Tesis doctoral de Carolina Deluca Silberberg
This thesis presents the measurement of the inclusive photon cross section for photons with |¿| <1.0, pt >30 gev/c and isolation <2 gev using 2.5/fb of data taken by the cdf detector between february 2002 and august 2007. This measurement includes 6 times more data than the last published result, extending its pt coverage by 100 gev/c. The cross section is measured up to 400 gev/c, and tests the theoretical predictions over 6 orders of magnitude, one order of magnitude more than in previous results. the prompt photon cross section measurement offers a unique opportunity to test the photon tools over a large energy range. In this thesis we have presented a new technique to suppress the irreducible isolated photons from meson decays. The method consists of fitting the calorimeter isolation distribution in the data to pure signal and background templates for every bin in the photon pt . The template method is simple and is based only on the calorimeter information. Moreover, it significantly reduces the systematic uncertainty associated to the photon purity. Pre- vious run i cdf measurements used techniques based on information collected by the ces and cpr detectors, which have considerable statistical dilution and systematics. With the method introduced in this thesis, the systematic uncertainty in the photon purity is reduced from 30% in the previous cdf run i measurements to 5% at high pt . With the improvement of the monte carlo simulations, the template method has the potential to become a powerful tool for future searches using photon signatures. data are unfolded back to hadron level to correct for eficiencies and detector acceptance and resolution effects using a bin-by-bin procedure implemented in a pythia inclusive photon monte carlo sample. The unfolding factors do not present strong dependence on the photon transverse momentum, and vary between 64% and 69% in the pt considered. we compare our results to the predictions given by jetphox using cteq6.1m pdf, bfgii fragmentation functions, and renormalization, fragmentation and factorization scales set equal to the transverse momentum of the photon. The theoretical predictions are corrected for non perturbative qcd effects. The systematic uncertainties in the data are around 13% at low pt , dominated by the signal fractions, while at high pt they are about 15%, mainly coming from the photon energy scale. The uncertainties in the theory are due to the pdf, of around 5% at low pt and increasing to about 15% at high pt . The dependence left in the prediction due to the choice of the scales is of 15% at low pt and decreases to around 8% at high pt . we find agreement between data and theory above 40 gev/c. In the pt range until 150 gev/c, the prompt photon production is dominated by the qcd compton diagram, while for higher pt gluons substantially contribute to the prompt photon production though they are not the dominant contribution. Therefore, in the pt range above 40 gev/c, our measurement might be useful to constrain the gluon pdf. For pt until 40 gev/c data shows an excess compared to the theory. This trend has been previously seen by many other experiments, both in colliders and fixed- target data, and it is probably not due to systematic effects in the experimental method but more likely to other physics effects that are not accounted for in the theoretical calculations. there was an attempt to explain these effects, together with the deviations seen by some fixed- target experiments, with the introduction of a new parameter in the calculations that accounted for soft gluon radiation effects in the initial state. However, its effect is not believed to affect pt higher than30 gev/c. The comparison to the predictions obtained using the mrst04 parametrization for the pdf results is in agreement with cteq6.1m for the whole measured range, with similar shapes at low pt , though in the whole pt range the ratio presents a slightly different slope that makes the cross section to decrease at high pt . finally, the measurement has been approved by the cdf collaboration and it is in process for a publication in physics review letters.
Datos académicos de la tesis doctoral «Measurement of the inclusive isolated prompt photon production cross section at the tevatron using the cdf detector«
- Título de la tesis: Measurement of the inclusive isolated prompt photon production cross section at the tevatron using the cdf detector
- Autor: Carolina Deluca Silberberg
- Universidad: Autónoma de barcelona
- Fecha de lectura de la tesis: 12/06/2009
Dirección y tribunal
- Director de la tesis
- Sebastian Grinstein
- Tribunal
- Presidente del tribunal: matteo Cavalli-sforza
- raymond Culbertson (vocal)
- (vocal)
- (vocal)