Toward triggering on hard single diffractoinin CMS

Gregory SnowUniversity of Nebraska

Physics with Forward Proton Taggers at the Tevatron and LHCManchester, 14-16 December, 2003

• Presently focusing on hard single diffraction as part of feasibility study on rapgap triggers in CMS, with or without proton tagging

• Signature:

( Gap )

p

pp

• Two or more forward di-jets, rapidity gap accompanying proton which emits Pomeron• Context: Low-medium luminosity ( 1033 cm-2 s-1) where there are significant bunch crossings with a single interaction

p

POMWIG

• Herwig for diffractive interactions• LANL hep-ph/0010303, 20 June 2001 for code download and instructions• Modified deep inelastic scattering process

Positron replacedby Proton

Hard scatter

Pomeron remnant

Proton

Proton remnant

Photon replaced by PomeronFlux(xPom, t), Pomeron structure function (β, Q2)

• Can choose different Pomeron structure (H1, Reggeon, user-defined)• Jets clustered at particle level with cone algorithm (R = 0.7)• Diffractive W, Higgs production available• Double Pomeron collisions also available

Note: In Pomwig, the proton traveling towardnegative always emits the Pomeron in the single

diffractive process

Jets clustered in POMWIG (cone size 0.7)are well separated from outgoing proton

Outgoing protonsometimes seen

as “jet” in POMWIG

Central andforward jets

Bigrapidity gap

xPomeron < 0.02

Jet axis pseudorapidity

Now looking at all POMWIG-generated particles in detail

Fairly highparticle multiplicity

Navg 80

Herwig/PDGParticle ID numbers

Pions, kaons, etc.Antiprotonsantineutrons

Protonsneutrons

Final state event multiplicity

Where are the outgoing protons whichemit the Pomeron?

Beam particle which emitsPomeron is Herwig’s

“positron”, mostly onlyone in final state

Outgoing Protons here

xPomeron < 0.02

Other real positrons

“Positron” pseudorapidity

Number of “positrons” per event

Let’s look where some other particularfinal state particles go

Protons

Number per event

Pseudorapidity

xPomeron < 0.02

Very forwardproton often in

diffractivelyproduced system

Antiprotons

xPomeron < 0.02

Few very forwardantiprotons indiffractively

produced system

Number per event

Pseudorapidity

Let’s look where some other particularfinal state particles go

Pions, charged and neutral

xPomeron < 0.02

Number per event

Pseudorapidity

Pions extend closest tooutgoingproton

Let’s look where some other particularfinal state particles go

Gap moves farther from outgoingproton for smaller xPOM

Considering all particles, which one isclosest to the outgoing proton?

of minimum- particle per event

xPomeron < 0.03

xPomeron < 0.02

xPomeron < 0.0075

Considering all particles, which one isclosest to the outgoing proton?

Both plots xPomeron < 0.02

Energy (GeV) of minimum- particle per event

of minimum- particle per event

HF coveragebetween red lines

• Note: If one requires no hits (rapgap) in inner half of HF (4 < || < 5), one retains 50% trigger efficiency for xPomeron < 0.02. • Greater efficiency requires rapgap in T2/CASTOR region (|| > 5)

Now shift to smaller xPomeron and observegap to outgoing proton widen slightly

Both plots xPomeron < 0.0075

Energy (GeV) of minimum- particle per event

of minimum- particle per event

HF coveragebetween red lines

• Efficiency now about 75% when requiring gap in 4 < || < 5 inner half of HF

Gap efficiency vs. maximum xPom

0

0.2

0.4

0.6

0.8

1

1.2

0 0.01 0.02 0.03 0.04 0.05

Maximum xPom

Fra

ctio

n o

f ev

ents

wit

h g

ap

Eta < -0.5

Eta < -0.4

Eta < -0.3

Gap in HF/T1 and T2/Castor

Gap in inner half HFand T2/Castor

Gap in T2/Castor

Good efficiency using gap trigger for “large” xPom

require gap in inner half of HF/T1plus T2/Castor regions

CMS Very Forward Calorimeters (HF)

HAD (143 cm)

EM (165 cm)

5mm

Finely segmented, fast, scintillating fiber calorimeter

|| = 3

|| = 4

|| = 5

TOTEM T2

CASTOR 9,71 λI

5.4 < |η| < 6.7

HF

TOTEM T2 and CASTOR Region

Comments and Next Steps

• Particle-level output of Pomwig understood and exercised for single hard diffraction; output topologies make sense physically. Simulated rapgap locations matched with physical detectors, selection efficiencies for varying kinematic ranges.

Some Next Steps

• Perform full detector and trigger simulation of POMWIG particle-level events

• POMWIG generator linked to CMS simulation software• Can simulate Level-1 trigger objects output (ET per trigger tower, etc.)

• Extend study to additional processes (double Pomeron, diffractive W/Z, Higgs, …)

• Try combining gap signatures with forward proton in Roman pots for increased power in trigger and offline

• Up to what instantaneous luminosity are rapgap signatures useful? Study gap survival vs. instantaneous luminosity.