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

Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu21