Article
Reference
Search for Diphoton Events with Large Missing Transverse Energy in 7 TeV Proton-Proton Collisions with the ATLAS Detector
ATLAS Collaboration
ABDELALIM ALY, Ahmed Aly (Collab.), et al.
Abstract
A search for diphoton events with large missing transverse energy is presented. The data were collected with the ATLAS detector in proton-proton collisions at √s=7 TeV at the CERN Large Hadron Collider and correspond to an integrated luminosity of 3.1 pb−1. No excess of such events is observed above the standard model background prediction. In the context of a specific model with one universal extra dimension with compactification radius R and gravity-induced decays, values of 1/R
ATLAS Collaboration, ABDELALIM ALY, Ahmed Aly (Collab.), et al . Search for Diphoton Events with Large Missing Transverse Energy in 7 TeV Proton-Proton Collisions with the ATLAS
Detector. Physical Review Letters , 2011, vol. 106, no. 12, p. 121803
DOI : 10.1103/PhysRevLett.106.121803
Available at:
http://archive-ouverte.unige.ch/unige:41592
Disclaimer: layout of this document may differ from the published version.
Search for Diphoton Events with Large Missing Transverse Energy in 7 TeV Proton-Proton Collisions with the ATLAS Detector
G. Aadet al.* (ATLAS Collaboration)
(Received 20 December 2010; published 23 March 2011)
A search for diphoton events with large missing transverse energy is presented. The data were collected with the ATLAS detector in proton-proton collisions at ffiffiffi
ps
¼7 TeVat the CERN Large Hadron Collider and correspond to an integrated luminosity of3:1 pb1. No excess of such events is observed above the standard model background prediction. In the context of a specific model with one universal extra dimension with compactification radiusR and gravity-induced decays, values of 1=R <729 GeV are excluded at 95% C. L., providing the most sensitive limit on this model to date.
DOI:10.1103/PhysRevLett.106.121803 PACS numbers: 13.85.Rm, 11.25.Wx
In the standard model (SM), the production in proton- proton (pp) collisions of diphoton () events with large missing transverse energy (EmissT ) is mainly due toW=Zþ processes. Taking into account the branching ratios of W=Z decays including at least one neutrino, the cross sections are only a few femtobarns for 7 TeVppcollisions.
In contrast, some new physics models predict much larger þEmissT rates. This Letter reports the firstþEmissT search with LHC data, using data recorded with the ATLAS detector. The results are interpreted in the context of a universal extra dimension (UED) model.
UED models [1] postulate the existence of additional spatial dimensions in which all SM particles can propagate, leading to the existence for each SM particle of a series of excitations, known as a Kaluza-Klein (KK) tower. This analysis considers the case of a singleTeV1-sized UED, with compactification radiusR. The masses of the states of successive levels in the tower are separated by1=R. For a given KK level, the approximate mass degeneracy of the KK excitations is broken by radiative corrections [2]. The lightest KK particle (LKP) is the KK photon of the first level, denoted . At the LHC, the main UED process would be production via the strong interaction of a pair of first-level KK quarks and/or gluons [3], which would decay via cascades involving other KK particles until reaching the LKP at the end of the decay chain. If the UED model is embedded in a larger space withN addi- tional eV1-sized dimensions accessible only to gravity [4], the LKP could decay gravitationally via !þG [5], where G represents one of a tower of eV-spaced graviton states. With two decay chains per event, the final state would beþEmissT þX, where EmissT results from
the escaping gravitons andXrepresents SM particles emit- ted in the cascade decays.
The UED model considered is defined by specifyingR and , the ultraviolet cutoff used in the calculation of radiative corrections to the KK masses. This analysis treats Ras a free parameter and, following the theory calculations [2], sets such thatR¼20. For1=R¼700 GeV, the masses of the first-level KK photon, quark, and gluon are 700, 815, and 865 GeV, respectively [6]. The mass is insensitive to , while other KK masses change by typi- cally a few percent when varying Rin the range 10–30.
The gravitational decay widths of the KK particles are set byNandMD, the Planck scale in the (4þN)-dimensional theory. For the chosen values ofN¼6andMD ¼5 TeV, and provided 1=R <1 TeV, the LKP is the only KK particle to have an appreciable rate of gravitational decay.
The same parameter values were used in the only previous study of this model, in which the D0 experiment excluded at 95% C. L. values of1=R <477 GeV[7].
Monte Carlo (MC) signal samples were produced for a range of 1=Rvalues using the implementation [6] of the UED model in PYTHIA [8] version 6.421, and using the MC09 parameter tune [9]. The MC samples were pro- cessed through the ATLAS detector simulation [10] based on GEANT4 [11]. In addition to the two high transverse energy (ET) photons and large EmissT , the signal events typically include several high-ET jets due to the cascade decays, with theET spectrum of the leading jet peaking at 100 GeVfor1=R¼700 GeV.
The ATLAS detector [12] is a multipurpose particle physics apparatus with a forward-backward symmetric cylindrical geometry and nearly4solid angle coverage.
ATLAS uses a Cartesian right-handed coordinate system, with the nominal collision point at the origin. The anti- clockwise beam direction defines the positivezaxis, while the positive x axis points from the collision point to the center of the LHC ring and the positive y axis points upward. The angles and are the azimuthal and polar angles. The pseudorapidity is defined as
*Full author list given at the end of the article.
Published by 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.
¼ ln½tanð=2Þ. Closest to the beam line are tracking detectors which use layers of silicon-based and straw-tube detectors, located inside a thin superconducting solenoid that provides a 2 T magnetic field, to measure the trajecto- ries of charged particles. The solenoid is surrounded by a hermetic calorimeter system. A liquid-argon (LAr) sam- pling calorimeter is divided into a central barrel calorime- ter and two end-cap calorimeters, each housed in a separate cryostat. Fine-grained LAr electromagnetic (EM) calorim- eters, with excellent energy resolution, provide coverage forjj<3:2. In the regionjj<2:5, the EM calorimeters are segmented into three longitudinal layers and the second layer, in which most of the EM shower energy is deposited, is divided into cells of granularity of¼0:025 0:025. A presampler, coveringjj<1:8, is used to correct for energy lost upstream of the calorimeter. An iron- scintillator tile calorimeter provides hadronic coverage in the range jj<1:7. In the end caps (jj>1:5), LAr hadronic calorimeters match the outer jj limits of the end-cap EM calorimeters. LAr forward calorimeters pro- vide both EM and hadronic energy measurements, and extend the coverage tojj<4:9. Outside the calorimeters is an extensive muon system including large superconduct- ing toroidal magnets.
The reconstruction of photons is described in detail in Ref. [13]. To select photon candidates, EM calorimeter clusters were required to pass several quality criteria and to lie outside problematic calorimeter regions. Photon can- didates were required to havejj<1:81and to be outside the transition region1:37<jj<1:52between the barrel and the end-cap calorimeters. The analysis uses a ‘‘loose’’
photon selection, which includes cuts on the energy in the hadronic calorimeter as well as on variables that require the transverse width of the shower, measured in the second EM calorimeter layer, be consistent with the narrow width ex- pected for an EM shower. The loose selection provides a high photon efficiency with modest rejection against the background from jets.
The reconstruction ofEmissT is based on topological calo- rimeter clusters [14] withjj<4:5that are seeded by any cell with energy higher than 4 times its noise level. In an iterative procedure, the cluster grows by including all neigh- boring cells with energy higher than twice the noise, plus all cells neighboring the boundary of this three-dimensional collection. Each cluster is classified as EM or hadronic, depending on its topology, and the cluster energy is cali- brated to correct for the noncompensating calorimeter re- sponse, energy losses in dead material, and out-of-cluster energies. Events reconstructed with largeEmissT were studied in detail with early data [15]. Rare background events with large transverse energies, unrelated to the collision and con- centrated in a few cells, due mainly to discharges and noise, have been observed. Cuts were applied to eliminate such backgrounds, rejecting less than 0.05% of the selected events while having a negligible impact on the signal efficiency.
The data sample was collected during stable beam peri- ods of 7 TeVppcollisions at the LHC, and corresponds to an integrated luminosity of3:1 pb1. The events selected had to satisfy a trigger requiring at least one loose photon candidate with ET >20 GeV, and had to contain at least one reconstructed primary vertex consistent with the aver- age beam spot position and with at least three associated tracks. The trigger and vertex requirements are 99%
efficient for signal MC events. The presence of multiple pp collisions within the same bunch crossing, known as
‘‘pileup,’’ can be analyzed by examiningNvtx, the number of reconstructed primary vertices in each event. In this data sample, the average value of Nvtx was 2:1. The MC signal samples included the simulation of pileup and were weighted to match theNvtxdistribution observed in data.
Events were retained if they had at least two photon candidates, each withET>25 GeV. In addition, a photon isolation cut was applied, wherein theETin a radius of 0.2 in the-space around the center of the cluster, excluding the cells belonging to the cluster in a region corresponding to 57 cells in in the second layer of the EM calorimeter, had to be less than 35 GeV. This requirement had a signal efficiency greater than 95% but rejected some of the background from multijet events. An event in which each of the two photon candidates satisfied the loose photon cuts was considered a candidate event. An independent ‘‘misidentified jet’’ control sample, enriched in events with jets misidentified as photons, was defined as those events where at least one of the photon candidates did not pass the loose photon identification. After all cuts, the and misidentified jet samples totaled 520 and 7323 events, respectively. Figure 1 shows the ET spectrum of the leading photon for the candidates and for UED 1=R¼700 GeVMC events; the UED spectrum extends to much higherET values.
The background was evaluated entirely using data.
Noncollision backgrounds, such as cosmic rays and beam-halo events, are reduced to a negligible level by the
[GeV]
ET
50 100 150 200 250 300 350 400 450 500
Entries / 10 GeV
1 10 102
Ldt = 3.1 pb-1
∫
ATLAS
= 7 TeV) s Data 2010 (
×100) UED 1/R = 700 GeV (
FIG. 1. ET spectrum of the leading photon for thecandi- date sample and for UED1=R¼700 GeVMC events (normal- ized to 100 times the leading order (LO) cross section).
selection cuts. The main background source, referred to hereafter as QCD background, arises from a mixture of SM processes includingproduction, andþjet and multi- jet events with at least one jet misidentified as a photon.
With the loose photon identification, it is expected thatþ jet and multijet events dominate, with only a small contribution. The misidentified jet sample provided a model of the EmissT response for events with jets faking photons. The response for events was modeled using the EmissT spectrum measured in a high purity sample of Z!ee events, selected by a combination of kinematic cuts and electron identification requirements [14]. The EmissT spectrum forZ!eeevents, which is dominated by the calorimeter response to two genuine EM objects, was verified in MC simulations to model theEmissT response in SMprocesses, despite their kinematic differences. As shown in Fig.2,Z!eeevents typically have somewhat lower EmissT values than events of the misidentified jet sample, as expected since the presence of jets faking photons should result in a broaderEmissT distribution. The spectrum for the candidates, which for low EmissT is dominated by the QCD background with an unknown mixture of events with zero, one, and two fake photons, lies between these two samples. TheEmissT spectrum of the total QCD background was modeled by a weighted sum of the spectra of the Z!ee and misidentified jet samples.
The QCD background was normalized to have the same number of events as thecandidate sample in the region EmissT <20 GeV, where any UED signal contribution can
be neglected. The relative contributions of theZ!eeand misidentified jet samples were determined by fitting the QCD background shape to the EmissT spectrum of the candidates in this same low EmissT region. The fraction attributed to production, as modeled with theZ!ee distribution, was determined to beð3622Þ%. The search result is not very sensitive to the exact composition of the QCD background, and the fit error was used to determine systematic uncertainties on the background prediction.
A small additional background results from W !ev events, which have genuine EmissT and which can pass the selection if the electron is misidentified as a photon and the second photon is either a real photon inWevents or a jet faking a photon inWþjets events. A high purity sample of inclusiveW !evevents was selected by a combination of kinematic and electron identification cuts [14]. Requiring in addition a loose photon with ET>25 GeV, a ‘‘Wþ’’
sample of only 5 events was selected. Accounting for the probability for an electron to be misidentified as a loose photon, as determined using theZ!ee sample, the total background contribution due to W!evevents was then estimated to be only0:4events. Since the number ofW events was too small to measure their EmissT spectrum, a sample ofWþjets events was used instead, requiring a jet reconstructed with an anti-kTclustering algorithm [16] with radius parameter 0.4 and EjT>25 GeV. TheWð!eÞ þ jets=background contribution was then estimated by nor- malizing theWþjetsEmissT spectrum to the expected total of0:4events, as shown on Fig.2.
Figure3shows theEmissT spectrum of thecandidates, superimposed on the total background prediction, as well
[GeV]
miss
ET
40 30 20 10
0 50 75
Entries / 5 GeV
10-2
10-1 1 10 102
= 7 TeV) s
Data 2010 ( Misidentified jets
→ ee
Z → eν)+jets/γ W(
Ldt = 3.1 pb-1
∫
ATLAS
FIG. 2 (color online). EmissT spectra for thecandidates, for theZ!eeand misidentified jet samples used to model the QCD background (each normalized to the number ofcandidates with EmissT <20 GeV), and for the Wð!eÞ þjets= back- ground (normalized to its expected total of 0:4 events).
Variable sized bins are used, and the vertical error bars and shaded bands show the statistical errors.
[GeV]
miss
ET
0 4 0 3 0 2 0 1
0 50 75 150 600
Entries / 5 GeV
10-3
10-2
10-1
1 10
102 Data 2010 ( s = 7 TeV)
Total background UED 1/R = 500 GeV UED 1/R = 700 GeV
Ldt = 3.1 pb-1
∫
ATLAS
FIG. 3 (color online). EmissT spectrum for the candidates, compared to the total SM background as estimated from data.
Also shown are the expected UED signals for1=R¼500 GeV and 700 GeV. Variable sized bins are used, and the vertical error bars and shaded bands show the statistical errors.
as example UED signals. TableIsummarizes the number of observed candidates, as well as the expected backgrounds and example UED signal contributions, in several EmissT ranges. The QCD background dominates, and falls steeply with rising EmissT , while the W!ev background is very small, and flatter as a function of EmissT . The UED signals would peak at large values of EmissT . There is good agreement between the data and predicted background over the entireEmissT range, with no indication of an excess at highEmissT values.
The signal search region was chosen to be EmissT >
75 GeV, before looking at the data, to obtain the best sensitivity to the UED signal. In the signal region, there are zero observed events, compared to an expectation of 0:320:16ðstatÞþ0:370:10ðsystÞ background events. The sys- tematic uncertainty was derived by studying variations of the background determination, including varying within its error the fraction determined in the fit of the QCD background, varying the definition of the misidentified jet sample, and eliminating the photon isolation cut.
The UED signal efficiency, determined from MC simulations, increases smoothly from 43% for 1=R¼500 GeVto48%for1=R¼700 GeV, with the lower efficiencies for smaller 1=R due mostly to the EmissT >75 GeVdefinition of the signal region. The various relative systematic uncertainties on the extraction of the UED signal cross section are summarized in Table II, including the dominant 11% uncertainty on the integrated luminosity [17]. Uncertainties on the efficiency for recon- structing and identifying the pair arise mainly due to
differences between MC simulations and data in the dis- tributions of the photon identification variables, the need to extrapolate to the higher ET values (see Fig.1) typical of the UED photons, the impact of the photon quality cuts, varying the scale of the photonETcut, and uncertainties in the detailed material composition of the detector. Together these provide a systematic uncertainty of 4%. The influ- ence of pileup, evaluated by comparing MC samples with and without pileup, gives a systematic uncertainty of 2%.
Systematic effects on theEmissT reconstruction [14], includ- ing pileup, varying the cluster energies within the current uncertainties, and varying the expected EmissT resolution between the measured performance and MC expectations, combine to give a 1% uncertainty on the signal efficiency.
Finally, the 1% statistical error on the signal efficiency as determined by MC simulations is treated as a systematic uncertainty on the result. Adding in quadrature, the total systematic uncertainty on the signal yield is 12%.
Given the good agreement between the measuredEmissT spectrum and the expected background, a limit was set on 1=R in the specific UED model considered here. A Bayesian approach was used to calculate a limit based on the number of observed and expected events withEmissT >
75 GeV. A Poisson distribution was used as the likelihood function for the expected number of signal events, and a flat prior was used for the signal cross section. Log-normal priors were used for the various sources of uncertainty, which were treated as nuisance parameters. It was verified that the result is not very sensitive to the detailed form of the assumed priors. Figure4depicts the resulting95%C:L:
upper limit within the context of the UED model consid- ered, together with the LO UED cross section as a function of1=R. The LO cross section was used since higher order corrections have not been calculated for the UED model.
An uncertainty on the signal cross section due to parton distribution functions (PDF’s) was determined by compar- ing the predictions using MRST2007 [18] PDF’s with those from the full set of error PDF’s of CTEQ6.6 [19].
The resultant uncertainty, namely 8% essentially inde- pendent of1=R, is shown by the width of the theory curve band. The observed 95%C:L: exclusion region is 1=R <
729 GeV. The result depends weakly on the systematic TABLE I. The number of observedcandidates, as well as the SM backgrounds estimated from data and expected UED signal for 1=Rvalues of 500 and 700 GeV, given in variousEmissT ranges. The uncertainties are statistical only. The first row, forEmissT <20 GeV, is the control region used to normalize the QCD background to the number of observedcandidates.
EmissT range Data Predicted background events Expected UED signal events
(GeV) events Total QCD Wð!eÞ þjets= 1=R¼500 GeV 1=R¼700 GeV
0–20 465 465:09:1 465:09:1 - 0:280:06 0:020:01
20–30 45 40:52:2 40:412:17 0:110:07 0:450:07 0:030:01
30–50 9 10:31:3 10:131:30 0:160:10 1:600:12 0:080:01
50–75 1 0:930:23 0:850:23 0:080:05 2:840:16 0:140:01
>75 0 0:320:16 0:280:15 0:040:03 40:450:62 4:210:06
TABLE II. Relative systematic uncertainties on the expected UED signal yield. For more details, see the text.
Source of uncertainty Uncertainty
Integrated luminosity 11%
Photon reconstruction and identification 4%
Effect of pileup 2%
EmissT reconstruction and scale 1%
Signal MC statistics 1%
Total 12%
uncertainties, and would only increase to 732 GeV if they were neglected. Changing theEmissT cut to 60 or 90 GeV would change the limit by only a few GeV. A cross-check using a higher puritysample, achieved by requiring that both photons pass tighter identification cuts that reject more of the background from jets, produced a consistent result.
In conclusion, a search forevents with largeEmissT , conducted using a3:1 pb1 sample of 7 TeVppcollisions recorded with the ATLAS detector at the LHC, found no evidence of an excess above the SM prediction. The results were used to set limits on a specific model with one UED and gravity-induced LKP decays, excluding at the 95%C:L:values of1=R <729 GeV, and significantly sur- passing the only existing experimental limit [7] on this model.
We wish to thank CERN for the efficient commissioning and operation of the LHC during this initial high-energy data-taking period 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;
CONICYT, Chile; CAS, MOST and NSFC, China;
COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; ARTEMIS, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNAS, Georgia; 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 Russia 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 Cantons of Bern and Geneva, Switzerland; NSC, Taiwan;
TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE and NSF, United States of America. The crucial computing support from all WLCG partners 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 (Taiwan), RAL (UK) and BNL (USA) and in the Tier-2 facilities worldwide.
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1/R [GeV]
400 500 600 700 800
[pb]σ
1 10 102
= 7 TeV
-1 s Ldt = 3.1pb
∫
95% CL Limit UED LO cross section
ATLAS
FIG. 4 (color online). 95%C:L: upper limits on the UED production cross section, and the LO theory cross section pre- diction, as a function of1=R. The shaded band shows the PDF uncertainty.
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S. Behar Harpaz,152P. K. Behera,63M. Beimforde,99C. Belanger-Champagne,166P. J. Bell,49W. H. Bell,49 G. Bella,153L. Bellagamba,19aF. Bellina,29G. Bellomo,89a,89bM. Bellomo,119aA. Belloni,57K. Belotskiy,96 O. Beltramello,29S. Ben Ami,152O. Benary,153D. Benchekroun,135aC. Benchouk,83M. Bendel,81B. H. Benedict,163
N. Benekos,165Y. Benhammou,153D. P. Benjamin,44M. Benoit,115J. R. Bensinger,22K. Benslama,130 S. Bentvelsen,105D. Berge,29E. Bergeaas Kuutmann,41N. Berger,4F. Berghaus,169E. Berglund,49J. Beringer,14
K. Bernardet,83P. Bernat,115R. Bernhard,48C. Bernius,24T. Berry,76A. Bertin,19a,19bF. Bertinelli,29 F. Bertolucci,122a,122bM. I. Besana,89a,89bN. Besson,136S. Bethke,99W. Bhimji,45R. M. Bianchi,29M. Bianco,72a,72b
O. Biebel,98J. Biesiada,14M. Biglietti,132a,132bH. Bilokon,47M. Bindi,19a,19bA. Bingul,18cC. Bini,132a,132b C. Biscarat,177U. Bitenc,48K. M. Black,21R. E. Blair,5J.-B. Blanchard,115G. Blanchot,29C. Blocker,22J. Blocki,38
A. Blondel,49W. Blum,81U. Blumenschein,54G. J. Bobbink,105V. B. Bobrovnikov,107A. Bocci,44R. Bock,29 C. R. Boddy,118M. Boehler,41J. Boek,174N. Boelaert,35S. Bo¨ser,77J. A. Bogaerts,29A. Bogdanchikov,107 A. Bogouch,90,aC. Bohm,146aV. Boisvert,76T. Bold,163,fV. Boldea,25aM. Bona,75M. Boonekamp,136G. Boorman,76 C. N. Booth,139P. Booth,139J. R. A. Booth,17S. Bordoni,78C. Borer,16A. Borisov,128G. Borissov,71I. Borjanovic,12a S. Borroni,132a,132bK. Bos,105D. Boscherini,19aM. Bosman,11H. Boterenbrood,105D. Botterill,129J. Bouchami,93
J. Boudreau,123E. V. Bouhova-Thacker,71C. Boulahouache,123C. Bourdarios,115N. Bousson,83A. Boveia,30 J. Boyd,29I. R. Boyko,65N. I. Bozhko,128I. Bozovic-Jelisavcic,12bJ. Bracinik,17A. Braem,29E. Brambilla,72a,72b P. Branchini,134aG. W. Brandenburg,57A. Brandt,7G. Brandt,41O. Brandt,54U. Bratzler,156B. Brau,84J. E. Brau,114
H. M. Braun,174B. Brelier,158J. Bremer,29R. Brenner,166S. Bressler,152D. Breton,115N. D. Brett,118 P. G. Bright-Thomas,17D. Britton,53F. M. Brochu,27I. Brock,20R. Brock,88T. J. Brodbeck,71E. Brodet,153
F. Broggi,89aC. Bromberg,88G. Brooijmans,34W. K. Brooks,31bG. Brown,82E. Brubaker,30 P. A. Bruckman de Renstrom,38D. Bruncko,144bR. Bruneliere,48S. Brunet,61A. Bruni,19aG. Bruni,19a M. Bruschi,19aT. Buanes,13F. Bucci,49J. Buchanan,118N. J. Buchanan,2P. Buchholz,141R. M. Buckingham,118
A. G. Buckley,45S. I. Buda,25aI. A. Budagov,65B. Budick,108V. Bu¨scher,81L. Bugge,117D. Buira-Clark,118 E. J. Buis,105O. Bulekov,96M. Bunse,42T. Buran,117H. Burckhart,29S. Burdin,73T. Burgess,13S. Burke,129
E. Busato,33P. Bussey,53C. P. Buszello,166F. Butin,29B. Butler,143J. M. Butler,21C. M. Buttar,53
J. M. Butterworth,77W. Buttinger,27T. Byatt,77S. Cabrera Urba´n,167M. Caccia,89a,89bD. Caforio,19a,19bO. Cakir,3a P. Calafiura,14G. Calderini,78P. Calfayan,98R. Calkins,106L. P. Caloba,23aR. Caloi,132a,132bD. Calvet,33S. Calvet,33
A. Camard,78P. Camarri,133a,133bM. Cambiaghi,119a,119bD. Cameron,117J. Cammin,20S. Campana,29 M. Campanelli,77V. Canale,102a,102bF. Canelli,30A. Canepa,159aJ. Cantero,80L. Capasso,102a,102b M. D. M. Capeans Garrido,29I. Caprini,25aM. Caprini,25aD. Capriotti,99M. Capua,36a,36bR. Caputo,148 C. Caramarcu,25aR. Cardarelli,133aT. Carli,29G. Carlino,102aL. Carminati,89a,89bB. Caron,159aS. Caron,48 C. Carpentieri,48G. D. Carrillo Montoya,172S. Carron Montero,158A. A. Carter,75J. R. Carter,27J. Carvalho,124a,g
D. Casadei,108M. P. Casado,11M. Cascella,122a,122bC. Caso,50a,50b,aA. M. Castaneda Hernandez,172 E. Castaneda-Miranda,172V. Castillo Gimenez,167N. F. Castro,124b,bG. Cataldi,72aF. Cataneo,29A. Catinaccio,29 J. R. Catmore,71A. Cattai,29G. Cattani,133a,133bS. Caughron,88A. Cavallari,132a,132bP. Cavalleri,78D. Cavalli,89a M. Cavalli-Sforza,11V. Cavasinni,122a,122bA. Cazzato,72a,72bF. Ceradini,134a,134bC. Cerna,83A. S. Cerqueira,23a A. Cerri,29L. Cerrito,75F. Cerutti,47S. A. Cetin,18bF. Cevenini,102a,102bA. Chafaq,135aD. Chakraborty,106K. Chan,2
B. Chapleau,85J. D. Chapman,27J. W. Chapman,87E. Chareyre,78D. G. Charlton,17V. Chavda,82S. Cheatham,71 S. Chekanov,5S. V. Chekulaev,159aG. A. Chelkov,65H. Chen,24L. Chen,2S. Chen,32cT. Chen,32cX. Chen,172
S. Cheng,32aA. Cheplakov,65V. F. Chepurnov,65R. Cherkaoui El Moursli,135dV. Chernyatin,24E. Cheu,6 S. L. Cheung,158L. Chevalier,136F. Chevallier,136G. Chiefari,102a,102bL. Chikovani,51J. T. Childers,58a A. Chilingarov,71G. Chiodini,72aM. V. Chizhov,65G. Choudalakis,30S. Chouridou,137I. A. Christidi,77 A. Christov,48D. Chromek-Burckhart,29M. L. Chu,151J. Chudoba,125G. Ciapetti,132a,132bA. K. Ciftci,3aR. Ciftci,3a D. Cinca,33V. Cindro,74M. D. Ciobotaru,163C. Ciocca,19a,19bA. Ciocio,14M. Cirilli,87M. Ciubancan,25aA. Clark,49
P. J. Clark,45W. Cleland,123J. C. Clemens,83B. Clement,55C. Clement,146a,146bR. W. Clifft,129Y. Coadou,83 M. Cobal,164a,164cA. Coccaro,50a,50bJ. Cochran,64P. Coe,118J. G. Cogan,143J. Coggeshall,165E. Cogneras,177 C. D. Cojocaru,28J. Colas,4A. P. Colijn,105C. Collard,115N. J. Collins,17C. Collins-Tooth,53J. Collot,55G. Colon,84
R. Coluccia,72a,72bG. Comune,88P. Conde Muin˜o,124aE. Coniavitis,118M. C. Conidi,11M. Consonni,104 S. Constantinescu,25aC. Conta,119a,119bF. Conventi,102a,hJ. Cook,29M. Cooke,14B. D. Cooper,75 A. M. Cooper-Sarkar,118N. J. Cooper-Smith,76K. Copic,34T. Cornelissen,50a,50bM. Corradi,19aS. Correard,83 F. Corriveau,85,iA. Cortes-Gonzalez,165G. Cortiana,99G. Costa,89aM. J. Costa,167D. Costanzo,139T. Costin,30
D. Coˆte´,29R. Coura Torres,23aL. Courneyea,169G. Cowan,76C. Cowden,27B. E. Cox,82K. Cranmer,108 M. Cristinziani,20G. Crosetti,36a,36bR. Crupi,72a,72bS. Cre´pe´-Renaudin,55C. Cuenca Almenar,175 T. Cuhadar Donszelmann,139S. Cuneo,50a,50bM. Curatolo,47C. J. Curtis,17P. Cwetanski,61H. Czirr,141
Z. Czyczula,117S. D’Auria,53M. D’Onofrio,73A. D’Orazio,132a,132bA. Da Rocha Gesualdi Mello,23a P. V. M. Da Silva,23aC. Da Via,82W. Dabrowski,37A. Dahlhoff,48T. Dai,87C. Dallapiccola,84S. J. Dallison,129,a
M. Dam,35M. Dameri,50a,50bD. S. Damiani,137H. O. Danielsson,29R. Dankers,105D. Dannheim,99V. Dao,49 G. Darbo,50aG. L. Darlea,25bC. Daum,105J. P. Dauvergne,29W. Davey,86T. Davidek,126N. Davidson,86 R. Davidson,71M. Davies,93A. R. Davison,77E. Dawe,142I. Dawson,139J. W. Dawson,5,aR. K. Daya,39K. De,7
R. de Asmundis,102aS. De Castro,19a,19bS. De Cecco,78J. de Graat,98N. De Groot,104P. de Jong,105 E. De La Cruz-Burelo,87C. De La Taille,115B. De Lotto,164a,164cL. De Mora,71L. De Nooij,105
M. De Oliveira Branco,29D. De Pedis,132aP. de Saintignon,55A. De Salvo,132aU. De Sanctis,164a,164cA. De Santo,149 J. B. De Vivie De Regie,115S. Dean,77G. Dedes,99D. V. Dedovich,65J. Degenhardt,120M. Dehchar,118M. Deile,98 C. Del Papa,164a,164cJ. Del Peso,80T. Del Prete,122a,122bA. Dell’Acqua,29L. Dell’Asta,89a,89bM. Della Pietra,102a,h D. della Volpe,102a,102bM. Delmastro,29P. Delpierre,83N. Delruelle,29P. A. Delsart,55C. Deluca,148S. Demers,175 M. Demichev,65B. Demirkoz,11J. Deng,163S. P. Denisov,128C. Dennis,118D. Derendarz,38J. E. Derkaoui,135c
F. Derue,78P. Dervan,73K. Desch,20E. Devetak,148P. O. Deviveiros,158A. Dewhurst,129B. DeWilde,148 S. Dhaliwal,158R. Dhullipudi,24,jA. Di Ciaccio,133a,133bL. Di Ciaccio,4A. Di Girolamo,29B. Di Girolamo,29 S. Di Luise,134a,134bA. Di Mattia,88R. Di Nardo,133a,133bA. Di Simone,133a,133bR. Di Sipio,19a,19bM. A. Diaz,31a
F. Diblen,18cE. B. Diehl,87H. Dietl,99J. Dietrich,48T. A. Dietzsch,58aS. Diglio,115K. Dindar Yagci,39 J. Dingfelder,20C. Dionisi,132a,132bP. Dita,25aS. Dita,25aF. Dittus,29F. Djama,83R. Djilkibaev,108T. Djobava,51
M. A. B. do Vale,23aA. Do Valle Wemans,124aT. K. O. Doan,4M. Dobbs,85R. Dobinson,29,aD. Dobos,42 E. Dobson,29M. Dobson,163J. Dodd,34O. B. Dogan,18a,aC. Doglioni,118T. Doherty,53Y. Doi,66J. Dolejsi,126
I. Dolenc,74Z. Dolezal,126B. A. Dolgoshein,96T. Dohmae,155M. Donadelli,23bM. Donega,120J. Donini,55 J. Dopke,174A. Doria,102aA. Dos Anjos,172M. Dosil,11A. Dotti,122a,122bM. T. Dova,70J. D. Dowell,17 A. D. Doxiadis,105A. T. Doyle,53Z. Drasal,126J. Drees,174N. Dressnandt,120H. Drevermann,29C. Driouichi,35
M. Dris,9J. G. Drohan,77J. Dubbert,99T. Dubbs,137S. Dube,14E. Duchovni,171G. Duckeck,98A. Dudarev,29 F. Dudziak,115M. Du¨hrssen,29I. P. Duerdoth,82L. Duflot,115M-A. Dufour,85M. Dunford,29H. Duran Yildiz,3b
R. Duxfield,139M. Dwuznik,37F. Dydak,29D. Dzahini,55M. Du¨ren,52J. Ebke,98S. Eckert,48S. Eckweiler,81 K. Edmonds,81C. A. Edwards,76I. Efthymiopoulos,49W. Ehrenfeld,41T. Ehrich,99T. Eifert,29G. Eigen,13 K. Einsweiler,14E. Eisenhandler,75T. Ekelof,166M. El Kacimi,4M. Ellert,166S. Elles,4F. Ellinghaus,81K. Ellis,75
N. Ellis,29J. Elmsheuser,98M. Elsing,29R. Ely,14D. Emeliyanov,129R. Engelmann,148A. Engl,98B. Epp,62 A. Eppig,87J. Erdmann,54A. Ereditato,16D. Eriksson,146aJ. Ernst,1M. Ernst,24J. Ernwein,136D. Errede,165
S. Errede,165E. Ertel,81M. Escalier,115C. Escobar,167X. Espinal Curull,11B. Esposito,47F. Etienne,83 A. I. Etienvre,136E. Etzion,153D. Evangelakou,54H. Evans,61L. Fabbri,19a,19bC. Fabre,29K. Facius,35 R. M. Fakhrutdinov,128S. Falciano,132aA. C. Falou,115Y. Fang,172M. Fanti,89a,89bA. Farbin,7A. Farilla,134a J. Farley,148T. Farooque,158S. M. Farrington,118P. Farthouat,29D. Fasching,172P. Fassnacht,29D. Fassouliotis,8 B. Fatholahzadeh,158A. Favareto,89a,89bL. Fayard,115S. Fazio,36a,36bR. Febbraro,33P. Federic,144aO. L. Fedin,121
I. Fedorko,29W. Fedorko,88M. Fehling-Kaschek,48L. Feligioni,83D. Fellmann,5C. U. Felzmann,86C. Feng,32d E. J. Feng,30A. B. Fenyuk,128J. Ferencei,144bD. Ferguson,172J. Ferland,93B. Fernandes,124a,cW. Fernando,109 S. Ferrag,53J. Ferrando,118V. Ferrara,41A. Ferrari,166P. Ferrari,105R. Ferrari,119aA. Ferrer,167M. L. Ferrer,47
D. Ferrere,49C. Ferretti,87A. Ferretto Parodi,50a,50bM. Fiascaris,30F. Fiedler,81A. Filipcˇicˇ,74A. Filippas,9 F. Filthaut,104M. Fincke-Keeler,169M. C. N. Fiolhais,124a,gL. Fiorini,11A. Firan,39G. Fischer,41P. Fischer,20
M. J. Fisher,109S. M. Fisher,129J. Flammer,29M. Flechl,48I. Fleck,141J. Fleckner,81P. Fleischmann,173 S. Fleischmann,20T. Flick,174L. R. Flores Castillo,172M. J. Flowerdew,99F. Fo¨hlisch,58aM. Fokitis,9 T. Fonseca Martin,16D. A. Forbush,138A. Formica,136A. Forti,82D. Fortin,159aJ. M. Foster,82D. Fournier,115 A. Foussat,29A. J. Fowler,44K. Fowler,137H. Fox,71P. Francavilla,122a,122bS. Franchino,119a,119bD. Francis,29
T. Frank,171M. Franklin,57S. Franz,29M. Fraternali,119a,119bS. Fratina,120S. T. French,27R. Froeschl,29 D. Froidevaux,29J. A. Frost,27C. Fukunaga,156E. Fullana Torregrosa,29J. Fuster,167C. Gabaldon,29O. Gabizon,171 T. Gadfort,24S. Gadomski,49G. Gagliardi,50a,50bP. Gagnon,61C. Galea,98E. J. Gallas,118M. V. Gallas,29V. Gallo,16
B. J. Gallop,129P. Gallus,125E. Galyaev,40K. K. Gan,109Y. S. Gao,143,kV. A. Gapienko,128A. Gaponenko,14 F. Garberson,175M. Garcia-Sciveres,14C. Garcı´a,167J. E. Garcı´a Navarro,49R. W. Gardner,30N. Garelli,29 H. Garitaonandia,105V. Garonne,29J. Garvey,17C. Gatti,47G. Gaudio,119aO. Gaumer,49B. Gaur,141L. Gauthier,136
I. L. Gavrilenko,94C. Gay,168G. Gaycken,20J-C. Gayde,29E. N. Gazis,9P. Ge,32dC. N. P. Gee,129 Ch. Geich-Gimbel,20K. Gellerstedt,146a,146bC. Gemme,50aA. Gemmell,53M. H. Genest,98S. Gentile,132a,132b
F. Georgatos,9S. George,76P. Gerlach,174A. Gershon,153C. Geweniger,58aH. Ghazlane,135dP. Ghez,4 N. Ghodbane,33B. Giacobbe,19aS. Giagu,132a,132bV. Giakoumopoulou,8V. Giangiobbe,122a,122bF. Gianotti,29
B. Gibbard,24A. Gibson,158S. M. Gibson,29G. F. Gieraltowski,5L. M. Gilbert,118M. Gilchriese,14 O. Gildemeister,29V. Gilewsky,91D. Gillberg,28A. R. Gillman,129D. M. Gingrich,2,eJ. Ginzburg,153N. Giokaris,8
R. Giordano,102a,102bF. M. Giorgi,15P. Giovannini,99P. F. Giraud,136D. Giugni,89aP. Giusti,19aB. K. Gjelsten,117 L. K. Gladilin,97C. Glasman,80J. Glatzer,48A. Glazov,41K. W. Glitza,174G. L. Glonti,65J. Godfrey,142 J. Godlewski,29M. Goebel,41T. Go¨pfert,43C. Goeringer,81C. Go¨ssling,42T. Go¨ttfert,99S. Goldfarb,87D. Goldin,39 T. Golling,175N. P. Gollub,29S. N. Golovnia,128A. Gomes,124a,cL. S. Gomez Fajardo,41R. Gonc¸alo,76L. Gonella,20 C. Gong,32bA. Gonidec,29S. Gonzalez,172S. Gonza´lez de la Hoz,167M. L. Gonzalez Silva,26S. Gonzalez-Sevilla,49
J. J. Goodson,148L. Goossens,29P. A. Gorbounov,95H. A. Gordon,24I. Gorelov,103G. Gorfine,174B. Gorini,29 E. Gorini,72a,72bA. Gorisˇek,74E. Gornicki,38S. A. Gorokhov,128B. T. Gorski,29V. N. Goryachev,128B. Gosdzik,41
M. Gosselink,105M. I. Gostkin,65M. Gouane`re,4I. Gough Eschrich,163M. Gouighri,135aD. Goujdami,135a M. P. Goulette,49A. G. Goussiou,138C. Goy,4I. Grabowska-Bold,163,fV. Grabski,176P. Grafstro¨m,29C. Grah,174
K-J. Grahn,147F. Grancagnolo,72aS. Grancagnolo,15V. Grassi,148V. Gratchev,121N. Grau,34H. M. Gray,34,l J. A. Gray,148E. Graziani,134aO. G. Grebenyuk,121D. Greenfield,129T. Greenshaw,73Z. D. Greenwood,24,j I. M. Gregor,41P. Grenier,143E. Griesmayer,46J. Griffiths,138N. Grigalashvili,65A. A. Grillo,137K. Grimm,148
S. Grinstein,11P. L. Y. Gris,33Y. V. Grishkevich,97J.-F. Grivaz,115J. Grognuz,29M. Groh,99E. Gross,171 J. Grosse-Knetter,54J. Groth-Jensen,79M. Gruwe,29K. Grybel,141V. J. Guarino,5C. Guicheney,33A. Guida,72a,72b
T. Guillemin,4S. Guindon,54H. Guler,85,mJ. Gunther,125B. Guo,158J. Guo,34A. Gupta,30Y. Gusakov,65
