1. Search for long-lived particles at ATLAS
Osamu JINNOUCHI (KEK)
on behalf of ATLAS SUSY (exotic) group
Supersymmetry in 2010’s at Hokkaido-university
June 21, 2007

2. Long-lived particles search in ATLAS
Long-lived particles search (long enough to pass through detector) and their discovery --would directly address many important open questions to particle physics
Dark matter in the universe
Hierarchy problem
Extra dimension
flavor question
charge quantization
... etc
If such particles produced at LHC, Can we(=ATLAS) effectively detect them ?
It is important to know and develop the detection ability of ATLAS for such particles
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

3. outline Introduction sensible detectors in ATLAS for the search
trigger issues
reconstruction of long-lived particles
summary
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

4. long-lived particles in the context of SUSY scenarios
many candidates on the market (already many in SUSY scenarios only!)
GMSB
NLSP decays to LSP only via the gravitational coupling, thus could be long-lived
Non-pointing Photons (decay on flight)
Penetrating Sleptons
Split SUSY (in MSSM scenario)
Squarks are heavy, suppressing Gluino decays
hence Gluino could be long-lived
Colored heavy particle (R-hadrons)
AMSB
and are mass de-generate
chargino could be long-lived (decay on flight : Kink track)
long
hep-ph/
many possible different event topologies
ATLAS could cover with multi-purpose detectors
June 21, 2007

5. possible event topologies, detection strategies
Regardless of the models, categorized by the event signatures
Such particles are generally produced in pairs
1) direct production (small s ) 2) cascade decay products (SUSY)
Decay length?
Charge (Electric? magnetic? color?)  different detector response
(A) Sleptons, R-hadrons
(heavy slow particles)
large ionization energy loss
nuclear int. (R-hadron case)
delay (TOF) reconstructed in Muon chamber
(B) Long-lived neutralino
(Non-pointing photon)
decay vertex is somewhere in the inner tracker volume
heavy slow
particles
kink track
(on plan!)
(A)
non-pointing
photons
mSugra like
(B)
detailed study using Geant4 full detector simulation is inevitable
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

6. sensitive to the long-lived particle search2.
Detectors in ATLAS
sensitive to the long-lived particle search
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

7. (A) interaction of heavy particles in ATLAS
Electromagnetic interactions
(Slepton, R-hadron)
Ionization losses dominate
(~1/b2 in low b, nearly MIP at b~1)
Nuclear interactions
(R-hadron)
gluino = spectator (reservoir of
kinetic energy)
interaction by p/r/K/p/n cloud low energy deposit = ~1GeV x interactions
charge flipping (~12) implemented
nuclear int. only for R-hadrons
ATLAS Prelim.
Energy loss per int. (GeV)
Geant4
300 GeV/c2 gluino in iron
R-hadron Energy (GeV)
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

8. (A) signature of heavy particles in ATLAS (1)
Inner detectors
slow penetrating heavy particles
TRT (transition radiation tracker)
(36 hits/track) -- good for dE/dx
heavily ionizing
==> can mimic TR
different behavior against muons
low-Pt end heavy particles Ionization
Higt-Pt end muons  TR
Calorimeters
similar longitudinal profile as muons
(R-hadrons) energy deposit - large fluctuation due to nuclear interactions m
g 300GeV/c2 ~
ATLAS Prelim.
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

9. (A) signature of heavy particles in ATLAS (2)
Muon detectors
muon spectrometer systems for TOF (b) meas.
At Level-2 trigger stage, quick calculation available with
RPC(barrel) 3.125ns resolution
In Offline, more time/cpu consuming but precise
MDT(barrel + end cap) ~0.7ns resolution
tracking reco assumes b=1
track fit c2 better for optimized t0
MDT drift time optimization
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

10. (B) detection of non-projecting photons
Readout electrode
Front layer
Middle layer
Back layer
=0
=0.8
Pre-sampler
=1.4 r
granularity (Dh x Df)
EM shower
 60 GeV
EM shower
 60 GeV
EM Cal
Barrel
End-cap
Front layer
0.003 x 0.1
0.00{3,6} x0.1
Middle layer
0.025 x 0.025
Middle
Front G ~
ATLAS ECal reconstruct the h in pointing geometry (from barycenter of the each layer)
good incident angle sensitivity in h, much less sensitivity in f c ~
pointing
non-pointing
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

11. 3. Trigger issues
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

12. (A) general issues of slow particles
large detector has advantage in TOF meas. with Muon system
timing is a critical issue with LHC BC (=25ns)
[ LEP(25ms), Tevatron(396ns), HERA(96ns) ]
only b > 0.5 will be triggered in current BC
offline is fine, but reconstruction is not optimized
25ns
Severer constraint for EndCap
Atlas level-1 muon trigger system
RPC (Barrel subsystem) and
TGC (Endcap subsystem)
RPC r = 6.8, 7.5 and 10m
TGC z = 12.9, 14, 14.5m
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

13. (A) trigger for slow heavy particles (sleptons)
main source of background is inclusive muons
development of physics trigger menu for stau is on-going
(LVL2 trigger) can measure b(=v/c) with RPC TOF (3.1ns resolution)
mass reconstruction is possible at LVL2 (from b, p)
pre-selection of ‘slepton like’ events possible even at the LVL-2
pT>40GeV
M>40GeV
b<0.97
< 2Hz at 1034cm-2s-1
muon
slepton
bm 1nb at pT=40GeV
ATLAS Prelim.
pTm [GeV]
inclusive single muon xsection
L2 mass [GeV]
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

14. (B) trigger for non-pointing photons
event topology much looks like a general SUSY signature
will use ordinary SUSY trigger menu i.e. EtMiss + Jets
feasibility to use the standard photon menu, or its extension is currently under investigation
ATLAS Std. photon trigger menu
menu
condition
2g20i
2 isolated photons pT>20GeV
g60
1 photon pT>60GeV G ~
jet g
missing G ~
ATLAS Prelim.
trigger (EF) efficiency
w.r.t. non-point MC photon (leading pT>60GeV) m
missing g
CAL ID
jet
jet e
dh = h(point) – h(geom)
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

15. 4. Offline reconstruction of the long-lived particles
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

16. (A) Reconstruction of the R-hadrons
Charge flip ID  Muon
[charge flipping]
charge flipping reproduces int. models
[mass determination]
average b obtained for momentum intervals
from the b vs. p correlation  mass
Mass scale determined to O(5-10%)
+ initial charge
- initial charge
ATLAS Prelim.
doubly charged
ATLAS Prelim.
ATLAS Prelim.
mean = 306GeV
= +/- 16GeV
(input: 300GeV)
MDT hits>10
|h |<2.5 b
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

17. (A) Reconstruction of the sleptons
Sleptons are reconstructed as muons
in the current software configuration, lower b (<0.5) lost due to the f info taken from RPC/TGC (using current BC)
inefficiency at 0.5<b<0.8, due to the bad reconstruction c2 from assuming b=1
development of offline muon software is on-going, b measurement O(5-10%)
the plan to recover the next bunch crossing is on discussions
reconstruction (b=1 assumed)
ID loose
(fit c2/ndof < 5
maching c2<20)
ID tight
(fit c2/ndof<2
matching c2<10)
ATLAS Prelim.
efficiency
hep-ph/
mt =100.1GeV
ATLAS Prelim.
m = pmeas/bgmeas 5%
15%
offline b reconstruction
bmeas
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

18. (B) Reconstruction of non-pointing photons
global goal of the non-pointing photon is
the ‘observation’
the ‘decay length’ measurements which directly connects to SUSY scale
efficiency, resolution in terms of “degree of non-pointing”
Efficiency
decay vertex distance from IP(0,0,0) 1m 2m
Rec+ID
Rec
ATLAS Prelim.
Incident angle dependence
Efficiency
Rec+ID
Rec
dh = h(point) – h(geom)
ATLAS Prelim.
resol. < 0.002
dh (Rec -- Truth)
ATLAS Prelim.
dh = h(point) – h(geom)
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

19. (B) Reconstruction of the non-pointing photons
with g only, decay vertex cannot be reconstructed
instead looking at inter section z’
reconstruction is ok, std photon ID has strong dependence
the work on-going for ‘non-pointing ID’ : save the non-pointing while keep the bkg rejection
usage of LAr timing, photon conversion is a next plan
EM shower
 60 GeV G ~ c ~
beam axis z’
ATLAS Prelim.
MC pT>60GeV
Reconstruction
Barrel
only
ATLAS Prelim.
std. IDs
(tight/loose)
recovery of ID-efficiency
(removing h width cut on 2nd layer)
Z’ distribution (cm)
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

20. Summary heavy long-lived particles are predicted in many models
ATLAS is equipped with multiple detector components sensitive to such particle searches
full detector simulations to describe the interactions and decays of these particles are ready
the customized menu for triggers, optimized offline particle reconstructions are being studied and still are developing -- tuned for the early discovery
Let’s fully prepared for the real data
and see what ATLAS will show us from 2008
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

21. reference [p4] hep-ph/0611040, M. Fairbairn et al.
[p7] MoriondQCD05, A. C. Kraan
QCHS-06, R. Mackeprang
[p8] ATLAS SUSY WG, Apr 07, R. Mackeprang
[p9] ATLAS SUSY WG, Sept 04, A. C. Kraan
[p13] ATAS SUSY WG, June 07, H.Nomoto et al.
[p16] flip, mass
[p17] ATAS SUSY WG, June 07, H. Nomoto et al.
hep-ph/ S. Ambrosanio et al.
[p18] ATAS SUSY WG, Sept 07, O. Jinnouchi
[p19] ATAS EG WG, June 07, H. Heywood
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

22. BACKUP SLIDES
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

23. (A) trigger for slow heavy particles (slepton, R-hadron)
GMSB Slepton
M=100GeV
The fate of the hadron-collider exp.
Data cannot be analyzed unless it is triggered !
Heavy penetrating particles are triggered as muons, generally produced in pairs
inclusive high-pT single muon menu
must reach the last trigger stations in time for coincidence
if faster one triggers in right bunch crossing, the other can be reconstructed in offline
pT threshold
Luminosity
20GeV
Low (1033cm-2/s-1)
40GeV
High (1034cm-2/s-1)
rate estimates are on-going discussion, menu not fixed yet
b spectrum
GMSB Slepton
M=100GeV
number of Muon trigger
candidates (b, acceptance)
June 21, 2007
JINNOUCHI (KEK), SUSY 2010's

24. June 21, 2007
JINNOUCHI (KEK), SUSY 2010's