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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 ?
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 2
Why bother with diffraction at the LHC ?
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 3
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++
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 4
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 5
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 6
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 7
How go about measuringcentral exclusive production ?
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 8
Measuring central exclusive production:
Experimental signature
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 9
Measuring central exclusive production:
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 10
Measuring central exclusive production:
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 11
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
Measuring central exclusive production:
Where to put the detectors (II)
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 12
Current experimental situation at the ATLAS and CMS IP’s:
ALFA and TOTEM
Possible extension of the ATLAS/CMS baseline detectors: FP420
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 13
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 14
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 15
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 16
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 17
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 18
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 19
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 20
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 21
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:
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 22
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 24
→ 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
!
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 25
H(120 GeV) → b bbar
L1 trigger threshold [GeV]
Eff
icie
ncy
420m
220m
420+420m
420+220m
Experimental challenge: Trigger
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 26
Experimental challenge:Pile-up background !
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 27
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 28
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 29
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 30
Current status of FP420 and
Summary
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 31
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 33
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 34
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 35
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 36
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 37
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
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 38
Forward detectors at ATLAS/CMS IP’s
possible upgrade RP220 with Si detectors
possibleaddition
SLHC
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 39
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)
Monika Grothe, Diffractive Higgs searches: The FP420 project, August 2007 40
Online: Beam-Position Monitors plus a wire-positioning system: aiming for 10 micron precision on beam-detector separation.
Alignment
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