TOTEM Physics

This article discusses the physics programme of the TOTEM experiment at the LHC. A new special beam optics with beta* = 90 m, enabling the measurements of the total cross-section, elastic pp scattering and diffractive phenomena already at early LHC runs, is explained. For this and the various other TOTEM running scenarios, the acceptances of the leading proton detectors and of the forward tracking stations for some physics processes are described.

Multivariate Techniques for Identifying Diffractive Interactions at the LHC

Close to one half of the LHC events are expected to be due to elastic or inelastic diffractive scattering. Still, predictions based on extrapolations of experimental data at lower energies differ by large factors in estimating the relative rate of diffractive event categories at the LHC energies. By identifying diffractive events, detailed studies on proton structure can be carried out. The combined forward physics objects: rapidity gaps, forward multiplicity and transverse energy flows can be used to efficiently classify proton-proton collisions. Data samples recorded by the forward detectors, with a simple extension, will allow first estimates of the single diffractive (SD), double diffractive (DD), central diffractive (CD), and non-diffractive (ND) cross sections. The approach, which uses the measurement of inelastic activity in forward and central detector systems, is complementary to the detection and measurement of leading beam-like protons. In this investigation, three different multivariate analysis approaches are assessed in classifying forward physics processes at the LHC. It is shown that with gene expression programming, neural networks and support vector machines, diffraction can be efficiently identified within a large sample of simulated proton-proton scattering events. The event characteristics are visualized by using the self-organizing map algorithm.

Diffractive W and Z production at the Fermilab Tevatron

We report on a measurement of the fraction of events with a W or Z boson produced diffractively in antiproton-proton collisions at a center of mass energy of 1.96 TeV, using data from 0.6 inverse femtobarns of integrated luminosity collected with the CDF-II detector equipped with a Roman-pot spectrometer that detects the antiproton (pbar) from pbar+p --> pbar+[X+W/Z]. We find that (0.97 +/- 0.11)% of Ws and (0.85 +/- 0.22)% of Zs are produced diffractively in a region of (anti)proton fractional momentum loss (\xi) of 0.03-1t p+[X+W/Z]+pbar, and on exclusive Z production, pbar+p-->pbar+Z+p. No signal is seen above background for these processes, and comparisons are made with expectations.

TOTEM early measurements

The status of the TOTEM experiment is described as well as the prospects for the measurements in the early LHC runs. The primary goal of TOTEM is the measurement of the total p-p cross section, using a method independent of the luminosity. A final accuracy of 1% is ex- pected with dedicated β∗ = 1540 m runs, while at the beginning a 5% resolution is achievable with a β∗ = 90 m optics. Accordingly to the running scenarios TOTEM will be able to measure the elastic scattering in a wide range of t and to study the cross-sections and the topologies of diffractive events. In a later stage, physics studies will be extended to low-x and forward physics collaborating with CMS as a whole experimental apparatus.

Planar Edgeless Detectors for the TOTEM Experiment at the LHC

The TOTEM experiment at the LHC will measure the total proton-proton cross-section with a precision better than 1%, elastic proton scattering over a wide range in momentum transfer -t= p^2 theta^2 up to 10 GeV^2 and diffractive dissociation, including single, double and central diffraction topologies. The total cross-section will be measured with the luminosity independent method that requires the simultaneous measurements of the total inelastic rate and the elastic proton scattering down to four-momentum transfers of a few 10^-3 GeV^2, corresponding to leading protons scattered in angles of microradians from the interaction point. This will be achieved using silicon microstrip detectors, which offer attractive properties such as good spatial resolution (<20 um), fast response (O(10ns)) to particles and radiation hardness up to 10^14 "n"/cm^2. This work reports about the development of an innovative structure at the detector edge reducing the conventional dead width of 0.5-1 mm to 50-60 um, compatible with the requirements of the experiment.

Search for a Light Higgs Boson in Central Exclusive Diffraction: Method and Detectors

By detecting leading protons produced in the Central Exclusive Diffractive process, p+p → p+X+p, one can measure the missing mass, and scan for possible new particle states such as the Higgs boson. This process augments - in a model independent way - the standard methods for new particle searches at the Large Hadron Collider (LHC) and will allow detailed analyses of the produced central system, such as the spin-parity properties of the Higgs boson. The exclusive central diffractive process makes possible precision studies of gluons at the LHC and complements the physics scenarios foreseen at the next e+e− linear collider. This thesis first presents the conclusions of the first systematic analysis of the expected precision measurement of the leading proton momentum and the accuracy of the reconstructed missing mass. In this initial analysis, the scattered protons are tracked along the LHC beam line and the uncertainties expected in beam transport and detection of the scattered leading protons are accounted for. The main focus of the thesis is in developing the necessary radiation hard precision detector technology for coping with the extremely demanding experimental environment of the LHC. This will be achieved by using a 3D silicon detector design, which in addition to the radiation hardness of up to 5×10^15 neutrons/cm2, offers properties such as a high signal-to- noise ratio, fast signal response to radiation and sensitivity close to the very edge of the detector. This work reports on the development of a novel semi-3D detector design that simplifies the 3D fabrication process, but conserves the necessary properties of the 3D detector design required in the LHC and in other imaging applications.

Characterization of non-imaging semiconductor X-ray solar monitors

The first observations of solar X-rays date back to late 1940 s. In order to observe solar X-rays the instruments have to be lifted above the Earth s atmosphere, since all high energy radiation from the space is almost totally attenuated by it. This is a good thing for all living creatures, but bad for X-ray astronomers. Detectors observing X-ray emission from space must be placed on-board satellites, which makes this particular discipline of astronomy technologically and operationally demanding, as well as very expensive. In this thesis, I have focused on detectors dedicated to observing solar X-rays in the energy range 1-20 keV. The purpose of these detectors was to measure solar X-rays simultaneously with another X-ray spectrometer measuring fluorescence X-ray emission from the Moon surface. The X-ray fluorescence emission is induced by the primary solar X-rays. If the elemental abundances on the Moon were to be determined with fluorescence analysis methods, the shape and intensity of the simultaneous solar X-ray spectrum must be known. The aim of this thesis is to describe the characterization and operation of our X-ray instruments on-board two Moon missions, SMART-1 and Chandrayaan-1. Also the independent solar science performance of these two almost similar X-ray spectrometers is described. These detectors have the following two features in common. Firstly, the primary detection element is made of a single crystal silicon diode. Secondly, the field of view is circular and very large. The data obtained from these detectors are spectra with a 16 second time resolution. Before launching an instrument into space, its performance must be characterized by ground calibrations. The basic operation of these detectors and their ground calibrations are described in detail. Two C-flares are analyzed as examples for introducing the spectral fitting process. The first flare analysis shows the fit of a single spectrum of the C1-flare obtained during the peak phase. The other analysis example shows how to derive the time evolution of fluxes, emission measures (EM) and temperatures through the whole single C4 flare with the time resolution of 16 s. The preparatory data analysis procedures are also introduced in detail. These are required in spectral fittings of the data. A new solar monitor design equipped with a concentrator optics and a moderate size of field of view is also introduced.

Accelerator Mass Spectrometry and Bayesian Data Analysis

Accelerator mass spectrometry (AMS) is an ultrasensitive technique for measuring the concentration of a single isotope. The electric and magnetic fields of an electrostatic accelerator system are used to filter out other isotopes from the ion beam. The high velocity means that molecules can be destroyed and removed from the measurement background. As a result, concentrations down to one atom in 10^16 atoms are measurable. This thesis describes the construction of the new AMS system in the Accelerator Laboratory of the University of Helsinki. The system is described in detail along with the relevant ion optics. System performance and some of the 14C measurements done with the system are described. In a second part of the thesis, a novel statistical model for the analysis of AMS data is presented. Bayesian methods are used in order to make the best use of the available information. In the new model, instrumental drift is modelled with a continuous first-order autoregressive process. This enables rigorous normalization to standards measured at different times. The Poisson statistical nature of a 14C measurement is also taken into account properly, so that uncertainty estimates are much more stable. It is shown that, overall, the new model improves both the accuracy and the precision of AMS measurements. In particular, the results can be improved for samples with very low 14C concentrations or measured only a few times.

Diffraction and Total Cross-Section at the Tevatron and the LHC

At the Tevatron, the total p_bar-p cross-section has been measured by CDF at 546 GeV and 1.8 TeV, and by E710/E811 at 1.8 TeV. The two results at 1.8 TeV disagree by 2.6 standard deviations, introducing big uncertainties into extrapolations to higher energies. At the LHC, the TOTEM collaboration is preparing to resolve the ambiguity by measuring the total p-p cross-section with a precision of about 1 %. Like at the Tevatron experiments, the luminosity-independent method based on the Optical Theorem will be used. The Tevatron experiments have also performed a vast range of studies about soft and hard diffractive events, partly with antiproton tagging by Roman Pots, partly with rapidity gap tagging. At the LHC, the combined CMS/TOTEM experiments will carry out their diffractive programme with an unprecedented rapidity coverage and Roman Pot spectrometers on both sides of the interaction point. The physics menu comprises detailed studies of soft diffractive differential cross-sections, diffractive structure functions, rapidity gap survival and exclusive central production by Double Pomeron Exchange.

Transverse momentum and pseudorapidity distributions of charged hadrons in pp collisions at sqrt(s) = 0.9 and 2.36 TeV

Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at sqrt(s) = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between -2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN(charged)/d(eta) for |eta|

Central Diffraction at ALICE

The ALICE experiment is shown to be well suited for studies of exclusive final states from central diffractive reactions. The gluon-rich environment ofthe central system allows detailed QCD studies and searches for exotic mesonstates, such as glueballs, hybrids and new charmonium-like states. It wouldalso provide a good testing ground for detailed studies of heavy quarkonia. Dueto its central barrel performance, ALICE can accurately measure the low-masscentral systems with good purity. The efficiency of the Forward MultiplicityDetector (FMD) and the Forward Shower Counter (FSC) system for detectingrapidity gaps is shown to be adequate for the proposed studies. With thisdetector arrangement, valuable new data can be obtained by tagging centraldiffractive processes.

High-precision diode-laser-based temperature measurement for air refractive index compensation

We present a laser-based system to measure the refractive index of air over a long path length. In optical distance measurements it is essential to know the refractive index of air with high accuracy. Commonly, the refractive index of air is calculated from the properties of the ambient air using either Ciddor or Edlén equations, where the dominant uncertainty component is in most cases the air temperature. The method developed in this work utilises direct absorption spectroscopy of oxygen to measure the average temperature of air and of water vapor to measure relative humidity. The method allows measurement of temperature and humidity over the same beam path as in optical distance measurement, providing spatially well matching data. Indoor and outdoor measurements demonstrate the effectiveness of the method. In particular, we demonstrate an effective compensation of the refractive index of air in an interferometric length measurement at a time-variant and spatially non-homogenous temperature over a long time period. Further, we were able to demonstrate 7 mK RMS noise over a 67 m path length using 120 s sample time. To our knowledge, this is the best temperature precision reported for a spectroscopic temperature measurement.

Tuning and stability of a singly resonant continuous-wave optical parametric oscillator close to degeneracy

Wavelength tuning and stability characteristics of a singly resonant continuous-wave optical parametric oscillator (cw OPO) in the proximity of signal-idler degeneracy have been studied. The OPO is made singly resonant by using a Bragg grating as a spectral filter in the OPO cavity. The signal-idler frequency difference can be tuned from 0.5 to 7 THz, which makes the OPO suitable for cw THz generation by optical heterodyning. The operation of the OPO within this singly-resonant regime is characterized by a strong self-stabilization effect. A gradual transition to an unstable, doubly-resonant regime is observed for a signal-idler detuning smaller than ~ 0.5 THz.

Frequency-comb-referenced molecular spectroscopy in the mid-infrared region

A simple method for absolute frequency measurements of molecular transitions in the mid-infrared region is reported. The method is based on a cw singly-resonant optical parametric oscillator (SRO), which is tunable from 3.2 to 3.45 µm. The mid- infrared frequency of the SRO is referenced to an optical frequency comb through its pump and signal beams. Sub-Doppler spectroscopy and absolute frequency measurement of the P(7) transition of the ν3 band of CH4 are demonstrated.