1,939 research outputs found
Charge collection properties of irradiated depleted CMOS pixel test structures
Edge-TCT and charge collection measurements with passive test structures made
in LFoundry 150 nm CMOS process on p-type substrate with initial resistivity of
over 3 kcm are presented. Measurements were made before and after
irradiation with reactor neutrons up to 210
n/cm. Two sets of devices were investigated: unthinned (700
m) with substrate biased through the implant on top and thinned (200
m) with processed and metallised back plane.
Depleted depth was estimated with Edge-TCT and collected charge was measured
with Sr source using an external amplifier with 25 ns shaping time.
Depleted depth at given bias voltage decreased with increasing neutron fluence
but it was still larger than 70 m at 250 V after the highest fluence.
After irradiation much higher collected charge was measured with thinned
detectors with processed back plane although the same depleted depth was
observed with Edge-TCT. Most probable value of collected charge of over 5000
electrons was measured also after irradiation to 210
n/cm. This is sufficient to ensure successful operation of
these detectors at the outer layer of the pixel detector in the ATLAS
experiment at the upgraded HL-LHC
Gain Recovery in Heavily Irradiated Low Gain Avalanche Detectors by High Temperature Annealing
Studies of annealing at temperatures up to 450C with LGADs irradiated
with neutrons are described. It was found that the performance of LGADs
irradiated with 1.5e15 n/cm was already improved at 5 minutes of annealing
at 250C. Isochronal annealing for 30 minutes in 50C steps
between 300C and 450C showed that the largest beneficial effect
of annealing is at around 350C. Another set of devices was annealed for
60 minutes at 350C and this annealing significantly increased
V. The effect is equivalent to reducing the effective acceptor
removal constant by a factor of 4. Increase of V is the
consequence of increased effective space charge in the gain layer caused by
formation of electrically active defects or re-activation of interstitial Boron
atoms
A novel type of proximity focusing RICH counter with multiple refractive index aerogel radiator
A proximity focusing ring imaging Cherenkov detector, with the radiator
consisting of two or more aerogel layers of different refractive indices, has
been tested in 1-4 GeV/c pion beams at KEK. Essentially, a multiple refractive
index aerogel radiator allows for an increase in Cherenkov photon yield on
account of the increase in overall radiator thickness, while avoiding the
simultaneous degradation in single photon angular resolution associated with
the increased uncertainty of the emission point. With the refractive index of
consecutive layers suitably increasing in the downstream direction, one may
achieve overlapping of the Cherenkov rings from a single charged particle. In
the opposite case of decreasing refractive index, one may obtain well separated
rings. In the former combination an approximately 40% increase in photon yield
is accompanied with just a minor degradation in single photon angular
resolution. The impact of this improvement on the pion/kaon separation at the
upgraded Belle detector is discussed.Comment: submitted to Nucl. Instr. Meth.
The HERA-B Ring Imaging Cherenkov Counter
The HERA-B RICH uses a radiation path length of 2.8 m in C_4F_10 gas and a
large 24 square meters spherical mirror for imaging Cherenkov rings. The photon
detector consists of 2240 Hamamatsu multi-anode photomultipliers with about
27000 channels. A 2:1 reducing two-lens telescope in front of each PMT
increases the sensitive area at the expense of increased pixel size, resulting
in a contribution to the resolution which roughly matches that of dispersion.
The counter was completed in January of 1999, and its performance has been
steady and reliable over the years it has been in operation. The design
performance of the RICH was fully reached: the average number of detected
photons in the RICH for a beta=1 particle was found to be 33 with a single hit
resolution of 0.7 mrad and 1 mrad in the fine and coarse granularity regions,
respectively.Comment: 29 pages, 23 figure
Evidence of the Purely Leptonic Decay B- --> tau- nu_tau-bar
We present the first evidence of the decay B- --> tau- nu_tau-bar using 414
fb^-1 of data collected at the Upsilon(4S) resonance with the Belle detector at
the KEKB asymmetric-energy e+e- collider. Events are tagged by fully
reconstructing one of the B mesons in hadronic modes. We detect the signal with
a significance of 3.5 standard deviations including systematics, and measure
the branching fraction to be Br(B- --> tau- nu_tau-bar) = (1.79
+0.56-0.49(stat) +0.46-0.51(syst))*10^-4. This implies that f_B = 0.229
+0.036-0.031(stat) +0.034-0.037(syst) GeV and is the first direct measurement
of this quantity.Comment: 6 pages, 3 figures, to appear in Physical Review Letter
Study of J/psi to p pbar, Lambda Lambdabar and observation of eta_c to Lambda Lambdabar at Belle
We study the baryonic charmonium decays of B mesons, B+ to etac K+ and B+ to
J/psi K+, where the etac and J/psi subsequently decay into a p pbar or Lambda
Lambdabar pair. We measure the J/psi to p pbar, Lambda Lambdabar anisotropy
parameters, alpha_B = -0.60 +- 0.13 +-0.14 (p pbar), -0.44 +- 0.51 +- 0.31
(Lambda Lambdabar) and compare to results from e+e- to J/psi formation
experiments. We also report the first observation of etac to Lambda Lambdabar.
The measured branching fraction is B(etac to Lambda Lambdabar) = (0.87 +0.24
-0.21(stat) +0.09 -0.14(syst) +- 0.27 (PDG)) x 10^-3. This study is based on a
357 fb^-1 data sample recorded on the Upsilon(4S) resonance with the Belle
detector at the KEKB asymmetric-energy e+e- collider.Comment: 8 pages, two figures (4 figure files), an update of hep-ex/0509020
for journal submissio
Search for Resonant Decays at Belle
We report measurements and searches for resonant decays where is a
meson or
the X(3872) particle.Comment: accepted by Physics Letters
Measurement of D0 -> pilnu (Klnu) Form Factors and Absolute Branching Fractions
Using a 282 1/fb data sample collected by the Belle experiment at the KEKB
e+e- collider, we study D0 decays to K-l+nu and pi-l+nu final states. The D0
flavor and momentum are tagged through a full reconstruction of the recoiling
charm meson and additional mesons from fragmentation. The reconstruction method
provides very good resolution in neutrino momentum and in q^2 = (p_l+p_nu)^2.
Normalizing to the total number of D0 tags, we measure the absolute branching
fractions to be B(D0 -> Klnu) =(3.45 +- 0.07stat +- 0.20syst)% and B(D0 ->
pilnu) = (0.255 +- 0.019stat +- 0.016syst)% and the semi-leptonic form factors
(within the modified pole model) f+^K(0) = 0.695 +- 0.007stat +- 0.022syst and
f+^pi(0) = 0.624 +- 0.020stat +- 0.030syst.Comment: 9 pages, 2 figures, submitted to Phys. Rev. Let
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