arXiv subjects

T. Ferber

Publications and source records attributed to T. Ferber.

355 records · Page 20Linked to original sources

arXiv2013

New results on $ν_μ\to ν_τ$ appearance with the OPERA experiment in the CNGS beam

The OPERA neutrino experiment is designed to perform the first observation of neutrino oscillations in direct appearance mode in the $ν_μ\to ν_τ$ channel, via the detection of the $τ$-leptons created in charged current $ν_τ$ interactions. The detector, located in the underground Gran Sasso Laboratory, consists of an emulsion/lead target with an average mass of about 1.2 kt, complemented by electronic detectors. It is exposed to the CERN Neutrinos to Gran Sasso beam, with a baseline of 730 km and a mean energy of 17 GeV. The observation of the first $ν_τ$ candidate event and the analysis of the 2008-2009 neutrino sample have been reported in previous publications. This work describes substantial improvements in the analysis and in the evaluation of the detection efficiencies and backgrounds using new simulation tools. The analysis is extended to a sub-sample of 2010 and 2011 data, resulting from an electronic detector-based pre-selection, in which an additional $ν_τ$ candidate has been observed. The significance of the two events in terms of a $ν_μ\to ν_τ$ oscillation signal is of 2.40 $σ$.

hep-ex↗

arXiv2013

Search for $ν_μ\rightarrow ν_e$ oscillations with the OPERA experiment in the CNGS beam

A first result of the search for \numu $\rightarrow$ \nue oscillations in the OPERA experiment, located at the Gran Sasso Underground Laboratory, is presented. The experiment looked for the appearance of \nue in the CNGS neutrino beam using the data collected in 2008 and 2009. Data are compatible with the non-oscillation hypothesis in the three-flavour mixing model. A further analysis of the same data constrains the non-standard oscillation parameters $θ_{new}$ and $Δm^2_{new}$ suggested by the LSND and MiniBooNE experiments. For large $Δm^{2}_{new}$ values ($>$0.1 eV$^{2}$), the OPERA 90% C.L. upper limit on sin$^{2}(2θ_{new})$ based on a Bayesian statistical method reaches the value $7.2 \times 10^{-3}$.

hep-ex↗

arXiv2013

Measurement of the Wrong-Sign Decay D0 -> K+ pi- pi+ pi-

A measurement of the rate for the "wrong-sign" decay D0 -> K+ pi- pi+ pi- relative to that for the "right-sign" decay D0 -> K- pi+ pi+ pi- is presented. Using 791 fb-1 of data collected with the Belle detector, we obtain a branching fraction ratio of R_WS = [0.324 +- 0.008 (stat) +- 0.007 (sys)]%. Multiplying this ratio by the world average value for the branching fraction B(D0 -> K- pi+ pi+ pi-) gives a branching fraction B(D0 -> K+ pi- pi+ pi-) = (2.61 +- 0.06 +0.09 -0.08) x 10-4.

hep-ex↗

arXiv2013

Evidence of a new narrow resonance decaying to $χ_{c1}γ$ in $B \to χ_{c1} γK$

We report measurements of $B \to χ_{c1} γK$ and $χ_{c2} γK$ decays using $772 \times 10^{6}$ $B\bar{B}$ events collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. Evidence of a new resonance in the $χ_{c1} γ$ final state is found with a statistical significance of $3.8 σ$. This state has a mass of $3823.1 \pm 1.8 {(stat)} \pm 0.7 {(syst)}$ MeV/$c^2$, a value that is consistent with theoretical expectations for the previously unseen $1^3 D_2$ $c\bar{c}$ meson. We find no other narrow resonance and set upper limits on the branching fractions of the $X(3872) \to χ_{c1} γ$ and $χ_{c2} γ$ decays.

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arXiv2013

Measurement of exclusive $Υ(1S)$ and $Υ(2S)$ decays into Vector-Pseudoscalar final states

Using samples of 102 million $Υ(1S)$ and 158 million $Υ(2S)$ events collected with the Belle detector, we study exclusive hadronic decays of these two bottomonium resonances to $\ks K^+ π^-$ and charge-conjugate (c.c.) states, $π^+ π^- π^0 π^0$, and $π^+ π^- π^0$, and to the two-body Vector-Pseudoscalar ($K^{\ast}(892)^0\bar{K}^0+ {\rm c.c.}$, $K^{\ast}(892)^-K^+ + {\rm c.c.}$, $ωπ^0$, and $ρπ$) final states. For the first time, signals are observed in the modes $Υ(1S) \to \ks K^+ π^- + {\rm c.c.}$, $π^+ π^- π^0 π^0$, and $Υ(2S) \to π^+ π^- π^0 π^0$, and evidence is found for the modes $Υ(1S)\to π^+ π^- π^0$, $K^{\ast}(892)^0 \bar{K}^0+ {\rm c.c.}$, and $Υ(2S) \to \ks K^+ π^- + {\rm c.c.}$ Branching fractions are measured for all the processes, while 90% confidence level upper limits on the branching fractions are also set for the modes with a statistical significance of less than $3σ$. The ratios of the branching fractions of $Υ(2S)$ and $Υ(1S)$ decays into the same final state are used to test a perturbative QCD prediction for OZI-suppressed bottomonium decays.

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arXiv2013

Study of Exclusive B->X_u l nu Decays and Extraction of |V_{ub}| using Full Reconstruction Tagging at the Belle Experiment

We report the results of a study of the exclusive semileptonic decays B->pi0lnu, B->pi+lnu, B->rho0lnu, B->rho+lnu and B->omegalnu, where l represents an electron or a muon. The events are tagged by fully reconstructing a second B meson in the event in a hadronic decay mode. The measured branching fractions are Br(B->pi0lnu) = (0.80 +- 0.08 +- 0.04)x10^-4, Br(B->pi+lnu) = (1.49 +- 0.09 +- 0.07)x10^-4, Br(B->rho0lnu) = (1.83 +- 0.10 +- 0.10)x10^-4, Br(B->rho+lnu) = (3.22 +- 0.27 +- 0.24)x10^-4, and Br(B->omegalnu) =(1.07 +- 0.16 +- 0.07)x10^-4, where the first error is statistical and the second one is systematic. The obtained branching fractions are inclusive of soft photon emission. We also determine the branching fractions as a function of the 4-momentum transfer squared to the leptonic system q^2=(p_l+p_nu)^2, where p_l and p_nu are the lepton and neutrino 4-momenta, respectively. Using the pion modes, a recent LCSR calculation, lattice QCD results and a model-independent description of the hadronic form factor, a value of the CKM matrix element |V_{ub}| = (3.52 +- 0.29)x10^-3 is extracted. For the first time, a charmless state with invariant mass greater than 1 GeV/c^2, which might be dominated by the decay B->f2lnu, is observed. These results are obtained from a 711 1/fb data sample that contains 772 millions BB pairs, collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider.

hep-ex↗

arXiv2013

Evidence for the decay B0 --> K+K-pi0

We report a search for charmless hadronic decays of neutral B mesons to the final state K+K-pi0. The results are based on a 711 fb^-1 data sample that contains 772x10^6 BB-bar pairs, and was collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find the first evidence for this decay with a significance of 3.5 standard deviations and measure its branching fraction as BF(B0 --> K+K-pi0) = [2.17 +/- 0.60(stat) +/- 0.24 (syst)]x10^-6.

hep-ex↗

arXiv2013

Study of $e^+ e^- \to π^+ π^- J/ψ$ and Observation of a Charged Charmonium-like State at Belle

The cross section for $e^+ e^- \to π^+ π^- J/ψ$ between 3.8 GeV and 5.5 GeV is measured with a 967 fb$^{-1}$ data sample collected by the Belle detector at or near the $Υ(nS)$ ($n = 1,\ 2,\ ...,\ 5$) resonances. The Y(4260) state is observed, and its resonance parameters are determined. In addition, an excess of $π^+ π^- J/ψ$ production around 4 GeV is observed. This feature can be described by a Breit-Wigner parameterization with properties that are consistent with the Y(4008) state that was previously reported by Belle. In a study of $Y(4260) \to π^+ π^- J/ψ$ decays, a structure is observed in the $M(π^\pm\jpsi)$ mass spectrum with $5.2σ$ significance, with mass $M=(3894.5\pm 6.6\pm 4.5) {\rm MeV}/c^2$ and width $Γ=(63\pm 24\pm 26)$ MeV/$c^{2}$, where the errors are statistical and systematic, respectively. This structure can be interpreted as a new charged charmonium-like state.

hep-ex↗

arXiv2012

Measurement of the neutrino velocity with the OPERA detector in the CNGS beam using the 2012 dedicated data

In spring 2012 CERN provided two weeks of a short bunch proton beam dedicated to the neutrino velocity measurement over a distance of 730 km. The OPERA neutrino experiment at the underground Gran Sasso Laboratory used an upgraded setup compared to the 2011 measurements, improving the measurement time accuracy. An independent timing system based on the Resistive Plate Chambers was exploited providing a time accuracy of $\sim$1 ns. Neutrino and anti-neutrino contributions were separated using the information provided by the OPERA magnetic spectrometers. The new analysis profited from the precision geodesy measurements of the neutrino baseline and of the CNGS/LNGS clock synchronization. The neutrino arrival time with respect to the one computed assuming the speed of light in vacuum is found to be $δt_ν\equiv TOF_c - TOF_ν= (0.6 \pm 0.4\ (stat.) \pm 3.0\ (syst.))$ ns and $δt_{\barν} \equiv TOF_c - TOF_{\barν} = (1.7 \pm 1.4\ (stat.) \pm 3.1\ (syst.))$ ns for $ν_μ$ and $\barν_μ$, respectively. This corresponds to a limit on the muon neutrino velocity with respect to the speed of light of $-1.8 \times 10^{-6} < (v_ν-c)/c < 2.3 \times 10^{-6}$ at 90% C.L. This new measurement confirms with higher accuracy the revised OPERA result.

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arXiv2012

DEPFET active pixel detectors for a future linear $e^+e^-$ collider

The DEPFET collaboration develops highly granular, ultra-transparent active pixel detectors for high-performance vertex reconstruction at future collider experiments. The characterization of detector prototypes has proven that the key principle, the integration of a first amplification stage in a detector-grade sensor material, can provide a comfortable signal to noise ratio of over 40 for a sensor thickness of 50-75 $\mathrm{\mathbf{μm}}$. ASICs have been designed and produced to operate a DEPFET pixel detector with the required read-out speed. A complete detector concept is being developed, including solutions for mechanical support, cooling and services. In this paper the status of DEPFET R & D project is reviewed in the light of the requirements of the vertex detector at a future linear $\mathbf{e^+ e^-}$ collider.

physics.ins-det↗

arXiv2012

Measurement of the neutrino velocity with the OPERA detector in the CNGS beam

The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km. The measurement is based on data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of (6.5 +/- 7.4(stat.)((+8.3)(-8.0)sys.))ns was measured corresponding to a relative difference of the muon neutrino velocity with respect to the speed of light (v-c)/c =(2.7 +/-3.1(stat.)((+3.4)(-3.3)(sys.))x10^(-6). The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5 microseconds long extractions, was confirmed by a test performed at the end of 2011 using a short bunch beam allowing to measure the neutrino time of flight at the single interaction level.

hep-ex↗

arXiv2012

Determination of a time-shift in the OPERA set-up using high energy horizontal muons in the LVD and OPERA detectors

The purpose of this work is to report the measurement of a time-shift in the OPERA set-up in a totally independent way from Time Of Flight (TOF) measurements of CNGS neutrino events. The LVD and OPERA experiments are both installed in the same laboratory: LNGS. The relative position of the two detectors, separated by an average distance of ~ 160 m, allows the use of very high energy horizontal muons to cross-calibrate the timing systems of the two detectors, using a TOF technique which is totally independent from TOF of CNGS neutrino events. Indeed, the OPERA-LVD direction lies along the so-called "Teramo anomaly", a region in the Gran Sasso massif where LVD has established, many years ago, the existence of an anomaly in the mountain structure, which exhibits a low m. w. e. thickness for horizontal directions. The "abundant" high-energy horizontal muons (nearly 100 per year) going through LVD and OPERA exist because of this anomaly in the mountain orography. The total live time of the data in coincidence correspond to 1200 days from mid 2007 until March 2012. The time coincidence study of LVD and OPERA detectors is based on 306 cosmic horizontal muon events and shows the existence of a negative time shift in the OPERA set-up of the order of deltaT(AB) = - (73 \pm 9) ns when two calendar periods, A and B, are compared. This result shows a systematic effect in the OPERA timing system from August 2008 until December 2011. The size of the effect is comparable with the neutrino velocity excess recently measured by OPERA. It is probably interesting not to forget that with the MRPC technology developed by the ALICE Bologna group the TOF world record accuracy of 20 ps was reached. That technology can be implemented at LNGS for a high precision determination of TOF with the CNGS neutrino beams of an order of magnitude smaller than the value of the OPERA systematic effect.

hep-ex↗

arXiv2010

Measurement of the atmospheric muon charge ratio with the OPERA detector

The OPERA detector at the Gran Sasso underground laboratory (LNGS) was used to measure the atmospheric muon charge ratio in the TeV energy region. We analyzed 403069 atmospheric muons corresponding to 113.4 days of livetime during the 2008 CNGS run. We computed separately the muon charge ratio for single and for multiple muon events in order to select different energy regions of the primary cosmic ray spectrum and to test the charge ratio dependence on the primary composition. The measured charge ratio values were corrected taking into account the charge-misidentification errors. Data have also been grouped in five bins of the "vertical surface energy". A fit to a simplified model of muon production in the atmosphere allowed the determination of the pion and kaon charge ratios weighted by the cosmic ray energy spectrum.

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