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Chris Quigg Symposium. Predicting MB & UE at the LHC. Rick Field University of Florida. Outline of Talk. The inelastic non-diffractive cross section. The “underlying event” in a hard scattering process. The QCD Monte-Carlo model tunes. CDF Run 2.

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Chris Quigg Symposium

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Chris quigg symposium

Chris Quigg Symposium

Predicting MB & UE at the LHC

Rick Field

University of Florida

Outline of Talk

  • The inelastic non-diffractive cross section.

  • The “underlying event” in a hard scattering process.

  • The QCD Monte-Carlo model tunes.

CDF Run 2

  • Relationship between the “underlying event” in a hard scattering process and “min-bias” collisions.

  • “Min-Bias” and the “underlying event” at the LHC.

UE&[email protected]

CMS at the LHC

Rick Field – Florida/CDF/CMS


J d j students

J.D.J. Students

“Older than Dirt” hat!

Chris Quigg

Bob Cahn

me

Gordy Kane

J.D.J

J.D.J

Jimmie & Rick

Rick Field – Florida/CDF/CMS


Proton proton collisions

Proton-Proton Collisions

stot = sEL + sSD+sDD+sHC

ND

“Inelastic Non-Diffractive Component”

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

Rick Field – Florida/CDF/CMS


Inelastic non diffractive cross section

Inelastic Non-Diffractive Cross-Section

  • The inelastic non-diffractive cross section versus center-of-mass energy from PYTHIA (×1.2).

My guess!

Linear scale!

Log scale!

stot = sEL + sSD+sDD+sND

  • sHC varies slowly. Only a 13% increase between 7 TeV (≈ 58 mb) and 14 teV (≈ 66 mb). Linear on a log scale!

Rick Field – Florida/CDF/CMS


Qcd monte carlo models high transverse momentum jets

“Hard Scattering” Component

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).

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

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

Rick Field – Florida/CDF/CMS


Mpi pile up and overlap

Proton

Proton

Proton

Proton

MPI, Pile-Up, and Overlap

MPI: Multiple Parton Interactions

  • MPI: Additional 2-to-2 parton-parton scatterings within a single hadron-hadron collision.

Pile-Up

Interaction Region Dz

  • Pile-Up: More than one hadron-hadron collision in the beam crossing.

Overlap

  • Overlap: An experimental timing issue where a hadron-hadron collision from the next beam crossing gets included in the hadron-hadron collision from the current beam crossing because the next crossing happened before the event could be read out.

Rick Field – Florida/CDF/CMS


Cdf run 1 evolution of charged jets underlying event

CDF Run 1: Evolution of Charged Jets“Underlying Event”

  • Look at charged particle correlations in the azimuthal angle Df relative to the leading charged particle jet.

  • Define |Df| < 60o as “Toward”, 60o < |Df| < 120o as “Transverse”, and |Df| > 120o as “Away”.

  • All three regions have the same size in h-f space, DhxDf = 2x120o = 4p/3.

Charged Particle Df Correlations PT > 0.5 GeV/c |h| < 1

Look at the charged particle density in the “transverse” region!

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

CDF Run 1 Analysis

Rick Field – Florida/CDF/CMS


Pythia 6 206 defaults

PYTHIA 6.206 Defaults

MPI constant

probability

scattering

  • Plot shows the “Transverse” charged particle density versus PT(chgjet#1) compared to the QCD hard scattering predictions of PYTHIA 6.206 (PT(hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L.

PYTHIA default parameters

Default parameters give very poor description of the “underlying event”!

Note Change

PARP(67) = 4.0 (< 6.138)

PARP(67) = 1.0 (> 6.138)

Rick Field – Florida/CDF/CMS


Tuning pythia multiple parton interaction parameters

Tuning PYTHIA:Multiple Parton Interaction Parameters

Hard Core

Determines the energy dependence of the MPI!

Determine by comparing

with 630 GeV data!

Affects the amount of

initial-state radiation!

Take E0 = 1.8 TeV

Reference point

at 1.8 TeV

Rick Field – Florida/CDF/CMS


Run 1 pythia tune a

Run 1 PYTHIA Tune A

CDF Default!

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

PYTHIA 6.206 CTEQ5L

Run 1 Analysis

Old PYTHIA default

(more initial-state radiation)

Old PYTHIA default

(more initial-state radiation)

New PYTHIA default

(less initial-state radiation)

New PYTHIA default

(less initial-state radiation)

Rick Field – Florida/CDF/CMS


Cdf run 1 min bias associated charged particle density

CDF Run 1 Min-Bias “Associated”Charged Particle Density

“Associated” densities do not include PTmax!

Highest pT charged particle!

  • Use the maximum pT charged particle in the event, PTmax, to define a direction and look at the the “associated” density, dNchg/dhdf, in “min-bias” collisions (pT > 0.5 GeV/c, |h| < 1).

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

  • Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged particle density, dNchg/dhdf, for “min-bias” events.

Rick Field – Florida/CDF/CMS


Cdf run 1 min bias associated charged particle density1

CDF Run 1 Min-Bias “Associated”Charged Particle Density

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

PTmax > 2.0 GeV/c

Transverse Region

Transverse Region

Ave Min-Bias

0.25 per unit h-f

PTmax > 0.5 GeV/c

  • Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” eventswith PTmax > 0.5, 1.0, and 2.0 GeV/c.

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

Rick Field – Florida/CDF/CMS


Min bias associated charged particle density

Min-Bias “Associated”Charged Particle Density

  • Shows the “associated” charged particle density in the “toward”, “away” and “transverse” regions as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 1.96 TeVfrom PYTHIA Tune A (generator level).

“Toward” Region

~ factor of 2!

“Transverse”

“Transverse”

  • Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events at 1.96 TeVwith PTmax > 0.5, 1.0, 2.0, 5.0, and 10.0 GeV/c from PYTHIA Tune A (generator level).

Rick Field – Florida/CDF/CMS


Charged particle multiplicity

Charged Particle Multiplicity

New

  • Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 1) for “min-bias” collisions at CDF Run 2.

Tune A!

No MPI!

7 decades!

  • The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI).

Rick Field – Florida/CDF/CMS


The underlying event

The “Underlying Event”

Select inelastic non-diffractive events that contain a hard scattering

Hard parton-parton collisions is hard

(pT > ≈2 GeV/c)

“Semi-hard” parton-parton collision

(pT < ≈2 GeV/c)

The “underlying-event” (UE)!

+

+

+ …

Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”.

Multiple-parton interactions (MPI)!

Rick Field – Florida/CDF/CMS


The inelastic non diffractive cross section

The Inelastic Non-Diffractive Cross-Section

Occasionally one of the parton-parton collisions is hard

(pT > ≈2 GeV/c)

Majority of “min-bias” events!

“Semi-hard” parton-parton collision

(pT < ≈2 GeV/c)

+

+

+

+ …

Multiple-parton interactions (MPI)!

Rick Field – Florida/CDF/CMS


The underlying event1

The “Underlying Event”

Select inelastic non-diffractive events that contain a hard scattering

Hard parton-parton collisions is hard

(pT > ≈2 GeV/c)

“Semi-hard” parton-parton collision

(pT < ≈2 GeV/c)

The “underlying-event” (UE)!

+

+

+ …

Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”.

Multiple-parton interactions (MPI)!

Rick Field – Florida/CDF/CMS


Min bias correlations

Min-Bias Correlations

New

  • Data at 1.96 TeV on the average pT of charged particles versus the number of charged particles (pT > 0.4 GeV/c, |h| < 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).

Rick Field – Florida/CDF/CMS


Min bias average pt versus nchg

Min-Bias: Average PT versus Nchg

  • Beam-beam remnants (i.e. soft hard core) produces low multiplicity and small <pT> with <pT> independent of the multiplicity.

  • Hard scattering (with no MPI) produces large multiplicity and large <pT>.

  • Hard scattering (with MPI) produces large multiplicity and medium <pT>.

This observable is sensitive to the MPI tuning!

=

+

+

The CDF “min-bias” trigger picks up most of the “hard core” component!

Rick Field – Florida/CDF/CMS


Charged particle multiplicity1

Charged Particle Multiplicity

  • Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 1) for “min-bias” collisions at CDF Run 2.

Tune A prediction at 900 GeV!

No MPI!

Tune A!

  • The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI).

  • Prediction from PYTHIA Tune A for proton-proton collisions at 900 GeV.

Rick Field – Florida/CDF/CMS


Peter s pythia tunes website

Peter’s Pythia Tunes WEBsite

  • http://home.fnal.gov/~skands/leshouches-plots/

Rick Field – Florida/CDF/CMS


Min bias associated charged particle density1

Min-Bias “Associated”Charged Particle Density

35% more at RHIC means 26% less at the LHC!

  • Shows the “associated” charged particle density in the “transverse” regions as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2 TeV and 14 TeVfrom PYTHIA Tune DW and Tune DWT at the particle level (i.e. generator level). The STAR data from RHIC favors Tune DW!

~1.35

~1.35

0.2 TeV → 14 TeV

(~factor of 70 increase)

RHIC

LHC

Rick Field – Florida/CDF/CMS


Min bias associated charged particle density2

Min-Bias “Associated”Charged Particle Density

  • Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 1.96 TeV and 14 TeVpredicted by PYTHIA Tune DW at the particle level (i.e. generator level).

~1.9

~2.7

0.2 TeV → 1.96 TeV

(UE increase ~2.7 times)

1.96 TeV → 14 TeV

(UE increase ~1.9 times)

RHIC

LHC

Tevatron

Rick Field – Florida/CDF/CMS


The underlying event at star

The “Underlying Event” at STAR

  • At STAR they have measured the “underlying event at W = 200 GeV (|h| < 1, pT > 0.2 GeV) and compared their uncorrected data with PYTHIA Tune A + STAR-SIM.

Rick Field – Florida/CDF/CMS


Lhc predictions 900 gev

LHC Predictions: 900 GeV

DD/NSD = 12±4%

(SD + DD)/INEL = 28±8%

  • Compares the 900 GeV data with my favorite PYTHIA Tunes (Tune DW and Tune S320 Perugia 0). Tune DW uses the old Q2-ordered parton shower and the old MPI model. Tune S320 uses the new pT-ordered parton shower and the new MPI model. The numbers in parentheses are the average value of dN/dh for the region |h| < 0.6.

Rick Field – Florida/CDF/CMS


Lhc predictions 900 gev1

LHC Predictions: 900 GeV

Off by 11%!

Require at least one charged particle to have pT > 1 GeV/c. This is > 99% HC only!

(SD + DD)/INEL = 28±8%

  • Shows the individual HC, DD, and SD predictions of PYTHIA Tune DW and Tune S320 Perugia 0. The numbers in parentheses are the average value of dN/dh for the region |h| < 0.6. I do not trust PYTHIA to model correctly the DD and SD contributions! I would like to know how well these tunes model the HC component. We need to look at observables where only HC contributes!

Rick Field – Florida/CDF/CMS


Min bias associated charged particle density3

Min-Bias “Associated”Charged Particle Density

  • Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 0.9 TeV, 1.96 TeV, 7 TeV, 10 TeV, 14 TeVpredicted by PYTHIA Tune DW at the particle level (i.e. generator level).

LHC14

LHC10

LHC7

Tevatron

900 GeV

RHIC

0.2 TeV → 1.96 TeV

(UE increase ~2.7 times)

1.96 TeV → 14 TeV

(UE increase ~1.9 times)

RHIC

LHC

Tevatron

Linear scale!

Rick Field – Florida/CDF/CMS


Min bias associated charged particle density4

Min-Bias “Associated”Charged Particle Density

  • Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 0.9 TeV, 1.96 TeV, 7 TeV, 10 TeV, 14 TeVpredicted by PYTHIA Tune DW at the particle level (i.e. generator level).

LHC14

LHC10

LHC7

Tevatron

900 GeV

RHIC

7 TeV → 14 TeV

(UE increase ~20%)

LHC7

LHC14

Linear on a log plot!

Log scale!

Rick Field – Florida/CDF/CMS


Transverse charge density

“Transverse” Charge Density

factor of 2!

900 GeV → 7 TeV

(UE increase ~ factor of 2.1)

LHC

900 GeV

LHC

7 TeV

  • Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 2) at 900 GeVas defined by PTmax from PYTHIATune DW and Tune S320 at the particle level (i.e. generator level).

Rick Field – Florida/CDF/CMS


Important 900 gev measurements

Important 900 GeV Measurements

It is very important to measure

BOTH “min-bias” and the and the

“underlying event” at 900 GeV!

To do this we need to collect

about 5,000,000 CMS

min-bias triggers!

  • The amount of activity in “min-bias” collisions (multiplicity distribution, pT distribution, PTsum distribution, dNchg/dh).

For every 1,000 events here

We get 3 events here!

  • The amount of activity in the “underlying event” in hard scattering events (“transverse” Nchg distribution, “transverse” pT distribution, “transverse” PTsum distribution for events with PTmax > 5 GeV/c).

  • We should map out the energy dependence of the “underlying event” in a hard scattering process from 900 GeV to 14 TeV!

Rick Field – Florida/CDF/CMS


The underlying event at 900 gev

The “Underlying Event” at 900 GeV

  • Show how well we could measure the “transverse” charged particle density versus PTmax with 10 M, 1 M, and 0.5 M “min-bias” (MB) events collected by CMS. Assumes that for all the events that the tracker is working well! The goal is to see how well the data (red squares) agree with the QCD MC prediction (black curve).

Unfortunately, looks like this is all we will get!

Rick Field – Florida/CDF/CMS


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