exclusive rr production in tagged gg interactions at lep
DESCRIPTION
Exclusive rr production in tagged gg interactions at LEP. I. Vorobiev. Carnegie Mellon University. On behalf of the L3 collaboration. The XXXXth Rencontres de Moriond, QCD AND HIGH ENERGY HADRONIC INTERACTIONS La Thuile, Italy - PowerPoint PPT PresentationTRANSCRIPT
Exclusive production in tagged interactions at LEP
I. VorobievCarnegie Mellon University
On behalf of the L3 collaboration
The XXXXth Rencontres de Moriond,QCD AND HIGH ENERGY HADRONIC INTERACTIONS
La Thuile, Italy March 12 - 19, 2005
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 2
The L3 experiment performed study of exclusive -pair production in the reactions:
Reactions studied
e+ e- e+ e- * e+ e- 0 0
e+ e- e+ e- * e+ e- + -
with one tagged electron or positron.
Tagging devices: Luminosity Monitor (LUMI)
Covers Q2 range at LEP I 1.2 - 8.5 GeV2
at LEP II 8.8 - 30 GeV2
Very Small Angle Tagger (VSAT)
Covers Q2 range 0.2 - 0.85 GeV2
(available only at LEP II)
LEP II
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 3
Data samples
Measurement with LUMI:
LEP I : s around 91 GeV
Integrated luminosity L = 148.7 pb-1
LEP II : s161 < < 209 GeV
L = 706.0 pb-1
Measurement with VSAT:
Total L = 854.7 pb-1
LEP II : s183 < < 209 GeV
L = 684.8 pb-1
)5.82.1( 222 GeVQGeV
)308.8( 222 GeVQGeV
)85.02.0( 222 GeVQGeV
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 4
tageeee
00 tageeee
Selected events:
LUMI - 934 ev.
VSAT - 1958 ev.
Selected events:
LUMI - 343 ev.
VSAT - 414 ev.
Underlying reactions
)302.1( 222 GeVQGeV
)302.1( 222 GeVQGeV
)85.02.0( 222 GeVQGeV
)85.02.0( 222 GeVQGeV
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 5
Distributions: LUMI,
GeVWGeV 31.1 - this cut is taken to measure cross section.
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 6
Distributions: VSAT,
00
GeVWGeV 31.1 - this cut is taken to measure cross section.
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 7
Contributing processes
for
00 for
00* 0*
*
0* * 00* (non resonant)
For VSAT also:0
2* )1270( f
)1270(2* f
)1320(2* a
MC model: isotropic production and phase space decays.
Maximum likelihood fit
i
n
j
n
jiijjP
1 1
1),(
- set of 6 variables, all 2 mass combinations,
jP is calculated using box method.
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 8
Result of fit : LUMI,
Shadowed histograms – contribution of00
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 9
Result of fit : VSAT,
a) cosine of the polar angle of the with respect to the axis in the center-of-mass system
b) cosine of the polar angle of the in its parent helicity-system
c) angle between the decay planes of the two mesons in the center-of-mass system
d) cosine of the opening angle between the two directions of flight, each one defined in its parent helicity-system
**
*
0 0
0
0
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 10
00 Q2 dependence ( )
QCD model for high Q2
M.Diehl et al, Phys.Rev.Lett. 81 (1998) 1782.
N.Kivel et al, Phys.Lett. B 467 (1999) 263.
A.Freund, Phys.Rev. D 61(2000) 074010.
M.Diehl et al, Phys.Rev. D 62 (2000) 073014.
Simplified formula:
2HDA – Two Hadron Distribution Amplitudes(or Generalized Distribution Amplitudes (GDA))
In our case <W> = 1.95 GeV
3.04.2 n
Fit to ))(/(1~/ 2222 WQQdQd nee
))(/(1~/ 22222 WQQdQd ee
22WQ
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 11
Dedicated theoretical analysis
I.V.Anikin, B.Pire, O.V.Teryaev, Phys. Rev. D 69 (2004) 014018.
Phenomenological parameter2
1 23.020.1 GeVC is defined from the fit, which gives normalization of GDA2
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 12
Q2 dependence ( )
4.05.2 n
,5.08.1/ 00
eeeeeeee
For the region
GeVWGeV 1.21.1 and222 5.82.1 GeVQGeV
compatible with the factor 2Expected for an isospin I=0 state.
02 QThis is in contrast with measurementsat , where cross section is fewtimes higher.
00
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 13
Full Q2 range
14.09.2 n15.03.2 n
00
The relative magnitude of and productionchanges in the vicinity of , suggesting different -pair production mechanismsat low and high .
22 1GeVQ
2Q
00
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 14
cross section
Extrapolation of GVDM dependenceto for gives nb7.06.13 02 Q 00
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 15
dependence of cross section
For and small there is an enhancement of production relative to .
1.06.0/ 00
eeeeeeee
W
GeVW 1.22Q
00
:1.2 GeVW
14 March 2005 Exclusive rho rho production in tagged gamma-gamma interactions at LEP 16
Conclusions
L3 measurements:00 , LUMI )302.1( 222 GeVQGeV
)85.02.0( 222 GeVQGeV
Phys. Lett. B 568 (2003) 11. , LUMI00 , VSAT
)302.1( 222 GeVQGeV
, VSAT )85.02.0( 222 GeVQGeV
Phys. Lett. B 597 (2004) 26.Phys. Lett. B 604 (2004) 48.In preparation.
•The measurements allow to follow the evolution of cross sections over a - region of two orders of magnitude.
2Q
GeVWGeV 31.1 2Q
•A QCD - based form is found to provide a good parametrisation in the entire interval, where the differential cross sections show a monotonic decrease of more than four orders of magnitude (for range ).
2Q
W•The dependence of the process is well reproduced by parametrisation based on GVDM model over the entire - region. But data cannot be satisfactory described by such a parametrisation in the whole - region.
00* 2Q
2Q
•A - pole description is excluded for both and data. 00
•The relative magnitude of and production changes in the vicinity of , suggesting different - pair production mechanisms at low and high .
0022 1GeVQ 2Q