LOW X MEETING, Paphos, Cyprus, 17 June -1 July 2012
LOW X MEETING, Paphos, Cyprus, 17 June -1 July 2012
LOW X MEETING, Paphos, Cyprus, 17 June -1 July 2012
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Predictions of Soft Processes at the LHC<br />
Implemented in PYTHIA8<br />
Konstantin Goulianos*<br />
The Rockefeller University<br />
* with:<br />
Robert Ciesielski<br />
1<br />
low-x <strong>2012</strong> <strong>Cyprus</strong> Soft Processes at LHC in PYTHIA8 K. Goulianos 1
CONTENTS<br />
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INTRODUCTION<br />
This is an adaptation of the MBR (Minimum Bias Rockefeller) simulation<br />
RENORM to PYTHIA8.<br />
‣ successfully tested at Fermilab fixed target and collider experiments.<br />
RENORM predictions are based on a parton model approach, in which<br />
diffraction is derived from inclusive PDFs and color factors.<br />
Gap Cross Sections:<br />
‣ Gap cross sections vs gap width:<br />
Absolute normalization!<br />
‣ Hadronization of dissociated proton:<br />
‣ Implemented by introducing a (non-perturbative) “quark string” and<br />
tuning it to reproduce the MBR multiplicity and p T distributions.<br />
‣ dN/dh, p T , and particle ID (new in this implementation; the original<br />
MBR produced only p ± and p 0 )<br />
‣ Unique unitarization procedure based on a saturated exchange.<br />
Total Cross section: based on a saturated Froissart bound leading to a ln 2 s<br />
dependence.<br />
‣ Immune to eikonaalization models that plague the field!<br />
low-x <strong>2012</strong> <strong>Cyprus</strong> Soft Processes at LHC in PYTHIA8 K. Goulianos 3
STUDIES OF DIFFRACTION IN QCD<br />
Non-diffractive<br />
color-exchange gaps<br />
exponentially suppressed<br />
Diffractive<br />
Colorless vacuum exchange<br />
large-gap signature<br />
Incident hadrons<br />
acquire color<br />
and break upart<br />
rapidity gap<br />
p<br />
Incident hadrons retain<br />
their quantum numbers<br />
remaining colorless<br />
CONFINEMENT<br />
Goal: probe the QCD nature of the diffractive exchange<br />
P<br />
O<br />
M<br />
E<br />
R<br />
O<br />
N<br />
p p p p<br />
low-x <strong>2012</strong> <strong>Cyprus</strong> Soft Processes at LHC in PYTHIA8 K. Goulianos 4
DEFINITIONS<br />
SINGLE DIFFRACTION<br />
x,t<br />
M X<br />
p p’<br />
xp<br />
p<br />
1- x L<br />
ξ<br />
CAL<br />
ξ<br />
<br />
Σ<br />
<br />
all<br />
i1<br />
M 2 X<br />
s<br />
E<br />
i-tower<br />
T<br />
since no radiation <br />
no price paid for increasing<br />
diffractive gap size<br />
s<br />
e<br />
<br />
η i<br />
<br />
<br />
<br />
dσ<br />
d Δη<br />
<br />
<br />
<br />
t0<br />
p’<br />
Rap-gap<br />
Dh=-lnx<br />
constant <br />
dσ<br />
dξ<br />
0<br />
dN/dh<br />
ln ln s<br />
dσ 1<br />
<br />
2 2<br />
1<br />
ξ<br />
ln Mx 2<br />
low-x <strong>2012</strong> <strong>Cyprus</strong> Soft Processes at LHC in PYTHIA8 K. Goulianos<br />
dM<br />
M X<br />
M<br />
5
DIFFRACTION AT CDF<br />
Elastic scattering s T =Im f el (t=0) Total cross section<br />
f<br />
gap<br />
h<br />
OPTICAL<br />
THEOREM<br />
f<br />
h<br />
SD DD DPE /CD SDD<br />
Single Diffraction or<br />
Single Dissociation<br />
Double Diffraction or<br />
Double Dissociation<br />
Double Pom. Exchange or<br />
Central Dissociation<br />
Single + Double<br />
Diffraction (SDD)<br />
JJ, b, J/y, W<br />
p<br />
exclusive<br />
JJ…ee…mm...gg<br />
p<br />
low-x <strong>2012</strong> <strong>Cyprus</strong> Soft Processes at LHC in PYTHIA8 K. Goulianos<br />
6
540 GeV<br />
1800 GeV<br />
FACTORIZATION BREAKING IN<br />
SOFT DIFFRACTION<br />
diffractive x-section suppressed relative<br />
to Regge prediction as √s increases<br />
p<br />
p<br />
x,t<br />
p’<br />
M<br />
Factor of ~8 (~5)<br />
suppression at<br />
√s = 1800 (540) GeV<br />
RENORMALIZATION<br />
√s=22 GeV<br />
C<br />
D<br />
F<br />
see KG, PLB 358, 379 (1995)<br />
Question:<br />
does factorization breaking<br />
affect t-distributions<br />
low-x <strong>2012</strong> <strong>Cyprus</strong> Soft Processes at LHC in PYTHIA8 K. Goulianos 7
DD at CDF<br />
gap probability<br />
x-section<br />
renormalized<br />
EDS-2011 Vietnam CDF Diffraction and Exclusive Production 8
SDD at CDF<br />
• Excellent agreement<br />
between data and MBR<br />
(MinBiasRockefeller) MC<br />
EDS-2011 Vietnam CDF Diffraction and Exclusive Production 9
CD (DPE) at CDF<br />
• Excellent agreement<br />
between data and MBR<br />
low and high masses are<br />
correctly implemented<br />
EDS-2011 Vietnam CDF Diffraction and Exclusive Production 10
Cross Sections<br />
tot<br />
el<br />
SD SD DD CD<br />
SD single diffraction (single dissociation)<br />
DD double dissociation (double diffraction)<br />
CD central dissociation (double pomeron exchange)<br />
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Total, elastic, and inelastic x-sections<br />
GeV 2<br />
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Total, elastic, and inelastic x-sections<br />
versus √s<br />
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Difractive x-sections<br />
a 1 =0.9, a 2 =0.1, b 1 =4.6 GeV -2 , b 2 =0.6 GeV -2 , s′=s e -Dy , k=0.<strong>17</strong>,<br />
kb 2 (0)=s 0 , s 0 =1 GeV 2 , s 0 =2.82 mb or 7.25 GeV -2<br />
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Difractive x-sections of √s<br />
Supress x-sections at small gaps by a factor S using the error function with<br />
Dy S =2 for SD and DD, and Dy=Dy 1 +Dy 2 =2 for CD (DPE).<br />
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SD and DD at 7 TeV<br />
MBR vs PYTHIA8-4C<br />
The differences between the PYTHIA8(4C) and MBR predictions are mainly<br />
due to the (1/M2) 1+e behavior, with e=1.104 in MBR vs 1,08 in PYTHIA8(4C).<br />
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CD (DPE) x-sections at 7 TeV versus<br />
(a) Dy=Dy1+Dy2 and (b) Dy1<br />
Both figures are MBR predictions with a Dy=2 cut-off in the error function.<br />
The normalization is absolute with no model uncertainty other than that due to the<br />
determination of the parameters in the formulas as determined from data<br />
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Thank you for your<br />
attention<br />
low-x <strong>2012</strong> <strong>Cyprus</strong> Soft Processes at LHC in PYTHIA8 K. Goulianos<br />
18
References in arXiv:1205.1446v1 [hep-ph]<br />
multiplicities<br />
low-x <strong>2012</strong> <strong>Cyprus</strong> Soft Processes at LHC in PYTHIA8 K. Goulianos 19
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