THE SHIP experiment and its detector for neutrino physics

SHIP is a new general purpose fixed target facility, proposed at the CERN SPS accelerator. In its initial phase the 400GeV proton beam will be dumped on a heavy target with the aim of integrating $2 \times 10^{20}$ pot in 5 years. A detector downstream of the target will allow to search long-lived exotic particles with masses below O(10) GeV/c2 forseen in extension of the Standard Model. Another dedicated detector, that will be the focus of this talk, will allow to study active neutrino cross- sections and angular distributions. The neutrino detector consists of an emulsion target, based on the Emulsion Cloud Chamber technology fruitfully employed in the OPERA experiment. The Emulsion Cloud Chamber will be placed in a magnetic field, with the so-called Compact Emulsion spectrometer, a few cm thick chamber for the charge and momentum measurement of hadrons. This will provide the leptonic number measurement also in the hadronic tau decay channels. The detector will be hybrid, using nuclear emulsions and electronic detectors for the time stamp of the events and the measurement of the muon momentum. The muon system will also be based on the design of the one used in the OPERA experiment

Neutrino physics with the SHIP experiment

Despite the Standard Model (SM) has been strongly confirmed by the Higgs discovery, several experimental facts are still not explained. The SHiP experiment (Search for Hidden Particles), a beam dump experiment at CERN, aims at the observation of long lived particles very weakly coupled with ordinary matter. These particles of the GeV mass scale, foreseen in many extensions of the SM, might come from the decay of charmed hadrons produced in the collision of a 400 GeV proton beam on a target. High rates of all the three active neutrinos are also expected. For the first time the properties and the cross section of the ντ will be studied thanks to a detector based on nuclear emulsions, with the micrometric resolution needed to identify the tau lepton produced in neutrino interactions. Measuring the charge of the tau daughters, will enable the first observation of the ντ and the study of its cross section

Study of tau neutrino properties with the SHiP experiment

The SHiP experiment (Search for Hidden Particles) is a beam dump experiment proposed at the CERN SPS with the submission of a Technical Proposal in April 2015. SHiP aims at the observation of long lived particles very weakly coupled with ordinary matter. These particles are mostly produced in the decay of charmed hadrons whose production is therefore enhanced through the definition of the characteristics of both the beam and the proton target. This makes the SHiP experiment a Standard Model neutrino factory too, in particular of tau neutrinos produced by the Ds decay chain. My studies have mainly focused on the design of the neutrino detector and on the evaluation of its performances. The Neutrino Detector is placed in a magnetic field and it exploits the Emulsion Cloud Chamber Technology with the micrometric position resolution needed to disentangle the tau lepton decay vertex from the neutrino interaction vertex. This peculiarity, together with the high electron identification efficiency, makes this detector also suitable to search for sub-GeV Dark Matter (produced in the decay of the dark photon) through its scattering with the electrons in the emulsion target. The main unit of the Neutrino Detector is the brick (lead plates interleaved with emulsion films) followed downstream by a Compact Emulsion Spectrometer (CES, 3 emulsion films interleaved with light material) needed to measure the charge and momentum of hadrons produced in neutrino interactions and short lived particles decays. A Muon Magnetic Spectrometer is placed immediately downstream to measure the charge and the momentum of muons produced in charged current muon neutrino interactions or in tau to muon decays. In this thesis the signal and background yield for all the different neutrino flavours are presented: more than twenty thousand nutau and nutau-bar charged current interactions are expected in five years of data taking. This unprecedented statistics of tau neutrinos will allow to measure the structure functions F4 and F5 entering the neutrino-nucleon cross section. The SHiP performances in the measurement of the tau neutrino anomalous magnetic moment are also reported with the estimation of the background yield for this searches. A preliminary estimate of the background events expected for LDM searches is also shown. Detailed studies will be performed with more general assumptions on the dark photon and the dark matter masses. Thanks to the large flux of electron and muon neutrinos interacting in the neutrino target, the measurement of the strange quark content of the nucleon has also been studied. The second to last chapter of the thesis is devoted to the description of the optimisation studies which are on going in view of the production of a Comprehensive Design Report to hand in to the CERN SPS Committee by the end of 2018. In this optimised version of the SHiP detector, the Neutrino Detector is roughly 20 m closer to the proton target, with a resulting increment in the incoming neutrino flux. However, being closer to the proton target has also generated the need for a complete redesign of the detector layout to fit the muon free region. A study of muon background rates on the Neutrino Detector and on the downstream Muon Magnetic Spectrometer is also reported. The last chapter describes the Test Beam activities conducted at CERN to study the performances of both the Compact Emulsion Spectrometer and of the gaseous electronic detectors (GEM) which complement the Neutrino Detector. The data analysis was carried out in the Napoli Emulsion Laboratory. The test beam for the CES has led us to discard the option of using the Rohacell as a light material interleaved to the emulsion films. The test beam with the GEM-emulsion coupled detector has shown a rapid degradation of the GEM performances in terms of position resolution when dealing with inclined tracks also in absence of magnetic field. The degradation is enhanced when the polarisation of the magnetic field contributes to the avalanche displacement. In case of a compensating magnetic field, the position resolution shows the same behaviour as in absence of field, except for a phase-shift of 15 degrees corresponding to the Lorentz angle of the generated electron avalanche

High-resolution tracking in a GEM-Emulsion detector

SHiP (Search for Hidden Particles) is a beam dump experiment proposed at the CERN SPS aiming at the observation of long lived particles very weakly coupled with ordinary matter mostly produced in the decay of charmed hadrons. The beam dump facility of SHiP is also a copious factory of neutrinos of all three kinds and therefore a dedicated neutrino detector is foreseen in the SHiP apparatus. The neutrino detector exploits the Emulsion Cloud Chamber technique with a modular structure, alternating walls of target units and planes of electronic detectors providing the time stamp to the event. GEM detectors are one of the possible choices for this task. This paper reports the results of the first exposure to a muon beam at CERN of a new hybrid chamber, obtained by coupling a GEM chamber and an emulsion detector. Thanks to the micrometric accuracy of the emulsion detector, the position resolution of the GEM chamber as a function of the particle inclination was evaluated in two configurations, with and without the magnetic fiel

Multidifferential study of identified charged hadron distributions in ZZ-tagged jets in proton-proton collisions at s=\sqrt{s}=13 TeV

Jet fragmentation functions are measured for the first time in proton-proton collisions for charged pions, kaons, and protons within jets recoiling against a $Z$ boson. The charged-hadron distributions are studied longitudinally and transversely to the jet direction for jets with transverse momentum 20 $< p_{\textrm{T}} < 100$ GeV and in the pseudorapidity range $2.5 < \eta < 4$. The data sample was collected with the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.64 fb$^{-1}$. Triple differential distributions as a function of the hadron longitudinal momentum fraction, hadron transverse momentum, and jet transverse momentum are also measured for the first time. This helps constrain transverse-momentum-dependent fragmentation functions. Differences in the shapes and magnitudes of the measured distributions for the different hadron species provide insights into the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb public pages

Study of the B−→Λc+Λˉc−K−B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-} decay

The decay $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV using data corresponding to an integrated luminosity of 5 $\mathrm{fb}^{-1}$ collected by the LHCb experiment. In the $\Lambda_{c}^+ K^{-}$ system, the $\Xi_{c}(2930)^{0}$ state observed at the BaBar and Belle experiments is resolved into two narrower states, $\Xi_{c}(2923)^{0}$ and $\Xi_{c}(2939)^{0}$, whose masses and widths are measured to be $$m(\Xi_{c}(2923)^{0}) = 2924.5 \pm 0.4 \pm 1.1 \,\mathrm{MeV}, \\ m(\Xi_{c}(2939)^{0}) = 2938.5 \pm 0.9 \pm 2.3 \,\mathrm{MeV}, \\ \Gamma(\Xi_{c}(2923)^{0}) = \phantom{000}4.8 \pm 0.9 \pm 1.5 \,\mathrm{MeV},\\ \Gamma(\Xi_{c}(2939)^{0}) = \phantom{00}11.0 \pm 1.9 \pm 7.5 \,\mathrm{MeV},$$ where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt $\Lambda_{c}^{+} K^{-}$ sample. Evidence of a new $\Xi_{c}(2880)^{0}$ state is found with a local significance of $3.8\,\sigma$, whose mass and width are measured to be $2881.8 \pm 3.1 \pm 8.5\,\mathrm{MeV}$ and $12.4 \pm 5.3 \pm 5.8 \,\mathrm{MeV}$, respectively. In addition, evidence of a new decay mode $\Xi_{c}(2790)^{0} \to \Lambda_{c}^{+} K^{-}$ is found with a significance of $3.7\,\sigma$. The relative branching fraction of $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ with respect to the $B^{-} \to D^{+} D^{-} K^{-}$ decay is measured to be $2.36 \pm 0.11 \pm 0.22 \pm 0.25$, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb public pages

Measurement of the ratios of branching fractions R(D∗)\mathcal{R}(D^{*}) and R(D0)\mathcal{R}(D^{0})

The ratios of branching fractions $\mathcal{R}(D^{*})\equiv\mathcal{B}(\bar{B}\to D^{*}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(\bar{B}\to D^{*}\mu^{-}\bar{\nu}_{\mu})$ and $\mathcal{R}(D^{0})\equiv\mathcal{B}(B^{-}\to D^{0}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(B^{-}\to D^{0}\mu^{-}\bar{\nu}_{\mu})$ are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb${ }^{-1}$ of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $\tau^{-}\to\mu^{-}\nu_{\tau}\bar{\nu}_{\mu}$. The measured values are $\mathcal{R}(D^{*})=0.281\pm0.018\pm0.024$ and $\mathcal{R}(D^{0})=0.441\pm0.060\pm0.066$, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is $\rho=-0.43$. Results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb public pages

Study of nu-tau properties with the SHiP experiment

The SHiP experiment (Search for Hidden Particles) is a beam dump experiment proposed at the CERN SPS with the submission of a Technical Proposal in April 2015. SHiP aims at the observation of long lived particles very weakly coupled with ordinary matter. These particles are mostly produced in the decay of charmed hadrons whose production is therefore enhanced through the definition of the characteristics of both the beam and the proton target. This makes the SHiP experiment a Standard Model neutrino factory too, in particular of tau neutrinos produced by the Ds decay chain. My studies have mainly focused on the design of the neutrino detector and on the evaluation of its performances. The Neutrino Detector is placed in a magnetic field and it exploits the Emulsion Cloud Chamber Technology with the micrometric position resolution needed to disentangle the tau lepton decay vertex from the neutrino interaction vertex. This peculiarity, together with the high electron identification efficiency, makes this detector also suitable to search for sub-GeV Dark Matter (produced in the decay of the dark photon) through its scattering with the electrons in the emulsion target. The main unit of the Neutrino Detector is the brick (lead plates interleaved with emulsion films) followed downstream by a Compact Emulsion Spectrometer (CES, 3 emulsion films interleaved with light material) needed to measure the charge and momentum of hadrons produced in neutrino interactions and short lived particles decays. A Muon Magnetic Spectrometer is placed immediately downstream to measure the charge and the momentum of muons produced in charged current muon neutrino interactions or in tau to muon decays. In this thesis the signal and background yield for all the different neutrino flavours are presented: more than twenty thousand nutau and nutau-bar charged current interactions are expected in five years of data taking. This unprecedented statistics of tau neutrinos will allow to measure the structure functions F4 and F5 entering the neutrino-nucleon cross section. The SHiP performances in the measurement of the tau neutrino anomalous magnetic moment are also reported with the estimation of the background yield for this searches. A preliminary estimate of the background events expected for LDM searches is also shown. Detailed studies will be performed with more general assumptions on the dark photon and the dark matter masses. Thanks to the large flux of electron and muon neutrinos interacting in the neutrino target, the measurement of the strange quark content of the nucleon has also been studied. The second to last chapter of the thesis is devoted to the description of the optimisation studies which are on going in view of the production of a Comprehensive Design Report to hand in to the CERN SPS Committee by the end of 2018. In this optimised version of the SHiP detector, the Neutrino Detector is roughly 20 m closer to the proton target, with a resulting increment in the incoming neutrino flux. However, being closer to the proton target has also generated the need for a complete redesign of the detector layout to fit the muon free region. A study of muon background rates on the Neutrino Detector and on the downstream Muon Magnetic Spectrometer is also reported. The last chapter describes the Test Beam activities conducted at CERN to study the performances of both the Compact Emulsion Spectrometer and of the gaseous electronic detectors (GEM) which complement the Neutrino Detector. The data analysis was carried out in the Napoli Emulsion Laboratory. The test beam for the CES has led us to discard the option of using the Rohacell as a light material interleaved to the emulsion films. The test beam with the GEM-emulsion coupled detector has shown a rapid degradation of the GEM performances in terms of position resolution when dealing with inclined tracks also in absence of magnetic field. The degradation is enhanced when the polarisation of the magnetic field contributes to the avalanche displacement. In case of a compensating magnetic field, the position resolution shows the same behaviour as in absence of field, except for a phase-shift of 15 degrees corresponding to the Lorentz angle of the generated electron avalanche

Status and physics of the SHiP experiment at CERN

SHIP is a new general purpose fixed target facility, whose Technical Proposal has been recently reviewed by the CERN SPS Committee and by the CERN Research Board. The two boards recommended that the experiment proceeds further to a Comprehensive Design phase in the context of the new CERN Working group "Physics Beyond Colliders", aiming at presenting a CERN strategy for the European Strategy meeting of 2019. In its initial phase, the 400GeV proton beam extracted from the SPS will be dumped on a heavy target with the aim of integrating $2 \times 10^{20}$ pot in 5 years. A dedicated detector, based on a long vacuum tank followed by a spectrometer and particle identification detectors, will allow probing a variety of models with light long-lived exotic particles and masses below O(10) GeV /c$^{2}$. The main focus will be the physics of the so-called Hidden Portals, i.e. search for Dark Photons, Light scalars and pseudo-scalars, and Heavy Neutrinos. The sensitivity to Heavy Neutrinos will allow for the first time to probe, in the mass range between the kaon and the charm meson mass, a coupling range for which Baryogenesis and active neutrino masses could also be explained. Another dedicated detector will allow the study of neutrino cross-sections and angular distributions. $\nu_{\tau}$ deep inelastic scattering cross sections will be measured with a statistics 1000 times larger than currently available, with the extraction of the $F_4$ and $F_5$ structure functions, never measured so far and allow for new tests of lepton non-universality with sensitivity to BSM physics

Neutrino physics with the SHiP experiment

Despite the Standard Model (SM) has been strongly confirmed by the Higgs discovery, several experimental facts are still not explained. The SHiP experiment (Search for Hidden Particles), a beam dump experiment at CERN, aims at the observation of long lived particles very weakly coupled with ordinary matter. These particles of the GeV mass scale, foreseen in many extensions of the SM, might come from the decay of charmed hadrons produced in the collision of a 400 GeV proton beam on a target. High rates of all the three active neutrinos are also expected. For the first time the properties and the cross section of the ντ will be studied thanks to a detector based on nuclear emulsions, with the micrometric resolution needed to identify the tau lepton produced in neutrino interactions. Measuring the charge of the tau daughters, will enable the first observation of the ν ̄τ and the study of its cross section