Date post: | 21-Dec-2015 |
Category: |
Documents |
View: | 213 times |
Download: | 0 times |
Strawman Detector
F.Forti, Università and INFN, Pisa
UK SuperB Meeting
Daresbury, April 26, 2006
April 27, 2006 F.Forti - SuperB Strawman Detector 2
Experimental issues• Babar and Belle designs have proven to be
very effective for B-Factory physics– Follow the same ideas for SuperB detector– Try to reuse same components as much as
possible
• Main issues– Machine backgrounds– Beam energy asymmetry– Strong interaction with machine design
• Impact on– Detector segmentation– Radius of beam pipe and first sensitive layer– Radiation hardness
April 27, 2006 F.Forti - SuperB Strawman Detector 3
EMC6580 CsI(Tl) crystals
Instrumented Flux Returniron / RPCs&LSTs ( / neutral hadrons)
Drift Chamber40 stereo layers
1.5 T solenoid
Silicon Vertex Tracker5 layers, double sided strips
DIRC PID)144 quartz bars
11000 PMs
e+ (3.1 GeV)
e- (9 GeV)
SVT: 97% efficiency, 15 m z hit resolution (inner layers, perp. tracks)SVT+DCH:(pT)/pT = 0.13 % pT + 0.45 %, (z0) = 65 m @ 1 GeV/c
DIRC: K- separation 4.2 @ 3.0 GeV/c 3.0 @ 4.0 GeV/c EMC: E/E = 2.3 %E-1/4 1.9 %
The BABAR Detector
April 27, 2006 F.Forti - SuperB Strawman Detector 5
Machine backgrounds• In “traditional” Super BFactory designs
– Luminosity obtained with large beam currents (among other things)
• 4.1/9.4 A for SuperKEKB @ 4x1035
• 6.8/15.5 A for SuperPEP-II @ 7x1035
– Background a significant problem
• In December Linear SuperB design– Small fraction of store beam extracted from damping
ring at each collision.– Very low current at the IP make backgrounds negligible– Low collision frequency implies event pileup
• In March SuperB design – Beam currents are moderate: 1.5A @ 1036
– Background important, but should not be a huge problem (smaller than in current BFactories)
– Collision at every turn: no pileup, and continuous time-structure as in current BFactories.
April 27, 2006 F.Forti - SuperB Strawman Detector 6
Types and level of backgrounds• Extrapolations from current machines
– Full simulation is needed to completely understand backgrounds
• Beam gas• Synchroton radiation Both proportional to current
– Should not be a problem at SuperB• They become a problem at higher currents
• Luminosity sources (eg radiative Bhabhas)– Need careful IR design. – Angle crossing helps (see PEP-II/KEKPB
comparison)
87.57
6.56
5.5
4
3.532.5
21.51
0.5
4.55
HER Radiative Bhabhas
-7.5 -5 -2.5 0 2.5 5 7.5
0
10
20
30
-10
-20
-30
m
cm
M. SullivanFeb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M
3.1 G
eV
3.1 G
eV
9 GeV
9 GeV
BABAR Interaction Region
Detector
0
10
20
-10
-20
cm
0 2 4-2-4m
KEK Interaction Region
QCSL QCSR
QC1EL
QC2PL QC1ER
CSL CSR
Detector
gammas
off-energy beam particles
Radiative Bhabhas
April 27, 2006 F.Forti - SuperB Strawman Detector 9
More sources of background• Beam-beam interactions
– Potentially important, but probably under control in the low disruption regime.
• Touschek background– Intra beam scattering. Goes like 1/E2. Improves
with smaller asymmetry. Increases with beam density. Need further study
• Thermal outgassing– Due to HOM losses. Not an issue with small
currents• Injection background
– Needs further study with the 1 collision/turn scheme.
• Bursts– Due to dust. No real cure. Need robustness of
detector
April 27, 2006 F.Forti - SuperB Strawman Detector 10
Background bottom line• Probably reasonable to assume machine
background is not larger than what with have today at Babar and Belle.
• Need to design a robust detector with enough segmentation and radiation hardness to withstand surprises (x5 safety margin)– Seems within reach of current technology– There are critical points, though:
• Inner detector radius likely to be reduced more background
• Bhabha scattering at small angle can become an issue because of smaller boost more occupancy, more radiation damage
• IR design is critical– Radiative Bhabhas– Syncrotron radiation shielding– Shielding from beam-beam blow up
April 27, 2006 F.Forti - SuperB Strawman Detector 11
Beam Energy Asymmetry• Machine design prefers lower boost
– Damping rings more similar– Babar: 9 + 3.1 βγ=0.56– Belle: 8 + 3.5 βγ=0.45– SuperB?: 7 + 4 βγ=0.28
• Most obvious effect on detector Larger solid angle coverage Smaller decay vertices separation
• We can afford to have a lower boost only if the vertexing resolution is good:– small radius beam pipe– very little material in b.p. and first layer– Studies indicate a b.p. of 1cm would be OK– Need a realistic beam pipe design to confirm the viability
of the lower boost. – How much cooling is needed in the beampipe ?
• Symmetric running is also being studied– Could reduce boost-induced energy smearing in
analysis
April 27, 2006 F.Forti - SuperB Strawman Detector 12
Beam Pipe Radius• Small beam pipe radius possible because of small beam size
– Studied impact of boost on vertex separation (B)– Beampipe hypothesis (no cooling)
• 5um Au shield to protect from soft photons• 0.5cm 200um Be and 5um hit resolution (0.21% X0)• 0.5cm 300um Be and 10um hit resolution (0.24% X0)• 0.5cm 500um Be and 10um hit resolution (0.29% X0)
– Rest of tracking is Babar
Separationsignificance Proper time
differenceresolution
April 27, 2006 F.Forti - SuperB Strawman Detector 13
Beam Pipe Thickness• With 1.5A beam currents the beam pipe
will require cooling.– Beampipe design is being developed– Study effect of beampipe thickness
• Assume boost=0.28• Bdecay• 10um hit resolution 1cm beampipe
should allow good performance even with =0.28
Proper timedifferenceresolution
BaBar
April 27, 2006 F.Forti - SuperB Strawman Detector 14
Energy• Is it interesting to run at different energies ?
– Υ(5s): not an issue for the machine– oscillation of Bs rapid for TD analysis
• Required resolution very hard to obtain
• Still it might be possible to measure through time-integrated measurement branching fractions
• BsD
• BsK++0
Renga/Pierini
April 27, 2006 F.Forti - SuperB Strawman Detector 15
Energy II• Is it interesting to run at the threshold or
at the (3770) ?– Luminosity will be around 1035
– Still more than at tau-charm factories– Studies going to on on physics case
• Absolute D branching fractions, rare decays• Form factors• Unitarity tests with charm• D mixing ? Use
coherence of initial state
• CP violation
• Boosted operation– Is there something
to be gained to run at low energywith boost ?
– It might be possible to separate (a little bit) the D vertices
zzvs
April 27, 2006 F.Forti - SuperB Strawman Detector 16
Silicon Vertex Tracker• Vertexing
– Two monolithic active pixel layers glued on beam pipe• Since active region is
only ~10um, silicon can be thinned down to ~50um.
• Good resolution O(5um).• Good aspect ratio for small
radius (compared to strips)• Improves pattern recognition robustness and
safety against background • needs R&D: feasability of MAPS, overlaps,
cables, cooling
• Quite a bit of R&D going on on MAPS
x5 scale with 10mm radius BP, 6mm pixel chip
April 27, 2006 F.Forti - SuperB Strawman Detector 17
MAPS R&DCAP chip (Belle collaborators)
TSMC 0.35m Process
Column Ctrl Logic
1.8mm 132col*48row ~6 Kpixels
CAP1: simple 3-transistor cell
Pixel size:
22.5 m x 22.5 m
CAPs sample tested: all detectors (>15) function.
TESTED IN BEAM.
Source follower buffering of collected charge
Restores potential to collection electrode
Reset
Vdd Vdd
Collection Electrode
Gnd
M1
M2
M3Row Bus Output
Column Select
April 27, 2006 F.Forti - SuperB Strawman Detector 18
MAPS R&D II• SLIM chip
(Babar collabor.)
PRE SHAPER DISC LATCH
=105 mV =12 mV
Landau peak 80 mV saturation
due to low energy particle.
1250
2200 3000 (e-)
1640
threshold
threshold
90Sr electrons
Noise only (no source)
55Fe X-rays
Charge sharing
ST 0.13um triple well technologySingle pixels tested with sourceFull signal processing chain
April 27, 2006 F.Forti - SuperB Strawman Detector 19
Silicon Vertex Tracker• Intermediate silicon tracking
– More or less like the current Si strip detectors:• 5 layers of 300um Si, strip lengths 5-20cm, pitch 50-200um,
shaping time 100-400ns
– Reduction in thickness would be desirable, but not essential• Possibility of 200um Si in inner layers
– Small angle region will require special attention due to the high Bhabha rate
40 cm30 cm
20 cm
April 27, 2006 F.Forti - SuperB Strawman Detector 20
Central Tracker• Babar and Belle Drift Chambers
– Both use He based gas mixture– Cell size 12-18mm– Maximum drift time ~500ns– Resolution in the best part of the cell
~100µm– Expect that either OK.
• Solid state tracking – an all-silicon solution evaluated, but
not performant at low momentum, expensive, and not really needed with moderate backgrounds
• Need to optimize cell size against occupancy– Belle has developed a fast gas small
cell DCH, but with a degraded resolutions (5.4mm, ~150µm)
• Solutions exists, although a full design is needed
Normal cell(17.3mm)
Small cell(5.4mm)
April 27, 2006 F.Forti - SuperB Strawman Detector 21
Particle Identification• Current solutions for K identification
– Low p: • dE/dx (both Babar and Belle) • TOF (Belle only)
– High p: dedicated Cherenkov detector• DIRC (Babar) – ring imaging cherenkov counter• ACC(Belle) – aerogel threshold cherenkov counter
– Coverage: • only barrel(Babar) • barrel+endcap (Belle)
• Evolution– Ring imaging is superior to threshold counters
• Need to resolve background and mechanical issues– Forward and backward endcap coverage very
desirable to increase effective luminosity• A different kind of problem
• R&D is needed
April 27, 2006 F.Forti - SuperB Strawman Detector 22
Babar PID
• Stand-off box, filled with water expands cone on PM– Source of backgrund
• Barrel-only device• Mechanical
interference in the backward direction
April 27, 2006 F.Forti - SuperB Strawman Detector 23
Belle PID• Aerogel Cherenkov Counters, Time of Flight
– No high mom. PID for endcap
– Material (ACC+TOF ~ 0.35X0)
April 27, 2006 F.Forti - SuperB Strawman Detector 24
Evolution: Babar-Style Fast DIRC• Replace SOB with
compact readout• Tested in beam
with– Hamamatsu Multi
Anode Photo Multipliers
– Burle Micro Channel Plate PMTs
April 27, 2006 F.Forti - SuperB Strawman Detector 25
DIRC with timing: TOP • Cherenkov ring imaging
with precise time measurement– Quartz radiator (2cm-thick)
• Basic study was already done.– Photon detector (MCP-PMT)
• Good time resolution < ~40ps• Single photon sensitive under 1.5T
– Test with GaAsP photo-catode + MCP-PMT very promising
Simulation2GeV/c, =90 deg.
-ray, had. int.
K
-K separation power
April 27, 2006 F.Forti - SuperB Strawman Detector 26
Focusing Aerogel-RICH• New imaging technique by introducing multiple radiators
Focusing type Defocusing type
n1 n2n1<n2 n1>n2
Increase Cherenkov photons without loosing single angle resolution due to emission point uncertainty
Take full advantage of controllable index of aerogel
n2
n4n3n2n1n4n3n2n1
n1<n2<n3<n4 n2<n1<n4<n3
April 27, 2006 F.Forti - SuperB Strawman Detector 27
Electromagnetic calorimeter• Both Babar and Belle use CsI(Tl)
calorimeters are suitable for SuperB – signal decay time of ~.75µs (dominant) and
~3µs are OK • CsI(Tl) is too slow for endcap
– need to deal with Bhabha rate spatial and temporal overlaps.
– especially if possible to extend coverage to 100 mrad, beam line elements allowing. • Babar forward is 350 mrad, Belle forward 200 mrad,
backward 400 mrad
• Encap replacement is needed– In the case of Babar, a backward endcap needs
to be added altogether• Solutions seem to be viable with some
R&D
April 27, 2006 F.Forti - SuperB Strawman Detector 28
Candidate materials• Pure CsI
Fast (16ns) Low light yield (2500 /MeV)
• LSO or LYSO High light yield (27000 /MeV) Speed OK (47ns) Expensive
April 27, 2006 F.Forti - SuperB Strawman Detector 29
Other Detector components• Muon and KL detector
– Inside the return yoke of magnet– It doesn’t seem to be a problem– avalanche mode RPC, LST, scintillator
are all viable
• Trigger/DAQ– Not substantially different from current
schemes.– Keep open trigger scheme– Need to try vetoing Bhabhas at level 1 – Data rate seems well manageable
April 27, 2006 F.Forti - SuperB Strawman Detector 30
Reusability of Babar and Belle• Large (expensive) portions of Babar or
Belle would be reusable– Barrel calorimeter– Magnet– Barrel LSTs for Babar
• But large subsystems need to be replaced or significantly upgraded– Tracking and vertexing– Particle ID– Endcap calorimeter– Trigger/DAQ
• Babar or Belle seem good foundations for a SuperB detector– But need to look in detail at integration and
mechanical structure issues
April 27, 2006 F.Forti - SuperB Strawman Detector 33
Outlook• A detector for SuperB seems to be
feasible• An R&D plan needs to be formulated
to address the remaining issues– Vertexing– Particle ID– Calorimetry
• Babar and Belle provide excellent foundations for a detector at SuperB
• More detailed studies will be possible once the machine parameters have settled.