Search for a Light Pseudoscalar Higgs Boson in the Dimuon Decay Channel in pp Collisions at ffiffiffi
p s
¼ 7 TeV
S. Chatrchyan et al.*
(CMS Collaboration)
(Received 27 June 2012; published 20 September 2012)
The dimuon invariant mass spectrum is searched in the range between 5.5 and 14 GeV for a light pseudoscalar Higgs boson a, predicted in a number of new physics models, including the next-to-minimal supersymmetric standard model. The data sample used in the search corresponds to an integrated luminosity of 1:3 fb1 collected in pp collisions at pffiffiffis
¼ 7 TeV with the CMS detector at the LHC.
No excess is observed above the background predictions and upper limits are set on the cross section times branching fraction Bðpp ! a ! þÞ in the range of 1.5–7.5 pb. These results improve on existing bounds on the ab b coupling for ma< mð1SÞand are the first significant limits for ma> mð3SÞ. Constraints on the supersymmetric parameter space are presented in the context of the next-to-minimal model.
DOI:10.1103/PhysRevLett.109.121801 PACS numbers: 14.80.Da, 13.85.Qk
Low energy supersymmetry is an elegant solution to the hierarchy problem that arises in the standard model, pro- vides a candidate for dark matter, and allows for the uni- fication of gauge couplings at the grand-unified-theory scale [1–5]. However, the minimal supersymmetric model (MSSM) has an ad hoc Higgs superfield mixing parameter () and requires very large masses for the supersymmetric partner of the top quark (stop) in order for the lightest CP-even Higgs boson to be heavier than 122 GeV without large stop mixing [6]. Both problems are solved in the next-to MSSM (NMSSM) (a review can be found in Ref. [7]), which extends the MSSM by introducing a complex singlet superfield which necessarily contains a scalar field component. Associated super- and scalar- potential terms generate an effective parameter and easily raise the mass of the light Higgs boson without requiring a heavy stop [8,9]. The added scalar field ex- pands the Higgs sector to three CP-even scalars (h1;h2;h3), two CP-odd scalars (a1; a2), and two charged scalars (Hþ; H). The a1is a superposition of the MSSM doublet pseudoscalar (aMSSM) and the additional singlet pseudo- scalar of the NMSSM (aS): a1 ¼ cosAaMSSMþ sinAaS, where A is the mixing angle. The NMSSM has two symmetries that, if imposed (e.g., at the grand-unified- theory scale), imply that small ma1, even ma1<2mB(where mBis the B meson mass), andjcosAj 1 are very natural possibilities [10]. However, the reduced couplings Ca1b b¼ Ca1þ¼ Ca1þ¼ tancosA can be sizeable for large values of tan, the ratio of neutral Higgs field vacuum
expectation values, even if cosA is small. More generally, superstring modeling suggests the possibility of many light a particles, at least some of which couple to þ, þ, and b b [11]. In the following, a (a1) denotes a general (NMSSM) light pseudoscalar Higgs boson.
Searches for a light a are mainly sensitive to Cab b [12,13]. For ma< mð3SÞ, the strongest constraints on Cab b are those from BABAR [14,15]. For ma> mð3SÞ, only the Tevatron and Large Hadron Collider (LHC) have sensitivity [16], using production via gg! a, where the coupling Cab b derives from quark (especially bottom and top) triangle loops. This process, plus higher-order corrections, leads to a large cross section due to the large gg parton luminosity at small gluon momentum fractions, provided the Cab b(q¼ t; b in particular) couplings are not too suppressed. This large cross section will typically lead to a significant number of gg! a ! þ events even thoughBða ! þÞ is small.
In the NMSSM context, where Ca1b b¼ tan cosA, the existing limits [17,18] translate to rather modest limits on j cosAj. Such bounds do not strongly constrain NMSSM models of interest for possibly hiding a light Higgs boson because of h! aa decays (with a ! 2, 2g, 2c, 2s decays being dominant [19]) that are not excluded by large electron-positron (LEP) collider experiments [20,21].
At tree level, the branching fraction for a! þ depends on ma and on tan, but not on cosA [16]. It is nearly constant for ma> 5 GeV and ranges from 103to 4 103for tan¼ 1 to tan ¼ 50, changing very little once tan > 2. In contrast, ðgg ! aÞ increases rapidly with tan due to the fact that Cab b/ tan. However, top- quark loop contributions and higher-order corrections im- ply a slower ðgg ! aÞ increase than tan2. In the context of the NMSSM, all q q couplings of the a1are proportional to cosA, implying that ðgg ! a1Þ / cos2A.
*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.
This Letter presents the results of a search in pp colli- sions for a light a with a mass near the resonances decaying into two oppositely charged muons. Data used for this analysis were recorded by the Compact Muon Solenoid (CMS) detector in pp collisions at a center- of-mass energy of 7 TeV, between August and November 2011. The sample corresponds to a total integrated lumi- nosity of 1:3 fb1, collected with a dedicated trigger. As estimated in Ref. [16] and explicitly demonstrated here, CMS has sensitivity beyond the BABAR and CDF limits, for the latter due to the higher production yield [LHCðpp ! aÞ 4:5Tevatronðp p ! aÞ] and the higher acceptance and efficiency of the muon detector.
Furthermore, the CMS analysis can extend the limits into the ma> mð3SÞmass range.
The central feature of the CMS detector is a supercon- ducting solenoid, of 6 m internal diameter, providing a magnetic field of 3.8 T. Within the field volume are the silicon pixel and strip tracker, the crystal electromagnetic calorimeter, and the brass-scintillator hadron calorimeter.
Muons are measured by gas-ionization detectors em- bedded in the steel return yoke in the pseudorapidity range jj < 2:4, ( ln½tanð=2Þ, where is the polar angle of the trajectory of a particle with respect to the direction of the counterclockwise proton beam) using three detector technologies: drift tubes (DT) (for the range jj < 1:2), resistive plate chambers (RPC) (forjj < 1:6) and cathode strip chambers (CSC) (for 0:9 <jj < 2:4). The DT and RPC are indicated as the central ‘‘barrel’’ while the CSC comprises the ‘‘end caps.’’ A more detailed description of the CMS detector can be found in [22].
We search the dimuon invariant mass distribution be- tween 5.5 and 8.8 GeV (defined as ‘‘mass range 1’’) and between 11.5 and 14 GeV (‘‘mass range 2’’) for a narrow resonance a, with a decay widthMeV, which is natural in the NMSSM context. We avoid the range between 9 and 11 GeV because the abundant contributions of the botto- monium resonances to the mass spectrum makes this search unfeasible. Selection criteria are applied to reduce backgrounds from the QCD continuum, and we perform a mass scan in mass ranges 1 and 2 to determine a potential contribution from an a signal. Given the better mass reso- lution in the barrel part of the detector than in the end caps, we also separate the mass scan into two acceptance re- gions, based on the dimuon , in order to improve the sensitivity.
We analyze events collected with an online selection that requires the detection of two opposite-sign muons with transverse momenta pT> 3:5 GeV and additional require- ments imposed at the high level trigger (HLT). All three muon systems, DT, CSC, and RPC, take part in the trigger decision. A good primary vertex is also required, as defined in Ref. [23]. The additional HLT requirements include pTðþÞ > 6 GeV, 5:5 < mþ< 14 GeV, and a dis- tance of the closest approach of the muon tracks to the
beam axis compatible with that expected for prompt decays. A prescale factor of 2 was imposed on the trigger to maintain a reasonable trigger rate.
The main backgrounds arise from QCD processes and, in the lower invariant mass range, from a residual tail of the
ð1SÞ resonance. We determine the background shape in the invariant mass directly from data, and use simulated events as a cross check. Signal samples, QCD, and resonances are simulated with PYTHIA 6.4.24, Tune D6T [24], and CTEQ6 parton distribution functions [25]. Tune Z2 gives compatible results. As the NMSSM is not fully implemented in PYTHIA, we generate the MSSM pseudo- scalar A boson in the mass range of 5.5 to 14 GeV and require dimuon decays. These samples also contain a simulation of the effects on the number of primary vertices from overlapping pp interactions in the same bunch crossing.
To select the best dimuon candidate in each event, quality criteria are applied to the tracks which reject mis- identified muons and muons from kaon and pion decays.
Muons are required to be within the geometrical accep- tance (jj 2:4) and to be in the plateau of the trigger efficiency, with pT> 5:5 GeV. Muon tracks are required to have at least 11 hits in the silicon tracker, at least one of which must be in the pixel detector, and a track fit
2=dof < 1:8. This value is chosen to maximize the signal significance with respect to the QCD continuum, which is extracted directly from data.
Isolation requirements suppress misidentified leptons from jets and nonprompt muons from hadron decays.
Muons are required to be isolated within a cone of radius
R¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðÞ2þ ðÞ2
p ¼ 0:3 around the muon direction, where is the azimuthal angle. The muon isolation, Irel, is defined as the sum of the pT (as measured in the silicon tracker) and transverse energy (as measured in the calo- rimeters) of all objects within this cone (excluding the muon itself), divided by the muon as measured by the tracker. We require Irel< 0:2. This requirement is opti- mized by comparing the simulated a signal with opposite-sign dimuons from data, and we verify that this value is appropriate for both the barrel and end cap dimuon pairs. This isolation requirement rejects a large fraction of the background arising from the QCD production of jets.
Dimuon candidates consist of two opposite-sign muons [26] with an invariant mass between 5.5 and 14 GeV. If more than one dimuon candidate is present, that with the highest 2probability associated to the kinematic fit of the dimuon vertex is retained.
The invariant mass spectrum in the search range has two main contributions: the QCD continuum and the bottomo- nium resonances. To characterize these shapes for use in the mass scan, we perform a binned maximum likelihood fit to the total invariant mass distribution. For the QCD continuum, we use a first-order polynomial probability density function (PDF). Each resonance is parametrized
via a double Crystal Ball (CB) function [27,28]. The resolution of one of the CB functions is left free in the fit but is constrained to be the same for all the three reso- nances. The resolution of the second CB function is deter- mined from the fit of the ð1SÞ peak, and forced to scale with the mass of the other two resonances. As the reso- nances overlap, we fit for the presence of all three states simultaneously using three double CB functions. The mean of the CB of the ð1SÞ is left free in the fit to accommodate a possible bias in the momentum scale calibration. The number of free parameters is reduced by fixing the ð2SÞ and ð3SÞ mass differences, relative to ð1SÞ, to their world average values [6].
The fits to the shape and continuum background are performed in the barrel and end cap regions separately, and are shown in Fig.1. The fitted numbers of events are given in Table I; the barrel-end caps ratio for the peaks is consistent with Monte Carlo (MC) predictions. Outside the
peak range, corresponding to the signal search mass ranges, the data are well described by a first-order poly- nomial. Figure 1 also shows hypothetical signals from pseudoscalar Higgs bosons a with masses 7 and 12 GeV, and 2 pb cross sections, scaled by a factor of 10 for visibility. We perform mass scans of the invariant mass spectra, dividing mass range 1 into 110 steps and mass
range 2 into 100 steps of 30 MeV each, and treating the barrel and end cap spectra separately. At each step, we build a signal Gaussian PDF with a mean fixed to the center of the step and a width determined by the mass resolution, use a first-order polynomial to characterize the back- ground, and perform an unbinned maximum likelihood fit to search for a possible contribution from the a. For each signal mass point, we determine the resolution by fitting the a invariant mass spectrum with two CB functions (as for the , the sum of two CB functions better describes the resolution) and the mass resolution is calculated as the weighted average of the widths of the two functions. The resulting dimuon invariant mass resolution ranges from 50 to 120 MeV (90 to 190 MeV) in the barrel (end caps) for the mass range 5.5 to 14 GeV. These agree well with the resolution obtained from the resonances in data and MC simulation. We fit the resolution as a function of mass using the simulated signal samples, and use this to extract the values of the dimuon mass resolution for each mass bin needed in the scan to determine the upper limit.
In mass range 1, we take into account the radiative tail of the ð1SÞ by including its shape determined from the full invariant mass spectrum fit. No significant discrepancy with SM background predictions is observed, and we proceed to set cross section limits, as described below.
The efficiency for the selection is factorized into three contributions, ¼ acc trig sel, where accis the kin- ematic acceptance for the a, trig is the efficiency of the muon trigger, and sel is the efficiency of the selection applied to the dimuon candidates. We use PYTHIA 6 to simulate the a signal and to determine acc. The trigger and selection efficiencies ( trigand sel) are measured with J=c events in data using the tag-and-probe technique [28].
We perform this study in bins of and pT of the probe muon. The efficiency values extracted from data are com- pared with those obtained from the simulation of prompt J=c ! þ. The difference between the efficiency in data and MC simulation is evaluated in bins of pT and and used as a correction to weight the MC events in order to accommodate possible discrepancies. These corrections are typically on the order of a few percent. For each dimuon candidate, the weight is the product of the correc- tions for the two muons.
The isolation requirement efficiency that contributes to sel cannot be measured using the J=c data set as one of the main production mechanisms for J=c is through B-meson decays, resulting in nonisolated muons. This is not well accounted for in simulation, and would result in biased data or MC efficiency corrections. In order to estimate this correction, we use Z! þ events and consider the lower pT spectrum of the probe muon.
The total efficiency is defined for each a mass sample as the fraction of generated signal events, weighted by the appropriate data-MC corrections, that satisfy all the selection requirements. This ranges from 1%–3.5% for the
Events/[0.1 GeV]
103
104 Barrel Data
Total Fit
6 7 8 9 10 11 12 13 14
Events/[0.1 GeV]
103 104
CMS
mµµ[GeV]
7 GeV Signal x10 12 GeV Signal x10
Endcap Data Total Fit 7 GeV Signal x10 12 GeV Signal x10 L = 1.3 fb-1
= 7 TeV s
FIG. 1 (color online). Dimuon invariant mass distribution for the barrel (upper) and end caps (lower) after the event selection.
The invariant mass distributions are fitted accounting for the three resonances and QCD continuum. Hypothetical signals from pseudoscalar Higgs bosons a at 7 and 12 GeV are shown.
TABLE I. Fitted numbers of and continuum background events in the invariant mass range 5.5–14 GeV. The contribu- tions are summed over the three resonances.
Contribution events (barrel) events (end caps)
93 753 396 95 876 454
Continuum 41 210 320 45 792 385
a mass range of 5.5–14 GeV, and we fit the distributions with second (third) order polynomial functions in the barrel (end caps) to use in the mass scan. The increase in the efficiency as a function of the invariant mass is mainly due to the pTrequirements on the muons at the HLT level.
Several sources of systematic uncertainty affect these results, including a 2.2% uncertainty on the integrated luminosity [29]. The efficiency corrections are determined using the tag-and-probe results described above. We de- termine, event-by-event, the uncertainty on the total effi- ciency corrections by propagating the uncertainties on the single muon corrections. This total event efficiency uncer- tainty is largely independent of mass, with a maximum value of 12%. We apply this value as a systematic uncer- tainty for every bin in the scan.
The isolation efficiency is uncertain at the 5% level, corresponding to the largest discrepancy between data and MC simulation in the entire relevant pT range. We evaluate the systematic uncertainty on the resolution of the a as the quadrature sum of the difference between the mass resolution of the a with a mass of 10 GeV and the resolu- tion of the ð2SÞ (which has the same mass) in MC simulation, and the difference between the latter and the mass resolution obtained for the ð2SÞ from data.
Additionally, the finite statistics for the determination of the mass resolution as a function of the dimuon mass contributes a source of uncertainty. We consider the mass ranges separately and include these systematic uncertain- ties in the calculation of the upper limit on the cross section times branching fraction. Overall, this adds an 11% (4%) effect for the barrel (end caps).
Systematic uncertainties on the background description include the shape uncertainty of the first-order polynomial fit of the background PDF. We fit the background with alternative functions (a second-order polynomial and an exponential function), generate MC pseudoexperiments using these functions, and fit the distributions using the first-order polynomial. The resulting systematic uncertain- ties, from the distribution of the fitted parameters, is of the order of a few percent.
No significant signal is observed, and we determine 95%
confidence level (C.L.) upper limits on Bðpp ! a !
þÞ as a function of the dimuon mass using the CLs
approach [30–32]. A few steps at the edges of the mass scans, where the fitting procedure has no predictive power on the signal shape, are not used. Figure2shows the upper limit results for the two mass ranges including the system- atic uncertainties discussed above. These limits are significant in the context of the NMSSM, and can be presented in terms of upper limits onj cosAj. The larger the value of tan, the stronger is the constraint. Figure3 presents upper limits,j cosAjmax as a function of ma1 for
¼ 1; 2; 3; 10; 30; 50. Our upper limits are compared to an earlier analysis of the BABAR ð1SÞ and ð3SÞ data [33], and are superior for ma1 7:5 GeV for tan ¼ 50,
decreasing to ma1 6 GeV for tan ¼ 2, and are superior for all masses at tan¼ 1. Further, these are the first significant limits for ma> mð3SÞ.
In conclusion, we performed a search for a narrow, low mass pseudoscalar a, which is produced by gg! a and decays via a! þin the mass ranges 5.5–8.8 GeV and
11.5 12 12.5 13 13.5 14
0 2 4 6 8 10 12
14 Observed
1 Expected
2 Expected
CMS
m [GeV]
= 7 TeV s L = 1.3 fb-1
5.5 6 6.5 7 7.5 8 8.5
0 2 4 6 8 10 12
14 Observed
1 Expected
2 Expected
CMS
m [GeV]
= 7 TeV s L = 1.3 fb-1
FIG. 2 (color online). Upper limits at 95% C.L. on
Bðpp ! a ! þÞ in mass range 1 (upper panel) and mass range 2 (lower panel) including systematic uncertainties.
The dotted lines correspond to the expected limits, and the bands correspond to 1- and 2- level uncertainties on the expected limits.
CMS L = 1.3 fb-1
CMS Limits BaBar Limits
= 7 TeV s
6 8 10 12 14 1.00
0.50
0.20 0.10 0.05
0.02 0.01
m [GeV]a1
|cos |Amax
FIG. 3 (color online). Upper limits on the NMSSM parameter j cosAj as a function of ma1 in the two mass ranges. The solid curves correspond to different tan values: from top to bottom, tan¼ 1, tan ¼ 2, tan ¼ 3, tan ¼ 10, tan ¼ 30, and tan¼ 50. For each tan value in mass range 1, the second, dotted curve shows the limits from the BABAR analysis. There are no BABAR limits for tan¼ 1 in mass range 1, or for any tan in mass range 2. The line atj cosAjmax¼ 1 is equivalent to no limit. Results from CDF are not shown as they are less stringent than the BABAR limits.
11.5–14 GeV, using a data sample corresponding to an integrated luminosity of 1:3 fb1collected with the CMS detector. No significant signal is observed, and we set upper limits on Bðpp ! a ! þÞ. These upper limits are applied in the context of the light pseudoscalar a1 of the NMSSM to yield upper limits on the NMSSM parameter j cosAj. These limits are superior to existing constraints for a significant portion of the ma1< mð1SÞ mass range, and are the first significant limits available in the ma1> mð3SÞmass range.
We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC machine. We thank the technical and administrative staff at CERN and other CMS institutes, and acknowledge sup- port from: FMSR (Austria); FNRS and FWO (Belgium);
CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China);
COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); MoER, SF0690030s09 and ERDF (Estonia);
Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal);
JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan);
MON, RosAtom, RAS and RFBR (Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (U.K.); DOE and NSF (U.S.).
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S. Chatrchyan,1V. Khachatryan,1A. M. Sirunyan,1A. Tumasyan,1W. Adam,2T. Bergauer,2M. Dragicevic,2J. Ero¨,2 C. Fabjan,2,bM. Friedl,2R. Fru¨hwirth,2,bV. M. Ghete,2J. Hammer,2N. Ho¨rmann,2J. Hrubec,2M. Jeitler,2,b W. Kiesenhofer,2V. Knu¨nz,2M. Krammer,2,bD. Liko,2I. Mikulec,2M. Pernicka,2,aB. Rahbaran,2C. Rohringer,2
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X. Janssen,4S. Luyckx,4T. Maes,4L. Mucibello,4S. Ochesanu,4B. Roland,4R. Rougny,4M. Selvaggi,4 Z. Staykova,4H. Van Haevermaet,4P. Van Mechelen,4N. Van Remortel,4A. Van Spilbeeck,4F. Blekman,5 S. Blyweert,5J. D’Hondt,5R. Gonzalez Suarez,5A. Kalogeropoulos,5M. Maes,5A. Olbrechts,5W. Van Doninck,5 P. Van Mulders,5G. P. Van Onsem,5I. Villella,5B. Clerbaux,6G. De Lentdecker,6V. Dero,6A. P. R. Gay,6T. Hreus,6 A. Le´onard,6P. E. Marage,6T. Reis,6L. Thomas,6C. Van der Velde,6P. Vanlaer,6J. Wang,6V. Adler,7K. Beernaert,7
A. Cimmino,7S. Costantini,7G. Garcia,7M. Grunewald,7B. Klein,7J. Lellouch,7A. Marinov,7J. Mccartin,7 A. A. Ocampo Rios,7D. Ryckbosch,7N. Strobbe,7F. Thyssen,7M. Tytgat,7L. Vanelderen,7P. Verwilligen,7 S. Walsh,7E. Yazgan,7N. Zaganidis,7S. Basegmez,8G. Bruno,8R. Castello,8A. Caudron,8L. Ceard,8C. Delaere,8
T. du Pree,8D. Favart,8L. Forthomme,8A. Giammanco,8,cJ. Hollar,8V. Lemaitre,8J. Liao,8O. Militaru,8 C. Nuttens,8D. Pagano,8L. Perrini,8A. Pin,8K. Piotrzkowski,8N. Schul,8J. M. Vizan Garcia,8N. Beliy,9 T. Caebergs,9E. Daubie,9G. H. Hammad,9G. A. Alves,10M. Correa Martins Junior,10D. De Jesus Damiao,10 T. Martins,10M. E. Pol,10M. H. G. Souza,10W. L. Alda´ Ju´nior,11W. Carvalho,11A. Custo´dio,11E. M. Da Costa,11 C. De Oliveira Martins,11S. Fonseca De Souza,11D. Matos Figueiredo,11L. Mundim,11H. Nogima,11V. Oguri,11
W. L. Prado Da Silva,11A. Santoro,11L. Soares Jorge,11A. Sznajder,11C. A. Bernardes,12,dF. A. Dias,12,e T. R. Fernandez Perez Tomei,12E. M. Gregores,12,dC. Lagana,12F. Marinho,12P. G. Mercadante,12,dS. F. Novaes,12
Sandra S. Padula,12V. Genchev,13,fP. Iaydjiev,13,fS. Piperov,13M. Rodozov,13S. Stoykova,13G. Sultanov,13 V. Tcholakov,13R. Trayanov,13M. Vutova,13A. Dimitrov,14R. Hadjiiska,14V. Kozhuharov,14L. Litov,14B. Pavlov,14
P. Petkov,14J. G. Bian,15G. M. Chen,15H. S. Chen,15C. H. Jiang,15D. Liang,15S. Liang,15X. Meng,15J. Tao,15 J. Wang,15X. Wang,15Z. Wang,15H. Xiao,15M. Xu,15J. Zang,15Z. Zhang,15C. Asawatangtrakuldee,16Y. Ban,16 S. Guo,16Y. Guo,16W. Li,16S. Liu,16Y. Mao,16S. J. Qian,16H. Teng,16S. Wang,16B. Zhu,16W. Zou,16C. Avila,17
J. P. Gomez,17B. Gomez Moreno,17A. F. Osorio Oliveros,17J. C. Sanabria,17N. Godinovic,18D. Lelas,18 R. Plestina,18,gD. Polic,18I. Puljak,18,fZ. Antunovic,19M. Kovac,19V. Brigljevic,20S. Duric,20K. Kadija,20 J. Luetic,20S. Morovic,20A. Attikis,21M. Galanti,21G. Mavromanolakis,21J. Mousa,21C. Nicolaou,21F. Ptochos,21
P. A. Razis,21M. Finger,22M. Finger, Jr.,22Y. Assran,23,hS. Elgammal,23,iA. Ellithi Kamel,23,jS. Khalil,23,i M. A. Mahmoud,23,kA. Radi,23,l,mM. Kadastik,24M. Mu¨ntel,24M. Raidal,24L. Rebane,24A. Tiko,24V. Azzolini,25
P. Eerola,25G. Fedi,25M. Voutilainen,25J. Ha¨rko¨nen,26A. Heikkinen,26V. Karima¨ki,26R. Kinnunen,26 M. J. Kortelainen,26T. Lampe´n,26K. Lassila-Perini,26S. Lehti,26T. Linde´n,26P. Luukka,26T. Ma¨enpa¨a¨,26 T. Peltola,26E. Tuominen,26J. Tuominiemi,26E. Tuovinen,26D. Ungaro,26L. Wendland,26K. Banzuzi,27 A. Karjalainen,27A. Korpela,27T. Tuuva,27M. Besancon,28S. Choudhury,28M. Dejardin,28D. Denegri,28 B. Fabbro,28J. L. Faure,28F. Ferri,28S. Ganjour,28A. Givernaud,28P. Gras,28G. Hamel de Monchenault,28P. Jarry,28
E. Locci,28J. Malcles,28L. Millischer,28A. Nayak,28J. Rander,28A. Rosowsky,28I. Shreyber,28M. Titov,28 S. Baffioni,29F. Beaudette,29L. Benhabib,29L. Bianchini,29M. Bluj,29,nC. Broutin,29P. Busson,29C. Charlot,29 N. Daci,29T. Dahms,29L. Dobrzynski,29R. Granier de Cassagnac,29M. Haguenauer,29P. Mine´,29C. Mironov,29
M. Nguyen,29C. Ochando,29P. Paganini,29D. Sabes,29R. Salerno,29Y. Sirois,29C. Veelken,29A. Zabi,29 J.-L. Agram,30,oJ. Andrea,30D. Bloch,30D. Bodin,30J.-M. Brom,30M. Cardaci,30E. C. Chabert,30C. Collard,30 E. Conte,30,oF. Drouhin,30,oC. Ferro,30J.-C. Fontaine,30,oD. Gele´,30U. Goerlach,30P. Juillot,30A.-C. Le Bihan,30 P. Van Hove,30F. Fassi,31D. Mercier,31S. Beauceron,32N. Beaupere,32O. Bondu,32G. Boudoul,32J. Chasserat,32 R. Chierici,32,fD. Contardo,32P. Depasse,32H. El Mamouni,32J. Fay,32S. Gascon,32M. Gouzevitch,32B. Ille,32 T. Kurca,32M. Lethuillier,32L. Mirabito,32S. Perries,32V. Sordini,32S. Tosi,32Y. Tschudi,32P. Verdier,32S. Viret,32
Z. Tsamalaidze,33,pG. Anagnostou,34S. Beranek,34M. Edelhoff,34L. Feld,34N. Heracleous,34O. Hindrichs,34 R. Jussen,34K. Klein,34J. Merz,34A. Ostapchuk,34A. Perieanu,34F. Raupach,34J. Sammet,34S. Schael,34 D. Sprenger,34H. Weber,34B. Wittmer,34V. Zhukov,34,qM. Ata,35J. Caudron,35E. Dietz-Laursonn,35D. Duchardt,35
M. Erdmann,35R. Fischer,35A. Gu¨th,35T. Hebbeker,35C. Heidemann,35K. Hoepfner,35D. Klingebiel,35 P. Kreuzer,35J. Lingemann,35C. Magass,35M. Merschmeyer,35A. Meyer,35M. Olschewski,35P. Papacz,35 H. Pieta,35H. Reithler,35S. A. Schmitz,35L. Sonnenschein,35J. Steggemann,35D. Teyssier,35M. Weber,35 M. Bontenackels,36V. Cherepanov,36G. Flu¨gge,36H. Geenen,36M. Geisler,36W. Haj Ahmad,36F. Hoehle,36 B. Kargoll,36T. Kress,36Y. Kuessel,36A. Nowack,36L. Perchalla,36O. Pooth,36J. Rennefeld,36P. Sauerland,36
A. Stahl,36M. Aldaya Martin,37J. Behr,37W. Behrenhoff,37U. Behrens,37M. Bergholz,37,rA. Bethani,37 K. Borras,37A. Burgmeier,37A. Cakir,37L. Calligaris,37A. Campbell,37E. Castro,37F. Costanza,37D. Dammann,37 C. Diez Pardos,37G. Eckerlin,37D. Eckstein,37G. Flucke,37A. Geiser,37I. Glushkov,37P. Gunnellini,37S. Habib,37
J. Hauk,37G. Hellwig,37H. Jung,37M. Kasemann,37P. Katsas,37C. Kleinwort,37H. Kluge,37A. Knutsson,37
M. Kra¨mer,37D. Kru¨cker,37E. Kuznetsova,37W. Lange,37W. Lohmann,37,rB. Lutz,37R. Mankel,37I. Marfin,37 M. Marienfeld,37I.-A. Melzer-Pellmann,37A. B. Meyer,37J. Mnich,37A. Mussgiller,37S. Naumann-Emme,37 J. Olzem,37H. Perrey,37A. Petrukhin,37D. Pitzl,37A. Raspereza,37P. M. Ribeiro Cipriano,37C. Riedl,37E. Ron,37
M. Rosin,37J. Salfeld-Nebgen,37R. Schmidt,37,rT. Schoerner-Sadenius,37N. Sen,37A. Spiridonov,37M. Stein,37 R. Walsh,37C. Wissing,37C. Autermann,38V. Blobel,38S. Bobrovskyi,38J. Draeger,38H. Enderle,38J. Erfle,38
U. Gebbert,38M. Go¨rner,38T. Hermanns,38R. S. Ho¨ing,38K. Kaschube,38G. Kaussen,38H. Kirschenmann,38 R. Klanner,38J. Lange,38B. Mura,38F. Nowak,38T. Peiffer,38N. Pietsch,38D. Rathjens,38C. Sander,38H. Schettler,38 P. Schleper,38E. Schlieckau,38A. Schmidt,38M. Schro¨der,38T. Schum,38M. Seidel,38H. Stadie,38G. Steinbru¨ck,38 J. Thomsen,38C. Barth,39J. Berger,39C. Bo¨ser,39T. Chwalek,39W. De Boer,39A. Descroix,39A. Dierlamm,39
M. Feindt,39M. Guthoff,39,fC. Hackstein,39F. Hartmann,39T. Hauth,39,fM. Heinrich,39H. Held,39 K. H. Hoffmann,39S. Honc,39I. Katkov,39,qJ. R. Komaragiri,39D. Martschei,39S. Mueller,39Th. Mu¨ller,39
M. Niegel,39A. Nu¨rnberg,39O. Oberst,39A. Oehler,39J. Ott,39G. Quast,39K. Rabbertz,39F. Ratnikov,39 N. Ratnikova,39S. Ro¨cker,39A. Scheurer,39F.-P. Schilling,39G. Schott,39H. J. Simonis,39F. M. Stober,39 D. Troendle,39R. Ulrich,39J. Wagner-Kuhr,39S. Wayand,39T. Weiler,39M. Zeise,39G. Daskalakis,40T. Geralis,40
S. Kesisoglou,40A. Kyriakis,40D. Loukas,40I. Manolakos,40A. Markou,40C. Markou,40C. Mavrommatis,40 E. Ntomari,40L. Gouskos,41T. J. Mertzimekis,41A. Panagiotou,41N. Saoulidou,41I. Evangelou,42C. Foudas,42,f P. Kokkas,42N. Manthos,42I. Papadopoulos,42V. Patras,42G. Bencze,43C. Hajdu,43,fP. Hidas,43D. Horvath,43,s F. Sikler,43V. Veszpremi,43G. Vesztergombi,43,tN. Beni,44S. Czellar,44J. Molnar,44J. Palinkas,44Z. Szillasi,44 J. Karancsi,45P. Raics,45Z. L. Trocsanyi,45B. Ujvari,45S. B. Beri,46V. Bhatnagar,46N. Dhingra,46R. Gupta,46
M. Jindal,46M. Kaur,46M. Z. Mehta,46N. Nishu,46L. K. Saini,46A. Sharma,46J. Singh,46Ashok Kumar,47 Arun Kumar,47S. Ahuja,47A. Bhardwaj,47B. C. Choudhary,47S. Malhotra,47M. Naimuddin,47K. Ranjan,47 V. Sharma,47R. K. Shivpuri,47S. Banerjee,48S. Bhattacharya,48S. Dutta,48B. Gomber,48Sa. Jain,48Sh. Jain,48 R. Khurana,48S. Sarkar,48M. Sharan,48A. Abdulsalam,49R. K. Choudhury,49D. Dutta,49S. Kailas,49V. Kumar,49
P. Mehta,49A. K. Mohanty,49,fL. M. Pant,49P. Shukla,49T. Aziz,50S. Ganguly,50M. Guchait,50,uM. Maity,50,v G. Majumder,50K. Mazumdar,50G. B. Mohanty,50B. Parida,50K. Sudhakar,50N. Wickramage,50S. Banerjee,51
S. Dugad,51H. Arfaei,52H. Bakhshiansohi,52,wS. M. Etesami,52,xA. Fahim,52,wM. Hashemi,52A. Jafari,52,w M. Khakzad,52A. Mohammadi,52,yM. Mohammadi Najafabadi,52S. Paktinat Mehdiabadi,52B. Safarzadeh,52,z
M. Zeinali,52,xM. Abbrescia,53a,53bL. Barbone,53a,53bC. Calabria,53a,53b,fS. S. Chhibra,53a,53bA. Colaleo,53a D. Creanza,53a,53cN. De Filippis,53a,53c,fM. De Palma,53a,53bL. Fiore,53aG. Iaselli,53a,53cL. Lusito,53a,53b G. Maggi,53a,53cM. Maggi,53aB. Marangelli,53a,53bS. My,53a,53cS. Nuzzo,53a,53bN. Pacifico,53a,53bA. Pompili,53a,53b
G. Pugliese,53a,53cG. Selvaggi,53a,53bL. Silvestris,53aG. Singh,53a,53bR. Venditti,53aG. Zito,53aG. Abbiendi,54a A. C. Benvenuti,54aD. Bonacorsi,54a,54bS. Braibant-Giacomelli,54a,54bL. Brigliadori,54a,54bP. Capiluppi,54a,54b
A. Castro,54a,54bF. R. Cavallo,54aM. Cuffiani,54a,54bG. M. Dallavalle,54aF. Fabbri,54aA. Fanfani,54a,54b D. Fasanella,54a,54b,fP. Giacomelli,54aC. Grandi,54aL. Guiducci,54a,54bS. Marcellini,54aG. Masetti,54a M. Meneghelli,54a,54b,fA. Montanari,54aF. L. Navarria,54a,54bF. Odorici,54aA. Perrotta,54aF. Primavera,54a,54b A. M. Rossi,54a,54bT. Rovelli,54a,54bG. Siroli,54a,54bR. Travaglini,54a,54bS. Albergo,55a,55bG. Cappello,55a,55b
M. Chiorboli,55a,55bS. Costa,55a,55bR. Potenza,55a,55bA. Tricomi,55a,55bC. Tuve,55a,55bG. Barbagli,56a V. Ciulli,56a,56bC. Civinini,56aR. D’Alessandro,56a,56bE. Focardi,56a,56bS. Frosali,56a,56bE. Gallo,56aS. Gonzi,56a,56b M. Meschini,56aS. Paoletti,56aG. Sguazzoni,56aA. Tropiano,56a,fL. Benussi,57S. Bianco,57S. Colafranceschi,57,aa
F. Fabbri,57D. Piccolo,57P. Fabbricatore,58R. Musenich,58A. Benaglia,59a,59b,fF. De Guio,59a,59b L. Di Matteo,59a,59b,fS. Fiorendi,59a,59bS. Gennai,59a,fA. Ghezzi,59a,59bS. Malvezzi,59aR. A. Manzoni,59a,59b
A. Martelli,59a,59bA. Massironi,59a,59b,fD. Menasce,59aL. Moroni,59aM. Paganoni,59a,59bD. Pedrini,59a S. Ragazzi,59a,59bN. Redaelli,59aS. Sala,59aT. Tabarelli de Fatis,59a,59bS. Buontempo,60aC. A. Carrillo Montoya,60a,f
N. Cavallo,60a,bbA. De Cosa,60a,60b,fO. Dogangun,60a,60bF. Fabozzi,60a,bbA. O. M. Iorio,60aL. Lista,60a S. Meola,60a,ccM. Merola,60a,60bP. Paolucci,60a,fP. Azzi,61aN. Bacchetta,61a,fD. Bisello,61a,61bA. Branca,61a,f
R. Carlin,61a,61bP. Checchia,61aT. Dorigo,61aF. Gasparini,61a,61bU. Gasparini,61a,61bA. Gozzelino,61a K. Kanishchev,61a,61cS. Lacaprara,61aI. Lazzizzera,61a,61cM. Margoni,61a,61bA. T. Meneguzzo,61a,61bJ. Pazzini,61a
N. Pozzobon,61a,61bP. Ronchese,61a,61bE. Torassa,61aM. Tosi,61a,61b,fS. Vanini,61a,61bP. Zotto,61a,61b A. Zucchetta,61aG. Zumerle,61a,61bM. Gabusi,62a,62bS. P. Ratti,62a,62bC. Riccardi,62a,62bP. Torre,62a,62b
P. Vitulo,62a,62bM. Biasini,63a,63bG. M. Bilei,63aL. Fano`,63a,63bP. Lariccia,63a,63bA. Lucaroni,63a,63b,f G. Mantovani,63a,63bM. Menichelli,63aA. Nappi,63a,63bF. Romeo,63a,63bA. Saha,63aA. Santocchia,63a,63b
