Article
Reference
Measurement of Z Boson Production in Pb-Pb Collisions at √s
NN=2.76 TeV with the ATLAS Detector
ATLAS Collaboration
ABDELALIM ALY, Ahmed Aly (Collab.), et al.
Abstract
The ATLAS experiment has observed 1995 Z boson candidates in data corresponding to 0.15 nb−1 of integrated luminosity obtained in the 2011 LHC Pb+Pb run at √sNN=2.76 TeV. The Z bosons are reconstructed via dielectron and dimuon decay channels, with a background contamination of less than 3%. Results from the two channels are consistent and are combined. Within the statistical and systematic uncertainties, the per-event Z boson yield is proportional to the number of binary collisions estimated by the Glauber model. The elliptic anisotropy of the azimuthal distribution of the Z boson with respect to the event plane is found to be consistent with zero.
ATLAS Collaboration, ABDELALIM ALY, Ahmed Aly (Collab.), et al . Measurement of Z Boson Production in Pb-Pb Collisions at √s
NN=2.76 TeV with the ATLAS Detector. Physical Review Letters , 2013, vol. 110, no. 02, p. 022301
DOI : 10.1103/PhysRevLett.110.022301
Available at:
http://archive-ouverte.unige.ch/unige:40038
Disclaimer: layout of this document may differ from the published version.
Measurement of Z Boson Production in Pb-Pb Collisions at p ffiffiffiffiffiffiffiffiffi s
NN¼ 2:76 TeV with the ATLAS Detector
G. Aadet al.* (ATLAS Collaboration)
(Received 24 October 2012; published 8 January 2013)
The ATLAS experiment has observed 1995Zboson candidates in data corresponding to0:15 nb1of integrated luminosity obtained in the 2011 LHCPbþPbrun atpffiffiffiffiffiffiffiffisNN¼2:76 TeV. TheZbosons are reconstructed via dielectron and dimuon decay channels, with a background contamination of less than 3%. Results from the two channels are consistent and are combined. Within the statistical and systematic uncertainties, the per-eventZboson yield is proportional to the number of binary collisions estimated by the Glauber model. The elliptic anisotropy of the azimuthal distribution of theZboson with respect to the event plane is found to be consistent with zero.
DOI:10.1103/PhysRevLett.110.022301 PACS numbers: 25.75.Cj, 14.70.Hp, 23.70.+j, 25.75.Dw
Extensive studies of heavy ion (HI) collisions carried out by the experiments at the Relativistic Heavy Ion Collider (RHIC) at BNL, and the Large Hadron Collider (LHC) at CERN, have established that the hot and dense matter produced in HI collisions causes a significant modification of the energetic color-charge carriers propagating through such a medium [1,2]. An understanding of this phenome- non requires measuring the unmodified production rates of the particles before they lose energy. The best candidates to perform such measurements are particles that do not inter- act via the strong force. The PHENIX experiment at RHIC measured the properties of photons [3]. At the LHC, the CMS experiment reported results on photons andWbosons [4,5]. The number of these bosons was found to scale with the number of incoherent nucelon-nucleon collisions. Both the ATLAS and CMS Collaborations have reported mea- surements of Z! production at pffiffiffiffiffiffiffiffisNN ¼2:76 TeV [6,7], which show, within a limited statistical precision, the same scaling behavior. This Letter presents a precise measurement ofZboson production inPbþPbcollisions
at pffiffiffiffiffiffiffiffisNN ¼2:76 TeV, using the dielectron and dimuon
decay channels. TheZboson production rate is measured as a function of centrality, rapidity (yZ), transverse mo- mentum (pZT), and orientation with respect to the event plane [8].
The ATLAS detector [9] at the LHC covers nearly the entire solid angle around the collision point. It consists of an inner tracking detector surrounded by a thin supercon- ducting solenoid, electromagnetic and hadronic calorime- ters, and a muon spectrometer incorporating three superconducting toroid magnet systems.
The inner detector system (ID) is immersed in a 2 T axial magnetic field and provides charged particle tracking in the rangejj<2:5. The high-granularity silicon pixel detector covers the vertex region and is surrounded by the silicon microstrip tracker and the transition radiation tracker.
The calorimeters cover the rangejj<4:9. Within the regionjj<3:2, electromagnetic calorimetry is provided by barrel and end-cap high-granularity lead liquid-argon (LAr) calorimeters, with an additional thin LAr presampler covering jj<1:8. The electromagnetic calorimeter is backed by a hadronic calorimeter. Forward calorimeters (FCal) are located in the range3:1<jj<4:9.
The muon spectrometer (MS) comprises separate trigger and high-precision tracking chambers that measure the deflection of muons in a magnetic field generated by super- conducting air-core toroids. The precision chambers cover the region jj<2:7 with three layers of monitored drift tubes (MDT), complemented by cathode strip chambers (CSC) in the innermost layer of the forward region. The muon trigger system covers the rangejj<2:4with resis- tive plate chambers in the barrel, and thin gap chambers in the end-cap regions.
This analysis uses the 2011 LHCPbþPbcollision data
atpffiffiffiffiffiffiffiffisNN ¼2:76 TeV, obtained by the ATLAS experiment
with integrated luminosity of approximately 0:15 nb1. The data sample for this study was collected using a three-level trigger system [10], which selected events with electron or muon candidates.
Electron candidates were identified at the first trigger level (L1) as a cluster of cells in the electromagnetic calorimeter, formed into ðÞ ¼0:10:1 trigger towers, within the rangejj<2:5, excluding the transition region between calorimeter sections (1:37<jj<1:52).
The cluster transverse energy was required to exceed ET ¼14 GeV.
Muon candidates were selected using all three trigger levels. The L1 muon trigger searched for patterns of hits in the trigger chambers consistent with muons. If a muon
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hadpTexceeding 4 GeV, the event was accepted for further processing by the high-level trigger (HLT). TheL1 muon algorithm also identified regions of interest (RoI) within the detector to be investigated by the HLT. In the HLT, the track parameters of each muon were recalculated by including the precision data from the MDT or CSC in the RoI defined by the previous trigger level. Muon candidates were reconstructed either solely from the MS or using combined data from the MS and ID. In addition to the events selected using the RoI-based muon trigger, the reconstruction was performed over the whole MS by the HLT to identify muons with pT>10 GeV. The full scan searched all events in which a neutral particle signal was detected in each of two zero degree calorimeters (ZDC) (jj>8:3), or which contained an energy deposi- tion in the calorimeters ofET>10 GeV.
In addition to the single-lepton trigger, each event had to pass the minimum-bias (MB) event selection, which required a timing signal coincidence of better than 3 ns between the MB trigger scintillators (2:1<jj<3:8), as well as the reconstruction of a collision vertex in the ID. The total number of sampled events isð1:030:02Þ 109[11].
Analyzed events are divided into centrality classes.
Centrality reflects the overlap volume of the two colliding nuclei. Collisions with a small (large) impact parameter are referred to as central (peripheral). The overlap volume is closely related to the average number of participant nucle- ons which scatter inelastically in each nuclear collision hNparti, and to the average number of binary collisions between the nucleons of the colliding nuclei hNcolli. Equivalently,hNcollimay be defined as the average nuclear thickness functionhTAAi multiplied by the total inelastic pþpcross section of645 mb[12].
ThePbþPbcollision centrality is measured using the scalar sum of transverse energy (P
ET) deposited in the FCal, calibrated at the electromagnetic energy scale [13].
The fraction of events with more than onePbþPbcolli- sion is estimated not to exceed 0.05%, except for the most central 5% of events in which the fraction does not exceed 0.5%. A cut on the FCal energy of P
ET<3:8 TeV is applied to prevent contamination by events with multiple PbþPb interactions. Glauber model calculations relate centrality to hNparti and hNcolli, following the procedure documented in Ref. [14]. In the present sample, hNcolli (hNparti) ranges from 1683130(3822) for the most central class, 0%–5%, to 787 (463) for the most peripheral class, 40%–80%.
The efficiencies of the electron and muon triggers are evaluated from 5:5107 events selected with the MB trigger during the 2011 run. The MB trigger required a transverse energy deposition ofET>50 GeVin the calo- rimeters or a coincidence of both ZDC signals and a track in the ID. The average trigger efficiency for muons with pT>10 GeVdecreases fromð98:20:5Þ%in peripheral events to ð90:90:5Þ% in central events, where the ID
occupancy is higher. The average trigger efficiency for electrons withjj<2:5andET>20GeVisð98:10:1Þ%, independent of centrality. The trigger efficiency for Z!decays ranges fromð99:00:6Þ%in peripheral events toð95:00:9Þ%in central events. ForZ!eedecays the efficiency isð99:90:1Þ%independent of centrality.
For theZ!eeanalysis, electron candidates are formed using the standard ATLAS reconstruction algorithm [15], requiring the matching of a track to an energy cluster in the electromagnetic calorimeter. Electron selection is lim- ited to jj<2:5 and both electrons are required to have ET>20 GeV. Following the reconstruction requirements, further electron identification cuts are made to reject back- ground. The standard electron identification cuts [15] used in the pþp environment are not suited to the PbþPb environment due to the large underlying event (UE) energy deposition in the calorimeter. To address this, a different set of cuts has been developed to accommodate the modi- fication of the calorimeter variables by the presence of the UE. The cuts used are based on the energy balance between the track momentum and cluster energy (E=p), as well as calorimeter shower shape variables. Furthermore, the UE energy is estimated (following Ref. [16]) and subtracted on an electron-by-electron basis to recover the proper electron energy.
The electron combined reconstruction and identification efficiency is evaluated in a Monte Carlo simulation using electrons from7105 PYTHIA(version 6.425) [17]
pþp!Z!ee events with 66< mZ<116 GeV and jyZj<2:5 embedded into PbþPb events generated by the HIJING event generator (version 1.38b) [18]. The response of the ATLAS detector to the generated particles is modeled using GEANT4 [19,20]. The combined recon- struction and identification efficiency for electrons ofET>
20 GeV ranges from 72% to 76% from central to periph- eral events, with a common absolute uncertainty of 5.4%.
For theZ!eeanalysis, all electrons found in triggered events are paired with each other, requiring that at least one electron in the pair matches a trigger object. The opposite- sign charged pairs with an invariant mass satisfying 66< mee<102 GeVare accepted as signalZboson can- didates. The same-sign pairs in this window are taken as an estimate of the combinatorial background. In total, 772 opposite-sign pairs and 42 same-sign pairs are reconstructed.
In theZ!analysis, single muons are reconstructed with several levels of quality [21]. High quality muons are reconstructed in both the MS and ID with consistent an- gular measurements, as well as with a good match to the event vertex. At least one muon in each pair, matched to the trigger, is required to be of such quality. If the second muon in the pair has hit patterns in the MS and ID satisfying criteria of high reconstruction quality, the minimum pT
threshold is set to 10 GeV for both muons. If the second muon fails this condition, both muons are required to satisfypT>20 GeV.
The muon combined reconstruction and identification efficiency is evaluated using muons from5:3105PYTHIA pþp!Z!events with 66< mZ<116 GeV and jyZj<2:5 embedded intoHIJING events. For muons with pT>20 GeV,jj<2:5and associated to the event ver- tex, the reconstruction efficiency of the MS varies from ð971Þ%toð981Þ%from central to peripheral events.
Requiring a match between the MS and ID reduces the efficiency to ð891Þ%andð911Þ%, respectively, due to track loss in the ID, predominantly atjj>1:5.
As in theZ!eeanalysis, an invariant mass window of 66< m<102 GeVis used to define oppositely charged muon pairs asZboson candidates and same-sign charged pairs as a background estimate. In total, 1223 opposite-sign candidates and 14 same-sign pairs are reconstructed in the Z!channel.
The invariant mass distributions of the selected pairs together with estimated combinatorial backgrounds for all pZT andyZ<2:5 are shown in Fig. 1, compared with the simulation normalized to the number of pairs in the region 66< m‘‘<102 GeV (‘¼e,). In order to cal- culate the yield, the combinatorial background estimated with the same-sign pairs must be subtracted. Backgrounds from electroweak processes and top pair decays [22] are small compared to the combinatorial backgrounds, and their contribution is accounted for in the systematic uncer- tainty related to the background.
The main sources of systematic uncertainty in both mea- surement channels are associated with the precision to which the corrections applied to the data can be calculated.
In the pþp environment, the muon reconstruction efficiencies in data and simulation agree to 1% (2% for pT<15 GeV) [23]. The MS maintains low occupancy in thePbþPbenvironment. The difference in the fraction of
muons reconstructed only in the MS, between data and simulation is used to estimate the systematic uncertainty on the reconstruction efficiency. To evaluate the uncertainty on the efficiency of the electron identification cuts stemming from the simulation, the efficiency is computed from the HI data using a tag-and-probe technique [15] and compared to the efficiency computed from simulation.
The systematic uncertainty due to momentum resolution is estimated by introducing additional momentum smearing to the simulation. The efficiency (resolution) uncertainties are5:5%(2.5%) forZ!, and 8% (2.5%) inZ!ee; these estimates vary withpZT andyZ.
The trigger efficiency uncertainties are estimated by using alternative methods and comparing their results with those obtained from the MB data set. For this com- parison the simulation trigger efficiency is used, as well as the conditional trigger efficiency of a second lepton in a triggered pair reconstructed as aZboson.
For eachZ!llanalysis, correction factors to account for the efficiency (relative to Z bosons produced with 66< mZ<116 GeV) and detector resolution within the selected acceptance based on the simulation are calculated differentially in event centrality,pZT, andyZ. In each decay channel, the correction factor is applied and the back- ground, estimated by the same-sign pairs, is subtracted.
The two measurements are averaged with weights set by their respective uncertainties.
The fully correctedyZdistribution is shown in Fig.2. No centrality dependence of this shape is observed. The data are compared to a model composed of PYTHIA events normalized to theZ!llcross section inpþpcollisions
at pffiffiffiffiffiffiffiffisNN¼2:76 TeVtaken from next-to-next-to-leading-
order (NNLO) calculations used in Ref. [24] and scaled by hTAAi. Using the same computational approach as in
70 80 90 100 110 ]-1 dm [GeV⁄dN
0 50
100 Z→ee Opposite sign: 772 Same sign: 42 ATLAS
= 2.76 TeV sNN
Pb+Pb
= 0.15 nb-1
Data 2011 Lint
70 80 90 100 110 µ
µ
→ Z
1223 14 Simulation
[GeV]
mee mµµ [GeV]
FIG. 1 (color online). The invariant mass distributions of Z!ee (left) andZ!(right) candidates, integrated over momentum, rapidity, and centrality. Bars represent the statistical uncertainty. The number of pairs with 66< m‘‘<102 GeV (marked by the vertical dashed lines) is listed. The simulation is weighted to match the centrality distribution in data and normalized in the region66< m‘‘<102 GeV.
-2 0 2
dy
ll→ Z dN eventsN
710
2 4 6
ATLAS
= 2.76 TeV sNN
Pb+Pb
= 0.15 nb-1
Data 2011 Lint
Centrality 0-80%
→ll
Z Model
yZ
-2 -1 0 1 2
ModelData
0.8 1.0 1.2
FIG. 2 (color online). The corrected per-event rapidity distri- bution of measuredZbosons. Bars and boxes represent statistical and systematic uncertainties, respectively. The data are com- pared to the model distribution shown as a band whose width is the normalization uncertainty.
Ref. [24] but incorporating pþn and nþn collisions would increase the cross section by 3%. The shape is well reproduced byPYTHIA, and the integrated yield is in good agreement with thehTAAi-scaled NNLO cross section.
The fully corrected pT distributions in five centrality classes are shown in the left panel of Fig.3along with the model prediction. The shape as a function of pZT is well reproduced byPYTHIA. The right panel of Fig.3shows the ratios of the data to thePYTHIAprediction scaled byhTAAi.
The ratios are constant within uncertainties for all central- ity classes over the range of measuredpZT.
To further examine the binary collision scaling of the data, theZboson per-event yields, divided byhNcolli, are shown in Fig.4as a function ofhNparti, in severalpZT bins.
The figure demonstrates that the Z!ee and Z! results are consistent within their uncertainties for allpZT and centrality regions. Within the statistical significance of the data sample, theZboson per-event yield obeys binary collision scaling.
The elliptic anisotropyv2 of theZboson is defined as v2 ¼ hcos2ð2Þi=2, whereis the azimuthal angle of theZboson momentum vector and2 is the azimuthal angle of the event plane, the plane containing the momen- tum vectors of both lead nuclei and measured with resolu- tion 2 [25]. The v2 values measured in the two decay channels are consistent and are combined. The main uncertainty on thev2 measurement arises from the event plane (EP) resolution, which is measured from the differ- ence of2 determined using the two sides of the FCal at
positive and negative rapidities [25]. To ensure that the jets associated with Z boson production do not affect the determination of 2, the EP resolution is also measured comparing the FCal signal on the side which may be affected by a recoiling jet to the one of the unaffected side. A systematic uncertainty of 12 mrad is assigned for possible EP distortion.
The v2 of theZboson is shown in Fig.5as a function of jyZj,pZT, and hNparti. The averaged v2 of the Z boson has been measured to be v2¼ 0:0150:018ðstatÞ 0:014ðsysÞ, which indicates an isotropic distribution. This observation is an independent measurement consistent with Z!ll yields being unaffected by the medium in HI collisions.
[GeV]
Z
pT
1 10 102
10-2
103
ATLAS = 2.76 TeV sNN
Pb+Pb
Data 2011 = 0.15 nb-1
Lint
100)
× 0%-5% (
× 20) 5%-10% (
× 5) 10%-20% ( 20%-40%
40%-80%
[GeV]
Z
pT
1 10 102
1
2 40%-80%
1
2 20%-40%
1
2 10%-20%
1
2 5%-10%
1
2 0%-5%
Data /Model
] -2 [GeV TdpTp
|y|<2.5ll→ ZdN eventsN
710
FIG. 3 (color online). Left: corrected per-eventpZT spectra of measuredZbosons in five centrality classes. The data are com- pared to aPYTHIAsimulation normalized to the NNLO pþp cross section and scaled byhTAAi, shown as bands. Right: ratios of the data to the model in each centrality class. Bars represent statistical uncertainties, boxes represent systematic uncertainties, and bands represent the normalization uncertainty.
part〉
〈N
0 100 200 300 400
eventsN
|y|<2.5ll→ Z N 〉collN〈
910
2 4 6
ATLAS
= 2.76 TeV sNN
Pb+Pb
= 0.15 nb-1
Data 2011 Lint
→ ee Z
→ll Z→µµ Z
Z
All pT
<10GeV
Z
pT
<30GeV
Z
10<pT
>30GeV
Z
pT
FIG. 4 (color online). Centrality dependence ofZboson yields divided byhNcolli. Results foree(upward pointing triangles) and (downward pointing triangles) channels are shifted left and right, respectively, from their weighted average (diamonds). Bars and boxes represent statistical and systematic uncertainties, respectively. For the combined results, the brackets show the combined uncertainty including the uncertainty on hNcolli, and the dashed lines show the results of fits, using a constant.
0 1 2 1 10 200 400
ATLAS
= 2.76 TeV sNN
Pb+Pb
= 0.15 nb-1
Data 2011 Lint
Centrality: 0-80%
[GeV]
Z
pT Z|
|y 〈Npart〉
2v
-0.1 0.0 0.1
FIG. 5. v2as a function ofjyZj(left),pZT(center), andhNparti (right). Bars and boxes represent statistical and systematic uncertainties, respectively. The dashed lines show the results of constant fits to the v2 values, considering only statistical uncertainties.
Using the ATLAS detector,Zboson production has been measured inPbþPbcollisions atpffiffiffiffiffiffiffiffisNN¼2:76 TeVusing 0:15 nb1 of integrated luminosity collected in the 2011 LHC physics run. Within jyZj<2:5, and 66< m‘‘<
102 GeV, a total of 772 and 1223Zboson candidates are reconstructed in the Z!ee and Z! channels, respectively. The combinatorial background is at the level of 5% in the dielectron channel and 1% for the dimuon channel. The Z boson production yield integrated over jyZj<2:5 is consistent between the two channels in all measured pT and centrality regions. The momentum and rapidity distributions of theZbosons are consistent with
PYTHIAsimulations ofZboson production inpþpcolli- sions scaled to the NNLO cross section and multiplied by hTAAi. Within the uncertainties theZboson yield is found to be proportional tohNcolli. The elliptic anisotropy of the Zboson measured as a function of rapidity,pZT andhNparti is consistent with zero within the uncertainties of the measurements.
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 and FWF, 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; EPLANET and ERC, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, 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;
BRF and 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 (U.K.) and BNL (U.S.) and in the Tier-2 facilities worldwide.
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P. Bagnaia,132a,132bS. Bahinipati,3Y. Bai,33aD. C. Bailey,158T. Bain,158J. T. Baines,129O. K. Baker,176 M. D. Baker,25S. Baker,77P. Balek,126E. Banas,39P. Banerjee,93Sw. Banerjee,173D. Banfi,30A. Bangert,150 V. Bansal,169H. S. Bansil,18L. Barak,172S. P. Baranov,94A. Barbaro Galtieri,15T. Barber,48E. L. Barberio,86 D. Barberis,50a,50bM. Barbero,21D. Y. Bardin,64T. Barillari,99M. Barisonzi,175T. Barklow,143N. Barlow,28
B. M. Barnett,129R. M. Barnett,15A. Baroncelli,134aG. Barone,49A. J. Barr,118F. Barreiro,80
J. Barreiro Guimara˜es da Costa,57P. Barrillon,115R. Bartoldus,143A. E. Barton,71V. Bartsch,149A. Basye,165 R. L. Bates,53L. Batkova,144aJ. R. Batley,28A. Battaglia,17M. Battistin,30F. Bauer,136H. S. Bawa,143,fS. Beale,98
T. Beau,78P. H. Beauchemin,161R. Beccherle,50aP. Bechtle,21H. P. Beck,17A. K. Becker,175S. Becker,98 M. Beckingham,138K. H. Becks,175A. J. Beddall,19cA. Beddall,19cS. Bedikian,176V. A. Bednyakov,64C. P. Bee,83
L. J. Beemster,105M. Begel,25S. Behar Harpaz,152P. K. Behera,62M. Beimforde,99C. Belanger-Champagne,85 P. J. Bell,49W. H. Bell,49G. Bella,153L. Bellagamba,20aM. Bellomo,30A. Belloni,57O. Beloborodova,107,g
K. Belotskiy,96O. Beltramello,30O. Benary,153D. Benchekroun,135aK. Bendtz,146a,146bN. Benekos,165 Y. Benhammou,153E. Benhar Noccioli,49J. A. Benitez Garcia,159bD. P. Benjamin,45M. Benoit,115J. R. Bensinger,23 K. Benslama,130S. Bentvelsen,105D. Berge,30E. Bergeaas Kuutmann,42N. Berger,5F. Berghaus,169E. Berglund,105
J. Beringer,15P. Bernat,77R. Bernhard,48C. Bernius,25T. Berry,76C. Bertella,83A. Bertin,20a,20b
F. Bertolucci,122a,122bM. I. Besana,89a,89bG. J. Besjes,104N. Besson,136S. Bethke,99W. Bhimji,46R. M. Bianchi,30 M. Bianco,72a,72bO. Biebel,98S. P. Bieniek,77K. Bierwagen,54J. Biesiada,15M. Biglietti,134aH. Bilokon,47 M. Bindi,20a,20bS. Binet,115A. Bingul,19cC. Bini,132a,132bC. Biscarat,178B. Bittner,99K. M. Black,22R. E. Blair,6
J.-B. Blanchard,136G. Blanchot,30T. Blazek,144aI. Bloch,42C. Blocker,23J. Blocki,39A. Blondel,49W. Blum,81 U. Blumenschein,54G. J. Bobbink,105V. B. Bobrovnikov,107S. S. Bocchetta,79A. Bocci,45C. R. Boddy,118 M. Boehler,48J. Boek,175N. Boelaert,36J. A. Bogaerts,30A. Bogdanchikov,107A. Bogouch,90,aC. Bohm,146a J. Bohm,125V. Boisvert,76T. Bold,38V. Boldea,26aN. M. Bolnet,136M. Bomben,78M. Bona,75M. Boonekamp,136
S. Bordoni,78C. Borer,17A. Borisov,128G. Borissov,71I. Borjanovic,13aM. Borri,82S. Borroni,87 V. Bortolotto,134a,134bK. Bos,105D. Boscherini,20aM. Bosman,12H. Boterenbrood,105J. Bouchami,93 J. Boudreau,123E. V. Bouhova-Thacker,71D. Boumediene,34C. Bourdarios,115N. Bousson,83A. Boveia,31 J. Boyd,30I. R. Boyko,64I. Bozovic-Jelisavcic,13bJ. Bracinik,18P. Branchini,134aG. W. Brandenburg,57A. Brandt,8
G. Brandt,118O. Brandt,54U. Bratzler,156B. Brau,84J. E. Brau,114H. M. Braun,175,aS. F. Brazzale,164a,164c B. Brelier,158J. Bremer,30K. Brendlinger,120R. Brenner,166S. Bressler,172D. Britton,53F. M. Brochu,28I. Brock,21 R. Brock,88F. Broggi,89aC. Bromberg,88J. Bronner,99G. Brooijmans,35T. Brooks,76W. K. Brooks,32bG. Brown,82 H. Brown,8P. A. Bruckman de Renstrom,39D. Bruncko,144bR. Bruneliere,48S. Brunet,60A. Bruni,20aG. Bruni,20a
M. Bruschi,20aT. Buanes,14Q. Buat,55F. Bucci,49J. Buchanan,118P. Buchholz,141R. M. Buckingham,118 A. G. Buckley,46S. I. Buda,26aI. A. Budagov,64B. Budick,108V. Bu¨scher,81L. Bugge,117O. Bulekov,96 A. C. Bundock,73M. Bunse,43T. Buran,117H. Burckhart,30S. Burdin,73T. Burgess,14S. Burke,129E. Busato,34
P. Bussey,53C. P. Buszello,166B. Butler,143J. M. Butler,22C. M. Buttar,53J. M. Butterworth,77W. Buttinger,28 M. Byszewski,30S. Cabrera Urba´n,167D. Caforio,20a,20bO. Cakir,4aP. Calafiura,15G. Calderini,78P. Calfayan,98 R. Calkins,106L. P. Caloba,24aR. Caloi,132a,132bD. Calvet,34S. Calvet,34R. Camacho Toro,34P. Camarri,133a,133b D. Cameron,117L. M. Caminada,15R. Caminal Armadans,12S. Campana,30M. Campanelli,77V. Canale,102a,102b
F. Canelli,31,hA. Canepa,159aJ. Cantero,80R. Cantrill,76L. Capasso,102a,102bM. D. M. Capeans Garrido,30 I. Caprini,26aM. Caprini,26aD. Capriotti,99M. Capua,37a,37bR. Caputo,81R. Cardarelli,133aT. Carli,30G. Carlino,102a L. Carminati,89a,89bB. Caron,85S. Caron,104E. Carquin,32bG. D. Carrillo Montoya,173A. A. Carter,75J. R. Carter,28
J. Carvalho,124a,iD. Casadei,108M. P. Casado,12M. Cascella,122a,122bC. Caso,50a,50b,a
A. M. Castaneda Hernandez,173,j E. Castaneda-Miranda,173V. Castillo Gimenez,167N. F. Castro,124aG. Cataldi,72a P. Catastini,57A. Catinaccio,30J. R. Catmore,30A. Cattai,30G. Cattani,133a,133bS. Caughron,88V. Cavaliere,165 P. Cavalleri,78D. Cavalli,89aM. Cavalli-Sforza,12V. Cavasinni,122a,122bF. Ceradini,134a,134bA. S. Cerqueira,24b A. Cerri,30L. Cerrito,75F. Cerutti,47S. A. Cetin,19bA. Chafaq,135aD. Chakraborty,106I. Chalupkova,126K. Chan,3
P. Chang,165B. Chapleau,85J. D. Chapman,28J. W. Chapman,87E. Chareyre,78D. G. Charlton,18V. Chavda,82 C. A. Chavez Barajas,30S. Cheatham,85S. Chekanov,6S. V. Chekulaev,159aG. A. Chelkov,64M. A. Chelstowska,104 C. Chen,63H. Chen,25S. Chen,33cX. Chen,173Y. Chen,35Y. Cheng,31A. Cheplakov,64R. Cherkaoui El Moursli,135e V. Chernyatin,25E. Cheu,7S. L. Cheung,158L. Chevalier,136G. Chiefari,102a,102bL. Chikovani,51a,aJ. T. Childers,30
A. Chilingarov,71G. Chiodini,72aA. S. Chisholm,18R. T. Chislett,77A. Chitan,26aM. V. Chizhov,64 G. Choudalakis,31S. Chouridou,137I. A. Christidi,77A. Christov,48D. Chromek-Burckhart,30M. L. Chu,151 J. Chudoba,125G. Ciapetti,132a,132bA. K. Ciftci,4aR. Ciftci,4aD. Cinca,34V. Cindro,74C. Ciocca,20a,20bA. Ciocio,15 M. Cirilli,87P. Cirkovic,13bZ. H. Citron,172M. Citterio,89aM. Ciubancan,26aA. Clark,49P. J. Clark,46R. N. Clarke,15 W. Cleland,123J. C. Clemens,83B. Clement,55C. Clement,146a,146bY. Coadou,83M. Cobal,164a,164cA. Coccaro,138 J. Cochran,63L. Coffey,23J. G. Cogan,143J. Coggeshall,165E. Cogneras,178J. Colas,5S. Cole,106A. P. Colijn,105
N. J. Collins,18C. Collins-Tooth,53J. Collot,55T. Colombo,119a,119bG. Colon,84G. Compostella,99 P. Conde Muin˜o,124aE. Coniavitis,166M. C. Conidi,12S. M. Consonni,89a,89bV. Consorti,48S. Constantinescu,26a C. Conta,119a,119bG. Conti,57F. Conventi,102a,kM. Cooke,15B. D. Cooper,77A. M. Cooper-Sarkar,118K. Copic,15 T. Cornelissen,175M. Corradi,20aF. Corriveau,85,lA. Cortes-Gonzalez,165G. Cortiana,99G. Costa,89aM. J. Costa,167
D. Costanzo,139D. Coˆte´,30L. Courneyea,169G. Cowan,76C. Cowden,28B. E. Cox,82K. Cranmer,108 F. Crescioli,122a,122bM. Cristinziani,21G. Crosetti,37a,37bS. Cre´pe´-Renaudin,55C.-M. Cuciuc,26a
C. Cuenca Almenar,176T. Cuhadar Donszelmann,139M. Curatolo,47C. J. Curtis,18C. Cuthbert,150P. Cwetanski,60 H. Czirr,141P. Czodrowski,44Z. Czyczula,176S. D’Auria,53M. D’Onofrio,73A. D’Orazio,132a,132b
M. J. Da Cunha Sargedas De Sousa,124aC. Da Via,82W. Dabrowski,38A. Dafinca,118T. Dai,87C. Dallapiccola,84 M. Dam,36M. Dameri,50a,50bD. S. Damiani,137H. O. Danielsson,30V. Dao,49G. Darbo,50aG. L. Darlea,26b
J. A. Dassoulas,42W. Davey,21T. Davidek,126N. Davidson,86R. Davidson,71E. Davies,118,dM. Davies,93 O. Davignon,78A. R. Davison,77Y. Davygora,58aE. Dawe,142I. Dawson,139R. K. Daya-Ishmukhametova,23K. De,8
R. de Asmundis,102aS. De Castro,20a,20bS. De Cecco,78J. de Graat,98N. De Groot,104P. de Jong,105 C. De La Taille,115H. De la Torre,80F. De Lorenzi,63L. de Mora,71L. De Nooij,105D. De Pedis,132aA. De Salvo,132a
U. De Sanctis,164a,164cA. De Santo,149J. B. De Vivie De Regie,115G. De Zorzi,132a,132bW. J. Dearnaley,71 R. Debbe,25C. Debenedetti,46B. Dechenaux,55D. V. Dedovich,64J. Degenhardt,120C. Del Papa,164a,164c J. Del Peso,80T. Del Prete,122a,122bT. Delemontex,55M. Deliyergiyev,74A. Dell’Acqua,30L. Dell’Asta,22
M. Della Pietra,102a,kD. della Volpe,102a,102bM. Delmastro,5P. A. Delsart,55C. Deluca,105S. Demers,176 M. Demichev,64B. Demirkoz,12,mJ. Deng,163S. P. Denisov,128D. Derendarz,39J. E. Derkaoui,135dF. Derue,78
P. Dervan,73K. Desch,21E. Devetak,148P. O. Deviveiros,105A. Dewhurst,129B. DeWilde,148S. Dhaliwal,158 R. Dhullipudi,25,nA. Di Ciaccio,133a,133bL. Di Ciaccio,5A. Di Girolamo,30B. Di Girolamo,30S. Di Luise,134a,134b
A. Di Mattia,173B. Di Micco,30R. Di Nardo,47A. Di Simone,133a,133bR. Di Sipio,20a,20bM. A. Diaz,32a E. B. Diehl,87J. Dietrich,42T. A. Dietzsch,58aS. Diglio,86K. Dindar Yagci,40J. Dingfelder,21F. Dinut,26a
C. Dionisi,132a,132bP. Dita,26aS. Dita,26aF. Dittus,30F. Djama,83T. Djobava,51bM. A. B. do Vale,24c A. Do Valle Wemans,124a,oT. K. O. Doan,5M. Dobbs,85R. Dobinson,30,aD. Dobos,30E. Dobson,30,pJ. Dodd,35 C. Doglioni,49T. Doherty,53Y. Doi,65,aJ. Dolejsi,126I. Dolenc,74Z. Dolezal,126B. A. Dolgoshein,96,aT. Dohmae,155
M. Donadelli,24dJ. Donini,34J. Dopke,30A. Doria,102aA. Dos Anjos,173A. Dotti,122a,122bM. T. Dova,70 A. D. Doxiadis,105A. T. Doyle,53N. Dressnandt,120M. Dris,10J. Dubbert,99S. Dube,15E. Duchovni,172 G. Duckeck,98D. Duda,175A. Dudarev,30F. Dudziak,63M. Du¨hrssen,30I. P. Duerdoth,82L. Duflot,115 M-A. Dufour,85L. Duguid,76M. Dunford,58aH. Duran Yildiz,4aR. Duxfield,139M. Dwuznik,38F. Dydak,30
M. Du¨ren,52W. L. Ebenstein,45J. Ebke,98S. Eckweiler,81K. Edmonds,81W. Edson,2C. A. Edwards,76 N. C. Edwards,53W. Ehrenfeld,42T. Eifert,143G. Eigen,14K. Einsweiler,15E. Eisenhandler,75T. Ekelof,166 M. El Kacimi,135cM. Ellert,166S. Elles,5F. Ellinghaus,81K. Ellis,75N. Ellis,30J. Elmsheuser,98M. Elsing,30
