jets in ep collisions at hera
DESCRIPTION
Jets in ep collisions at HERA. Alexander A. Savin. on behalf of the H1 and ZEUS collaborations. Hadron Structure and QCD 2004, 18-22 May 2004, St.Petersburg, Russia. Kinematic variables. e +(-). p. (820). Photon virtuality. * P center-of-mass energy squared. inelasticity. - PowerPoint PPT PresentationTRANSCRIPT
2/27A.Savin – Jets at HERA -
Kinematic variablesKinematic variables
222 kkqQ 22 )( pqW
2)( kps
kp
qpy
Bjorken scaling variable
inelasticity
Photon virtuality
*P center-of-mass energy squared
ep enter-of-mass energy squared
Pq
Qx2
2
e+(-)
p(820)
3/27A.Savin – Jets at HERA -
)( 01S
)( 11S
1S
1S
Boson-gluon fusionQCD Compton
1 jet
2 jets
Jets at HERAJets at HERA
5/27A.Savin – Jets at HERA -
Detecto
r Sim
ulatio
n
Parton Level
Hadron Level
LO:ARIADNELEPTOPYTHIARAPGAP
NLO:DISENTDISASTER++MEPJETNLOJETS
GEANTCDM+LUND etc
Uncertainties: pdf FR , hadronisation detector
Events simulationEvents simulation
6/27A.Savin – Jets at HERA -
i
j
Jet FindingJet Finding Breit FrameBreit Frame
La
b F
ram
eB
reit
Fra
me
Bre
it F
ram
e
DIS Event
PT
PL
2,iTi Ed
2
222,
2,
))()((},min{
REEd jTiTij
Inclusive mode,combine if: jiij ddd
Exclusive mode:
combine until cutij yy
Longitudinally invariantkT cluster algorithm
02 qxP
)cos1}(,min{2 222 ijjiij EE
Qy
7/27A.Savin – Jets at HERA -
DGLAP:
BFKL:
Bjxxx ...21
Bjxxx ...21
222,
21, ... Qkk TT
no ordering in kT
Unordered parton evolution, e.g. CCFM (Cascade)
Ariadne/LEPTO
Different parton-shower models: BFKL/DGLAP-like
DGLAP vs BFKLDGLAP vs BFKL
8/27A.Savin – Jets at HERA -
High Pt jets at Pt > Q probe the photon structure.
resolveddirect
In the BFKL both are taken in account due to arbitrary ordering of the kT
E
eEx jets
jetTobs
jets
2
)8.0(75.0obsx )8.0(75.0obsx
Real and virtual photon structureReal and virtual photon structure
9/27A.Savin – Jets at HERA -
Comparison with NLO
GeVE
GeVW
GeVQ
pb
jetT
jet
755
5.21
28595
1
1.2422
1
H1
Real photon structure: inclusive jet PHP at high EtReal photon structure: inclusive jet PHP at high EtNon-perturbative effects: multiple interactions and hadronisation are small
10/27A.Savin – Jets at HERA -
5.1||,3:
5
4.2||
280130
1
120
*
22
1
GeVpD
GeVE
GeVW
GeVQ
pb
T
jetT
jetZEUS
Real photon structure: dijet PHP with charmReal photon structure: dijet PHP with charm
11/27A.Savin – Jets at HERA -
Comparison with NLO
ZEUS
GeVEE
y
GeVQ
pb
jetT
jetT
jet
5.6,5.7
03
55.02.0
20001.0
6.38
2,1,
22
1
Virtual photon structure: dijet DIS at hight Et Virtual photon structure: dijet DIS at hight Et
12/27A.Savin – Jets at HERA -
Comparison with Herwig and Cascade
H1
GeVE
GeVEE
y
GeVQ
pb
t
jetT
jetT
jet
6
5,5
05.2
85.01.0
802
6.38
2,1,
22
1
Virtual photon structure: dijet DIS at hight Et Virtual photon structure: dijet DIS at hight Et
13/27A.Savin – Jets at HERA -
5.1||,3:
5.6;5.7
4.2||
65.02.0
104
*
2,1,
1
GeVpD
GeVEE
y
pb
T
jetT
jetT
jetZEUS
Virtual photon structure: dijet DIS with charmVirtual photon structure: dijet DIS with charm
14/27A.Savin – Jets at HERA -
Uncertainties:-NLO QCD due to terms beyong NLO;-NLO QCD due to -statistical and correlated systematic uncertainties(fits);-hadronisation etc.
)( Zs MPDF
New results on PDFs using jets in global PDF fits!
15/27A.Savin – Jets at HERA -
GeVE
GeVQ
pb
BreitjetT
Breitjet
HAD
8
8.12
5.0cos7.0
125
6.38
,
22
1
ZEUS
22,
22,
)(
)(cos
HADZHADT
HADZHADTHAD PEP
PEP
Structure of the proton: inclusive jets in DIS Structure of the proton: inclusive jets in DIS
16/27A.Savin – Jets at HERA -
Use jet data to tie down the high-x region in PDFanalysis
The improvement in the determination of the gluondistribution at moderate to high-x is striking
Structure of the proton: jets in the PDF fitStructure of the proton: jets in the PDF fit
17/27A.Savin – Jets at HERA -
22 105 GeVQ 22 2010 GeVQ 22 3520 GeVQ 22 7035 GeVQ 22 10070 GeVQ
8.25.1 LAB
GeVE
y
GeVQ
pb
LABjetT
LABjet
5
8.21
6.02.0
1005
1.21
,
22
1
H1
Structure of the proton: inclusive jets in DIS Structure of the proton: inclusive jets in DIS
18/27A.Savin – Jets at HERA -
7.01.0
855 22
y
GeVQH1
222,
21, ... Qkk TT
DGLAP
22., Qp jetforwt
The probability for
is low
BFKL
Low xBj,high Q2 ,
high pt,jet2 in the
p-direction25.0
035.0
79.274.1
5.3
2
2,
,
Q
p
E
Ex
GeVp
jett
p
jetjet
jet
jett
Forward jets Forward jets
19/27A.Savin – Jets at HERA -
0cos
22
1
6
32
25
7.38
2
2,
22
1
HAD
jetT
jetT
jet
Q
E
GeVE
GeVQ
pb
ZEUS
Comparison with NLO
to suppress
Forward jets Forward jets
20/27A.Savin – Jets at HERA -
Jet
Jet
Gap
-remnant P- remnant
0
2
R
R
-2.4 2.4
dd
ddf
gap
/
/)(
Dijet events with Rapidity Gap
All Dijet events
Interjet energy flowInterjet energy flow
H1GeVW
GeVQ
pb
233165
01.0
6.622
1
Color singlet added
21/27A.Savin – Jets at HERA -
Ratios: R2/1 and R3/2
GeVE
GeVQ
pb
jetT
jet
5
5.21
500010
2.8222
1
ZEUS
Multijet productionMultijet production
22/27A.Savin – Jets at HERA -
Multijet production: ratio 3jets/2jetsMultijet production: ratio 3jets/2jets
23/27A.Savin – Jets at HERA -
At high ET,jet and ycut not too low,fragmentation effects are small –subjet multiplicity in pQCD
kT inclusive - for jetskT exclusive - for subjets
2
222,
2,2
,
))()((},min{
1
REE
Ey jTiT
jetTij
Jets substructureJets substructure
24/27A.Savin – Jets at HERA -
GeVE
pbjetT 17
2.82 1
ZEUS
PHP and DIS
Jets substructureJets substructure