PoS( EPS-HEP 2013)435

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1 AL-PHYS-PROC-0-5/09/0 Inclusive and dijet jet production measured with the ALAS detector University of Oxford Inclusive jet and dijet double differential cross sections have been measured in proton proton collisionsat s =.76eVand s =7eVusingtheALASdetector.hedijetcrosssection hasbeenmeasureduptoadijetinvariantmassof.6ev.hecrosssectionshavebeenmeasured usingjetsdefinedwiththeanti-k algorithm. hedataarecomparedtopredictionsbasedon next-to-leading order QCD calculations corrected for non perturbative effects, as well as to Monte Carlo predictions at next-to-leading order using parton shower matching. Ratios of cross sections measured at different centre-of-mass energies allow for reduced experimental and/or theoretical. A NLO QCD analysis of the data indicates constraining power for the gluon density in the proton. PoS( EPS-HEP 0)5 he European Physical Society Conference on High Energy Physics 8- July, 0 Stockholm, Sweden Speaker. OnbehalfoftheALAScollaboration. c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

2 Inclusive and dijet jet production measured with the ALAS detector. Introduction he production of jets is an important process in high energy proton-proton collisions at the LHC. Precise measurements of jet production and the properties of jets provide a test of perturbative quantum chromodynamics(pqcd) calculations at next-to-leading order(nlo). Jet production is also an important background for many physics measurements and new physics searches and so accurate measurements of the jet cross section are important. Dijet and inclusive jet cross sections measured with the ALAS detector[] are presented here.highmassdijetcrosssections[]havebeenmeasuredat s =7eVwith.8fb ofdata collectedin0witharangeofdijetinvariantmassfrom60gevto.6evandindifferent rangesofy = y y /wherey andy aretherapiditiesofthetwoleadingjets.heinclusivejet crosssectionwasmeasuredat s =.76eVusing0.pb ofdatafromproton-protoncollisions collectedin0[].heratiooftheinclusivejetcrosssectionat s =.76eVtothatmeasured at s =7eVwith7pb ofdatacollectedin00[]isshown[]. hejetcrosssections at s =.76eVand s =7eVarealsousedforananalysisofpartondistributionfunctions (PDFs). Constraining power is achieved due to the strong correlation of the dominant systematic uncertainty(due to the jet calibration) at the two different centre-of-mass energies.. heoretical predictions he results presented here are compared to NLO pqcd predictions. Particle-level jets are builtfromstable,interactingparticlesafterdetectorsimulationusingtheanti-k algorithm.wo generators are used for the hard scatter: NLOJE++[5] and with the BOX package[6]. NLOJE++ uses fixed order pqcd calculations to predict the parton level cross sections. he predictions are then corrected for non-perturbative effects using multiplicative factors. hese factors are derived using the ratio of cross sections from leading order Monte Carlo generators with a leading logarithmic parton shower with and without hadronisation and the underlying event. he baseline correction is derived using PYHIA 6.5[7] with the AUEB CEQ6L tune[8]. he uncertainty on these corrections is evaluated by taking the envelope of the correction factors derived from several different generators and tunes[]. he generator uses a matrix element calculation with parton shower matching. It can be interfaced to PYHIA or HERWIG[9] for the hadronisation and the underlying event. his procedure is expected to give improved theoretical predictions although there are also additional due to the matching procedure and tuning of the parton shower. For the inclusive jet cross section predictions with NLOJE++ the renormalisation and factorisationscalesarechosentobe µ = µ R = µ F =p max (y i )wherep max (y i )isthemaximumjetp inrapiditybiny i. Forthedijetcrosssectionpredictions µ =p e 0.y. hischoicegivesamore stable cross section in the forward region[]. he scale were derived by varying the renormalisation and factorisation scales by a factor of and with respect to the nominal values. Forpredictions µ =p wherep isthemaximumjetp t atleadingorder. hec0[0]nlopdfsetisusedasthedefaultpdfforbothgenerators.nloje++isalso used with the MSW008, NNPDF., HERAPDF and ABM PDF sets. he due tothepdfsetand α s areevaluatedaccordingtotherecommendationsofthepdflhcgroup[]. PoS( EPS-HEP 0)5

3 Inclusive and dijet jet production measured with the ALAS detector. Event selection and experimental Jetsarereconstructedwiththeanti-k algorithmwithadistanceparameterofr =0.and0.6 from clusters of topologically connected calorimeter energy deposits[] which are calibrated to the energy scale of an electromagnetic shower. A correction factor, the Jet Energy Scale(JES), is applied in order to correct for the non-compensation of the calorimeter, dead material in the detectorandnoisethresholds. At s =7eVthejetenergyiscorrectedforadditionalenergy depositsduetomultipleproton-protoninteractionswhereasat s =.76eVthiscorrectionwas not needed due to the low number of proton-proton interactions in each bunch crossing. he dijet cross section measurement covers the dijet invariant mass range from 60 GeV to.6ev.heleadingandsubleadingjetsareselectedfromjetswithintherange y <..heleadingjetmusthavep >00GeVandthesubleadingjetp >50GeV.heleadingandsubleading jetsarerequiredtoliewithin y <.8.hecrosssectionismeasuredasafunctionoftheinvariant massoftheleadingandsubleadingjets,m,andbinnediny,coveringtherangey <.5. he inclusive jet cross section was measured within y <. and covers the transverse momentumrangeof0 p 0GeVforthe s =.76eVresultsand0 p 500GeVfor the s =7eVresults. he distributions in data are unfolded to particle-level using an iterative dynamically stabilised unfolding method[]. his method is based on a transfer matrix which relates the particle-level and reconstruction level observable and corrects for all detector and resolution effects except for thejes[,]. Experimental which are considered are the trigger efficiency, jet reconstruction and calibration, the uncertainty due to the unfolding procedure and the luminosity measurement. he dominant experimental uncertainty for the inclusive and dijet measurements is due to the JES calibration. he JES uncertainty is derived from single hadron response measurements and Monte Carlosimulationsandisconfirmedin-situ[].Anuncertaintyof.5%forjetsinthecentral calorimeterregionisachievedovertherange60 p 800GeV.heuncertaintyislargerforjets withlowerp andforjetsintheforwardregion.allthesystematicarepropagated through the unfolding procedure in order to evaluate their effect on the measured jet cross section.. Results heratioofthemeasureddijetdifferentialcrosssectionasafunctionofm totheprediction ofnloje++usingc0isshowninfigureforr =0.6anddifferentrangesofy. InFigure (a) the results are compared to the NLOJE++ predictions based on the C0, NNPDF., HERAPDF.5 and MSW008 PDF sets. In Figure (b) the results are compared to the predictions of with different generators and tunes. It is observed that the measured dijet cross section is in good agreement with the theoretical predictions from NLOJE++ and within systematic,althoughdifferencesofupto0%canbeseenathighm andlargey. he data are better described by the predictions of showered with PYHIA 6 AUEB than those of NLOJE++. InclusivejetcrosssectionswithR =0.and0.6at s =.76eVand s =7eVwere compared to the NLOJE++ predictions. he data and the NLOJE++ predictions were found to PoS( EPS-HEP 0)5

4 Inclusive and dijet jet production measured with the ALAS detector Ratio wrt C0 Ratio wrt C0 Ratio wrt C0 Ratio wrt C0 Ratio wrt C0.5 y* < 0 m [ev].5 y* <.0 0 m [ev].5.0 y* < [ev] m.5 y* < m [ev] 0.0 y* <.5 ALAS Preliminary 5 [ev] m (a) L dt =.8 fb 0 Data s = 7 ev anti k t jets, R = 0.6 statistical error NLOJE++ (µ=p exp(0. y*)) Non pert. corr. C0 NNPDF. HERAPDF.5 MSW008 Ratio wrt NLOJE++ Ratio wrt NLOJE++ Ratio wrt NLOJE++ Ratio wrt NLOJE++ Ratio wrt NLOJE++.5 y* < 0 m [ev].5 y* <.0 0 m [ev].5.0 y* < [ev] m.5 y* < m [ev] 0.0 y* <.5 ALAS Preliminary 5 [ev] m (b) L dt =.8 fb 0 Data s = 7 ev anti k t jets, R = 0.6 statistical error NLOJE++ (C0, µ=p exp(0. y*)) Non pert. corr. (C0, µ=p ) PYHIA6 AUEB (C0, µ=p ) PYHIA6 Perugia 0 (C0, µ=p ) HERWIG AUE (C0, µ=p ) PYHIA8 A Figure : he ratio of the measured dijet double differential cross section to the NLOJE++ predictionasafunctionofm forr=0.6anddifferentrangesiny [].heratiosofthenloje++ predictionbasedonnnpdf.,herapdf.5andmsw008tothatbasedonc0areshown in(a).heratiosofthepredictioninterfacedtopyhia6,pyhia8andherwig partonshowerstothatofnloje++withc0areshownin(b). agree within systematic. However, the data are seen to be systematically lower than thenloje++predictionforr=0.jetsandintheforwardregiononlyforr=0.6jets[]. At s =7eVsignificantdifferenceswereobservedbetweenthemeasuredinclusivejet cross section and predictions from interfaced to PYHIA or HERWIG using differenttunes[]. Forthe s =.76eVresultsrevision69ofBOXwasusedwitha new option which avoids fluctuations in the final observables after the showering process[6]. As canbeseeninfigureverygoodagreementisnowseenbetweenthemeasuredinclusivejetcross section and interfaced to the AUEB and the Perugia 0 tunes. It is also observed that the measured jet cross section agrees equally well with the prediction interfaced to PYHIAforbothR =0.and0.6jets. heratioofthemeasuredinclusivejetcrosssectionsat s =.76eVand s =7eVwere takenforthesamerangesinyandp (ρ(y,p ))aswellasforthesamerangesinyandx = p s (ρ(y,x ))[]: PoS( EPS-HEP 0)5 ( ).76eV σ(y,x,.76ev) ρ(y,x ) = 7eV σ(y,x,7ev) and ρ(y,p ) = σ(y,p,.76ev) σ(y,p,7ev) (.) Due to correlations between the at the two centre of mass energies the ontheratioarereduced. Inthequarkpartonmodel ρ(y,x )ispredictedtobeunity,while

5 Inclusive and dijet jet production measured with the ALAS detector QCD introduces scaling violations which result in deviations from that prediction. he theoretical ontheratio ρ(y,x )areverysmallascanbeseeninfigureandthetheoreticalpredictionsfromnloje++andagreewellwiththedata.hemeasurementsof ρ(y,p ) are shown in Figure in comparison to NLOJE++ predictions with the MSW 008, NNPDF.,HERAPDF.5andABMNLOPDFsets. Itisobservedthatthepredictionsareslightly lowerinthecentralregionandhigherintheforwardregioncomparedtothedata.noneofthepdf sets used here follow this trend well with ABM showing the largest tension with the data. Fortheratio ρ(y,p )theexperimentalaresignificantlysmallerthanthetheoretical.hissuggeststhatthejetcrosssectionsat s =.76eVand s =7eVmay be used to constrain the PDFs if the correlations between the two datasets are taken into account. AnNLOpQCDanalysisusingtheinclusivejetcrosssectionsforR =0.6measuredwiththeA- LASdetectorat s =.76eVand s =7eVandHERAIdatahasbeenperformedusingthe HERAFitter package[]. he gluon distribution derived from this analysis is shown in Figure 5. Using data from HERA and the measurements of inclusive jet cross sections from ALAS at both centre-of-mass energies and accounting properly for correlations between the systematic results in a harder gluon distribution and a reduced uncertainty compared to the fit using HERA data alone. Ratio wrt NLO pqcd (C0).5 y < y <.5 y <..5. y < p [GeV] Ratio wrt NLO pqcd (C0).5.5. y <.8.8 y < y < p [GeV] ALAS L dt = 0.0 pb s =.76 ev anti k t R = 0.6 statistical uncertainty NLO pqcd non pert. corr. max (C0, µ=p ) PYHIA tune AUEB (C0, µ=p ) PYHIA tune Perugia 0 (C0, µ=p ) Figure:Ratiooftheinclusivejetdoubledifferentialcrosssectionat s =.76eVtotheNLO- JE++predictionwiththeC0PDFsetasafunctionofjetp fordifferentrangesinjetrapidity[].heratiosofthedataandthepredictioninterfacedtopyhiawiththeaueb tuneandtheperugia0tunetothatofnloje++withthec0pdfsetarealsoshown.only the statistical uncertainty on the prediction is shown. he.7% uncertainty due to the luminosity measurement is omitted. PoS( EPS-HEP 0)5 5. Conclusions Highmassdijetcrosssectionsat s =7eVandinclusivejetcrosssectionsat s =7eV and s =.76eVhavebeenmeasuredwiththeALASdetectorforjetsdefinedwiththeanti-k 5

6 Inclusive and dijet jet production measured with the ALAS detector ) ρ (y, x.5 y < y <.5 y <..5. y < x ) ρ (y, x.5. y < y < y <. 0 x ALAS L dt = 0.0 pb σ.76ev.76ev jet ρ = 7eV σ 7eV jet anti k t R = 0.6 statistical uncertainty NLO pqcd non pert. corr. max (C0, µ=p ) PYHIA tune AUEB (C0, µ=p ) PYHIA tune Perugia 0 (C0, µ=p ) Figure:Measurementsof ρ(y,x )asafunctionofx fordifferentrangesinjetrapidity[].he predictionsofnloje++withc0aswellasthoseofinterfacedtopyhiawiththe AUEB and Perugia 0 tunes are also shown. Only the statistical uncertainty on the prediction is shown. he.% uncertainty due to the luminosity measurement is omitted. ) ratio wrt NLO pqcd (C0) ρ (y, p. y < y < y < y < p [GeV] ) ratio wrt NLO pqcd (C0) ρ (y, p.. y <.8.8 y < y < p [GeV] ALAS L dt = 0.0 pb.76ev ρ = σ / σ 7eV jet jet R = 0.6 anti k t statistical uncertainty NLO pqcd non pert. corrections C0 MSW 008 NNPDF. HERAPDF.5 ABM NLO Figure:Ratioofthemeasured ρ(y,p )tothenloje++predictionsasafunctionofp for different ranges in jet rapidity[]. he ratios of the NLOJE++ prediction based on MSW 008, NNPDF.,HERAPDF.5andABMNLOtothatonC0arealsoshown. he.% uncertainty due to the luminosity measurement is omitted. PoS( EPS-HEP 0)5 algorithmwithr =0.and0.6. hehighmassdijetcrosssectionsweremeasureduptoadijet invariantmassof.6evandwerefoundtobeingoodagreementwithnlopqcdpredictions withinsystematicwithsomedifferencesofupto0%athighdijetmassandlargey. Ingeneral,inclusivejetcrosssectionsat s =7eVand s =.76eV,uptoajetp of.5ev and0gevrespectively,aswellastheratiooftheinclusivejetcrosssectionatthetwocentre- 6

7 0 0 0 Inclusive and dijet jet production measured with the ALAS detector xg(x).5 ALAS.5 0 Q =.9 GeV HERA I fit HERA+ALAS jets R=0.6 fit HERA+ALAS jets.76 ev R=0.6 fit HERA+ALAS jets 7 ev R=0.6 fit rel. uncert x Figure 5: he momentum distribution of the gluon xg(x) and the relative experimental uncertainty asafunctionofxforq =.9GeV [].hefilledareaindicatesafittoheradataonly.he bandsshowfitstoheradataincombinationwithbothalasjetdatasetsandtheindividual ALASjetdatasetsseparatelyforjetswithR=0.6.heuncertaintyonthePDFiscentredonunity foreachfit. of-mass energies were found to agree with NLO pqcd predictions, confirming that perturbative QCD can describe jet production at high jet transverse momentum. he ALAS inclusive jet cross sectiondatawerealsousedincombinationwithheradatatoperformfitsoftheprotonpdfs resulting in a harder gluon distribution. References [] ALAS Collaboration, JINS (008) S0800 [] ALAS Collaboration, ALAS-CONF-0-0, [] ALAS Collaboration, Eur. Phys. J. C7(0) 509,[arXiv:0.79] [] ALAS Collaboration, Phys. Rev. D86(0) 00,[arXiv:.697] [5] Z. Nagy, Phys. Rev. D68(00) 0900,[hep-ph/00768] [6] S. Alioli, P. Nason, C. Oleari, E. Re, JHEP 006(00) 0[arXiv:08], 00; P. Nason, C. Oleari, 0, arxiv:0.9 [7]. Sjostrand, M. Mrenna, P. Skands, JHEP 0605(006) 06,[hep-ph/06075] [8] ALAS Collaboration, AL-PHYS-PUB-0-009, [9] M.Bahretal.,Eur.Phys.JC58(008)69,[arXiv: ] [0] H.L. Lai et al., Phys. Rev. D8(00) 070,[arXiv:007.] [] M. Botje et al, 0, arxiv:0.058 [] ALAS Collaboration, Eur. Phys. J. C7(0) 0,[arXiv:.66] [] B. Malaescu, 009, arxiv: PoS( EPS-HEP 0)5 7