Detection of Cerenkov light emission in LAr

Ettore Segreto

University of L’Aquila

Cryodet International Workshop

Laboratori Nazionali del Gran Sasso 13-14 March 2006

OUTLINE

     Detection of

visible light

in coincidence with cosmic ray muons in the

ICARUS 10m 3 prototype

during a dedicate test run at

Gran Sasso Laboratory external facility

.

Geometrical features

muons tracks.

of the 3D reconstructed

Monte Carlo simulation

the cosmic muon flux.

of the detector and of

Comparison

of Data with Monte Carlo results.

Cerenkov radiation

mass LAr TPC (?) in a next generation large 13 March 2006 Cryodet workshop 2

13 March 2006 3

128

ICARUS 10m

3

prototype

   The module : ~ 10m

TPC

3 of LAr (14 tons). (

2.00m (w) x 3.26m (h) x 0.35m( l)



drift length)

with

two read-out planes

: two independent representations of the ionizing event (and  possibility of 3D reconstruction).

2” quartz windowed PMT

(EMI 9814BQ) -spectral sensitivity: 160 nm-600 nm-

sensitive to 128 nm LAr not scintillation radiation

. Cryodet workshop 4 13 March 2006



Data sample

The detector was exposed to

cosmic ray flux at surface

complete test (cryogenics, electronic, acquisition system…) held in the external facility (Hall di Montaggio) of LNGS during a

(January-May 2000).

 The installation inside the 10m 3 LAr volume of the EMI 9814BQ PMT was designed in order to

ionization processes.

check any possible light emission phenomena, apart from VUV scintillation emission, accompanying

 In a

limited period

during the test run a sub-sample of the collected data have been acquired using the

PMT signal as trigger for the detector

. In principle, if no visible light emission is registered by the PMT in coincidence with the passage of particles in the liquid, no events are recorded. Indeed, we acquired a large sample of events during this dedicated test, indicating that

visible light signals are associated to through-going particles

.

 About

1200 events

produced by

single penetrating muons

selected for the present analysis 13 March 2006 Cryodet workshop have been 5

Events selection and reconstruction (I)

Collection view Induction view

Typical event produced by a crossing muon the 10m 3 in detector triggered with the internal PMT PMT

13 March 2006 Cryodet workshop

Each view of each selected event is linearly fitted to obtain the geometric parameters of the two 2D projections of the event.

6

Events selection and reconstruction (II)

The analytic combination of the two 2D projection of the events allows to obtain a complete 3D reconstruction of the muon track : (

 

Entry point in the detector.

Zenith (



and Azimuth



angles. Hall di Montaggio

7 13 March 2006 Cryodet workshop

Geometrical features of selected tracks (I)

 The

peak position the PMT window

in  distribution means that

muons propagating towards

are strongly favored, i.e. strong directionality

(characteristic of Cerenkov radiation)

 The

left-right asymmetry

(white histogram)

is mainly due to the

geographycal location of the detector

. The presence of the

Gran Sasso massif

strongly suppresses the cosmic muon flux with larger values of zenith angles (  >45 0 ) in the region  ~ [200 0 ,340 0 ].

 A

cut was applied

: only

vertical muons are considered

13 March 2006 Cryodet workshop (  <45 0 ) to remove asymmetry

(yellow histogram)

. The residual asymmetry is due to the PMT position, not perfectly symmetric with resepect to the wire chamber 8

Geometrical features of selected tracks (II)

Track Impact parameter w.r.t. the PMT optical window

Most of the events are broadly distributed between 5 cm and 20 cm. The average value is < d > ≈ 10 cm .

13 March 2006 Cryodet workshop 9

Cerenkov radiation in LAr by cosmic muons.

A

cosmic muon

1) propagating in (z= ± 1) in

ultra-relativistic LAr

regime (   (n  1.22) radiates visible Cerenkov photons with an angle w.r.t. its direction: cos 

C

 1  

n Ar

 

C

 34

o

The spectrum is continuous:

d

2

N d

 

dx

 2  sin 2 

C c

of Cerenkov photons

detectable by the installed PMT

(160nm-600nm):

dN photons



dx

 700

cm

13 March 2006 Cryodet workshop 10 

Monte Carlo simulation

      Simulation code based on the GEANT 3 package.

Precise description of the

geometrical features and of the materials constituting the detector.

Exact spectrum

cosmic muons.

(energy, azimuth and zenith angles) for

Cerenkov photons

production and propagation.

Optical properties

of the materials:  

Refelectivity

steel).

of the internal structures (aluminium/stainless

Rayleigh scattering

in LAr (and no absorption).

PMT response

(Quartz window transmittance and photo cathode quantum efficiency).

13 March 2006 Cryodet workshop 11

Real data vs. MC simulation

Yellow Data Red MC

The detected light is consistent with Cerenkov radiation emission by cosmic muons.

13 March 2006 Cryodet workshop 12

13 March 2006

From Carlo Rubbia talk

Cryodet workshop 13

Single detector: charge imaging, scintillation,

Cerenkov light

Charge readout plane

E ≈ 3 kV/cm

GAr Electronic racks Extraction grid LAr

E≈ 1 kV/cm

Field shaping electrodes Cathode (- HV)

13 March 2006

UV & Cerenkov light readout PMTs

Cryodet workshop 14

Cerenkov photons: additional discrimination

Idea:

use combination of charge readout and Cerenkov light

to determine mass of particle

(hep-ph/0402110 A. Rubbia)

Spectrum: 200nm<



<600nm Full GEANT-4 simulation

The track in the LAr TPC  + with 500 MeV of kinetic energy 13 March 2006 Cryodet workshop 15

Example:



/



discrimination in beta beams

 e    Signal  e Background     e

The combination of the information from the tracking and calorimetric measurements with the Cerenkov light provides improved particle identification . For example one can separate in this way pions from muons , a very important tool in the context of beta-beams

Energy(MeV) 200 600 <#  >  10168 97284 193080

20% coverage and 20% Q.E

.   400 2940 <#  > 16412  108918 204293   620 3485 6244 16

Conclusions

 Ionizing tracks from

cosmic ray muons

crossing the

ICARUS 10m 3

active volume have been collected

in coincidence with visible light

signals from a PMT immersed in liquid argon.

 By means of a detailed

Monte Carlo simulation

we have shown that the

geometrical characteristics

of the events are

compatible with the hypotesys of Cerenkov light emission

as the source of the PMT signals.

13 March 2006 Cryodet workshop 17

Backup Slides

13 March 2006 Cryodet workshop 18

Combinig Cerenkov and charge read-out (I)

 Non destructive multiple read-out of a LAr TPC allows to reconstruct particle tracks with bubble-chamber quality.

 Fine granularity allows precise calorimetric measurements.

 Tracking and calorimetry provide momenta, particle identification, clean

e

/   separation … 19 13 March 2006 Cryodet workshop

Why detect Cerenkov radiation in a LAr TPC of next generation?

Electronic crates



≈70 m h =20 m Max drift length Passive perlite insulation

A “general-purpose” detector for superbeams, beta-beams and neutrino factories with broad non-accelerator physics program (SN  , p-decay, atm  , …)

Neutrino detection: LAr TPC vs water Cerenkov

   

X

   

many prongs

Multi prong event detection not possible with water Cerenkov K2K ICARUS 50 liters     

p

    

p

21

Pion contamination for 90% muon acceptance

Q

.

Efficiency

  coverage   q.e.PMT

Kinetic energy (MeV) Q.Efficiency = Q.Efficiency = Q.Efficiency = 1 4% 2% 200 0 2.07 e-14 1.93 e-08 300 1.45 e-13 1.98 e-07 4.69 e-05 400 500 600 700 1.08 e-06 9.76 e-04 2.21 e-02 8.85 e-02 2.18 e-04 7.6 e-03 5.38 e-02 1.49 e-01 2.75 e-03 2.5 e-02 9.61 e-02 2.11 e-01 800 900 1000 2000 3000 13 March 2006 2.17 e-01 3.73 e-01 4.34 e-01 8.71 e-01 2.78 e-01 4.23 e-01 4.78 e-01 8.73 e-01 9.53 e-01 9.53 e-01 Cryodet workshop 3.33 e-01 4.67 e-01 5.16 e-01 8.75 e-01 9.52 e-01 22