1. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 1 Silvia Ochesanu Thomas Maes, Hans Van Havermaet University of Antwerpen October 26, 2007 CASTOR TRIGGER STUDY

2. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 2 Outline Background rate and signal efficiency –Drell –Yan process –Forward jets Rapidity Gap with CASTOR/HF. Conclusions

3. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 3 Generator study Why a generator study? CASTOR simulation in CMSSW was completed October 9 th, 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

4. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 4 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+ l-l-

5. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 5 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

6. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 6 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)

7. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 7 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.

8. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 8 Drell Yan :background rate ( L=10 32 cm -2 s -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

9. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 9 Drell Yan :background rate ( L=10 33 cm -2 s -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

10. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 10 Drell Yan :signal efficiency -> 20% efficienty in x Bj < 5 x 10 -7 for DY (no pile -up) -> lower efficiency in x Bj for pile –up events L1 condition:2 φ-sector with Eem>E 0 ● Eem > 300 GeV ● Ehad < 5 GeV

11. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 11 Lower threshold to study the nature 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 a charged hadron Background study

12. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 12 Forward jets qg → qg gg → gg Forward jets are mainly produced through: ● Total cross section for events with highest E T jet in CASTOR (from PYTHIA): 465 μb ● Trigger: ask for large hadronic energy deposit Forward jets

13. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 13 Forward jets: background rate ● L1 condition: − 1 calorimeter with Etot>E 0 − 2-3 adjacent φ-sectors with Etot>E0 ● O(1kHz) rate possible for Etot > 3000 GeV (corresponding to E T ≳ 15GeV) ● further strategies to be studied (e.g. For HLT) − require highest E T jet to be in CASTOR − cut on maximum E T of central jets

14. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 14 Forward jets: signal range x Bj distribution for events with highest E T jet (E T >5 GeV) in CASTOR: ● Weak correlation between highest E T jet rapidity and xBj ● Efficiency study suffers from low statistics

15. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 15 Rapidity Gap ● Diffractive production of jets: pp → p jet jet p → possible to trigger on E T >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| 40 GeV ( 2.6 kHz CMS Note-2007/002) L = 1032 cm-2 s-1 → multiply rate by 10! 1-jet 2-jet

16. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 16 Level 1 condition: 2 jets with |η| 40 GeV) ; Etot (single sided HF/CASTOR) < E 0 ); Single Rapidity Gap ( dijet+gap) with CASTOR/HF

17. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 17 Level 1 condition: 2 jets with |η| 40 GeV) ; Etot (single sided HF/CASTOR) < E 0 ); Double Rapidity Gap with CASTOR/HF gap+dijet+gap

18. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 18 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

19. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 19

20. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 20

21. Trigger study with CASTOR – Forward and Diffractive Meeting, Antwerpen –October 26, 2007 – Silvia Ocheşanu 21