measurements of the photon structure function at lep
DESCRIPTION
Measurements of the Photon Structure Function at LEP. Albert De Roeck / CERN Representing the LEP Collaborations HEP2003 Europhysics Conference Aachen/Germany 17-23 July. New Photon Structure Function Developments. Total F 2 . q q. q q. PQCD. +. Pointlike part. Hadron-like part. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/1.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 1
Measurements of the Photon Structure Function at LEP
Albert De Roeck / CERN Representing the LEP Collaborations
HEP2003 Europhysics ConferenceAachen/Germany 17-23 July
![Page 2: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/2.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 2
New Photon Structure Function Developments
Progress on measurements of F2 using the full LEP statistics
(DELPHI/ALEPH) Measurement of F2
charm (OPAL) First measurement of the electron structure function F2
e
(DELPHI) New parton density parametrizations based on recent data and extraction of s
Outlook & Future
Pointlike part Hadron-like part
+
Total F2
PQCDqq
![Page 3: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/3.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 3
Introduction: Kinematics Measurements at LEP: Single tag two-photon interactions (DIS)
Tagged electron
Target photon
Reconstruction of x needs hadronic final state
see = 91 209 GeV
![Page 4: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/4.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 4
New Data from ALEPH (preliminary)
LEP2 data from ALEPH based on 548.4 pb-1
Tikhonov unfolding procedure usedTwo ranges in Q2: 17.3 GeV2 and 67.3 GeV2
Comparison ofF2
for x 0.1
![Page 5: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/5.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 5
New Data from DELPHILEP1 and LEP2 data from DELPHI based on 78/548 pb-1
No unfolding but fitting of different cross section componentsto data distributions
LEP1 data
![Page 6: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/6.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 6
New Data from DELPHI
LEP2 data
Note: DELPHI chooses to present different F2 values calculated/corrected with
different hadronic models difficult to compare with other LEP measurements
![Page 7: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/7.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 7
New Data from DELPHI
<F2 > measurements
in different x intervals as a function of <Q2>
DELPHI points extractedusing one model (TWOGAM)only.Large spread due to different models not shown
![Page 8: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/8.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 8
Data on F2charm from OPAL
Pointlike part (PQCD)
Hadron-like partdepends on gluon in the photon
D*
![Page 9: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/9.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 9
Data on F2charm from OPAL
Limited by statistics (data other LEP experiments?)
High-x: well described by PQCDcalculation, essentially pointlike
Low-x: somewhat higher thanPredicted but large error
Subtract NLO pointlike part at low x
GRV-NLO/ Laenen et al.
![Page 10: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/10.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 10
Electron Structure Function
Does not need hadronic final state to calculate x Kinematics better constrainedNo corrections due virtuality of the target photon (P) needed
Photon flux spectrum obscures the sensitivity to the photon structureRadiative corrections large at small x
x-resolution x=0.1
z-resolution z= 0.01
x z
![Page 11: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/11.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 11
Electron Structure Function
Measurements consistent with F2
Note: Real structure functions have to be “given” virtuality before comparing with F2e
![Page 12: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/12.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 12
Electron Structure Function
Measurements consistent with F2 /reduced sensitivity
![Page 13: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/13.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 13
The World Data: F2 versus x
More than 50 measurements
Kinematical coverage 10-3 x 0.9 1.9 <Q2> 780 GeV2
Used for new fits and the extraction of s
Thanks to R. Nisius, see http://www.mppmu.mpg.de/~nisius/welcomeaux/struc.html
All except new DELPHI-LEP2 points
![Page 14: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/14.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 14
The World Data: F2 versus Q2
Fit: Significant increase of the slope with increasing x
![Page 15: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/15.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 15
Parametrizations and Fits
New radiatively generated (LO) quark and gluon densities in the photon on all F2
data available by summer 2002 (208 data points) NLO densities in progress…
Cornet,Jankowski,Krawczyk & Lorca, hep-ph/0212160
ACOT HF scheme
Fit s from the F2 data
Use data with (x>0.45, Q2 > 59 GeV2) and fit s
Parametrizations
Albino, Klasen & Soldner Rembold, hep-ph/0205069
NLO/MS
Use all data, 5 parameter fit for (N, ,,s,Q02)
![Page 16: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/16.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 16
Outlook I
Near Future
What can be still expected from the LEP experiments?
ALEPH: Possibly an analysis at larger Q2
L3: Full analysis with all statistics
OPAL: Low-x, Q2 analysis for F2 and F2
e
![Page 17: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/17.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 17
Outlook II
Far Future: Large extension of the kinematic range at a future linear collider
e+e- option
Photon collider option
F2 measurements with a quality similar
to proton structure functions today !!
![Page 18: Measurements of the Photon Structure Function at LEP](https://reader036.vdocument.in/reader036/viewer/2022081504/568144e3550346895db1b354/html5/thumbnails/18.jpg)
HEP2003 Photon Structure Albert De Roeck (CERN) 18
Summary
• The photon structure has now been investigated in a large range
10-3 x 0.9 1.9 <Q2> 780 GeV2
• Precision has been improving over the years• The charm content of the photon has been measured Will need data from the other 3 experiments• The electron structure function has been measured, and
serves as a valuable cross check of the photon structure function, but does not seem to add more discriminative power.
• New parametrizations of the parton densities in the photon become available. s values have been extracted from fits to the photon structure data.
Thanks to A. Finch, C. Mariotti, B. Muryn, R. Nisius, T. Szumlack, T. Wengler