⁴³, J.M. Butler²², C.M. Buttar⁵³, J.M. Butterworth⁷⁷, W. Buttinger²⁸, S. Cabrera Urb´an¹⁶⁷, D. Caforio^20a,20b, O. Cakir^4a, P. Calafiura¹⁵,

G. Calderini⁷⁸, P. Calfayan⁹⁸, R. Calkins¹⁰⁶, L.P. Caloba^24a, R. Caloi^132a,132b, D. Calvet³⁴, S. Calvet³⁴,

R. Camacho Toro³⁴, P. Camarri^133a,133b, D. Cameron¹¹⁷, L.M. Caminada¹⁵, R. Caminal Armadans¹²,

S. Campana³⁰, M. Campanelli⁷⁷, V. Canale^102a,102b, F. Canelli^31,g, A. Canepa^159a, J. Cantero⁸⁰, R. Cantrill⁷⁶, L. Capasso^102a,102b, M.D.M. Capeans Garrido³⁰, I. Caprini^26a, M. Caprini^26a, D. Capriotti⁹⁹, M. Capua^37a,37b, R. Caputo⁸¹, R. Cardarelli^133a, T. Carli³⁰, G. Carlino^102a, L. Carminati^89a,89b, B. Caron⁸⁵, S. Caron¹⁰⁴, E. Carquin^32b, G.D. Carrillo Montoya¹⁷³, A.A. Carter⁷⁵, J.R. Carter²⁸, J. Carvalho^124a,h, D. Casadei¹⁰⁸,

M.P. Casado¹², M. Cascella^122a,122b, C. Caso^50a,50b,∗, A.M. Castaneda Hernandez^173,i, E. Castaneda-Miranda¹⁷³, V. Castillo Gimenez¹⁶⁷, N.F. Castro^124a, G. Cataldi^72a, P. Catastini⁵⁷, A. Catinaccio³⁰, J.R. Catmore³⁰,

A. Cattai³⁰, G. Cattani^133a,133b, S. Caughron⁸⁸, V. Cavaliere¹⁶⁵, P. Cavalleri⁷⁸, D. Cavalli^89a, M. Cavalli-Sforza¹², V. Cavasinni^122a,122b, F. Ceradini^134a,134b, A.S. Cerqueira^24b, A. Cerri³⁰, L. Cerrito⁷⁵, F. Cerutti⁴⁷, S.A. Cetin^19b, A. Chafaq^135a, D. Chakraborty¹⁰⁶, I. Chalupkova¹²⁶, K. Chan³, P. Chang¹⁶⁵, B. Chapleau⁸⁵, J.D. Chapman²⁸, J.W. Chapman⁸⁷, E. Chareyre⁷⁸, D.G. Charlton¹⁸, V. Chavda⁸², C.A. Chavez Barajas³⁰, S. Cheatham⁸⁵, S. Chekanov⁶, S.V. Chekulaev^159a, G.A. Chelkov⁶⁴, M.A. Chelstowska¹⁰⁴, C. Chen⁶³, H. Chen²⁵, S. Chen^33c, X. Chen¹⁷³, Y. Chen³⁵, A. Cheplakov⁶⁴, R. Cherkaoui El Moursli^135e, V. Chernyatin²⁵, E. Cheu⁷, S.L. Cheung¹⁵⁸, L. Chevalier¹³⁶, G. Chiefari^102a,102b, L. Chikovani^51a,∗, J.T. Childers³⁰, A. Chilingarov⁷¹, G. Chiodini^72a,

A.S. Chisholm¹⁸, R.T. Chislett⁷⁷, A. Chitan^26a, M.V. Chizhov⁶⁴, G. Choudalakis³¹, S. Chouridou¹³⁷, I.A. Christidi⁷⁷, A. Christov⁴⁸, D. Chromek-Burckhart³⁰, M.L. Chu¹⁵¹, J. Chudoba¹²⁵, G. Ciapetti^132a,132b, A.K. Ciftci^4a, R. Ciftci^4a, D. Cinca³⁴, V. Cindro⁷⁴, C. Ciocca^20a,20b, A. Ciocio¹⁵, M. Cirilli⁸⁷, P. Cirkovic^13b, Z.H. Citron¹⁷², M. Citterio^89a, M. Ciubancan^26a, A. Clark⁴⁹, P.J. Clark⁴⁶, R.N. Clarke¹⁵, W. Cleland¹²³,

J.C. Clemens⁸³, B. Clement⁵⁵, C. Clement^146a,146b, Y. Coadou⁸³, M. Cobal^164a,164c, A. Coccaro¹³⁸, J. Cochran⁶³, L. Coffey²³, J.G. Cogan¹⁴³, J. Coggeshall¹⁶⁵, E. Cogneras¹⁷⁸, J. Colas⁵, S. Cole¹⁰⁶, A.P. Colijn¹⁰⁵, N.J. Collins¹⁸, C. Collins-Tooth⁵³, J. Collot⁵⁵, T. Colombo^119a,119b, G. Colon⁸⁴, P. Conde Mui˜no^124a, E. Coniavitis¹¹⁸,

M.C. Conidi¹², S.M. Consonni^89a,89b, V. Consorti⁴⁸, S. Constantinescu^26a, C. Conta^119a,119b, G. Conti⁵⁷,

F. Conventi^102a,j, M. Cooke¹⁵, B.D. Cooper⁷⁷, A.M. Cooper-Sarkar¹¹⁸, K. Copic¹⁵, T. Cornelissen¹⁷⁵, M. Corradi^20a, F. Corriveau^85,k, A. Cortes-Gonzalez¹⁶⁵, G. Cortiana⁹⁹, G. Costa^89a, M.J. Costa¹⁶⁷, D. Costanzo¹³⁹, D. Cˆot´e³⁰, L. Courneyea¹⁶⁹, G. Cowan⁷⁶, C. Cowden²⁸, B.E. Cox⁸², K. Cranmer¹⁰⁸, F. Crescioli^122a,122b, M. Cristinziani²¹, G. Crosetti^37a,37b, S. Cr´ep´e-Renaudin⁵⁵, C.-M. Cuciuc^26a, C. Cuenca Almenar¹⁷⁶, T. Cuhadar Donszelmann¹³⁹, M. Curatolo⁴⁷, C.J. Curtis¹⁸, C. Cuthbert¹⁵⁰, P. Cwetanski⁶⁰, H. Czirr¹⁴¹, P. Czodrowski⁴⁴, Z. Czyczula¹⁷⁶, S. D’Auria⁵³, M. D’Onofrio⁷³, A. D’Orazio^132a,132b, M.J. Da Cunha Sargedas De Sousa^124a, C. Da Via⁸², W. Dabrowski³⁸, A. Dafinca¹¹⁸, T. Dai⁸⁷, C. Dallapiccola⁸⁴, M. Dam³⁶, M. Dameri^50a,50b, D.S. Damiani¹³⁷, H.O. Danielsson³⁰, V. Dao⁴⁹, G. Darbo^50a, G.L. Darlea^26b, J.A. Dassoulas⁴², W. Davey²¹, T. Davidek¹²⁶, N. Davidson⁸⁶, R. Davidson⁷¹, E. Davies^118,c, M. Davies⁹³, O. Davignon⁷⁸, A.R. Davison⁷⁷, Y. Davygora^58a, E. Dawe¹⁴², I. Dawson¹³⁹, R.K. Daya-Ishmukhametova²³, K. De⁸, R. de Asmundis^102a, S. De Castro^20a,20b,

S. De Cecco⁷⁸, J. de Graat⁹⁸, N. De Groot¹⁰⁴, P. de Jong¹⁰⁵, C. De La Taille¹¹⁵, H. De la Torre⁸⁰, F. De Lorenzi⁶³, L. de Mora⁷¹, L. De Nooij¹⁰⁵, D. De Pedis^132a, A. De Salvo^132a, U. De Sanctis^164a,164c, A. De Santo¹⁴⁹,

J.B. De Vivie De Regie¹¹⁵, G. De Zorzi^132a,132b, W.J. Dearnaley⁷¹, R. Debbe²⁵, C. Debenedetti⁴⁶, B. Dechenaux⁵⁵, D.V. Dedovich⁶⁴, J. Degenhardt¹²⁰, C. Del Papa^164a,164c, J. Del Peso⁸⁰, T. Del Prete^122a,122b, T. Delemontex⁵⁵, M. Deliyergiyev⁷⁴, A. Dell’Acqua³⁰, L. Dell’Asta²², M. Della Pietra^102a,j, D. della Volpe^102a,102b, M. Delmastro⁵, P.A. Delsart⁵⁵, C. Deluca¹⁰⁵, S. Demers¹⁷⁶, M. Demichev⁶⁴, B. Demirkoz^12,l, J. Deng¹⁶³, S.P. Denisov¹²⁸, D. Derendarz³⁹, J.E. Derkaoui^135d, F. Derue⁷⁸, P. Dervan⁷³, K. Desch²¹, E. Devetak¹⁴⁸, P.O. Deviveiros¹⁰⁵, A. Dewhurst¹²⁹, B. DeWilde¹⁴⁸, S. Dhaliwal¹⁵⁸, R. Dhullipudi^25,m, A. Di Ciaccio^133a,133b, L. Di Ciaccio⁵, A. Di Girolamo³⁰, B. Di Girolamo³⁰, S. Di Luise^134a,134b, A. Di Mattia¹⁷³, B. Di Micco³⁰, R. Di Nardo⁴⁷, A. Di Simone^133a,133b, R. Di Sipio^20a,20b, M.A. Diaz^32a, E.B. Diehl⁸⁷, J. Dietrich⁴², T.A. Dietzsch^58a, S. Diglio⁸⁶, K. Dindar Yagci⁴⁰, J. Dingfelder²¹, F. Dinut^26a, C. Dionisi^132a,132b, P. Dita^26a, S. Dita^26a, F. Dittus³⁰, F. Djama⁸³, T. Djobava^51b, M.A.B. do Vale^24c, A. Do Valle Wemans^124a,n, T.K.O. Doan⁵, M. Dobbs⁸⁵, R. Dobinson^30,∗, D. Dobos³⁰, E. Dobson^30,o, J. Dodd³⁵, C. Doglioni⁴⁹, T. Doherty⁵³, Y. Doi^65,∗, J. Dolejsi¹²⁶, I. Dolenc⁷⁴, Z. Dolezal¹²⁶, B.A. Dolgoshein^96,∗, T. Dohmae¹⁵⁵, M. Donadelli^24d, J. Donini³⁴, J. Dopke³⁰, A. Doria^102a, A. Dos Anjos¹⁷³, A. Dotti^122a,122b, M.T. Dova⁷⁰, A.D. Doxiadis¹⁰⁵, A.T. Doyle⁵³, M. Dris¹⁰, J. Dubbert⁹⁹, S. Dube¹⁵, E. Duchovni¹⁷², G. Duckeck⁹⁸, D. Duda¹⁷⁵, A. Dudarev³⁰, F. Dudziak⁶³, M. D¨uhrssen³⁰,

I.P. Duerdoth⁸², L. Duflot¹¹⁵, M-A. Dufour⁸⁵, L. Duguid⁷⁶, M. Dunford³⁰, H. Duran Yildiz^4a, R. Duxfield¹³⁹, M. Dwuznik³⁸, F. Dydak³⁰, M. D¨uren⁵², J. Ebke⁹⁸, S. Eckweiler⁸¹, K. Edmonds⁸¹, W. Edson², C.A. Edwards⁷⁶, N.C. Edwards⁵³, W. Ehrenfeld⁴², T. Eifert¹⁴³, G. Eigen¹⁴, K. Einsweiler¹⁵, E. Eisenhandler⁷⁵, T. Ekelof¹⁶⁶, M. El Kacimi^135c, M. Ellert¹⁶⁶, S. Elles⁵, F. Ellinghaus⁸¹, K. Ellis⁷⁵, N. Ellis³⁰, J. Elmsheuser⁹⁸, M. Elsing³⁰, D. Emeliyanov¹²⁹, R. Engelmann¹⁴⁸, A. Engl⁹⁸, B. Epp⁶¹, J. Erdmann⁵⁴, A. Ereditato¹⁷, D. Eriksson^146a, J. Ernst², M. Ernst²⁵, J. Ernwein¹³⁶, D. Errede¹⁶⁵, S. Errede¹⁶⁵, E. Ertel⁸¹, M. Escalier¹¹⁵, H. Esch⁴³, C. Escobar¹²³,

X. Espinal Curull¹², B. Esposito⁴⁷, F. Etienne⁸³, A.I. Etienvre¹³⁶, E. Etzion¹⁵³, D. Evangelakou⁵⁴, H. Evans⁶⁰, L. Fabbri^20a,20b, C. Fabre³⁰, R.M. Fakhrutdinov¹²⁸, S. Falciano^132a, Y. Fang¹⁷³, M. Fanti^89a,89b, A. Farbin⁸,