# Presentation: 523579

## XXXIV International Meeting on Fundamental Physics

**Rick Field**
**University of Florida**
**(*****for the CDF & D0 Collaborations*****)**

**CDF Run 2**

***Real Colegio Maria Cristina, El Escorial, Spain***

**From ****HERA**** and the ****TEVATRON**** **
**to the ****LHC**

_**1**__**st**__** Lecture**_
**From Field-Feynman to the Tevatron**

- IMFP2006 - Day 1                                                  April 3, 2006

## The Fermilab Tevatron

**Fermi National Laboratory (****Fermilab****) is near Chicago, Illinois. ****CDF**** and ****D****Ø**** are the the two collider detector experiments at Fermilab.**

**Protons collide with antiprotons at a center-of-mass energy of *****almost***** ****2 TeV**** (actually 1.96 TeV).**

- IMFP2006 - Day 1                                                  April 3, 2006

## Tevatron Performance

**Highest-energy accelerator currently operational.**

**Peak luminosity: 1.8****×****10****32**** cm****-2**** s****-1****.**
**Integrated luminosity/week: about  25 pb****-1****.**

**CDF and D****Ø****: ~1.2 fb****-1**** on tape!**

- IMFP2006 - Day 1                                                  April 3, 2006

## CDF and DØ in Run 2

**L2 trigger on displaced vertices!**
**Excellent tracking resolution!           **

**Excellent muon identification and acceptance!**
**Excellent tracking acceptance |********| < 2-3!**

**Both detectors:**
**Silicon microvertex tracker**
**Solenoid**
**High rate trigger/DAQ**
**Calorimeters and muons**

**D****Ø**

**CDF**

- IMFP2006 - Day 1                                                  April 3, 2006

## From HERA and the TEVATRON to the LHC

**Lecture 1:**** From Field-Feynman to the Tevatron.   **

**Lecture 2:**** Heavy Quark Physics at the Tevatron.   **

**Lecture 3:**** Photons, Bosons, and Jets at the Tevatron.   **

**Lecture 4:**** A Detailed Study of the “Underlying Event” at the Tevatron.   **

**From 7 GeV/c ********0****’s to 600 GeV/c Jets!**

**QCD Monte-Carlo Models (PYTHIA Tune A).**

**“****Min-Bias” Collisions at the Tevatron.**

**→ ****extrapolations to the LHC!**

**QCD Monte-Carlo Models tunes at the Tevatron.**

**→ ****extrapolations to the LHC!**

**http://www.phys.ufl.edu/~rfield/cdf/rdf_talks.html**

**All talks at**

- IMFP2006 - Day 1                                                  April 3, 2006

## Feynman-Field Phenomenology

**Jet Model”**

**Feynman****-Field**** ****Phenomenology**

**FF1: “Quark Elastic Scattering as a Source of High Transverse Momentum Mesons”****,  R. D. Field and R. P. Feynman, Phys. Rev. D15, 2590-2616 (1977).**
**FFF1: “Correlations Among Particles and Jets Produced with Large Transverse Momenta”****, R. P. Feynman, R. D. Field and G. C. Fox,  Nucl. Phys. B128, 1-65 (1977).**
**FF2: “A Parameterization of the properties of Quark Jets”****,  R. D. Field and R. P. Feynman, Nucl. Phys. B136, 1-76 (1978).**
**F1: “Can Existing High Transverse Momentum Hadron Experiments be Interpreted by Contemporary Quantum Chromodynamics Ideas?”****, R. D. Field,  Phys. Rev. Letters 40, 997-1000 (1978).**
**FFF2: “A Quantum Chromodynamic Approach for the Large Transverse Momentum Production of Particles and Jets”****, R. P. Feynman, R. D. Field and G. C. Fox, Phys. Rev. D18, 3320-3343 (1978).**

**1973-1980**

**FW1: “A QCD Model for e****+****e****-**** Annihilation”****, R. D. Field and S. Wolfram,  Nucl. Phys. B213, 65-84 (1983).**

**My 1****st**** graduate student!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Hadron-Hadron Collisions

**What happens when two hadrons collide at high energy?**

**Most of the time the hadrons ooze through each other and fall apart (*****i.e.***** ****no hard scattering****).  The outgoing particles continue in roughly the same direction as initial proton and antiproton.**

**Occasionally there will be a ****large transverse momentum meson****.  ****Question: Where did it come from?**

**We assumed it came from quark-quark elastic scattering, but we did not know how to calculate it!  **

**FF1 1977 (preQCD)**

_**Feynman quote from FF1**_
**“****The model we shall choose is not a popular one,**
**so that we will not duplicate too much of the**
**work of others who are similarly analyzing **
**various models (e.g. constituent interchange **
**model, multiperipheral models, etc.).  We shall **
**assume that the high P****T**** particles arise from **
**direct hard collisions between constituent **
**quarks in the incoming particles, which **
**fragment or cascade down into several hadrons.”**

**“****Black-Box Model”**

- IMFP2006 - Day 1                                                  April 3, 2006

## Quark-QuarkBlack-Box Model

**Quark****-****Quark****Black****-****Box Model**

**FF1 1977 (preQCD)**

_**Quark Distribution Functions**_
**determined from deep-inelastic**
**lepton-hadron collisions**

_**Quark Fragmentation Functions**_
**determined from e****+****e****-**** annihilations**

_**Quark-Quark Cross-Section**_
**Unknown! Deteremined from**
**hadron-hadron collisions.**

**No gluons!**

_**Feynman quote from FF1**_
**“****Because of the incomplete knowledge of **
**our functions some things can be predicted **
**with more certainty than others.  Those **
**experimental results that are not well **
**predicted can be “used up” to determine **
**these functions in greater detail to permit **
**better predictions of further experiments.  **
**Our papers will be a bit long because we **
**wish to discuss this interplay in detail.”**

- IMFP2006 - Day 1                                                  April 3, 2006

## Quark-QuarkBlack-Box Model

**FF1 1977 (preQCD)**

_**Predict**_
**particle ratios**

_**Predict**_
**increase with increasing **
**CM energy W**

_**Predict**_
**overall event topology**
**(FFF1 paper 1977)**

**“****Beam-Beam Remnants”**

**7 GeV/c ********0****’s!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Telagram from Feynman

**July 1976**

**SAW CRONIN AM NOW CONVINCED WERE RIGHT TRACK QUICK WRITE**
**FEYNMAN**

- IMFP2006 - Day 1                                                  April 3, 2006

## Letter from Feynman

**July 1976**

- IMFP2006 - Day 1                                                  April 3, 2006

## Letter from Feynman:page 1

- Spelling?

- IMFP2006 - Day 1                                                  April 3, 2006

## Letter from Feynman:page 3

**It is fun!**

**Onward!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Feynman Talk at Coral Gables in December 1976

**“****Feynman-Field **
**Jet Model”**

**1****st**** transparency**

**Last transparency**

- IMFP2006 - Day 1                                                  April 3, 2006

## QCD ApproachQuarks & Gluons

**FFF2 1978**

_**Parton Distribution Functions**_
**Q****2**** dependence predicted from QCD**

_**Quark & Gluon Fragmentation Functions**_
**Q****2**** dependence predicted from QCD**

_**Quark & Gluon Cross-Sections**_
**Calculated from QCD**

_**Feynman quote from FFF2**_
**“****We investigate whether the present **
**experimental behavior of mesons with **
**large transverse momentum in hadron-hadron **
**collisions is consistent with the theory of **
**quantum-chromodynamics (QCD) with **
**asymptotic freedom, at least as the theory **
**is now partially understood.”**

- IMFP2006 - Day 1                                                  April 3, 2006

## High PT Jets

**High P****T**** Jets**

**30 GeV/c!**

_**Predict**_
**large “jet” cross-section**

**Feynman, Field, & Fox (1978)**

**CDF (2006)**

**600 GeV/c Jets!**

_**Feynman quote from FFF**_
**“****At the time of this writing, there is **
**still no sharp quantitative test of QCD.**
**An important test will come in connection **
**with the phenomena of high P****T**** discussed here.”**

- IMFP2006 - Day 1                                                  April 3, 2006

## A Parameterization of the Properties of Jets

**Assumed that jets could be analyzed on a “recursive” principle.**

**Field-Feynman 1978**

**Original quark with flavor “a” and momentum P****0**

**Let f(********)d******** be the probability that the rank 1 meson *****leaves***** fractional momentum ******** to the remaining cascade, leaving quark “b” with momentum P****1**** = ********1****P****0****.**

**Primary Mesons**

**Assume that the mesons originating from quark “b” are distributed in presisely the same way as the mesons which came from quark a (*****i.e.***** same function  f(********)), leaving quark “c” with momentum P****2**** = ********2****P****1 ****= ********2********1****P****0****.**

**Add in flavor dependence by letting ********u**** = probabliity of producing u-ubar pair, ********d**** = probability of producing d-dbar pair, etc.**

**Let F(z)dz be the probability of finding a meson (*****independent of rank*****) with fractional mementum z of the original quark “a” within the jet.**

**Rank 2**

**continue**

**Calculate F(z) from f(********) and ********i****!**

**Rank 1**

**Secondary Mesons**
**(after decay)**

- IMFP2006 - Day 1                                                  April 3, 2006

## A Parameterization of the Properties of Jets

_**R. P. Feynman**_** **
**ISMD, Kaysersberg, France, June 12, 1977**

_**Feynman quote from FF2**_
**“****The predictions of the model are reasonable **
**enough physically that we expect it may **
**be close enough to reality to be useful in **
**designing future experiments and to serve **
**as a reasonable approximation to compare **
**to data.  We do not think of the model **
**as a sound physical theory, ....”**

- IMFP2006 - Day 1                                                  April 3, 2006

## Monte-Carlo Simulationof Hadron-Hadron Collisions

_**FF1-FFF1 (1977)**_** “Black-Box” Model**

_**F1-FFF2 (1978)**_** QCD Approach**

_**FF2 (1978)**_** **
**Monte-Carlo simulation of “jets”**

_**FFFW “FieldJet” (1980)**_** **
**QCD “leading-log order” simulation **
**of hadron-hadron collisions**

_**ISAJET**_
**(“FF” Fragmentation)**

_**HERWIG**_
**(“FW” Fragmentation)**

_**PYTHIA**_

**today**

**“****FF” or “FW” Fragmentation**

**the past**

**tomorrow**

_**SHERPA**_

_**PYTHIA 6.3**_

- IMFP2006 - Day 1                                                  April 3, 2006

## Monte-Carlo Simulationof Hadron-Hadron Collisions

**Color singlet proton collides with a color singlet antiproton.**

**A ****red quark**** gets knocked out of the proton and a ****blue antiquark**** gets knocked out of the antiproton.**

**At short times (*****small distances*****) the color forces are weak and the outgoing partons move away from the beam-beam remnants.**

**At long times (*****large distances*****) the color forces become strong and ****quark-antiquark pairs**** are pulled out of the vacuum and hadrons are formed.**

**The resulting event consists of hadrons and leptons in the form of two large transverse momentum ****outgoing jets**** plus the ****beam-beam remnants****.**

- IMFP2006 - Day 1                                                  April 3, 2006

## Monte-Carlo Simulationof Quark and Gluon Jets

**ISAJET:**** Evolve the parton-shower from Q****2**** (*****virtual photon invariant mass*****) to Q****min**** ~ 5 GeV. Use a complicated fragmentation model to evolve from Q****min**** to outgoing hadrons.**

**Q****2**

**5 GeV**

**1 GeV**

**200 MeV**

**HERWIG:**** Evolve the parton-shower from Q****2**** (*****virtual photon invariant mass*****) to Q****min**** ~ 1 GeV. Form color singlet clusters which “decay” into hadrons according to 2-particle phase space.**

**MLLA:**** Evolve the parton-shower from Q****2**** (*****virtual photon invariant mass*****) to Q****min**** ~ 230 MeV. Assume that the charged particles behave the same as the partons with N****chg****/N****parton**** = 0.56!**

**MLLA Curve!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Collider Coordinates

**The z-axis is defined to be the beam axis with the xy-plane being the “transverse” plane.**

******cm**** is the center-of-mass scattering angle and ******** is the azimuthal angle.  The “transverse” momentum of a particle is given by ****P****T**** = P cos(********cm****)****.**

|  | cm |
| --- | --- |
| 0 | 90o |
| 1 | 40o |
| 2 | 15o |
| 3 | 6o |
| 4 | 2o |

**Use ******** and ******** to determine the direction of an outgoing particle, where ******** is the “pseudo-rapidity” defined by ********= -log(tan(********cm****/2))****.**

**The “rapidity” is defined by ****y = log((E+p****z****)/(E-p****z****))/2**** and is equal to ******** in the limit E >> mc****2****.**

- IMFP2006 - Day 1                                                  April 3, 2006

## Quark & Gluon Jets

**The CDF calorimeter measures energy deposited in a cell of size ********x******** = 0.11x15****o****, whch is converted into ****transverse energy****, E****T**** = E cos(********cm****).**

**“****Jets”**** are defined to be clusters of transverse energy with a radius R in ********-******** space.  A “jet” is the representation in the detector of an outgoing parton (quark or gluon).**
**The sum of the E****T**** of the cells within a “jet” corresponds roughly to the E****T**** of the outgoing parton and the position of the cluster in the grid gives the parton’s direction.**

**Calorimeter Jets**

**Can also construct jets from the charged particles!**

- IMFP2006 - Day 1                                                  April 3, 2006

## CDF Run 2 DiJet EventJuly 2002

- ETjet1 = 403 GeV
- ETjet2 = 322 GeV

**Raw E****T**** values!!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Proton-AntiProton Collisionsat the Tevatron

******tot**** = ********EL********SD**** ******** ********DD**** ******** ********HC**

**1.8 TeV:  78mb     =   18mb     + 9mb      + (4-7)mb  + (47-44)mb**

**The CDF “Min-Bias” trigger picks up most of the “hard core” cross-section plus a small amount of single & double diffraction.**

**The “hard core” component contains both “hard” and “soft” collisions.**

**Beam-Beam Counters**
**3.2 < |********| < 5.9**

_**CDF “Min-Bias” trigger**_
**1 charged particle in forward BBC**
**AND**
**1 charged particle in backward BBC**

******tot**** = ********EL********IN**** **

- IMFP2006 - Day 1                                                  April 3, 2006

## Proton-AntiProton Collisions at the Tevatron

**“****Hard core”**** does not imply that a ****“hard”**** parton-parton collision has occured?**

**90% of “hard core” collisions are ****“soft hard core”**** and the proton and antiproton ooze through each other and fall apart (*****i.e.***** ****no hard scattering****,**** ****P****T****(hard) < 5 GeV/c****).  The outgoing particles continue in roughly the same direction as initial proton and antiproton.**

**10% of the “hard core” collisions arise from a ****“hard” parton-parton collision**** (****P****T****(hard) > 5 GeV/c****) resulting in large transverse momentum outgoing partons.**

**About 0.3% of all parton-parton collisions produce a ****b-bbar**** quark pair (about 1/1,000 of all interactions).  **

- IMFP2006 - Day 1                                                  April 3, 2006

## CDF “Min-Bias” DataCharged Particle Density

**Shows CDF “Min-Bias” data on the number of charged particles per unit pseudo-rapidity at 630 and 1,800 GeV.  There are about ****4.2 charged particles per unit ******** in “Min-Bias” collisions at 1.8 TeV**** (|********| < 1, all P****T****).  **

**<dN****chg****/d********> = 4.2**

**<dN****chg****/d********d********> = 0.67**

**Convert to charged particle density, dN****chg****/d********d******** by dividing by 2********.  There are about ****0.67 charged particles per unit ********-******** in “Min-Bias” collisions at 1.8 TeV**** (|********| < 1, all P****T****).  **

- IMFP2006 - Day 1                                                  April 3, 2006

## Particle Densities

**Particle Densities**

**Study the charged particles (p****T**** > 0.5 GeV/c, |********| < 1) and form the charged particle density, ****dN****chg****/d********d********, and the charged scalar p****T**** sum density, ****dPT****sum****/d********d********. **

**Charged Particles**
** ****p****T**** > 0.5 GeV/c |********| < 1**

****** ****= 4******** = 12.6**

|  | CDF Run 2 “Min-Bias”
Observable | Average | Average Density
per unit - |
| --- | --- | --- | --- |
| Nchg | Number of Charged Particles
(pT > 0.5 GeV/c, || < 1) | 3.17 +/- 0.31 | 0.252 +/- 0.025 |
| PTsum (GeV/c) | Scalar pT sum of Charged Particles
(pT > 0.5 GeV/c, || < 1) | 2.97 +/- 0.23 | 0.236 +/- 0.018 |

**CDF Run 2 “Min-Bias”**

- IMFP2006 - Day 1                                                  April 3, 2006

## CDF “Min-Bias” DataEnergy Dependence

**Shows the center-of-mass energy dependence of the charged particle density, dN****chg****/d********d******** for “Min-Bias” collisions at ******** = 0.  Also show a log fit (Fit 1) and a (log)****2**** fit (Fit 2) to the CDF plus UA5 data.  **

**What should we expect for the LHC?****  **

**LHC?**

- IMFP2006 - Day 1                                                  April 3, 2006

## Herwig “Soft” Min-Bias

**Shows the center-of-mass energy dependence of the charged particle density, dN****chg****/d********d******** for “Min-Bias” collisions compared with the ****HERWIG “Soft” Min-Bias**** Monte-Carlo model.  Note: there is no “hard” scattering in HERWIG “Soft” Min-Bias.**

**HERWIG “Soft” Min-Bias contains no hard parton-parton interactions and describes fairly well the charged particle density, dN****chg****/d********d********, in “Min-Bias” collisions.**

**HERWIG “Soft” Min-Bias predicts a 45% rise in dN****chg****/d********d******** at ******** = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV).****  4 charged particles per unit ******** becomes 6.**

**Can we believe HERWIG “soft” Min-Bias?**

**Can we believe HERWIG “soft” Min-Bias? ****No!**

**LHC?**

- IMFP2006 - Day 1                                                  April 3, 2006

## CDF “Min-Bias” DataPT Dependence

**Shows the P****T**** dependence of the charged particle density, dN****chg****/d********d********dP****T****, for “Min-Bias” collisions at 1.8 TeV collisions compared with ****HERWIG “Soft” Min-Bias****.  **

**HERWIG “Soft” Min-Bias**** does not describe the “Min-Bias” data!  ****The “Min-Bias” data contain a lot of “hard” parton-parton collisions**** which results in many more particles at large P****T**** than are produces by any “soft” model.  **

**Shows the energy dependence of the charged particle density, dN****chg****/d********d******** for “Min-Bias” collisions compared with ****HERWIG “Soft” Min-Bias****.**

**Lots of “hard” scattering in “Min-Bias”!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Min-Bias: Combining“Hard” and “Soft” Collisions

**HERWIG “hard” QCD**** with P****T****(hard) > 3 GeV/c describes well the high P****T**** tail but produces too many charged particles overall.  Not all of the “Min-Bias” collisions have a hard scattering with P****T****(hard) > 3 GeV/c!  **

**One cannot run the HERWIG “hard” QCD Monte-Carlo with P****T****(hard) < 3 GeV/c because the perturbative 2-to-2 cross-sections diverge like 1/P****T****(hard)****4****?  **

**HERWIG “soft” Min-Bias does not fit the “Min-Bias” data!**

******HC**

**HERWIG diverges!**

**PYTHIA cuts off the divergence. Can run P****T****(hard)>0!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Monte-Carlo Simulationof Hadron-Hadron Collisions

**The underlying event in a hard scattering process has a “hard” component (particles that arise from initial & final-state radiation and from the outgoing hard scattered partons) and a “soft?” component (“beam-beam remnants”).**

**Clearly? the “underlying event” in a hard scattering process should not look like a “Min-Bias” event because of the “hard” component (*****i.e.***** ****initial & final-state radiation****).**

**However, perhaps ****“Min-Bias”**** collisions are a good model for the ****“beam-beam remnant”**** component of the “underlying event”.**

**Are these the same?**

**The “beam-beam remnant” component is, however, ****color connected**** to the “hard” component so this comparison is (at best) an approximation.**

**Maybe not all “soft”!**

- IMFP2006 - Day 1                                                  April 3, 2006

## MPI: Multiple PartonInteractions

**PYTHIA models the “soft” component of the underlying event with color string fragmentation, but in addition includes a contribution arising from multiple parton interactions (****MPI****)  in which one interaction is hard and the other is “semi-hard”. **

**The probability that a hard scattering events also contains a semi-hard multiple parton interaction can be varied but adjusting the ****cut-off for the MPI****. **
**One can also adjust whether the probability of a MPI depends on the P****T**** of the hard scattering, P****T****(hard) (****constant cross section or varying with impact parameter****).  **
**One can adjust the color connections and flavor of the MPI (****singlet or nearest neighbor, q-qbar or glue-glue****).**
**Also, one can adjust how the probability of a MPI depends on P****T****(hard) (****single or double Gaussian matter distribution****).**

- IMFP2006 - Day 1                                                  April 3, 2006

## PYTHIA 6.2: Multiple PartonInteraction Parameters

**Pythia uses multiple parton**
**interactions to enhance**
**the underlying event.**

| Parameter  | Value   | Description  |
| --- | --- | --- |
| MSTP(81)  | 0 | Multiple-Parton Scattering off  |
|  | 1 | Multiple-Parton Scattering on  |
| MSTP(82)  | 1 | Multiple interactions assuming the same probability, with an abrupt cut-off PTmin=PARP(81)  |
|  | 3 | Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a single Gaussian matter distribution, with a smooth turn-off PT0=PARP(82)  |
|  | 4 | Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a double Gaussian matter distribution (governed by PARP(83) and PARP(84)), with a smooth turn-off PT0=PARP(82)  |

**Hard Core**

**Multiple parton interaction more likely in a hard (central) collision!**

**and now HERWIG!**

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

**Same parameter that cuts-off the hard 2-to-2 parton cross sections!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Tuning PYTHIA 6.2:Multiple Parton Interaction Parameters

**Tuning PYTHIA 6.2:****Multiple Parton Interaction Parameters**

| Parameter  | Default   | Description  |
| --- | --- | --- |
| PARP(83)  | 0.5 | Double-Gaussian: Fraction of total hadronic matter within PARP(84)  |
| PARP(84) | 0.2 | Double-Gaussian: Fraction of the overall hadron radius containing the fraction PARP(83) of the total hadronic matter. |
| PARP(85)  | 0.33 | Probability that the MPI produces two gluons with color connections to the “nearest neighbors.  |
| PARP(86) | 0.66 | Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop.  The remaining fraction consists of quark-antiquark pairs.  |
| PARP(89) | 1 TeV | Determines the reference energy E0. |
| PARP(90)
 | 0.16 | Determines the energy dependence of the cut-off
PT0 as follows PT0(Ecm) = PT0(Ecm/E0)  with           = PARP(90) |
| PARP(67) | 1.0 | A scale factor that determines the maximum parton virtuality for space-like showers.  The larger the value of PARP(67) the more initial-state radiation.  |

**Hard Core**

**Take E****0**** = 1.8 TeV**

**Reference point**
**at 1.8 TeV**

**Determine by comparing**
**with 630 GeV data!**

**Affects the amount of**
**initial-state radiation!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Tuned PYTHIA 6.206

**(more initial-state radiation)**

**New PYTHIA default**
**(less initial-state radiation)**

| Parameter | Tune B | Tune A |
| --- | --- | --- |
| 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(67) | 1.0 | 4.0 |

**Old PYTHIA default**
**(more initial-state radiation)**

**New PYTHIA default**
**(less initial-state radiation)**

**Tuned PYTHIA 6.206**

**Plot shows the ****“Transverse” charged particle density versus P****T****(chgjet#1)**** compared to the QCD hard scattering predictions of two ****tuned**** versions of ****PYTHIA 6.206**** **** (CTEQ5L, ****Set B**** (PARP(67)=1)**** ****and**** ****Set A**** ****(PARP(67)=4)).**

**PYTHIA 6.206 CTEQ5L**

**CDF Default!**

**Run 1 Analysis**

- IMFP2006 - Day 1                                                  April 3, 2006

## PYTHIA Min-Bias“Soft” + ”Hard”

**PYTHIA regulates the perturbative 2-to-2 parton-parton cross sections with cut-off parameters which allows one to run with P****T****(hard) > 0.  ****One can simulate both “hard” and “soft” collisions in one program.****  **

**The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.  **

**Tuned to fit the “underlying event”!**

**12% of “Min-Bias” events have P****T****(hard) > 5 GeV/c!**

**1% of “Min-Bias” events have P****T****(hard) > 10 GeV/c!**

**This PYTHIA fit predicts that 12% of all “Min-Bias” events are a result of a hard 2-to-2 parton-parton scattering with P****T****(hard) > 5 GeV/c (****1% with P****T****(hard) > 10 GeV/c****)!  **

**Lots of “hard” scattering in “Min-Bias”!**

**PYTHIA ****Tune A**
**CDF Run 2 Default**

- IMFP2006 - Day 1                                                  April 3, 2006

## Min-Bias “Associated”Charged Particle Density

**Use the ****maximum p****T**** charged particle in the event, PTmax****, to define a direction and look at the the “associated” density, dN****chg****/d********d********, in ****“min-bias” collisions**** (p****T**** > 0.5 GeV/c, |********| < 1).**

**“****Associated” densities do not include PTmax!**

**Highest p****T**** charged particle!**

**Shows the data on the ******** dependence of the “associated” charged particle density****, dN****chg****/d********d********, for charged particles (p****T**** > 0.5 GeV/c, |********| < 1, *****not including PTmax*****) relative to PTmax (rotated to 180****o****) for ****“min-bias” events****.  ****Also shown is the average charged particle density, dN****chg****/d********d********, for “min-bias” events****.**

**It is more probable to find a particle accompanying PTmax than it is to find a particle in the central region!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Min-Bias “Associated”Charged Particle Density

**Min-Bias**** “Associated”****Charged Particle Density**

**Shows the data on the ******** dependence of the “associated” charged particle density****, dN****chg****/d********d********, for charged particles (p****T**** > 0.5 GeV/c, |********| < 1, *****not including PTmax*****) relative to PTmax (rotated to 180****o****) for ****“min-bias” events**** ****with PTmax > 0.5, 1.0, and 2.0 GeV/c.**

**Transverse Region**

**Transverse Region**

**Shows ****“jet structure” in “min-bias” collisions**** (*****i.e.***** ****the “birth” of the leading two jets!****).**

**Ave Min-Bias**
**0.25 per unit ********-******

**PTmax > 0.5 GeV/c**

**PTmax > 2.0 GeV/c**

**Rapid rise in the particle density in the “transverse” region as PTmax increases!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Min-Bias “Associated”Charged PTsum Density

**Min-Bias**** “Associated”****Charged PTsum Density**

**Use the ****maximum p****T**** charged particle in the event, PTmax****, to define a direction and look at the the “associated” PTsum density, dPT****sum****/d********d********.**
**Shows the data on the ******** dependence of the “associated” charged PTsum density****, dPT****sum****/d********d********, for charged particles (p****T**** > 0.5 GeV/c, |********| < 1, *****not including PTmax*****) relative to PTmax (rotated to 180****o****) for ****“min-bias” events****.  ****Also shown is the average charged particle density, dPT****sum****/d********d********, for “min-bias” events****.**

**“****Associated” densities do not include PTmax!**

**Highest p****T**** charged particle!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Min-Bias “Associated”Charged PTsum Density

**Min-Bias**** “Associated”****Charged PTsum Density**

**Shows the data on the ******** dependence of the “associated” charged PTsum density****, dPT****sum****/d********d********, for charged particles (p****T**** > 0.5 GeV/c, |********| < 1, *****not including PTmax*****) relative to PTmax (rotated to 180****o****) for ****“min-bias” events**** ****with PTmax > 0.5, 1.0, and 2.0 GeV/c.**

**Transverse Region**

**Transverse Region**

**Shows ****“jet structure” in “min-bias” collisions**** (*****i.e.***** ****the “birth” of the leading two jets!****).**

**Ave Min-Bias**
**0.24 GeV/c per unit ********-******

**Rapid rise in the PTsum density in the “transverse” region as PTmax increases!**

- IMFP2006 - Day 1                                                  April 3, 2006

## Min-Bias “Associated”Charged Particle Density

**Min-Bias**** “Associated”****Charged Particle Density**

**Shows the data on the ******** dependence of the “associated” charged particle density****, dN****chg****/d********d********, for charged particles (p****T**** > 0.5 GeV/c, |********| < 1, *****not including PTmax*****) relative to PTmax (rotated to 180****o****) for ****“min-bias” events**** ****with PTmax > 0.5 GeV/c and PTmax > 2.0 GeV/c compared with ****PYTHIA Tune A**** (after CDFSIM).**

**PYTHIA Tune A**** predicts a larger correlation than is seen in the “min-bias” data (*****i.e.***** ****Tune A “min-bias” is a bit too “jetty”****).**

**PTmax > 2.0 GeV/c**

**PTmax > 0.5 GeV/c**

**Transverse Region**

**Transverse Region**

**PY Tune A**

- IMFP2006 - Day 1                                                  April 3, 2006

## Min-Bias “Associated”Charged PTsum Density

**Min-Bias**** “Associated”****Charged PTsum Density**

**Shows the data on the ******** dependence of the “associated” charged PTsum density****, dPT****sum****/d********d********, for charged particles (p****T**** > 0.5 GeV/c, |********| < 1, *****not including PTmax*****) relative to PTmax (rotated to 180****o****) for ****“min-bias” events**** ****with PTmax > 0.5 GeV/c and PTmax > 2.0 GeV/c compared with ****PYTHIA Tune A**** (after CDFSIM).**

**PYTHIA Tune A**** predicts a larger correlation than is seen in the “min-bias” data (*****i.e.***** ****Tune A “min-bias” is a bit too “jetty”****).**

**PTmax > 2.0 GeV/c**

**PTmax > 0.5 GeV/c**

**Transverse Region**

**Transverse Region**

**PY Tune A**

- IMFP2006 - Day 1                                                  April 3, 2006

## PYTHIA Tune ALHC Predictions

**PYTHIA was tuned to fit the “underlying event” in hard-scattering processes at 1.8 TeV and 630 GeV.  **

**Shows the center-of-mass energy dependence of the charged particle density, dN****chg****/d********d******** for “Min-Bias” collisions compared with ****PYTHIA Tune A**** with P****T****(hard) > 0.**

**PYTHIA Tune A**** predicts a 42% rise in dN****chg****/d********d******** at ******** = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV).  Similar to HERWIG “soft” min-bias, ****4 charged particles per unit ******** becomes 6.**

**LHC?**

- IMFP2006 - Day 1                                                  April 3, 2006

## PYTHIA Tune ALHC Predictions

**Shows the center-of-mass energy dependence of the charged particle density, dN****chg****/d********d********dP****T****, for “Min-Bias” collisions compared with ****PYTHIA Tune A**** with P****T****(hard) > 0.**

**PYTHIA Tune A**** predicts that 1% of all “Min-Bias” events  at 1.8 TeV are a result of a hard 2-to-2 parton-parton scattering with P****T****(hard) > 10 GeV/c which increases to ****12% at 14 TeV****!**

**1% of “Min-Bias” events have P****T****(hard) > 10 GeV/c!**

**12% of “Min-Bias” events have P****T****(hard) > 10 GeV/c!**

**LHC?**

- IMFP2006 - Day 1                                                  April 3, 2006

## LHC Min-Bias Predictions

**Tevatron           LHC**

**Both HERWIG and the tuned PYTHIA Tune A predict a 40-45% rise in dN****chg****/d********d******** at ******** = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV).  ****4 charged particles per unit ******** at the Tevatron becomes 6 per unit ******** at the LHC.**

**12 times more likely to find a 10 GeV “jet” in “Min-Bias” at the LHC!**

**The tuned PYTHIA Tune A predicts that 1% of all “Min-Bias” events at the Tevatron (1.8 TeV) are the result of a hard 2-to-2 parton-parton scattering with ****P****T****(hard) > 10 GeV/c**** which increases to ****12% at LHC**** (14 TeV)!**

- IMFP2006 - Day 1                                                  April 3, 2006