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

Search for long-lived particles Search for long-lived particles at ATLAS at ATLAS

Osamu JINNOUCHI (KEK)Osamu JINNOUCHI (KEK)on behalf of ATLAS SUSY (exotic) groupon behalf of ATLAS SUSY (exotic) group

Supersymmetry in 2010’sSupersymmetry in 2010’s at Hokkaido-university at Hokkaido-university

June 21, 2007June 21, 2007

Long-lived particles search in ATLASLong-lived particles search in ATLAS

● Long-lived particles search (long enough to pass Long-lived particles search (long enough to pass through detector) and their discovery --would directly through detector) and their discovery --would directly address many important open questions to particle address many important open questions to particle physicsphysics Dark matter in the universeDark matter in the universe Hierarchy problemHierarchy problem Extra dimensionExtra dimension flavor questionflavor question charge quantization charge quantization ... etc... etc

● If such particles produced at LHC, Can we(=ATLAS) If such particles produced at LHC, Can we(=ATLAS) effectively detect them ?effectively detect them ?

June 21, 2007 JINNOUCHI (KEK), SUSY 2010's 2

It is important to know and develop the detection ability of ATLAS for such particles

It is important to know and develop the detection ability of ATLAS for such particles

outlineoutline

1.1. IntroductionIntroduction

2.2. sensible detectorssensible detectors in ATLAS for the in ATLAS for the searchsearch

3.3. trigger issues trigger issues

4.4. reconstruction of long-lived particlesreconstruction of long-lived particles

5.5. summarysummary


long-lived particles in the context of SUSY scenarioslong-lived particles in the context of SUSY scenarios

many candidates on the market (already many many candidates on the market (already many in SUSY scenarios only!)in SUSY scenarios only!)

GMSBGMSBNLSP decays to LSP only via the gravitational NLSP decays to LSP only via the gravitational coupling, thus could be long-livedcoupling, thus could be long-lived

Non-pointing Photons Non-pointing Photons (decay on flight)(decay on flight)

Penetrating SleptonsPenetrating Sleptons

Split SUSY Split SUSY (in MSSM scenario)(in MSSM scenario)Squarks are heavy, suppressing Gluino decays Squarks are heavy, suppressing Gluino decays

hence Gluino could be long-livedhence Gluino could be long-lived

Colored heavy particle (R-hadrons)Colored heavy particle (R-hadrons)

AMSBAMSB and are mass de-generateand are mass de-generate

chargino could be long-lived chargino could be long-lived (decay on flight : Kink (decay on flight : Kink track) track)

June 21, 2007 4

hep-ph/0611040

many possible different event topologiesATLAS could cover with multi-purpose detectorsmany possible different event topologiesATLAS could cover with multi-purpose detectors

~Â10 ! ° + ~G (Nmes =1)

~̀! ! `+ ~G (Nmes >1)long

R = ~gq¹q;~gqqq;etc

~Â01 ~Â§1

possible event topologies, detection strategiespossible event topologies, detection strategies


Regardless of the models, categorized by the event signaturesRegardless of the models, categorized by the event signatures

1.1. Such particles are generally produced in pairsSuch particles are generally produced in pairs 1) direct production (small 1) direct production (small ) 2) cascade decay products (SUSY) ) 2) cascade decay products (SUSY)

2.2. Decay length?Decay length?

3.3. Charge (Electric? magnetic? color?) Charge (Electric? magnetic? color?) different detector response different detector response

detailed study using Geant4 full detector simulation is inevitable detailed study using Geant4 full detector simulation is inevitable

(A) Sleptons, R-hadrons (A) Sleptons, R-hadrons (heavy slow particles)(heavy slow particles)

large ionization energy loss nuclear int. (R-hadron case) delay (TOF) reconstructed in Muon chamber

(B) Long-lived neutralino(B) Long-lived neutralino (Non-pointing photon)(Non-pointing photon) decay vertex is somewhere in the inner tracker volume

mSugra likemSugra like

kink trackkink track(on plan!)(on plan!)

~̀! ~G`

R-hadrons

~Â01 ! ~G°

heavy slow heavy slow particlesparticles

non-pointingnon-pointingphotonsphotons

(~Â§1 ! ~Â01+¼§ )

(A)

(B)

2.2.

Detectors in ATLASDetectors in ATLASsensitive to the long-lived particle searchsensitive to the long-lived particle search


(A) interaction of heavy particles in ATLAS(A) interaction of heavy particles in ATLAS


nuclear int. only for R-hadrons

Geant4

ATLAS Prelim.

300 GeV/c300 GeV/c22 gluino in iron gluino in iron

Electromagnetic interactionsElectromagnetic interactions ((SleptonSlepton, , R-hadronR-hadron))

Ionization losses dominateIonization losses dominate

(~1/(~1/22 in low in low , nearly MIP at , nearly MIP at ~1)~1)

Nuclear interactionsNuclear interactions (R-hadron)(R-hadron)

gluino = spectator (reservoir of gluino = spectator (reservoir of kinetic energy)kinetic energy) interaction by interaction by ///K/p/n cloud low energy /K/p/n cloud low energy

deposit deposit = ~1GeV x 10-15 = ~1GeV x 10-15 interactionsinteractions charge flipping (~12) implementedcharge flipping (~12) implemented

R-hadron Energy (GeV)

En

erg

y l

os

s p

er

int.

(G

eV

)

(A) signature of heavy particles in ATLAS (1) (A) signature of heavy particles in ATLAS (1)


● Inner detectorsInner detectors slow penetrating heavy particlesslow penetrating heavy particles TRT (TRT (transition radiation trackertransition radiation tracker))

(36 hits/track) -- good for dE/dx (36 hits/track) -- good for dE/dx heavily ionizingheavily ionizing

==> can mimic TR==> can mimic TR different behavior against muonsdifferent behavior against muons

low-Pt end heavy particleslow-Pt end heavy particles Ionization Ionization

Higt-Pt end muons Higt-Pt end muons TR TR

● CalorimetersCalorimeters similar longitudinal profile as muonssimilar longitudinal profile as muons (R-hadrons) energy deposit - large (R-hadrons) energy deposit - large

fluctuation due to nuclear interactionsfluctuation due to nuclear interactions

g 300GeV/c2~

ATLAS Prelim.

● Muon detectorsMuon detectors muon spectrometer systems for TOF (muon spectrometer systems for TOF () meas.) meas.

At Level-2 trigger stage, quick calculation available withAt Level-2 trigger stage, quick calculation available with RPC(barrel) RPC(barrel) 3.125ns resolution3.125ns resolution

In Offline, more time/cpu consuming but preciseIn Offline, more time/cpu consuming but precise MDT(barrel + end cap) ~0.7ns resolution MDT(barrel + end cap) ~0.7ns resolution tracking reco assumes tracking reco assumes =1=1 track fit track fit 22 better for optimized t better for optimized t00


~̀or R-hadron track

best track ¯t with ¯ 6= 1radius with¯ = 1

(A) signature of heavy particles in ATLAS (2) (A) signature of heavy particles in ATLAS (2)

MDT drift time optimization

Readout Readout electrodeelectrode

Front layerMiddle layer

Back layer=0 =0.8

Pre-sampler

(B) detection of non-projecting photons(B) detection of non-projecting photons

● ATLAS ECal reconstruct the ATLAS ECal reconstruct the in pointing in pointing geometry (from barycenter of the each layer)geometry (from barycenter of the each layer)

● good incident angle sensitivity in good incident angle sensitivity in , much , much less sensitivity in less sensitivity in


=1.4

MiddleMiddle

FrontFront

r

0

EM showerEM shower 60 GeV60 GeV

~

EM showerEM shower 60 GeV60 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 0.025 x 0.025

granularity ( x )

G~

´r ec = ´geom ´r ec 6= ´geom

pointing non-pointing

3.3.

Trigger issuesTrigger issues


(A) general issues of slow particles (A) general issues of slow particles ● large detector has advantage in TOF meas. with large detector has advantage in TOF meas. with

Muon systemMuon system

● timing is a critical issue with timing is a critical issue with LHC BC (=25ns)LHC BC (=25ns)

[ [ LEP(25LEP(25s), Tevatron(396ns), HERA(96ns) ]s), Tevatron(396ns), HERA(96ns) ]

● only only 0.5 will be triggered in current BC 0.5 will be triggered in current BC

● offline is fine, but reconstruction is not optimizedoffline is fine, but reconstruction is not optimized


Atlas level-1 muon trigger systemRPCRPC (Barrel subsystem) and TGCTGC (Endcap subsystem)

Atlas level-1 muon trigger systemRPCRPC (Barrel subsystem) and TGCTGC (Endcap subsystem)

25ns

Severer constraint for EndCap

RPC r = 6.8, 7.5 and 10mTGC z = 12.9, 14, 14.5m


● main source of background is inclusive muonsmain source of background is inclusive muons● development of physics trigger menu for stau is on-goingdevelopment of physics trigger menu for stau is on-going● (LVL2 trigger) can measure (LVL2 trigger) can measure (=v/c) with RPC TOF (3.1ns (=v/c) with RPC TOF (3.1ns

resolution)resolution)● mass reconstruction is possible at LVL2 (from mass reconstruction is possible at LVL2 (from , p), p)● pre-selection of pre-selection of ‘slepton like’ ‘slepton like’ events possible even at the LVL-2events possible even at the LVL-2

L2 mass [GeV]

slepton

muon

(A) trigger for slow heavy particles (sleptons)(A) trigger for slow heavy particles (sleptons)

b 1nb at pT=40GeV

inclusive single muon xsectionpT [GeV]

pT>40GeVM>40GeV<0.97

< 2Hz at 1034cm-2s-1

ATLAS Prelim.

(B) trigger for non-pointing photons(B) trigger for non-pointing photons● event topology much looks like a general SUSY signatureevent topology much looks like a general SUSY signature● will use ordinary SUSY trigger menu i.e. EtMiss + Jetswill use ordinary SUSY trigger menu i.e. EtMiss + Jets● feasibility to use the standard photon menu, or its feasibility to use the standard photon menu, or its

extension is currently under investigationextension is currently under investigation


jet

jet jete

G~

G~

CALCAL IDID

missing

missing

menu condition2g20i 2 isolated photons pT>20GeV

g60 1 photon pT>60GeV

ATLAS Prelim.

ATLAS Std. photon trigger menu

dd = = (point) – (point) – (geom)(geom)

trigger (EF) efficiencyw.r.t. non-point MC photon (leading pT>60GeV)

4.4.

Offline reconstruction of Offline reconstruction of

the long-lived particlesthe long-lived particles


(A) Reconstruction of the R-hadrons(A) Reconstruction of the R-hadrons

[charge flipping][charge flipping]● charge flipping reproduces int. modelscharge flipping reproduces int. models

[mass determination][mass determination]● average average obtained for momentum obtained for momentum

intervalsintervals● from the from the vs. p correlation vs. p correlation mass mass● Mass scale determined to O(5-10%)Mass scale determined to O(5-10%)

mean = 306GeV= +/- 16GeV(input: 300GeV)

June 21, 2007 16JINNOUCHI (KEK), SUSY 2010's

MDT hits>10||<2.5

ATLAS Prelim.

ATLAS Prelim.

+ initial charge

- initial charge

Charge flip ID Muon

doubly charged

ATLAS Prelim.

(A) Reconstruction of the sleptons(A) Reconstruction of the sleptons● Sleptons are reconstructed as muonsSleptons are reconstructed as muons● in the current software configuration, lower in the current software configuration, lower

(<0.5) lost due to the (<0.5) lost due to the info taken from info taken from RPC/TGC (using current BC)RPC/TGC (using current BC)

● inefficiency at 0.5<inefficiency at 0.5<<0.8, due to the bad <0.8, due to the bad reconstruction reconstruction 22 from assuming from assuming =1=1

● development of offline muon software is on-development of offline muon software is on-going, going, measurement measurement OO(5-10%) (5-10%)

● the plan to recover the next bunch the plan to recover the next bunch crossing is on discussions crossing is on discussions


offline reconstruction

reconstruction (=1 assumed)

ID loose (fit 2/ndof < 5maching 2<20)

ID tight(fit 2/ndof<2matching 2<10)

effi

cien

cy

hep-ph/0010081m =100.1GeV

measmeas

m =

pm

= p

mea

sm

eas//

mea

sm

eas

5%5% 15%15%

ATLAS Prelim.

ATLAS Prelim.

(B) Reconstruction of non-pointing photons(B) Reconstruction of non-pointing photons● global goal of the non-pointing global goal of the non-pointing

photon is photon is the the ‘observation’ ‘observation’ the the ‘decay length’ ‘decay length’ measurements measurements

which directly connects to SUSY which directly connects to SUSY scalescale

● efficiency, resolution in terms of efficiency, resolution in terms of “degree of non-pointing” “degree of non-pointing”


Eff

icie

ncy

Eff

icie

ncy

Rec+IDRec+ID

RecRec

Eff

icie

ncy

Eff

icie

ncy

decay vertex distance from IP(0,0,0)decay vertex distance from IP(0,0,0)

1m1m 2m2m

Rec+IDRec+ID

RecRec

dd = = (point) – (point) – (geom)(geom)dd = = (point) – (point) – (geom)(geom)

ATLAS Prelim.

ATLAS Prelim.

ATLAS Prelim.

d

(Rec

--

Tru

th)

resol. < 0.002

Incident angle dependenceIncident angle dependence

(B) Reconstruction of the non-pointing photons(B) Reconstruction of the non-pointing photons● with with only, decay vertex cannot be reconstructed only, decay vertex cannot be reconstructed● instead looking at inter section instead looking at inter section z’z’ ● reconstruction is ok, std photon ID has strong reconstruction is ok, std photon ID has strong

dependence dependence ● the work on-going for the work on-going for ‘non-pointing ID’ ‘non-pointing ID’ : save the : save the

non-pointing while keep the bkg rejectionnon-pointing while keep the bkg rejection● usage of LAr timing, photon conversion is a next usage of LAr timing, photon conversion is a next plan plan


ATLAS Prelim.

EM showerEM shower 60 GeV60 GeV

~G~

beam axis

z’z’0

MC pT>60GeV

Reconstruction

std. IDs(tight/loose)

Z’ distribution (cm)

recovery of ID-efficiency(removing width cut on 2nd layer)

ATLAS Prelim.Barrelonly

SummarySummary● heavy long-lived particles are predicted in many modelsheavy long-lived particles are predicted in many models● ATLAS is equipped with multiple detector components ATLAS is equipped with multiple detector components

sensitive to such particle searchessensitive to such particle searches● full detector simulations to describe the interactions and full detector simulations to describe the interactions and

decays of these particles are readydecays of these particles are ready● the customized menu for triggers, optimized offline the customized menu for triggers, optimized offline

particle reconstructions particle reconstructions are being studied and still are are being studied and still are developingdeveloping -- tuned for the early discovery -- tuned for the early discovery


Let’s fully prepared for the real data and see what ATLAS will show us from 2008

referencereference

● [p4] hep-ph/0611040, M. Fairbairn et al.[p4] hep-ph/0611040, M. Fairbairn et al.

● [p7] MoriondQCD05, A. C. Kraan[p7] MoriondQCD05, A. C. Kraan

QCHS-06, R. Mackeprang QCHS-06, R. Mackeprang

● [p8] ATLAS SUSY WG, Apr 07, R. Mackeprang[p8] ATLAS SUSY WG, Apr 07, R. Mackeprang

● [p9] ATLAS SUSY WG, Sept 04, A. C. Kraan[p9] ATLAS SUSY WG, Sept 04, A. C. Kraan

● [p13] ATAS SUSY WG, June 07, H.Nomoto et al.[p13] ATAS SUSY WG, June 07, H.Nomoto et al.

● [p16] flip, mass[p16] flip, mass

● [p17] ATAS SUSY WG, June 07, H. Nomoto et al.[p17] ATAS SUSY WG, June 07, H. Nomoto et al.

hep-ph/0010081 S. Ambrosanio et al.hep-ph/0010081 S. Ambrosanio et al.

● [p18] ATAS SUSY WG, Sept 07, O. Jinnouchi[p18] ATAS SUSY WG, Sept 07, O. Jinnouchi

● [p19] ATAS EG WG, June 07, H. Heywood[p19] ATAS EG WG, June 07, H. Heywood


BACKUP SLIDESBACKUP SLIDES


(A) trigger for slow heavy particles (slepton, R-hadron)(A) trigger for slow heavy particles (slepton, R-hadron)

The fate of the hadron-colliderThe fate of the hadron-collider exp. exp.

Data cannot be analyzed unless it is triggered !Data cannot be analyzed unless it is triggered !

● Heavy penetrating particles are triggered as Heavy penetrating particles are triggered as muons, muons, generally produced in pairsgenerally produced in pairs inclusive high-pT single muon menuinclusive high-pT single muon menu

must reach the last trigger stations in time for must reach the last trigger stations in time for coincidencecoincidence

if faster one triggers in right bunch crossing, the if faster one triggers in right bunch crossing, the other can be reconstructed in offlineother can be reconstructed in offline


GMSB Slepton M=100GeV

spectrum

number of Muon triggercandidates (, acceptance)

tar r ival < t¹ +25nsec

GMSB Slepton M=100GeV

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


Documents

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