Summary of CR Studies

Summary of findings so far

Changes in PYTHIAV64

LBL MC studies and MTM3 results

Andrea Castro's studies

Comparison of tagged b jets in data with MC

Color Reconnection Systematics(1)

New models of Color Reconnection (CR) have been introduced in recent versions of PYTHIA starting with V6.3. In our analyses we have been using PYTHIA V6.2 (tune A).

The latest version (PYTHIA V6.4) includes, in addition to a new model for color reconnection, new models for the parton shower

(ISR and FSR), and the Underlying Event, UE, ( Multiple Parton Interaction (MPI) and beam remnants).

The CDF and D0 collaborations work together on understanding the

effects of these changes and on defining a common procedure to include them in the systematic uncertainties.

Tuning of PYTHIA V6.4 to data is in progress. Tunes which include LEP data (called “pro”) are now available in PYTHIA V6.4.20.

(see Perugia MC meeting, October 2008)

So far we have looked at two recent tunes: ACR(pro) and S0A(pro).

Color Reconnection systematics (2)

Tune ACR(pro): includes only the new color reconnection model.

Tune S0A(pro): uses new modeling for the parton shower, UE and CR. For this tune, we have to investigate possible overlaps with the systematic uncertainties we are now using.

At this stage of our studies we evaluate the CR systematics using the

ACR(pro) tune, that includes only changes in the CR model. We compare ACR(pro) to the A(pro) (tune A in V6.4) tune.

This has been done in the di-lepton, the lepton+jets and the all hadronic channels. The three mass shifts agree within statistics

Mtop = Mtop(A(pro))–Mtop(ACR(pro)) = (0.4-0.5)  0.3 GeV/c2

Work is in progress to compare jet shapes in PYTHIA V6.4 with data from various samples to isolate the effects of the new parton shower from the CR contribution.

Procedures for MC Studies

A. Given a MC sample, for each event we match the partons from top decays to the observed jets (Ntight = 4)

We then know which jet is light quark jet and which ones are b-jets. We correct the jets at L5 (no out of cone correction)

To check the changes between the 2 MC's we do the following:

Compare Pt5/Pt(parton) and dE in cone of R=0.4

We calculate M(W) and M(top) using the matched jets

B. We apply to each sample the top mass measurement analysis

to obtain a mass and an uncertainty.

For methods A and B, we compare results obtained for V6.2(tune A) old MC (used for CDF measurements ) V6.4 (tune ACR) only CR added to old shower V6.4 (tune NOCR, S0) new shower, wo/w CR

Use the l+jets sample: events with 1 lepton + 4 jets (Et>20 GeV)

Comparison of Different MC Versions

We have compared jet properties after generation + detector simulation.

Preliminary studies find the ACR(pro) jets agree with PYTHIA V6.2, but:

Light quark jets

b-quark jets

Jets in the S0(pro) sample

are wider and shifted

S0(pro) -Nominal

 E (cone) GeV

W-jets -0.38 ± 0.15

b-jets -1.43 ± 0.15

E (R=0.4 cone) S0 sample < E (R=0.4 cone) PYTHIA V6.2 sample

Energy in the cone affects the top mass directly. Studies are continuing

Comparison of matching

The whole event is matched using R for each parton-jet pair. An overall 2 is calculated, best 2 < 200 are accepted as matched

M=175 GeV

V6.2 (tune A) 68%

V6.4 ACR 68%

V6.4 NOCR 60%

V6.4 S0 59%

Samples with new parton shower have:

wider 2 distributions

wider R “

Samples with new parton shower have:

larger

Samples with new parton shower have:

larger

Jets with new parton shower are more displaced from the partons.

Previous MC studies (LBL)

Studies have shown that the difference between the parton energy and the jet energy in a DR=0.4 cone is larger for the new tunes. That is, the predicted energy of the b-jets is lower in the S0 tune.

M=175 GeV

V6.2 (tune A)

V6.4 ACR-pro

V6.4 S0-pro

Nominal- S0-pro

D(EOOC ) in GeV

lquarks 0.38 ± 0.15

b-jets 1.43 ± 0.15

Comparison made for same lumi profile

(to P8)

What did we learn about jets?

The jets are wider in S0, i.e. less energy in a cone of 0.4 radius. We get on the average b-jets with a shift of -1.3 GeV.

The ACR case has smaller effects than S0

The NOCR shows less visible effects than S0 (-0.58 GeV b-jet shift)

Tunes with the new parton shower give jets with less energy in cone of R =0.4

Largest discrepancies in the “pro” files found in the variable EOOCt

More about Jet Variables

E = E(parton) – E(jet)R=0.4

= E(Out of Cone)= EOOC

We have compared some jets properties after generation + detector simulation

PT = jet PT(R=0.4) after simulation + reconstruc.

Mj = mass of jet (R=0.4) after sim+ reconstruc.

E OOC= E(Out of Cone of 0.4) after matching + simulation + reconstruction

Comparing the old tune A with the ACR (pro) and S0(pro) we find that the S0(pro) tune differs the most from the Nominal tune (tune A). The b-jets

are the most affected with a shift of 1.3 GeV

Reconstructed W and top masses

MW is somewhat shifted . Mtop shifted for both the NOCR and the S0 samples

M=175 GeV

V6.2 (tune A)

V6.4 ACR

V6.4 NOCR

V6.4 S0

Using event matching we find:

Summary of studies on Mtop

Comparison of V6.2 (nominal) to V6.4 (the “pro” files)

Using both methods, i.e., reconstructing top mass with our ME method.

ACR (old shower+CR) shows little effect from CR = -0.33  0.31 GeV

NOCR: Event matching finds large MW, ME fit compensated for this with a large value of JES, resulting in Mtop = -1.3 GeV

S0 : Mtop = -1.7 GeV, expected because of -1.3 GeV b-jet shift. comparing NOCR and S0, we find CR (sys)= -0.45  0.46 GeV

Summary for ACR and S0 tunes

We find the following CR values : -0.33  0.31 GeV from ACR -0.45  0.46 GeV from S0-NOCR, consistent with zero, <0.46 GeV

The S0 tune gives Mtop = -1.7 GeV this is directly related to different jet shapes, i.e., different p-shower

Tune S0 includes systematics that we are already taking into account ,i.e. , for the MTM3 analysis: generator: (mt) = 0.51 GeV ISR/FSR: (mt) = 0.29 GeV OOC : (mt) = 0.28 GeV b-jets : (mt) = 0.38 GeV that is, most MC related systematics (0.75 GeV)

More comparison of the S0 tune with Tevatron data need to be done before we use it. We also need to disentangle the various sys contributions

Tune S0 includes systematics that we are already taking into account

We (MTM3 as an example) have the following systematics: generator: (mt) = 0.51 +- 0.37 GeV ISR/FSR: (mt) = 0.29 +- 0.26 GeV

Using V6.416 (S0) to estimate systematics should cover most of these systematics, in addition to color reconnection.

We have to avoid double counting, so we should try to separate the two effects . Not clear how to do this.

Comparison of data and MC

Use Lepton+jet mass sample.

Up to period P19 = 3.2 fb-1

PTjet > 20 GeV at L5

We have 577 events.

N(1 b-tag) = 458, N(> 1tag) = 119

698 tagged b-jets

We compare data and MC.

Luminosity profile :

For the CR sample (S0-pro), ACR-pro

lumi up to P8

Default PYTHIA V6.2: we have two samples, low lum and high lum, mid-lum is missing.

I have added the two with 0.45,0.55 ratio

Preliminary lumi profile

0.45ttop75+0.55 otop40

data

Comparison of data and MC (2)

b-tagged jets in lepton+jets up to period 19 (698 jets). MC:M(top)=175 GeV

variables shown are: jet PT, ET, E, and Mass. Jet Mass is bad (KS=0.01)

Low lumi sample used for ttkt75

KS test shows that all distributions, except for jet Mass, agree with data

Comparison of S0-pro with b-jets data

Luminosity for data up to P19, for S0-pro up to P8

Jet PT, ET, E agree with data

Jet mass has

KS value = 0.02

Luminosity profiles

Can the bad KS for the reconstructed jet mass be due to the luminosity profile?

The average mass value depends on the Number of Z vertices.

The effect is less pronounced for ET,PT,E of the b-jet, in both data and MC.

Jet Mass data and MC

172

175 lowl

S0pro

175 hilum

175 hilum

175 lowlum

Results of the jet-mass from different samples. The hilum MC gives KS=0.44, the low lum case gives KS=0.01

Jet Mass with better lumi profile

Using the new “preliminary” lumi profile the KS for the jet mass improves

Summary

From CDF-9691

MTM3 with 3.2 fb-1

We have compared some jet variables obtained in b-tagged jets with predictions from MC.

We do not observe deviations of the b-jets variables we looked at from PYTHIA V6.2 nominal MC, except for the jet mass.

There is a dependence of the measured jet mass on the observed number of z vertices. Taking this into account the discrepancy is somewhat smaller.

WARNING: we need to use the correct lumi profile!! It is too dangerous to keep using the MC up to P8!!

DM=0.40  0.31 GeV

Eta-Moments Studies

Andrea Castro has been looking at the eta and phi moments of jets with cone DR=0.4.

Hyunsu Lee, has been following up on these studies,

using the TMT analysis of lepton+jets events.

Andrea Castro's plots (Nov. 6, '08

Plots for the L+jets data and MC for different MC samples

1.9 fb-1, N(tight jets) >=3 (700 events). Only W+jets background shape used.

Why the green curve (left plot) , is shifted to the left? Hyunsu looking at this.

Sasha's sample M=170 GeV

Nate's sample M=175 GeV

Andrea's moment analysis

The Et of the jets seems to agree with the MC, the eta-moments do not agree with any MC samples at a mass of 175 GeV.

These plots have been revised from the talk of January 21.

Reweighting the events for the difference in Nvertices 1,2 and Nzvertices>=3.

Lina's comparison at 170 GeV (11/12/08)

S0 case run by Nate and Sasha show definite shifts in top and W masses

Parameter settings (12/11/08)

Sasha and Nathan have been looking at the parameter settings as

well as talking to Peter Skands.

Results are confusing at this point. Need more comparisons, more samples.

Sasha's gives m=-0.97 GeV

JES fixes the W mass shift

Nate's gives m= -0.90 GeV

From Paul's talk, Nov. 6/08

For M(top)=170 GeV, the two S0 runs find the same mass shift.

The moments do not agree.

Hyunsu recent studies (March 18/09

Eta moments at M=175 GeV (Nate's sample) do not agree with data

Hyunsu recent studies (March 18/09)

Eta moments at M=170 GeV (Sasha's sample) agrees with the data

Summary of problems

The eta-moments data seem to agree with the M=170 GeV S0 sample of Sasha and disagree with the 175 GeV S0 sample of Nate (see Andrea and Hyunsu plots)

The eta-moments data disagrees with all 175 GeV MC samples. (see Andrea's plots, ttkt75 of Hyunsu confirms this)

Paul's results show that both S0 files at 170 GeV produce a shift of ~ 0.9 GeV in the MTM3 analysis

Lina's plots show that the two S0 files give different W and top masses, so expectation is that they give differentM(top) shifts.

Suggestions:

David to generate 170 GeV S0-pro samples (2M events?)

(check if eta-moments are mass dependent)

Compare parameters of old files?

Color Reconnection Systematics

Backup slides

New PYTHIA

PYTHIA V6.4 versus V6.2

Our top mass measurements have been done using V6.2 (2003)

Color reconnection effects are included in PYTHIA V6.4.

Changes in V6.4

Parton shower uses pT ordering rather then Q2 ordering

ISR and FSR also uses a pT ordering algorithm

Multiparton (MPI) interactions are now part of the parton shower

Model interleaves MPI process with ISR evolution off the hard process

New model for beam renmants, including baryon junctions

Color reconnection added with an “annealing model” by M. Sandhoff and P. Skands

P. Skands and D. Wicke hep-ph/0703081v1 (March 2007)

D. Wicke and P. Skands hep-ph/0807.3248 v1 (July 2008)

D. Wicke and P. Skands TOP08

New PYTHIA model (P. Skands etc.)

Color Reconnection Systematics

Strong color correlations between the hard process and the underlying event are implied by tune A and similar tunes. These effects may be interpreted as sign for color reconnection.

The issue has been studied at LEP for the W mass measurement

CR effects on the MW

measurement at LEP

contribute to systematics

CR(sys) = 8 MeV

out of 22 MeV (total sys)

(LEPEWWG hep-ex/061203)

Preliminary MC studies have

indicated possible contributions

to the top mass

systematics of order

CR(sys) 0.5 GeV

D. Wicke and P. Skands arXiv:0807.3248V1

LEP

Tevatron

Some Tevatron plots with new tunes

From Hendrix Hoeth talk (Perugia 2008). New tunes (called professor from tools used) use LEP data: event shapes, fragmentation functions and flavor spectra. The flavor and hadronization parameters are tuned for the new PT ordered shower. New UE and MPI model not tuned. (Done for old Q 2 ordered parton shower).

Some comparison with Tevatron data has been shown at Perugia

Tune S0 (used by CDF), Tune Moraies (used by ATLAS).

2002-04-21T14:25:46