Mätningar av lågenergi-diffraktion och partikel-multiplicitet vid små spridningsvinklar med TOTEM

A summary of recent TOTEM double diffraction and charged particle pseudorapidity density results is given, and single diffraction results are also discussed.Non peer reviewe

Diffraktiivinen sironta protoni-protonitörmäyksissä mitattuna TOTEM-kokeella LHC:ssä

The understanding of the strong interaction with low-momentum transfer is of primary importance for our understanding of the behaviour of nuclear matter. Suitable processes to study such low-momentum transfers are soft diffractive high energy physics processes. In this thesis, soft Single Diffraction (SD) in proton-proton scattering was studied at 7 TeV centre-of-mass energy with the TOTEM experiment at CERN's Large Hadron Collider (LHC), in Geneva, Switzerland. SD is a significant part of the total inelastic proton-proton scattering but despite that not so well known, nor much studied. SD events are characterized by an intact proton opposite a diffractive system with a large rapidity region without primary particles, a so-called rapidity gap, in between. In these studies, the out-going intact protons are measured at 5-30 mm from the out-going beam using the TOTEM Roman Pots (RP), movable beam-insertion detectors located about 220 m from the collision point. The proton track in the RP is used to reconstruct the scattering angle and proton longitudinal momentum loss. The diffractive system and the rapidity gap are both tagged and measured using the TOTEM T1 and T2 charged particle telescopes. The data used for the studies was taken in a special run at the LHC in 2011 with β∗ = 90 m optics that optimized the proton acceptance for low scattering angles at any proton longitudinal momentum loss value below 20%. Results are presented for the total SD cross section and differential cross section versus |t| – the absolute momentum transfer squared – in four ranges of the proton longitudinal momentum loss ξ, inferred from the size of the rapidity gap measured by T1 and T2. The data are unfolded with the Pythia and EPOS event generators, and the final results are selected to be the average of these two estimates. The results are compared to expectations from various event generators as well as earlier SD measurements at the LHC. The total SD cross section obtained is 11.10 ± 1.66 mb for the range 2.7 ∗ 10−7 < ξ < 20 %. Compared to earlier studies, these studies cover a significantly larger ξ range. They also show, for the first time at the LHC, the expected dependence of the exponential slope of the |t| distribution as function of ξ, i.e. that the |t| distribution becomes less steep with increasing ξ. The results provide relevant information regarding the proton structure, as well as valuable input to the modelling of cosmic-ray air showers and inelastic collisions.Proton-proton-kollisioner vid mycket hög energi undersöktes, speciellt så kallade ”diffraktiva” processer, kollektiva effekter vid mycket liten impulsöverföring (”momentum transfer”), som resulterar i att en av de kolliderande protonerna förblir intakt efter kollisionen och kan uppmätas att endast ha förlorat en liten del av dess energi och endast minimalt ändrat dess riktning i kollisionen. Motivationen för mätningarna är ökad förståelse av den starka växelverkan vid liten impulsöverföring samt en bättre förståelse av protonens inre struktur. Den studerade partikel-processen är singel diffraktion (SD): p p → p + X. ”X” betecknar här ett hadroniskt system, som sönderfaller till många sluttillståndspartiklar, och +–tecken ett rapiditetshål, d.v.s. fasrymdsintervall där ingen produktion av sluttillståndspartiklar skett. Just detta särskiljer diffraktiva processer från andra starka processer där man tvärtemot förväntar sig att fasrymden fylls av partiklar. I den stora hadron-kollideraren (Large Hadron Collider, LHC) kolliderade man protoner med en energi på 3,5+3,5 TeV 2010–2011. Doktorsavhandlingen baserar sig på data tagen med TOTEM-experimentet, som specialiserat sig på att mäta partiklar som spritts i små vinklar vid kollisionerna. De diffraktivt spridda protoner mättes av TOTEM i Roman Pot (RP)-detektorer väldigt nära den utgående strålen ca 220 m från kollisionspunkten. Data som analyserats togs under körningar med speciella inställningar för LHC:s magneter så att protoner spridda till små vinklar kunde mätas med TOTEM:s RP-detektorer. Utöver RP-detektorerna tog TOTEM också data med T1- och T2-teleskopen, som kan mäta laddade partiklar från systemet ”X”. De resultat som presenteras i denna avhandling är mätningar av protonens SD-tvärsnitt uppdelat i fyra klasser baserat på storleken av rapiditetshålet i T2 och T1, samt det exponentiella beroendet av protonens impulsöverföring för varje klass. För första gången vid LHC mäts protonens impulsöverförings beroende av rapiditetshålets storlek

Characterisation of the dip-bump structure observed in proton-proton elastic scattering at root s=8 TeV

We describe an analysis comparing the p (p) over bar elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96 TeV to that in pp collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13 TeVusing a model-independent approach. The TOTEM cross sections, extrapolated to a center-of-mass energy of root s = 1.96 TeV, are compared with the D0 measurement in the region of the diffractive minimum and the second maximum of the pp cross section. The two data sets disagree at the 3.4s level and thus provide evidence for the t-channel exchange of a colorless, C-odd gluonic compound, also known as the odderon. We combine these results with a TOTEM analysis of the same C-odd exchange based on the total cross section and the ratio of the real to imaginary parts of the forward elastic strong interaction scattering amplitude in pp scattering for which the significance is between 3.4s and 4.6s. The combined significance is larger than 5 sigma and is interpreted as the first observation of the exchange of a colorless, C-odd gluonic compound.Peer reviewe

Odderon Exchange from Elastic Scattering Differences between pp and p(p)over-bar Data at 1.96 TeV and from pp Forward Scattering Measurements

We describe an analysis comparing the p (p) over bar elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96 TeV to that in pp collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13 TeVusing a model-independent approach. The TOTEM cross sections, extrapolated to a center-of-mass energy of root s = 1.96 TeV, are compared with the D0 measurement in the region of the diffractive minimum and the second maximum of the pp cross section. The two data sets disagree at the 3.4s level and thus provide evidence for the t-channel exchange of a colorless, C-odd gluonic compound, also known as the odderon. We combine these results with a TOTEM analysis of the same C-odd exchange based on the total cross section and the ratio of the real to imaginary parts of the forward elastic strong interaction scattering amplitude in pp scattering for which the significance is between 3.4s and 4.6s. The combined significance is larger than 5 sigma and is interpreted as the first observation of the exchange of a colorless, C-odd gluonic compound.Peer reviewe

Tests of a Roman Pot Prototype for the TOTEM Experiment

3 pages, 8 figures, proceedings of PAC05, Knoxville, Tennessee, USA, May 2005The TOTEM collaboration has developed and tested the first prototype of its Roman Pots to be operated in the LHC. TOTEM Roman Pots contain stacks of 10 silicon detectors with strips oriented in two orthogonal directions. To measure proton scattering angles of a few microradians, the detectors will approach the beam centre to a distance of 10 sigma + 0.5 mm (= 1.3 mm). Dead space near the detector edge is minimised by using two novel "edgeless" detector technologies. The silicon detectors are used both for precise track reconstruction and for triggering. The first full-sized prototypes of both detector technologies as well as their read-out electronics have been developed, built and operated. The tests took place first in a fixed-target muon beam at CERN's SPS, and then in the proton beam-line of the SPS accelerator ring. We present the test beam results demonstrating the successful functionality of the system despite slight technical shortcomings to be improved in the near future.Peer reviewe

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.Peer reviewe

First Search for Exclusive Diphoton Production at High Mass with Tagged Protons in Proton-Proton Collisions at root s=13 TeV

A search for exclusive two-photon production via photon exchange in proton-proton collisions, pp -> p gamma gamma p with intact protons, is presented. The data correspond to an integrated luminosity of 9.4 fb(-1) collected in 2016 using the CMS and TOTEM detectors at a center-of-mass energy of 13 TeVat the LHC. Events are selected with a diphoton invariant mass above 350 GeVand with both protons intact in the final state, to reduce backgrounds from strong interactions. The events of interest are those where the invariant mass and rapidity calculated from the momentum losses of the forward-moving protons match the mass and rapidity of the central, two-photon system. No events are found that satisfy this condition. Interpreting this result in an effective dimension-8 extension of the standard model, the first limits are set on the two anomalous four-photon coupling parameters. If the other parameter is constrained to its standard model value, the limits at 95% confidence level are vertical bar zeta(1)vertical bar < 2.9 x 10(-1)3 GeV-4 and vertical bar zeta(2)vertical bar < 6.0 x 10(-13) GeV-4.Peer reviewe

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.Peer reviewe

3D Active Edge Silicon Detector Tests With 120 GeV Muons

3D detectors with electrodes penetrating through the silicon wafer and covering the edges were tested in the SPS beam line X5 at CERN in autumn 2003. Detector parameters including efficiency, signal-to-noise ratio, and edge sensitivity were measured using a silicon telescope as a reference system. The measured sensitive width and the known silicon width were equal within less than 10 mum

Search for high-mass exclusive γγ → WW and γγ → ZZ production in proton-proton collisions at √s=13 TeV

Peer reviewe