Diffractive Higgs searches The Pomeron as little helper

Diffractive Higgs searches: The Pomeron as little helper in tracking down the Higgs ? The FP 420 project Monika Grothe U Turin/ U Wisconsin Johns-Hopkins workshop Heidelberg August 2007 � Why ? How in principle ? What’s available already ? Specific challenges ? Current status ? Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

� Why bother with diffraction at the LHC ? � Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 2

Suppose you want to detect a light SM Higgs (say MH=120 Ge. V) at the LHC. . . shields color charge of other two gluons Vacuum quantum numbers “Double Pomeron exchange” SM Higgs with ~120 Ge. V: gg H, H b bbar highest BR But signal swamped by gg jet Best bet with CMS: H Central exclusive production pp p. Xp Suppression of gg jet because of selection rules forcing central system to be (to good approx) JPC = 0++ Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

Diffraction as tool for discovery physics: Central exclusive production pp p. Xp Experimental assets of central exclusive production: Selection rules: central system is JPC = 0++ (to good approx) I. e. a particle produced with proton tags has known quantum # Excellent mass resolution achievable from protons, independent of decay products of X in central detector: “CEP as superior lineshape analyser” CP quantum numbers and CP violation in Higgs sector directly measurable from azimuthal asymmetry of the protons: “CEP as spin-parity analyzer” Proton tagging improves S/B for SM Higgs dramatically Case in point: pp p. Hp with H(120 Ge. V) b bbar In non-diffractive production hopeless, signal swamped by QCD di-jet background CEP may be discovery channel in certain regions in MSSM where the Xsection can be much larger than in SM Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

Central exclusive production: Standard Model light Higgs Standard Model Higgs Generator studies with detector cuts b jets : MH = 120 Ge. V; = 2 fb (uncertainty factor ~ 2. 5) MH = 140 Ge. V; = 0. 7 fb H MH = 120 Ge. V : 11 signal / O(10) background in 30 fb-1 with detector cuts Note: This H decay channel is impossible in non-CEP production ! WW* : MH = 120 Ge. V; = 0. 4 fb MH = 140 Ge. V; = 1 fb MH = 140 Ge. V : 8 signal / O(3) background in 30 fb-1 with detector cuts Note: Use semi-leptonic decays for measurement Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 5

Central exclusive production: Observation at Fermilab Search for exclusive ü 3 candidate events found ü 1 (+2/-1) predicted from Ex. Hu. ME MC* hep-ex/0707237 Same type of diagrams as for Higgs validation of KMR model ! Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 6

� How go about measuring central exclusive production ? � Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 7

Measuring central exclusive production: Experimental signature Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 8

Measuring central exclusive production: Principle of measurement Diffractively scattered protons survive interaction intact and lose only a small fraction of their initial momentum in the process Needed: Proton spectrometer using the LHC beam magnets Detect protons that are very slightly off-momentum wrt beam protons, i. e. detection needed inside of beam pipe beam dipole p’ roman pots Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

Measuring central exclusive production: Where to put the detectors beam dipole p’ roman pots With nominal LHC optics: 1 2 s = M 2 =0. 015 =0. 002 With √s=14 Te. V, M=120 Ge. V on average: =0 (beam) 0. 009 1% fractional momentum loss of the proton Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

Measuring central exclusive production: Where to put the detectors (II) 1 2 s = M 2 With √s=14 Te. V, M=120 Ge. V on average: 0. 009 1% Nominal LHC beam optics Low * (0. 5 m): Lumi 1033 -1034 cm-2 s-1 @220 m: 0. 02 < < 0. 2 @420 m: 0. 002 < < 0. 02 Detectors at 420 m • complement acceptance of 220 m detectors • needed to extend acceptance down to low values, i. e. low MHiggs Detectors closer to IP, e. g. ~220 m • optimize acceptance (tails of distr. ) • can be used in L 1 trigger, while 420 m too far away for detector signals to reach L 1 trigger within latency Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

� Current experimental situation at the ATLAS and CMS IP’s: ALFA and TOTEM Possible extension of the ATLAS/CMS baseline detectors: FP 420 Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 12

d (ep e. Xp)/dx. L [nb] Existing proton tagging detectors TOTEM det @420 data points from ZEUS x. L=P’/Pbeam= 1 - CMS IP: TOTEM ATLAS IP: ALFA § Approved experiment for tot, elastic meas. § Detectors to determine absolute luminosity by way of measuring elastic scattering in Coulomb interference region § Uses same IP as CMS § Roman-pot housed Silicon tracking detectors at 180 m and 220 m from IP § TOTEM’s trigger/DAQ system will be integrated with those of CMS , i. e. common data taking CMS + TOTEM possible § However, operation at highest LHC lumi would require rad hard upgrade of Totem Si § Approved part of ATLAS experiment § Roman-pot housed scintillating fiber detectors at 240 m from IP § Operation at nominal LHC lumi requires rad-hard upgrade - option subject of an R&D effort by several ATLAS groups Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

The FP 420 R&D project The aim of FP 420 is to install high precision silicon tracking and fast timing detectors close to the beams at 420 m from ATLAS and / or CMS Proposal to the LHCC in June 2005: CERN-LHCC-2005 -025 “FP 420: An R&D Proposal to Investigate the Feasibility of Installing Proton Tagging Detectors in the 220 m Region at LHC” Signed by 29 institutes from 11 countries “The LHCC acknowledges the scientific merit of the FP 420 physics program and the interest in its exploring its feasibility. ” - LHCC Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

FP 420 project: How to integrate detectors into the cold section of the LHC scattered protons emerge here 420 m 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 Turin / Cockcroft Institute / CERN Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

FP 420: How to move detectors close to the beam Movable beam-pipe with detector stations attached Move detectors toward beam envelope once beam is stable Beam position monitor Silicon detector box Gastof or Quartic Turin / Louvain / Helsinki Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

FP 420: Which technology for the detectors 3 D edgeless Silicon detectors: §Edgeless, i. e. distance to beam envelope can be minimized §Radiation hard, can withstand 5 years at 1035 cm-2 s-1 §Use ATLAS pixel chip (rad hard) for readout Active edges: the edge is itself an electrode, so dead volume at the edge < 5. § Prototype in CERN testbeams 2006 and 2007 § Technology is candidate for ATLAS tracker SLHC upgrade Electrodes are processed inside the detector bulk instead of being implanted on the wafer’s surface. Manchester / Stanford Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

FP 420 project: Silicon Detector Stations Manchester / Mullard Space Science Lab 3 detector stations with 8 layers each 7. 2 mm x 24 mm 8 mm Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

FP 420 project: Fast timing detectors Micro channel plate photo-multiplier tubes (MCP-PMT) were successfully employed in building Cherenkov-light based TOF detector with resolution of ~10 ps (NIM A 528(2004) 763) Would translate in z-vertex resolution of better than 3 mm Needed to veto protons from pile-up events Two technologies; both in FERMILAB test beams 2006 and 2007 Ejection of gas Injection of gas (~ atmospheric pressure) pump Aluminium proton Protons Cherenkov light ~ 5 cm Cerenkov medium (ethane) Mirror (Flat or Spherical? ) ~ 15 cm ~ 10 cm Lens? (focusing) PMT QUARTIC (U Texas-Arlington): Cherenkov medium is fused Silica GASTOF (UC Louvain) Cherenkov medium is a gas Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

Putting it all together FP 420 project: ATM BPM Line X Bus Bar Cryostat Vacuum Space BPM L QR Fixed Beampipe ATM ort p s ran e sid Pockets T Vacuum Space Benoît Florins, Krzysztof Piotrzkowski, Guido Ryckewaert Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 20

FP 420: What resolution does one achieve ? CEP of Higgs: Si pitch 40 -50 m x and y orientation (x) ~ (y) ~15 m CMS IP ATLAS IP S/B for 120 Ge. V Higgs b bbar depends critically on mass window width around signal peak Glasgow / Manchester Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

� Central problems to solve in the analysis of diffractive events at the LHC� Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 22

Experimental challenge: Trigger The difficulty of triggering on a 120 Ge. V Higgs Trigger at ATLAS/CMS based on high p. T/ET jet and lepton candidates in event In order to keep output rate at acceptable level, for example at 2 x 1033 cm-1 s-1: L 1 2 -jet trigger threshold O(100 Ge. V) per jet But: 120 Ge. V Higgs decays preferably into 2 b-jets with ~60 Ge. V each Possible strategies: § Rely on muon trigger only, where 2 -muon trigger thresholds are 3 Ge. V Take hit in statistics § Allow lower jet thresholds by assigning bigger chunk of available bandwidth Could be considered once Higgs has been found and one knows where to look § Allow lower jet thresholds without increase in assigned bandwidth by combining central detector jet condition with condition on forward proton taggers Note: 220 m proton taggers usable in L 1 trigger, 420 m taggers only on HLT because 420 m too far away from IP for signal to arrive within L 1 latency of 3. 2 s Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 23

Experimental challenge: Trigger A dedicated forward detectors L 1 trigger stream → Trigger thresholds for nominal LHC running too high for diffractive events → Use information of forward detectors to lower in particular CMS jet trigger thresholds → The CMS trigger menus now foresee a dedicated forward detectors trigger stream with 1% of the total bandwidth on L 1 and HLT (1 k. Hz and 1 Hz) ! single-sided 220 m condition without and with cut on Achievable total reduction: 10 (single-sided 220 m) x 2 (jet iso) x 2 (2 jets same hemisphere as p) = 40 Demonstrated that for luminosities up to 2 x 1033 cm-1 s-1 including 220 m detectors into the L 1 trigger provides a rate reduction sufficient to lower the 2 -jet threshold substantially, to 40 Ge. V, while requiring only 1% of L 1 bandwidth Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 24

Experimental challenge: Trigger Efficiency for central exclusive Higgs production Efficiency Central exclusive production pp p. Hp with H (120 Ge. V) bb: 420 m Assuming 1% of total bandwidth available: 220 m Di-jet trigger threshold of 40 Ge. V & single-sided 220 m condition possible, would retain 10% of the events 420+420 m 420+220 m H(120 Ge. V) → b bbar This would double the efficiency provided by the CMS muon trigger (no fwd detectors condition) L 1 trigger threshold [Ge. V] Central exclusive production pp p. Hp with H (140 Ge. V) WW: Same efficiency as non-CEP production, no improvement from fwd detectors jet trigger condition Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 25

Experimental challenge: Pile-up background ! Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 26

Experimental challenge: Pile-up background (II) Number of PU events with protons within acceptance of near-beam detectors on either side: ~2 % with p @ 420 m ~6 % with p @ 220 m d (ep e. Xp)/dx. L [nb] Diff events characterized by low fractional proton momentum loss diffractive peak TOTEM det@420 x. L=P’/Pbeam= 1 - Coincidence of non-diffractive event with protons from pile-up events in the near-beam detectors: fake double-Pomeron exchange signature Non-diffractive event with signature in the central CMS detector identical to some DPE signal event: At 2 x 1033 cm-2 s-1 10% of these non-diffractive events will be mis-identified as DPE event. This is independent of the specific signal. Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

Experimental challenge: Pile-up background Handles against pile-up background Can be reduced on the High Level trigger: ; Fast timing detectors that can determine whether the protons seen in the near-beam detector came from the same vertex as the hard scatter within 3 mm (jets) Requiring correlation between ξ, M measured in the central detector and ξ, M measured by the near-beam detectors CEP H(120) bb 1 2 s = M 2 incl QCD di-jets + PU Further offline cuts possible: Condition that no second vertex be found within 3 mm vertex window left open by fast timing detectors (p tagger) Exploiting difference in multiplicity between diff signal and non-diff background CEP of H(120 Ge. V) → b bbar and H(140 Ge. V) → WW: S/B of unity for a SM Higgs M(2 -jets)/M(p’s) Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 28

Side remark: CMS + Totem (+ FP 420) program Experimental issues of detecting diffractive processes at the LHC discussed in: Prospects for diffractive and forward physics at the LHC, CERN/LHC 2006 -039/G-124 Written by CMS and TOTEM to express interest in carrying out a joint program of diffractive and forward physics as part of the routine data taking at the CMS IP, i. e. up to the highest available luminosities and spanning the full lifetime of the LHC. Program covers in addition to central exclusive production: • Diffraction in the presence of a hard scale: “Looking at the proton through a lense that filters out anything but the vacuum quantum numbers • Diffractive structure functions • Soft rescattering effects/underlying event and rapidity gap survival factor • Low x. BJ structure of the proton • Saturation, color glass condensates • Rich program of and p physics • Validation of cosmic ray air shower MC Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

� Current status of FP 420 and Summary� Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 30

§ FP 420 is an R&D collaboration with members from ATLAS, CMS and the LHC § FP 420 aims at providing the necessary tools for measuring central exclusive production at the LHC under nominal LHC running conditions § FP 420 suggests to instrument the location 420 m from the ATLAS/CMS IP with Silicon tracking detectors and fast TOF detectors FP 420 will extend the physics potential of the ATLAS/CMS baseline detectors: For the SM Higgs, FP 420 makes feasible observing a light SM Higgs in the bb decay channel For the MSSM Higgs, in certain parts of the parameter space FP 420 has discovery potential FP 420 renders possible a direct measurement of the Higgs quantum numbers § Both in ATLAS and CMS internal evaluation of FP 420 proposal has started § FP 420 is preparing a Technical Design Proposal with the results of R&D studies § If approved by ATLAS (CMS) as proper ATLAS (CMS) project, independent Technical Design Proposals for ATLAS-FP 420 and CMS-FP 420, building on common R&D Installation could take place in 2009/2010, i. e. no interference with LHC start-up Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 31

BACKUP Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 32

The physics case for FP 420 MSSM: intense coupling regime Intense-coupling regime of the MSSM: Mh~MA ~ MH ~ O(100 Ge. V): their coupling to , WW*, ZZ* strongly suppressed discovery challenging at the LHC Cross section of two scalar (0+) Higgs bosons enhanced compared to SM Higgs 100 fb Production of pseudo-scalar (O-) Higgs suppressed because of JZ selection rule Superior missing mass resolution from tagged protons allows to separate h, H - 1 fb 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 120 140 Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 see Kaidalov et al, hep-ph/0307064, hep-ph/0311023

The physics case for FP 420 MSSM: intense coupling regime Azimuthal angle between outgoing protons sensitive to Higgs spin-parity: JP=0+ vs JP=0 - (recall JZ selection rule only approximate) 100 fb 01 fb 0+ Kaidalov et al. , hep-ph/0307064 Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

MSSM Scenario Studies MA = 130 Ge. V tan = 50 H bb S. Heinemeyer et al to appear No-mixing scenario Contours of ratio of signal events in the MSSM over the SM Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 35

CMS + TOTEM (+ FP 420) Unprecedented kinematic coverage Castor CMS Castor thungsten/quartz Cherenkov calorimeter TOTEM T 2: GEM tracking detector d (ep e. Xp)/dx. L [nb] TOTEM Silicon tracking det. housed in Roman pots ZDC TOTEM det @420 CMS ZDC thungsten/quartz Cherenkov calorimeter x. L=P’/Pbeam= 1 - Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

ALFA and LUCID ALFA: Absolute Luminosity for ATLAS LUCID: Luminosity measurement with a Cherenkov Integrating Detector 2 stations at 240 m from ATLAS IP approaching the beam to within 1. 2 mm 10+10 planes of scintillating fibre detectors spatial resolution 30 m edge <100 m Installation of detectors during first long LHC shutdown (2009 ? ) Aluminium tubes filled with isobutane in cylinder (length 1. 5 m, diameter 13. 7 cm) around beam pipe 17 m from ATLAS IP Absolute lumi measurement at ~ 10 -27 cm-2 s-1 Extrapolation from there to luminosity at nominal LHC running via track counting in LUCID Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

Forward detectors at ATLAS/CMS IP’s possible upgrade RP 220 with Si detectors possible addition SLHC Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007

CDF: exclusive processes at Fermilab (II) On the way to diffractive Higgs production: p p cc c J/y cc p c g p • H proceeds via the same diagram but t-loop instead of c-loop • Important for calibrating models on diffractive Higgs 10 candidate events (but unknown background) < 49 18 (stat) 39 (syst) pb for exclusive cc production for |y|<0. 6 Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 MJ/y-g 39

Alignment Online: Beam-Position Monitors plus a wirepositioning system: aiming for 10 micron precision on beam-detector separation. Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 40

Monika Grothe, Diffractive Higgs searches: The FP 420 project, August 2007 41