E. Olaiya

We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of Standard Model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). In most cases the LLP lifetime can be treated as a free parameter from the $\mu$m scale up to the Big Bang Nucleosynthesis limit of $\sim 10^7$m. Neutral LLPs with lifetimes above $\sim$ 100m are particularly difficult to probe, as the sensitivity of the LHC main detectors is limited by challenging backgrounds, triggers, and small acceptances. MATHUSLA is a proposal for a minimally instrumented, large-volume surface detector near ATLAS or CMS. It would search for neutral LLPs produced in HL-LHC collisions by reconstructing displaced vertices (DVs) in a low-background environment, extending the sensitivity of the main detectors by orders of magnitude in the long-lifetime regime. In this white paper we study the LLP physics opportunities afforded by a MATHUSLA-like detector at the HL-LHC. We develop a model-independent approach to describe the sensitivity of MATHUSLA to BSM LLP signals, and compare it to DV and missing energy searches at ATLAS or CMS. We then explore the BSM motivations for LLPs in considerable detail, presenting a large number of new sensitivity studies. While our discussion is especially oriented towards the long-lifetime regime at MATHUSLA, this survey underlines the importance of a varied LLP search program at the LHC in general. By synthesizing these results into a general discussion of the top-down and bottom-up motivations for LLP searches, it is our aim to demonstrate the exceptional strength and breadth of the physics case for the construction of the MATHUSLA detector.

The direct CP violation parameter Re(epsilon'/epsilon) has been measured from the decay rates of neutral kaons into two pions using the NA48 detector at the CERN SPS. The 2001 running period was devoted to collecting additional data under varied conditions compared to earlier years (1997-99). The new data yield the result: Re(epsilon'/epsilon) = (13.7 +/- 3.1) times 10^{-4}. Combining this result with that published from the 1997, 98 and 99 data, an overall value of Re(epsilon'/epsilon) = (14.7 +/- 2.2) times 10^{-4} is obtained from the NA48 experiment.

The beam and detector, used for the NA48 experiment, devoted to the measurement of Re(ε′/ε), and for the NA48/1 experiment on rare KS and neutral hyperon decays, are described.

A precise measurement of the cross section of the process $e^+e^-\to\pi^+\pi^-(\gamma)$ from threshold to an energy of 3GeV is obtained with the initial-state radiation (ISR) method using 232fb$^{-1}$ of data collected with the BaBar detector at $e^+e^-$ center-of-mass energies near 10.6GeV. The ISR luminosity is determined from a study of the leptonic process $e^+e^-\to\mu^+\mu^-(\gamma)\gamma_{\rm ISR}$, which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process $e^+e^-\to\pi^+\pi^-(\gamma)$ is obtained with a systematic uncertainty of 0.5% in the dominant $\rho$ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured $\pi\pi$ cross section from threshold to 1.8GeV is $(514.1 \pm 2.2({\rm stat}) \pm 3.1({\rm syst}))\times 10^{-10}$.

We examine the observability of heavy neutrino (ν h ) signatures of a U(1)′ enlarged Standard Model (SM) encompassing three heavy Majorana neutrinos alongside the known light neutrino states at the the Large Hadron Collider (LHC). We show that heavy neutrinos can be rather long-lived particles producing distinctive displaced vertices that can be accessed in the CERN LHC detectors. We concentrate here on the gluon fusion production mechanism gg → H 1,2 → ν h ν h , where H 1 is the discovered SM-like Higgs and H 2 is a heavier state, yielding displaced leptons following ν h decays into weak gauge bosons. Using data collected by the end of the LHC Run 2, these signatures would prove to be accessible with negligibly small background.

In this paper, we discuss the potential of observing heavy neutrino ($\nu_h$) signatures of a $U(1)_{B-L}$ enlarged Standard Model (SM) encompassing three heavy Majorana neutrinos alongside the known light neutrino states at the Large Hadron Collider (LHC). We exploit the theoretical decay via a pair of heavy (non-SM-like) Higgs boson and $Z'$ production followed by $\nu_h \rightarrow l^\pm W^{\mp (*)}$ and $\nu_h \rightarrow \nu_l Z^{(*)}$ decays, ultimately yielding a $3l+2j+E_{T}^{\rm{miss}}$ signature and, depending upon how boosted the final state objects are, we define different possible selections aimed at improving the signal to background ratio in LHC Run 2 data for a wide range of heavy neutrino masses.

We present a new measurement of the branching ratio R of the decay KL -> pi e nu (Ke3), relative to all charged KL decays with two tracks, based on data taken with the NA48 detector at the CERN SPS. We measure R = 0.4978 +- 0.0035. From this we derive the Ke3 branching fraction and the weak coupling parameter |Vus| in the CKM matrix. We obtain |Vus|f+(0) = 0.2146 +- 0.0016, where f+(0) is the vector form factor in the Ke3 decay.

The decay rate of KL→π0γγ has been measured with the NA48 detector at the CERN SPS. A total of 2558 KL→π0γγ candidates have been observed with a residual background of 3.2%. The branching ratio is determined to be (1.36±0.03(stat)±0.03(syst)±0.03(norm))×10−6 and the vector coupling constant av=−0.46±0.03(stat)±0.04(syst). This result suggests that the CP-violation effects are dominating in the KL→π0e+e− decay. An upper limit for the KL→π0γγ decay rate in the two photon mass region mγγ<mπ0 is also given.

This Letter reports on a new high precision measurement of the form factors of the KL→π±μ∓νμ decay. The data sample of about 2.3×106 events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, λ+′=(20.5±2.2stat±2.4syst)×10−3, and a quadratic, λ+″=(2.6±0.9stat±1.0syst)×10−3 term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be λ0=(9.5±1.1stat±0.8syst)×10−3. Using a linear fit our results were: λ+=(26.7±0.6stat±0.8syst)×10−3 and λ0=(11.7±0.7stat±1.0syst)×10−3. A pole fit of the form factors yields: mV=(905±9stat±17syst)MeV/c2 and mS=(1400±46stat±53syst)MeV/c2.

The semileptonic decay of the neutral K meson, KL -> pi e nu (Ke3), was used to study the strangeness-changing weak interaction of hadrons. A sample of 5.6 million reconstructed events recorded by the NA48 experiment was used to measure the Dalitz plot density. Admitting all possible Lorentz-covariant couplings, the form factors for vector (f_+(q^2)), scalar (f_S) and tensor (f_T) interactions were measured. The linear slope of the vector form factor lambda_+ = 0.0284+-0.0007+-0.0013 and values for the ratios |f_S/f_+(0)| = 0.015^{+0.007}_{-0.010}+-0.012 and |f_T/f_+(0)| = 0.05^{+0.03}_{-0.04}+-0.03 were obtained. The values for f_S and f_T are consistent with zero. Assuming only Vector-Axial vector couplings, lambda_+ = 0.0288+-0.0004+-0.0011 and a good fit consistent with pure V-A couplings were obtained. Alternatively, a fit to a dipole form factor yields a pole mass of M = 859+-18 MeV, consistent with the K^*(892) mass.

New measurements of the $\eta$ and $K^0$ masses have been performed using decays to 3$\pi^0$ with the NA48 detector at the CERN SPS. Using symmetric decays to reduce systematic effects, the results $M(\eta) = 547.843\pm0.051$ MeV/c$^2$ and $M(K^0) = 497.625\pm0.031$ MeV/c$^2$ were obtained.

We present a measurement of the ratio of the decay rates Gamma(KL -> pi+ pi-)/Gamma(KL -> pi e nu), denoted as Gamma(K2pi)/Gamma(Ke3). The analysis is based on data taken during a dedicated run in 1999 by the NA48 experiment at the CERN SPS. Using a sample of 47000 K2pi and five million Ke3 decays, we find Gamma(K2pi)/Gamma(Ke3) = (4.835 +- 0.022(stat) +- 0.016(syst)) x 10^-3. From this we derive the branching ratio of the CP violating decay KL -> pi+ pi- and the CP violation parameter |eta+-|. Excluding the CP conserving direct photon emission component KL -> pi+ pi- gamma, we obtain the results BR(KL -> pi+ pi-) = (1.941 +- 0.019) x 10^-3 and |eta+-| = (2.223 +- 0.012) x 10^-3.

The KS→γγ decay rate has been measured with the NA48 detector using a high intensity short neutral beam from the CERN SPS. The measured branching ratio BR(KS→γγ)=(2.78±0.06stat±0.04syst)×10−6, obtained from 7461±172 KS→γγ events, is significantly higher than the O(p4) prediction of chiral perturbation theory. Using a KL beam the ratio Γ(KL→γγ)Γ(KL→π0π0π0)=(2.81±0.01stat±0.02syst)×10−3 has been measured.

Using data taken during the year 2000 with the NA48 detector at the CERN SPS, a search for the CP violating decay K_S -> 3 pi0 has been performed. From a fit to the lifetime distribution of about 4.9 million reconstructed K0/K0bar -> 3 pi0 decays, the CP violating amplitude eta_000 = A(K_S -> 3 pi0)/A(K_L -> 3 pi0) has been found to be Re(eta_000) = -0.002 +- 0.011 +- 0.015 and Im(eta_000) = -0.003 +- 0.013 +- 0.017. This corresponds to an upper limit on the branching fraction of Br(K_S -> 3 pi0) < 7.4 x 10^-7 at 90% confidence level. The result is used to improve knowledge of Re(epsilon) and the CPT violating quantity Im(delta) via the Bell-Steinberger relation.

In data taken with the NA48 experiment at the CERN SPS in 1999, 730 candidates of the weak radiative hyperon decay Ξ0→Λγ have been found with an estimated background of 58±8 events. From these events the Ξ0→Λγ decay asymmetry has been determined to α(Ξ0→Λγ)=−0.78±0.18stat±0.06syst, which is the first evidence of a decay asymmetry in Ξ0→Λγ. The branching fraction of the decay has been measured to be Br(Ξ0→Λγ)=(1.16±0.05stat±0.06syst)×10−3.

A measurement of the KS lifetime is presented using data recorded by the NA48 experiment at the CERN-SPS during 1998 and 1999. The KS lifetime is derived from the ratio of decay time distributions in simultaneous, collinear KS and KL beams, giving a result which is approximately independent of the detector acceptance and with reduced systematic errors. The result obtained is τS=(0.89598±0.00048±0.00051)×10−10 s, where the first error is statistical and the second systematic.

We present the first observation of the decay KS→π+π−e+e− based upon the data collected in 1998 by the NA48 experiment at CERN. We have identified a clean sample of 56 events with negligible background contamination. Using KL→π+π−π0D decays as normalization sample, the branching ratio is measured to be BR(KS→π+π−e+e−)=[4.5±0.7(stat)±0.4(syst)]×10−5. This result is in good agreement with the theoretical expectations from the mechanism of inner bremsstrahlung.

Using the NA48 detector at the CERN SPS, 31 KS->pi0 gamma gamma candidates with an estimated background of 13.7 +- 3.2 events have been observed. This first observation leads to a branching ratio of BR(KS->pi0 gamma gamma) = (4.9 +- 1.6(stat) +- 0.9(syst)) x 10^-8 in agreement with Chiral Perturbation theory predictions.

A search for the decay KS→π0γγ has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity KS beam, an upper limit for the branching ratio BR(KS→π0γγ,z⩾0.2)<3.3×10−7 has been obtained at 90% confidence level, where z=mγγ2/mK02.

We investigate the potential of the Large Hadron Collider (LHC) to probe one of the most compelling beyond the Standard Model frameworks---walking technicolor (WTC), involving strong dynamics and having a slowly running (walking) new strong coupling. For this purpose we use recent LHC Run 2 data to explore the full parameter space of the minimal WTC model using dilepton signatures from heavy neutral ${Z}^{\ensuremath{'}}$ and ${Z}^{\ensuremath{'}\ensuremath{'}}$ resonances predicted by the model. This signature is the most promising one for discovery of WTC at the LHC for the low-intermediate values of the $\stackrel{\texttildelow{}}{g}$ coupling---one of the principle parameters of WTC. We have demonstrated complementarity of the dilepton signals from both resonances, established the most up-to-date limit on the WTC parameter space, and provided projections for the LHC potential to probe the WTC parameter space at higher future luminosities and upgraded energy. We have explored the whole four-dimensional parameter space of the model and have found the most conservative limit on the WTC scale ${M}_{A}$ above 3 TeV for the low values of $\stackrel{\texttildelow{}}{g}$, which is significantly higher than previous limits established by the LHC collaborations.

Abstract We assess the performance of different jet-clustering algorithms, in the presence of different resolution parameters and reconstruction procedures, in resolving fully hadronic final states emerging from the chain decay of the discovered Higgs boson into pairs of new identical Higgs states, the latter in turn decaying into bottom-antibottom quark pairs. We show that, at the large hadron collider (LHC), both the efficiency of selecting the multi-jet final state and the ability to reconstruct from it the masses of the Higgs bosons (potentially) present in an event sample depend strongly on the choice of acceptance cuts, jet-clustering algorithm as well as its settings. Hence, we indicate the optimal choice of the latter for the purpose of establishing such a benchmark Beyond the SM (BSM) signal. We then repeat the exercise for a heavy Higgs boson cascading into two SM-like Higgs states, obtaining similar results.

The decay rate of the long-lived neutral K meson into the e+e−e+e− final state has been measured with the NA48 detector at the CERN SPS. Using data collected in 1998 and 1999, a total of 200 events has been observed with negligible background. This observation corresponds to a branching ratio of Br(KL→e+e−e+e−)=(3.30±0.24stat±0.23syst±0.10norm)×10−8.

The decay rate of KS → γγ has been measured with the NA48 detector at the CERN SPS. A total of 149 KS → γγ events have been observed. The branching ratio is determined to be (2.58±0.36(stat)±0.22(sys))×10−6.

We investigate the possibility of detectable 2-Higgs Doublet Model (2HDM) type-II cross-sections at the High-Luminosity phase of the Large Hadron Collider (HL-LHC) for the production of the Standard Model (SM)-like Higgs boson ($h$) in association with a single top (anti)quark over the parameter space region corresponding to the so-called `wrong-sign solution' of the bottom (anti)quark Yukawa coupling. We isolate the latter by using the toolbox Magellan, which performs Markov Chain Monte Carlo (MCMC) scans in the presence of all current theoretical and experimental constraints, which relevance is accounted for accurately by using built-in Bayesian statistical methods. It is found that the allowed points in the 2HDM type-II parameter space of the aforementioned kind would not only provide inclusive rates considerably above those of the equivalent SM process but also distributions in several kinematical observables that are very different from the SM, both of which can help disentangle the SM from the 2HDM hypothesis. This difference is a consequence of the bottom-gluon fusion sub-process, which in the 2HDM becomes dominant over all others, with the latter remaining very close to the SM yields. We prove that this phenomenology would be observable at the HL-LHC for the illustrative example of $h$ to bottom-antibottom quark decays.

The KL→π±π0e∓νe(ν̄e) decay was investigated with the NA48 detector at CERN SPS using a beam of long-lived neutral kaons. The branching ratio Br(KL→π±π0e∓νe(ν̄e))=(5.21±0.07stat±0.09syst)×10−5 was fixed from a sample of 5464 events with 62 background events. The form factors f̄s, f̄p, λg and h̄ were found to be in agreement with previous measurements but with higher accuracy. The coupling parameter of the chiral Lagrangian L3=(−4.1±0.2)×10−3 was evaluated from the data.

A value of (-6.1 +- 0.9_{stat} +- 0.5_{syst})*10^{-3} is obtained for the quadratic slope parameter h in the K_L -> 3\pi^0 decay Dalitz plot at the NA48 experiment at the CERN SPS. The result is based on 14.7*10^6 fully reconstructed K_L -> 3\pi^0 -> 6\gamma decays. This is the most precise measurement of any of the Dalitz plot slope parameters in the charged and neutral kaon decays so far.

We report a Dalitz plot analysis of charmless hadronic decays of charged $B$ mesons to the final state $K_{\rm S}^{0}\pi^{+}\pi^{0}$ using the full BaBar dataset of $470.9\pm2.8$ million $B\bar{B}$ events collected at the $\Upsilon(4S)$ resonance. We measure the overall branching fraction and $CP$ asymmetry to be ${\cal B}\left(B^{+}\to K^{0}\pi^{+}\pi^{0}\right) = \left(45.9 \pm 2.6 \pm 3.0^{+8.6}_{-0.0}\right)\times10^{-6}$ and $A_{CP}\left(B^{+}\to K^{0}\pi^{+}\pi^{0}\right) = 0.07 \pm 0.05 \pm 0.03^{+0.02}_{-0.03}$, where the uncertainties are statistical, systematic, and due to the signal model, respectively. This is the first measurement of the branching fraction for $B^{+} \to K^{0}\pi^{+}\pi^{0}$. We find first evidence of a $CP$ asymmetry in $B^{+}\to K^{*}(892)^{+}\pi^{0}$ decays: $A_{CP}\left(B^{+}\to K^{*}(892)^{+}\pi^{0}\right)=-0.52 \pm 0.14 \pm 0.04^{+0.04}_{-0.02}$. The significance of this asymmetry, including systematic and model uncertainties, is $3.4$ standard deviations. We also measure the branching fractions and $CP$ asymmetries for three other intermediate decay modes.

Binned data frames are a generalisation of multi-dimensional histograms, represented in a tabular format with one category per row containing the labels, bin contents, uncertainties and so on. Pandas is an industry-standard tool, which provides a data frame implementation complete with routines for data frame manipultion, persistency, visualisation, and easy access to “big data” scientific libraries and machine learning tools. FAST (the Faster Analysis Software Taskforce) has developed a generic approach for typical binned HEP analyses, driving the summary of ROOT Trees to multiple binned DataFrames with a yaml-based analysis description. Using Continuous Integration to run subsets of the analysis, we can monitor and test changes to the analysis itself, and deploy documentation automatically. This report describes this approach using examples from a public CMS tutorial and details the benefit over traditional methods.

We present results of B -> vector-vector (VV) and B -> vector-axial vector (VA) decays B0 -> phi X (X = phi, rho+ or rho0), B+ -> phi K(*)+, B0 -> K*K*, B0 -> rho+b_1- and B+ -> K*0a_1+. The largest dataset used for these results is based on 465 * 10^6 Y(4S) -> BB decays, collected with the BABAR detector at the PEP-II B meson factory located at the Stanford Linear Accelerator Center (SLAC).

We present results of B -&gt; vector-vector (VV) and B -&gt; vector-axial vector (VA) decays B0 -&gt; phi X (X = phi, rho+ or rho0), B+ -&gt; phi K(*)+, B0 -&gt; K*K*, B0 -&gt; rho+b_1- and B+ -&gt; K*0a_1+. The largest dataset used for these results is based on 465 * 10^6 Y(4S) -&gt; BB decays, collected with the BABAR detector at the PEP-II B meson factory located at the Stanford Linear Accelerator Center (SLAC).

The ultimate motivation of our study is to look for signs of physics beyond the Standard Model (BSM). We investigate whether different jet clustering techniques might be more or less suited to the particular final states of interest. In particular, we are interested in fully hadronic final states emerging from the decay chain of the Standard Model like Higgs boson into pairs of light Higgs states, the latter in turn decaying into bottom-anti bottom pairs. We show that, the ability of selecting the multi-jet final state and to reconstruct invariant masses of the Higgs bosons from it depend strongly on the choice of acceptance cuts, resolution parameters and reconstruction algorithm as well as its settings. Hence, we indicate the optimal choice of the latter for the purpose of establishing such a benchmark as a BSM signal. We then repeat the exercise for a heavy Higgs boson cascading into two SM-like Higgs states, obtaining similar results.

The ultimate motivation of our study is to look for signs of physics beyond the Standard Model (BSM). We investigate whether different jet clustering techniques might be more or less suited to the particular final states of interest. In particular, we are interested in fully hadronic final states emerging from the decay chain of the Standard Model like Higgs boson into pairs of light Higgs states, the latter in turn decaying into 𝑏𝑏 pairs. We show that the ability to select the multi-jet final state and to reconstruct invariant masses of the Higgs bosons from it depends strongly on the choice of acceptance cuts, resolution parameters, and reconstruction algorithm as well as its settings. Hence, we indicate the optimal choice of the latter for the purpose of establishing such a benchmark as a BSM signal. We then repeat the exercise for a heavy Higgs boson cascading into two SM-like Higgs states, obtaining similar results.

We assess the performance of different jet-clustering algorithms, in the presence of different resolution parameters and reconstruction procedures, in resolving fully hadronic final states emerging from the chain decay of the discovered Higgs boson into pairs of new identical Higgs states, the latter in turn decaying into bottom-antibottom quark pairs. We show that, at the Large Hadron Collider (LHC), both the efficiency of selecting the multi-jet final state and the ability to reconstruct from it the masses of the Higgs bosons (potentially) present in an event sample depend strongly on the choice of acceptance cuts, jet-clustering algorithm as well as its settings. Hence, we indicate the optimal choice of the latter for the purpose of establishing such a benchmark Beyond the SM (BSM) signal.