Janauschek, Ludger (2005): Elastic Photoproduction of J/psi Vector Mesons at high PhotonProton CentreofMass Energy at the H1 Experiment at HERA. Dissertation, LMU München: Faculty of Physics 

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Abstract
The elastic photoproduction of J/psi vector mesons at large values of the photonproton centreofmass energy 135GeV<W_{gamma p}<305GeV is studied. The elastic photoproduction cross section sigma(W_{gamma p}) is measured as a function of W_{gamma p}. The differential cross section dsigma/dt is determined in the range t<=1.2GeV^2/c^2. This analysis extends the measurements of sigma(W_{gamma p}) and dsigma/dt using H1 data up to highest W_{gamma p} near the kinematic limit given by the parameters of the accelerator of approx. 318GeV. Data for two different event topologies were collected with the H1 detector at the epcollider HERA during the years 1999 and 2000 resulting in an integrated luminosity of 30.26pb^1 and 26.90pb^1 for the analysed data. The level 2 neural network trigger and the backward silicon tracker are important components of the H1 experiment which make this analysis possible. From the W_{gamma p} dependence of the elastic cross section sigma(W_{gamma p})~W_{gamma p}^delta the parameter delta is extracted to be delta=1.17+0.11+0.16 for the high W_{gamma p} results of this analysis alone and delta=0.76+0.03+0.04 including data of the complete kinematic range of the H1 experiment. The exponential slope b of the differential cross section dsigma/dt~e^{bt} is determined in the high W_{gamma p} regime: b(<W_{gamma p}>=180.6GeV)=(5.1+0.3+0.2)GeV^2c^2, b(<W_{gamma p}>=250.7GeV)=(5.4+0.4+0.2)GeV^2c^2. The intercept alpha_0 and slope alpha' of an effective pomeron trajectory are determined. The W_{gamma p} dependence of the bslope gives alpha'_b=(0.17+0.04+0.01)GeV^2c^2. The W_{gamma p} dependence of the differential cross section dsigma/dt yields both parameters: alpha_0=1.21+0.01+0.01 and alpha'=(0.14+0.03+0.03)GeV^2c^2. The two determined slope parameters alpha'_b and alpha' are compatible within errors. Different theoretical approaches are compared to the data. The single pomeron model based on Regge theory does not describe the strong rise of sigma(W_{gamma p}) as a function of W_{gamma p}. The two pomeron model is able to describe the W_{gamma p} dependence of the cross section sigma(W_{gamma p}) within the kinematic regime of HERA, but is not able to describe the combined results of HERA and of fixed target experiments at low values of W_{gamma p}. QCD predictions using different parameterisations of the gluon distribution in the proton are also compared to the measured cross section sigma(W_{gamma p}). The predictions show a strong dependence on the gluon distribution, since the gluon distribution enters the cross section quadratically. The comparison to the measured cross section sigma(W_{gamma p}) is therefore a sensitive test for the gluon distributions, which are determined in an indirect way from inclusive measurements. While some of these analyses result in gluon distributions consistent with the J/psi measurements presented here, others can definitely be excluded.
Item Type:  Thesis (Dissertation, LMU Munich) 

Keywords:  J/psi photoproduction, H1, HERA, neural network, trigger 
Subjects:  600 Natural sciences and mathematics 600 Natural sciences and mathematics > 530 Physics 
Faculties:  Faculty of Physics 
Language:  English 
Date Accepted:  17. January 2005 
1. Referee:  Kiesling, Christian 
Persistent Identifier (URN):  urn:nbn:de:bvb:1930630 
MD5 Checksum of the PDFfile:  93bb73c367ed50d8ef817a67380af851 
Signature of the printed copy:  0001/UMC 14246 
ID Code:  3063 
Deposited On:  07. Feb 2005 
Last Modified:  16. Oct 2012 07:45 