Monika Grothe U Turin/ U Wisconsin Johns-Hopkins workshop Heidelberg August 2007

Diffractive Higgs searches:The Pomeron as little helper in tracking down the Higgs ? -The FP420 project

Monika GrotheU Turin/ U WisconsinJohns-Hopkins workshopHeidelberg August 2007Why ?How in principle ?Whats available already ?Specific challenges ?Current status ?

Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007

Why bother with diffraction at the LHC ?


Suppose you want to detect a light SM Higgs (say MH=120 GeV) at the LHC...SM Higgs with ~120 GeV:gg H, H b bbar highest BRBut signal swamped by gg jet jetBest bet with CMS: H Central exclusive productionpp pXpSuppression of gg jet jetbecause of selection rules forcingcentral system to be (to good approx) JPC = 0++


Diffraction as tool for discovery physics:Central exclusive production pp pXp

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 pHp with H(120 GeV) 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


H b jets : MH = 120 GeV; = 2 fb (uncertainty factor ~ 2.5)MH = 140 GeV; = 0.7 fbMH = 120 GeV : 11 signal / O(10) background in 30 fb-1 with detector cutsWW* : MH = 120 GeV; = 0.4 fbMH = 140 GeV; = 1 fbMH = 140 GeV : 8 signal / O(3) background in 30 fb-1 with detector cuts Standard Model Higgs Generator studies with detector cutsCentral exclusive production:Standard Model light Higgs

Note: This H decay channel is impossible innon-CEP production ! Note: Use semi-leptonic decays for measurement


Search for exclusive gg

3 candidate events found 1 (+2/-1) predicted from ExHuME MC*

Same type of diagrams as for Higgs validation of KMR model !hep-ex/0707237Central exclusive production:Observation at Fermilab


How go about measuringcentral exclusive production ?


Measuring central exclusive production:Experimental signature


Measuring central exclusive production:Principle of measurement

Needed: Proton spectrometer using the LHC beam magnetsDetect protons that are very slightly off-momentum wrt beam protons, i.e. detection needed inside of beam pipeDiffractively scattered protons survive interaction intact and loseonly a small fraction of their initial momentum in the process


Measuring central exclusive production:Where to put the detectors

1 2 s = M2

With s=14TeV, M=120GeVon average:

0.009 1%With nominal LHC optics: fractional momentum loss of the proton


Measuring central exclusive production:Where to put the detectors (II)

Nominal LHC beam opticsLow * (0.5m): Lumi 1033-1034cm-2s-1 @220m: 0.02 < < 0.2 @420m: 0.002 < < 0.02 1 2 s = M2With s=14TeV, M=120GeV on average: 0.009 1%Detectors at 420m complement acceptance of 220m detectorsneeded to extend acceptance down to low values, i.e. low MHiggsDetectors closer to IP, e.g. ~220m optimize acceptance (tails of distr.) can be used in L1 trigger, while 420m too far away for detector signals to reach L1 trigger within latency


Current experimental situation at the ATLAS and CMS IPs:ALFA and TOTEM

Possible extension of the ATLAS/CMS baseline detectors: FP420


Existing proton tagging detectorsCMS IP: TOTEM Approved experiment for tot, elastic meas. Uses same IP as CMS Roman-pot housed Silicon tracking detectors at 180m and 220m from IP TOTEMs 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 ATLAS IP: ALFA Detectors to determine absolute luminosity by way of measuring elastic scattering in Coulomb interference region Approved part of ATLAS experiment Roman-pot housed scintillating fiber detectors at 240m from IP Operation at nominal LHC lumi requires rad-hard upgrade - option subject of an R&D effort by several ATLAS groupsdata points from ZEUS


The FP420 R&D projectProposal to the LHCC in June 2005: CERN-LHCC-2005-025FP420: An R&D Proposal to Investigate the Feasibility of Installing Proton Tagging Detectors in the 220m Region at LHCSigned by 29 institutes from 11 countriesThe aim of FP420 is to install high precision silicon tracking and fast timing detectors close to the beams at 420m from ATLAS and / or CMSThe LHCC acknowledges the scientific merit of the FP420 physics program and the interest in its exploring its feasibility. - LHCC


FP420 project: How to integrate detectors into the cold section of the LHCTurin / 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 temperaturescattered protons emerge here


FP420: How to move detectors close to the beamTurin / Louvain / HelsinkiMovable beam-pipewith detector stations attachedMove detectors toward beam envelope once beam is stableGastof or QuarticSilicon detector boxBeam position monitor


FP420: Which technology for the detectors 3D edgeless Silicon detectors:Edgeless, i.e. distance to beam envelope can be minimizedRadiation hard, can withstand 5 years at 1035 cm-2 s-1 Use ATLAS pixel chip (rad hard) for readoutManchester / Stanford Prototype in CERN testbeams 2006 and 2007 Technology is candidate for ATLAS tracker SLHC upgrade


FP420 project: Silicon Detector StationsManchester / Mullard Space Science Lab7.2 mm x 24mm 3 detector stations with 8 layers each8 mm8 mm


FP420 project: Fast timing detectorsGASTOF (UC Louvain)Cherenkov medium is a gasMicro channel plate photo-multiplier tubes (MCP-PMT) were successfully employed inbuilding Cherenkov-light based TOF detector with resolution of ~10ps (NIM A 528(2004) 763) Would translate in z-vertex resolution of better than 3mm

Needed to veto protons from pile-up events

Two technologies; both in FERMILAB test beams 2006 and 2007 QUARTIC (U Texas-Arlington):Cherenkov medium is fused SilicaprotonCherenkov light


FP420 project: Putting it all togetherBenot Florins, Krzysztof Piotrzkowski, Guido RyckewaertATMVacuum SpaceBPMPocketsATMLine XBus Bar CryostatBPMVacuum SpaceTransport sideQRLFixed Beampipe


FP420: What resolution does one achieve ?Si pitch 40-50 mx and y orientation(x) ~ (y) ~15 mGlasgow / Manchester S/B for 120GeV Higgs b bbar depends critically on mass window width around signal peakCMS IPATLAS IPCEP of Higgs:


Central problems to solve in the analysis of diffractive events at the LHC


Experimental challenge: TriggerThe difficulty of triggering on a 120GeV HiggsNote: 220m proton taggers usable in L1 trigger, 420m taggers only on HLT because 420m too far away from IP for signal to arrive within L1 latency of 3.2 sTrigger at ATLAS/CMS based on high pT/ET jet and lepton candidates in eventIn order to keep output rate at acceptable level, for example at 2x 1033 cm-1 s-1: L1 2-jet trigger threshold O(100 GeV) per jetBut: 120 GeV Higgs decays preferably into 2 b-jets with ~60 GeV each

Possible strategies: Rely on muon trigger only, where 2-muon trigger thresholds are 3 GeV 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


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 L1 and HLT (1 kHz and 1 Hz)single-sided 220m conditionwithout and withcut on Achievable total reduction: 10 (single-sided 220m) x 2 (jet iso) x 2 (2 jets same hemisphere as p) = 40 Experimental challenge: Trigger A dedicated forward detectors L1 trigger stream Demonstrated that for luminosities up to 2x 1033 cm-1 s-1 including 220m detectors into the L1 trigger provides a rate reduction sufficient to lower the 2-jet threshold substantially, to 40GeV, while requiring only 1% of L1 bandwidth!


Experimental challenge: Trigger Trigger Efficiency for central exclusive Higgs productionCentral exclusive production pp pHp with H (120GeV) bb:Assuming 1% of total bandwidth available:

Di-jet trigger threshold of 40GeV & single-sided 220m condition possible, would retain 10% of the events

This would double the efficiency providedby the CMS muon trigger (no fwd detectorscondition)Central exclusive production pp pHp with H (140GeV) WW:Same efficiency as non-CEP production, no improvement from fwd detectors jet trigger condition


Experimental challenge:Pile-up background !


Number of PU events with protons within acceptance of near-beamdetectors on either side: ~2 % with p @ 420m ~6 % with p @ 220m

Coincidence of non-diffractive event with protons from pile-up events in the near-beamdetectors: fake double-Pomeron exchange signature Experimental challenge: Pile-up background Pile-up background (II)Non-diffractive event with signature in the central CMS detector identical to some DPE signal event: At 2x 1033 cm-2s-1 10% of these non-diffractive events will be mis-identified as DPE event. This is independent of the specific signal.Diff events characterized by low fractional proton momentum loss diffractivepeak


Can be reduced on the High Level trigger:Requiring correlation between , M measured in the central detector and, M measured by the near-beam detectorsFast timing detectors that can determine whether the protons seen in the near-beam detector came from the same vertex as the hard scatter within 3mm

Further offline cuts possible:Condition that no second vertex befound within 3mm vertex windowleft open by fast timing detectorsExploiting difference inmultiplicity between diff signal and non-diff backgroundExperimental challenge: Pile-up backgroundHandles against pile-up background; 1 2 s = M2(p tagger)(jets)CEP H(120) bbincl QCD di-jets + PUM(2-jets)/M(ps)CEP of H(120 GeV) b bbar andH(140 GeV) WW:S/B of unity for a SM Higgs


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. Side remark:CMS + Totem (+ FP420) programProgram 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 xBJ structure of the proton Saturation, color glass condensates Rich program of and p physics Validation of cosmic ray air shower MC


Current status of FP420 and Summary


FP420 is an R&D collaboration with members from ATLAS, CMS and the LHC FP420 aims at providing the necessary tools for measuring central exclusive production at the LHC under nominal LHC running conditions FP420 suggests to instrument the location 420m from the ATLAS/CMS IP with Silicon tracking detectors and fast TOF detectors

FP420 will extend the physics potential of the ATLAS/CMS baseline detectors: For the SM Higgs, FP420 makes feasible observing a light SM Higgs in the bb decay channel For the MSSM Higgs, in certain parts of the parameter space FP420 has discoverypotential FP420 renders possible a direct measurement of the Higgs quantum numbers

Both in ATLAS and CMS internal evaluation of FP420 proposal has started FP420 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-FP420 and CMS-FP420, building on common R&D

Installation could take place in 2009/2010, i.e. no interference with LHC start-up


BACKUP


The physics case for FP420 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/0311023100 fb1 fb 120 140-


The physics case for FP420 MSSM: intense coupling regime 100 fb1 fb Azimuthal angle between outgoing protons sensitive to Higgs spin-parity: JP=0+ vs JP=0- (recall JZ selection rule only approximate)0 -0 +Kaidalov et al.,hep-ph/0307064


MSSM Scenario StudiesMA = 130 GeV tan = 50 HbbS. Heinemeyer et alto appearContours of ratio of signal events in the MSSM over the SMNo-mixing scenario


CMS + TOTEM (+ FP420) Unprecedented kinematic coverage TOTEM T2:GEM tracking detectorCMS Castor thungsten/quartzCherenkov calorimeterCMS ZDC thungsten/quartzCherenkov calorimeterTOTEM Silicon trackingdet. housed in Roman pots


ALFA and LUCIDALFA: Absolute Luminosity for ATLAS

2 stations at 240mfrom ATLAS IPapproaching the beam to within 1.2mm

10+10 planes ofscintillating fibredetectors spatial resolution 30m edge

Forward detectors at ATLAS/CMS IPspossible upgrade RP220 with Si detectorspossibleadditionSLHC


ccH proceeds via the same diagram but t-loop instead of c-loop

Important for calibrating models on diffractive HiggsMJ/y-gOn the way to diffractive Higgs production:10 candidate events (but unknown background)s< 49 18 (stat) 39 (syst) pb for exclusive cc production for |y|

Online: Beam-Position Monitors plus a wire-positioning system: aiming for 10 micron precision on beam-detector separation.Alignment


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Monika Grothe U Turin/ U Wisconsin Johns-Hopkins workshop Heidelberg August 2007