QCD Measurements at DØ University of Texas -Arlington- Seminar, University of Virginia January 24th 27
TeVatron Collider at Fermilab Proton-Antiproton Collisions at Center-of-Mass s = 1.96 TeV Two Multi-Purpose Detectors: CDF and DØ Many Recent Improvements to Accelerator and Detector Operations Delivered / Recorded Integrated Luminosities L > 1 fb 1 1
ements QCD Processes at the TeVatron Inclusive ProductionPSfrag replacements Single Diffraction p X p X t 2 t 1 s s e.g Jets PSfrag replacements p p Y Diffractive Central Production t p(ξ p ) p t 1 p(ξ p ) s M p t 2 p(ξ p ) Simultaneous Probe of Different Final States s =1.96 TeV p p c.o.m energy t 4-mom. transfer ξp fractional proton ξ p fractional antiproton (Run II) squared mom. loss mom. loss 2
DØ Detector: Experimental Signatures µ Run 175332 Event 33114 Thu Apr 8 16:49: 24 15 NORTH SOUTH 36 E (GeV) p µ +z p Bins: 484 Mean:.595 Rms:.961 Min:.366 Max: 11.3 phi 18-4.7-3 -2-1 1 eta 2 3 me_t: 6.3 phi_t: 325 deg High Energy Proton Dissociates Large Energy Deposits in South Side Detectors 4.7 High Energy Antiproton Scatters through Small Angle No Scattered Antiproton in Main Detectors Region of Low Level Energy Deposition: North Side Detectors Two Identified Large p T Muon Tracks Candidate Single Diffractive Z µ + µ Event 3
Probing Parton Distributions in the Proton... Photons, Jets, W etc., P 1 PDF x 1 P 1 x 2 P 2 ˆσ Underlying Event P 2 PDF Cross Sections Predictions Require PDF inputs σ = Σ dx 1 dx 2 f(x 1, Q 2 )f(x 2, Q 2 )ˆσ Fragmentation Jets x 1,2 : Momentum Fraction Carried by Struck Parton Q 2 : Momentum Transfer Squared 4
Inclusive Jet Production Probe Parton Distributions fractional contribution 1.8.6.4.2 gg subprocesses for central inclusive jet cross section gq qq 2 4 6 8 data / theory 2.5 2 1.5 1 NLO µ = µ = p R R F T cone with threshold corrections (2-loop) Hadronization corrections applied CTEQ6.1M MRST24 Alekhin22 Data scaled to theory for CTEQ6.1M at p = GeV/c at y <.4 T jet to remove luminosity uncertainty =.7 data / theory 2.5 2 1.5 1 NLO µ = µ = p R R F T cone with threshold corrections (2-loop) Hadronization corrections applied CTEQ6.1M MRST24 Alekhin22 Data scaled to theory for CTEQ6.1M at p = GeV/c at y <.4 T jet to remove luminosity uncertainty =.7 transverse jet momentum (GeV).5 DØ Run II preliminary.5 DØ Run II preliminary dy (pb/(gev/c)) T σ/dp 2 d 5 4 3 2 1-1 -2-3 -4 s = 1.96 TeV -1 L ~.8 fb R cone =.7 DØ Run II preliminary NLO pqcd plus threshold corrections (2-loop) Hadronization corrections applied CTEQ6.1M µ = µ = p R F T y <.4 (x) jet.4 < y <.8 jet 5 2 3 p T (GeV/c) -1-1 y <.4 L ~.8 fb.4 < y <.8 L ~.8 fb jet jet 2 3 4 5 6 7 2 3 4 5 6 p (GeV/c) p (GeV/c) Data / Theory Normalised at P T = GeV T Shape Consistent with Expectations (PYTHIA) 5 T
Jet Selected in a Cone: R = ( φ) 2 + ( y) 2 ) DØ Jet Selection: Midpoint Cone Algorithm Additional Iteration: Use Midpoints between Pairs of Jets Jets with Overlapping Cones: Merged or Splitted Measured Jet Energies Scaled: E corr = E meas Ω RS where Ω : Offset R : Response S : Showering Now Extending Forward with Reduced JES Syst. Uncertainties. 6
Dijet χ Distribution Search for Deviations from Point-like Parton Behaviour 1/σ dijet dσ dijet /dχ dijet.12.4 < M jj /TeV <.5.1.8.6.12.5 < M jj /TeV <.6.6 < M jj /TeV <.7.1.8.6 dijet production @ 1.96 TeV QCD at NLO µ=p T Compos. Λ q =2.7TeV, η=+1 ADD LED M S =1.6TeV, n=4 TeV -1 ED M C =1.6TeV In Progress: Extension to Large Measured Dijet Masses.12.1.7 < M jj /TeV <.8.8 < M jj /TeV <.9.8.6.12.1.9 < M jj /TeV < 1. M jj /TeV > 1..8.6 5 15 5 15 Expected Stronger Sensitivity at Large M jj (e.g. Improved Limits) χ dijet = exp( y ) 1/N dn/dχ.14.12.1 4 < M jj < 5.8.6.4.2 2 4 6 8 12 14 16.14.12.1 6 < M jj < 7.8.6.4.2 2 4 6 8 12 14 16 χ = exp(y 1 y 2 ) 7
Probe of Strange Quark Contribution Select Charm Jets with Muon Tag W + Charm Jet Production Signal Channel: Opposite Sign Lepton from W Decay Electron Channel Muon Channel Events 8 6 4 2 W->e ν Wc Wj Wcc Wbb ttbar Zj pred 2 4 6 8 12 14 16 18 2 OS µ tagged jet P_T Events 9 8 7 6 5 4 3 2 W-> µ ν data Wc Wj Wcc Wbb ttbar Zj Pred 2 4 6 8 12 14 16 18 2 OS µ tagged jet P_T Extraction of Charm Jet Fraction + Systematic Uncertainties in Progress 8
Production of Heavy Flavor Jets Select HF Jets with µ and Secondary Vertex µ 2.5 2 Pythia NLO µ-tag Primary Vertex Secondary Vertex Data/Theory 1.5 1 Prompt Tracks Extract B Contribution (In Progress): Selected Jets Examined using Neural Net.5 All Error JES Only NO HF D Preliminary 5 15 2 25 3 35 4 Pt (Gev/C) Background Area Determined for Signal Region P T [GeV ] 9
Photon + Jet Production Probe of Gluon Distribution at Large P γ t Photon + Jet σ/ dp T /dη (pb/gev) 2 d Can extract G(x, Q 2 ) 3 data NLO QCD 2 1-1 -2-3 Inclusive Photon -1 L = 326 pb γ (µ R =µ F =µ f =p T ) CTEQ6.1M 5 15 2 25 3 γ p T DØ Differential Distributions in Four Regions: Jet CC: γ same side / opposite side Jet EC: γ same side / opposite side Prel. Comparisons to JetPhox in Progress (GeV)
Di-Photon Production Acceptance and Efficiency Corrections in Progress Extract Di-Photon Contribution from Candidate EM Clusters (Matrix Method) Differential Di-Photon Angular (and Mass) Distributions 11
replacements in the Pomeron... p Probing Parton Distributions Lowest Order: Two Gluon Exchange Evolve to Higher Orders J 1 J 2 p t p QCD Pomeron: Non-Trivial Effective Gluonic Exchange Can Introduce an Effective Pomeron Structure Function Ingelman, Schlein (1985) Phys. Lett. B152 12
Single Diffractive Z Production Select Events with Small Fractional Beam Momentum Loss: ξ p = ET exp( η) s Events Selected via Z µ + µ Decay Minimum Accessible ξ from Mass and Decay Properties: ξ M 2 X s Diffracted System Boosted (Details Depend on Structure Func.) 13
Data / MC Comparisons MC POMWIG Gives Reasonable Description of Data 14
BKGD Suppression Expect Low Activity in Forward Detectors DATA: J/ψ Events LM multiplicity X sum energy cell - north side LMmult_calenergy_north_st Entries 447783 Mean x 2.5 Mean y 144.4 RMS x 4.39 RMS y 76.93 5 4 3 MC Expectations: Di-Jet Events 2 N selected /N total POMWIG events per ESUM cut.9.8.7.6.5.4.3.2.1 POMEsum Entries 117362 Mean 127.3 RMS 58.71 POMWIG N selected /N total PYTHIA events per ESUM cut.5.4.3.2.1 PYTEsum Entries 11748 Mean 152.9 RMS 47.54 PYTHIA Ecal 3 25 2 15 5 5 15 2 25 LM Mult. Tuning Low Activity Cut 2 4 6 8 12 14 16 18 2 22 ESUM 2 4 6 8 12 14 16 18 2 22 ESUM Demand Low Summed Energy Deposit in Forward Calorimeter 15
Diffractive p p px p Scattering Search for Exclusive Production of Central Systems p 2 placements p 1 p 1 p 2 X Arbitrary Units MC Expectations.6.5.4.3.2.1 PYTHIA DPEMC.1.2.3.4.5.6.7.8.9 1 EM CC Cells Energy / EM Cells Energy.45.4.35.3.25.2.15.1 Inclusive Central Jet Events Jet Events with Gaps DATA: Dijet Events Measure Energy Deposited in Central System Compare to Total Event Energy.5 1 2 3 4 5 6 7 8 9 Dijet Energy / cell Energy Sum Constrain Predictions for LHC 16
Run II: DØ Forward Proton Detectors Nine Momentum Spectrometers Each Comprised of 2 Scintillating Fiber Detectors Located behind Existing Dipole and (low-β) Quadrupole Accelerator Magnets Position Detectors Housed Inside Steel Containers (Roman Pots) Operate mm from Beam (Outside Ultra High Vacuum) Can Reconstruct High Energy Scattered Protons and Antiprotons 17
DØ Forward Proton Detector 6 Layers of Scintillating Fiber Channels: U,U,X,X,V,V (Each Channel is made up of four fibers) 2 Fiber Channels in U and V layers; 16 Fiber Channels in X layers 1 Trigger Scintillator layer (Fast Photomultiplier Tube Readout) Channels of U and V layers orientated at ±45 to X 3 Planes for Reconstruction Primed and Unprimed Channels Offset w.r.t each other (by 2/3 Fiber) Finer Hit Resolution Since Jan. 24: All 18 Scintillating Fiber Detectors regularly brought close to the beam line (Dipole Detectors since Feb 23) 18
replacements Elastic p p p p Scattering p p s p t p Events Selected using Forward Quadrupole Spectrometers FPD Detector Alignment dσ/d t [mb GeV 2 ] + E7 ( s= 18 GeV) - Block et. al t [GeV 2 ] Proton and Antiproton Hits in Back-to-Back Spectrometers 19
Special TeVatron Stores Single High-β / Low Luminosity Store Narrower Beam at Detectors, p p Collisions at DØ Only (Beam Separators Off, 1-on-1 Bunch Structure) 2
FPD Trigger System Level 1 Trigger Based on Detector Fiber Information Digital Front End: Calculate No. of Wide Segment Hits in Each Detector Forms Spectrometer Decisions based on Product of Hit Multiplicities Trigger Manager: Forms Elastic and Double Pomeron Spectrometer Coincidences Developed / Implemented / Commissioned / Completed in 25 21
X2[mm] X 1 [mm] 22
Halo Background Suppression Dedicated Studies: Particles Passing Intime through Spectrometer, Pass Earlier through Opposite Spectrometer Measure Pulse Times using Individual Detector Scintillators (FPD Timing Electronics) Signal Timing Bit: Set if Pulse (Leading Edge) Detected above Threshold Intime Halo Timing Bit: If Pulse Also Detected (Above Threshold) in Earlier Timing Window 23
Detector Timing Distributions Relative Pulse Heights Arbitrary Time Units Signal Thresholds Optimisation Increased Efficiency 24
Elastic p p p p Scattering Differential Measurement of Elastic t Distribution dncorr/d t Correction for FPD Detector Efficiencies in Progress t [GeV 2 ] 25
Summary and Outlook QCD Measurements Already Providing Insight into: Parton Distributions Structure of the Diffractive Exchange Extensive Forward Proton System at DØ First Diffractive Measurements with Large Triggered Data Samples Future Increase in Statistics: Higher Precision Tests over a Larger Kinematic Region 26