Background Measurement: December 2011

Background Measurement:December 2011

Thomas E. VidebaekStony Brook University, RHIG

SoLID Collaboration Meeting 2/3/20121

Spring TestThomas K HemmickStony Brook University, RHIG

Outline:• Reminder: HBD Principle.• Goals.• December experiment:

• Run conditions• Data

o Scintillator Datao Neutron rateso GEM detector rates and spectra

o March test plans:o Ringso Trackso EMCo TOFo Offline software


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HBD Principle

Mesh

CsI layer

Triple GEM

Readout Pads

e-

primary ionization

gHV photo

electron

Readout Pads

charged

particle

or photon

primaryionization

HV

• BRIGHT! ~20 photo-electrons in 50 cm of gas:• Principle source of photons at LOW WAVELENGTH!• dN/dl ~ 1/l2 • QE falls linearly as l increases.

• Single electron gain ~104 (a bit limited by the CsI).• You can see a blob…single p.e. difficult.

• More GEMs = higher gain…BUT there is a cost in hadron blindness.

Reverse Bias (HBD) Forward Bias

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• At slightly negative Ed, photoelectron detection efficiency is preserved whereas charge collection is largely suppressed.

• Charge collected from ~150μ layer above top GEM AND the gaps between GEMs.

• With n GEMs, reverse bias suppresses hadron gain from Gn to Gn-1

Hadron Blindness: UV photons vs charged particles

Target Ed ~0.1 kV/cm

Three Birds with One Stone EIC & sPHENIX:

Develop CsI technology to measure rings. Mirror technology. Precision position measurement via charge division. REQUIRES HIGHER GAIN!

SoLID Threshold detector using mirror. Less sensitive to neutron and low-E gammas.

Test Program: December: Background measurement. Spring: RINGS!


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December Goals:• How fast does a scintillator fire in the Hall?

• What are the rates of neutrons (fast & slow)?

• How quickly does our GEM detector fire?o Will we be able to see single photoelectrons?o What stack size will provide best conditions for

running in March?o What is the degradation of hadron blindness for

large numbers of GEMs?o Triple, Quadruple, Quintuple stacks.


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SIMPLER “NOVEMBER” APPARATUS??

CsI Gemstack in CF44 Pad readout (~50

channels)Are THICK (1/2” SS) walls

an issue?Is this viable?

“DECEMBER”

Experimental Setup• High purity recirculating gas

• ~1 ppm H2O & O2• CAMAC DAQ• LeCroy High Voltage• GEM detector

o Divider box allows for 'on the fly' stack size changes

• Neutron Counters• BF3

10B + n 7Li + 4Heo Bare counter (slow)o Wax counter (slow & fast)

• Scintillators


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DAQ – dead simple• PC in the Hall

• Remote desktop allows:• HV via serial port.• CAMAC via USB

• USB CAMAC controller.

• NIM Trigger: OR from the scintillators, three of the GEM pads, and either of the neutron counters.

• Digitized trigger signals to provide a mask for the data.SoLID Collaboration Meeting 2/3/2012

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Run conditions in Hall A• Average beam current held around 1 microA for most

of our runso Some were taken at 20nA or 100nA.

Collection rates much slower, usually.

• Depending upon the tune of the beam (either on target, hitting target holder, calorimeter run, etc.) background rates varied dramatically.o Anywhere from 1Hz to 1kHz.


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Scintillator Data• When we first turned on our phototubes, we saw

7 million triggers in less than a minute.

• Upon viewing data, could not parse the file.

• Turned HV off phototubes for the rest of the runs.


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Neutron Data: Beam on Target

Rate from typical on target run:

Wax


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Rate from typical on traget run:

Bare

• Bare Neutron Counter shows few, if any, counts while beam is on target. Some runs show rates of ~0.6 Hz.

• Average rate for Fast and Slow neutrons ~34.75 Hz.• Ratio of rates ~58.• Counter sensitivity: 1.9 cps per thermal neutron/cm2/sec

Neutron Data: Beam Off-Target

Rate from a calorimeter run:

Wax


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• Rate for Fast and Slow neutrons ~1.6 kHz.• During the tuning or calorimeter runs, the rates increase,

but the ratio should remain constant.• Ratio of rates is ~35 on average.• Implies Slow neutrons are produced more during off

target (i.e. striking collimators etc…) conditions.

Neutron Rates• Wanted a plot of neutron

rate vs. beam current, unfortunately we had a low number of records for low beam current.

• Also lot of off target data.

• Rough fit:~0.11 Hz/nA or ~0.06 therm-n/cm2/sec


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GEM Detector: Hadron Blindness


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Legend: Blue = +40 V Teal = +20 V Pink = 0 V Green = -20 V Red = -40 V

• As the stack has few GEMs, you are able to achieve a better hadron blindness.

• This is because ionization can occur in the gap between the first and second GEM.

• For fewer GEMs we were unable to get small signals above the hardware threshold.

GEM Detector: Presence of MIPs

• When the difference is taken between the forward-most and reverse-most bias, one should see MIPs.

• Best for fewer GEMs via the Gn-1 principle.• Normally we expect ~15 p.e. for 1.5mm of CF4.• Here tracks are inclined ~17o above horizontal.• 15/sin(17) ~ 50….SWEET!


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GEM Detector: Threshold Rate

Rates of the different stacks as a threshold of primary electrons falls off rapidly.

For 5 stacks, rate ~0.1 Hz/nA with 0.5 p.e. threshold…


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GEM Detector: Neighbors

Finally, we looked at the response of trigger pads only when a neighboring pad fired as well.

Idea is that Cherenkov blob would fall on multiple pads more often than electron clouds from hadron.

Analysis not finished, but rates cut DRAMATICALLY!


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Spring Test: Point at Target.

“Beam” consists of scattered electrons & pions.

Particles must be collimated. Need to “point” detector at target. Slide jack post back&forth via remote control.


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Small Table Layout

All aboard! Quintuple GEMstack (can always “shrink”). Need trackers to know each particle’s

trajectory. PbGl is used to identify electrons (enough???) Bore site laser of initial alignment. Coarse pads in case scintillators fire too fast. MRCP—why not? (TOF PID!!!) SoLID Collaboration Meeting 2/3/2012

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Cherenkov Optics

Optics defined by GEM size (Rring < 5 cm). Rad-length for SoLID perfect fit for optics! Should see 20 p.e. or more. NOTE: Not all rings will be fully contained.


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VUV Mirror

Require mirror reflectance DEEP in the VUV. Ordinary MgF2 cutoff l<140nm. Overcoat thickness =

thin film reflection max! Test Beam: Acton Optics Future: Make our own


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Interference Maximum

8’ diameter vessel

Pad Segmentation

RING images produce POSITION CORRELATION! Ambiguity for Compass (Cartesian)

Coordinates SOLN: New pad plane

¼ rings in four quadrants STAR-style strip-pixels. SoLID Collaboration Meeting 2/3/2012

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Pad Plane Arrives Monday

DAQ: SRS (w/ cheats!) MUST get aux detectors into data stream. SRS does not work & play well with others. SBU pad plane sends 8 input channels of

APV25 cards to LEMO connectors.

Choosing the resistors & capallows any signal to coupleinto datastream.

MRCP: Use a TAC Desire custom LEMOAPV25 card(s)


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Pattern Recognition Require ONLINE Tracking (to find target). Huijun Ge writing “light environment”.

Must run “out of box”. No dependences except root.

FRODO (son of AVATAR): Singleton factory for context independent access. STL vectors of simple objects:

Strips; PadStrips; Blobs; Clusters; ALL objects can be drawn to root canvas (EVT

DISPLAY) URGENT: NEED TO UNDERSTAND SRS

FILE FORMAT!SoLID Collaboration Meeting 2/3/2012

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Rates


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MINIMUM:1 day running-Magnet off-Magnet orientation=0

Summary Success depends upon multiple factors:

Sufficient beam time & conditions. Reliable & Homogeneous DAQ Multi-institutional efforts:

SBU, U.Va, J-Lab, Temple, Duke. Online pattern recognition & tracking

Also depends upon: Clean gas, high QE cathode, high/stable gain, accurate

alignment, phase of the moon. Schedule:

Last critical part (mirrors) arrive ~March 1. Kondo & Kiad SBU @ this time. Delivery to hall Ides of March


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Background Measurement: December 2011

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Transcript of Background Measurement: December 2011