Hadron Collider Physics, HCP2004, June 14-18

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1 ) " % "" ' & % % " ) " % '% &* ' ) * ' + " ' ) ( $#! ' "") ( * " ) +% % )( (. ' + -, '+ % &* ' ) ( 021 % # / ( * *' 5 4* 3 %( '' ' " + +% Hadron Collider Physics, HCP2004, June 14-18

2 The Run II DØ Detector N Forward Mini- Drift Tubes Muon Toroid Muon Scintillation Counters S PDTs CC Shielding EC EC Platform Tracking System: : Silicon, Fiber Tracker, Solenoid, Central & Forward Preshowers Fiber Tracker/Preshower VLPC Readout System Tevatron Run II: p p collisions at s = 1.96 TeV / average rate: 1.7 MHz Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

3 The DØ Calorimeter END CALORIMETER Outer Hadronic (Coarse) Middle Hadronic (Fine & Coarse) uniform and hermetic active material: liquid Argon absorber: Uranium Inner Hadronic (Fine & Coarse) Electromagnetic 1m CENTRAL CALORIMETER Electromagnetic Fine Hadronic Coarse Hadronic segmentation: η φ = for EM showers max.: coverage up to η 5 Run II upgrades: shorter times between bunch crossing 396 ns faster trigger and readout electronics more material in front of calorimeter magnet, tracker, new pre-shower detector Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

4 QCD at the Tevatron parton jets particle jets calorimeter jets theory experiment Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

5 QCD processes at the Tevatron unique possibilities: test of pqcd predictions up to highest s on earth! direct sensitivity to quark and gluon densities at large x search for new physics - hunting for resonances - at highest p T and largest M final state quark compositeness?? QCD processes are main backgrounds for most new physics signals sensitivity to new physics need very good understanding: of QCD signals of QCD models (Monte Carlo event generators) Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

6 The Run II cone algorithm particle = {experiment: energy deposits / MC: stable particles / pqcd: partons} three parameters: R cone = 0.7, p T min = 8 GeV, overlap fraction f = 50% Use all particles as seeds make cone of radius R = p ( y 2 + φ 2 ) < R cone around seed direction proto jet: add particles within cone in the E-scheme (adding four-vectors) iterate until stable solution is found with: cone axis = jet-axis Use all midpoints between pairs of jets as additional seeds = infrared safety!!! (repeat procedure as described above) Take all solutions from the first two steps: remove double solutions remove proto-jets with p T jet < p T min Look for jets with overlapping cones: merge jets, if more than a fraction f of p T jet is contained in the overlap region otherwise split jets: assign the particles in the overlap region to the nearest jet ( and recompute jet-axes) G.C. Blazey et al., hep-ex/ Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

7 Differences: Run I and Run II the cone algorithm used by DØ in Run I differed in the following ways: Particles were combined into jets in the E T -scheme ( snowmass convention ) instead of the E-scheme (adding four-vectors) in Run I by definition jet four-vectors were massless pseudorapidity η was used instead of rapidity y transverse energy E T = P E sin θ was used instead of transverse momentum p T please note: E E T scheme T p E scheme T and M E T scheme dijet M E scheme dijet no midpoints were used as additional seeds procedure not infrared safe no predictions from perturbative QCD possible Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

8 Jet Production at s = 1960 GeV inclusive jet cross section at s=1960 GeV and s=1800 GeV dσ incl. jet /dp T / (pb/gev) inclusive jet cross section cone algorithm R cone =0.7 (central region) NLO (JETRAD) sqrt(s) = 1960 GeV sqrt(s) = 1800 GeV decomposition of partonic subprocesses for the inclusive jet cross section fractional contribution gg subprocesses for central inclusive jet cross section gq qq transverse jet momentum / GeV p T / GeV increase between 20% and > 200% significant gluon contributions at largest p T Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

9 Jet Energy Correction correction of the jet energy reconstructed in the detector particle level jet Offset - energy not associated with the hard interaction Response (calorimeter response to jet energy deposits) EM calibrated on mass peak Z ee measured from energy balance in γ + jets events measured for energies below 200 GeV ( extrapolation) Showering energy losses due to showering outside the reconstructed jet cone (detector effect! no correction for physics effects) determine resolutions correct for smearing effects (unsmearing procedure) Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

10 Highest p T / Largest Dijet Mass jet 1 jet 2 p T = 616 GeV p T = 557 GeV y = 0.19 y = 0.25 φ = 0.65 φ = 3.78 M jj = 1206 GeV Markus Wobisch HCP2004 Run II QCD Results from DØ June 14, 2004

11 Inclusive Jet Cross Section dσ / dp T [pb / (GeV/c)] DO Run II preliminary DO data, Cone R=0.7 y < < y < < y < 2.4 NLO (JETRAD) CTEQ6M max R sep =1.3, µ F = µ R = 0.5 p T s=1.96tev analyzed data sample: L = 143 pb 1 measure rapidity dependence (Run I sensitivity to high-x gluon) y jet < 0.5 (central region) 1.5 < y jet < 2.4 (forward region) = 143 pb L int [GeV/c] p T event selection: inclusive jet triggers inclusive jet cross section falls over six orders of magnitude strong rapidity dependence Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

12 Inclusive Jet Cross Section comparison with theory: ratio data / NLO pqcd (µ r,f = 0.5 p max T, CTEQ6M pdfs) data / theory DO Run II preliminary y < 0.5 Systematics uncertainties PDF uncertainties Cone R=0.7-1 = 143 pb L int data / theory DO Run II preliminary 1.5 < y < 2.0 Systematics uncertainties PDF uncertainties Cone R=0.7-1 = 143 pb L int data / theory DO Run II preliminary 2.0 < y < 2.4 Systematics uncertainties PDF uncertainties Cone R=0.7-1 = 143 pb L int 3 2 NLO (JETRAD) CTEQ6M max R sep =1.3, µ F = µ R = 0.5 p T 3 2 NLO (JETRAD) CTEQ6M max R sep =1.3, µ F = µ R = 0.5 p T 3 2 NLO (JETRAD) CTEQ6M max R sep =1.3, µ F = µ R = 0.5 p T [GeV/c] p T [GeV/c] p T [GeV/c] p T theory: increased uncertainty due to pdfs in the forward region good agreement between data and theory at all rapidities large uncertainties in the measurement due to jet energy scale need better understanding! = significant improvements already achieved... Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

13 Dijet Cross Section data sample: L = 143 pb 1 rapidities: y jet < 0.5 (central region) <dσ/dm JJ >, pb/gev DØ Run II preliminary -1 DØ Data, L = 143 pb NLO (JETRAD) CTEQ6M max R sep = 1.3, µ R = µ F = 0.5 p T data / theory DØ Run II preliminary NLO (JETRAD) CTEQ6M max R sep = 1.3, µ R = µ F = 0.5 p T systematic uncertainty pdf uncertainty < 0.5 cone R = 0.7, y jet M JJ, GeV/c 0.5 cone R = 0.7, y jet < M JJ, GeV/c message: consistent with results from inclusive jet cross section Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

14 Dijets: Azimuthal Decorrelations Dijet production in lowest order pqcd: three-jet production in lowest order pqcd: p T balance φ dijet = π hard third jet: (k large) φ dijet < π soft third jet: (divergence in LO pqcd) (k 0) φ dijet π = Delta Phi distribution is directly sensitive to higher-order QCD radiation without explicitly measuring a third jet test O(α 3 s ) calculations Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

15 Dijet Azimuthal Decorrelations (1/σ) dσ/d φ dijet 3 2 DØ Run II preliminary p T max > 180 GeV ( 125) 130 < p T max < 180 GeV ( 25) 0 < p T max < 130 GeV ( 5) 75 < p T max < 0 GeV ( 1) inclusive dijet event sample: central region: y < 0.5 p T, jet 2 > 40 GeV p T max : 75, GeV p T jet2 R cone = s = 1.96 TeV, L = 150 pb > 40 GeV, y jet < 0.5 measure: 1/σ dijet dσ dijet φ dijet (normalize by inclusive dijet cross section) measurement only for: φ dijet π/2 (avoid region where two leading jets overlap) φ dijet [rad] towards larger p T : increased correlation in φ / spectrum more strongly peaked at π Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

16 Dijet Azimuthal Decorrelations 1/σ dijet dσ dijet / d φ dijet DØ Run II preliminary p T max > 180 GeV ( 3 ) 130 < p T max < 180 GeV ( 2 ) 0 < p T max < 130 GeV ( ) 75 < p T max < 0 GeV NLO LO NLOJET++ / CTEQ6.1M µ r = µ f = 0.5 p T max π/2 3π/4 π φ dijet / rad compare with pqcd in fixed order: leading order clear limitations: divergence at φ dijet = π (soft processes) no phase space at < 2/3π (only three partons) next-to-leading order very good description over whole range except extreme φ dijet regions: low φ dijet : only tree-level large φ dijet : third jet is soft (huge scale dependences) Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

17 Dijet Azimuthal Decorrelations 1/σ dijet dσ dijet / d φ dijet DØ preliminary p T max > 180 GeV ( 0) 75 < p T max < 0 GeV test Monte Carlos third and fourth jet generated by parton shower (soft and collinear approximations) HERWIG v6.505: very good overall description! slightly too high only at intermediate φ dijet -2-3 HERWIG PYTHIA (CTEQ6L pdfs) π/2 3π/4 π φ dijet / rad PYTHIA v6.223 (default:) very different shape too strongly peaked too low in the tail (factor of 5!) amazing success for parton shower implementation in HERWIG Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

18 Dijet Azimuthal Decorrelations 1/σ dijet dσ dijet / d φ dijet DØ preliminary p T max > 180 GeV ( 0) 75 < p T max < 0 GeV check prospects for tuning of PYTHIA parameters increase initial-state radiation: PARP(67) = 1 = 4 multiplicative factor, applied to the hard scale Q -1 ISR shower starts at Q*PARP(67) -2-3 PYTHIA default variation of ISR (CTEQ6L pdfs) π/2 3π/4 π φ dijet / rad with more ISR: significant improvement! much closer to the data high flexibility in PYTHIA tuning required!! huge sensitivity of data = important for usage of PYTHIA in new-physics searches!!! Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

19 Elastic Scattering and Diffraction So far: investigations of very rare hard, inelastic processes About 40% of the total p p cross section is elastic scattering and diffraction color singlet exchange (vacuum quantum numbers: no charge/color) Pomeron?? intact proton in final state no color flow between proton and final state experimental signatures: rapidity gap, identified final-state proton present two types of analyses: Single Diffraction (either p or p intact) search for rapidity gap in forward regions: absence of particles / detected energies in proton direction (Luminosity Monitor and Calorimeter) Elastic Scattering p and p both intact no momentum loss scattered at small angle w.r.t. beam direction no other particles produced search for intact protons in beam pipe (Forward Proton Detector) Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

20 Diffractive Z Production In Pomeron picture: factorize interaction QCD subprocess Pomeron pdfs diffractive jet production (Tevatron, HERA) dominated by gluon pdf diffractive W / Z production in LO: only sensitive to quark pdfs DØ Run I publication: diffractively produced W and Z bosons nine single diffractive Z e + e events. No result in muon channel. Run II: first search for Z µ + µ events with forward rapidity gaps define rapidity gap: use calorimeter and luminosity monitors calorimeter: sum of cell energies in electromagnetic and fine hadronic layers (above threshold) in forward region luminosity monitors: sum charges on each side (North/South) either on/off +z (based on prelim. studies / to be optimized / need to understand background/efficiency!!) Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

21 Diffractive Z Production Events / GeV No Gaps no gaps Mean: GeV 89.8 ± 0.1 GeV work in progress Events / 2 GeV Gap N or S gap N & S combined Mean: GeV 89.6 ± 1.0 GeV North = negative rapidities South = positive rapidities Invariant mass confirms that these events are all Drell-Yan type Z events Events / 2 GeV Mass (GeV) 5 Gap South gap south Mean: GeV 90.2 ± 1.3 GeV Mass (GeV) Events / 2 GeV Mass (GeV) 5 Gap North gap north Mean: GeV 89.3 ± 2.0 GeV Mass (GeV) Will be able to compare Z boson kinematics (p T, p z, rapidity) need quantitative study of gap definition to understand backgrounds, efficiency evidence of Z events with a rapidity gap signature no interpretation yet!! background / efficiency effects could be large Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

22 Forward Proton Detector (FPD) A series of momentum spectrometers that make use of accelerator magnets in conjunction with position detectors along the beam line A D2 Roman Pot Detector A 1S A 1Q p Q 4 D S Q 2 Q 3 Q 3 S A D1 A 2S A 2Q P 2Q Q 4 p Q 2 P 1Q P 1S P 2S total: 9 spectrometers composed of 18 Roman Pots so far: stand-alone operation Dipole Spectrometer inside the beam ring in the horizontal plane use dipole magnet (bends beam) Z(m) Quadrupole Spectrometers surround the beam: up, down, in, out use quadrupole magnets (focus beam) also shown here: separators (bring beams together for collision) now: fully integrated in DØ readout (for Z analysis not yet calibrated) Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

23 Elastic Scattering ξ kinematic variables: t = (p f p i ) 2 four-momentum transfer ξ = 1 p f L /pi L fractional longitudinal momentum lost by proton (p i initial-state proton / p f final state proton) elastic scattering: ξ = 0 distribution is peaked at zero, as expected, with a resolution of σ(ξ) = Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

24 Prelim. Elastic Scattering Results new DØ dn/dt distribution at s = 1.96 TeV arbitrary normalization shape comparison! the dσ/dt data collected by different experiments at different energies arbitrary factors between successive curves are applied Compare slope with model: Bloch et al., Phys. Rev. D41 (1990) 978. Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

25 Summary and Outlook Tevatron Run II physics program is on the way present results: integrated luminosities 150 pb 1 > Run I inclusive jet and dijet cross sections larger reach due to increased center-of-mass energy good agreement between theory and data (large exp. uncertainties jet energy scale) dijet azimuthal decorrelations sensitive to higher order QCD processes (beyond dijet production) test of 3-jet NLO pqcd at Tevatron Diffractive Z Production signatures of diffractive Z µ + µ production observed Elastic Scattering Forward Proton Spectrometer dn/dt analysis from FPD commissioning data FPD now integrated into DØ readout outlook: in the meantime collected: twice the integrated luminosity jet energy scale has already been significantly improved = use FPD to explore diffractive physics = jet data: explore highest p T and M JJ over large rapidity regions = test QCD / pin down the high-x gluon / hope to observe new physics!! Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,

26 Backup: Unsmearing Procedure problem: due to p T (M dijet ) resolutions, the reconstructed spectra are smeared assume: there exists a continuous representation of the true underlying distributions solution: make a (QCD inspired) ansatz representing the true spectrum smear this ansatz, according to the resolutions iterate = fit smeared ansatz to data when done: correction (bin-by-bin) = ratio unsmeared / smeared ansatz Markus Wobisch HCP2004 Run II QCD Results from DØ June 14,