Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 1 Forward Proton Detectors at High Luminosity at the LHC Monika Grothe U Turin & U Wisconsin QCD soft interactions, ICHEP06 28 July 2006 Definition: “High luminosity” == luminosities at which event pile-up is significant  In 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. Forshaw on diffractive Higgs and P.Bartalini on underlying event physics Will 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 J PC = 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 of other two gluons In addition: Rich QCD program Looking 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 = M 2 With √s=14TeV, M=120GeV on average:    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 = M 2 With √s=14TeV, M=120GeV on average:    1% Nominal LHC beam optics  * =0.5m: Lumi cm -2 s 0.02 <  < <  < 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 “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 LHC Modify LHC Arc Termination Modules for cold-to-warm transition such that detectors can be 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 attached Move detectors toward beam envelope once 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 minimized  Radiation hard, can withstand 5 years at 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 Stations Manchester / Mullard Space Science Lab 7.2 mm x 24mm (7.2 x 8 mm 2 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  m x 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 IP ATLAS 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 events Average number of pile-up events overlaid to any hard scatter 2x10 33 cm -2 s -1, 1x10 34 cm -2 s -1 Average number of protons per PU event on either side of the IP: Example: H(120GeV)-> b 2x10 33 cm -2 s -1 Coincidence of non-diffractive dijet production with  either 2 single-diffractive PU events  or one double-Pomeron exchange PU event is the most important background source Preliminary MC studies with Pythia and Exhume indicate S/B PU ~O(1/100). Fast timing detectors that can determine whether the protons seen at 420m came from the same vertex as the hard scatter within better than 3mm: Would reduce S/B PU ~ 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) Mirror Cerenkov 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 successfully employed in building a Cherenkov-light based Time-of-Flight detector with a time 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 ? detectors at ~220m FP420 x L =P’/P beam =  At nominal LHC optics (*=0.5m): diffractive peak Acceptance: Detectors at 420m and 220m are complementary in their  coverage Detectors 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 of defining a joint diffractive physics program TOTEM/CMS low luminosity program: Few days of special optics running with cm -2 s -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 of 2x2 cm 2 would have 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 > cm -2 s -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 high masses) 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 CMS  If accepted by ATLAS and/or CMS, Technical Design Report(s) could go to LHCC in spring 2007  Detector 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 authors 29 institutes Authors from: ATLAS, CMS, TOTEM CDF, 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: M h ~M A ~ M H ~ 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 J Z 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 J Z rule only approximate)  CEP as discovery channel see Kaidalov et al, hep-ph/ , hep-ph/ fb 1 fb  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 tagged proton allows disentangling the Higgs 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/ )  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/ Hadronic level cross section when Higgs bosons decay into b bbar, for different values 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: J P =0 + vs J P =0 - (recall J Z selection rule only approximate)     Kaidalov et al., hep-ph/

Monika Grothe, Forward Proton Detectors at High Luminosities at the LHC, ICHEP06 22 FP420 1 x 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)