Article
Reference
Determination of the Strange-Quark Density of the Proton from ATLAS Measurements of the W -> ℓν and Z -> ℓℓ Cross Sections
ATLAS Collaboration
ABDELALIM ALY, Ahmed Aly (Collab.), et al.
Abstract
A QCD analysis is reported of ATLAS data on inclusive W± and Z boson production in pp collisions at the LHC, jointly with ep deep-inelastic scattering data from HERA. The ATLAS data exhibit sensitivity to the light quark sea composition and magnitude at Bjorken x∼0.01.
Specifically, the data support the hypothesis of a symmetric composition of the light quark sea at low x. The ratio of the strange-to-down sea quark distributions is determined to be 1.00+0.25−0.28 at absolute four-momentum transfer squared Q2=1.9 GeV2 and x=0.023.
ATLAS Collaboration, ABDELALIM ALY, Ahmed Aly (Collab.), et al . Determination of the Strange-Quark Density of the Proton from ATLAS Measurements of the W -> ℓν and Z -> ℓℓ Cross Sections. Physical Review Letters , 2012, vol. 109, no. 01, p. 012001
DOI : 10.1103/PhysRevLett.109.012001
Available at:
http://archive-ouverte.unige.ch/unige:40200
Disclaimer: layout of this document may differ from the published version.
Determination of the Strange-Quark Density of the Proton from ATLAS Measurements of the W ! ‘ and Z ! ‘‘ Cross Sections
G. Aadet al.* (ATLAS Collaboration)
(Received 19 March 2012; published 5 July 2012)
A QCD analysis is reported of ATLAS data on inclusiveWandZboson production inppcollisions at the LHC, jointly withepdeep-inelastic scattering data from HERA. The ATLAS data exhibit sensitivity to the light quark sea composition and magnitude at Bjorkenx0:01. Specifically, the data support the hypothesis of a symmetric composition of the light quark sea at lowx. The ratio of the strange-to-down sea quark distributions is determined to be1:00þ0:250:28at absolute four-momentum transfer squaredQ2¼ 1:9 GeV2andx¼0:023.
DOI:10.1103/PhysRevLett.109.012001 PACS numbers: 12.38.Qk, 13.38.Be, 13.38.Dg, 14.20.Dh
Little is known about the strange-quark distribution in the proton. FlavorSUð3Þsymmetry suggests that the three light sea quark distributions are equal. However, the strange quarks may be suppressed due to their larger mass. The nucleon strange density plays an important role for a number of physics processes, ranging from measurements at proton-proton colliders ofW boson pro- duction associated with charm jets [1] and of theWboson mass [2], to the formation of strange matter [3] and neu- trino interactions at ultrahigh energies [4].
Knowledge of the parton distribution functions (PDFs) of the proton comes mainly from deep-inelastic lepton proton scattering experiments covering a broad range of Q2, the absolute four-momentum transfer squared, and of Bjorken x. The PDFs are determined from data using perturbative quantum chromodynamics (pQCD). The re-
gionx&0:01is primarily constrained by the precise mea-
surement of the proton structure function F2ðx; Q2Þ at HERA [5], which determines a specific combination of light quark and antiquark distributions. However, the flavor composition of the total light sea, x¼2xðuþdþsÞ, has not been determined at thesexvalues.
The strange-quark distribution has been accessed in charged current neutrino scattering through the subpro- cesses Wþs!c and Ws!c. This measurement has been made by the NuTeV [6] and CCFR [7] experiments, providing information on the strange and antistrange den- sity atx0:1andQ210 GeV2. However, the interpre- tation of these data is sensitive to uncertainties from charm fragmentation and nuclear corrections. The analyses of Refs. [8–11] suggest strangeness suppression, with
s=d&0:5, whereas the analysis of Ref. [12] is consistent
with s= d’1 (unsuppressed strangeness). Recent HERMES kaon multiplicity data [13] point to a strong x dependence of the strange-quark density and a rather large value of xðsþsÞ at x’0:04 and Q2’1:3 GeV2. However, the interpretation of these data depends on the knowledge of the fragmentation of strange quarks to K mesons at lowQ2.
In the present Letter it is shown that the differential measurements of the inclusive W and Z boson cross sections at the LHC, recently performed by the ATLAS collaboration using35 pb1 ofppcollision data recorded in 2010 [14], provide new constraints on the strange-quark distribution at high scale, Q2MW;Z2 , which imply con- straints at lowQ2through pQCD evolution. Because of the weak couplings of the quarks involved, complementary information to F2 is provided which also constrains x. A quantity of special interest is the ratio of the (WþþW) andZcross sections which is sensitive to the flavor com- position of the quark sea [12,15,16] and is rather insensi- tive to the influence of higher order pQCD corrections [17].
The inclusive electromagnetic and weak Drell-Yan scatter- ing process is theoretically well understood [18,19]. The parton distribution analysis is performed here in next-to- next-to leading order (NNLO) QCD using the ATLAS data jointly with inclusive deep-inelastic scattering data from HERA.
The combined epcross-section measurements of H1 and ZEUS [5] cover a kinematic range of Q2 from near 1 GeV2 to above104 GeV2 and ofxfrom0:6down to 104. The ATLAS data access a kinematic range pre- scribed by the boson masses,MW;Z, and the proton beam energy, Ep¼3:5 TeV, corresponding to Q2 ’M2W;Z and anxrange0:001&x&0:1, with a meanx¼MZ=2Ep¼ 0:013for the Zboson. The W andZboson differential cross sections have been measured [14] as functions of the W decay lepton (e, ) pseudorapidity, l, and of the Z boson rapidity,yZ, respectively, with an experimental pre- cision of typically ð1–2Þ%in each bin. The absolute nor- malization of the three cross sections is known to within
*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.
3.4%. Many systematic uncertainties on the measurements of theWandZboson cross sections are fully correlated.
These correlations are taken into account in the analysis.
The present QCD analysis uses theHERAFITTERframe- work [5,20,21]. The light quark coefficient functions are calculated to NNLO as implemented inQCDNUM[22]. The contributions of heavy quarks are calculated in the general- mass variable-flavor-number scheme of Refs. [23,24]. The electroweak parameters and corrections relevant for theW andZboson production processes are determined follow- ing the procedure described in Ref. [14], and the results are cross-checked between theFEWZ[19] and theDYNNLO[18]
programs. The HERAFITTER package uses the APPLGRID
code [25] interfaced to the MCFM program [26] for fast calculation of the differentialWandZboson cross sections at NLO and aK-factor technique to correct from NLO to NNLO predictions. The data are compared to the theory using the2function defined in Refs. [27–29].
The evolution equations yield the PDFs at any value of Q2given that they are parametrized as functions ofxat an initial scaleQ20. In the present analysis, this scale is chosen to beQ20 ¼1:9 GeV2 such that it is below the charm mass threshold m2c. The heavy quark masses are chosen to be mc ¼1:4 GeVandmb¼4:75 GeV. The strong coupling constant is fixed to SðMZÞ ¼0:1176, as in Ref. [5]. A minimum Q2 cut ofQ2min 7:5 GeV2 is imposed on the HERA data.
The quark distributions at the initial scale are repre- sented by the generic form
xqiðxÞ ¼AixBið1xÞCiPiðxÞ; (1) where PiðxÞ denotes polynomials in powers of x. The parametrized quark distributions, xqi, are chosen to be the valence quark distributions (xuv, xdv) and the light antiquark distributions (xu, xd, xs). The gluon distribution is parametrized with the more flexible form xgðxÞ ¼ AgxBgð1xÞCgPgðxÞ A0gxB0gð1xÞC0g, where C0g is set to 25 to suppress negative contributions at high x. The parametersAuvandAdvare fixed using the quark counting rule andAg using the momentum sum rule. The normal- ization and slope parameters,AandB, ofu andd are set equal such thatxu ¼xdatx!0. Terms are added in the polynomial expansionPiðxÞ only if required by the data, following the procedure described in Ref. [5]. This leads to one additional term,PuvðxÞ ¼1þEuvx2.
Two types of NNLO fit, termedepWZ, are performed with different treatments of strangeness. First, the strange- quark distribution is fully coupled to the down sea quark distribution and suppressed by fixing s= d¼0:5 at the initial scale Q20 (‘‘fixed s fit’’) as suggested by Refs. [5,8–11]. In a second fit, xs is parametrized as in Eq. (1), with Ps¼1 and Bs¼Bd, leaving two free strangeness parameters,AsandCs(‘‘freesfit’’). By default it is assumed thatxs¼xs.
Both fits result in good overall 2=NDF values of 546:1=567 with 13 free parameters, for fixed s, and of 538:4=565with 15 free parameters, for frees. For the fixed
s fit, the partial 2 of the ATLAS data is 44.5 for 30 data points. This improves significantly to 33.9 for the fit with frees. This fit determines the value of rs¼0:5ðsþsÞ=d to be
rs¼1:000:20 exp0:07modþ0:100:15parþ0:060:07S0:08th; (2) at Q20 and x¼0:023, the x value, which corresponds to x¼0:013atQ2 ¼MZ2 as a result of QCD evolution. The combined result isrs¼1:00þ0:250:28.
The uncertainty of rs, Eq. (2), is dominated by the experimental (exp) uncertainty, which is mostly driven by the statistical and systematic uncertainties of the W andZcross-section measurements. The model (mod) un- certainty includes effects due to variations (1:25< mc<
1:55 GeV and 4:5< mb<5:0 GeV) of the charm and beauty quark masses following Ref. [30], of the minimum Q2 cut value (5< Q2min<10 GeV2), and the value of the starting scale (Q20 lowered to 1:5 GeV2). The largest con- tribution to the model uncertainty of0:05comes from the variation of the charm quark mass. The parametrization (par) uncertainty corresponds to the envelope of the results obtained with the polynomialsPi, in Eq. (1), extended by one or two terms, resulting in somewhat different parton distributions with similar 2 as for the nominal fit. The parametrization uncertainty also includes a fit withBsfree.
The s uncertainty corresponds to a variation of sðMZÞ from 0.114 to 0.121. Finally, a theoretical (th) uncertainty is assessed by comparing the DYNNLO and FEWZ predic- tions on theZ,Wþ, andWfiducial cross sections, which agree at the level of 0.2, 0.5, and 1.0%, respectively. In addition, remaining missing pure electroweak corrections may alter the QCD predictions at the per-thousand level.
Both effects are well covered by an uncertainty of 1% on theW=Zcross-section ratio and this results in a theoretical uncertainty onrsof 0.08.
The fits impose small shifts, typically much smaller than 1 standard deviation, on the correlated systematic uncer- tainties of the data. The global normalization is observed to be shifted upward for both fits by about the size of the luminosity measurement uncertainty. TheWandZcross- section measurements are compared in Fig.1to the NNLO fit results, after these shifts are applied to the predictions.
Also shown are the ratios of the fits with free sand with fixed s. It is apparent that the enhanced strange-quark fraction in the free s fit has no significant effect on the prediction of theldistributions for both theWþandW decay leptons, while it leads to an improvement in the prediction of theyZ distribution. An improvement is also observed in the description of the ratio of the (WþþW) to theZ boson cross sections in the fiducial phase space.
This is predicted to be 11.10 in the fit with fixeds, while
the measured value of 10:700:15 is almost exactly reproduced in the fit with free s, which gives a value of 10.74.
In order to check the robustness of the present result for rs, a series of cross-checks is performed. A fit without allowing an adjustment of the correlated errors yields a value of rs¼0:970:26 exp, in good agreement with Eq. (2). A fit with identical input parameters is repeated at NLO and also yields a consistent result: rs¼1:03 0:19 exp. If this NLO fit is performed with a massless heavy quark treatment then rs¼1:050:19 exp is ob- tained. In a separate NLO study, the constraint ðxu xdÞ !0 for x!0 is relaxed. The xdðxÞ distribution is found to be consistent with xuðxÞ, albeit with large uncertainties (15% at x0:01 and Q20). The fraction of strangeness is again consistent with unity,rs¼0:96 0:25 exp. Finally the data are fitted, to NNLO, with sepa- rate strange and antistrange normalizations. The resulting value of rs is consistent with unity and the ratio s=s is 0:930:15 expatx¼0:023andQ2 ¼Q20.
W, Z cross-section measurements performed at the Tevatron may potentially have sensitivity tors similar to that of the ATLAS data. A NLO fit to the HERA with the CDFWasymmetry [31] andZrapidity [32] data givesrs¼ 0:660:29 exp at a meanx of about 0.081. This is con- sistent within uncertainties with both suppressed strange- ness and with the present result. A NLO fit to the combined HERA, ATLAS, and CDF data yields rs¼0:95 0:17 exp.
The provision of the full differential cross sections for both Wþ, W, and Z boson production, besides the ep cross sections, is essential for the determination of xs: if the ATLASZcross-section data are fitted together with the ATLAS W charge asymmetry data, rather than with the separateWþ andW cross-section measurements, a less precise result is obtained withrs¼0:920:31 exp.
In Fig. 2 the present result for rs is compared with predictions obtained from four global PDF determinations.
The CT10 (NLO) [12] determination gives a large fraction consistent with the present result. On the other hand, the MSTW08 [8] and ABKM09 [9] determinations give a much lower value ofrs’0:5, and the NNPDF2.1 [10,11]
result ofrs’0:25is even lower.
The enlarged fraction of the strange-quark sea leads to a decrease of the down and up quark sea densities at the initial scaleQ20, becausexs, xd, and xuare tied together at low x by the precise F2 data. In compensation for the increase of xs, the xdandxu distributions are diminished by’10%. The total sea,x, is correspondingly enhanced by’8%, as illustrated in Fig.3.
The result onrs, Eq. (2), evolves to
rs¼1:000:07exp0:03modþ0:040:06par0:02S0:03th (3) at Q2 ¼M2Z and x¼0:013, corresponding to a value of rsð0:013; M2ZÞ ¼1:00þ0:090:10, which is more than twice as precise as at the initial scaleQ20. Uncertainties are smaller atQ2 ¼MZ2because the gluon splitting probability intoqq pairs is flavor independent, thus reducing any initial flavor asymmetries. This also causesrsto increase from 0.5 atQ20 to a value of about 0.8 atQ2¼MZ2 in the fixedsfit.
rs
-0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
ABKM09 NNPDF2.1 MSTW08 CT10 (NLO) total uncertainty experimental uncertainty
ATLAS , x=0.023
= 1.9 GeV2
Q2 epWZ free s
FIG. 2 (color online). Predictions for the ratio rs¼0:5ðsþ sÞ= d, at Q2¼1:9 GeV2, x¼0:023. Points: global fit results using the PDF uncertainties as quoted; bands: this analysis; inner band, experimental uncertainty; outer band, total uncertainty.
l| η
|
0 0.5 1 1.5 2 2.5
sfree/fixed
0.981 1.02
| [pb]lη/d|σd
500 550 600 650 700
L dt = 33-36 pb-1
∫
νl
l+ +→ W
= 7 TeV) s Data 2010 (
stat. uncertainty)
⊕ (uncorr. sys.
s epWZ fixed
s epWZ free
ATLAS
l| η
|
0 0.5 1 1.5 2 2.5
sfree/fixed
0.981 1.02
| [pb]lη/d|σd
350 400 450 500
L dt = 33-36 pb-1
∫
νl
l- -→ W
= 7 TeV) s Data 2010 (
stat. uncertainty)
⊕ (uncorr. sys.
s epWZ fixed
s epWZ free
ATLAS
Z|
|y 0 0.5 1 1.5 2 2.5 3 3.5
sfree/fixed
0.981 1.02
| [pb]Z/d|yσd
60 80 100 120 140
L dt = 33-36 pb-1
∫
l-
l+
→ Z
= 7 TeV) s Data 2010 (
stat. uncertainty)
⊕ (uncorr. sys.
s epWZ fixed
s epWZ free
ATLAS
FIG. 1 (color online). Differentiald=dj‘þj(left) andd=dj‘j(middle) cross-section measurements forW!‘andd=djyZj cross-section measurement ford=djyZj(right). The error bars represent the statistical and uncorrelated systematic uncertainties added in quadrature while the theoretical curves are adjusted to the correlated error shifts (see text). The NNLO fit results with free and fixed strangeness are also indicated, and their ratios are shown in the panels below the cross-section plots.
In summary, a NNLO pQCD analysis is presented of the first differential ATLAS W, Z pp cross sections with HERA ep data. The W, Z measurements introduce a novel sensitivity to the strange-quark density atx0:01, which is exploited here. The ratio of the strange-to-down sea quark density is found to bers¼1:00þ0:250:28, at Bjorken x¼0:023 and the initial scale of the QCD fit Q20 ¼ 1:9 GeV2. This is consistent with the prediction that the light quark sea at lowxis flavor symmetric. A consequence of this initial observation is that the total sea,x¼2xðuþ dþsÞ, is enhanced by about 8%, as compared to the result when the strange quark is suppressed to half the magnitude of the down sea quark.
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 ac- knowledge 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; EPLANET and ERC, 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 com- puting 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.
[1] U. Baur, F. Halzen, S. Keller, M. L. Mangano, and K.
Riesselmann,Phys. Lett. B318, 544 (1993).
[2] M. Krasny, F. Dydak, F. Fayette, W. Placzek, and A.
Siodmok,Eur. Phys. J. C69, 379 (2010).
[3] E. Farhi and R. L. Jaffe,Phys. Rev. D30, 2379 (1984).
[4] R. Gandhi, C. Quigg, M. H. Reno, and I. Sarcevic,Phys.
Rev. D58, 093009 (1998).
[5] F. D. Aaron et al. (H1 Collaboration and ZEUS Collaboration),J. High Energy Phys. 01 (2010) 109.
[6] D. Masonet al.(NuTeV Collaboration),Phys. Rev. Lett.
99, 192001 (2007).
[7] M. Goncharov et al. (CCFR Collaboration and NuTeV Collaboration),Phys. Rev. D64, 112006 (2001).
[8] A. Martin, W. Stirling, R. Thorne, and G. Watt,Eur. Phys.
J. C63, 189 (2009).
[9] S. Alekhin, J. Blumlein, S. Klein, and S. Moch,Phys. Rev.
D81, 014032 (2010).
[10] R. D. Ball, L. Del Debbio, S. Forte, A. Guffanti, J. Latorre, A.
Piccione, J. Rojo, and M. Ubiali,Nucl. Phys.B809, 1 (2009).
[11] R. D. Ball, V. Bertone, F. Cerutti, L. Del Debbio, S. Forte, A. Guffanti, J. Latorre, J. Rojo, and M. Ubiali,Nucl. Phys.
B855, 153 (2012).
[12] H.-L. Lai, M. Guzzi, J. Huston, Z. Li, P. Nadolsky, J.
Pumplin, and C.-P. Yuan,Phys. Rev. D82, 074024 (2010).
[13] A. Airapetianet al.(HERMES Collaboration),Phys. Lett.
B666, 446 (2008).
[14] G. Aadet al. (ATLAS Collaboration),Phys. Rev. D85, 072004 (2012).
[15] K. Kovarik, T. Stavreva, A. Kusina, T. Jezo, F. Olness, I.
Schienbein, and J. Yu, Nucl. Phys. B, Proc. Suppl.222- 224, 52 (2012).
[16] P. Nadolsky, Report No. SMU-HEP-09-21, 2006 (unpub- lished).
[17] W. van Neerven and E. Zijlstra,Nucl. Phys.B382, 11 (1992).
[18] S. Catani, L. Cieri, G. Ferrera, D. de Florian, and M.
Grazzini,Phys. Rev. Lett.103, 082001 (2009).
[19] C. Anastasiou, L. J. Dixon, K. Melnikov, and F. Petriello, Phys. Rev. D69, 094008 (2004).
[20] ‘‘HERAFITTER,’’http://projects.hepforge.org/herafitter.
[21] F. Aaronet al.(H1 Collaboration),Eur. Phys. J. C64, 561 (2009).
[22] M. Botje,Comput. Phys. Commun.182, 490 (2011).
[23] R. S. Thorne and R. G. Roberts,Phys. Rev. D57, 6871 (1998).
[24] R. S. Thorne,Phys. Rev. D73, 054019 (2006).
[25] T. Carli, D. Clements, A. Cooper-Sarkar, C. Gwenlan, G. P. Salam, F. Siegert, P. Starovoitov, and M. Sutton, Eur. Phys. J. C66, 503 (2010).
[26] J. M. Campbell and R. K. Ellis,Nucl. Phys. B, Proc. Suppl.
205–206, 10 (2010).
x
10-3 10-2 10-1
)s+d+u = 2x(Σx
0 0.5 1 1.5 2
2.5 Q2 = 1.9 GeV2
s epWZ fixed
s epWZ free
ATLAS
FIG. 3 (color online). Distribution of the light sea quarks, x¼2xðuþdþsÞ, in the NNLO analysis of HERA and ATLAS data with a fixed fraction of strangeness (lower green curve) and with a fitted fraction of about unity (upper blue curve). The bands represent the experimental uncertainties.
[27] F. Aaronet al.(H1 Collaboration),Eur. Phys. J. C63, 625 (2009).
[28] C. Adloffet al.(H1 Collaboration),Eur. Phys. J. C30, 1 (2003).
[29] S. Chekanov et al.(ZEUS Collaboration), Phys. Rev. D 67, 012007 (2003).
[30] A. Martin, W. Stirling, R. Thorne, and G. Watt,Eur. Phys.
J. C70, 51 (2010).
[31] T. A. Aaltonenet al.(CDF Collaboration),Phys. Rev. Lett.
102, 181801 (2009).
[32] T. A. Aaltonenet al.(CDF Collaboration), Phys. Lett. B 692, 232 (2010).
G. Aad,47B. Abbott,110J. Abdallah,11A. A. Abdelalim,48A. Abdesselam,117O. Abdinov,10B. Abi,111M. Abolins,87 O. S. AbouZeid,157H. Abramowicz,152H. Abreu,114E. Acerbi,88a,88bB. S. Acharya,163a,163bL. Adamczyk,37 D. L. Adams,24T. N. Addy,55J. Adelman,174M. Aderholz,98S. Adomeit,97P. Adragna,74T. Adye,128S. Aefsky,22
J. A. Aguilar-Saavedra,123b,bM. Aharrouche,80S. P. Ahlen,21F. Ahles,47A. Ahmad,147M. Ahsan,40 G. Aielli,132a,132bT. Akdogan,18aT. P. A. A˚ kesson,78G. Akimoto,154A. V. Akimov,93A. Akiyama,66M. S. Alam,1
M. A. Alam,75J. Albert,168S. Albrand,54M. Aleksa,29I. N. Aleksandrov,64F. Alessandria,88aC. Alexa,25a G. Alexander,152G. Alexandre,48T. Alexopoulos,9M. Alhroob,20M. Aliev,15G. Alimonti,88aJ. Alison,119 M. Aliyev,10B. M. M. Allbrooke,17P. P. Allport,72S. E. Allwood-Spiers,52J. Almond,81A. Aloisio,101a,101b R. Alon,170A. Alonso,78B. Alvarez Gonzalez,87M. G. Alviggi,101a,101bK. Amako,65P. Amaral,29C. Amelung,22 V. V. Ammosov,127A. Amorim,123a,cG. Amoro´s,166N. Amram,152C. Anastopoulos,29L. S. Ancu,16N. Andari,114 T. Andeen,34C. F. Anders,20G. Anders,57aK. J. Anderson,30A. Andreazza,88a,88bV. Andrei,57aM-L. Andrieux,54
X. S. Anduaga,69A. Angerami,34F. Anghinolfi,29A. Anisenkov,106N. Anjos,123aA. Annovi,46A. Antonaki,8 M. Antonelli,46A. Antonov,95J. Antos,143bF. Anulli,131aS. Aoun,82L. Aperio Bella,4R. Apolle,117,dG. Arabidze,87
I. Aracena,142Y. Arai,65A. T. H. Arce,44S. Arfaoui,147J-F. Arguin,14E. Arik,18a,aM. Arik,18aA. J. Armbruster,86 O. Arnaez,80C. Arnault,114A. Artamonov,94G. Artoni,131a,131bD. Arutinov,20S. Asai,154R. Asfandiyarov,171
S. Ask,27B. A˚ sman,145a,145bL. Asquith,5K. Assamagan,24A. Astbury,168A. Astvatsatourov,51B. Aubert,4 E. Auge,114K. Augsten,126M. Aurousseau,144aG. Avolio,162R. Avramidou,9D. Axen,167C. Ay,53G. Azuelos,92,e
Y. Azuma,154M. A. Baak,29G. Baccaglioni,88aC. Bacci,133a,133bA. M. Bach,14H. Bachacou,135K. Bachas,29 M. Backes,48M. Backhaus,20E. Badescu,25aP. Bagnaia,131a,131bS. Bahinipati,2Y. Bai,32aD. C. Bailey,157T. Bain,157
J. T. Baines,128O. K. Baker,174M. D. Baker,24S. Baker,76E. Banas,38P. Banerjee,92Sw. Banerjee,171D. Banfi,29 A. Bangert,149V. Bansal,168H. S. Bansil,17L. Barak,170S. P. Baranov,93A. Barashkou,64A. Barbaro Galtieri,14
T. Barber,47E. L. Barberio,85D. Barberis,49a,49bM. Barbero,20D. Y. Bardin,64T. Barillari,98M. Barisonzi,173 T. Barklow,142N. Barlow,27B. M. Barnett,128R. M. Barnett,14A. Baroncelli,133aG. Barone,48A. J. Barr,117 F. Barreiro,79J. Barreiro Guimara˜es da Costa,56P. Barrillon,114R. Bartoldus,142A. E. Barton,70V. Bartsch,148 R. L. Bates,52L. Batkova,143aJ. R. Batley,27A. Battaglia,16M. Battistin,29F. Bauer,135H. S. Bawa,142,fS. Beale,97
T. Beau,77P. H. Beauchemin,160R. Beccherle,49aP. Bechtle,20H. P. Beck,16S. Becker,97M. Beckingham,137 K. H. Becks,173A. J. Beddall,18cA. Beddall,18cS. Bedikian,174V. A. Bednyakov,64C. P. Bee,82M. Begel,24
S. Behar Harpaz,151P. K. Behera,62M. Beimforde,98C. Belanger-Champagne,84P. J. Bell,48W. H. Bell,48 G. Bella,152L. Bellagamba,19aF. Bellina,29M. Bellomo,29A. Belloni,56O. Beloborodova,106,gK. Belotskiy,95 O. Beltramello,29S. Ben Ami,151O. Benary,152D. Benchekroun,134aC. Benchouk,82M. Bendel,80N. Benekos,164 Y. Benhammou,152E. Benhar Noccioli,48J. A. Benitez Garcia,158bD. P. Benjamin,44M. Benoit,114J. R. Bensinger,22 K. Benslama,129S. Bentvelsen,104D. Berge,29E. Bergeaas Kuutmann,41N. Berger,4F. Berghaus,168E. Berglund,104 J. Beringer,14P. Bernat,76R. Bernhard,47C. Bernius,24T. Berry,75C. Bertella,82A. Bertin,19a,19bF. Bertinelli,29 F. Bertolucci,121a,121bM. I. Besana,88a,88bN. Besson,135S. Bethke,98W. Bhimji,45R. M. Bianchi,29M. Bianco,71a,71b
O. Biebel,97S. P. Bieniek,76K. Bierwagen,53J. Biesiada,14M. Biglietti,133aH. Bilokon,46M. Bindi,19a,19b S. Binet,114A. Bingul,18cC. Bini,131a,131bC. Biscarat,176U. Bitenc,47K. M. Black,21R. E. Blair,5J.-B. Blanchard,135
G. Blanchot,29T. Blazek,143aC. Blocker,22J. Blocki,38A. Blondel,48W. Blum,80U. Blumenschein,53 G. J. Bobbink,104V. B. Bobrovnikov,106S. S. Bocchetta,78A. Bocci,44C. R. Boddy,117M. Boehler,41J. Boek,173
N. Boelaert,35J. A. Bogaerts,29A. Bogdanchikov,106A. Bogouch,89,aC. Bohm,145aV. Boisvert,75T. Bold,37 V. Boldea,25aN. M. Bolnet,135M. Bona,74V. G. Bondarenko,95M. Bondioli,162M. Boonekamp,135C. N. Booth,138
S. Bordoni,77C. Borer,16A. Borisov,127G. Borissov,70I. Borjanovic,12aM. Borri,81S. Borroni,86
V. Bortolotto,133a,133bK. Bos,104D. Boscherini,19aM. Bosman,11H. Boterenbrood,104D. Botterill,128J. Bouchami,92 J. Boudreau,122E. V. Bouhova-Thacker,70D. Boumediene,33C. Bourdarios,114N. Bousson,82A. Boveia,30J. Boyd,29
I. R. Boyko,64N. I. Bozhko,127I. Bozovic-Jelisavcic,12bJ. Bracinik,17A. Braem,29P. Branchini,133a
G. W. Brandenburg,56A. Brandt,7G. Brandt,117O. Brandt,53U. Bratzler,155B. Brau,83J. E. Brau,113H. M. Braun,173 B. Brelier,157J. Bremer,29R. Brenner,165S. Bressler,170D. Britton,52F. M. Brochu,27I. Brock,20R. Brock,87 T. J. Brodbeck,70E. Brodet,152F. Broggi,88aC. Bromberg,87J. Bronner,98G. Brooijmans,34W. K. Brooks,31b G. Brown,81H. Brown,7P. A. Bruckman de Renstrom,38D. Bruncko,143bR. Bruneliere,47S. Brunet,60A. Bruni,19a
G. Bruni,19aM. Bruschi,19aT. Buanes,13Q. Buat,54F. Bucci,48J. Buchanan,117N. J. Buchanan,2P. Buchholz,140 R. M. Buckingham,117A. G. Buckley,45S. I. Buda,25aI. A. Budagov,64B. Budick,107V. Bu¨scher,80L. Bugge,116
O. Bulekov,95M. Bunse,42T. Buran,116H. Burckhart,29S. Burdin,72T. Burgess,13S. Burke,128E. Busato,33 P. Bussey,52C. P. Buszello,165F. Butin,29B. Butler,142J. M. Butler,21C. M. Buttar,52J. M. Butterworth,76 W. Buttinger,27S. Cabrera Urba´n,166D. Caforio,19a,19bO. Cakir,3aP. Calafiura,14G. Calderini,77P. Calfayan,97 R. Calkins,105L. P. Caloba,23aR. Caloi,131a,131bD. Calvet,33S. Calvet,33R. Camacho Toro,33P. Camarri,132a,132b
M. Cambiaghi,118a,118bD. Cameron,116L. M. Caminada,14S. Campana,29M. Campanelli,76V. Canale,101a,101b F. Canelli,30,iiA. Canepa,158aJ. Cantero,79L. Capasso,101a,101bM. D. M. Capeans Garrido,29I. Caprini,25a M. Caprini,25aD. Capriotti,98M. Capua,36a,36bR. Caputo,80C. Caramarcu,24R. Cardarelli,132aT. Carli,29 G. Carlino,101aL. Carminati,88a,88bB. Caron,84S. Caron,103G. D. Carrillo Montoya,171A. A. Carter,74J. R. Carter,27
J. Carvalho,123a,hD. Casadei,107M. P. Casado,11M. Cascella,121a,121bC. Caso,49a,49b,a
A. M. Castaneda Hernandez,171E. Castaneda-Miranda,171V. Castillo Gimenez,166N. F. Castro,123aG. Cataldi,71a F. Cataneo,29A. Catinaccio,29J. R. Catmore,29A. Cattai,29G. Cattani,132a,132bS. Caughron,87D. Cauz,163a,163c
P. Cavalleri,77D. Cavalli,88aM. Cavalli-Sforza,11V. Cavasinni,121a,121bF. Ceradini,133a,133bA. S. Cerqueira,23b A. Cerri,29L. Cerrito,74F. Cerutti,46S. A. Cetin,18bF. Cevenini,101a,101bA. Chafaq,134aD. Chakraborty,105K. Chan,2
B. Chapleau,84J. D. Chapman,27J. W. Chapman,86E. Chareyre,77D. G. Charlton,17V. Chavda,81
C. A. Chavez Barajas,29S. Cheatham,84S. Chekanov,5S. V. Chekulaev,158aG. A. Chelkov,64M. A. Chelstowska,103 C. Chen,63H. Chen,24S. Chen,32cT. Chen,32cX. Chen,171S. Cheng,32aA. Cheplakov,64V. F. Chepurnov,64 R. Cherkaoui El Moursli,134eV. Chernyatin,24E. Cheu,6S. L. Cheung,157L. Chevalier,135G. Chiefari,101a,101b
L. Chikovani,50aJ. T. Childers,29A. Chilingarov,70G. Chiodini,71aA. S. Chisholm,17M. V. Chizhov,64 G. Choudalakis,30S. Chouridou,136I. A. Christidi,76A. Christov,47D. Chromek-Burckhart,29M. L. Chu,150 J. Chudoba,124G. Ciapetti,131a,131bK. Ciba,37A. K. Ciftci,3aR. Ciftci,3aD. Cinca,33V. Cindro,73M. D. Ciobotaru,162
C. Ciocca,19aA. Ciocio,14M. Cirilli,86M. Citterio,88aM. Ciubancan,25aA. Clark,48P. J. Clark,45W. Cleland,122 J. C. Clemens,82B. Clement,54C. Clement,145a,145bR. W. Clifft,128Y. Coadou,82M. Cobal,163a,163cA. Coccaro,171 J. Cochran,63P. Coe,117J. G. Cogan,142J. Coggeshall,164E. Cogneras,176J. Colas,4A. P. Colijn,104N. J. Collins,17 C. Collins-Tooth,52J. Collot,54G. Colon,83P. Conde Muin˜o,123aE. Coniavitis,117M. C. Conidi,11M. Consonni,103 V. Consorti,47S. Constantinescu,25aC. Conta,118a,118bF. Conventi,101a,iJ. Cook,29M. Cooke,14B. D. Cooper,76
A. M. Cooper-Sarkar,117K. Copic,14T. Cornelissen,173M. Corradi,19aF. Corriveau,84,jA. Cortes-Gonzalez,164 G. Cortiana,98G. Costa,88aM. J. Costa,166D. Costanzo,138T. Costin,30D. Coˆte´,29R. Coura Torres,23a L. Courneyea,168G. Cowan,75C. Cowden,27B. E. Cox,81K. Cranmer,107F. Crescioli,121a,121bM. Cristinziani,20
G. Crosetti,36a,36bR. Crupi,71a,71bS. Cre´pe´-Renaudin,54C.-M. Cuciuc,25aC. Cuenca Almenar,174 T. Cuhadar Donszelmann,138M. Curatolo,46C. J. Curtis,17C. Cuthbert,149P. Cwetanski,60H. Czirr,140 P. Czodrowski,43Z. Czyczula,174S. D’Auria,52M. D’Onofrio,72A. D’Orazio,131a,131bP. V. M. Da Silva,23a
C. Da Via,81W. Dabrowski,37T. Dai,86C. Dallapiccola,83M. Dam,35M. Dameri,49a,49bD. S. Damiani,136 H. O. Danielsson,29D. Dannheim,98V. Dao,48G. Darbo,49aG. L. Darlea,25bW. Davey,20T. Davidek,125 N. Davidson,85R. Davidson,70E. Davies,117,dM. Davies,92A. R. Davison,76Y. Davygora,57aE. Dawe,141 I. Dawson,138J. W. Dawson,5,aR. K. Daya-Ishmukhametova,22K. De,7R. de Asmundis,101aS. De Castro,19a,19b P. E. De Castro Faria Salgado,24S. De Cecco,77J. de Graat,97N. De Groot,103P. de Jong,104C. De La Taille,114
H. De la Torre,79B. De Lotto,163a,163cL. de Mora,70L. De Nooij,104D. De Pedis,131aA. De Salvo,131a U. De Sanctis,163a,163cA. De Santo,148J. B. De Vivie De Regie,114S. Dean,76W. J. Dearnaley,70R. Debbe,24
C. Debenedetti,45D. V. Dedovich,64J. Degenhardt,119M. Dehchar,117C. Del Papa,163a,163cJ. Del Peso,79 T. Del Prete,121a,121bT. Delemontex,54M. Deliyergiyev,73A. Dell’Acqua,29L. Dell’Asta,21M. Della Pietra,101a,i D. della Volpe,101a,101bM. Delmastro,4N. Delruelle,29P. A. Delsart,54C. Deluca,147S. Demers,174M. Demichev,64
B. Demirkoz,11,kJ. Deng,162S. P. Denisov,127D. Derendarz,38J. E. Derkaoui,134dF. Derue,77P. Dervan,72 K. Desch,20E. Devetak,147P. O. Deviveiros,104A. Dewhurst,128B. DeWilde,147S. Dhaliwal,157R. Dhullipudi,24,l A. Di Ciaccio,132a,132bL. Di Ciaccio,4A. Di Girolamo,29B. Di Girolamo,29S. Di Luise,133a,133bA. Di Mattia,171 B. Di Micco,29R. Di Nardo,46A. Di Simone,132a,132bR. Di Sipio,19a,19bM. A. Diaz,31aF. Diblen,18cE. B. Diehl,86
J. Dietrich,41T. A. Dietzsch,57aS. Diglio,85K. Dindar Yagci,39J. Dingfelder,20C. Dionisi,131a,131bP. Dita,25a S. Dita,25aF. Dittus,29F. Djama,82T. Djobava,50bM. A. B. do Vale,23cA. Do Valle Wemans,123aT. K. O. Doan,4
M. Dobbs,84R. Dobinson,29,aD. Dobos,29E. Dobson,29,mJ. Dodd,34C. Doglioni,48T. Doherty,52Y. Doi,65,a J. Dolejsi,125I. Dolenc,73Z. Dolezal,125B. A. Dolgoshein,95,aT. Dohmae,154M. Donadelli,23dM. Donega,119 J. Donini,33J. Dopke,29A. Doria,101aA. Dos Anjos,171M. Dosil,11A. Dotti,121a,121bM. T. Dova,69J. D. Dowell,17
A. D. Doxiadis,104A. T. Doyle,52Z. Drasal,125J. Drees,173N. Dressnandt,119H. Drevermann,29C. Driouichi,35 M. Dris,9J. Dubbert,98S. Dube,14E. Duchovni,170G. Duckeck,97A. Dudarev,29F. Dudziak,63M. Du¨hrssen,29 I. P. Duerdoth,81L. Duflot,114M-A. Dufour,84M. Dunford,29H. Duran Yildiz,3aR. Duxfield,138M. Dwuznik,37
F. Dydak,29M. Du¨ren,51W. L. Ebenstein,44J. Ebke,97S. Eckweiler,80K. Edmonds,80C. A. Edwards,75 N. C. Edwards,52W. Ehrenfeld,41T. Ehrich,98T. Eifert,142G. Eigen,13K. Einsweiler,14E. Eisenhandler,74 T. Ekelof,165M. El Kacimi,134cM. Ellert,165S. Elles,4F. Ellinghaus,80K. Ellis,74N. Ellis,29J. Elmsheuser,97 M. Elsing,29D. Emeliyanov,128R. Engelmann,147A. Engl,97B. Epp,61A. Eppig,86J. Erdmann,53A. Ereditato,16
D. Eriksson,145aJ. Ernst,1M. Ernst,24J. Ernwein,135D. Errede,164S. Errede,164E. Ertel,80M. Escalier,114 C. Escobar,122X. Espinal Curull,11B. Esposito,46F. Etienne,82A. I. Etienvre,135E. Etzion,152D. Evangelakou,53
H. Evans,60L. Fabbri,19a,19bC. Fabre,29R. M. Fakhrutdinov,127S. Falciano,131aY. Fang,171M. Fanti,88a,88b A. Farbin,7A. Farilla,133aJ. Farley,147T. Farooque,157S. M. Farrington,117P. Farthouat,29P. Fassnacht,29 D. Fassouliotis,8B. Fatholahzadeh,157A. Favareto,88a,88bL. Fayard,114S. Fazio,36a,36bR. Febbraro,33P. Federic,143a
O. L. Fedin,120W. Fedorko,87M. Fehling-Kaschek,47L. Feligioni,82D. Fellmann,5C. Feng,32dE. J. Feng,30 A. B. Fenyuk,127J. Ferencei,143bJ. Ferland,92W. Fernando,108S. Ferrag,52J. Ferrando,52V. Ferrara,41A. Ferrari,165
P. Ferrari,104R. Ferrari,118aD. E. Ferreira de Lima,52A. Ferrer,166M. L. Ferrer,46D. Ferrere,48C. Ferretti,86 A. Ferretto Parodi,49a,49bM. Fiascaris,30F. Fiedler,80A. Filipcˇicˇ,73A. Filippas,9F. Filthaut,103M. Fincke-Keeler,168 M. C. N. Fiolhais,123a,hL. Fiorini,166A. Firan,39G. Fischer,41P. Fischer,20M. J. Fisher,108M. Flechl,47I. Fleck,140
J. Fleckner,80P. Fleischmann,172S. Fleischmann,173T. Flick,173A. Floderus,78L. R. Flores Castillo,171 M. J. Flowerdew,98M. Fokitis,9T. Fonseca Martin,16D. A. Forbush,137A. Formica,135A. Forti,81D. Fortin,158a
J. M. Foster,81D. Fournier,114A. Foussat,29A. J. Fowler,44K. Fowler,136H. Fox,70P. Francavilla,11 S. Franchino,118a,118bD. Francis,29T. Frank,170M. Franklin,56S. Franz,29M. Fraternali,118a,118bS. Fratina,119 S. T. French,27F. Friedrich,43R. Froeschl,29D. Froidevaux,29J. A. Frost,27C. Fukunaga,155E. Fullana Torregrosa,29 J. Fuster,166C. Gabaldon,29O. Gabizon,170T. Gadfort,24S. Gadomski,48G. Gagliardi,49a,49bP. Gagnon,60C. Galea,97
E. J. Gallas,117V. Gallo,16B. J. Gallop,128P. Gallus,124K. K. Gan,108Y. S. Gao,142,fV. A. Gapienko,127 A. Gaponenko,14F. Garberson,174M. Garcia-Sciveres,14C. Garcı´a,166J. E. Garcı´a Navarro,166R. W. Gardner,30 N. Garelli,29H. Garitaonandia,104V. Garonne,29J. Garvey,17C. Gatti,46G. Gaudio,118aB. Gaur,140L. Gauthier,135 I. L. Gavrilenko,93C. Gay,167G. Gaycken,20J-C. Gayde,29E. N. Gazis,9P. Ge,32dC. N. P. Gee,128D. A. A. Geerts,104
Ch. Geich-Gimbel,20K. Gellerstedt,145a,145bC. Gemme,49aA. Gemmell,52M. H. Genest,54S. Gentile,131a,131b M. George,53S. George,75P. Gerlach,173A. Gershon,152C. Geweniger,57aH. Ghazlane,134bN. Ghodbane,33 B. Giacobbe,19aS. Giagu,131a,131bV. Giakoumopoulou,8V. Giangiobbe,11F. Gianotti,29B. Gibbard,24A. Gibson,157 S. M. Gibson,29L. M. Gilbert,117V. Gilewsky,90D. Gillberg,28A. R. Gillman,128D. M. Gingrich,2,eJ. Ginzburg,152 N. Giokaris,8M. P. Giordani,163cR. Giordano,101a,101bF. M. Giorgi,15P. Giovannini,98P. F. Giraud,135D. Giugni,88a M. Giunta,92P. Giusti,19aB. K. Gjelsten,116L. K. Gladilin,96C. Glasman,79J. Glatzer,47A. Glazov,41K. W. Glitza,173
G. L. Glonti,64J. R. Goddard,74J. Godfrey,141J. Godlewski,29M. Goebel,41T. Go¨pfert,43C. Goeringer,80 C. Go¨ssling,42T. Go¨ttfert,98S. Goldfarb,86T. Golling,174A. Gomes,123a,cL. S. Gomez Fajardo,41R. Gonc¸alo,75
J. Goncalves Pinto Firmino Da Costa,41L. Gonella,20A. Gonidec,29S. Gonzalez,171S. Gonza´lez de la Hoz,166 G. Gonzalez Parra,11M. L. Gonzalez Silva,26S. Gonzalez-Sevilla,48J. J. Goodson,147L. Goossens,29 P. A. Gorbounov,94H. A. Gordon,24I. Gorelov,102G. Gorfine,173B. Gorini,29E. Gorini,71a,71bA. Gorisˇek,73
E. Gornicki,38S. A. Gorokhov,127V. N. Goryachev,127B. Gosdzik,41M. Gosselink,104M. I. Gostkin,64 I. Gough Eschrich,162M. Gouighri,134aD. Goujdami,134cM. P. Goulette,48A. G. Goussiou,137C. Goy,4 S. Gozpinar,22I. Grabowska-Bold,37P. Grafstro¨m,29K-J. Grahn,41F. Grancagnolo,71aS. Grancagnolo,15 V. Grassi,147V. Gratchev,120N. Grau,34H. M. Gray,29J. A. Gray,147E. Graziani,133aO. G. Grebenyuk,120 T. Greenshaw,72Z. D. Greenwood,24,lK. Gregersen,35I. M. Gregor,41P. Grenier,142J. Griffiths,137N. Grigalashvili,64
A. A. Grillo,136S. Grinstein,11Y. V. Grishkevich,96J.-F. Grivaz,114M. Groh,98E. Gross,170J. Grosse-Knetter,53 J. Groth-Jensen,170K. Grybel,140V. J. Guarino,5D. Guest,174C. Guicheney,33A. Guida,71a,71bS. Guindon,53 H. Guler,84,nJ. Gunther,124B. Guo,157J. Guo,34A. Gupta,30Y. Gusakov,64V. N. Gushchin,127P. Gutierrez,110