# Presentation: 523578

## Studying the Underlying Event at CDF and the LHC

**Studying the Underlying Event ****at CDF and the LHC**

**Rick Field**
**University of Florida**

_**Outline of Talk**_

**CMS at the LHC**

**CDF Run 2**

***Perugia, Italy ***
***October 27. 2008***

**“****Leading Jet” vs Z-Boson**

**Rick Field**
**Craig Group**
**Deepak Kar**

**The “Towards”, “Away”, and “Transverse” regions of ********-******** space.**

**Four Jet Topologies plus Drell-Yan.**

**The “transMAX” and “transMIN” regions.**

**Look at <p****T****> versus Nchg in “min-bias” and Drell-Yan.**

**Show some extrapolations of Drell-Yan to the LHC.**

**The observables:  First look at average quantities.  Then do distributions.**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## UE&MB@CMS

**UE&MB@CMS**

**Measure Min-Bias and the “Underlying Event” at CMS**

**The plan involves two phases.  **
**Phase 1 would be to measure min-bias and the “underlying event” as soon as possible (when the luminosity is low), perhaps during commissioning.  We would then tune the QCD Monte-Carlo models for all the other CMS analyses.  Phase 1 would be a service to the rest of the collaboration.  As the measurements become more reliable we would re-tune the QCD Monte-Carlo models if necessary and begin Phase 2.  **
**Phase 2 is “physics” and would include comparing the min-bias and “underlying event” measurements at the LHC with the measurements we have done (and are doing now) at CDF and then writing a physics publication.**

_**Initial Group Members**_
**Rick Field (Florida)**
**Darin Acosta (Florida) **
**Paolo Bartalini (Florida)**
**Albert De Roeck (CERN)**
**Livio Fano' (INFN/Perugia at CERN)**
**Filippo Ambroglini (INFN/Perugia at CERN)**
**Khristian Kotov (UF Student, Acosta)**

**UE&MB@CMS**

***Perugia, Italy, March 2006***

**University of Perugia**

**Florida-Perugia-CERN**

**PTDR Volume 2 Section 3.3.2**

**See the talks by **
**Filippo Ambroglini**
**and**
**Florian Bechtel**
**tomorrow morning!**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## QCD Monte-Carlo Models:High Transverse Momentum Jets

**Start with the perturbative 2-to-2 (or sometimes 2-to-3) parton-parton scattering and add initial and final-state gluon radiation (in the leading log approximation or modified leading log approximation). **

**“****Underlying Event”**

**The “underlying event” consists of the “beam-beam remnants” and from particles arising from soft or semi-soft multiple parton interactions (MPI).**

**Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event” observables receive contributions from initial and final-state radiation.**

**The “underlying event” is an unavoidable background to most collider observables and having good understand of it leads to more precise collider measurements!**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## QCD Monte-Carlo Models:Lepton-Pair Production

**Start with the perturbative Drell-Yan muon pair production and add initial-state gluon radiation (in the leading log approximation or modified leading log approximation). **

**“****Underlying Event”**

**The “underlying event” consists of the “beam-beam remnants” and from particles arising from soft or semi-soft multiple parton interactions (MPI).**

**Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event” observables receive contributions from initial-state radiation.**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## “Towards”, “Away”, “Transverse”

**“****Towards”, “Away”, “Transverse”**

**Look at correlations in the azimuthal angle ********relative to the leading charged particle jet (|********| < 1) or the leading calorimeter jet (|********| < 2).**
**Define ****|********| < 60****o**** as “Toward”****, ****60****o**** < |******** < 120****o ****as “Transverse ”****, and ****|********| > 120****o**** as “Away”****.  Each of the three regions have area ******** = 2****×****120****o ****= 4********/3.**

_****__** **__**Correlations relative to the leading jet**_
**Charged particles p****T**** > 0.5 GeV/c |********| < 1**
**Calorimeter towers E****T**** > 0.1 GeV |********| < 1**

**“****Transverse” region is very sensitive to the “underlying event”!**

**Look at the charged particle density, the charged PTsum density and the ETsum density in all 3 regions!**

**Z-Boson Direction**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Event Topologies

**“****Leading Jet”**** events correspond to the leading calorimeter jet (MidPoint R = 0.7) in the region |********| < 2 with no other conditions.**

**“****Leading Jet”**

**“****Leading ChgJet”**** events correspond to the leading charged particle jet (R = 0.7) in the region |********| < 1 with no other conditions.**

**“****Charged Jet”**

**“****Inc2J Back-to-Back”**

**“****Exc2J Back-to-Back”**

**“****Inclusive 2-Jet Back-to-Back”**** events are selected to have at least two jets with Jet#1 and Jet#2 nearly “back-to-back” (********12**** > 150****o****) with almost equal transverse energies (P****T****(jet#2)/P****T****(jet#1) > 0.8) with no other conditions .**

**“****Exclusive 2-Jet Back-to-Back”**** events are selected to have at least two jets with Jet#1 and Jet#2 nearly “back-to-back” (********12**** > 150****o****) with almost equal transverse energies (P****T****(jet#2)/P****T****(jet#1) > 0.8) and P****T****(jet#3) < 15 GeV/c.**

**subset**

**subset**

**Z-Boson**

**“****Z-Boson”**** events are Drell-Yan events with 70 < M(lepton-pair) < 110 GeV with no other conditions.**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## “transMAX” & “transMIN”

**Define the MAX and MIN “transverse” regions (****“transMAX”**** and ****“transMIN”****)  on an event-by-event basis with MAX (MIN) having the largest (smallest) density.  Each of the two “transverse” regions have an area in ********-******** space of 4********/6.**

**The “transMIN” region is very sensitive to the “beam-beam remnant” and the soft multiple parton interaction components of the “underlying event”.**

**The difference, ****“transDIF”**** (“transMAX” minus “transMIN”), is very sensitive to the “hard scattering” component of the “underlying event” (*****i.e.***** hard initial and final-state radiation).**

**Area = 4********/6**

**“****transMIN” very sensitive to the “beam-beam remnants”!**

**The overall ****“transverse”**** density is the average of the “transMAX” and “transMIN” densities.**

**Z-Boson Direction**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Observables at theParticle and Detector Level

**“****Back-to-Back” **

| Observable | Particle Level | Detector Level |
| --- | --- | --- |
| dNchg/dd | Number of charged particles
per unit -
(pT > 0.5 GeV/c, || < 1) | Number of “good” charged tracks
per unit -
(pT > 0.5 GeV/c, || < 1) |
| dPTsum/dd | Scalar pT sum of charged particles per unit -
(pT > 0.5 GeV/c, || < 1) | Scalar pT sum of “good” charged tracks per unit -
(pT > 0.5 GeV/c, || < 1) |
| <pT> | Average pT of charged particles
(pT > 0.5 GeV/c, || < 1) | Average pT of “good” charged tracks
(pT > 0.5 GeV/c, || < 1) |
| PTmax | Maximum pT charged particle
(pT > 0.5 GeV/c, || < 1)
Require Nchg ≥ 1 | Maximum pT “good” charged tracks
(pT > 0.5 GeV/c, || < 1)
Require Nchg ≥ 1 |
| dETsum/dd | Scalar ET sum of all particles 
per unit -
(all pT, || < 1) | Scalar ET sum of all calorimeter towers 
per unit -
(ET > 0.1 GeV, || < 1) |
| PTsum/ETsum | Scalar pT sum of charged particles 
(pT > 0.5 GeV/c, || < 1)
divided by the scalar ET sum of 
all particles  (all pT, || < 1)  | Scalar pT sum of “good” charged tracks 
(pT > 0.5 GeV/c, || < 1)
divided by the scalar ET sum of 
calorimeter towers (ET > 0.1 GeV, || < 1) |

**“****Leading Jet” **

**Observables at the****Particle and Detector Level**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## CDF Run 1 PT(Z)

**Shows the Run 1 Z-boson p****T**** distribution (<p****T****(Z)> ≈ 11.5 GeV/c) compared with ****PYTHIA Tune A**** (<p****T****(Z)> = 9.7 GeV/c), and ****PYTHIA Tune AW**** (<p****T****(Z)> = 11.7 GeV/c).**

| Parameter | Tune A | Tune AW |
| --- | --- | --- |
| MSTP(81) | 1 | 1 |
| MSTP(82) | 4 | 4 |
| PARP(82) | 2.0 GeV | 2.0 GeV |
| PARP(83) | 0.5 | 0.5 |
| PARP(84) | 0.4 | 0.4 |
| PARP(85) | 0.9 | 0.9 |
| PARP(86) | 0.95 | 0.95 |
| PARP(89) | 1.8 TeV | 1.8 TeV |
| PARP(90) | 0.25 | 0.25 |
| PARP(62) | 1.0 | 1.25 |
| PARP(64) | 1.0 | 0.2 |
| PARP(67) | 4.0 | 4.0 |
| MSTP(91) | 1 | 1 |
| PARP(91) | 1.0 | 2.1 |
| PARP(93) | 5.0 | 15.0 |

**The Q****2**** = k****T****2**** in ********s**** for space-like showers is scaled by PARP(64)! **

**Effective Q cut-off, below which space-like showers are not evolved.**

**UE Parameters**

**ISR Parameters**

**Intrensic KT**

**PYTHIA 6.2 CTEQ5L**

**Tune used by the **
**CDF-EWK group!**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Jet-Jet Correlations (DØ)

**MidPoint Cone Algorithm  (R = 0.7, f****merge**** = 0.5) **
***L****** *****= 150 pb****-1**** (Phys. Rev. Lett. 94 221801 (2005))**
**Data/NLO agreement good. Data/HERWIG agreement good.**
**Data/PYTHIA agreement good provided PARP(67)   =  1.0****→4.0 (i.e. like Tune A, ****best fit 2.5****).**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## CDF Run 1 PT(Z)

**Shows the Run 1 Z-boson p****T**** distribution (<p****T****(Z)> ≈ 11.5 GeV/c) compared with ****PYTHIA Tune DW****, and ****HERWIG****.**

| Parameter | Tune DW | Tune AW |
| --- | --- | --- |
| MSTP(81) | 1 | 1 |
| MSTP(82) | 4 | 4 |
| PARP(82) | 1.9 GeV | 2.0 GeV |
| PARP(83) | 0.5 | 0.5 |
| PARP(84) | 0.4 | 0.4 |
| PARP(85) | 1.0 | 0.9 |
| PARP(86) | 1.0 | 0.95 |
| PARP(89) | 1.8 TeV | 1.8 TeV |
| PARP(90) | 0.25 | 0.25 |
| PARP(62) | 1.25 | 1.25 |
| PARP(64) | 0.2 | 0.2 |
| PARP(67) | 2.5 | 4.0 |
| MSTP(91) | 1 | 1 |
| PARP(91) | 2.1 | 2.1 |
| PARP(93) | 15.0 | 15.0 |

**UE Parameters**

**ISR Parameters**

**Intrensic KT**

**PYTHIA 6.2 CTEQ5L**

**Tune DW has a lower value of PARP(67) and slightly more MPI!**

**Tune DW uses D0’s perfered value of PARP(67)!**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## PYTHIA 6.2 Tunes

| Parameter | Tune AW | Tune DW | Tune D6 |
| --- | --- | --- | --- |
| PDF | CTEQ5L | CTEQ5L | CTEQ6L |
| MSTP(81) | 1 | 1 | 1 |
| MSTP(82) | 4 | 4 | 4 |
| PARP(82) | 2.0 GeV | 1.9 GeV | 1.8 GeV |
| PARP(83) | 0.5 | 0.5 | 0.5 |
| PARP(84) | 0.4 | 0.4 | 0.4 |
| PARP(85) | 0.9 | 1.0 | 1.0 |
| PARP(86) | 0.95 | 1.0 | 1.0 |
| PARP(89) | 1.8 TeV | 1.8 TeV | 1.8 TeV |
| PARP(90) | 0.25 | 0.25 | 0.25 |
| PARP(62) | 1.25 | 1.25 | 1.25 |
| PARP(64) | 0.2 | 0.2 | 0.2 |
| PARP(67) | 4.0 | 2.5 | 2.5 |
| MSTP(91) | 1 | 1 | 1 |
| PARP(91) | 2.1 | 2.1 | 2.1 |
| PARP(93) | 15.0 | 15.0 | 15.0 |

**Intrinsic KT**

**ISR Parameter**

**UE Parameters**

**Uses CTEQ6L**

**All use LO ********s**** **
**with ******** = 192 MeV!**

**Tune A energy dependence!**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## PYTHIA 6.2 Tunes

| Parameter | Tune DWT | Tune D6T | ATLAS |
| --- | --- | --- | --- |
| PDF | CTEQ5L | CTEQ6L | CTEQ5L |
| MSTP(81) | 1 | 1 | 1 |
| MSTP(82) | 4 | 4 | 4 |
| PARP(82) | 1.9409 GeV | 1.8387 GeV | 1.8 GeV |
| PARP(83) | 0.5 | 0.5 | 0.5 |
| PARP(84) | 0.4 | 0.4 | 0.5 |
| PARP(85) | 1.0 | 1.0 | 0.33 |
| PARP(86) | 1.0 | 1.0 | 0.66 |
| PARP(89) | 1.96 TeV | 1.96 TeV | 1.0 TeV |
| PARP(90) | 0.16 | 0.16 | 0.16 |
| PARP(62) | 1.25 | 1.25 | 1.0 |
| PARP(64) | 0.2 | 0.2 | 1.0 |
| PARP(67) | 2.5 | 2.5 | 1.0 |
| MSTP(91) | 1 | 1 | 1 |
| PARP(91) | 2.1 | 2.1 | 1.0 |
| PARP(93) | 15.0 | 15.0 | 5.0 |

**Intrinsic KT**

**ISR Parameter**

**UE Parameters**

**All use LO ********s**** **
**with ******** = 192 MeV!**

**ATLAS energy dependence!**

**These are “old” PYTHIA 6.2 tunes!  **
**See the talks by**
**Arthur Moraes**
**and**
**Hendrik Hoeth**
**for “new” tunes!**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## JIMMY at CDF

**The Energy in the “Underlying Event” in High P****T**** Jet Production**

**“****Transverse” <Densities> vs P****T****(jet#1)**

**JIMMY: MPI**
**J. M. Butterworth**
**J. R. Forshaw**
**M. H. Seymour**

**JIMMY was tuned to fit the energy density in the “transverse” region for “leading jet” events!**

_**JIMMY**_
**Runs with HERWIG and adds multiple parton interactions!**

**PT(JIM)= 2.5 GeV/c.**

**PT(JIM)= 3.25 GeV/c.**

_**The Drell-Yan JIMMY Tune**_
**PTJIM = 3.6 GeV/c,**
**JMRAD(73) = 1.8**
**JMRAD(91) = 1.8**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Charged Particle Density

**Charged Particle Density**

**Data at 1.96 TeV on the density of charged particles, dN/d********d********, with p****T**** > 0.5 GeV/c and |********| < 1 for “Z-Boson” and “Leading Jet” events as a function of the leading jet p****T**** or P****T****(Z) for the ****“toward”****, ****“away”****, and ****“transverse”**** regions.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (*****i.e.***** generator level).**

**HERWIG + JIMMY**
**Tune (PTJIM = 3.6)**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Charged PTsum Density

**Charged PTsum Density**

**Data at 1.96 TeV on the charged *****scalar***** PTsum density, dPT/d********d********, with p****T**** > 0.5 GeV/c and |********| < 1 for “Z-Boson” and “Leading Jet” events as a function of the leading jet p****T**** or P****T****(Z) for the ****“toward”****, ****“away”****, and ****“transverse”**** regions.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (*****i.e.***** generator level).**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## The “TransMAX/MIN” Regions

**The “TransMAX/MIN” Regions**

**Data at 1.96 TeV on the charged particle density, dN/d********d********, with p****T**** > 0.5 GeV/c and |********| < 1 for “Z-Boson” and “Leading Jet” events as a function of P****T****(Z) or the leading jet p****T**** for the ****“transMAX”****, and ****“transMIN”**** regions.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (*****i.e.***** generator level).**

**Data at 1.96 TeV on the density of charged particles, dN/d********d********, with p****T**** > 0.5 GeV/c and |********| < 1 for “leading jet” events as a function of the leading jet p****T**** and for Z-Boson events as a function of P****T****(Z) for ****“TransDIF” =**** ****“transMAX”**** minus ****“transMIN”**** regions.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune A and HERWIG (without MPI) at the particle level (*****i.e.***** generator level).**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## The “TransMAX/MIN” Regions

**The “TransMAX/MIN” Regions**

**Data at 1.96 TeV on the charged *****scalar***** PTsum density, dPT/d********d********, with p****T**** > 0.5 GeV/c and |********| < 1 for “Z-Boson” and “Leading Jet” events as a function of P****T****(Z) or the leading jet p****T**** for the ****“transMAX”****, and ****“transMIN”**** regions.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (*****i.e.***** generator level).**

**Data at 1.96 TeV on the charged *****scalar***** PTsum density, dPT/d********d********, with p****T**** > 0.5 GeV/c and |********| < 1 for “leading jet” events as a function of the leading jet p****T**** and for Z-Boson events as a function of P****T****(Z) for ****“TransDIF” =**** ****“transMAX”**** minus ****“transMIN”**** regions.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune A and HERWIG (without MPI) at the particle level (*****i.e.***** generator level).**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Charged Particle <pT>

**Charged Particle <p****T****>**

**Data at 1.96 TeV on the charged particle average p****T****, with p****T**** > 0.5 GeV/c and |********| < 1 for the ****“toward”**** region for “Z-Boson” and the ****“transverse”**** region for “Leading Jet” events as a function of the leading jet p****T**** or P****T****(Z).  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune AW and Tune A, respectively, at the particle level (*****i.e.***** generator level). The Z-Boson data are also compared with PYTHIA Tune DW, the ATLAS tune, and HERWIG (without MPI)**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Z-Boson: “Towards”, Transverse”, & “TransMIN” Charge Density

**Z-Boson: “Towards”, Transverse”, & “TransMIN” Charge Density**

**Data at 1.96 TeV on the density of charged particles, dN/d********d********, with p****T**** > 0.5 GeV/c and |********| < 1 for “Z-Boson” events as a function of P****T****(Z) for the ****“toward”**** and ****“transverse”**** regions.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune AW and HERWIG (without MPI) at the particle level (*****i.e.***** generator level).**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Z-Boson: “Towards”, Transverse”, & “TransMIN” Charge Density

**Z-Boson: “Towards”, Transverse”, & “TransMIN” Charge Density**

**Data at 1.96 TeV on the charged *****scalar***** PTsum density, dPT/d********d********, with p****T**** > 0.5 GeV/c and |********| < 1 for “Z-Boson” events as a function of P****T****(Z) for the ****“toward”**** and ****“transverse”**** regions.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune AW and HERWIG (without MPI) at the particle level (*****i.e.***** generator level).**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Z-Boson: “Towards” Region

**Z-Boson: “Towards” Region**

**Data at 1.96 TeV on the density of charged particles, dN/d********d********, with p****T**** > 0.5 GeV/c and |********| < 1 for “Z-Boson” events as a function of P****T****(Z) for the ****“toward”**** region.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune AW and HERWIG (without MPI) at the particle level (*****i.e.***** generator level).**

**HW without MPI **

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Z-Boson: “Towards” Region

**Z-Boson: “Towards” Region**

**Data at 1.96 TeV on the average p****T**** of charged particles with p****T**** > 0.5 GeV/c and |********| < 1 for “Z-Boson” events as a function of P****T****(Z) for the ****“toward”**** region.  The data are corrected to the particle level (*****with errors that include both the statistical error and the systematic uncertainty*****) and are compared with PYTHIA Tune AW and HERWIG (without MPI) at the particle level (*****i.e.***** generator level).**

**HW (without MPI)**
**almost no change! **

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Shows the average transverse momentum of charged particles (||<1, pT>0.5 GeV) versus the number of charged particles, Nchg, at the detector level for the CDF Run 2 Min-Bias events.

**The charged <PT> rises with Nchg!**

**Charged <P****T****> versus N****chg**

**See the talk by **
**Peter Skands**
**on Thursday morning!**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Min-Bias Correlations

**Min-Bias Correlations**

**Data at 1.96 TeV on the ****average p****T**** of charged particles versus the number of charged particles**** (p****T**** > 0.4 GeV/c, |********| < 1) for “min-bias” collisions at CDF Run 2.  The data are corrected to the particle level and are compared with PYTHIA Tune A at the particle level (*****i.e.***** generator level).**

- New

**See the talk by **
**Niccolo Moggi**
**this afternoon!**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Average PT versus Nchg

**Average PT versus Nchg**

**Data at 1.96 TeV on the ****average p****T**** of charged particles versus the number of charged particles**** (p****T**** > 0.4 GeV/c, |********| < 1) for ****“min-bias” collisions**** at CDF Run 2.  The data are corrected to the particle leveland are compared with PYTHIA Tune A, Tune DW, and the ATLAS tune at the particle level (*****i.e.***** generator level).**

**Particle level predictions for the ****average p****T**** of charged particles versus the number of charged particles**** (p****T**** > 0.5 GeV/c, |********| < 1, excluding the lepton-pair) for for ****Drell-Yan production**** (70 < M(pair) < 110 GeV) at CDF Run 2.  **

- New

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Average PT(Z) versus Nchg

**Average PT(Z) versus Nchg**

**Data on the ****average p****T**** of charged particles versus the number of charged particles**** (p****T**** > 0.5 GeV/c, |********| < 1, excluding the lepton-pair) for for ****Drell-Yan production**** (70 < M(pair) < 110 GeV) at CDF Run 2. The data are corrected to the particle level and are compared with various Monte-Carlo tunes at the particle level (*****i.e.***** generator level).**

**No MPI!**

**Predictions for the ****average P****T****(Z-Boson) versus the number of charged particles**** (p****T**** > 0.5 GeV/c, |********| < 1, excluding the lepton-pair) for for ****Drell-Yan production**** (70 < M(pair) < 110 GeV) at CDF Run 2. **

- New

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Average PT versus Nchg

**Average PT versus Nchg**

**Predictions for the ****average p****T**** of charged particles versus the number of charged particles**** (p****T**** > 0.5 GeV/c, |********| < 1, excluding the lepton-pair) for for ****Drell-Yan production**** (70 < M(pair) < 110 GeV, ****P****T****(pair) < 10 GeV/c****) at CDF Run 2. **

**Data the ****average p****T**** of charged particles versus the number of charged particles**** (p****T**** > 0.5 GeV/c, |********| < 1, excluding the lepton-pair) for for ****Drell-Yan production**** (70 < M(pair) < 110 GeV, ****P****T****(pair) < 10 GeV/c****) at CDF Run 2. The data are corrected to the particle level and are compared with various Monte-Carlo tunes at the particle level (*****i.e.***** generator level).**

**P****T****(Z) < 10 GeV/c**

**No MPI!**

- New

**Remarkably similar behavior! Perhaps indicating that MPI playing an important role in both processes.**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008

## Summary

**It is important to produce a lot of plots (*****corrected to the particle level*****) so that the theorists can tune and improve the QCD Monte-Carlo models.  If they improve the “transverse” region they might miss-up the “toward” region etc..  We need to show the whole story! **

**There are over ****128 plots to get “blessed”**** and then to published. So far we have only looked at average quantities.  We plan to also produce distributions and flow plots. **

**We are making good progress in understanding and modeling the “underlying event” in jet production and in Drell-Yan.  Tune A and Tune AW describe the data very well, although not perfect.  However, ****we do not yet have a perfect fit to all the features of the CDF “underlying event” data!**

**I plan to construct a “CDF-QCD Data for Theory” WEBsite with the “blessed” plots together with tables of the data points and errors so that people can have access to the results .**

**CDF-QCD Data for Theory**

**Looking at <p****T****> versus Nchg in Drell-Yan with 70 < Mpair) < 110 GeV and P****T****(pair) < 5 GeV is a good way to look at MPI and the color connections. ****The data show the correlations expected from MPI!**

**CDF Run 2 publication.  Should be out by the end of the year!**

- MPI@LHC08, Perugia, Italy                                                           October 27, 2008