Measurement of the azimuthal angle dependence of inclusive jet yields in Pb+Pb collisions at $\sqrt{^SNN} = 2.76$  TeV with the ATLAS detector

Measurement of the Azimuthal Angle Dependence of Inclusive Jet Yields in Pb þ Pb Collisions at p ffiffiffiffiffiffiffiffiffi s

¼ 2:76 TeV with the ATLAS Detector

G. Aad et al.*

(ATLAS Collaboration)

(Received 26 June 2013; published 9 October 2013)

Measurements of the variation of inclusive jet suppression as a function of relative azimuthal angle,

, with respect to the elliptic event plane provide insight into the path-length dependence of jet quenching. ATLAS has measured the

dependence of jet yields in 0:14 nb
¹ of ffiffiffiffiffiffiffiffi

sNN

p ¼ 2:76 TeV Pb þ Pb collisions at the LHC for jet transverse momenta p_T> 45 GeV in different collision centrality bins using an underlying event subtraction procedure that accounts for elliptic flow. The variation of the jet yield with

was characterized by the parameter, v^jet₂ , and the ratio of out-of-plane (

 =2) to in- plane (

 0) yields. Nonzero v^jet₂ values were measured in all centrality bins for pT< 160 GeV. The jet yields are observed to vary by as much as 20% between in-plane and out-of-plane directions.

DOI:10.1103/PhysRevLett.111.152301 PACS numbers: 25.75.
q

Studies of jet production inPb þ Pb collisions at the LHC [1,2] show behavior consistent with ‘‘jet quenching,’’ a general term for the modification of parton showers in the hot dense medium created in ultrarelativistic nuclear colli- sions. For example, the inclusive yield of jets was observed to be suppressed by a factor of approximately 2 in central Pb þ Pb collisions relative to peripheral collisions [3], con- sistent with a medium-induced reduction in the jet energies.

Perturbative or weak-coupling calculations model jet energy loss, dE=dx, through a combination of collisional and radia- tive energy loss of the partons traversing the medium. The radiative contributions are subject to coherence effects [4]

that explicitly depend on the in-medium path length of the parton. Strong-coupling calculations also have an explicit path-length dependence that differs from that predicted by weak-coupling calculations [5,6]. Measurements of the jet yield as a function of quantities providing indirect control over the jet path lengths may provide insight into the physical mechanisms responsible for jet quenching [7,8]. Such quan- tities include thePb þ Pb collision centrality and the azimu- thal angle of the jet with respect to the elliptic event plane.

Elliptic flow refers to acos2
modulation of the azimu- thal angle (
) distribution of particles produced in ultra- relativistic nuclear collisions [9]. This modulation is understood to arise from an approximately elliptic anisot- ropy of the initial-state transverse energy density profile that is imprinted on the azimuthal angle distribution of final-state particles [10] by the strong collective evolution of the medium. The resulting azimuthal angle distribution is often parametrized by the form

dN

d
/ 1 þ 2v₂cos2 ð

₂Þ; (1)

where the elliptic event plane angle, ₂, specifies the orientation of the initial density profile in the transverse plane, and the parameter v2 quantifies the magnitude of the modulation. Jets measured at different azimuthal angles relative to the event plane,


_jet
₂, result from partons that traverse, on average, different path lengths and density profiles in the medium. Thus, a measurement of the variation of the jet yield as a function of

should provide a direct constraint on theoretical models of the path-length dependence of the energy loss. This mea- surement is not directly sensitive to potential variations in the jet yield with respect to higher-order event plane angles. Such variations may result from fluctuations in the initial geometry that also give rise to higher-order flow harmonics [11–13].

Variations in jet yield as a function of

have been observed indirectly through measurements of single had- rons with large transverse momentum (pT) at the RHIC [14–16] and the LHC [17–19]. The utility of such mea- surements is limited by the weak relationship between hadron pT and the transverse momentum of the parent parton shower. This Letter presents the results of measure- ments using fully reconstructed jets, which have kinematic properties that are more closely related to those of the parent partons. The

dependence of the inclusive jet yield was measured in ffiffiffiffiffiffiffiffi

s_NN

p ¼ 2:76 TeV Pb þ Pb colli- sions as a function of jet pTandPb þ Pb collision central- ity. The measurement was performed with the anti-kt

algorithm [20] with distance parameter R ¼ 0:2, chosen to limit the contribution of the underlying event (UE) to the measurement. The

dependence was characterized by the jet v₂, v^jet₂ , and the ratio of out-of-plane (3=8 

 =2) to in-plane (0 

< =8) jet yields at

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

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

fixed p_Tand centrality. Such dependence is expected to be small in either the most central or most peripheral colli- sions, due to the lack of initial-state anisotropy and the lack of quenching, respectively. For intermediate centralities, measurement of the

dependence of the jet yields probes the interplay between dependence of quenching on the overall system size and energy density, as well as on the initial-state anisotropy.

The measurements presented here were performed with the ATLAS detector [21] using its calorimeter, inner detec- tor, trigger, and data acquisition systems. The calorimeter system consists of a liquid-argon electromagnetic (EM) calorimeter coveringjj < 3:2, a steel-scintillator sampling hadronic calorimeter covering jj < 1:7, a liquid-argon hadronic calorimeter covering 1:5 < jj < 3:2, and a forward calorimeter (FCal) covering 3:2 < jj < 4:9.

Charged-particle tracks were measured over the range jj < 2:5 using the inner detector [22], which is composed of silicon pixel detectors in the innermost layers, followed by silicon microstrip detectors and a straw-tube transition- radiation tracker (jj < 2:0), all immersed in a 2 T axial magnetic field. The zero-degree calorimeters (ZDCs) are located symmetrically at z ¼ 140 m and cover jj > 8:3. In Pb þ Pb collisions the ZDCs primarily mea- sure noninteracting ‘‘spectator’’ neutrons from the incident nuclei. A ZDC coincidence trigger was defined by requiring a signal consistent with one or more neutrons in each of the calorimeters.

Pb þ Pb collisions corresponding to a total integrated luminosity of0:14 nb
¹were analyzed. The events were recorded using either a minimum-bias trigger, formed from the logical OR of triggers based on a ZDC coincidence or total transverse energy in the event, or a jet trigger imple- mented using the Pb þ Pb jet reconstruction algorithm.

The jet trigger selected events having at least one jet with transverse energy ET > 20 GeV. Event selection and background rejection criteria were applied [17] yield- ing 52  10⁶ and 14  10⁶ events in the minimum-bias and jet-triggered samples, respectively. For each event,₂ was computed from the azimuthal distribution of the trans- verse energy measured in the FCal [17,23], and angles with respect to ₂ were defined over 0 

 =2. The centrality of Pb þ Pb collisions was characterized by

E^FCal_T , the total transverse energy measured in the FCal [17]. The results reported here were obtained using the following centrality intervals defined according to succes- sive percentiles of theE^FCal_T distribution ordered from the most central (highestE^FCal_T ) to the most peripheral colli- sions: 5%–10%, 10%–20%, 20%–30%, 30%–40%, 40%–50%, and 50%–60%. The centrality interval 5%–60% coincides to the range over which the₂ reso- lution is adequate for the measurement. A Glauber model analysis [24,25] of theE^FCal_T distribution [17] was used to evaluate the average number of nucleons participating in the collision,hN_parti, in each centrality interval.

The jet reconstruction and underlying event subtraction procedures are the same as those used in Ref. [3], which is summarized in the following. The anti-k_t algorithm was applied to calorimeter towers with segmentation

 

¼ 0:1  0:1. A two-step iterative procedure was used to obtain an event-by-event estimate of the aver- age -dependent UE energy density while excluding actual jets from that estimate. The jet kinematics were obtained by subtracting the UE energy from the towers within the jet. This subtraction accounts for elliptic flow by modulat- ing the average background density by the magnitude of the elliptic flow measured by the calorimeter, v^calo₂ , over the intervaljj < 3:2 and excluding  regions containing jets. Following reconstruction, the jet energies were cor- rected to account for the calorimeter energy response using an - and ET-dependent multiplicative factor that was derived from Monte Carlo (MC) simulations [26].

Separate from the calorimeter jets, ‘‘track jets’’ were reconstructed by applying the anti-k_t algorithm with R ¼ 0:4 to charged particles having p_T> 4 GeV. The p_T of the track jets, p^trkjet_T , is largely unaffected by the UE due to the pT> 4 GeV requirement. To exclude the con- tribution to the jet yield from UE fluctuations of soft particles falsely identified as calorimeter jets, the jets used in this analysis were required to be withinffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
R ¼

²þ

²

p ¼ 0:2 of a track jet with p^trkjet_T > 10 GeV or an EM cluster [27] with pT> 9 GeV.

The performance of the jet reconstruction was evaluated using the GEANT4-simulated detector response [28,29] in a MC sample of pp hard scattering events at ffiffiffiffiffiffiffiffi

sNN

p ¼

2:76 TeV. The events were produced with the ^PYTHIA event generator [30] version 6.423 using the AUET2B tune [31] and overlaid on minimum-bias Pb þ Pb colli- sions recorded by ATLAS. Through this embedding pro- cedure, the MC sample contains a UE contribution that is identical in all respects to the data, including azimuthal modulation of the UE due to harmonic flow. Jets recon- structed in the MC events using the same algorithms as applied to data were compared to generator-level jets reconstructed from final-state PYTHIA hadrons. Potential variations in the jet energy resolution (JER) and jet energy scale (JES) with

due to elliptic and higher-order modulation [11–13] of the UE were investigated in the MC sample; no significant variation was found.

The dependence of the JES on

was further con- strained by comparing the calorimeter jets to matched track jets in the data. For different values of

, the mean p_Tof calorimeter jets was evaluated as a function of the p_Tof the matched track jet, and no significant variation with

was observed. This study provides an upper limit on the variation in the JES between jets at

¼ 0 and

¼ =2 of 0.1% for p_T> 45 GeV.

Double differential jet yields, d²N_jet=dp_Td

, were measured over jj<2:1 for each of the centrality ranges described above and in five pT intervals: 45–60 GeV,

60–80 GeV, 80–110 GeV, 110–160 GeV, and 160–210 GeV. The measurement in each p_T range was performed using events selected by the jet trigger except for the 45–60 GeV p_T range, in which minimum-bias events were used. The

dependence of the jet yields in the 60–80 GeV pTinterval is shown for each centrality range in Fig.1. A significant

variation that is consistent with a cos2

modulation is seen for all centrality intervals.

The measured yields and the resulting v^jet₂ jmeas values are distorted by the finite resolutions in₂ and the jet p_T. The ₂ resolution was evaluated using a subevent tech- nique [17,23] in which₂was measured separately in the positive and negative  halves of the FCal yielding values

^þ₂ and 
₂, respectively. The width of the ^þ₂

₂ distribution was used [23] to estimate a factor, , that was used to correct each measured v₂ value for the finite

₂ resolution according to

v₂ ¼ v₂j_meas=: (2) This factor was evaluated for events containing jets to account for the relevant distribution of events within each centrality interval.

The p_T dependence, and possibly also the

depen- dence, of the measured yields are affected by the JER, which arises from both fluctuations in the UE and the

detector response. The MC study shows that for the R ¼ 0:2 jets used in this analysis, the JER-induced migra- tion between jet p_T intervals is sufficiently small that a

‘‘bin-by-bin’’ unfolding method, utilizing multiplicative corrections to the jet yields, is appropriate. The bin-by-bin correction factors are defined to be the number of generator- level jets divided by the number of reconstructed jets in each pT,

, and centrality interval. The MC studies show no significant

variation of the JER, JES, and the correction factors, and so these correction factors were taken to be

independent. Since the measurements presented here depend only on the ratios of jet yields between different

intervals for the same p_T range, the correction factors do not affect any of the final results; the potential for a

dependence of the correction factors is included in the estimates of the systematic uncertainty.

Systematic uncertainties on the corrected v₂values arise due to uncertainties on the two correction procedures described above. Uncertainties on  were estimated by using the values obtained in previous studies [17]. The uncertainties were found to vary between 1% and 4%

from central to peripheral collisions. Potential distortions in the measurement of2due to the production of jets in the FCal pseudorapidity range were studied in the MC sample and found to be negligible for the centrality inter- vals included in this analysis.

Uncertainties on the measurements arising from

-dependent systematic uncertainties on the bin-by-bin correction factors were estimated by determining the sen- sitivity of these correction factors to each systematic varia- tion and then parametrizing that sensitivity with acos2

dependence. The sensitivity to the

dependence of the spectrum was evaluated by varying the p_T spectrum of the generator-level jets in each

interval within a range consistent with the measured v^jet₂ values. The JES and JER contributions to the uncertainty were obtained by varying the relationship between generator-level and reconstructed jet p_T in the determination of the correction factors. These procedures utilized the JES constraints obtained from track jets and direct measurements of the UE contribution to the JER [3]. Parametrizations of the measured v^calo₂ and the average background E_T underlying a typical jet measured in the data were used to provide the dependence of variations on centrality.

The azimuthal dependence of jet suppression can be characterized by v^jet₂ , which was obtained by correcting the v^jet₂ jmeas values using Eq. (2). Figure 2 shows the resulting v^jet₂ values as a function of jet p_Tfor all centrality intervals. Significant, nonzero values are observed over the range 45 < p_T < 160 GeV for all centrality intervals. A direct comparison between the v₂ of single high-p_T charged particles and v^jet₂ is generally not possible; how- ever, the fact that both quantities exhibit only a weak pT

dependence leads to the expectation that they should be of similar magnitude. In the charged-particle measurements,

0.028 0.03 0.032

0.034 5 - 10 %

0.002

± = 0.016

|meas jet

v2

= 0.14 nb-1

t d

∫

= 2.76 TeV sNN

Pb+Pb

10 - 20 % 0.002

± = 0.032

|meas jet

v2

ATLAS

= 0.2

tR k anti-

< 80 GeV pT

60 <

]-1 [GeV measφ∆dTpd

jetN2d jetN1

0.028 0.03 0.032

0.034 20 - 30 %

0.002

± = 0.042

|meas jet

v2

30 - 40 % 0.002

± = 0.041

|meas jet

v2

φ

∆

0 0.5 1 1.5

0.028 0.03 0.032

0.034 40 - 50 %

0.003

± = 0.034

|meas jet

v2

φ

∆

0 0.5 1 1.5

50 - 60 % 0.004

± = 0.027

|meas jet

v2

FIG. 1 (color online).

dependence of measured d²Njet=dpTd

in the 60 < pT< 80 GeV interval for six ranges of collision centrality. The yields are normalized by the total number of jets in the pTinterval. The solid curves indicate the results of fitting the data to the functional form of Eq. (1), with the resulting v2 values, v^jet₂ j_meas, listed in each panel. The error bars and errors on v^jet₂ j_measindicate statistical uncertainties.

the v2values of charged particles with28 < pT < 48 GeV were found to vary between 0.02 and 0.05 for the 10%–50% centrality range [18], which are generally in agreement with v^jet₂ values reported here indicating no obvious inconsistencies between the two results.

The centrality dependence of v^jet₂ is shown in Fig.3as a function ofhN_parti for different ranges in p_T. The variation of jet yields with

can also be characterized by the ratio of jet yields between the most out-of-plane and most in- plane bins,

R^max

 d²N_jet=dpTd

j_out=d²N_jet=dpTd

j_in: (3) This quantity is more general than v^jet₂ as it does not assume a functional form for the

dependence of the jet yields.

The nuclear modification factor, RAA, is a measure of the effect of quenching on hard scattering rates, and R^max

can be interpreted as the ratio of

-dependent R_AA factors, R^max

¼ RAAjout=RAAjin[16]. The yields were corrected for

₂resolution assuming that the

variation is dominated by thecos2

modulation,

d²N^corr_jet

dpTd

¼ d²N_jet^meas dpTd

 1 þ 2v^jet₂ cos2

1 þ 2v^jet₂ jmeascos2

 : (4)

The results, expressed in terms of the quantity f2 1
R^max

, show as much as a 20% variation between the out-of-plane and in-plane jet yields, but they are reduced slightly from the maximal difference, evaluated

at

¼ =2 and

¼ 0, by the finite bin size used in the measurement. That reduction was corrected by assum- ing a 1 þ 2v^jet₂ cos2

variation of the jet yields within the

bins containing

¼ 0 and =2, and calculating the corresponding yields at those

values. From these yields, f^corr₂ was calculated analogously to f₂. The magni- tude of the correction is typically a few percent. The f₂^corr values are shown in Fig.3. For a purecos2

modulation of the jet yields, f^corr₂ would be given by4v^jet₂ =ð1 þ 2v^jet₂ Þ.

To test for deviations of the

dependence of the jet yields from a purecos2

variation, 4v^jet₂ =ð1 þ 2v^jet₂ Þ was calculated using the measured v^jet₂ values and is shown for each p_Tand centrality interval in Fig.3.

Similar variations of v^jet₂ , f^corr₂ , and 4v^jet₂ =ð1 þ 2v^jet₂ Þ with hNparti are seen in the 60–80 GeV range, which has the best statistical precision. A reduction in f₂^corrand v^jet₂ in both the most central and peripheral collisions is not surprising; for very central collisions, the anisotropy of the initial state is small and the possible

variation of path lengths in the medium is limited. Although the an- isotropy is greater in peripheral collisions, there is little suppression in the jet yields [3]. Therefore large variations in jet yield as a function of

would be unexpected. The f^corr₂ and 4v^jet₂ =ð1 þ 2v^jet₂ Þ values are generally in agree- ment within uncertainties, indicating an azimuthal

0 0.1 0.2

< 60 GeV pT

45 < < 80 GeV

pT

60 <

ATLAS = 0.2

tR k anti-

part〉

〈N

0 100 200 300

0 0.1 0.2

< 110 GeV pT

80 <

jet

v2 _jet

v2

1+2

jet

v2

4

corr

f2

part〉

〈N

0 100 200 300

< 160 GeV pT

110 <

= 2.76 TeV sNN

Pb+Pb

= 0.14 nb-1

t d

∫

FIG. 3 (color online). ThehN_parti dependence of v^jet₂ (), f^corr₂ (j), and 4v^jet₂ =ð1 þ 2v^jet₂ Þ (d). All quantities have statistical and systematic uncertainties that are indicated by error bars and shaded bands, respectively. The uncertainties for all quantities are strongly correlated. The horizontal positions of the points have been offset slightly for presentation purposes and the width of the error bands indicates the uncertainty onhNparti.

jet 2v

0 0.02 0.04 0.06

5 - 10 % anti-ktR = 0.2 10 - 20 % ATLAS

jet 2v

0 0.02 0.04 0.06

20 - 30 %

= 2.76 TeV sNN

Pb+Pb

= 0.14 nb-1

t d

∫

[GeV]

pT

50 100 150 200

jet 2v

0 0.02 0.04 0.06

40 - 50 %

[GeV]

pT

50 100 150 200

50 - 60 %

FIG. 2 (color online). v^jet₂ as a function of jet pT in each centrality interval. The error bars on the points indicate statistical uncertainties while the shaded boxes represent the systematic uncertainties (see text). The horizontal width of the systematic error band is chosen for presentation purposes only.

dependence of relative suppression when measured with respect to the elliptic event plane that is dominated by second-harmonic modulation.

This Letter has presented results of ATLAS measure- ments of the variation of R ¼ 0:2 anti-kffiffiffiffiffiffiffiffi _t jet yields in

sNN

p ¼ 2:76 TeV Pb þ Pb collisions as a function of

, the relative azimuthal angle of the jet with respect to the elliptic event plane. A significant

variation in the jet yield is observed for all centrality intervals and in all p_T ranges except for the 160–210 GeV pT interval where the statistical uncertainties are large. The observed azimuthal variation of jet yields amounts to a reduction of 10%–20%

in the jet yields between in-plane and out-of-plane direc- tions. These results establish a relationship between jet suppression and the initial nuclear geometry that should constrain models of the path-length dependence of the quenching mechanism.

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, ERC, and NSRF, European Union; IN2P3-CNRS, CEA-DSM/

IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG, and AvH Foundation, Germany; GSRT and NSRF, 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 (UK), and BNL (USA) and in the Tier-2 facilities worldwide.

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A. Angerami,³⁵F. Anghinolfi,³⁰A. V. Anisenkov,¹⁰⁸N. Anjos,^125aA. Annovi,⁴⁷A. Antonaki,⁹M. Antonelli,⁴⁷ A. Antonov,⁹⁷J. Antos,^145bF. Anulli,^133aM. Aoki,¹⁰²L. Aperio Bella,¹⁸R. Apolle,^119,eG. Arabidze,⁸⁹I. Aracena,¹⁴⁴

Y. Arai,⁶⁵A. T. H. Arce,⁴⁵S. Arfaoui,¹⁴⁹J-F. Arguin,⁹⁴S. Argyropoulos,⁴²E. Arik,^19a,aM. Arik,^19a A. J. Armbruster,⁸⁸O. Arnaez,⁸²V. Arnal,⁸¹A. Artamonov,⁹⁶G. Artoni,^133a,133bD. Arutinov,²¹S. Asai,¹⁵⁶

N. Asbah,⁹⁴S. Ask,²⁸B. A˚ sman,^147a,147bL. Asquith,⁶K. Assamagan,²⁵R. Astalos,^145aA. Astbury,¹⁷⁰ M. Atkinson,¹⁶⁶N. B. Atlay,¹⁴²B. Auerbach,⁶E. Auge,¹¹⁶K. Augsten,¹²⁷M. Aurousseau,^146bG. Avolio,³⁰

D. Axen,¹⁶⁹G. Azuelos,^94,fY. Azuma,¹⁵⁶M. A. Baak,³⁰C. Bacci,^135a,135bA. M. Bach,¹⁵H. Bachacou,¹³⁷ K. Bachas,¹⁵⁵M. Backes,⁴⁹M. Backhaus,²¹J. Backus Mayes,¹⁴⁴E. Badescu,^26aP. Bagiacchi,^133a,133b P. Bagnaia,^133a,133bY. Bai,^33aD. C. Bailey,¹⁵⁹T. Bain,³⁵J. T. Baines,¹³⁰O. K. Baker,¹⁷⁷S. Baker,⁷⁷P. Balek,¹²⁸

F. Balli,¹³⁷E. Banas,³⁹Sw. Banerjee,¹⁷⁴D. Banfi,³⁰A. Bangert,¹⁵¹V. Bansal,¹⁷⁰H. S. Bansil,¹⁸L. Barak,¹⁷³ S. P. Baranov,⁹⁵T. Barber,⁴⁸E. L. Barberio,⁸⁷D. Barberis,^50a,50bM. Barbero,⁸⁴D. Y. Bardin,⁶⁴T. Barillari,¹⁰⁰ M. Barisonzi,¹⁷⁶T. Barklow,¹⁴⁴N. Barlow,²⁸B. M. Barnett,¹³⁰R. M. Barnett,¹⁵A. Baroncelli,^135aG. Barone,⁴⁹

A. J. Barr,¹¹⁹F. Barreiro,⁸¹J. Barreiro Guimara˜es da Costa,⁵⁷R. Bartoldus,¹⁴⁴A. E. Barton,⁷¹V. Bartsch,¹⁵⁰ A. Basye,¹⁶⁶R. L. Bates,⁵³L. Batkova,^145aJ. R. Batley,²⁸M. Battistin,³⁰F. Bauer,¹³⁷H. S. Bawa,^144,gS. Beale,⁹⁹

T. Beau,⁷⁹P. H. Beauchemin,¹⁶²R. Beccherle,^50aP. Bechtle,²¹H. P. Beck,¹⁷K. Becker,¹⁷⁶S. Becker,⁹⁹ M. Beckingham,¹³⁹K. H. Becks,¹⁷⁶A. J. Beddall,^19cA. Beddall,^19cS. Bedikian,¹⁷⁷V. A. Bednyakov,⁶⁴C. P. Bee,⁸⁴ L. J. Beemster,¹⁰⁶T. A. Beermann,¹⁷⁶M. Begel,²⁵C. Belanger-Champagne,⁸⁶P. J. Bell,⁴⁹W. H. Bell,⁴⁹G. Bella,¹⁵⁴

L. Bellagamba,^20aA. Bellerive,²⁹M. Bellomo,³⁰A. Belloni,⁵⁷O. L. Beloborodova,^108,hK. Belotskiy,⁹⁷ O. Beltramello,³⁰O. Benary,¹⁵⁴D. Benchekroun,^136aK. Bendtz,^147a,147bN. Benekos,¹⁶⁶Y. Benhammou,¹⁵⁴

E. Benhar Noccioli,⁴⁹J. A. Benitez Garcia,^160bD. P. Benjamin,⁴⁵J. R. Bensinger,²³K. Benslama,¹³¹ S. Bentvelsen,¹⁰⁶D. Berge,³⁰E. Bergeaas Kuutmann,¹⁶N. Berger,⁵F. Berghaus,¹⁷⁰E. Berglund,¹⁰⁶J. Beringer,¹⁵

C. Bernard,²²P. Bernat,⁷⁷R. Bernhard,⁴⁸C. Bernius,⁷⁸F. U. Bernlochner,¹⁷⁰T. Berry,⁷⁶C. Bertella,⁸⁴ F. Bertolucci,^123a,123bM. I. Besana,^90a,90bG. J. Besjes,¹⁰⁵O. Bessidskaia,^147a,147bN. Besson,¹³⁷S. Bethke,¹⁰⁰ W. Bhimji,⁴⁶R. M. Bianchi,¹²⁴L. Bianchini,²³M. Bianco,^72a,72bO. Biebel,⁹⁹S. P. Bieniek,⁷⁷K. Bierwagen,⁵⁴ J. Biesiada,¹⁵M. Biglietti,^135aJ. Bilbao De Mendizabal,⁴⁹H. Bilokon,⁴⁷M. Bindi,^20a,20bS. Binet,¹¹⁶A. Bingul,^19c

C. Bini,^133a,133bB. Bittner,¹⁰⁰C. W. Black,¹⁵¹J. E. Black,¹⁴⁴K. M. Black,²²D. Blackburn,¹³⁹R. E. Blair,⁶ J.-B. Blanchard,¹³⁷T. Blazek,^145aI. Bloch,⁴²C. Blocker,²³J. Blocki,³⁹W. Blum,^82,aU. Blumenschein,⁵⁴ G. J. Bobbink,¹⁰⁶V. S. Bobrovnikov,¹⁰⁸S. S. Bocchetta,⁸⁰A. Bocci,⁴⁵C. R. Boddy,¹¹⁹M. Boehler,⁴⁸J. Boek,¹⁷⁶ T. T. Boek,¹⁷⁶N. Boelaert,³⁶J. A. Bogaerts,³⁰A. G. Bogdanchikov,¹⁰⁸A. Bogouch,^91,aC. Bohm,^147aJ. Bohm,¹²⁶ V. Boisvert,⁷⁶T. Bold,^38aV. Boldea,^26aN. M. Bolnet,¹³⁷M. Bomben,⁷⁹M. Bona,⁷⁵M. Boonekamp,¹³⁷S. Bordoni,⁷⁹

C. Borer,¹⁷A. Borisov,¹²⁹G. Borissov,⁷¹M. Borri,⁸³S. Borroni,⁴²J. Bortfeldt,⁹⁹V. Bortolotto,^135a,135bK. Bos,¹⁰⁶ D. Boscherini,^20aM. Bosman,¹²H. Boterenbrood,¹⁰⁶J. Bouchami,⁹⁴J. Boudreau,¹²⁴E. V. Bouhova-Thacker,⁷¹

D. Boumediene,³⁴C. Bourdarios,¹¹⁶N. Bousson,⁸⁴S. Boutouil,^136dA. Boveia,³¹J. Boyd,³⁰I. R. Boyko,⁶⁴ I. Bozovic-Jelisavcic,^13bJ. Bracinik,¹⁸P. Branchini,^135aA. Brandt,⁸G. Brandt,¹⁵O. Brandt,⁵⁴U. Bratzler,¹⁵⁷ B. Brau,⁸⁵J. E. Brau,¹¹⁵H. M. Braun,^176,aS. F. Brazzale,^165a,165cB. Brelier,¹⁵⁹J. Bremer,³⁰K. Brendlinger,¹²¹ R. Brenner,¹⁶⁷S. Bressler,¹⁷³T. M. Bristow,⁴⁶D. Britton,⁵³F. M. Brochu,²⁸I. Brock,²¹R. Brock,⁸⁹F. Broggi,^90a C. Bromberg,⁸⁹J. Bronner,¹⁰⁰G. Brooijmans,³⁵T. Brooks,⁷⁶W. K. Brooks,^32bE. Brost,¹¹⁵G. Brown,⁸³J. Brown,⁵⁵

P. A. Bruckman de Renstrom,³⁹D. Bruncko,^145bR. Bruneliere,⁴⁸S. Brunet,⁶⁰A. Bruni,^20aG. Bruni,^20a M. Bruschi,^20aL. Bryngemark,⁸⁰T. Buanes,¹⁴Q. Buat,⁵⁵F. Bucci,⁴⁹J. Buchanan,¹¹⁹P. Buchholz,¹⁴² R. M. Buckingham,¹¹⁹A. G. Buckley,⁴⁶S. I. Buda,^26aI. A. Budagov,⁶⁴B. Budick,¹⁰⁹L. Bugge,¹¹⁸O. Bulekov,⁹⁷ A. C. Bundock,⁷³M. Bunse,⁴³T. Buran,^118,aH. Burckhart,³⁰S. Burdin,⁷³T. Burgess,¹⁴S. Burke,¹³⁰E. Busato,³⁴

V. Bu¨scher,⁸²P. Bussey,⁵³C. P. Buszello,¹⁶⁷B. Butler,⁵⁷J. M. Butler,²²C. M. Buttar,⁵³J. M. Butterworth,⁷⁷ W. Buttinger,²⁸M. Byszewski,¹⁰S. Cabrera Urba´n,¹⁶⁸D. Caforio,^20a,20bO. Cakir,^4aP. Calafiura,¹⁵G. Calderini,⁷⁹

P. Calfayan,⁹⁹R. Calkins,¹⁰⁷L. P. Caloba,^24aR. Caloi,^133a,133bD. Calvet,³⁴S. Calvet,³⁴R. Camacho Toro,⁴⁹ P. Camarri,^134a,134bD. Cameron,¹¹⁸L. M. Caminada,¹⁵R. Caminal Armadans,¹²S. Campana,³⁰M. Campanelli,⁷⁷

V. Canale,^103a,103bF. Canelli,³¹A. Canepa,^160aJ. Cantero,⁸¹R. Cantrill,⁷⁶T. Cao,⁴⁰M. D. M. Capeans Garrido,³⁰ I. Caprini,^26aM. Caprini,^26aD. Capriotti,¹⁰⁰M. Capua,^37a,37bR. Caputo,⁸²R. Cardarelli,^134aT. Carli,³⁰ G. Carlino,^103aL. Carminati,^90a,90bS. Caron,¹⁰⁵E. Carquin,^32bG. D. Carrillo-Montoya,^146cA. A. Carter,⁷⁵

J. R. Carter,²⁸J. Carvalho,^125a,iD. Casadei,⁷⁷M. P. Casado,¹²M. Cascella,^123a,123bC. Caso,^50a,50b,a E. Castaneda-Miranda,¹⁷⁴A. Castelli,¹⁰⁶V. Castillo Gimenez,¹⁶⁸N. F. Castro,^125aG. Cataldi,^72aP. Catastini,⁵⁷ A. Catinaccio,³⁰J. R. Catmore,³⁰A. Cattai,³⁰G. Cattani,^134a,134bS. Caughron,⁸⁹V. Cavaliere,¹⁶⁶D. Cavalli,^90a

M. Cavalli-Sforza,¹²V. Cavasinni,^123a,123bF. Ceradini,^135a,135bB. Cerio,⁴⁵A. S. Cerqueira,^24bA. Cerri,¹⁵ L. Cerrito,⁷⁵F. Cerutti,¹⁵A. Cervelli,¹⁷S. A. Cetin,^19bA. Chafaq,^136aD. Chakraborty,¹⁰⁷I. Chalupkova,¹²⁸K. Chan,³

P. Chang,¹⁶⁶B. Chapleau,⁸⁶J. D. Chapman,²⁸J. W. Chapman,⁸⁸D. G. Charlton,¹⁸V. Chavda,⁸³

C. A. Chavez Barajas,³⁰S. Cheatham,⁸⁶S. Chekanov,⁶S. V. Chekulaev,^160aG. A. Chelkov,⁶⁴M. A. Chelstowska,⁸⁸ C. Chen,⁶³H. Chen,²⁵S. Chen,^33cX. Chen,¹⁷⁴Y. Chen,³⁵Y. Cheng,³¹A. Cheplakov,⁶⁴R. Cherkaoui El Moursli,^136e V. Chernyatin,^25,aE. Cheu,⁷L. Chevalier,¹³⁷V. Chiarella,⁴⁷G. Chiefari,^103a,103bJ. T. Childers,³⁰A. Chilingarov,⁷¹ G. Chiodini,^72aA. S. Chisholm,¹⁸R. T. Chislett,⁷⁷A. Chitan,^26aM. V. Chizhov,⁶⁴G. Choudalakis,³¹S. Chouridou,⁹

B. K. B. Chow,⁹⁹I. A. Christidi,⁷⁷A. Christov,⁴⁸D. Chromek-Burckhart,³⁰M. L. Chu,¹⁵²J. Chudoba,¹²⁶ G. Ciapetti,^133a,133bA. K. Ciftci,^4aR. Ciftci,^4aD. Cinca,⁶²V. Cindro,⁷⁴A. Ciocio,¹⁵M. Cirilli,⁸⁸P. Cirkovic,^13b

Z. H. Citron,¹⁷³M. Citterio,^90aM. Ciubancan,^26aA. Clark,⁴⁹P. J. Clark,⁴⁶R. N. Clarke,¹⁵J. C. Clemens,⁸⁴ B. Clement,⁵⁵C. Clement,^147a,147bY. Coadou,⁸⁴M. Cobal,^165a,165cA. Coccaro,¹³⁹J. Cochran,⁶³S. Coelli,^90a L. Coffey,²³J. G. Cogan,¹⁴⁴J. Coggeshall,¹⁶⁶J. Colas,⁵B. Cole,³⁵S. Cole,¹⁰⁷A. P. Colijn,¹⁰⁶C. Collins-Tooth,⁵³

J. Collot,⁵⁵T. Colombo,^120a,120bG. Colon,⁸⁵G. Compostella,¹⁰⁰P. Conde Muin˜o,^125aE. Coniavitis,¹⁶⁷ M. C. Conidi,¹²S. M. Consonni,^90a,90bV. Consorti,⁴⁸S. Constantinescu,^26aC. Conta,^120a,120bG. Conti,⁵⁷ F. Conventi,^103a,jM. Cooke,¹⁵B. D. Cooper,⁷⁷A. M. Cooper-Sarkar,¹¹⁹N. J. Cooper-Smith,⁷⁶K. Copic,¹⁵ T. Cornelissen,¹⁷⁶M. Corradi,^20aF. Corriveau,^86,kA. Corso-Radu,¹⁶⁴A. Cortes-Gonzalez,¹⁶⁶G. Cortiana,¹⁰⁰ G. Costa,^90aM. J. Costa,¹⁶⁸D. Costanzo,¹⁴⁰D. Coˆte´,⁸G. Cottin,^32aL. Courneyea,¹⁷⁰G. Cowan,⁷⁶B. E. Cox,⁸³

K. Cranmer,¹⁰⁹S. Cre´pe´-Renaudin,⁵⁵F. Crescioli,⁷⁹M. Cristinziani,²¹G. Crosetti,^37a,37bC.-M. Cuciuc,^26a C. Cuenca Almenar,¹⁷⁷T. Cuhadar Donszelmann,¹⁴⁰J. Cummings,¹⁷⁷M. Curatolo,⁴⁷C. Cuthbert,¹⁵¹H. Czirr,¹⁴²

P. Czodrowski,⁴⁴Z. Czyczula,¹⁷⁷S. D’Auria,⁵³M. D’Onofrio,⁷³A. D’Orazio,^133a,133b

M. J. Da Cunha Sargedas De Sousa,^125aC. Da Via,⁸³W. Dabrowski,^38aA. Dafinca,¹¹⁹T. Dai,⁸⁸F. Dallaire,⁹⁴ C. Dallapiccola,⁸⁵M. Dam,³⁶D. S. Damiani,¹³⁸A. C. Daniells,¹⁸H. O. Danielsson,³⁰V. Dao,¹⁰⁵G. Darbo,^50a G. L. Darlea,^26cS. Darmora,⁸J. A. Dassoulas,⁴²W. Davey,²¹C. David,¹⁷⁰T. Davidek,¹²⁸E. Davies,^119,eM. Davies,⁹⁴ O. Davignon,⁷⁹A. R. Davison,⁷⁷Y. Davygora,^58aE. Dawe,¹⁴³I. Dawson,¹⁴⁰R. K. Daya-Ishmukhametova,²³K. De,⁸

R. de Asmundis,^103aS. De Castro,^20a,20bS. De Cecco,⁷⁹J. de Graat,⁹⁹N. De Groot,¹⁰⁵P. de Jong,¹⁰⁶ C. De La Taille,¹¹⁶H. De la Torre,⁸¹F. De Lorenzi,⁶³L. De Nooij,¹⁰⁶D. De Pedis,^133aA. De Salvo,^133a U. De Sanctis,^165a,165cA. De Santo,¹⁵⁰J. B. De Vivie De Regie,¹¹⁶G. De Zorzi,^133a,133bW. J. Dearnaley,⁷¹

R. Debbe,²⁵C. Debenedetti,⁴⁶B. Dechenaux,⁵⁵D. V. Dedovich,⁶⁴J. Degenhardt,¹²¹J. Del Peso,⁸¹ T. Del Prete,^123a,123bT. Delemontex,⁵⁵M. Deliyergiyev,⁷⁴A. Dell’Acqua,³⁰L. Dell’Asta,²²M. Della Pietra,^103a,j D. della Volpe,^103a,103bM. Delmastro,⁵P. A. Delsart,⁵⁵C. Deluca,¹⁰⁶S. Demers,¹⁷⁷M. Demichev,⁶⁴A. Demilly,⁷⁹

B. Demirkoz,^12,lS. P. Denisov,¹²⁹D. Derendarz,³⁹J. E. Derkaoui,^136dF. Derue,⁷⁹P. Dervan,⁷³K. Desch,²¹ P. O. Deviveiros,¹⁰⁶A. Dewhurst,¹³⁰B. DeWilde,¹⁴⁹S. Dhaliwal,¹⁰⁶R. Dhullipudi,^78,mA. Di Ciaccio,^134a,134b L. Di Ciaccio,⁵C. Di Donato,^103a,103bA. Di Girolamo,³⁰B. Di Girolamo,³⁰S. Di Luise,^135a,135bA. Di Mattia,¹⁵³ B. Di Micco,^135a,135bR. Di Nardo,⁴⁷A. Di Simone,⁴⁸R. Di Sipio,^20a,20bM. A. Diaz,^32aE. B. Diehl,⁸⁸J. Dietrich,⁴²

T. A. Dietzsch,^58aS. Diglio,⁸⁷K. Dindar Yagci,⁴⁰J. Dingfelder,²¹F. Dinut,^26aC. Dionisi,^133a,133bP. Dita,^26a S. Dita,^26aF. Dittus,³⁰F. Djama,⁸⁴T. Djobava,^51bM. A. B. do Vale,^24cA. Do Valle Wemans,^125a,nT. K. O. Doan,⁵

D. Dobos,³⁰E. Dobson,⁷⁷J. Dodd,³⁵C. Doglioni,⁴⁹T. Doherty,⁵³T. Dohmae,¹⁵⁶Y. Doi,^65,aJ. Dolejsi,¹²⁸ Z. Dolezal,¹²⁸B. A. Dolgoshein,^97,aM. Donadelli,^24dJ. Donini,³⁴J. Dopke,³⁰A. Doria,^103aA. Dos Anjos,¹⁷⁴ A. Dotti,^123a,123bM. T. Dova,⁷⁰A. T. Doyle,⁵³M. Dris,¹⁰J. Dubbert,⁸⁸S. Dube,¹⁵E. Dubreuil,³⁴E. Duchovni,¹⁷³ G. Duckeck,⁹⁹D. Duda,¹⁷⁶A. Dudarev,³⁰F. Dudziak,⁶³L. Duflot,¹¹⁶M-A. Dufour,⁸⁶L. Duguid,⁷⁶M. Du¨hrssen,³⁰

M. Dunford,^58aH. Duran Yildiz,^4aM. Du¨ren,⁵²M. Dwuznik,^38aJ. Ebke,⁹⁹W. Edson,²C. A. Edwards,⁷⁶