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Jets Photoproduction from ZEUS. Alexander A. Savin. Workshop on PHP at collider energies: from RHIC and HERA to LHC, 15-19 January 2007, Trento, Italy. Recent Results Interesting for LHC. - PowerPoint PPT Presentation
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A.Savin Jets photoproduction from ZEUS 1/26
Alexander A. Savin
Workshop onPHP at collider energies: from RHIC and HERA to LHC,
15-19 January 2007, Trento, Italy
A.Savin Jets photoproduction from ZEUS 2/26
Recent Results Interesting for LHC
• Multijet (three and four jets) photoproduction - Multi-Parton Interactions (MPI) – is almost being published ;
• Hard dijet production via color-singlet exchange – events with rapidity gap between jets (DESY-06-215)
A.Savin Jets photoproduction from ZEUS 3/26
Kinematics and Jets Reconstruction • Kinematic variables and jets are
reconstructed using Energy Flow Objects – combination of tracking and calorimeter information ;
• Jets are reconstructed using kT algorithm in the longitudinally invariant inclusive mode.
Q2<1 GeV2, 0.2<y<0.85(0.75)
ETjet1>7(6) GeV, ET
jet2>7(5) GeV, ETjet3,4>5 GeV
+ some specific cuts for each analysis
A.Savin Jets photoproduction from ZEUS 4/26
Monte Carlo Parameters and Tuning IHERWIG + JIMMY for MPI
– Proton PDF: CTEQ 5L (CTEQ 5L)– Photon PDF: GRV-G (SaS-G 2D)– Square factor to reduce proton radius: 3.0 (default 1.0)– Probability of Soft Underlying Event: 0.03 (default 1.0)– Photon to resolve - 1/150 (default 1/300)
– Multijets: pTMin 1= 2.0 pT
Min 2= 1.8 (new HERWIG)
– Jets with RG: PTMIN1 = 2.7 GeV (default 1.8 GeV)
A.Savin Jets photoproduction from ZEUS 5/26
Monte Carlo Parameters and Tuning IIPYTHIA + “simple model” for MPI
– Proton PDF: CTEQ 5L (CTEQ 5L)– Photon PDF: GRV-G (SaS-G 2D)
– pTMin 1= 2.0 pT
Min 2= 1.5 (1.9 GeV, 1.7 GeV)
For the multijets publication default values
pTMin 1= 2.5 pT
Min 2= 1.9 are used
• Cross sections have to be scaled to describe the data normalization
A.Savin Jets photoproduction from ZEUS 6/26
Direct and Resolved PHP
E
eEx jets
jetTobs
jets
2
75.0obsx75.0obsx
A.Savin Jets photoproduction from ZEUS 7/26
Three Jets at ZEUS
A.Savin Jets photoproduction from ZEUS 8/26
Multijets: Soft and Hard MPI
Moving jets into the kinematic region Adding jets
A.Savin Jets photoproduction from ZEUS 9/26
Hard MPI and LO Four Jets
direct
resolved
A.Savin Jets photoproduction from ZEUS 10/26
-distributionsobsx
Low x-region Direct contribution
A.Savin Jets photoproduction from ZEUS 11/26
-distributions
Low x-region Direct contribution
obsx
A.Savin Jets photoproduction from ZEUS 12/26
Jet Mass Distributions
High mass tail is described even without MPI
A.Savin Jets photoproduction from ZEUS 13/26
y-distribution
A.Savin Jets photoproduction from ZEUS 14/26
)( 2sO
The pQCD Calculation
by Klasen,Kleinwort,Kramer
Average hadronization and MPIcorrections from HERWIG and Pythia. ET
jet1 as renormalizationand factorization scales
A.Savin Jets photoproduction from ZEUS 15/26
Hard Diffractive Dijet Photoproduction
Rapidity Gap Between Jets and Proton Remnant
Rapidity Gap Between Jets
A.Savin Jets photoproduction from ZEUS 16/26
Rapidity Gap Topology
• Distance between leading and trailing jet centers: • Gap definition based on ET : ET
Gap - total ET between leading and trailing jet centers
A.Savin Jets photoproduction from ZEUS 17/26
The Gap Fraction f()
Expectation for Behavior of Gap Fraction (J. D. Bjorken, V. Del Duca, W.-K. Tung)
fgapsinglet fgap
n-s
fgap
2 3 4
dd
ddf
gap
/
/)(
Dijet Events with large Rapidity separation between jets
& ETGap < ET
Cut
All Dijet Events with large Rapidity separation between jets
singletnonsinglet gapgapgap
A.Savin Jets photoproduction from ZEUS 18/26
Color-Singlet Exchange in the MC
HERWIG: BFKL Pomeron as exchange object
PYTHIA: High-t exchange
• Used to match data only – Rapidity Gap not due to photon exchange
A.Savin Jets photoproduction from ZEUS 19/26
Previous HERA Measurements
• ZEUS 1995: Gap Fraction defined by multiplicity• H1 2002: Gap Fraction defined by ET
Gap
H1
ETGAP < 1.0 GeV
ZEUS 1995
Data ●PYTHIA o
A.Savin Jets photoproduction from ZEUS 20/26
Cross Section Estimate of the CS
)%10.075.2(
)%25.004.2( HERWIG
Pythia
45.2
A.Savin Jets photoproduction from ZEUS 21/26
Gap Fraction
This differenceIs the CScontribution
Data are well described by the MC
A.Savin Jets photoproduction from ZEUS 22/26
Comparison to H1
A.Savin Jets photoproduction from ZEUS 23/26
Resummed Calculation
Appleby, Banfi, Dasgupta, Seymour
A.Savin Jets photoproduction from ZEUS 24/26
Resolved Contribution
CS only
A.Savin Jets photoproduction from ZEUS 25/26
Resolved Contribution:
Energy Dependence
A.Savin Jets photoproduction from ZEUS 26/26
HERA has collected a lot of information which can be used for better understanding of
physics and tuning the models also for LHC …
Will we get use of it ?
A.Savin Jets photoproduction from ZEUS 27/26
A.Savin Jets photoproduction from ZEUS 28/26