Searches for double partons Lee Pondrom April 2, 2012
Jet20 Data Stntuple gjt1bk & gjt1bj 3E6 events Require only one vertex Require at least two jets with |η|<1. ET1>20 GeV. Other jet ET>5 GeV Apply level 5 jet energy corrections Events Jet1&2 Jet3 Jet4 Lum(live) 110203 61769 21174 151694/nb 56% 19% Prescaled σ ≈ 0.7 nb; unprescaled σ≈1.2b
Jet20 data Jet ET
Jet20 data Δφ distributions
Following Rick Field, define the transverse region relative to jet1φ Look at charged tracks with |η|<1, pT>.5 GeV, and with /3<Δφ<2/3, where Δφ is the azimuthal angle between the track and the highest ET (trigger) jet. These tracks are sensitive to the underlying event, and hence at least in part depend on multiparton interactions.
Jet20 data properties of the transverse tracks
Jet20 transverse track pT cut Based on the idea that the transverse region has some sensitivity to what is going on in the event other than the two primary jets, we make a cut on the scalar sum of track pT>15 GeV. This cut leaves 1611events – 1.5% of all dijets. The fraction increases with jet energy. The cut moves jet3 into the Δφ region of the tracks.
Effect of the ∑transtrackpT>15GeV on the jet φ distributions
Effect of the ∑transtrack pT>15 GeV cut on jet φ Of the 1611events, 1495, or 93%, have jet3ET >5 GeV, and these jets are clustered around /2 relative to the trigger jet. 15 GeV is too high relative to the main jet activity, so the correlation Δφ12 is strongly perturbed.
Δφ34 and the high pT transverse tracks The idea is that jets 3 and 4 could be result of independent scattering of two other partons. If that is true, a good place to look is in the Δφ region of the underlying event. The ∑transtrack pT>15 GeV serves as a ‘trigger’. Δφ34 should peak near .
Δφ34 and jet3ET before and after track∑pT>15 GeV cut
Enhancement near Δφ=? Normalizing the two distributions to Δφ<1.5 gives a difference 2.4<Δφ<3.2 of -8±17 events. Transverse jet energies for jets3 and 4 are increased by the track pT cut
Look at jet100 data 1E6 events gjt4bk & Pythia bt0stb Same requirements: only one good vertex, trigger jet ET>100 GeV, level5 jetECorr Yields for 1E6 events Jet1&2 jet3 jet4 pT>15GeV Lum 170710 101231 35034 10247 126342/nb Jet3 and jet4 fractions same as jet20 pT>15 GeV fraction 4x larger than jet20 σ ≈ 1.3 nb no prescale
Jet100 data and Pythia ET
Jet100 & Pythia transtrack pT and Δφ12
Jet100 data effect of the transverse tracks on Δφ12 and Δφ13
Jet100 effect of transverse tracks on jetET3 and Δφ34
Jet100 & Pythia effect of ∑pT>15 GeV cut on transverse tracks
Jet100 effect of transverse tracks Jet100 similar to jet20. Pythia & data agree. Perturbation of Δφ12 considerably less than for jet20. Δφ13 shifts so that jet3 is /2 away from jet1 Jet3 ET shifts to larger values
Compare jet100 and Pythia Δφ34 before and after ∑pT>15GeV cut
Jet100 data and Pythia Δφ34 The data and Pythia agree qualitatively in the shapes of the Δφ34 angular distributions before and after the ∑pT>15 GeV cut on the scalar sum of transverse tracks. Near Δφ34≈ Pythia has a smaller excess than the data.
Now compare Δφ34 before and after ∑pT>15 GeV cut
Excess near Δφ34≈ Normalize the plots to .5<Δφ34<1.5 Subtract (after cut)-(before cut) 2.4<Δφ34<3.2. Jet100 data difference = 295±50 events Pythia difference = 54±30 events
Does this excess mean anything? There are 170710 jet100 good dijet events So the excess 2.4<Δφ34<3.2 is 0.0017±0.0003. If the number of MPI’s per hard scatter is 5, which comes from Field’s analysis of Drell Yan (PRD?), the probability of a second hard scatter is 0.00034±0.00005, or about 4E-4. Pythia excess is smaller: 0.0007±0.0004.
Look at the second vertex Jet100 data gjt4bk and gjt4bm 12E6 events Exactly two vertices in the event, separated by at least 10 cm. Jets 1 and 2 are on vertex number 1. At least 3 tracks with |η|<1 and pT>0.5 GeV are on vertex number 2 Cross section for a vertex defined by these track cuts is about 6 mb.
Tracks on the second vertex
Jet ET on 2nd vertex with ∑trackpT>15 GeV ‘trigger’
JetET on 2nd vertex The transverse track scalar ∑pT>15GeV ‘trigger’ selects events on the second vertex which are softer than Jet20, the lowest transverse energy jet trigger in the data.
Effect of the second vertex ∑pT>15 GeV on jet Δφ
Effect of second vertex tracks on jets3 and 4
Add first and second vertex Δφ34 distributions
Δφ34 correlation The peak near Δφ= corresponds to: 2.4<Δφ34<3.2 = 141±12 events This is 3.7E-4 of all two vertex events. This fraction is in agreement with the excess observed in jet100 data, provided that there are 5 multiparton interactions per hard collision. The Pythia effect is about 3σ smaller than the data. More Pythia MC would be useful
Extend the study to Drell-Yan pairs Use high pT muon trigger stntuples 5E9 events total available. 1E6 events takes about 4 hours to analyze So 5E9 would take 2 years, unless I can speed things up. 3.2E7, or less than 1%, analyzed so far
± pair yields from high pT muon trigger Stntuples Require two muons opposite charge |η|<1. Eliminate events with cosmic rays Require at least one CMU*CMP muon 34723 events 30GeV<m<130GeV 28811 events 80GeV<m<100 GeV 12252 events pair pT>10 GeV
D-Y mass and pT plots
D-Y mass and pT Gauss fit to peak at 90.8 GeV, width 3.8 GeV Pair pT compared to recoil jet ET with level5 jet energy corrections is much harder than jet20 ET spectrum
Compare to Pythia D-Y
Δφ and ΔET for track pair and recoil jets
Data compared to Pythia D-Y
Δφ and ΔET for track pair and recoil jets Pair pT>10GeV. Central Δφ peak consistent with jet-jet Δφ12 for jet20 data. Δφ=|(recoil jetsφ) – tracksφ| - is asymmetric, with a tail towards negative values, ie jets and tracks in the same quadrant. ΔET is nearly symmetric, with a shift such that jet ET is about 4 GeV low relative to the tracks, even with level5 jetEcorr. Pythia agrees with both plots.
Scalar sum pair pT for transverse tracks Z data, jet20data, and Pythia
Transverse track scalar ∑pT relative to the pair axis The trans track ∑pT distributions for D-Y pairs and for QCD jet20 dijets look very similar. pTZ > 10 GeV required to define ‘transverse track’. Again Pythia agrees well with the data
ET distributions jets 1&2 for Z-> data and Pythia D-Y
Effect of pTZ on jet ET There are plenty of dijets with ET>5 GeV in events with pTZ<10 GeV Requiring pTZ>10 GeV cuts out the low ET jets, particularly for jet 1. While this has been done only for Pythia, because it is faster to process, we expect the same result in the data.
Recoil jets 1&2: dijet mass and Δφ
Dijet mass and Δφ12 Average dijet mass changes very little: <mass12>=19 GeV for no cut on pTZ, each jet ET>5 GeV <mass12>=22 GeV for pTZ>10 GeV, each jet ET>5 GeV Δφ12 shows a distinct peak at for no cut on pTZ, which goes away with pTZ>10 GeV
Closer look at Δφ12 near
Closer look at Δφ12 near Normalizing the red curve to the black from 0<Δφ12<2 radians gives an excess from 2.5<Δφ12< of 1121 events. The difference in the two histograms is compared to jet20 data in the second plot. It is possible for two jets to be created in D-Y events where the pT of the pair is less than 10 GeV. For very low pair pT the two jets have to balance each other.
scalar∑transtrack pT>15 GeV For Z-> data with pTZ>10 GeV define the transverse tracks after all muons have been removed as those tracks with pT>.5 GeV and |η|<1 at /3<Δφ<2/3 relative to pTZ.. Then require the scalar ∑pT of these tracks to be >15GeV, as a ‘trigger’ analogous to the jet20 and jet100 analyses.
Effect of ∑pT>15 GeV on Δφ(jets-Z) and jet1 ET
Effect of ∑pT>15 GeV on jet2 ET and Δφjets1 and 2
Effect of ∑pT>15 GeV on Δφjets2-3
Discussion Remember that jet1 in the jet20 and jet100 data becomes the Z in the D-Y data, so jet20 jet2->D-Y jet1, jet20 jet3->D-Y jet2, etc. The ∑pT>15 GeV leaves only 129 events in D-Y, so the statistics are limited. There are clear parallels: ∑pT>15 GeV increases recoil jet ET’s, and smears Δφ(Z-jets), just like in the jet20/jet100 data.
More discussion However, there is no sign of an enhancement in Δφ(jets2-3) near . In fact, Δφ(jets2-3) looks more isotropic with the ∑pT>15 GeV cut than without it. This represents about 6% of the total available high pT muon data.