Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 –...
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Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu1
Silvia OchesanuThomas Maes, Hans Van Havermaet
University of Antwerpen October 26, 2007
CASTOR TRIGGER STUDY
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu2
Outline
• Background rate and signal efficiency
– Drell –Yan process
– Forward jets
• Rapidity Gap with CASTOR/HF.
• Conclusions
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu3
Generator studyWhy a generator study?
• CASTOR simulation in CMSSW was completed October 9th, 2007
and was not available for this study
Is a generator level study good enough?
– the jet rate obtained by a generator level version of the L1 jet finding
algorithm is very similar to that presented in the CMS L1 Trigger TDR
→we can rely on the additional rate reduction provided by rapidity gap
conditions
– the CASTOR energy resolution is very good:
• resolution of 1 readout unit: σE ≈ 10 → 20 GeV for E = 0 → 5000 GeV
→the effect of smearing across the trigger threshold will be limited
– problem: electromagnetic/hadronic energy separation
→a simulation study is still needed
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu4
if x- ≪ x+ → access to low-xBjorken proton structure;
→ at LHC (for Q 1 GeV and ≳ η = 8): xBjorken 10-8≳
→ xBjorken decreases by factor 10 for each 2 units in rapidity
Drell Yan Process
p
p
l+
l-
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu5
CASTOR cherenkov calorimeter● Electromagnetic and hadronic sections● 16-fold segmentation in φ● 2(em)+12(had)-fold segmentation in z(readout units within one φ-sector will be grouped together for the trigger)● No segmentation in η
CASTOR Detector
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu6
Monte Carlo Generator
• PYTHIA(6.402) used in standard mode (CTEQ 5M1 pdf)
– background: minimum bias QCD (MSEL = 2)
= 101.4 mb
– signal:
● select Drell Yan process (electron –positron pairs) channel, switching off gamma decays to anything except e+e-;
= 88.19 nb (2.6 nb with e+e- in CASTOR)
~ 26 million events for 10 fb-
● QCD jets (MSEL = 1)
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu7
Level 1 Trigger variables
Definition of the variables:• Electromagnetic energy :e+, e- and • Hadronic energy :energy sum of other particles• Hits (yes/no): charged particles present
All variables calculated in 16 azimuthal segments
Additional variables can be used (HLT/offline) to reduces the background:• charged multiplicity• theta , phi of charged particles• invariant mass of lepton pair
Trigger :
Ask for energy deposit in the electromagnetic part of CASTOR above threshold in combination with a veto for energy deposits in the hadronic part of the calorimeter.
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu8
Drell Yan :background rate (L=1032cm-2s-1)
L1 condition:• 2 φ-sector with Eem>E0● Eem > 300 GeV ~ 30kHz● Eem > 600 GeV ~ 0.6 kHz
Additional conditions:• + hadronic energy <5 GeV; ~ 3kHz ~ 0.07kHz• +At least one charged particle (hits) in T2 in front of electromagnetic segment <0.01kHz
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu9
Drell Yan :background rate (L=1033cm-2s-1)
L1 condition:• 2 φ-sector with Eem>E0
● Eem > 300 GeV ~ 3000kHz
● Eem > 600 GeV ~ 80 kHz
Additional conditions:• + hadronic energy <5 GeV;
~60kHz
~1kHz• At least one charged particle
(hits) in T2 in front of
electromagnetic segment
<0.01kHz
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu10
Drell Yan :signal efficiency
-> 20% efficienty in xBj< 5 x 10-7 for DY (no pile -up)-> lower efficiency in xBj for pile –up events
L1 condition:2 φ-sector with Eem>E0
● Eem > 300 GeV ● Ehad < 5 GeV
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu11
Lower threshold to study thenature of background processes (-> high rates)
• Elastic and diffractive processes hardly contribute
• Background comes from QCD 2->2 processes, mostly gg ->gg
• Background consist of forward
energetic π0 in coincidence with acharged hadron
Background study
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu12
qg → qg gg → gg
Forward jets are mainly produced through:
● Total cross section for events withhighest ET jet in CASTOR (from PYTHIA):
465 μb
● Trigger: ask for large hadronic energy deposit
Forward jets
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu13
Forward jets: background rate
● L1 condition:
− 1 calorimeter with Etot>E0
− 2-3 adjacent φ-sectors with Etot>E0
● O(1kHz) rate possible for Etot > 3000 GeV
(corresponding to ET 15GeV)≳● further strategies to be
studied (e.g. For HLT)
− require highest ET jet to be in CASTOR
− cut on maximum ET of central jets
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu14
Forward jets: signal rangexBj distribution for events with highest ET jet (ET>5 GeV) in CASTOR:
● Weak correlation between highest ET jet rapidity and xBj● Efficiency study suffers from low statistics
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu15
Rapidity Gap
● Diffractive production of jets:
pp → p jet jet p
→ possible to trigger on ET >40 GeV
dijets with proton tag in L1 trigger
[CMS Note-2007/002]
● No proton tags available on L1 in 2008
→ need for single/double gap triggers
with CASTOR and/or HF
→ check L1 jet rates on
generator level 2.4 kHz for dijets
with |η| < 2.5 and ET > 40 GeV
( 2.6 kHz CMS Note-2007/002)
L = 1032 cm-2 s-1
→ multiply rate by 10!
1-jet
2-jet
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu16
Level 1 condition:• 2 jets with |η| < 2.5 and ET > 40 GeV) ;• Etot (single sided HF/CASTOR) < E0);
Single Rapidity Gap (dijet+gap)
with CASTOR/HF
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu17
Level 1 condition:• 2 jets with |η| < 2.5 and ET > 40 GeV) ;• Etot (single sided HF/CASTOR) < E0);
Double Rapidity Gap with CASTOR/HFgap+dijet+gap
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu18
Conclusions• generator study of L1 rate and efficiencies for Drell –Yan , forward jets at
large Δη, single and double hard diffraction
• Several trigger strategies are feasible using CASTOR alone• Additional information from T2 can reduce L1 trigger rates
• Still a lot of problem with background• Full simulation study is need it
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu19
Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu20