Hard QCD Results with Jets at the LHC SvenMenke1,aonbehalfoftheATLASandCMScollaborations Max-Planck-Institutfu¨rPhysik,Fo¨hringerRing6,80805Mu¨nchen,Germany √ Abstract. HardQCDresultsinproton-protoncollisionsat s=7TeVwithjetsfromdatarecordeduptothe endof2010bytheCMSandATLASexperimentsattheLHCarereported.Inclusivejetanddi-jetcrosssection measurementsaswellasobservablessensitivetomulti-jetactivityareshownandcomparedtosimulationsbased onleadinglogpartonshowersaswellasNLOQCDpredictions.Novelapproachestoidentifyhighlyboosted 2 1 massivefinalstatesbyexploitingthejetsubstructurearetestedonthedominantQCDbackground. 0 2 1 Introduction uncertainty are validated with in-situ methods using p n ⊥ a balanceindi-jetandγ-jeteventsandthemomentumpro- J TheATLAS[1]andCMS[2]experimentsbothhaverich jectionfractionmethodinγ-jetevents.TheMonnteCarlo 5 QCDprogramsinvolvinghigh p jetsaimingtoprobethe based correction factors are validated with single particle ⊥ 2 structure of the colliding protons, to measure the strong test-beamdataandE/pmeasurementsofisolatedhadrons coupling constant and to test the standard model (SM) at in collision data which are then extrapolated using frag- ] the shortest distance scales accessible today in the high- mentationpredictionstothejet-level.ThesystematicJES x e center-of-mass proton-proton collisions of the LHC. Fur- uncertaintyistypically3−6%forbothATLASandCMS - thermoredeviationsfromtheSMwouldindicatethepres- over a large range of pseudo-rapidities and p⊥, with the p enceofnewphysicsbeyondtheSM.Thedatasetsrecorded largervaluesatlarge|η|,verylowandveryhigh p⊥. e h uptotheendof2010andcorrespondingtointegratedlu- [ minositiesofL (cid:39) 35pb−1 perexperimenthavebeenused byATLASandCMStoupdatetheirmeasurementsofin- 3 Inclusive jet cross section 2 clusive jet and di-jet cross sections, as well as to mea- v measurements sure multi-jet and angular di-jet distributions. New meth- 8 ods based on the sub-structure of jets to detect heavily 7 9 boostedmassiveobjectsendingupinsinglejetsattheLHC TheinclusivejetcrosssectionismeasuredbyATLAS[10] 4 have also been tested on the dominant QCD background and CMS [11] as a function of transverse jet momentum . andcomparedtoexpectations. p⊥ andjetrapidityy.Thedataiscorrectedbin-by-binfor 1 migrationeffectsin p duetothesteeplyfallingspectrum 0 ⊥ in p and the finite p resolution. In CMS the corrected 2 ⊥ ⊥ 1 2 Jet reconstruction and calibration : v arXi Tgr0e.oh7creo.itnIihnnsmtpfrruua[tcr3ett]iodo-insthamuensdojeeddcteoablwllyginiotbehroaittrdhh-ismsaetafxaenprceeAern4impt-iav-ereknac⊥tmtsojeeritsntercststlheue0ms.t4iemnrc≤iinnluggRsiaev≤lie-- 2σ [pb/TeV]|yd|m/dd12max1111111000000011111220246801 ×NS yLNsOote npm QpaeCtriDct. uc(CnocrTre.ErtQa in6t.i6e)s 2100 .... 1283 <<<< |||||yyyyy|||||mmmmmaaaaaxxxxx <<<<< 22100.....81283 (((((××××× 111110000086420))))) ther from stable particles in generator-level simulations, 108 106 partonsinNLOcalculations,topologicalcalorimeterclus- 104 ters [4,5] in ATLAS or particle flow (PF) objects [6,7] in 102 asn t=i k7t TjeetVs,, ∫ RL =d t0 =.4 37 pb 1 CMSinfullsimulationsanddata.Topologicalclusterscan 1 ATLASPreliminary 10 2 10 1 2×10 1 1 2 3 45 becalibratedpriortothejetmaking[5]inATLASorleft m12 [TeV] attheelectromagnetic(EM)scale.ThePFobjectsusein- Fig.1.InclusivejetcrosssectionfromCMS(left)forAnti-k jets formationfromallCMSsubsystemsandarecalibratedto ⊥ withR=0.5asfunctionof p for6rapidityintervalsscaledfor correspondtostableparticleslikeγ’s,leptons,chargedand ⊥ easierviewing.Thedatapoints(symbols)arecomparedtoNLO neutral hadrons. In all cases residual jet-level corrections predictions (solid lines) corrected for non-perturbative effects. areneededtoaccountforparticlelossesnotdetectableon Experimental uncertainties are indicated by the yellow bands; clusterorPFobjectlevel[8,9]withlargercorrections(up DoubledifferentialcrosssectionfromATLAS(right)forAnti-k ⊥ toafactorof2)forEM-scaleinputsandsmallcorrections di-jeteventswithR=0.4asfunctionofdi-jetmassm for5in- (onthelevelof5−10%)foralreadycalibratedinputs.The 12 tervalsofmaximumrapidity|y |withsystematicexperimental max jet-levelcalibrationsareMonteCarlo(MC)basedcorrec- uncertainties(greyband).NLOpredictionswithNPcorrections tion functions in |η| and p⊥. Jet energy scale (JES) and anduncertaintiesareshownaswell(yellowband). a e-mail:menke@mppmu.mpg.de EPJWebofConferences JJ σσ22/d|y|(CTEQ 6.6)/dp/d|y|/d/dpd0TT0001111.......468246821 AanTti kLtDCC AaTT jetE1at0SQs. 6R.P 6=0r.4e (l0i.m0<|iyn|=R 3128654328=66100001600 s000000000.p6 = bGGGGGGGGG 71 epeeeeeeeeVVVVVVVV VTT> (((((((((1e×××××××××0111111111V0000000000 017654328G)))))))))eV |y|<0.8 /d d1//d d1//d d1//d d1//d d1//d d1//d d1//d d1//d d1//d d1/χσσχσσχσσχσσχσσχσσχσσχσσχσσχσσdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijetdijet0000000000000000000000000000000000000000........................................4567456745674567456745674567456745674567 DΛΛQ+-aC t==Da 55 p TTreeedVVicti11Mo..n84jj <<> MM2.2jjjj T<< e21LV..s28 = C=TT 3ee M7VV6 S TpebV-(((1+++000...435))) Gap fraction345 2211197418520000000 ≤≤ ≤≤≤≤≤ pp pppppTT TTTTT<< <<<<<19 20222110 74185G 00000Ge GGGGGeVVeeeee VVVVV ( +( +0(((((0)+++++.322115).).))55)) LQAe0aT =d Li2n0gADHPP GOOaEpStTeJWWa Vd (HH2pij0eaEE1trGG t0so en++l e lPHecYvEtieoTRlnH)WIAIG RR32320000....686811 sC= M7 TSeV aLnintt=i-3K6T pRb=-10.5 102 1.1 < Mjj < 1.4 TeV (+0.25) 1110010 10 321 π/2 2π/3PNscDLaOFle &p u5Q nαπCcs ./Du6n cO.(α4s) π 000000000000000000000000000000..............................232323232323232323231111111111 00000.....58632 5555< <<<< M MMMMjj jjjjjjjj< <<<< 0 1000.6....18535 5 5 TTT TTeeeVeVeVVV((((++++0000....1210))55)) 21 0000....242400 00..55 11DPPPMAHSYYYLyaEAsPtTTTRDatGHHHeWGmIIIEAAARIGaN668At + i+Pcttt11+uuu HUP nnnt.. ueeeYn+55n cT ZD2PeeHC26r Y2tITaAT.3i6Hn tItyAun6e t uD22n6eT D6T 22..55 ∆φ [radians] 2222222222 4444444444 6666666666 8888888888 11111111110000000000 11111111112222222222 11111111114444444444χχχχχχχχχχ 11111111116666666666 00 1 2 3 4 5 ∆y6 HHTT ((TTeeVV)) ddddddddddiiiiiiiiiijjjjjjjjjjeeeeeeeeeetttttttttt Fig.4.Azimuthalde-correlation∆φofthetwomostenergeticjets Fig. 5. Gap-fraction (left) for the two leading jets in p as a ⊥ asmeasuredbyATLAS(left)forAnti-k⊥ jetswithR = 0.6for function of ∆y for various intervals of p¯⊥ as measured by AT- differentpmaxintervals(blackmarkers)comparedtoNLOpQCD LAS(markersandyellowerrorband)comparedtoHEJcalcula- ⊥ calculations(redlines)withassociatederrors(hatchpattern);The tions(blueband)andNLOsimulationswithPOWHEGinterfaced distributionofχ (blackpoints)fordifferentM rangesasmea- toPYTHIA(reddashes)andHERWIG(bluedot-dashes);Ratioof dijet jj suredbyCMS(right)forAnti-k⊥jetswithR=0.5comparedto inclusive3-jetoverthe2-jetcrosssectionsR32asfunctionofto- NLO pQCD calculations (shaded band) and predictions includ- taltransversemomentumH (right)asmeasuredbyCMS(black ⊥ ingcontactinteractions(coloredlines)forcompositenessscales dots and yellow uncertainty band) compared to various simu- ofΛ+/−=5TeV. lations using different PYTHIA tunes, MADGRAPH, ALPGEN and HERWIG++. destructive(constructive)interferencehasbeenobtainedat 5 Jet mass and sub-structure 95% CL. A complementary study of the rapidity gap be- tweenthetwojetswitheitherleading p orthelargestra- ⊥ In the high energy regime of LHC, heavy objects with piditygap∆yhasbeendonebyATLAS[17].Theso-called massesO(100GeV),canreceivelargeLorentzboostssuch gap-fractionisdefinedasthefractionofeventswithoutad- thattheirdecayproductsaremeasuredinasinglejet.Sev- ditionaljetactivityintherapidityintervalbetweenthetwo eralapproachesareconsideredtoexplorethesub-structure jets.Anyadditionaljetwithinthegaphastohaveatrans- of these jets with the aim to identify such heavy objects. verse momentum above a veto scale p > Q , with the ⊥ 0 default choice Q = 20GeV to stay far away from Λ . Amongthemare: 0 QCD The gap-fraction is shown in the left plot of figure 5 for C/Afiltering: Theclusteringoflarge(R(cid:39)1.2)Cambridge- the choice of leading jets in p⊥ as a function of ∆y for Aachen (C/A) [19] type jets is reversed until a large various intervals of the average transverse momentum of dropinjet-massisobserved.Theremainingconstituents the two leading jets p¯⊥. The comparison with HEJ calcu- arere-clusteredwithasmallerRparameter. lationsshowssomedeviationsinthelarge p¯⊥ regionsbut Jetpruning: C/Aork⊥[20,21]jet-clusteringisperformed theagreementimprovesasp¯⊥approachesQ0,whichisex- ontheconstituentsofalargejetandineachclustering pectedsinceHEJisdesignedtogiveagooddescriptionof step the softer of the two clusters being combined is QCDinthelimitwherealljetshavesimilar p⊥.Thebest discarded if it’s transverse momentum is below a cer- descriptionisachievedwithPOWHEGinterfacedtoPYTHIA tainfractionoftheoriginaljet p andtheangulardis- ⊥ although deviations are observed at large ∆y. POWHEG in- tancebetweenthetwoclustersislarge. terfaced to HERWIG tends to predict smaller gap fractions Forthejetsubstructurealgorithmstobeusefultheyhave over the full phase space and the deviations increase for larger∆yasforthePOWHEG+PYTHIAcase. to be tested on QCD jets as this will be the main background.C/AFilteringisusefulforthedecaysofheavypar- The right hand plot in figure 5 shows the cross sec- ticles to two low mass objects and the QCD behavior has tion ratio of three-jet over two-jet events R as a func- tionofthetotaltransversemomentumsum H32 = (cid:80) p beenstudiedinATLASin[22].Themassdropm1/mjet of ⊥ jets ⊥ theleadingsubjetisrequiredtobesmallerthan0.67(light asmeasuredbyCMS[18].Manysystematicuncertainties (cid:16) (cid:17)2 suchasthoseduetotheJESandthejetselectionefficiency subjet)andthe p⊥asymmetry min(p1⊥,p2⊥)×∆R1,2/mjet largely cancel in this ratio, while the uncertainty due to largerthan0.09(fairlysymmetric).Onceareversedclus- the integrated luminosity vanishes entirely. Therefore R teringstepwiththesepropertiesisfoundthecurrentjetis 32 provides a stringent test of QCD predictions. Events with re-clusteredwithC/AandR=min(0.3,∆R /2)findingn 1,2 two or more Anti-k jets with R = 0.5 with |y| < 2.5 new subjets of which the leading min(3,n) are combined ⊥ and p > 50GeV and H > 0.2TeV are selected and togivethefinalC/Afilteredjet.Figure6showsthespec- ⊥ ⊥ compared to various PYTHIA6, PYTHIA8 and HERWIG++ trum of jet masses for C/A jets with R = 1.2 before and based tunes and to simulations using the multi-parton fi- afterthefilteringprocedureineventswithexactlyonepri- nalstategeneratorsMADPGRAPHandALPGENinterfacedto mary vertex (to remove pile-up) and at least one jet with PYTHIA6.Allpredictionsdescribetheobservedratiowell p > 300GeV and |y| < 2. The agreement with all three ⊥ in the region H > 0.5TeV but, with the exception of predictionsisgoodalthoughHERWIG++producesjetswith ⊥ MADPGRAPH,overshootbetween10−30%atlowerH . larger mass (before filtering) compared to data. Jet prun- ⊥ EPJWebofConferences σd 1 σdm [GeV]000...0000.00106821 ATLAS Preliminary CNPaVm =b r1id, gpAPHHeTTyeet Lrr h>wwAAiaii Sgga3J+ c20i+m0h01me 0Gyn D eaRVta=,, 1L| y.=2| 3 wwAAia ii Sggwa3J+ c20ii+mt0h0h1me 0GRyn D qeaRqVt a=>,, 1L |0 y.=2.| 3 3 200GeVjets ⊥ tion), Phys.Rev.Lett. 106, 201804 (2011), with ∆φ > 2.1 and |η| < 2.5 in comparison to two differ- arXiv:1102.2020 ent PYTHIA tunes and HERWIG++. The overall agreement 17. G.Aadetal.(ATLASCollaboration),JHEP1109,053 of the data with simulation is good – especially with the (2011),arXiv:1107.1641 HERWIG++tune. 18. S. Chatrchyan et al. (CMS Collaboration), Phys.Lett. B702,336(2011),arXiv:1106.0647 19. Y.L. Dokshitzer, G. Leder, S. Moretti, B. Webber, JHEP9708,001(1997),hep-ph/9707323 6 Conclusions 20. S. Catani, Y.L. Dokshitzer, M. Seymour, B. Webber, Nucl.Phys.B406,187(1993) 21. S.D. Ellis, D.E. Soper, Phys.Rev. D48, 3160 (1993), Both ATLAS and CMS have made comprehensive stud- hep-ph/9305266 iesofhardQCDinvolvingjets.Excellentagreementwith 22. ATLAS Collaboration, Tech. rep., CERN, Geneva NLO pQCD calculations has been found and constraints (2011),ATLAS-CONF-2011-073 onnewphysicsweresetbytheobservedagreement.Novel 23. CMS Collaboartion, Tech. rep., CERN, Geneva techniques to identify massive boosted objects were suc- (2011),CMS-PAS-JME-10-013 cessfully tested on the large QCD background expected. The challenge will be to continue the studies presented hereundertheincreasedpile-upconditionsinthedatataken beyond2010.

Hard QCD Results with Jets at the LHC

Similar Hard QCD Results with Jets at the LHC