Overview of low-x and diffraction at HERA Henri Kowalski DESY Rencontres de Moriond La Thuile, March...
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Transcript of Overview of low-x and diffraction at HERA Henri Kowalski DESY Rencontres de Moriond La Thuile, March...
Overview of low-x and diffraction at HERA
Henri KowalskiDESY
Rencontres de Moriond La Thuile, March 2006
0)t,(WImAW
1σ 2el2
γptot
2
22Pγ
totem
2
22
2 WQx)Q(W,σ
α π4 Q)Q(x,F
*
F2 is dominated by single ladder exchange
ladder symbolizes a QCD evol. process( DGLAP or others )
Gluon density
Gluon density dominates F2 for x < 0.01
Diffractive ScatteringNon-Diffractive Event ZEUS detector
Diffractive Event
MX - invariant mass of all particles seen in the central detector t - momentum transfer to the diffractively scattered proton t - conjugate variable to the impact parameter
Non-Diffraction Diffraction
- Rapidity
uniform, uncorrelated particle emission along the rapidity axis => probability to see a gap Y is ~ exp(-<n>Y) <n> - average multipl. per unit of Y
Diffractive Signature
dN/dM2X ~ 1/M2
X => dN/dlog M2
X ~ const
Non-diff
diff
~ Y= log(W2/M2X)
Observation of diffraction indicates that single ladder may not be sufficient(partons produced from a single chain have exponentially suppressed rap. gaps)
Inclusive DIS Hard Diffraction
Optical T
GBW – first Dipole Saturation Mode Golec-Biernat, Wuesthoff BGBK – DSM with DGLAP Bartels, Golec-Biernat, Kowalski
IIM - BFKL-CGC motivated ansatz Iancu, Itakura, Munier FS – Regge ansatz with saturation Forshaw and Shaw
....4/))2/exp(1(2 XS Dipole 22 bd
d
Dipole Models equivalent to LO perturbative QCD for small dipoles
Glauber Mueller
Impact Parameter Dipole Saturation Model
)2
exp(12*21
0
2*
bddzrdptot
)2/exp(~)(
)exp(~
2 BbbT
tBdt
d diff
KT - Kowalski TeaneyKMW – Kowalski, Motyka, Watt
2*1
0
22 |)2
exp(12|16
1*
VM
bip
VM dzebdrddt
d
proton shape )(),()( 222
2
bTxxgrN s
C
x < 10-2
universal rate of rise of all hadronic cross-sections
tottot xWp )/1(~)(~ 2*
Total *p cross-section
6.520
202
2
)1(1),( xx
Axxg
rC
g
g
KT KMW
Inclusive Diffraction
from fit to tot predict diff
GBW, BGBK, ….
-LPS
Dipole cross section determined by fit to F2
Simultaneous description of many reactions
F2 C
KMW
KT
KMW
)2/exp(~)( )exp(~ 2GD
diff
BbbTtBdt
d
KMW
BG BG
))1(( rzbibi ee
Description of the size of interaction region BD
Modification by Bartels, Golec-Biernat, Peters
proton size
Diffractive Di-jets Q2 > 5 GeV2
-RapGap
Satrap
Saturation scale (a measure of gluon density)
HERA RHIC
22
22
22
GeV 1
fm 7 1000
11
4
S
C
CsS
Q
RdydN
dydN
RNNQ
qSqSF
CgS QQ
CNQ )(
49)()( 222
QSRHIC ~ QS
HERA
22
12
2
)),(exp()(
SS
s
rQ
ebrbS
)(20
2 xRQ
Geometrical Scaling A. Stasto & Golec-Biernat J. Kwiecinski
02
20
1)(xx
GeVxR
GS is an effective property of HERA data
b-Dipole Model analysis: GS seen in the center of the proton
Theoretical importance: property of non-linear evolution in QCD BK, JIMWLK
2-Pomeron exchange in QCD
Final States(naïve picture)
0-cut
1-cut
2-cut
Diffraction
<n>
<2n>
Multiple Interactions and Long Range Correlation
QCD diagrams
Note: AGK rules underestimate the amount of diffraction in DIS
)exp(!2
kbdd k
k )(),()( 2222
bTxxgrN s
C
AGK rules in theDipole Model
)2
exp(12 2bdd qq
)exp(!2
kbdd k
k
)(),()( 2222
bTxxgrN s
C
Exclusive Double Diffractive Reactions at LHC
low x QCD reactions: pp => pp + gJet gJet ~ 1 nb for M(jj) ~ 50 GeV ~ 0.5 pb for M(jj) ~ 200 GeV JET| < 1
xIP = p/p, pT xIP ~ 0.2-1.5%
High momentummeasurementprecision
pp => pp + Higgs 3) fb SM O(100) fb MSSM
1 event/sec
xIP = p/p, pT xIP ~ 0.2-1.5%
OSMyLM
LDiff
22
2
ˆ
2
214
2
2 ),(),()1(
tgtgt
t
c
exclusive QxfQxfQdQ
bNO
Absorptive corrections from BK equation Resummation of BFKL pomeron fan diagrams
Conclusions We are developing a very good understanding of inclusive and diffractive DIS interactions: F2 , F2
D(3) , F2c , Vector Mesons (J/Psi
HERA measurements suggests presence of Saturation phenomena Saturation scale determined at HERA agrees with RHIC
Observation of diffraction indicates multi-gluon interaction effects -> Underlying events at LHC may be process dependent
Diffractive LHC ~ pure Gluon Collider => investigations of properties of the gluon cloud in the new region Gluon Cloud is a fundamental QCD object - SOLVE QCD!!!!
_____________________________________________________ Diffractive vector mesons scattering - an excellent probe of nuclear matter
Ideal device: e-RHIC like machine with ~1/3 of HERA energy