Alice valk rov on behalf of h1 collaboration low x meeting 2005 sinaia
Download
1 / 17

29.6.2005 - PowerPoint PPT Presentation


  • 131 Views
  • Uploaded on

Alice Valk árová on behalf of H1 collaboration LOW x meeting 2005, Sinaia. H1 measurements of the structure of diffraction and tests of factorisation. HERA experiments and diffraction. ´. HERA: ~ 10% of low-x DIS events are diffractive.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about '29.6.2005' - tivona


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Alice valk rov on behalf of h1 collaboration low x meeting 2005 sinaia

Alice Valkárová

on behalf of H1 collaboration

LOW x meeting 2005, Sinaia

H1 measurements of the structureof diffraction and tests of

factorisation

Low x meeting, Sinai 2005


HERA experiments and diffraction

´

HERA:~10% of low-x DIS events are diffractive

 study QCD structure of high energy diffraction with virtual photon

DIS: Probe structure of proton → F2

e

´

Diffractive DIS:Probe structure of color singlet exchange → F2D

Low x meeting, Sinai 2005

2


Diffraction kinematics

Large rapidity gap between leading proton p´ and X

ηmax

´

W

´

Momentum fraction of proton carried by color singlet exchange:

Momentum fraction of color singlet carried by struck quark:

Low x meeting, Sinai 2005


Qcd factorisation
QCD factorisation

get PDFs from inclusive diffraction ⇨predict cross sections for exclusive diffraction

inclusive

dijet

hard scattering QCD

matrix element, perturbatively

calculated, process dependent

  • proven for DIS (J.Collins (1998))

  • not proven for photoproduction!

Universal diffractive parton densities

identical for all processes

  • universal hard scattering cross section (same as in inclusive DIS)

  • diffractive parton distribution functions→obey DGLAP

  • universal for diffractive ep DIS (inclusive, di-jets, charm)

Low x meeting, Sinai 2005


Results from inclusive diffraction

Q2

β

Regge factorisation is an additional assumption,

there is no PROOF!!

pomeron flux factor

pomeron PDF

σdiff = flux(xP) · object (β,Q2)

Reduced cross section from

inclusive diffractive data

  • get diffractive PDFs from a NLO (LO)

  • DGLAP QCD Fit to inclusive data from

  • 6.5 GeV2 to 120 GeV2

  • extrapolation of the Fit

  • to lower Q2

  • to higher Q2

  • gives a reasonably good description of

  • inclusive data from ∼3.5 GeV2 –1600 GeV2

Low x meeting, Sinai 2005


Diffractive parton densities
Diffractive Parton Densities

  • determined from NLO QCD

  • analysis of diffractive structure

  • function

  • more sensitive to quarks

  • gluons from scaling violation,

  • poorer constraint

  • gluon carries about 75% of pome-

  • ron momentum

  • large uncertainty at large zP

Assuming factorisation holds,

the jet and HQ cross sections give

better constraint on the gluon density

Low x meeting, Sinai 2005


Jet and hq production
Jet and HQ production

Hard scale is ET of the jet or HQ mass

Direct access to gluon

density

Can reconstruct zPin dijet events

  • tests of universality of PDF’s

  • (=QCD factorisation)

  • test of DGLAP evolution

Low x meeting, Sinai 2005


Charm cross section dis
Charm cross section (DIS)

Good agreementwithin experimental & theoretical

uncertainties.

Factorisation holds !

NLO calculations with PDFs from inclusive diffraction

NLO calculations HVQDIS

(Harris&Smith)

Good description of diffractive D* production in DIS

(2GeV2 <Q2<100 GeV2)

Low x meeting, Sinai 2005


Dijet s in dis
Dijetsin DIS

NLO calculations = diffractive extension of

DISENT Catani&Seymour (Nucl.Phys.B485 (1997) 29),

interfaced to diffr.PDFs of H1

Hadronisation corrections – RAPGAP MC

Low x meeting, Sinai 2005


Dijets in dis
Dijets in DIS

  • NLO corrections to LO

  • are significant – factor 1.9

  • excess at high xγ is

  • kinematically connected

  • with the lack of events with

  • ηlab of jets < -0.4 in

  • comparison with NLO

Factorisation holds!

Good agreement with

NLO within exp.&theor.

uncertainties

Low x meeting, Sinai 2005


CDF Tevatron data:

γ*p

pp

Exporting PDFs from HERA to

the Tevatron.........

At Tevatron HERA PDF’s

do not work….????

Dijet cross section factor 5-10 lower

than the QCD calculation using HERA

PDFs

Breakdown of factorisation!

?

Low x meeting, Sinai 2005


Direct and resolved processes at hera
Direct and resolved processes at HERA

xγ - fraction of photon’s momentum

inhard subprocess

  • DIS (Q2>5GeV2) and direct photoproduction (Q2≃0):

  • photon directly involved in hard scattering

  • xγ=1

?

unsuppressed!

  • Resolved photoproduction:

  • photon fluctuates into hadronic system, which

  • takespart in hadronic scattering

  • dominant at Q2≃0

  • xγ<1

?

suppressed!

Low x meeting, Sinai 2005


Photoproduction as hadronic process
Photoproduction ashadronic process

HERA resolved photoproduction

Secondary interactions

between spectators

Jets in photoproduction thought to be

ideal testing ground for rescattering

Typical models that describe suppression at Tevatron assume secondary

interactions of spectators as the cause:

resolved contribution expected to be suppressed by factor 0.34

(Kaidalov,Khoze,Martin,Ryskin:Phys.Lett.B567 (2003),61)

Low x meeting, Sinai 2005


Dijets in photoproduction
Dijets in photoproduction

The same kinematical region as for DIS

  • NLO overestimates the cross section by

  • factor ∼2

  • both direct and resolved are suppressed

  • RAPGAP LO – good description

Low x meeting, Sinai 2005


Dijets in photoproduction1
Dijets in photoproduction

If only resolved part is suppressed (by factor 0.34,

according to Kaidalov et al.)

⇨ data are not described by NLO

Low x meeting, Sinai 2005


Ratio data over nlo prediction
Ratio:data over NLO prediction

  • no suppression observed for DIS

  • overall suppression factor of

  • about 2 observed for both

  • resolved and direct

  • components in photoproduction

  • suppression is independent of the

  • cms energy W

Low x meeting, Sinai 2005


Summary
Summary

  • Dijets in DIS & D* cross section:

  • agree with the NLO prediction with the H1 2002 diffractive pDFs

  • factorisation holds (assuming PDF is correct)

  • Dijets in photoproduction:

  • to investigate the puzzle of disagreement of HERA/Tevatron data

  • (expectation: resolved will be suppressed and direct not)

  • data are half of NLO prediction – both resolved and direct are

  • suppressed ⇨ conflict with the theoretical expectation

  • More ideas?

Low x meeting, Sinai 2005


ad