A Measurement of the ATLAS Di-Muon Trigger Efficiency in Proton-Proton Collision at $\sqrt{s}=7$ TeV

1.4 MB·English

by  A. Picazio

A measurement of the ATLAS di-muon trigger
efficiency in proton-proton collisions at = 7 TeV.
s
Francesco A. Conventi on behalf of the ATLAS Collaboration
€
Abstract– The B physics programme of the ATLAS experiment LHC bunch crossing rate of 40 MHz. The first level trigger,
includes the study of the production cross sections, searches for Level 1 (L1), is hardware based. The L1 receives its inputs
rare B decays signatures which are sensitive to new physics at the from the Calorimeter, Muon and additional forward detectors
TeV energy scale and measurements of CP violation effects in B- and provides a decision with a latency of less than 2.5 µs.
events, such as B 0→J /ψ φ and B 0 →J /ψ K 0 .
S d S Note that Muon trigger produces Region of Interest (RoI), too:
The key to the detection of these B signals in ATLAS is to achieve
these geometrical information are then used by Level 2 trigger
a high trigger efficiency for low-p di-muon events, keeping an
T to deeply inspect the events for their acceptation.
acceptable trigger rate. ATLAS developed two approaches for
The Level 2 (L2) and the third level of trigger (so called Event
triggering on di-muon events from a resonance such as J/ψ and
ϒ. The first approach is to start from a di-muon signature at Filter, EF), collectively referred to as the High Level Trigger
Level 1, whilst the second is based on a dedicated Level 2 or HLT, are based on software algorithms analyzing data on
algorithm. These trigger scheme has been studied using collision large computing farms. A schematic diagram of the ATLAS
data at √s= 7 TeV. Results are shown and compared to Monte trigger is shown in Fig. 1.
Carlo predictions. ATLAS prepared a program for measurements of production
cross sections both of b-hadrons and Onia in central proton-
proton collisions. Dedicated triggers based on muon, di-muon
I. INTRODUCTION or electron signatures are designed to accommodate large
The ATLAS AdetMecetoar s[1u] ries ma √meunltti-opufrpthosee aApTpaLraAtuSs wDitih- Ma uosntatTisrtiicgs gweithr eEarflfiy cdiaetan. Acyfteirn a fPewro ptbo-1n o-f P7TroeVto cnollision
cylindrical geCoomleltirsy ioconvearitng aslm=ost7 thTee Ventire solid angle data have been taken at the LHC, ATLAS has been able to
around the interaction point. Closest to the beam pipe are start probing the new energy regime with decays of the psi and
silicon basedA TtTraILckIOinPgI CdAeZteIOctaoorsn baenhdal fsotfrathwe-AtuTbLeA StrCaonlsliatbioorna tionUpsilon families of mesons into pairs of muons, the open
radiation detectors, located inside a superconducting solenoid charm and open beauty sector. With higher statistics collected
De´partementdephysiquenucle´aireetcorpusculaire,Universite´ deGene`ve,1211Geneva4,Switzerland
that provides a 2T magnetic field. Outside the solenoid, fine- in the 2010 and 2011 B-hadron properties via measurement of
granularity LAr electromagnetic (EM) calorimeters with an exclusive B-lifetimes and CP violation with study of the
accordion geometry proAvbisdter accotv.eTrhaegeB upphy tsoic s|ηp|r o<g r3a.m2m. eAonf tihreoAnT-LASexexcpleursimiveen tdiencclauyde Bssm→easJu/ψre mφe nhtasvoef pbreoedunc tsitoundcireodss.
scintillating hadronic cseacltoiornims,esetaerrc heexstfeonrdrasr etoB- d|ηec|a y<s i1gn.7at uwrehsiwleh ichaCrerusecnisailt ivteo toalnle wofp hthyseiscse amtteheasTuerVemeneenrgtys sacarele tahnde performance of
4
1-04 cc012oopvpereirn ga nthde rLeAgiro nte 1c.h7osn tf<uotd lh|oiηeegss|e yo<B f i3Cssi.P g2nu.v asiIloesnlda itnt ihoAiennT veLffetAherScyet sifseointnrowdBac-caeahrvpidee nvretrese,aggsihuioiocgnhnh, atrsigBgti0shderee→e nffimtiJcf/uiiψeconφanctya inotfdronir,gB lg0doawes→r -swp TJea/dlnψli- dKma s0su.t ohTtnehh eeevo kefienfnytlsni,tneower t hhdimelsetduteekotceenetcpo tiirrone ngpcoernfsotrrmucatniocne aanndd
1 an acceptable trigger rate. ATLAS developed two septarraactekainppgr.o aches for triggering on di-muon events from
0 32.2 < |η| < 4.5, copperr easnodna ntucensgssutcehna sLJA/ψr acnadloUrpismiloente(rΥs) .pTrhoevfiidrset approachistostartfromadi-muontriggerselectedatLevel-1
2
C-1 mneasurements of the wEhMile athneds echoanddriosnbiacs√ edshoonwdeedrisc.a teTdhLee vmel-u2oanlg orithms.Theperformanceforthesetriggershasbeenstudied
O1 sapectrometer consistsu siongf cotlhlisrieoen dastuapatercso=nd7uTcetVincgo lletcoterdoiind2a0l 11.
Q-PRmber20 mT27 Juabgense t(sM wDitTh1) pIurnepct ritosoid o|nuη c|t rt<aioc k2ni.n4g a pnrdo vCidaethdo bdye MStorinpi toCrheadm Dbreirfst
A ( CSC) in the very forward region. Triggering for muons is
Dve ]
L-No pxrovided usinTghe RATesLiAstSivdee tePcltaotre[ 1C]ihsaammbueltris- pu(RrpPoCse)a pipna rbataursrewli th
T reegion and Tahicny lGinadpri cCalhgaemombeertrsy (cToGveCri)n gina lmthoes tftohreweanrtdir eresogliiodna n-
A8 -
2 upp to |η| < 2g.l4e. aTrohuen dAthTeLiAnteSr adcteitoenctpoorisn t.pCrolovsiedset tiontphuet bteoa mthpei pe
theree levels oafr ethsieli ctoringgbaesre dsytsratecmkin gthadte tepcrtoovrsidaensd fsatsrat wf-itlutebreintrga n-
chapabilities ansidti ocnaprtaudrieat ieovnendteste ocfto irnst,elroecsatt etod pinhsyidseicas wsuiptehr choingdhu ct-
[
ing solenoid that provides a 2T magnetic field. Outside
e fficiency. The LHC started single-beam operations in 2008
1 the solenoid, fine-granularity LAr electromagnetic (EM)
and achieved its first proton-proton (pp) collisions in 2009. In
v calorimeterswithanaccordiongeometryprovidecoverage
2010, the LHC began colliding protons on protons at a centre
2 up to |η| < 3.2. An iron-scintillating hadronic calorimeter
o5f mass eneregxyte nodfs 7to T|ηe|V<. 1D.7urwinhgil eac opprpoelronangdedL Aorpetercahtinoonlo giny is
27010, ATLAuSs edcoinllethceteedn d4ca5p rpebg-i1o nofc ovdeartian gwthiethr egluiomni1n.o7s<itie|ηs| <
5
ranging from3 1.20.2I7 ncmthe-2sv-1e rtyo f2o r.w1a0r3d2 cremgi-2osn-1,. 3A.2t t<he|η t|im<e4 .o5f, cthopisp er
.
c1onference, AaTndLAtuSng hstaedn cLoAllreccatelodr iamne taedrsdiptiroovniadle 1m feba-1s uinre m20e1nt1s, of
0 the EM and hadronic showers. The Muon Spectrometer
with instantaneous luminosities exceeding 1033 cm-2s-1. The
2 (MS) consists of three superconducting toroidal magnets
A1TLAS Trigger System is designed to reduce the output
withprecisiontrackingprovidedbyMonitoredDriftTubes Fig. F1.i gA.1 s.cAhesmchaetimc aotfi cthoef tAheTLAATLSA TSriTggriegrg SerySstyesmtesm asndan idtsi tisntienrtfear-ces to the
sv:torage rate t(oM ~D2T0)0u pHtoz |η(|a<bo2u.4t a3n0d0C MathBo/dseecS)t rifproCmha manb eirnsi(tCiaSl C) detecftaocre asntdo rtheaeddoeutte cstyosrteamnds. readoutsystems.
Xi i n t h e v e r y f o r w a r d r e g i o n. Triggering for muons is pro-
vided using Resistive Plate Chambers (RPC) in barrel re-

r gionandThinGapChambers(TGC)intheforwardregion
a
upto|η| < 2.4.TheATLASdetectorsprovideinputtothe which run on a large computing farm close to the detec-
tor. A schematic diagram of the ATLAS trigger is shown
three levels of the trigger system that provides fast filter-
inFig.1.
ing capabilities and capture events of interest to physics
with high efficiency. The ATLAS Trigger System is de- The LHC started single-beam operations in 2008 and
signedtoreducetheoutputstoragerateto 200Hz(about achieveditsfirstproton-proton(pp)collisionsin2009.In
300 MB/sec) from an initial LHC bunch crossing rate of 2010, the LHC began colliding protons on protons at a
40MHz.Thefirstleveltrigger,Level-1(L1),ishardware centre of mass energy of 7 TeV. During a prolonged op-
based. The L1 receives its inputs from the Calorimeter, eration in 2010, ATLAS collected 45 pb−1 of data with
Muonandadditionalforwarddetectorsandprovidesade- luminositiesrangingfrom1027cm−2s−1to2.1032cm−2s−1.
cisionwithalatencyoflessthan2.5µs.So-calledRegions At the time of this conference, ATLAS had collected 4.8
of Interest (RoIs) are defined around the L1 signatures; fb−1 in 2011, with instantaneous luminosities exceeding
theL2algorithms(whichalsoaccessinnertrackinginfor- 3.65×1033cm−2s−1.
mation) operate only in these regions, reducing the time ATLAS prepared a programme for measurements of
taken for the L2 decision to be made. The L2 and third- production cross sections both of B-hadrons and Onia in
level Event Filter (EF) together comprise the High Level centralproton-protoncollisions.Dedicatedtriggersbased
Trigger(HLT),andthesearebasedonsoftwarealgorithms onmuon,di-muonorelectronsignaturesweredesignedto
accommodate the large statistics provided by LHC. With
a e-mail:[email protected] highstatisticscollectedin2010and2011B-hadronproper-
II. ATLAS DIMUON TRIGGER FOR B-PHYSICS III. TRIGGER EFFICIENCY FOR DIMUON TRIGGER
The output rate of the Level 1 trigger at a luminosity of 1033
cm−2 s−1 is expected to contain about 20 kHz of events where Cross section measurements require a good understanding of
one muon passed the transverse momentum (p ) threshold of 6 the efficiency of the event selections. A precise understanding
T
GeV. In 2010 data taking has been possible to include even of the trigger efficiency is crucial and we must have a strategy
lower p thresholds, down to the lowest threshold achievable for measuring it from data with high precision.
T
in the Level 1 hardware. At Level 2 this rate of events must be We develop an alternative method based on Bayes theorem
reduced to 1-2 kHz, of which 5-10% are available for channels which not require the knowledge of the angular distribution of
of interest only to B-physics. Currently this goal is achieved the decay muons from the J /ψ or ϒ and can be applied on any
for Level 2 muon triggers by first confirming that a muon over data stream without any bias on the efficiency measurement
the nominal threshold is reconstructed in the muon even if the data stream has been selected by a muon trigger
spectrometer (MS), and then confirming that there is a item.
matching track in the Inner detector (ID). This selection In this approach the efficiency for a di-muon trigger item can
criterion removes many muons from K and π decays, but does be written as:
not by itself produce the required rate reduction. To achieve
the required rate p thresholds need to be raised and many ε(T )ε(T |T )
T ε(T )= 1µ 2µ 1µ
interesting b events are likely to be filtered out. To achieve 2µ ε(T |T )
high efficiency for B-signals, specific di-muon trigger 1µ 2µ

algorithms have been developed which achieve high efficiency
where T is the di-muon trigger item, T is the efficiency for
at L2. Since most of the relevant processes involve a di-muon 2µ 1µ
(either directly from the B-hadron in the case of rare decays, a single muon trigger item (for example the EventFilter
or via a J/psi or an upsilon) a significant proportion of the d€ec ision with a pT threshold of 4 GeV/c), ε( T2µ| T1µ)
heavy flavour and quarkonia decays falling in the detector is the conditional probability for the di-muon trigger given the
acceptance can be captured by ATLAS. single muon trigger and ε( T1µ| T2µ) represent the conditional
There are two possible approaches at Level 2 for selecting di- probability for single muon trigger given the di-muon trigger.
muon events from a resonance such as J /ψ and ϒ. The first The latter terms ( ε( T1µ| T2µ) ) is equal to 1 for topological
approach is to start from a selected di-muon trigger at Level-1. trigger and close to 1 for the “TrigDimuon trigger”.
In this approach each muon is confirmed separately, and the The T terms have been obtained with the Tag and Probe
1µ
invariant mass of the pair can then be calculated and a mass method with an uncertainty of O(1%) using 2010 data as
window cut applied. We will refer to this trigger as the described in [3] and shown in fig. 3. The conditional
“topological di-muon trigger”. probabilities could be measured directly from data without any
An alternative approach is to start with a Level-1 single muon bias. This new approach has been tested on a large Monte
trigger and search for the second muon track inside a wide η-φ Carlo sample first showing very encouraging results and then
region of the Inner detector and then extrapolating the track to applied on 2010 collision data.
the muon spectrometer to tag muon tracks. Since this method
does not explicitly require the second muon at Level-1, it has IV. DIMUON TRIGGER EFFICIENCY ON 2010 DATA
an advantage for reconstructing J /ψ even if the second muon
The 2010 data sample corresponding to an integrated
has a p lower than the lowest Level-1 threshold. We will refer
T luminosity of 38 pb－1 has been used to measure the di-muon
to this trigger as the “TrigDimuon trigger”. The basic idea for
trigger efficiency for two trigger item, namely
this two approaches (topological and TrigDi-muon) are
EPJWebofCEoFn_fmerue4n_cJepssimumu (TrigDimuon trigger item operating in the
illustrated in Fig. 2.
invariant mass region 2.8÷4.3 GeV/c2) and

EF_2mu4_Jpsimumu (topological trigger item operating in the
invAarpiarnetc ismeaussn dreergsitoann d2in.8g÷o4.f3t hGeetVri/gcg2)e.r Beffiotchi etnricgygeisr eistesmen -
opteiaraltefos rina twheid ienvraarniganet omfaasnsa rlaynsgees ,[e2s.8p÷e4c.i5a]l lyGecVro/css2 wsehcetrieo n
measurements.Adata-drivenmethodofestimatingthedi-
the larger contribution to the di-muon final state come from
muontriggerefficiency,basedonBayesTheorem,hasbeen
the J/ψ →µµ decays.
developed.Itisindependentoftheangulardistributionof
The method described previously has been used for the two
tritghgeers iitgenmasl umsiunogn fsorf rthoem sitnhgeleJ t/rψiggoerr Υite,man tdhec an be applied
theo nEvaennytFdialttear sdtreecaismionw withitohu at pan ythbreisahsooldn othf e4 eGffieVci/ecn. cymea-
T
Thseu rdei-mmeunotn, etrvigengeirf etfhfiecidenactay sdterpeeanmdsh oans pbTe, eηn asnedl eϕc toefd bbotyh a
mumounos nintsriidgeg tehrei tdeim-m.uIonnt hpiasira. pInp rfoiga.c 4h tthhee teriffiggceire nefcfyicfieonrcaiedsi -
FFiigg. .22: .AA scshcehmematiac tipcicptuircet udrie-mduio-nm turiogngetrr, igtogpeorlo,gtiocpalo ltorigggicera l(lterfitg) gaenrd fomr tuhoe nEtFr_igmgue4r_iJtepmsimcuamnub eitwemri twteintha rse:spect to the higher (a)
(s eleefdte)da bnyd a sseinegdlee dLebvyel-a1 sminugonle (rLig1htm). uon(right). and lower pT muon (b) (cid:79)inside the di-m(cid:79)uon pair a1re shown.
Thahse bpeeernf osrtmudainecde u soifn gb o2t0h1 a0p cporlolaiscihoens d faotar atht e√ sd i=- m7 uToenV t.r igger D(traitaan ghlaev(cid:15)se,( TMb2eµCe)n s= acmo(cid:15)m(pTlpe1a µrh)eads tboe et(cid:15)hn(e Tg J2eµ/nψ|eT r→1aµt)eµdµ wMitCh(cid:15) ( asT ip1gµTn| aTclu2 µst a)emqupal(el1 )
tiesandCPviolation(viatheexclusivedecayB → J/ψφ) to 2.5 GeV/c on both decay muons). For the results shown in
s where(cid:15)(T )isthedi-muontriggeritemefficiency,(cid:15)(T )
are being studied. Crucial to all of these measurements is Fig. 4.a the 2dµata efficiency evaluated at plateau (for muo1nµ
theperformanceofthemuontriggersandtheofflinemuon pTia>sm8 tpGhleeeVeth)ffi eisc Ei0eF.n7c8dy7e cf±io s0rio.0an0s5wi nwigthhlielaem tphueo MnthrCter iseghfgfoielcdrieinotecfym4 isG( f0oe.Vr78/e6cx )-,
reconstructionandidentification,aswellastheInnerDe- T
(cid:15)(T |T ) is the conditional probability for the di-muon
tector(ID)performance. 2µ 1µ
trigger given the single muon trigger and (cid:15)(T |T ) rep-
1µ 2µ
resentstheconditionalprobabilityforsinglemuontrigger
given the di-muon trigger. The latter term ((cid:15)(T |T )) is
1µ 2µ
2 ATLAS Di-Muon Trigger for B-Physics equaltounityfortopologicaltriggerandclosetounityfor
theTrigDiMuontrigger.The(cid:15)(T )termhasbeenobtained
1µ
The output rate of the L1 trigger at a luminosity of 1033 with the Tag and Probe method using 2011 data with the
cm−2s−1 is expected to contain about 20 kHz of events same procedure described in [3]. The conditional proba-
whereonemuonexceededthetransversemomentum(p ) bilities can be measured directly from data - in particu-
threshold of 6 GeV/c. In 2010 it has been possible to iTn- lar,theefficiency(cid:15)(T2µ|T1µ)correspondstothenumberof
cludeevenlowerpT thresholds,downtothelowestthresh- eventsforwhichbothT2µ andT1µ fired,dividedbytheto-
old achievable in the Level 1 hardware. At L2 this rate talnumberofeventsthatpassedtheT1µ triggerthreshold.
of events must be reduced to 1-2 kHz, of which 5-10 % This approach for evaluating (cid:15)(T2µ) was tested on a large
are available for channels of interest only to B-physics. Monte Carlo sample and on 2010 collision data showing
Currently this goal is achieved for L2 muon triggers by verygoodagreementbetweendataandMonteCarlosim-
first confirming that a muon over the nominal threshold ulation[4].Inthisworktheresultsobtainedon2011colli-
isreconstructedintheMS,andthenconfirmingthatthere siondataareshown.
is a matching track in the ID. This selection criterion re-
movesmanymuonsfromKandπdecays,butdoesnotby
itself produce the required rate reduction. To achieve the 3 Di-Muon Trigger Efficiency on 2011 Data
requiredrate p thresholdsneedtoberaisedandmanyin-
T
teresting B-events are likely to be filtered out. To achieve The2011datasampleusedtomeasurethedi-muontrigger
high efficiency for these signals at L2, specific di-muon efficiency for the trigger item EF 2mu4 Jpsimumu corre-
triggeralgorithmsweredeveloped.Sincemostoftherele- spondstoanintegratedluminosityof1.25 fb−1.Thistopo-
vantprocessesinvolveadi-muon(eitherdirectlyfromthe logical trigger item operates in the invariant mass range
B-hadron in the case of rare decays, or via a J/ψ, ψ(2s), [2.8−4.5]GeV/c2 wherethelargercontributiontothedi-
oran Υ)a significantproportionofthe heavyflavourand muonfinalstatecomesfromthe J/ψ → µ+µ− decaysand,
quarkoniadecaysfallinginthedetectoracceptancecanbe asalreadymentioned,itrequiresthatbothmuonspassthe
captured by ATLAS. There are two possible approaches EF mu4trigger.Themethoddescribedpreviouslywasde-
atL2forselectingdi-muoneventsfromaresonancesuch ployed for this trigger item, using the single trigger the
as J/φandΥ.Thefirstistostartfromaselecteddi-muon EF decision with a pT threshold of 4 GeV/c. In Fig. 3
triggeratL1.Inthisapproacheachmuonisconfirmedsep- the efficiency of the di-muon trigger EF 2mu4 Jpsimumu
arately,andtheinvariantmassofthepaircanthenbecal- with respect to J/ψ pT is shown, evaluated on candidate
culated and a mass window cut applied. This trigger will J/ψ→µ+µ−eventswithrespecttoofflinecombinedmuon
bereferredtoasthe“topologicaldi-muontrigger”.Anal- reconstruction.Fromthisplotthetriggerefficiencyforthe
ternativeapproachistostartwithaL1singlemuontrigger physicssignatureselectedbythisitemcanbeunderstood.
andsearchforthesecondmuontrackinsideawideη−φ Thestatisticaluncertaintyisdominatedbythelargeprescale
regionoftheIDandthenextrapolatingthetracktotheMS factorappliedontheEF mu4triggeritem.Inprinciple,the
to tag muon tracks. Since this method does not explicitly di-muontriggerefficiencydependson pT,ηandφofboth
requirethesecondmuonatL1,ithasanadvantageforre- muons inside the di-muon pair and on the opening angle
constructing J/ψevenifthesecondmuonhasa p lower betweenthetwomuons(∆R),definedas:
T
thanthelowestL1threshold.Thistriggerwillbereferred (cid:113)
to as the “TrigDiMuon’. The basic ideas for this two ap- ∆R= ∆φ2+∆η2 (2)
proaches (topological and TrigDiMuon) are illustrated in
Fig.2. InFig.4theefficiencyofthetriggerEF 2mu4 Jpsimumu
The performance of the topological di-muon trigger withrespecttothe p ofthehigher p muonintheJ/ψ→
√ T T
approach was studied using 2011 data at s = 7 TeV. µ+µ− candidatepairisshown.Theefficiencywithrespect
Trigger Efficiency EF_2mu4_Jpsimumu
Trigger Notreviewed,forinternalcirculationonlyEEfficiencyffi000000......c456789 iency EAFTL_AS2 PrmelimHuinaar4dyro_nJCpollsidiemrPhuysimcsSNotreviewed,forinternalcirculationonlyuym posEfficiencyium000000......45678920A1T1LAS Preliminary |D"amtua1 ,2m0u121|<2.4
0.3 Data 2011 0.3
|" |<2.4
0.2 mu1,mu2 0.2
0.1 0.1
00 2 4 6 8 10 12 14 16 18 20 22 00.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
pT(J/!) [GeV] ! R
Fcaignudried a1t:e EJFwf/fi(cid:2)iigcthi.e (cid:3)3nrce.µysEp µoeffi fec ctvthieetenon tdcsJ yiw-/mψiotuhfo prtnTehs,se pteredivgcia-gtl muetoaru tooEeFnfdf_li2tonrnmieg ugcc4oae_mnrJdbEpiidsFniaemt2deum mmJuFu/u4 iψovgnsJ u pJ→rsr/eie(cid:2)cmo µ4nu +psm:tµ Tr u−ueEcvftafioilcunia. e tFwenidcigty h.o n6or e.fs Epthefficect idetoni-ctmyheuoof∆nRtsh e(tarindggi-gumleaurro EnseFpt_rai2rgamgteiuorn4E)_FoJfp2msthimue4utwmJpous immvsuu om(cid:1)nusR of the two muons
eventswithrespecttoofflinecombinedmuonreconestvrauclutiaonte.d in withe vraeluspateedcto tno coanffdliidnaete coJ/mψb→ineµd+ µm−ueovne nrtescwointhstrreuscpteiocnt.t o of-
The EF_2mu4_Jpsimumu trigger item requires that both muons pass the EF_mu4 trigger.
The EF_2mu4_Jpflsiinmeucmomu btirnigedgmeru oitnermec roenqsturuircetiso nt.hat both muons pass the EF_mu4 trigger.
The events have been selected applying a cut of pT>4GeV on the two combined muons.
TrDaitga cgoreresrpo nEdinfg ftoi cani ientengracteyd luEminFosit_y o2f 1m.25u fb(cid:4)41 t_aTkJehne p ine vtsheein 2mts0 1h1au v(demo tbs)e. uen selected applying a cut of pT>4GeV on the two combined muons.
TEhFe_ mstua4t istrtiicgagle Notreviewed,forinternalcirculationonlyurn icteermtaEfficiency. inty00000..... 56789is dominated by the lAaTrLgAeS p Prreeslcimailnea fryaIsdTtcnrahtui ogemterhg paestetopl aers p ett liihiitlsseeeet diccm c sotoaem.mn ld atiu hnlinelgn c at4Ammv renfaiaerrgdCmroatsgiasTmsaeoeu itrrnno nhritttgeefoh yc ffiDmdtet lhhi iuacsbeMJe isas/edd ssuJn(cid:2)ii oe/-oorcdmmapny n(cid:3)niousoinsigtno.afe eµnmttB heµt(asred2 i.ydgt .Ie8obgetsp yech-otra a htl4esyhoeffi.e ogb5ar iec)lcene iaameGdnrln geadcthhepyiVa-e psmb/p ldoibcrue2teerodh oes ntcnfpthooat edrralmi eetgltova egfleparaealogsrorculegpootrorenege rdi ctt c(cid:1)hhoataoeenplRtpr iilbsie uadt i okoinnn e ttomh e ad tEaicFta_alm euf4fe ct
0.4
2011datasamplecollectedbytheATLASdetectoratLHC
0.3 √
at s=7TeV.
0.2 Data 2011
0.1 |!|<2.4
0
0 2 4 6 8 10 12 14 16 18 20 22
References
p(µ) [GeV]
T
Figure 2: EffFiciige.ncy4 o.f thEeffi dci-iemnucoyns troifggerth EeF_2dmi-um4u_oJpnsimturmigug evrs muiotenm p (the1 h.igThheer pAtT LAS Collaboration, The ATLAS experiment at
muon) evaluaEteFd2 omnu c4anJpdsidimautem Ju/(cid:2)wi t(cid:3)h µrµes peevcetntsto wimthu roenspepcTt t(oth oefflhinigeh ceormT bined tmheuonC ERN Large Hadron Collider, JINST 3 (2008)
reconstructionrp.e T spmecutotno)offlevianleuactoemdboinnedcamnduiodnatreecJo/nψstru→ctioµn+.µ− events with S08003
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The EF_2mu4_Jpsimumu trigger item requires that both muons pass the EF_mu4 trigger.
theATLASExperiment,arXiv:0901.0512CERN-OPEN-
The events have been selected applying a cut of pT>4GeV on the two combined muons.
Trigger Efficiency EF_2mu4_Jpsimumu
2008-020
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0.3 http://cdsweb.cern.ch/record/1401937
0.2
0.1
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-3 -2 -1 0 1 2 3
q(µ)*!(µ)
Figure 3: EfFfiicgi.en5c.yE offif ctiheen cdyi-omfutohnes dtrii-gmgueorn EFtr_ig2gmeru4E_FJp2smimuu4mJup svims mumuoun q*η(the higher
with respect to muon η∗q (the higher p muon) evaluated on
pt muon) evaluated on candidate J/(cid:2) (cid:3)µµ eventsT with respect to offline combined muon
candidate J/ψ → µ+µ− eventswithrespecttoofflinecombined
reconstruction.
muonreconstruction.
The EF_2mu4_Jpsimumu trigger item requires that both muons pass the EF_mu4 trigger.
The events have been selected applying a cut of pT>4GeV on the two combined muons.
Data corresponding to an integrated luminosity of 1.25 fb(cid:4)1 taken in the 2011 (dots).
The statistical uncertainty is dominated by the large prescale factor applied on the
EF_mu4 triggtoert hiteepmr.o ductofηandthechargeofthehigher p muonis
T
showninFig.5.Thelattervariableisusefultoobservethe
effectontheefficiencyduetothetoroidalmagneticfieldin
theforwardregionofthedetectorthataffectmainlylow-p
T
muons. Finally, in Fig. 6 the trigger efficiency is reported
withrespecttothe∆Rofthemuons.Thedropatlarge∆R
isakinematicaleffectduetothesmallmassoftheJ/ψ.