Search for contact interactions in dimuon events from <em>pp</em> collisions at √s=7 TeV with the ATLAS detector

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Article

Reference

Search for contact interactions in dimuon events from pp collisions at

√s=7 TeV with the ATLAS detector

ATLAS Collaboration

ABDELALIM ALY, Ahmed Aly (Collab.), et al.

Abstract

A search for contact interactions has been performed using dimuon events recorded with the ATLAS detector in proton-proton collisions at s√=7 TeV. The data sample corresponds to an integrated luminosity of 42 pb−1. No significant deviation from the standard model is observed in the dimuon mass spectrum, allowing the following 95% C.L. limits to be set on the energy scale of contact interactions: Λ>4.9 TeV (4.5 TeV) for constructive (destructive) interference in the left-left isoscalar compositeness model. These limits are the most stringent to date for μμqq contact interactions.

ATLAS Collaboration, ABDELALIM ALY, Ahmed Aly (Collab.), et al . Search for contact

interactions in dimuon events from pp collisions at √s=7 TeV with the ATLAS detector. Physical Review. D , 2011, vol. 84, no. 01, p. 011101

DOI : 10.1103/PhysRevD.84.011101

Available at:

http://archive-ouverte.unige.ch/unige:41125

Disclaimer: layout of this document may differ from the published version.

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Search for contact interactions in dimuon events from pp collisions at ffiffiffi

p s

¼ 7 TeV with the ATLAS detector

G. Aadet al.* (ATLAS Collaboration)

(Received 22 April 2011; published 1 July 2011)

A search for contact interactions has been performed using dimuon events recorded with the ATLAS detector in proton-proton collisions at ffiffiffi

ps

¼7 TeV. The data sample corresponds to an integrated luminosity of 42 pb¹. No significant deviation from the standard model is observed in the dimuon mass spectrum, allowing the following 95% C.L. limits to be set on the energy scale of contact interactions:>4:9 TeV(4.5 TeV) for constructive (destructive) interference in the left-left isoscalar compositeness model. These limits are the most stringent to date forqqcontact interactions.

DOI:10.1103/PhysRevD.84.011101 PACS numbers: 12.60.Rc, 13.85.Qk, 14.70.Pw

Phenomena beyond the standard model (SM), such as large extra spatial dimensions [1] or quark/lepton compositeness [2], may be described as a four-fermion contact interaction (CI) in the low energy limit. Such an approach is similar to that used by Fermi to describe nucleardecay [3] long before the discovery of the W boson. One can describe a new interaction at a higher energy scale with an effective Lagrangian of the form [2]

L ¼ g²

2²½LLcLcLcLcL

þ_RRcRcRcRcR

þ2_LRcLcLcRcR; (1) wheregis a coupling constant,is the energy scale below which fermion constituents are bound (in the context of compositeness models), and cL;R are left-handed and right-handed fermion fields, respectively. The scale is defined by the choices g²=4¼1 and _LL, _LR, _RR¼ 1. Different choices of the parameters _LL, _LR, and_RR determine the helicity structure of the new interaction. For example, the analysis presented in this paper applies specifically to the left-left isoscalar model (LLIM) commonly used as a benchmark for contact interaction searches [4]. This model is defined by setting_LL ¼ 1and_LR¼_RR ¼0. With the introduction of a contact interaction, the differential cross section for the pro- cessqq!^þbecomes

d

dm ¼ d_DY

dm_LLF_IðmÞ

² þF_CðmÞ ⁴ ; (2)

wheremis the final-state dimuon mass. The expression above includes a SM Drell-Yan (DY) term, as well as DY-CI interference (F_I) and pure contact interaction (F_C) terms (see Ref. [5] for a detailed expression). The DY term here incorporates both photon andZ⁰boson contributions.

At the largest values that this analysis is sensitive to, both interference and pure contact interaction terms play a significant role.

This paper presents the results of a search for contact interactions in the dimuon channel, taking advantage of the highppcollision energy of the LHC and the capabilities of ATLAS to detect and measure muons. The search strategy focuses on identifying a deviation from the SM in the dimuon mass spectrum, which is expected to be dominated by the DY process. Contributions from a new interaction would undergo either constructive (_LL¼ 1) or destructive (_LL¼ þ1) interference with the DY contribution. If present, a signal would result in a broad deviation from the SM expectation rather than a peak in the mass spectrum.

Given current experimental bounds on(see below), such a deviation would appear at masses well above the Z⁰ boson peak. Therefore, the measurement requires excellent muon identification and reconstruction at high momentum.

A separate paper presents the results of a search for new heavy resonances in the dimuon mass spectrum [6].

Previous searches for contact interactions have been carried out in neutrino scattering [7], as well as at electron-positron [8–11], electron-proton [12,13], and hadron colliders [14–22]. For the channel under study, the best limits in the LLIM are >4:2 TeV for constructive interference and ^þ>2:9 TeV for destructive interference, at 95% C.L. [14].

ATLAS is a multipurpose particle detector [23] designed for physics at the TeV scale. Charged particle tracking is provided by an inner detector consisting of a pixel detector, a silicon-strip tracker, and a transition radiation tracker, immersed in a 2 T solenoidal magnetic field. A high-granularity liquid-argon electromagnetic calorimeter surrounds the solenoid. Hadron calorimetry is provided by

*

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

PHYSICAL REVIEW D84,011101(R) (2011)

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an iron-scintillator tile calorimeter in the central rapidity range and a liquid-argon calorimeter in the end cap and forward rapidity range. A key detector component for this analysis is the muon spectrometer, which is designed to identify muons and measure both their trajectories and momenta with high accuracy: the design momentum resolution is 10% at momenta transverse to the beam line (p_T) of 1 TeV. The muon spectrometer comprises three toroidal magnet systems consisting of eight coils each with a bend- ing powerR

Bd‘¼1–7:5 Tm, a trigger system consisting of both resistive plate chambers and thin-gap chambers, and a set of precision monitored drift tubes and cathode strip chambers with a single-hit spatial resolution better than 100m to accurately measure muon curvature.

Precision chambers are continuously monitored by an optical alignment system designed to determine relative chamber positions to an accuracy of50mor better.

The data sample for this analysis was collected during LHC operations in 2010 and corresponds to a total integrated luminosity of 42 pb¹ collected with stable beam conditions and fully operational inner detector and muon spectrometer systems. Events with muons were selected by requiring the presence of at least one high-momentum muon passing all three rejection levels of the muon trigger system. Thep_T threshold was initially set to 10 GeV but was raised to 13 GeV in the later parts of the data taking due to increasing luminosity.

This analysis follows the same event selection as the search for new heavy resonances. A summary is provided below; see Ref. [6] for a more complete description. Events with a good primary vertex are selected to suppress cosmic-ray events. Muon tracks reconstructed indepen- dently in the inner detector and muon spectrometer are combined with a fit to all associated hits, taking the energy loss in the calorimeter into account. The energy loss estimate uses either the parametrized expected energy loss or the energy measured in the calorimeter if this energy significantly exceeds the most probable energy loss. The combined tracks are required to have hits in all inner detector tracking systems, at least one hit in the nonbend- ing plane, and at least three hits in each of the inner, middle, and outer precision chambers of the muon spectrometer. Tracks passing through poorly aligned chambers are rejected. The above hit requirements guarantee a reli- able momentum measurement and good modeling by the detector simulation. Muon tracks are required to have p_T>25 GeV, pseudorapidityjj<2:4[24] to be within the acceptance of the inner detector tracking and muon spectrometer trigger systems, and a relative track isolation Ppⁱ_T=p_T<0:05, where the sum is over all inner detector tracksi within aR¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

²þ²

p cone of 0.3 around

the muon trajectory, to suppress backgrounds from heavy flavor decays. Additional requirements are placed on the impact parameter of the muon track to reduce cosmic-ray backgrounds to a negligible level. Finally, dimuon candi-

dates are formed from all pairs of opposite-charge muons satisfying the above criteria, and the mass of those pairs is required to be greater than 70 GeV. There are 7743 dimuon events passing all selection requirements.

Drell-Yan,Wþjets, and multijet events were generated with PYTHIA6.421 [25] and MRST2007LO* parton distribution functions (PDFs) [26]. Diboson (WW,WZ, andZZ) events were produced with HERWIG 6.510 [27] and

MRST2007 LO* PDFs. In the case of tt, events were generated with MC@NLO 3.41 [28] to compute matrix elements, JIMMY 4.31 [29] to simulate the underlying event, HERWIG 6.510 to model parton showering and ha- dronization, and CTEQ 6.6 [30] for PDFs. For signal samples, PYTHIA 6.421 was used to produce the DY and CI processes simultaneously in order to properly account for the interference between the two processes. A mass- dependent QCD K factor corresponding to the ratio between next-to-next-to-leading order [31] andPYTHIALO*

DY differential cross sections was applied to these signal samples as well as pure DY samples. Similarly, a mass- dependent electroweakKfactor was applied to account for higher order electroweak effects due to virtual gauge boson loops [32]. This correction was only applied to the DY cross section since the new physics included in the CI term has unknown couplings to SM gauge bosons. Implicitly, higher order electroweak corrections to the new interaction are included in the value of. The QCD (electroweak)K factor varies between 1.16 (1.04) at low dimuon mass and 0.86 (0.85) at a mass of 2 TeV. The response of the ATLAS detector to these generated event samples was simulated withGEANT 4[33,34].

Figure 1 shows the dimuon mass distribution for all selected events along with the predicted contributions

(GeV)

µ

mµ

8010² 2×10² 10³ 2×10³

Events / bin

10-2

10-1

1 10 102

103

104

105

Data 2010 µ µ

→ DY Diboson

t t W + jets

= 3 TeV Λ-

= 5 TeV Λ-

= 5 TeV Λ+

(GeV)

µ

mµ

8010² 2×10² 10³ 2×10³

Events / bin

10-2

10-1

1 10 102

103

104

105

ATLAS L dt = 42 pb-1

∫

= 7 TeV s

FIG. 1 (color online). Dimuon invariant mass distribution for data (points) and Monte Carlo simulations (histograms). The red (blue) line corresponds to the distribution expected in the presence of contact interactions with ¼3 TeV (5 TeV) for constructive interference. The dashed blue line corresponds to ^þ¼5 TeVfor destructive interference.

G. AADet al. PHYSICAL REVIEW D84,011101(R) (2011)

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from SM processes and CI for selected values.

Predictions for the various background processes are ex- tracted from the Monte Carlo (MC) simulation. Besides the dominant DY contribution, we also account for a small dimuon yield from ttand diboson production. The small predicted yield fromtthas been confirmed in the data by selecting events with high-mass electron-muon pairs (see Ref. [6]). Backgrounds fromW production are effectively suppressed by requiring two selected muons in the event.

Likewise, multijet backgrounds are reduced to a negligible amount (<0:1events in the selected sample) by the muon p_T and isolation requirements.

TableIpresents the number of events in different bins of dimuon mass for data and MC simulation. The sum of MC predictions is normalized to the number of data events in theZ⁰peak mass region between 70 and 110 GeV. It should be noted that, prior to normalization, data and MC event yields agree within the uncertainty in the integrated luminosity. This normalization procedure removes sensitivity to mass-independent uncertainties such as the luminosity uncertainty. The overall acceptance of the selection is estimated to be 36% for simulated DY events in the signal region defined bym>150 GeV.

To estimate the level of agreement between the observed mass spectrum and the SM prediction, a large ensemble of SM-only pseudoexperiments was generated. For each such pseudoexperiment, a binned likelihood was computed to quantify the deviation from the SM expectation. In 56% of these pseudoexperiments, the deviation was found to be more significant than that observed in the data for the signal region, indicating good consistency between the data and the predicted spectrum. This level of agreement is illustrated in Fig.2, which shows the number of events above a minimum mass m^min. Since no significant deviation is observed in the dimuon mass spectrum, we proceed with setting a limit on the energy scaleusing a Bayesian method. Here, the prior probability distribution is chosen to be flat in 1=², motivated by the form of Eq. (2).

Systematic uncertainties are incorporated in the limit setting by treating them as nuisance parameters () that are marginalized in the calculation of the posterior probability P. The 95% confidence level limit is then obtained by finding the value lim that satisfies R _lim

0 Pð jn; Þd ¼ 0:95, where ¼1=²andnrepresents the observed number of events in the mass bins above 150 GeV, with bin boundaries as defined in Table I. Table II shows the expected number of events in each mass bin within the signal

TABLE I. Expected and observed number of events in the dimuon channel. The errors quoted originate from the limited MC statistics.

m(GeV) 70–110 110–130 130–150 150–170 170–200 200–240

DY 75477 98:40:8 33:40:5 17:20:3 12:80:3 7:80:2

tt 6:00:2 2:40:1 1:70:1 1:240:04 1:220:03 1:030:03

Diboson 10:10:1 0:80:1 0:560:04 0:480:04 0:410:03 0:280:03

Wþjets 0:140:08 <0:05 <0:05 <0:05 <0:05 <0:05

Total 75637 101:60:8 35:70:5 18:90:3 14:40:3 9:10:2

Data 7563 101 41 11 11 7

m(GeV) 240–300 300–400 400–550 550–800 800–1200 1200–2000

DY 5:050:11 2:490:04 0:990:01 0:290:01 0:060:01 <0:05

tt 0:730:02 0:370:01 0:110:01 <0:05 <0:05 <0:05

Diboson 0:240:02 0:160:02 0:060:01 <0:05 <0:05 <0:05

Wþjets <0:05 <0:05 <0:05 <0:05 <0:05 <0:05

Total 6:020:11 3:030:05 1:160:02 0:330:01 0:070:01 <0:05

Data 6 2 0 1 0 0

(GeV)

minµ

mµ

8010² 2×10² 10³ 2×10³

min µµNumber of events above m

10-2

10-1

1 10 102

103

104

105

106

(GeV)

minµ

mµ

2 2

×10

2 ³ × ³

µ

-2 -1

1

2 3 4 5 6

Data 2010

Standard Model Λ^- = 3 TeV = 4 TeV Λ-

= 5 TeV Λ-

= 3 TeV Λ+

= 4 TeV Λ+

= 5 TeV Λ+

ATLAS L dt = 42 pb-1

∫

= 7 TeV s

FIG. 2 (color online). Distribution of the number of events with dimuon mass abovem^minfor data (points) and Monte Carlo simulations (histograms). The SM prediction is shown as the shaded grey histogram, whereas the solid (dashed) histograms correspond to the expected distributions in the presence of contact interactions with various scalesfor constructive (destructive) interference.

SEARCH FOR CONTACT INTERACTIONS IN DIMUON. . . PHYSICAL REVIEW D84,011101(R) (2011)

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region for different scales, as used in the calculation of the posterior probability.

Systematic errors are of both theoretical and experimental origins. Because the expected event yields are normalized to the Z⁰ peak region, only momentum- or mass-dependent uncertainties are relevant. Theoretical uncertainties include PDF variations evaluated using the

MSTW2008PDF error set [35] in the absence of a full error set for theMRST2007 LO* PDF. This choice leads to con- servative uncertainties in the event yields that grow from 3% at theZ⁰pole to 6% (9%) at a mass of 1 TeV (1.5 TeV).

A cross-check was made by computing cross sections for both MSTW2008 and CTEQ 6.6 PDFs for a wide range of dimuon masses. Differences between the two choices of PDFs were always found to be smaller than the assigned uncertainty obtained from the MSTW2008 PDF set. The QCD K factor uncertainty in the DY and DYþCIcross sections is taken to be the difference between next-to-next- to-leading order and next-to-leading order DY cross sections as a function of dimuon mass. The electroweak K factor uncertainty in the DY cross section is taken to be the entire magnitude of the correction relative to the LO cross section. Uncertainties in the QCD (electroweak)K factor are mass dependent; for example, they amount to 3.0%

(4.5%) at a mass of 1 TeV. Uncertainties in thett, diboson, andWþjets cross sections have a negligible impact on the limit. Finally, the statistical error of the DYþCI MC (shown in TableII) is included as a source of systematic error and has the largest effect on the limits.

The MC simulation is used to determine all acceptance and efficiency effects. Therefore, detailed comparisons between data and Monte Carlo simulation were performed to make sure that the simulation models the data well for our choice of muon track selection criteria, especially at higherp_T. Experimental uncertainties arise from the slight p_T dependence of muon efficiencies and from the impact of the intrinsic detector spatial resolution on the momentum resolution. At transverse momenta above 200 GeV, radiative losses due to bremsstrahlung in the detector material begin to affect the muon track pattern recognition.

An uncertainty of 3% per TeV is assigned to the muon efficiency to conservatively account for the small p_T dependence predicted by the simulation. Muon momentum resolution at highp_T is most affected by the quality of the muon spectrometer alignment. The latter has been studied with high-momentum cosmic-ray muons traversing the center of the detector. It has also been studied in collision data with muons passing through detector regions with overlapping muon spectrometer chambers, thereby provid- ing independent track fits from the redundant sets of hits in neighboring chambers and allowing the impact of the alignment of adjacent detector regions to be measured.

Curvature smearing parameters derived from these studies are found to be ðq=pTÞ ¼0:180:04 TeV¹ for jj<2:0andðq=p_TÞ ¼0:70:2 TeV¹ for jj>2:0, whereqis the charge of the muon track. These parameters reflect the current level of understanding of the detector alignment and are expected to decrease with further data taking. We take the full magnitude of these smearing corrections as the systematic uncertainty in the momentum resolution. Comparison of the inclusive muon momentum spectrum between data and MC simulation does not show evidence for significant non-Gaussian tails in the data.

Using the Bayesian method described above, the expected 95% C.L. lower limits on the scaleare found to be5:10:3 TeVand4:80:3 TeVfor constructive and destructive interference, respectively. The quoted uncertainty range is estimated with a large set of pseudoexperiments and corresponds to a 68% range around the median value of all the limits obtained from those pseudoexperiments. Systematic errors are already folded into the limit setting procedure and result in a decrease of the limit by about 0.1 TeV. The dominant source of uncertainty origi- nates from the limited signal MC statistics. For the selected data sample, we set the following limits at 95% C.L.:

>4:9 TeV for constructive interference and ^þ>

4:5 TeV for destructive interference in the LLIM with a prior flat in 1=². These values are compatible with the expected limits. If a prior flat in1=⁴is chosen, both limits decrease by 0.3 TeV.

TABLE II. Expected number of events in the signal region of the analysis for various contact interaction scales with constructive () and destructive (^þ) interference. The errors quoted originate from the limited MC statistics.

m(GeV) 150–170 170–200 200–240 240–300 300–400 400–550 550–800 800–1200 1200–2000 ¼3 TeV 19:10:5 15:70:4 11:20:4 8:50:3 7:90:3 6:00:3 6:50:3 5:10:2 3:00:2 ¼4 TeV 18:80:4 14:30:4 10:00:3 6:50:2 5:00:2 3:00:2 2:30:2 1:450:12 1:080:09 ¼5 TeV 17:40:4 14:30:4 9:40:3 6:20:2 4:30:2 1:950:13 1:290:11 0:720:08 0:360:06 ¼7 TeV 17:30:4 13:80:4 9:30:3 6:30:2 3:30:2 1:260:10 0:580:07 0:210:04 0:110:03 ^þ¼2 TeV 21:60:6 19:30:6 15:80:5 15:20:5 21:20:6 21:60:6 25:50:6 21:40:6 15:10:5 ^þ¼3 TeV 18:60:4 15:20:4 10:10:3 7:20:3 5:50:2 4:60:2 5:30:2 4:30:2 3:10:2 ^þ¼4 TeV 18:20:4 14:30:4 8:80:3 6:10:2 3:60:2 2:100:14 1:590:12 1:520:12 0:840:08 ^þ¼5 TeV 18:50:4 13:60:3 8:80:3 5:40:2 2:90:2 1:610:12 0:880:09 0:530:07 0:280:05

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To conclude, a search for contact interactions has been carried out in a sample of dimuon events recorded by the ATLAS detector inppcollisions from the LHC at ffiffiffi

ps

¼ 7 TeV. No significant deviation from the standard model is observed in the dimuon mass spectrum obtained from a data sample corresponding to an integrated luminosity of 42 pb¹. Limits placed on the energy scaleare the most stringent to date forqqcontact interactions.

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

We acknowledge the support of ANPCyT, Argentina;

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

ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC, and CFI, Canada; CERN;

CONICYT, Chile; CAS, MOST, and NSFC, China;

COLCIENCIAS, Colombia; MSMT CR, MPO CR, and VSC CR, Czech Republic; DNRF, DNSRC, and Lundbeck Foundation, Denmark; ARTEMIS, European Union;

IN2P3-CNRS, CEA-DSM/IRFU, France; GNAS,

Georgia; BMBF, DFG, HGF, MPG, and AvH Foundation, Germany; GSRT, Greece; ISF, MINERVA, GIF, DIP, and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW, Poland; GRICES and FCT, Portugal; MERYS (MECTS), Romania; MES of Russia and ROSATOM, Russian Federation; JINR;

MSTD, Serbia; MSSR, Slovakia; ARRS and MVZT, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SER, SNSF, and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan;

TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; and DOE and NSF, USA. 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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C. F. Anders,²⁰K. J. Anderson,³⁰A. Andreazza,^89a,89bV. Andrei,^58aM-L. Andrieux,⁵⁵X. S. Anduaga,⁷⁰ A. Angerami,³⁴F. Anghinolfi,²⁹N. Anjos,^124aA. Annovi,⁴⁷A. Antonaki,⁸M. Antonelli,⁴⁷S. Antonelli,^19a,19b A. Antonov,⁹⁶J. Antos,^144bF. Anulli,^132aS. Aoun,⁸³L. Aperio Bella,⁴R. Apolle,¹¹⁸G. Arabidze,⁸⁸I. Aracena,¹⁴³

Y. Arai,⁶⁶A. T. H. Arce,⁴⁴J. P. Archambault,²⁸S. Arfaoui,^29,dJ-F. Arguin,¹⁴E. Arik,^18a,aM. Arik,^18a A. J. Armbruster,⁸⁷O. Arnaez,⁸¹C. Arnault,¹¹⁵A. Artamonov,⁹⁵G. Artoni,^132a,132bD. Arutinov,²⁰S. Asai,¹⁵⁵ R. Asfandiyarov,¹⁷²S. Ask,²⁷B. A˚ sman,^146a,146bL. Asquith,⁵K. Assamagan,²⁴A. Astbury,¹⁶⁹A. Astvatsatourov,⁵²

G. Atoian,¹⁷⁵B. Aubert,⁴B. Auerbach,¹⁷⁵E. Auge,¹¹⁵K. Augsten,¹²⁷M. Aurousseau,^145aN. Austin,⁷³ R. Avramidou,⁹D. Axen,¹⁶⁸C. Ay,⁵⁴G. Azuelos,^93,eY. Azuma,¹⁵⁵M. A. Baak,²⁹G. Baccaglioni,^89a C. Bacci,^134a,134bA. M. Bach,¹⁴H. Bachacou,¹³⁶K. Bachas,²⁹G. Bachy,²⁹M. Backes,⁴⁹M. Backhaus,²⁰

E. Badescu,^25aP. Bagnaia,^132a,132bS. Bahinipati,²Y. Bai,^32aD. C. Bailey,¹⁵⁸T. Bain,¹⁵⁸J. T. Baines,¹²⁹ O. K. Baker,¹⁷⁵M. D. Baker,²⁴S. Baker,⁷⁷F. Baltasar Dos Santos Pedrosa,²⁹E. Banas,³⁸P. Banerjee,⁹³ Sw. Banerjee,¹⁶⁹D. Banfi,²⁹A. Bangert,¹³⁷V. Bansal,¹⁶⁹H. S. Bansil,¹⁷L. Barak,¹⁷¹S. P. Baranov,⁹⁴A. Barashkou,⁶⁵ A. Barbaro Galtieri,¹⁴T. Barber,²⁷E. L. Barberio,⁸⁶D. Barberis,^50a,50bM. Barbero,²⁰D. Y. Bardin,⁶⁵T. Barillari,⁹⁹ M. Barisonzi,¹⁷⁴T. Barklow,¹⁴³N. Barlow,²⁷B. M. Barnett,¹²⁹R. M. Barnett,¹⁴A. Baroncelli,^134aA. J. Barr,¹¹⁸

F. Barreiro,⁸⁰J. Barreiro Guimara˜es da Costa,⁵⁷P. Barrillon,¹¹⁵R. Bartoldus,¹⁴³A. E. Barton,⁷¹D. Bartsch,²⁰ V. Bartsch,¹⁴⁹R. L. Bates,⁵³L. Batkova,^144aJ. R. Batley,²⁷A. Battaglia,¹⁶M. Battistin,²⁹G. Battistoni,^89a F. Bauer,¹³⁶H. S. Bawa,^143,fB. Beare,¹⁵⁸T. Beau,⁷⁸P. H. Beauchemin,¹¹⁸R. Beccherle,^50aP. Bechtle,⁴¹H. P. Beck,¹⁶ M. Beckingham,⁴⁸K. H. Becks,¹⁷⁴A. J. Beddall,^18cA. Beddall,^18cS. Bedikian,¹⁷⁵V. A. Bednyakov,⁶⁵C. P. Bee,⁸³

M. Begel,²⁴S. Behar Harpaz,¹⁵²P. K. Behera,⁶³M. Beimforde,⁹⁹C. Belanger-Champagne,¹⁶⁶P. J. Bell,⁴⁹ W. H. Bell,⁴⁹G. Bella,¹⁵³L. Bellagamba,^19aF. Bellina,²⁹M. Bellomo,^119aA. Belloni,⁵⁷O. Beloborodova,¹⁰⁷ K. Belotskiy,⁹⁶O. Beltramello,²⁹S. Ben Ami,¹⁵²O. Benary,¹⁵³D. Benchekroun,^135aC. Benchouk,⁸³M. Bendel,⁸¹

B. H. Benedict,¹⁶³N. Benekos,¹⁶⁵Y. Benhammou,¹⁵³D. P. Benjamin,⁴⁴M. Benoit,¹¹⁵J. R. Bensinger,²² K. Benslama,¹³⁰S. Bentvelsen,¹⁰⁵D. Berge,²⁹E. Bergeaas Kuutmann,⁴¹N. Berger,⁴F. Berghaus,¹⁶⁹E. Berglund,⁴⁹ J. Beringer,¹⁴K. Bernardet,⁸³P. Bernat,⁷⁷R. Bernhard,⁴⁸C. Bernius,²⁴T. Berry,⁷⁶A. Bertin,^19a,19bF. Bertinelli,²⁹ F. Bertolucci,^122a,122bM. I. Besana,^89a,89bN. Besson,¹³⁶S. Bethke,⁹⁹W. Bhimji,⁴⁵R. M. Bianchi,²⁹M. Bianco,^72a,72b

O. Biebel,⁹⁸S. P. Bieniek,⁷⁷J. Biesiada,¹⁴M. Biglietti,^134a,134bH. Bilokon,⁴⁷M. Bindi,^19a,19bS. Binet,¹¹⁵ A. Bingul,^18cC. Bini,^132a,132bC. Biscarat,¹⁷⁷U. Bitenc,⁴⁸K. M. Black,²¹R. E. Blair,⁵J.-B. Blanchard,¹¹⁵ G. Blanchot,²⁹T. Blazek,^144aC. Blocker,²²J. Blocki,³⁸A. Blondel,⁴⁹W. Blum,⁸¹U. Blumenschein,⁵⁴ G. J. Bobbink,¹⁰⁵V. B. Bobrovnikov,¹⁰⁷S. S. Bocchetta,⁷⁹A. Bocci,⁴⁴C. R. Boddy,¹¹⁸M. Boehler,⁴¹J. Boek,¹⁷⁴

N. Boelaert,³⁵S. Bo¨ser,⁷⁷J. A. Bogaerts,²⁹A. Bogdanchikov,¹⁰⁷A. Bogouch,^90,aC. Bohm,^146aV. Boisvert,⁷⁶ T. Bold,^163,gV. Boldea,^25aN. M. Bolnet,¹³⁶M. Bona,⁷⁵V. G. Bondarenko,⁹⁶M. Boonekamp,¹³⁶G. Boorman,⁷⁶

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M. D. M. Capeans Garrido,²⁹I. Caprini,^25aM. Caprini,^25aD. Capriotti,⁹⁹M. Capua,^36a,36bR. Caputo,¹⁴⁸ C. Caramarcu,^25aR. Cardarelli,^133aT. Carli,²⁹G. Carlino,^102aL. Carminati,^89a,89bB. Caron,^159aS. Caron,⁴⁸

G. D. Carrillo Montoya,¹⁷²A. A. Carter,⁷⁵J. R. Carter,²⁷J. Carvalho,^124a,hD. Casadei,¹⁰⁸M. P. Casado,¹¹ M. Cascella,^122a,122bC. Caso,^50a,50b,aA. M. Castaneda Hernandez,¹⁷²E. Castaneda-Miranda,¹⁷²

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T. Frank,¹⁷¹M. Franklin,⁵⁷S. Franz,²⁹M. Fraternali,^119a,119bS. Fratina,¹²⁰S. T. French,²⁷R. Froeschl,²⁹ D. Froidevaux,²⁹J. A. Frost,²⁷C. Fukunaga,¹⁵⁶E. Fullana Torregrosa,²⁹J. Fuster,¹⁶⁷C. Gabaldon,²⁹O. Gabizon,¹⁷¹ T. Gadfort,²⁴S. Gadomski,⁴⁹G. Gagliardi,^50a,50bP. Gagnon,⁶¹C. Galea,⁹⁸E. J. Gallas,¹¹⁸M. V. Gallas,²⁹V. Gallo,¹⁶

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Ch. Geich-Gimbel,²⁰K. Gellerstedt,^146a,146bC. Gemme,^50aA. Gemmell,⁵³M. H. Genest,⁹⁸S. Gentile,^132a,132b M. George,⁵⁴S. George,⁷⁶P. Gerlach,¹⁷⁴A. Gershon,¹⁵³C. Geweniger,^58aH. Ghazlane,^135bP. Ghez,⁴ N. Ghodbane,³³B. Giacobbe,^19aS. Giagu,^132a,132bV. Giakoumopoulou,⁸V. Giangiobbe,^122a,122bF. Gianotti,²⁹

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