monika grothe, forward proton detectors at high luminosities at the lhc, ichep06 1 forward proton...

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 1

Forward Proton Detectors at High Luminosity

at the LHC

Monika GrotheU Turin & U Wisconsin

QCD soft interactions, ICHEP0628 July 2006

Definition: “High luminosity” == luminosities at which event pile-up is significantIn the presence of pile-up, rapidity gap selection is no longer possible, diffractive events can only be selected with the help of forward proton taggers

Physics motivation given in two previous talks in this session, J. Forshawon diffractive Higgs and P.Bartalini on underlying event physicsWill concentrate on the specific aspects of the FP420 R&D project

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 2

Why detect diffractively scattered protons at the LHC at high luminosity ?

Selection rules: central system is JPC = 0++ (to good approx)

I.e. a particle produced with proton tags has known quantum numbers

Excellent mass resolution (~GeV) from the protons, independent of decay products of the central system

For light (~120 GeV) Higgs: Proton tagging improves S/B for SM Higgs dramatically CEP may be the discovery channel in certain regions in MSSM

CP quantum numbers and CP violation in Higgs sector directly measurable from azimuthal asymmetry of the protons

Central exclusive production pp pXp: Discover a light (~120 GeV) Higgs

Vacuum quantum numbers“Double Pomeron exchange”

shields color charge ofother two gluons

In addition: Rich QCD programLooking at the proton in QCD through a lens that filters out everything but the vacuum quantum numbers: measure diff PDFs, learn about parton correlations via GPDs, quantify soft multiple scattering effects via diff factorization breaking, ...

In addition: Rich program of gamma-gamma mediated processes

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 3

Where to put the detectors ?

=0 (beam)

=0.002

=0.015

In CEP: 1 2 s = M2

With √s=14TeV, M=120GeVon average:

0.009 1%

With nominal LHC optics:

For slightly off-momentum protons, the LHC beam line with its magnets is essentially a spectrometer If diffractively scattered protons are bent sufficiently to leave the beam envelope, but little enough to remain within the circumference of the beam pipe, they can be detected by means of detectors inserted into the beam-pipe and approaching the beam envelope as closely as possible

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 4

Where to put the detectors (II) ?

1 2 s = M2

With √s=14TeV, M=120GeVon average:

0.009 1%

Nominal LHC beam optics* =0.5m: Lumi 1033-1034cm-2s-1 @220m: 0.02 < < 0.2 @420m: 0.002 < < 0.02

CEP of Higgs:

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 5

The FP420 R&D project

Proposal to the LHCC in June 2005: CERN-LHCC-2005-025“FP420: An R&D Proposal to Investigate the Feasibility of Installing Proton Tagging Detectors in the 220m Region at LHC”Signed by 29 institutes from 11 countries - more in the process of joining

The aim of FP420 is to install high precision silicon tracking and fast timing detectors close to the beams at 420m from ATLAS and / or CMS

“The LHCC acknowledges the scientific merit of the FP420 physics program and the interest in its exploring its feasibility.” - LHCC

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 6

How to integrate detectors into the cold section of the LHC

Turin / Cockcroft Institute / CERN

420m from the IP is in the cold section of the LHCModify LHC Arc Termination Modulesfor cold-to-warm transition such that detectors canbe operated at ~ room temperature

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 7

How to move detectors close to the beam

Turin / Louvain / Helsinki

Movable beam-pipe (pipelets)with detector stations attachedMove detectors toward beam envelopeonce beam is stable

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 8

Which technology for the detectors ?3D edgeless Silicon detectors:Edgeless, i.e. distance to the beam envelope can be minimizedRadiation hard, can withstand 5 years at 1035 cm-2 s-1 Use ATLAS pixel chip (rad hard) for readout

Brunel / Stanford

3D Silicon in CERN testbeam this summer

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 9

Silicon Detector StationsManchester / Mullard Space Science Lab

7.2 mm x 24mm

(7.2 x 8 mm2 sensors)

2-3 detector stations with 8 layers each

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 10

What resolution does one achieve ?

Si pitch 40-50 mx and y orientation(x) ~ (y) ~15 m

Glasgow / Manchester

S/B for 120GeV Higgs -> b bbar depends critically on mass window around signal peak

CMS IPATLAS IP

CEP of Higgs:

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 11

Why also fast timing detectors ?25% of the inclusive QCD cross section at the LHC is diffractive eventsAverage number of pile-up events overlaid to any hard scatter 7 @ 2x1033 cm-2s-1, 35 @ 1x1034 cm-2s-1 Average number of protons per PU event on either side of the IP: 0.012 @420m 0.055 @220m

Example: H(120GeV)-> b bbar @ 2x1033 cm-2s-1

Coincidence of non-diffractive dijet production with either 2 single-diffractive PU events or one double-Pomeron exchange PU eventis the most important background sourcePreliminary MC studies with Pythia and Exhume indicate S/BPU~O(1/100).

Fast timing detectors that can determine whether the protons seen at 420mcame from the same vertex as the hard scatter within better than 3mm:Would reduce S/BPU ~ O(1)

For diffraction at the LHC:Fake diffractive events with protons from PU is major background source

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 12

Fast timing detectors

QUARTIC (U Texas-Arlington):Cherenkov medium is fused Silica

Protons

PMT

Lens? (focusing)

MirrorCerenkov medium (ethane)

~ 15 cm~ 5 cm

(Flat or Spherical?)

Aluminium pump

Injection of gas (~ atmospheric pressure)

Ejection of gas

~ 10 cm

GASTOF (UC Louvain)Cherenkov medium is a gas

Micro channel plate photo-multiplier tubes (MCP-PMT) were successfullyemployed in building a Cherenkov-light based Time-of-Flight detector with atime resolution of ~10ps (see NIM A 528(2004) 763) Would translate in z-vertex resolution of better than 3mm

Two prototypes being worked on; both in FERMILAB test beam this summer

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 13

Why also detectors at ~220m from the IP ?

detectorsat ~220m

FP420

xL=P’/Pbeam=

At nominal LHC optics (*=0.5m):

diffractive peak

Acceptance:Detectors at 420m and 220m are complementary in their coverageDetectors at 220m enhance acceptance for diffractively produced masses of high values

Trigger:420m is too far away from IP for detector signals to be used in the L1 trigger of ATLAS or CMS,i.e. needs to trigger either with the central apparatus alone or with detectors closer to the IP:H(120GeV) b bbar: 2-jet trigger: thresholds too high for any of signal events to pass 2-jet + 220m trigger: lower the jet trigger thresholds and still respect the L1 bandwidth limits Gains 10% of signal efficiency, in addition to the 10% achievable with the L1 muon trigger alone

~220/240m region only suitable region <420m with space for detectors

=0 (beam)

=0.002=0.015

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 14

TOTEM:

•An approved experiment at LHC for measuring tot and elastic, uses same IP as CMS

•TOTEM has RP detectors at ~220m from the CMS IP

•TOTEM’s trigger and DAQ system will be integrated with those of CMS , i.e. common data taking CMS + TOTEM possible

CMS and TOTEM are in the process ofdefining a joint diffractive physics program

TOTEM/CMS low luminosity program:Few days of special optics running with *=90m @ 1031 cm-2s-1, better coverage for diff events compared to *=0.5m

CMS/TOTEM high luminosity program unclear:•Want to operate 220m detectors routinely as part of CMS data taking•Longevity of TOTEM Si detectors limited by radiation damage to O(1) fb-1

•Replacement with radiation hard detectors ?

Detectors at 220m from the IP: TOTEM/CMS

TOTEM

t: 4-momentum transfer at proton vertex

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 15

Detectors at 220m from the IP: ATLAS

ATLAS groups Saclay, Prague, Cracow and Stony Brook consider placing detectors at ~220m away from the ATLAS IP:

Place two horizontal RP stations around 220m Run at high luminosity with collision optics Si detectors studied Cerenkov counters for timing considered extension of the ATLAS luminosity program, complementary to FP420

0<ξ<0.18

Detectors of2x2 cm2 wouldhave acceptance:• up to ~0.16 • down to ~0.016 at 20 beam

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 16

Summary

Measuring diffractive events at the LHC at luminosities > 1032 cm-2s-1 requires forward proton tagging capabilities; rapidity gap selection is no longer possible because of the presence of pile-up events

The FP420 R&D project aims at providing the appropriate means:•Rad-hard Si detectors in the cold region of the LHC at 420m•Fast timing detectors to reject fake diff events (protons from pile-up)

Ways of complementing with detectors at 220m (trigger, acceptance for highmasses) under study/discussion in both ATLAS and CMS/TOTEM

FP420 would add real discovery potential to ATLAS / CMS

FP420 R&D fully funded for next 12 months (~1000K CHF)Technical design proposal by Feb 2007 to ATLAS and CMSIf accepted by ATLAS and/or CMS, Technical Design Report(s) could go to LHCC in spring 2007Detector installation could take place during first long LHC break (~2008/2009)

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 17

Backup

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 18

Proposal submitted to LHCC last June

58 authors29 institutes

Authors from:ATLAS, CMS, TOTEMCDF, D0, LHC

Close collaboration with ATLAS and CMS

Contacts: B. Cox (Manchester, ATLAS) A. De Roeck (CERN, CMS)

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 19

The physics interest of CEP

MSSM: intense coupling regime

Intense-coupling regime of the MSSM: Mh~MA ~ MH ~ O(100GeV): their coupling to, WW*, ZZ* strongly suppressed discovery very challenging at the LHC

Cross section of two scalar (0+) Higgs bosons enhanced compared to SM Higgs

Production of pseudo-scalar (O-) Higgs suppressed because of JZ selection rule

Superior missing mass resolution from tagged protons allows to separate h, H

Spin-partity of Higgs can be determined from the azimuthal angles between the two tagged protons (recall JZ rule only approximate)

CEP as discovery channel

see Kaidalov et al, hep-ph/0307064, hep-ph/0311023

100 fb

1 fb

120 140

10 fb

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 20

“3-way mixing” scenario of CP-violating MSSM: the 3 neutral Higgs bosons are nearly degenerate, mix strongly and have masses close to 120 GeV

Superior mass resolution from taggedproton allows disentangling theHiggs bosons by measuring their production line shape

Explicit CP-violation in Higgs sector manifests itself as asymmetry in the azimuthal distribution of tagged protons (interference of P- and P+ amplitudes) (Khoze et al., hep-ph/0401078)

CEP as CP and line-shape analyzer !

The physics interest of CEP

MSSM: CP violation in the Higgs sector

J. Ellis et al., hep-ph/0502251

120 124

Hadronic level crosssection when Higgs bosons decay into b bbar, for differentvalues of mixing angles

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 21

The physics interest of CEP

MSSM: intense coupling regime

100 fb

1 fb

Azimuthal angle between outgoing protons sensitive to Higgs spin-parity: JP=0+ vs JP=0- (recall JZ selection rule only approximate)

Kaidalov et al.,hep-ph/0307064

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 22

FP420 alignment

• @ 1 x 1033 cm-2 s-1 expect ~ 100 - events / fill with standard trigger thresholds

• Simulations indicate precision is better than necessary (theoretical limit is LHC beam energy uncertainty , 0 = 0.77 GeV ~ 50 microns)