Overview of QCD measurements at high pt

Transcription

1 Overview of QCD measurements at high p () Material from ALAS, CMS, LHCb and evatron

2 QCD in all its beauty in MCs Hadronization Parton Shower Hard Process Beam Beam Underlying Event

3 Challenges at the LHC Huge integrated luminosity delivered by the LHC, over 0 fb - in 0 at 8 ev recorded integrated lumi Reconstructed vertices In order to cope with the large rate, need to filter events by different triggers which select events of physics interest Reconstruction deals with multiple additional events per collisions (pile-up) 3

4 Run II progress LHC delivered around.5 fb - to the experiments at 3 ev CMS Integrated Luminosity, pp, 05, p s = 3 ev otal Integrated Luminosity (pb ) Jun Data included from :4 to :44 UC LHC Delivered: 44.8 pb CMS Recorded: pb Preliminary Offline Luminosity Jun 6 Jul 0 Jul 3 Aug 7 Aug Date (UC) 3 Aug 4 Sep 8 Sep LHC runs now with a bunch spacing of 5 ns, compared to 50 ns at Run I 4

5 Standard Model Summary plot σ [pb] Production Cross Section, Mar 05 CMS Preliminary - 7 ev CMS measurement (L 5.0 fb ) - 8 ev CMS measurement (L 9.6 fb ) 7 ev heory prediction 8 ev heory prediction CMS 95%CL limit Impressive agreement of theory and measurements - W Z Wγ Zγ WW WZ ZZ All results at: γγ WW EW qqll WVγ tt tt-ch tw ts-ch 5 ttγ ttz ggh VBF VH qqh h. Δσ H in exp. Δσ tth

6 Inclusive jets 6

7 Jets in general Good understanding of jets crucial for many experimental signatures est perturbative QCD calculations and MC predictions over several orders of magnitude Study parton distribution functions High precision measurements Very small background rates Small experimental uncertainty crucial (Jet energy scale) Study extreme kinematic selections of QCD JEC uncertainty [%] CMS preliminary, L = 9 fb s = 8 ev otal uncertainty 9 Absolute scale 8 Relative scale Extrapolation 7 Pile-up, NPV=4 Jet flavor (QCD) 6 ime stability 5 Anti-k R=0.5 PF 4 η 3 0 =0 jet p - (GeV) 7

8 Inclusive high p jet cross-section at 8eV (pb/gev) σ dy d dp s = 8eV anti-k R=0.7 L =.7fb - CMS Preliminary < y < 0.5 ( ) < y <.0 ( ) 3.0 < y <.5 ( ).5 < y <.0 ( ).0 < y <.5 ( ) 0.5 < y < 3.0 ( ) Ratio o C s = 8eV anti-k R=0.7 L =.7fb Exp. Uncertainty Data HERA.5 MSW008 NNPDF. ABM CMS 0.0 < y < NNPDF. NLO NP 0.5 CMS Preliminary Jet p (GeV) Jet p (GeV) Inclusive jet p cross-section at 8 ev in 6 rapidity bins from 75 to 500 GeV (anti-k ΔR=0.7), over orders of magnitude. Comparisons to NLOJet++ prediction with many PDF sets. C provides best description, ABM off, HERAPDF shows deviations for more forward rapidities 8 CMS-PAS-SMP--0

9 Inclusive jet cross-section ratios: 8 over.76 ev 0.4 CMS Preliminary pb (.76 ev).5 CMS Preliminary pb (.76 ev) (8 ev) Data heo. Prediction CMS Data/heory heo. Prediction σ dy (.76 ev) / d dp σ dy Data / heory.5 d dp 0.0 C NLO NP.0 y < C NLO NP.0 y < Jet p (GeV) Jet p (GeV) Inclusive jet spectra measured at several centre of mass energies. Ratios take into account correlations between uncertainties à many uncertainties cancel partially in ratios CMS-PAS-SMP

10 Inclusive jet cross-sections: 3 ev [pb/gev] dy σ/dp d - jets, anti-k t - 3 ev, 78 pb Data 4 R=0.4; y < 0.5 Systematic uncertainties NLOJE++ (C) Non-pert. corr. 5 6 ALAS Relative uncertainty of 9% in the integrated luminosity not included Preliminary 7 p 8 [GeV] Ratio w.r.t. NLO pqcd (C) First comparison of inclusive jet data with predictions at 3 ev using ak4 jets. Prediction is higher than yield measured in data offset in normalisation is completely within the jet+lumi systematicssystematics at this stage.. ALAS-CONF ALAS Relative uncertainty of 9% in the integrated luminosity not included p [GeV] ALAS 78 pb 3 ev Preliminary - anti-k t jets, R=0.4 y < 0.5 DAA (syst., total) NLOJE++ Non-pert. corr. µ = µ = p F R C MMH NNPDF3 max

11 Strong coupling constant α S α S (Q) D0 inclusive jets D0 angular correlation H ZEUS CMS incl. jets : α S (M ) = 0.85 CMS R 3 CMS tt cross section CMS inclusive jets CMS 3-Jet mass Z CMS Q (GeV) ALAS MSW 008 Extract α S as function of Q from CMS jet measurements at 7 ev C EEC Results NNPDF.3 HERAPDF.5 ALAS s = 7 ev PDF Uncertainty otal Uncertainty PDG 04 PDG otal uncertainty α S (m ) Z Latest result from ALAS transverse energy energy correlations EPJC 75 (05) 88 arxiv:

12 PDF sensitivity at the LHC PDFs determined through global fits to many observables High precision on PDF s allows for more accurate extraction of theory parameters LHC data provides huge amount of data in unexplored kinematic regions Provide constraints on PDF in vastly unchartered space Largest reach in momentum scale Q beyond the ev range (using DGLAP evolution) Reach to very low momentum fraction x ( -4 CMS and ALAS, reach to lower values using LHCb data) LHC HERA LHC evatron Fixed target S. Glazov, Braz.J.Ph. 37 (007) 793

13 PDF extractions: example NNPDF Large impact of LHC jet data on gluon PDF, especially at high x For quark PDF s less contribution from inclusive jet spectrum, but e.g. W charge asymmetry measurement EPJC 75 (05) 88 3 arxiv:

14 Multijets 4

15 Dijet azimuthal decorrelation at 8 ev ) - (rad dσ Dijet dδφ Dijet Dijet σ CMS Preliminary anti-k R = 0.7 p max >0 GeV (x ) max 900<p <0 GeV (x ) max 8 700<p <900 GeV (x ) max 6 500<p <700 GeV (x ) max 4 400<p <500 GeV (x ) max 300<p <400 GeV (x ) max 0 00<p <300 GeV (x ) heory C-NLO fb (8 ev) heoretical uncertainties CMS π /6 π /3 / π /3 π 5π/6 π Δφ (rad) Dijet heory: NLOJet++ as 3 jet production at α S 4 accuracy Δϕ Dijet Sensitive to higher order effects, p,j >0 GeV fixed, 7 bins in jet p Good agreement in a subrange, missing higher orders for low Δϕ Dijet values, points close to π excluded in theory treatment, would need merging of fixed-order and resummation 5 CMS-PAS-SMP-4-05

16 Multijets at 8 ev ALAS Several mass, momentum and angular variables are compared to several MC predictions and NLO calculations. MadGraph+Pythia give shapewise best prediction, within uncertainties NLO predictions provide good description as well See alk by Nuno Anjos 6 arxiv:

17 Multijets at 8 ev (II) ALAS Several mass, momentum and angular variables are compared to several MC predictions and NLO calculations. MadGraph+Pythia give shapewise best prediction, within uncertainties NLO predictions provide good description as well 7 arxiv:

18 Hard QCD with jets in a nutshell Inclusive jet cross-section in good agreement with NLO prediction over orders of magnitude heory predictions which can confront measurements of inclusive dijets and very high multiplicities of desire à so far theory predictions for pure hadronic multijet signatures rarely trusted enough to be used in searches First global PDF fits including 7 ev LHC data show a sizable improvement especially for the gluon PDF many production processes at the LHC involve gluons More constrained PDF s lead to lower theory uncertainties on cross-section predictions First extraction of the strong coupling constant and testing of its running 8

19 Vector bosons 9

20 Vector Bosons W and Z an be measured very accurately through their leptonic decays, photon energies precisely measured in the electromagnetic calorimeter Z and photons used for calibration of jets, Z used as candle to determine lepton efficiencies Charge asymmetry distribution of W + and W - provide input for u and d valence quark PDF s Vector boson plus jets major backgrounds in beyond standard model searches and excellent testing ground for QCD NLO predictions à data allows for large amount of precise measurements to tune MC predictions, targeting better predictions in tails of important background processes for searches 0

21 dσ/dh (jets) [pb/gev] Sherpa/Data MadGraph/Data CMS Preliminary fb (8 ev) anti-k (R = 0.5) Jets jet jet p > 30 GeV, η <.4 Z/γ* ll channel Stat. unc. (gen) Stat. unc. (gen) Data Sherpa ( j@nlo 3,4j@LO + PS) Madgraph + Pythia6 ( 4j@LO + PS) H, N [GeV] jets V plus jets precision measurements Z+Jets 8 ev H CMS-PAS-SMP See alk by Vieri Candelise ) +)/σ(z( ee)+n σ(z( ee)+ N jets jets Z e e ALAS + jets - 3 ev, 85 pb Preliminary Data Sherpa Madgraph anti-k t, R=0.4 > 30 GeV / 0 / 3/ 3 4/ 4 3 (N +)/N Very precise measurements of jets properties in Z+jets, W+Jets, γ +jets First testing of Z+ & jet NLO matrix element +PS generator Sherpa with 8 ev CMS and 3 ev ALAS Z+jets data, performance on par with multileg LO+PS generator MadGraph p jet y jet <.5 jets jets ALAS-CONF-05-04

22 Z plus jets precision measurements (II) ) j /p Z (p dσ/d log CMS Ratio of leading jet p and Z p NLO predicts shape and rate for large subrange, Parton shower necessary for mult-jet high end. LO+PS of MadGraph shows trend, but within uncertainty band, Sherpa off both in shape and rate + - Z l l, n Data jets, p Stat.+syst. > 40 GeV Z j log (p /p ) ll BlackHat(Z+jet) Sherpa k NNLO MadGraph k NNLO arxiv: fb (8 ev) BlackHat/Data Sherpa k NNLO /Data MadGraph k NNLO /Data CMS PDF Z j log (p /p ) Sherpa Stat. Err. Scale Z j.8 log (p /p ) MadGraph Stat. Err fb (8 ev) Z j log (p /p )

23 W plus heavy (forward) jets at the LHC Forward muons (p >5 GeV,.0<η<4.5) tagged jets (50<p <0 GeV,.<η<4.) LHCb 8 ev NLO SM W+c prediction from MCFM agrees with data distribution of vector sum p of muon plus tagged jets Need sum of NLO SM Wb and top production to reproduce yield of muon plus b- tagged jets in data PRL 5 (05) 00 3

24 W plus heavy jets at the DØ muons (p >0 GeV, η <.7) central jets (0<p <0 GeV, η <.5) dominant.96 ev More important at high p W c MCFM underpredicts data at high p, Alpgen & Sherpa off in shape and scale à Missing higher orders?, gluon splitting? s-quark PDF enhanced c PLB (05) 743 4

25 Cross Section Ratios 5

26 j j Cross-section ratios Differential cross section ratios: large cancellation of systematics à more stringent test of theory predictions possible In full hadronic searches photon p spectrum used to describe high end tail of Zà νν W+jets can be used to predict Z+jets as well (or vice versa) γ / dσ/dp Z dσ/dp CMS y V <.4, n jets Z over γ fb (8 ev) Data Stat.+syst. BlackHat MadGraph Z/γ p [GeV] BlackHat/Data MadGraph/Data Z/γ CMS PDF Scale MadGraph stat. error fb (8 ev) [GeV] Z/γ p [GeV] predictions for Z over γ ratio flat, but even NLO prediction off by % in scale Z over W ratio reproduced by NLO in shape and rate, Alpgen agrees in shape, sherpa a bit more off p ) )/(dσ Z+ j /dp )(dσ W+ j /dp j (/R NLO / Data MC / Data MC / Data ALAS + - (W( lν))/(z( l l )) + jet anti-k t jets, R=0.4, Data, s=7 ev, 4.6 fb j j p > 30 GeV, y < 4.4 BLACKHA+SHERPA ALPGEN+HERWIG SHERPA.3 BLACKHA+SHERPA arxiv: EPJC (04) ALPGEN j. p (leading jet) [GeV] SHERPA j. p (leading jet) [GeV] j p (leading jet) [GeV] -

27 Summary Only a handful of results out of the rich long list of measurements performed by several experiments Run I data analysis at the LHC still going strong, Run II LHC results start to show up, keep an eye on final results from evatron In general predictions provide a good description of data Results provide valuable input for theory e.g. updated PDF sets and couplings Differential measurements more challenging for predictions Ready to test new generators, e.g. multileg NLO ME+PS type Measurements of strong coupling constant and its running compatible with world average With new data coming in at the highest center of mass energies achieved more exciting times to come for LHC physicists 7

28 BACKUP 8

29 Cross Section Measurements Summary Standard Model Production Cross Section Measurements Status: March 05 σ [pb] 6 80 µb 0. < p < ev ALAS Run Preliminary s =7,8eV < m jj < 5 ev n j 0 35 pb n j n j 0 35 pb n j n j e, µ+x n j 3 n j n j 4 n j 3 n j 4 n j 5 n j 5 n j 4 n j 6 n j 6 n j 5 n j 7 n j 8 n j 6 n j 7 n j 7 ggf.0 fb H WW total (γγ, ZZ ) 3.0 fb H ττ VBF H WW H γγ H ZZ 4l LHC pp s =7eV heory Observed fb LHC pp s =8eV 95% CL upper limit heory Observed 0.3 fb 95% CL upper limit 0.7 fb pp Jets Dijets W Z t t t t chan WW γγ R=0.4 R=0.4 total y <3.0 y <3.0 fiducial fiducial fiducial total total fiducial y <3.0 Wt total H WZ fiducial total ZZ total Wγ WW+ Zγ t tw WZ fiducial fiducial fiducial total semilept. t tz total t tγ Zjj EWK Wγγ W ± W ± jjt s chan EWK fiducial fiducial fiducial fiducial total njet=0 Remarkable agreement between data and SM theory predictions 9

30 Inclusive jet cross-section ratio: 7 vs.76 ev ) ratio wrt NLO pqcd (C) ρ (y, p.4 y < y < y <..4. y < p [GeV] ) ratio wrt NLO pqcd (C) ρ (y, p y <.8.8 y < y < 4.4 [GeV] Similar data/mc trend than observed for.76 over 8 ev data by CMS p ALAS L - dt = 0.0 pb.76ev ρ = σ / σ 7eV jet jet anti-k t R = 0.6 Data with statistical uncertainty Systematic uncertainties NLO pqcd non-pert. corrections C HERA+ALAS HERA I EPJC (03)

31 ransverse Energy-Energy Correlation ϕ is the azimuthal angle between jet i and j (/σ) dσ/d(cos φ) ALAS s = 7 ev anti-k t jets R = L dt = 58 pb Detector Level Data 0 Pythia Herwig++ Alpgen he transverse energy-energy correlation is proportional to α S squared - Distribution fairly well described by Pythia6 and Alpgen, Herwig++ shows larger deviation MC / Data cos φ 3 arxiv:

32 Photon plus Jets: CDF and CMS CDF:.96 ev CMS: 8 ev fb (8 ev) BlackHat/Data CMS PDF Scale CDF photon inclusive E spectrum agrees with MCFM and Sherpa prediction, Pythia6 off in shape MadGraph/Data MadGraph stat. error γ p [GeV] Shape off both for BlackHat+Sherpa and MadGraph+Pythia6, but rather flat for BlackHat, also closer in scale than for MG For ALAS results: see talk by Claudia Kuguel 3

33 PDF reach of LHC experiments at 7 ev LHC data provides huge amount of data in unexplored kinematic regions Provide constraints on PDF in vastly unchartered space Largest reach in momentum scale Q beyond the ev range (using DGLAP evolution) Reach to very low momentum fraction x ( -5 CMS and ALAS, below -6 for LHCb) 33

34 Jet pull Jet pull handle to study color connection between jets, can be used to discriminate between jets originating from color singlets (Higgs) and color octets (e.g. gluons) Accumulated p after showering PRL 5, 000 (0) Definition jet pull vector: arxiv: Vectors of constituents relative to jet axis

35 Jet pull (II) Jet pull tested in ttbar decays using hadronic W decays, alernative: hypothetical W octet model b b ) dσ fid dθ P (J,J σ fid MC/Data.3 ALAS s = 8 ev, 0.3 fb Data SM tt Powheg+Pythia6 Flipped tt Powheg+Pythia6 SM tt Powheg+Herwig All particles θ P (J,J ) [rad]/π t ncolour Singlet W + q q 0 t ncolour Octet Data agrees with ttbar SM model (i.e. W as Colour Singlet) MC prediction from Powheg with Pythia6 shows best agreement q q 0 arxiv:

36 LHC LHCb ALAS CMS ALICE 36