monika grothe, diffractive higgs searches: the fp420 project, august 2007 1 diffractive higgs...

$: Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 1 Diffractive Higgs searches: The Pomeron as little helper in tracking down the$
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 1

Diffractive Higgs searches:The Pomeron as little helper in

tracking down the Higgs ? -The FP420 project

Monika GrotheU Turin/ U WisconsinJohns-Hopkins workshopHeidelberg August 2007

Why ?How in principle ?What’s available already ?Specific challenges ?Current status ?


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

Vacuum quantum numbers“Double Pomeron exchange”

shields color charge ofother two gluons

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 fb

MH = 120 GeV : 11 signal / O(10) background in 30 fb-1

with detector cuts

WW* : MH = 120 GeV; = 0.4 fb

MH = 140 GeV; = 1 fb

MH = 140 GeV : 8 signal / O(3) background in 30 fb-1

with detector cuts

Standard Model

Higgs

Generator studies with detector cuts

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

Same type of diagrams as for Higgs validation of KMR model !

hep-ex/0707237

Central exclusive production:

Observation at Fermilab


How go about measuringcentral exclusive production ?


Measuring central exclusive production:

Experimental signature



Principle of measurement

beam

p’

p’roman potsroman pots

dipoledipole

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 pipe

Diffractively scattered protons survive interaction intact and loseonly a small fraction of their initial momentum in the process



Where to put the detectors

=0 (beam)

=0.002

=0.015

1 2 s = M2

With √s=14TeV, M=120GeVon average:

0.009 1%

With nominal LHC optics:

fractional momentum loss of the proton

beam

p’

p’roman potsroman pots

dipoledipole


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

1 2 s = M2

With √s=14TeV, M=120GeV on average:

0.009 1%

Detectors at 420m •complement acceptance of 220m detectors•needed to extend acceptance down to low values, i.e. low MHiggs

Detectors 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


Where to put the detectors (II)


Current experimental situation at the ATLAS and CMS IP’s:

ALFA and TOTEM

Possible extension of the ATLAS/CMS baseline detectors: FP420


TOTEM

xL=P’/Pbeam=

det@420

d(

ep

eXp

)/d

x L [n

b]

Existing proton tagging detectors

CMS 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

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

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 groups

data points from ZEUS


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

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


FP420 project: 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

scattered protons emerge here


FP420: How to move detectors close to the beam

Turin / Louvain / Helsinki

Movable beam-pipewith detector stations attachedMove detectors toward beam envelope once beam is stable

Gastof or Quartic

Silicon detector box

Beam 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 readout

Active edges:the edge is itself an electrode, so dead volume at the edge < 5.

Electrodes are processed insidethe detector bulk instead of being implanted on the wafer’ssurface.

Manchester / Stanford

Prototype in CERN testbeams 2006 and 2007 Technology is candidate for ATLAS tracker SLHC upgrade


FP420 project: Silicon Detector StationsManchester / Mullard Space Science Lab

7.2 mm x 24mm

3 detector stations with 8 layers each

8 mm 8 mm


FP420 project: Fast timing detectors

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 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 Silica

protonCherenkov light


Benoît Florins, Krzysztof Piotrzkowski, Guido Ryckewaert

ATM

Vacuum Space

BPM

Pockets

ATM

Line X

Bus Bar Cryostat

BPM

Vacuum Space

Transport side

QRLFixed Beampipe

FP420 project: Putting it all together


FP420: 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 width around signal peak

CMS IPATLAS IP

CEP of Higgs:


Central problems to solve in the analysis of diffractive events

at the LHC

Experimental challenge: Trigger

The difficulty of triggering on a 120GeV Higgs

Note: 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 s

Trigger 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 jet

But: 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


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

!


H(120 GeV) → b bbar

L1 trigger threshold [GeV]

Eff

icie

ncy

420m

220m

420+420m

420+220m


Trigger Efficiency for central exclusive Higgs production

Central 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 !


TOTEM

xL=P’/Pbeam=

det@420d(

ep

eXp

)/d

x L [n

b]

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 ξ, M measured in the central detector andξ, M measured by the near-beam detectors

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 3mm

Further offline cuts possible:

Condition that no second vertex befound within 3mm vertex windowleft open by fast timing detectors

Exploiting difference inmultiplicity between diff signal and non-diff background

Experimental challenge: Pile-up background

Handles against pile-up background

; 1 2 s = M2

(p tagger)(

jets

)

CEP H(120) bb incl QCD di-jets + PU

M(2-jets)/M(p’s)

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) program

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 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 discovery potential 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/0311023

100 fb

1 fb

120 140


The physics case for FP420 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


MSSM Scenario Studies

MA = 130 GeV tan = 50 HbbS. Heinemeyer et alto appear

Contours of ratio of signal events in the MSSM over the SM

No-mixing scenario


TOTEM

xL=P’/Pbeam=

det@420

d(

ep

eXp

)/d

x L [n

b]

CMS + TOTEM (+ FP420) Unprecedented kinematic coverage

TOTEM T2:GEM tracking detector

CMS Castor thungsten/quartzCherenkov calorimeter

CMS ZDC thungsten/quartzCherenkov calorimeterTOTEM Silicon tracking

det. housed in Roman pots

Castor Castor

ZDC ZDC


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 <100m

Installation of detectors during firstlong LHC shutdown (2009 ?)

LUCID: Luminosity measurement with a Cherenkov Integrating Detector

Aluminium tubes filled with isobutane incylinder (length 1.5m, diameter 13.7cm)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


Forward detectors at ATLAS/CMS IP’s

possible upgrade RP220 with Si detectors

possibleaddition

SLHC


cc

c

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

•Important for calibrating models on diffractive Higgs

MJ/

pp

p p

J

c

On the way to diffractive Higgs production:

10 candidate events (but unknown background)49 18 (stat) 39 (syst) pb for exclusive c production for |y|<0.6

CDF: exclusive processes at Fermilab (II)


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

Alignment

monika grothe, diffractive higgs searches: the fp420 project, august 2007 1 diffractive higgs...

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