A new proposal to measure O(100) events
_
+
+
of K  p n n at the CERN SPS
Riccardo Fantechi INFN - Sezione di Pisa
On behalf of the P326 Collaboration
CERN, Dubna, Ferrara, Firenze, Frascati, Mainz,
Merced, Moscow, Napoli, Perugia, Protvino,
Pisa, Roma, Saclay, Sofia, Torino
July 23rd, 2005
HEPP - EPS 2005
Riccardo Fantechi
1
Outline
• Physics motivations
• The goals
• The beam
• The detector
July 23rd, 2005
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Riccardo Fantechi
2
Physics motivations
•
K+→p+
–
–
–
–
_
nn: process predicted with high accuracy
Short distance only
No EM penguins
Matrix element derived from experiment (K+→p0 e+n)
There is an intrinsic theoretical error of 5-7% on the amplitude,
due to charm quark loops, which can be reduced to few %
_
• BR(K+→p+ nn) = (8.0 1.1) 10 –11 in the SM @ NLO
Constrain the CKM triangle only
from the Kaon sector,
_ together
with future K0→p0 nn experiments
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Possibly the Cleanest SM test
• In K  pnn the phase b derives from Z0 diagrams
(DS=1) whereas in A(J/y KS) originates in the Bd0  Bd0 box
diagram (DB=2)
• Any non-minimal contribution to Z0 diagrams would reflect
on a violation of the relation:
(sin 2b ) K pnn  (sin 2b ) BJ /y K
S
• A deviation from the predicted rates of SM would be a clear
indication of new physics
• Complementary programme to the high energy frontier:
– When new physics will appear at the LHC, the rare decays may
help to understand the nature of it
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Some BSM Predictions
BR( K +  p +nn ) 1011
SM
8.0 ± 1.1
MFV
19.1
hep-ph/0310208
EEWP
7.5 ± 2.1
NP B697 133
EDSQ
15
hep-ph/0407021
MSSM
40
hep-ph/0408142
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K+→p+
_
nn : State of the art
3 events from E949
ek,Dmd,sin(2b)
(All DF=2 processes)
Stopped K
~0.1 % acceptance
_
+
+
BR(K → p nn ) =
1.47+1.30-0.89 × 10-10
Compatible with SM within
errors
hep-ex/0403036, PRL93 (2004)
July 23rd, 2005
HEPP - EPS 2005
100 events, SM
Riccardo Fantechi
100 events, E949 value
6
Prospects on
K+→p+
_
nn
• Decays at rest:
– Window of opportunity to accumulate more data at BNL until
2010 (before KOPIO data taking starts)
– Letter of intent for an experiment with stopped kaon decays at
JPARC (>2009)
– Established technique…
– …but hard to extrapolate to O(100) events
• Decays in flight
– Large acceptances, good photon rejection
– Separated beam: FNAL CKM (Approved but Not Ratified)
• Limited to about PK<30 GeV/c
– Un-separated beam: FNAL-P940 (now canceled)
– Un-separated beam: CERN-P326 (expected data in 2009)
• Limited by rate in beam trackers
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•
_
P326 - The goal
Collect 80 K+→ p+ nn events in
about two years of data taking for:
– 4  1012 Kaon decays/SPS year
_
– BR( K+→ p+ nn ) ~ 10-10
– Acceptance ~ 10%
•
Decay in flight, unseparated beam
– Higher K momentum
• Larger yield of K decays
• Better veto performance
– Higher acceptance
– Different systematics
– Disadvantage:
• p/K ratio ~ 10/1
• 1 Ghz rate in the beam tracker
ahead of the decay volume
• Keep pions and pion decays
inside a “beam pipe”
July 23rd, 2005
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Region I
K+ →p+p0
Region II
K+ →p+nn
K+ →p+p0p0
K+ →p+p+p
Riccardo Fantechi
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Background reduction
• Main background from Km2
and K+→p+ p0
• 3 handles for background
reduction:
– Missing mass cuts
– Photon vetoes
– Particle identification
• Redundant measurements
to control the background
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Kinematics
m
2
miss
 m + mp  2( E K Ep  pK pp cos  K p )
2
K
2
Measured quantities
• Resolution and MS tails for two and three body decays
• Cut on m2miss around p0 mass and on m2miss >0
– To have a S/N 10/1, need to cut at Dm2 ~ 8 10-3 GeV2/c4
• Need a resolution of ~ 10-3 GeV2/c4
– On p momentum: <1% a 30 GeV/c
• redundant p momentum measurement with tracker in vacuum
– On K momentum: 0.3%
• performant beam tracker
– On K-p angle: 50-60 mrad
• Contributions to background rejection
510-3 to K+ → p0 p+
210-5 to K+ → m+ n
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Vetoes
• Advantage using high momentum
– 75 Gev/c K+ and p+ momentum < 35 Gev/c, then 40 Gev of EM
energy to be detected
• Require at least 10-8 rejection for p0
• Low energy, large angle photons (low inefficiency)
correlated with high energy ones at small angle
• Wide coverage of the photon angles
– Hermetic up to 50 mrad
– Few blind zones where photons are correlated with high
energy ones at small angles
– Possible to have an average p0 inefficiency of better than 10-8
• Use different devices for different angles
– Small calorimeters to cover the hole inside the LKr calo
– The LKr calorimeter itself for up to 15 mrad
– 13 annular calorimeters (either lead/scintillator or lead/sci
fibers calorimeters) along the decay region
» Inefficiency for low energies (< 1Gev/c) photons shown to be
enough (10-4)
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Particle ID
• Electron ID from the NA48 Liquid Krypton
calorimeter
– Reject Ke3, Ke4
• Muon ID from EM, mu+hadronic calorimeter
– Reject Km2, Km2g, Km3
– A RICH is needed to have redundant measurement and
improve rejection
• Require at least a rejection factor of 105 on
muons
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New high-intensity K+ beam for NA48/3
Beam:
SPS protons per pulse on T10
Duty cycle (s./s.)
Present K12
(NA48/2)
New HI K+
> 2006
Factor
wrt 2004
1 x 1012
3 x 1012
3.0
4.8 / 16.8
Solid angle (msterad)
Already
Available
1.0
 0.40
 16
40
Av. K+momentum <pK> (GeV/c)
60
75
Total : 1.35
Mom. band RMS: (Dp/p in %)
 4
 1
~0.25
 7.0
 20
 2.8
Total beam per pulse (x 107)
per Effective spill length MHz
MHz/cm2 (gigatracker)
5.5
18
2.5
250
800
40
~45 (~27)
Eff. running time / yr (pulses)
3* x 105
3.1 * 105
1.0
K+ decays per year
1.0x1011
4.0x1012
 40
Area at Gigatracker (cm2)
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~45 (~27)
~16 (~10)
13
P326 Detector Layout
1.5 m
p+
K+
n
n
800 MHz
(p/K/p)
10 MHz Kaon
decays
Only the upstream detectors
Are exposed to the 800 MHz beam
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•
•
•
•
•
•
•
•
•
Detectors
CEDAR
– Differential Cherenkov counter for positive kaon
identification
GIGATRACKER
– To Track the beam before it enters the decay region
ANTI
– Photon vetoes surrounding the decay tank
SPECTROMETER
– 2 magnets + 6 straw chambers to track the kaon decay
products
RICH
– For redundant muon/pion separation
CHOD
– Fast hodoscope to make a tight kaon-pion time
coincidence (~100 ps)
LKR
– Forward photon veto and e.m. calorimeter
MAMUD
– Hadron calorimeter, muon veto and sweeping magnet
SAC
– Small angle photon vetoes
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Challenging detector!
Ineff. 10-4 for Eg>100 Mev
Ineff. 10-5 for Eg> 1 Gev
Get rid of the tails form MS
Inefficiency: 10-2
Ineff. <10-5 for Eg> 1 Gev
10-3 electron inefficiency
Inefficiency: 10-5
Ineff. 10-6 for Eg> 6 Gev
15
Gigatracker
•
Challenging beam tracker ahead of the decay region
•
Specifications:
– Momentum resolution to ~ 0.5 %
– Angular resolution ~ 10 mrad
– Time resolution ~ 100 ps
– Minimal material budget
– Perform all of the above in
• 800 MHz hadron beam, 60 MHz / cm2
•
Hybrid Detector:
– SPIBES (Fast Si micro-pixels bonded to r/o ICs)
• Momentum measurement
• Facilitate pattern recognition in subsequent FTPC
• Time coincidence with CHOD
– FTPC (NA48/2 KABES micromegas technology with FADC r/o)
• Track direction
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Time Schedule
•
2004
– Parasitic tests in NA48/2 beam done
– Startup of working groups
– Submission of a Letter of Intent for the Villars meeting
From the Villars
report to the SPSC
•
2005
– Gigatracker R&D started
– Preparation of the proposal
– Proposal submitted to SPSC
– Evaluation process for the proposal started
•
2006-2008
– Costruction, Installation and beam-tests
2009-2010
– Data Taking
•
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Conclusions
• An experiment
to measure the decay in flight
_
K+→p+ nn is being proposed at CERN
• The goal is to collect O(100) events in 2 years
• The experiment will use some of the existing
facilities of NA48
– It is not definitely a continuation of NA48
• There are new detectors with challenging aspects
• The Collaboration is being formed
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Spares
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Physics Introduction:
CKM matrix and CP-Violation
Quark mixing is described by the
Cabibbo-Kobayashi-Maskawa (CKM) matrix
 d '   Vud Vus Vub  d 
  
 
s
'

V
V
V
s
cd
cs
cb
  
 
 b '   V V V  b 
ts
tb  
   td
KM mechanism:
Ng=2
Nphase=0  No CP-Violation
Ng=3
Nphase=1  CP-Violation Possible
e.g. Im lt= Im Vts*Vtd ≠ 0  CP
KM mechanism appears to be the main source of CP-violation in quarks:
•Direct-CP Violation exists: e’/e  0 NA48, KTeV
•CP violation in the B meson sector: ACP(J/y Ks), BaBar, Belle
Now look for inconsistencies in SM using independent observables
affected by small theoretical uncertainties and different sensitivity
to new physics
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Kaon Rare Decays and the SM
(holy grail)
|Vtd|
Kaons provide
quantitative tests
of SM independent
from B mesons…
…and a large window
of opportunity
exists!
Im lt = A2 l5 h
Re lt = A2 l5 r
July 23rd, 2005
G. Isidori
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K→p nn : Theory in Standard
Model
2
2
 Im lt
Re lc
  Re lt
 
B ( K  p nn )   +   5 X ( xt )  +  5 X ( xt ) +
Pc ( X )  
l
  l
 
 l
+
B ( K L0
+
 Im l

 p nn )   L   5 t X ( xt ) 
 l

l  Vus
lc  Vcs*Vcd
lt  Vts*Vtd
charm
contribution
top
contributions
3 2 Br ( K +  p 0e+n ) 8
 +  rK + 
l
2
4
2p sin W
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2
0
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The Hadronic Matrix Element is
measured and isospin rotated
(~10% correction)
Riccardo Fantechi
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Predictions in SM
+
+
BR( K  p nn )  (8.0  1.1) 10
11
(latest CKM workshop)
Error ~ 14% Mainly parametric
Theory error due to charm (Buras04):
Pc ( X )  0.389  0.033(mc )  0.045( mc )  0.010( s )
For long distance contribution
see:"LIGHT-QUARK LOOPS IN K->PI NU NU"
By G. Isidori, C.Smith, F.Mescia.
e-Print Archive: hep-ph/0503107
Largest contribution
from scale error. To be
reduced by NNLO
calculation
BR( K L0  p 0nn )  (3.0  0.6) 1011
(Buras et al. 04)
The error is almost purely parametric
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K0L  p0nn :State of the Art
Data
MC BG Sum
Lnp0 MC
XLp0 MC
Signal MC
KTeV 1997 Data
Dalitz Analysis
Still far from the model
independent limit:
BR(K0 → p0nn) < 4.4 × BR(K+p+nn) ~ 1.4 × 10-9
Grossman & Nir, PL B407 (1997)
BR(KL  p0nn)  5.9 x 10-7 (p0eeg, 1997 Data) [PRD 61,072006 (2000)]
BR (KL p0nn)  1.6 x 10-6 (p0gg, 1997 1 Day) [PLB 447, 240 (1999)]
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Prospects
•
K0L  p0nn
–
–
–
–
•
K0L  p0ee(mm)
–
–
–
–
–
•
Large window of opportunity exists.
Upper limit is 4 order of magnitude from the SM prediction
Expect results from data collected by E391a (proposed SES~3 10-10)
Next experiment KOPIO@ BNL
Long distance contributions under better control
Measurement of KS modes by NA48/1 bound the KL measurement
KS rates to be better measured (KLOE?)
Background limited (study time dep. Interference?)
100-fold increase in kaon flux to be envisaged
K+ p+nn
–
–
–
–
July 23rd, 2005
The situation is different: 3 clean events are published
Experiment in agreement with SM
Next round of exp. need to collect O(100) events to be useful
Move from stopped to in flight experiments
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Message from the CERN Director
General to the staff (Jan 05)
• The top priority is to maintain the goal of starting
up the Large Hadron Collider (LHC) in 2007
• “…Meanwhile, the natural break we have in the
fixed-target programme in 2005 is already
allowing the community to develop a wellfocused programme for the future”
The possible Non-LHC Future Programme was reviewed by
the SPSC in Villars (September 22-27, 2004)
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John Dainton
Villars 2004
October 7th 2004
CERN seminar
SPSC@Villars
● new rare decay frontier in K physics at CERN
● new experiments planned for Kπνν important
● support R&D now for K+π +νν results ≤ 2010
From the Villars Report…
CERN-SPSC-2005-010
SPSC-M-730
February 28, 2005
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Riduzione del background
m
2
miss
 m + mp  2( E K Ep  pK pp cos  K p )
2
K
2
Measured quantities
• Taglio sulla m2miss intorno alla massa del p0
–
–
–
–
Inefficienza sui veti di 10-8
Inefficienza sui m di 5 10-6
Rapporto S/N 10/1 con accettanza >1
Il taglio intorno alla massa del p0: Dm2 ~ 8 10-3 GeV2/c4
• Risoluzione necessaria ~ 10-3 GeV2/c4
– Risoluzione impulso K: 0.3%
– Risoluzione impulso p: <1% a 30 GeV/c
– Risoluzione angolo K-p: 50-60 mrad
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DPp (Spectrometer 2)GeV/c
Gaussian MSC (old)
DPp
(Spectrometer 1) GeV/c
DPp
(Spectrometer 2) GeV/c
NA48/3 simulation
Non-Gaussian MSC
DPp
(Spectrometer 1) GeV/c
New MSC
REGION I
Uncorrelated non gaussian
tails
REGION II
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2
(GeV/c
HEPP -M(miss)
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2)2
30
Acceptance
K+ momentum: (75.0 ± 0.8) GeV/c
P = [15- 35] GeV/c
(RICH)
P = [10 - 40] GeV/c
4×1012 decays/year
@ BR = 10-10
July 23rd, 2005
Region I
Region II
2
0.  mmiss
 0.01 (GeV / c 2 )2
2
0.026  mmiss
 0.068 (GeV / c 2 )2
2.8 × 102
14.8 × 102
3.9 × 102
21.7 × 102
I+II (RICH)
70 events/year
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Rapporti segnale/fondo
Segnale: K+→ p+ n n (BR≈ 8.0 × 10-11 )
BR
July 23rd, 2005
Veto
rej.
Kinem.
Rej.
Acceptance
Bgnd
m+n
63 %
5 10-6
2 10-6
p+p0
21 %
3 10-7
2 10-5
27%
~1
p+p+p
6%
10-6
(2 10-5)
20%
~1
p+p0p0
2%
<10-8
(2 10-5)
15%
<<1
p0m+n
3%
Non crea
problemi
<<1
p0e+n
5%
e/p <10-3
<<1
30%(20%*) 8(<1*)
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* RICH
32
CEDAR
Db
b
Db
K/p
m12  m22

b
2 p2
Cedar-W
Cedar-N
p (GeV / c )
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8 Condensors “focus” the photons
on the detectors (32-channel
linear array multianode PM)
Simulation allows to calculate the
image size and to optimise
location of the photon detectors
4000
+
p
+
3500
K
Number of entries
3000
2500
Diaphragm 1mm
2000
1500
1000
500
0
90
92
94
96
98
100
102
104
106
108
Radial distance of g at diaphragm [mm]
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Tagging eff. ≈ 90% 34
Misident. prob. < 1%
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FTPC
SPIBES2
SPIBES1
GIGATRACKER
•
momentum: use SP1 and SP2 to measure y =
40 mm displacement. Assuming σp~50µm from
pixel and 350µm thick Si (0.37% X0)

σ = (σp√2 ‡ σMS ) ⁄ 40 mm = 0.25%
•
direction: use SP2 and FTPC. Assuming
σp~100µm from pixel and similar from FTPC and
no MS from FTPC (from SP2 no influence)

∆х= σp√2 ⁄ 12.4m = 11µrad
•
time resolution: essential to obtain a low
background due to accidental hits and to allow the
pattern recognition.
 Need 100 ps for S/B=10
6.25
12.45 m
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FTPC (KABES+FADC)
•
•
NA48/2
– KABES has achieved very good performance
– Position resolution ~ 70 micron
– Time resolution ~ 0.6 ns
– Rate per micro-strip ~ 2 MHz
NA48/3
– Intensity ~ 10 higher per unit area
– 600 ns drift
– The long drift (600 ns) makes a standalone pattern recognition
very difficult or just impossible ( That’s why we plan to have
SPIBES in front)
– To reduce double pulse resolution and improve the time resolution
one has to reduce the pulse duration and possibly read-out every
micro-strip with 1 GHz FADC
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Doppio
spettrometro
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Straw 2.3m, Ø9.6 mm
Kapton films 12mm+25mm
Ogni half-layer:
112 straws
 per DCH:
4×4×112=1792
Perdita di accettanza
dovuta al foro centrale: <10%
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Doppio
spettrometro
≈11 000 straws,
130 mm di risoluzione per vista
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Anticontatori
•
•
•
•
•
•
Set of ring-shaped photon vetoes surrounding the decay tank
Specification: inefficiency to detect photons above 100 MeV < 10-4
The NA48 ANTI’s (AKL) need to be replaced
Extensive R&D performed by American and Japanese groups
Claims that inefficiency as low as 10-5 can be achieved
Baseline solution: Lead/ Plastic scintillator sandwich (1-2 mm lead /
5 mm plastic scintillator)
• SPACAL (a la Kloe) option also being studied
CKM design
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Anticontatori
Questo rivelatore deve consentire di vetare i p0, con
inefficienza massima tollerabile ≈10-7, ovvero, mediamente,
dell’ordine di 10-4 o meglio sul singolo fotone.
Naturalmente, la capacità di veto dipende dall’energia del g
e l’effetto complessivo richiede un’integrazione
sull’accettanza, nonchè la combinazione con il segnale dal LKr
e dai piccoli rivelatori (SAC e IRC) a piccolo angolo.
Da una simulazione della cinematica, assumendo ragionevoli
inefficienze per i vari rivelatori, si ottiene una inefficienza
media per il p0 di circa 10-8 dopo il taglio sull’impulso del p+.
Il contributo maggiore all’inefficienza media viene dall’1%
circa di fotoni che mancano i rivelatori
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Anticontatori
Soluzione alla CKM
•
•
•
•
•
•
1mm Pb/5 mm scintillatore (+WLS fiber)
80 layers, 16 X0
13 corone circolari di 16 settori (22.50)
Superficie totale vista dai fotoni: 28 m2
Superficie totale di Pb e Sci: 2270 m2
Lunghezza delle fibre per la raccolta di
luce: 220 Km
• 13 x 64 = 832 fototubi
• Montaggio tra due sezioni del tubo a
vuoto in tasche sotto vuoto
Rext = 1100 mm
Rint = 880 mm
– Per mantenere il vuoto del tubo di
decadimento migliore di 10-7 mbar
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Anticontatori
Soluzione alla KLOE
• 0.5mm Pb/ 1mm fibre scintillanti
• Spessore 24 cm  20 X0
• 13 corone circolari, in U o in
anello (da studiare)
• Superficie totale del Pb: 5600 m2
• Lunghezza delle fibre: 4100 Km
• 96x13=1248 fototubi
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Odoscopio veloce
L’idea è quella di usare Glass Multigap RPCs, sullo stile di
quanto realizzato nel sistema di TOF di ALICE
A questo rivelatore infatti è richiesto di essere efficiente
(>99%) e di avere un’ottima risoluzione temporale (50ps)
in modo da ridurre al massimo la possibilità di associazioni
accidentali fra il pione di decadimento ed il K che lo origina.
E’ necessario pero’ valutare l’ efficienza di questi rivelatori
nelle zone piu’calde, dove il rate per unita’ di area e’ superiore
a quanto finora provato da ALICE.
July 23rd, 2005
HEPP - EPS 2005 Riccardo
Fantechi
44
July 23rd, 2005
~80 K+ HEPP
πνν
- EPS 2005
Fantechi
Riccardo
45
Odoscopio veloce - Struttura
4×2 modules, each equipped
with horizontal and vertical
strips, respectively.
2.4 m
With strips 20x1280 mm2
(20 = 19strip + 1 interstrip)
the total number of channel
is 60×4×2 = 480 ( ×2 …)
The estimated material
budget is ≈ 15% X0
July 23rd, 2005
HEPP - EPS 2005 Riccardo
Fantechi
46
LKR Calorimeter
•
•
•
•
•
Must achieve inefficiency < 10-5 to detect
photons above 1 GeV
– Need to take data in 2006 to measure
the inefficiency
It is needed to identify electrons
Advantages:
– It exists
– Homogeneous (not sampling)
ionization calorimeter
– Very good granularity (~2 2 cm2)
– Fast read-out (Initial current,
FWHM~70 ns)
– Very good energy (~1%, time ~ 300ps
and position (~1 mm) resolution
Disadvantages
– 0.5 X0 of passive material in front of
active LKR
– The cryogenic control system needs
to be updated
The readout electronics should be rebuilt
July 23rd, 2005
HEPP - EPS 2005 Riccardo
Fantechi
47
MAMUD
• To provide pion/muon separation
and beam sweeping.
–Iron is subdivided in 150 2 cm
thick plates (260  260 cm2 )
•Two coils magnetise the iron plates
to provide a 0.9 T dipole field in the
beam region
•Active detector:
– Strips of extruded polystyrene
scintillator (1 x 4 x130 cm3)
– Only half the slots instrumented
– Light is collected by WLS fibres
with 1.2 mm diameter
Pole gap is 2 x 11 cm V x 30 cm H – Two planes of fast scintillator in
the last part for a fast muon
Coils cross section 10 cm x 20cm
trigger
July 23rd, 2005
HEPP - EPS 2005 Riccardo
Fantechi
48
Trigger
• Il rate di traccia singola passa da 1 MHz (NA48/2) a
circa 20 MHz
– 10 dai decadimenti del K e 7 dall’alone del fascio
– Necessita’ di un trigger di livello 0 con una reiezione di ~20 e
poi utilizzo di un trigger software in una batteria di PC
– Massima flessibilita’ nello sviluppo e aggiornamento degli
algoritmi
• Con l’uso del segnale dell’ odoscopio, del mu e di
depositi di energia in quadranti del calorimetro, si
riesce ad ottenere la reiezione voluta
– Semplificazione del trigger veloce
– Si evitano il piu’possibile correlazioni tra rivelatori diversi
– Facilita’ di imporre offline tagli piu’severi
July 23rd, 2005
HEPP - EPS 2005 Riccardo
Fantechi
49
Trigger
• Limitare al massimo lo sviluppo di soluzioni ad hoc
– Molto e’stato sviluppato per LHC (LHCB, Alice, etc)
– Necessita’ di uniformare I moduli di readout di tutti I rivelatori
– Utilizzo di hardware commerciale (PC, Switch Eth Gb, etc)
• Quindi trigger di livello 0 semplice seguito da una
farm di PC
– Riduzione del rate in ingresso ai PC sotto il Mhz (come
LHCB)
– Trigger software sull’informazione completa
– In totale 150000 canali
• 100000 Gigatracker e 15000 dalle camere a ridottissima
occupazione
• 13500 canali del calorimetro compattati, con zero
suppression fatta a software nei PC
July 23rd, 2005
HEPP - EPS 2005 Riccardo
Fantechi
50
Trigger
July 23rd, 2005
HEPP - EPS 2005 Riccardo
Fantechi
51