Light (anti)nuclei production at the LHC measured in pp collisions at 13 TeV

ALICE (A Large Ion Collider Experiment) collected over two billion proton-proton collision events at a center-of-mass energy of 13 TeV during the second running period (from 2016 to 2018) of the Large Hadron Collider (LHC). This rich data sample allows for studies of at this collision energy rarely produced objects, such as light nuclei. In this work, the first multiplicity and transverse-momentum (pT) differential measurement of helium (3He) nuclei and triton (3H) as well as their corresponding antinuclei in proton-proton collisions at the LHC is presented. The interaction of quarks and gluons, the constituents of all hadrons, is described by quantum chromodynamics (QCD), the theory of the strong interaction. Thus, QCD is the underlying theory of the formation process of light nuclei. In practice, the light nuclei formation in collisions at relativistic energies is modeled using two phenomenological approaches: the statistical hadronization model and the coalescence model. The first expresses the production of all hadrons according to the laws of statistical physics, assuming emission from a medium in local thermal equilibrium. In this approach, the hadron yields are determined by the hadron mass, the chemical freeze-out temperature, the baryon chemical potential, and the system volume. The statistical hadronization model successfully describes the hadron yields over a wide mass range, going from the lowest (a few GeV) to the highest (a few TeV) center-of-mass collision energies. It is effectively applied to small and large systems ranging from e+e− to central uranium-uranium collision. The coalescence model, on the other hand, describes the production mechanism of nuclei on the microscopic level. In the simplest version, a nucleus is formed when its constituent nucleons are close in phase space (momentum and spatial distance are small). More sophisticated versions of the coalescence model take the emission source size and the nuclear radius into account. The key parameter of the model is the coalescence parameter BA, with A being the mass number of the nucleus. Experimentally BA is accessed as the ratio of the nucleus yield to the product of its constituent nucleon yields. The coalescence model is successfully used to describe and predict the formation of nuclei in relativistic collisions. Additionally, it is systematically used by the astrophysics community to predict antinuclei fluxes originating from collisions of cosmic rays with the interstellar medium. The ALICE detector at the LHC is perfectly suited to track and identify light nuclei. The identification capability of the ALICE Time Projection Chamber (TPC) allows for excellent separation power in the low-pT region via the measurement of the specific energy loss and it is complemented by a Time-of-Flight (TOF) detector extending the pT reach of the particle identification. Due to being doubly charged the helium nucleus is very well separated via its specific energy loss in the TPC and the measurement can be performed in the 1 ≤ pT ≤ 6 GeV/c interval. The 3H nucleus on other hand is identified using the combined information from TPC and TOF detectors limiting the transverse-momentum reach of the measurement to 1 ≤ pT ≤ 2.5 GeV/c. Additionally, the multiplicity and pT differential (anti)proton spectra serving as important references for light nuclei are measured in a transverse-momentum interval of 0.6 ≤ pT ≤ 5 GeV/c. In this work, two new data-driven correction methods have been developed, exploiting recent ALICE measurements of the inelastic hadronic interaction cross section. In the first method, the inelastic hadronic interaction cross section implemented in the Monte Carlo simulations, which are needed for the efficiency and acceptance correction, are reweighted, reducing the systematic uncertainty of this contribution by a factor of three compared to previous analyses. The second method uses the well-known proton inelastic cross section to evaluate the effect of the material budget on the particle spectra when using the TOF detector. The pT-spectra and the resulting integrated yields obtained in this work are used to study the formation process of light nuclei. Additionally, the pT-spectra of deuterons in pp collisions at a center-of-mass energy of 13 TeV are presented and compared to the proton measurements. To study the light nuclei formation process as a function of the emission source radius, the results obtained in this work are discussed in the context of previously published ALICE results of light nuclei. The integrated deuteron-to-proton and helium-to-proton yield ratios show a smoothly increasing evolution with the event averaged charged-particle multiplicity density (dNch/dη), going from pp to central lead-lead collisions. The trend is in both cases described by the statistical hadronization and the coalescence model. However, in the intermediate multiplicity region (dNch/dη ≈ 30), a tension between the models and the measured helium-to-proton yield ratio is observed. The coalescence parameters B2 and B3 follow a decreasing trend with the average charged-particle multiplicity, which is, to first order, described by the latest coalescence models. The coalescence parameters are determined as a function of pT, showing a clear dependence on pT. The pT dependent coalescence parameter is compared to coalescence-model predictions using different nuclear wave functions. Surprisingly, B2 agrees best with the prediction using the solution of a harmonic oscillator as the wave function, while more sophisticated wave functions (e.g. van Hulthen) do not describe the data. B3 on the other hand is not predicted using a Gaussian nuclear wave function, which is the only one available at the moment. In the future, this approach can be used to study the nuclear wave function of exotic hyperons. Additionally, the measurement of the coalescence parameter will give a fundamental baseline for space-bound experiments measuring cosmic antinuclei fluxes. The experiments try to discover physics beyond the standard model via indirect dark matter searches. Antinuclei are one of the most potent probes due to their low background component originating from hadronic interactions in the galaxy. The proper estimate of this component is nevertheless crucial and BA measurements as presented in this work are therefore essential. With the third running period of the LHC starting in 2022 a new precision era for light-(anti)nuclei measurements will start. Among many new and exciting opportunities, the measurement of the triton-to-helium yield ratio, which at the moment does not have the necessary precision, will give a defined answer on the underlying nuclei formation process

Cerebral microbleeds and intracranial haemorrhage risk in patients anticoagulated for atrial fibrillation after acute ischaemic stroke or transient ischaemic attack (CROMIS-2):a multicentre observational cohort study

Background: Cerebral microbleeds are a potential neuroimaging biomarker of cerebral small vessel diseases that are prone to intracranial bleeding. We aimed to determine whether presence of cerebral microbleeds can identify patients at high risk of symptomatic intracranial haemorrhage when anticoagulated for atrial fibrillation after recent ischaemic stroke or transient ischaemic attack. Methods: Our observational, multicentre, prospective inception cohort study recruited adults aged 18 years or older from 79 hospitals in the UK and one in the Netherlands with atrial fibrillation and recent acute ischaemic stroke or transient ischaemic attack, treated with a vitamin K antagonist or direct oral anticoagulant, and followed up for 24 months using general practitioner and patient postal questionnaires, telephone interviews, hospital visits, and National Health Service digital data on hospital admissions or death. We excluded patients if they could not undergo MRI, had a definite contraindication to anticoagulation, or had previously received therapeutic anticoagulation. The primary outcome was symptomatic intracranial haemorrhage occurring at any time before the final follow-up at 24 months. The log-rank test was used to compare rates of intracranial haemorrhage between those with and without cerebral microbleeds. We developed two prediction models using Cox regression: first, including all predictors associated with intracranial haemorrhage at the 20% level in univariable analysis; and second, including cerebral microbleed presence and HAS-BLED score. We then compared these with the HAS-BLED score alone. This study is registered with ClinicalTrials.gov, number NCT02513316. Findings: Between Aug 4, 2011, and July 31, 2015, we recruited 1490 participants of whom follow-up data were available for 1447 (97%), over a mean period of 850 days (SD 373; 3366 patient-years). The symptomatic intracranial haemorrhage rate in patients with cerebral microbleeds was 9·8 per 1000 patient-years (95% CI 4·0–20·3) compared with 2·6 per 1000 patient-years (95% CI 1·1–5·4) in those without cerebral microbleeds (adjusted hazard ratio 3·67, 95% CI 1·27–10·60). Compared with the HAS-BLED score alone (C-index 0·41, 95% CI 0·29–0·53), models including cerebral microbleeds and HAS-BLED (0·66, 0·53–0·80) and cerebral microbleeds, diabetes, anticoagulant type, and HAS-BLED (0·74, 0·60–0·88) predicted symptomatic intracranial haemorrhage significantly better (difference in C-index 0·25, 95% CI 0·07–0·43, p=0·0065; and 0·33, 0·14–0·51, p=0·00059, respectively). Interpretation: In patients with atrial fibrillation anticoagulated after recent ischaemic stroke or transient ischaemic attack, cerebral microbleed presence is independently associated with symptomatic intracranial haemorrhage risk and could be used to inform anticoagulation decisions. Large-scale collaborative observational cohort analyses are needed to refine and validate intracranial haemorrhage risk scores incorporating cerebral microbleeds to identify patients at risk of net harm from oral anticoagulation. Funding: The Stroke Association and the British Heart Foundation

Search for heavy resonances decaying to two Higgs bosons in final states containing four b quarks

A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (H) in proton-proton collisions collected by the CMS experiment at the LHC at root s = 8 TeV. The data correspond to an integrated luminosity of 19.7 fb(-1). The search considers HH resonances with masses between 1 and 3 TeV, having final states of two b quark pairs. Each Higgs boson is produced with large momentum, and the hadronization products of the pair of b quarks can usually be reconstructed as single large jets. The background from multijet and t (t) over bar events is significantly reduced by applying requirements related to the flavor of the jet, its mass, and its substructure. The signal would be identified as a peak on top of the dijet invariant mass spectrum of the remaining background events. No evidence is observed for such a signal. Upper limits obtained at 95 confidence level for the product of the production cross section and branching fraction sigma(gg -> X) B(X -> HH -> b (b) over barb (b) over bar) range from 10 to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantly extending previous searches. For a warped extra dimension theory with amass scale Lambda(R) = 1 TeV, the data exclude radion scalar masses between 1.15 and 1.55 TeV

Measurement of the top quark mass using charged particles in pp collisions at root s=8 TeV

Peer reviewe

Measurement of the underlying event activity in pp collisions at √s = 0.9 and 7 TeV with the novel jet-area/median approach

Open Access: This article is distributed under the terms of the Creative Commons Attribution License.-- Chatrchyan, S. et al.The first measurement of the charged component of the underlying event using the novel >jet-area/median> approach is presented for proton-proton collisions at centre-of-mass energies of 0.9 and 7 TeV. The data were recorded in 2010 with the CMS experiment at the LHC. A new observable, sensitive to soft particle production, is introduced and investigated inclusively and as a function of the event scale defined by the transverse momentum of the leading jet. Various phenomenological models are compared to data, with and without corrections for detector effects. None of the examined models describe the data satisfactorily. © 2012 SISSA.Acknowledge support from BMWF and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); MoER, SF0690030s09 and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France);BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MON, RosAtom, RAS and RFBR (Russia); MSTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); ThEP, IPST and NECTEC (Thailand); TUBITAK and TAEK (Turkey); NASU (Ukraine); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie program and the European Research Council (European Union); the Leventis Foundation; the A. P. Sloan Foundation; the Alexander von Humboldt Foundation; the Austrian Science Fund (FWF); the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWTBelgium); the Ministry of Education, Youth and Sports (MEYS) of Czech Republic; the Council of Science and Industrial Research, India; the Compagnia di San Paolo (Torino); and the HOMING PLUS program of Foundation for Polish Science, cofinanced from European Union, Regional Development Fund.Peer Reviewe

Search for physics beyond the standard model in events with a Z boson, jets, and missing transverse energy in pp collisions at √s̅ = 7 TeV

Peer reviewe

Measurement of the t(t)over-bar production cross section in pp collisions at root s=7 TeV in dilepton final states containing a tau

The top quark pair production cross section is measured in dilepton events with one electron or muon, and one hadronically decaying tau lepton from the decay t (t) over bar -> (l nu(l))((sic)(h)nu((sic)))b (b) over bar, (l = e, mu). The data sample corresponds to an integrated luminosity of 2.0 fb(-1) for the electron channel and 2.2 fb(-1) for the muon channel, collected by the CMS detector at the LHC. This is the first measurement of the t (t) over bar cross section explicitly including tau leptons in proton- proton collisions at root s = 7 TeV. The measured value sigma(t (t) over bar) = 143 +/- 14(stat) +/- 22(syst) +/- 3(lumi) pb is consistent with the standard model predictions

Cerebral microbleeds and intracranial haemorrhage risk in patients anticoagulated for atrial fibrillation after acute ischaemic stroke or transient ischaemic attack (CROMIS-2): a multicentre observational cohort study

Summary Background: Cerebral microbleeds are a potential neuroimaging biomarker of cerebral small vessel diseases that are prone to intracranial bleeding. We aimed to determine whether presence of cerebral microbleeds can identify patients at high risk of symptomatic intracranial haemorrhage when anticoagulated for atrial fibrillation after recent ischaemic stroke or transient ischaemic attack. Methods: Our observational, multicentre, prospective inception cohort study recruited adults aged 18 years or older from 79 hospitals in the UK and one in the Netherlands with atrial fibrillation and recent acute ischaemic stroke or transient ischaemic attack, treated with a vitamin K antagonist or direct oral anticoagulant, and followed up for 24 months using general practitioner and patient postal questionnaires, telephone interviews, hospital visits, and National Health Service digital data on hospital admissions or death. We excluded patients if they could not undergo MRI, had a definite contraindication to anticoagulation, or had previously received therapeutic anticoagulation. The primary outcome was symptomatic intracranial haemorrhage occurring at any time before the final follow-up at 24 months. The log-rank test was used to compare rates of intracranial haemorrhage between those with and without cerebral microbleeds. We developed two prediction models using Cox regression: first, including all predictors associated with intracranial haemorrhage at the 20% level in univariable analysis; and second, including cerebral microbleed presence and HAS-BLED score. We then compared these with the HAS-BLED score alone. This study is registered with ClinicalTrials.gov, number NCT02513316. Findings: Between Aug 4, 2011, and July 31, 2015, we recruited 1490 participants of whom follow-up data were available for 1447 (97%), over a mean period of 850 days (SD 373; 3366 patient-years). The symptomatic intracranial haemorrhage rate in patients with cerebral microbleeds was 9·8 per 1000 patient-years (95% CI 4·0–20·3) compared with 2·6 per 1000 patient-years (95% CI 1·1–5·4) in those without cerebral microbleeds (adjusted hazard ratio 3·67, 95% CI 1·27–10·60). Compared with the HAS-BLED score alone (C-index 0·41, 95% CI 0·29–0·53), models including cerebral microbleeds and HAS-BLED (0·66, 0·53–0·80) and cerebral microbleeds, diabetes, anticoagulant type, and HAS-BLED (0·74, 0·60–0·88) predicted symptomatic intracranial haemorrhage significantly better (difference in C-index 0·25, 95% CI 0·07–0·43, p=0·0065; and 0·33, 0·14–0·51, p=0·00059, respectively). Interpretation In patients with atrial fibrillation anticoagulated after recent ischaemic stroke or transient ischaemic attack, cerebral microbleed presence is independently associated with symptomatic intracranial haemorrhage risk and could be used to inform anticoagulation decisions. Large-scale collaborative observational cohort analyses are needed to refine and validate intracranial haemorrhage risk scores incorporating cerebral microbleeds to identify patients at risk of net harm from oral anticoagulation. Funding The Stroke Association and the British Heart Foundation