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Transcript of Impact of δ-rays on the performance of Kaon Aerogel Detector · delta-electrons in a material,...
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Impact of δ-rays on the performance of Kaon Aerogel Detector
Marco Carmignotto, Tanja Horn, Indra Sapkota
Hamlet Mkrtchyan, Simon Zhamkochyan, Vardan Tadevosyan, Arthur Mkrtchyan,
Mariana Khachatryan
Hall C Collaboration Meeting, 21 February 2014
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Outline- The Kaon Aerogel Detector
– Objectives and (brief) status update
- Delta rays and positioning of HMS and SHMS aerogel detectors
– Are there important effects of δ-rays on the
position of the Aerogel Detector in SHMS?
- Impact of delta rays on PID
– Effects in Cerenkov Threshold detectors
– Proton misidentification in aerogel
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Kaon Aerogel Cerenkov Detector
Threshold Cerenkov detector to be used in SHMS
SHMS base detector system provides particle identification for e, π, p over the full momentum range
• Noble gas Cerenkov: e/π• Heavy gas Cerenkov: π/K• Lead glass: e/π
Kaon x ProtonAEROGEL CERENKOV DETECTOR
But no K/p!
[JLab]
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Experiments (potentially) benefiting of the Aerogel detector
Approved 12 GeV experiments
E12-06-104 Measurement of the Ratio R=sigmaL/sigmaT in Semi-Inclusive Deep-Inelastic Scattering
E12-06-107 The Search for Color Transparency at 12 GeV
E12-09-011 Studies of the L-T Separated Kaon Electroproduction Cross Section from 5-11 GeV
E12-06-101 Measurement of the Charged Pion Form Factor to High Q2
E12-07-105 Scaling Study of the L-T Separated Pion Electroproduction Cross Section at 11 GeV
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Aerogel detector characteristics
PMTs to collect Cerenkov light radiated in the aerogel
4 exchangeable aerogel trays, possibility of different momentum ranges:
Inner surfaces covered with diffusive reflector
Refractive Index
π threshold (GeV/c)
K threshold (GeV/c)
P threshold (GeV/c)
1.030 0.57 2.00 3.80
1.020 0.67 2.46 4.67
1.015 0.81 2.84 5.40
1.011 0.94 3.32 6.31
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Status of detector construction
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(More details on these tests in Simon Zhamkochyan talk)
Machined at CUABrought to Jlab for assembly and tests
Ongoing tests with cosmic raysAerogel tiles stacking
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Delta rays and order of detectorsin HMS and SHMS
HMS SHMS
Detectors before the Aerogel
- Drift chambers - Heavy gas Cherenkov- Drift chambers- Hodoscope- Gas Cherenkov
Gas Cherenkov relative position
- After the aerogel: can we “detect” δ-rays produced in aerogel?
- In front of aerogel
Is the impact of δ-rays intensified due to the order of the detectors in the SHMS?
HMSSHMS
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Delta-rays in the Aerogel Detector
Example of a simulated event with delta-ray(images from the same event)
Also known as:
- Secondary electrons- Knock-on electrons- Delta electrons
Incident pion (above Cerenkov threshold)
Cone of Cerenkov radiation from pion
δ-ray
Cerenkov radiation from δ-ray
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Delta-rays in the Aerogel Detector- Charged particles, like delta electrons, radiate Cerenkov photons above the velocity threshold v
t :
vt = c / n
- A particle with momentum below the threshold (e.g. 3.0 GeV/c proton) may create delta-electrons in a material, e.g., the aerogel detector of the SHMS.
- This particle, e.g., a proton, was not supposed to create signal in the aerogel detector, but the created delta-electrons may be above threshold in the detector, and thus give a signal
- A particle with momentum below the threshold (e.g. 3.0 GeV/c proton) may create delta-electrons in a material, e.g., the aerogel detector of the SHMS.
- This particle, e.g., a proton, was not supposed to create signal in the aerogel detector, but the created delta-electrons may be above threshold in the detector, and thus give a signal
Electron threshold: 2.1 MeV/c (n=1.030)
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Analytical estimative of δ-rays in the Aerogel Detector
- Number of delta-electrons derived from Bethe-Block dE/dx (PDG, section 30.2.5):
where
F(T) = T – kinetic energy of delta-rayK – 4.π.N
A.r
e2.m
e.c2
Z – atomic number of absorberA – atomic mass of absorberz – charge of incident particleE – kinetic energy of incident particleβ – v/c of incident particle
- spin 0 particles
- spin ½ particles
and
is the maximum T of the delta-electrons
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δ-rays Kinematic Limits for Aerogel
- Lower limit: higher than threshold of Cerenkov radiation (1.6 MeV)We chose Tmin = 3.5 MeV (for n = 1.030) assuming:
* Photon yield is important already* dE/dx for electrons in aerogel
- Upper limit: the maximum T (depends on incident particle type and momentum)
- Range of delta-rays for the Aerogel Detector (according to their kinetic energy T):
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Range and Angular distribution of δ-rays in Aerogel Detector (from Protons)
Range of delta-rays in aerogel
These delta-rays can go through the entire layer of aerogel radiating Cerenkov photons
Angular distribution of delta-rays
They are created in a forward cone within the acceptance of the SHMS
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Analytical estimate of total number of δ-rays in SHMS Aerogel Detector
Total number is obtained by integrating the distribution of delta-rays:
– Assuming 10cm of aerogel n=1.030
– Only those above Tmin
δ-rays only from Aerogel itself
For 3 GeV protons, about 2% of the events will create δ-rays above Tmin
2% 2 : 100 1 : 50
Rejection factor:
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Total number of δ-rays in SHMS/HMSIn the HMS:
δ-rays in the Aerogel Detector are mainly created in the aerogel itself
[Hamlet]
In the SHMS:Number of δ-rays in the Aerogel
Detector has significative influence of detectors that comes before it
Detectors before the Aerogel double the total number of delta-rays in the Aerogel
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Geant-4 Simulation of δ-rays from protons in SHMS Aerogel Detector
Geant4 Simulation: (Simon) Including:
– Effects of all detectors– Cherenkov radiation yield– PMT quantum-efficiency– Detector light collection efficiency (light absorption) – NO electronics effects
[Simon]
- Effects of δ-rays are translated to number of photo-electrons in the Aerogel
- We can see how it affects PID efficiency
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Geant4: δ-rays in SHMS Aerogel due to detectors before Aerogel detector
Present configuration
Significative changes in Aerogel PID performance
[Simon]
If the hodoscope, heavy gas and gas Cherenkov were not
before the aerogel
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HMS Aerogel: estimative of Gas Cerenkov cut impact on δ-rays
Aim: try to estimate the number of misidentified protons from 6 GeV elastic runs (only protons)
Example: elastic run in FPI-2
Aerogel Signal
Proton rejection
Proton rejection
[Marco]
– Good agreement with analytical estimate of proton
rejection
– Difficult to improve rejection with Gas-Cherenkov software cut: analyzer may be rejecting
δ-rays already
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HMS: estimative of dependence on aerogel refractive index
1.030(Fpi-2 experiment)
Aerogel density vs. refractive index:
1.015(Meson duality
experiment)
(n - 1) = ρ . d
Number of accidental events (pions?) in this run is high
[Hamlet]
[Hamlet]
As seen in HMS Aerogel detector, PID performance for lower refractive
index can be lower.
(further detailed studies are coming for lower refractive indexes)
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Summary– δ-rays effects in the misidentification of particles should be taken into account in all experiments in the precision frontier.
– Order of detectors in the SHMS is important (from analytical calculations and simulations):
* With the present configuration, the total number of δ-rays in Aerogel is doubled due to detectors placed before it (heavy gas, drift chambers, hodoscope, gas Cherenkov).
– Delta electron contribution can affect PID and seems to depend on refractive index
* We showed results for aerogel n = 1.030. Preliminary analysis of HMS Aerogel shows the rejection is worse for lower refractive indexes (further studies needed to have better quantitative estimate for SHMS).
THANK YOU!
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Model of delta-ray emission
- Fast hadrons loses energy in material by three main processes:
* Bremsstrahlung* Excitation of atoms/molecules* Ionization
- Bethe-Block formula describes energy loss. For p/M in range [0.1, 1000], it has accuracy of few percent!
- Number of delta-electrons proportional to dE/dx.
[PDG]