pushing the limits: triggering and forward physics at the lhc

Monika Grothe, Triggering and forward physics at the LHC, July 2007 1

Pushing the limits: Triggering and forward physics

at the LHC

Monika GrotheU Wisconsin/ U Turin

• Boundary conditions for triggering at the LHC

• Trigger architecture at the LHC/CMS

• Level-1 trigger algorithm at the LHC/CMS

• High level trigger algorithms at the LHC/CMS

• Pushing the limits: Triggering on forward physics

• Diffractive and forward physics with CMS + Totem (+ FP420)

• Outlook: A Level-1 track trigger for the SLHC


Boundary conditions for triggering

at the LHC


Simple example of a trigger

trigger decision

some logicoperation and synchronizationof signals:“trigger logic”

data is storeddepending on trigger decision

Record pulse height spectrumof cosmic rays in a 30 degree slice

An interesting event:Pulses with height above a threshold are seen in coincidence with Z12 in 30o slice around Z12

(U Bonn)


Boundary conditions

First try: A trigger at the LHC

Simple-minded approach: At the LHC, each crossing of bunches that leads to one (or more) pp collisions is an interesting event. Why don’t we simply trigger oneach of them and record all associated subdetector data ?

At the LHC, per year 1016 eventsFor each event total size of data to eventually store is about 1 MByte

1016 x 1 MHz = 107 PetaByte

Job of a trigger:Indicate that something of interest was seen in the detectorIf an interesting “event” occured, record all its data for later detailed analysis

Attention: An event not flagged as interesting by the trigger is lost forever

! ?Need to compromise between physics and affordabilityAffordable ? CMS Tier-1 centers will provide about O(1) PByte of storage in 2008

Reduction of 7 orders of magnitude !! What does this mean for physics ?


Boundary conditions

Event rates at the LHC

• Inelastic pp reactions: 109 / s • bb pairs 5 106 / s • tt pairs 8 / s

• W e 150 / s• Z e e 15 / s

• Higgs (150 GeV) 0.2 / s• Gluino, Squarks (1 TeV) 0.03 / s

Rates for L = 1034 cm-2 s-1: (LHC)

For cost reasons:First level trigger output limited to

~100 kHzHigher level triggers output limited to

~100 Hz


s = 14 TeV search for new massive particles up to m ~ 5 TeV7 x higher than Tevatron

Ldesign = 1034 cm-2 s-1 search for rare processes with small (N = L )102 x higher than Tevatron

s = 14 TeV search for new massive particles up to m ~ 5 TeV7 x higher than Tevatron

Ldesign = 1034 cm-2 s-1 search for rare processes with small (N = L )102 x higher than Tevatron

Boundary conditions

The LHC and its experiments

ATLAS and CMS :pp, general purpose

pp

ALICE : heavy ions LHCb :

pp, B-physics

27 km ring used fore+e- LEP machine in 1989-2000 + TOTEM at the CMS IP

+ LHCf at the ATLAS IP


Most interactions are due to interactions at large distance between incoming protons→ small momentum transfer, particles in the final state have large longitudinal, but small transverse momentum

Boundary conditions

Physics at a proton-proton collider

p

pT

pT = p sin

plane perpendicular to the beam

“Interesting events”: Processes with large transverse momentum pT

sx1p x2p

Proton beam can be seen as beam of quarks and gluons with a wide band of energiesHard scatter between these proton constituents

p pqq

qq

H

WW


Boundary conditions

Event pile-up

Because of very high particle density in LHC proton bunches:

Event pile-up per bunch crossing

Consequence: High particle density in detector

H ZZ, Z cleanest "golden" signature

But at L = 1034 cm-2 s-1

overlapped by O(25) non-elastic events

And this (not the Higgs though) repeats every 25 ns


Boundary conditions for triggering at the LHC:

Affordability limits read-out bandwidth and storage capacity

Huge cross section at LHC energies

Rate reduction of overall 7 orders of magnitude needed

High particle density in detector because of event pile-up

Discovery physics with relatively high ET/pT

Base trigger on selection of high ET/pT objects

Recap: Boundary conditions


Trigger architectureat the LHC/CMS


Trigger architecture Multi level trigger


L1: trigger decision algorithms implemented in fast, custom-made electronics only very much reduced information on event at its disposalHLT: implemented as software algorithms run on a processor farm in principle full event information at it disposal

107 channels

1000 units

103 x 103 switch fabric

4x106 MIPS

Trigger architecture Multi level trigger (II)

L1 In: 1 GHzL1 Out: 100 kHz

HLT In: 100 kHzHLT Out: 100 Hz

Decision within a few s

Decision within a few 100 ms


Trigger architecture Pipelines on L1

Speed of light in air: 0.3m/nsOuter diameter of CMS detector ~7m, hence particle needs up to 23ns to cause signal in CMS muon chamber

At LHC 25ns btw bunch crossings

It is impossible to form a trigger decision within 25 ns of each bunch crossing

Since in principle every bunch crossing could result in an interesting event, need way to store them till trigger came to a decision: pipelines

L1 trigger latency = depth of pipeline = maximum time available for L1 trigger decision

g


General trigger architecture at the LHC/CMS:

Pipelined, multi-level trigger

L1: latency a few s, coarse granularity information, custom-made electronics

HLT: latency a few 100 ms, full event info, computer farm

Recap: Trigger architecture


Trigger algorithms for Level-1 and Higher Levels Trigger

at the LHC/CMS


L1 trigger algorithms

Information used for L1 algorithms



Why no track information on L1 ?



Example: L1 calorimeter trigger

Trigger towers:smallest unit trigger electronics looks at

L1 calorimeter trigger searchesfor trigger tower clusters with maximum ET

Small cluster: L1 electron or photonBig cluster: L1 jet



L1 electrons/photons and jets

Sliding 3x3 region windowRegion = 4x4 trigger towers

L1 electron or photon:

L1 jet:


Algorithm implemented in asics

isolated L1 electron or photon


Algo example: Isolated electron/photon


3 safety factor 50 kHz (expected start-up DAQ bandwidth)


Example L1 trigger table (L = 2x1033 cm-2 s-1)

Background to e/ are mainly in em-rich jetsBackground to jets are jets - huge rate of QCD jets

Purity is not the issue, but 100%efficiency for “interesting events”while respecting bandwidth limits


HLT trigger algorithms

HLT electron algorithm“Level 2” step:Starting from L1 em object information as seed, reconstruct cluster of ECAL crystals in which electron has deposited its energy reconstruct electron energy and position from cluster

“Level 2.5” step:Match cluster with hits in the pixel detector

“Level 3” step:Starting from pixel detector seed, reconstruct full track information

e efficiency vs jet rejectionfor L2.5 pixel matching:

CMS pixel detector coverageECAl barrel

ECALendcap

1 trigger tower= 5x5 crystals


Trigger algorithms on L1 and HLT at LHC/CMS:

Algorithms on L1 based on calorimeter and muon system information, tracking only on HLT

Main objective of L1 trigger: Keep output rate under control, i.e. purity is not the issue, but maximum signal efficiency is

Example L1 calo trigger: Looks for local maxima in ET, large cluster = L1 jet , small cluster: L1 electron/photon

Example HLT electron trigger: Reduction of jet background by factor 10 by requiring matching pixel track stub

Allocated trigger bandwidth per trigger condition summarized in L1 and HLT trigger menus

Trigger menus determine physics reach of experiment

Recap: Trigger algorithms


Pushing the limits: Triggering on

forward physics


Triggering on forward physics

Forward physics

Experimental definition:All processes in which particles are produced at small polar angles.

= 90o = 0

= 10o 2.4 = 170o -2.4

= 1o 5.0edge of coverage of centralCMS/ATLAS detectors



Example of forward physics:Diffraction


Diffraction as tool for discovery physics ! ?

Great. And why bother 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:

CEP pp pXp with X = H(~120 GeV) b bbar

In non-diffractive production hopeless, signal swamped by QCD di-jet background

Selection rules: central system is JPC = 0++ (to good approx) I.e. a particle produced with proton tags has known quantum #

For light (~120 GeV) Higgs: Proton tagging improves S/B for SM Higgs dramatically CEP may be discovery channel in certain regions in MSSM

CP quantum numbers and CP violation in Higgs sector directly measurable from azimuthal asymmetry of the protons

beam

p’

p’roman potsroman pots

dipoledipole

Needed: Proton spectrometer using the LHC beam magnetsDetect diffractively scattered protons inside of beam pipe


CMS IP T1/T2, Castor ZDC RPs@150m RPs@220m

possibly detectors@420m


CMS + TOTEM (+ FP420)

Possible addition FP420: Silicon tracking detectors and fast timing Cherenkov detectors, integrated into a LHC cryostat at 420m from IP

TOTEM: An approved experiment at LHC for measuring tot and elastic

uses same IP as CMS

TOTEM’s trigger and DAQ system will be integrated with those of CMS , i.e. common data taking CMS + TOTEM possible

TOTEM aims at start-up at the same timescale as CMS (2008)


The difficulty of triggering on a 120GeV Higgs

120 GeV Higgs decays preferably into 2 b-jets with ~60 GeV each

At 2x 1033 cm-1 s-1 without any additional condition on fwd detectors:

L1 1-jet trigger threshold O(150 GeV)

L1 2-jet trigger threshold O(100 GeV)

2 x 1033 cm-2 s-1 L1 jet trigger rates

L1 outputbandwidth:100 kHz

Is it possible to lower the CMS jet triggerthresholds significantly by combiningcentral CMS jet trigger condition withcondition on forward detectors ?

Attention: Cumulative rate shownTotal number of events with ET abovethreshold and function of threshold

L1 ET threshold (GeV)

Rat

e (k

Hz)

10

1

100

60

Note: Usable in L1 trigger only 220m proton taggers, 420m too far away from IP for signal to arrive within L1 latency of 3.2 s


→ CMS 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 still meeting the CMS L1 bandwidth limits

!


H(120 GeV) → b bbar

L1 trigger threshold [GeV]

Eff

icie

ncy 420m

220m

420+420m

420+220m


Efficiency of forward detectors L1 stream for diffractive events

Central exclusive production pp pHp with H (120GeV) bb:

Can gain another 10% from trigger

pp p jj X2-jet trigger

Attention: Gap survival probability not taken into account; normalized to number of events with 0.001 < < 0.2 and with jets with pT>10GeV

Eff

icie

ncy

L1 trigger threshold [GeV]

no fwd detectorscondition

single-arm 220m

single-arm 420m

Eve

nts

per

pb

-1



Experimental challenge:Pile-up background !


TOTEM

xL=P’/Pbeam=

det@420

d(

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


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


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


CMS trigger menus now foresee a dedicated forward detectors trigger stream:

Trigger at LHC designed for high pT physics, trigger thresholds generally too high for forward physics which has by definition lower pT

Combining central CMS detector trigger conditions with condition on Totem 220m proton tagger allows to lower in particular L1 jet trigger thresholds substantially while respecting trigger output rate limits

HLT forward detectors trigger algorithms reduce background from pile-up substantially and could use 420m proton tagger information

Central exclusive production of a low mass Higgs boson is physics channel profits substantially from new stream

Recap: Triggering on forward physics


Diffractive and forward physics with CMS + Totem *

at nominal LHC optics

* possibly also including FP420

The thus designed dedicated forward detectors trigger stream forms an essential part of an extension of its baseline program that CMS wishes to implement:


The CMS + Totem (+ FP420) program

CERN/LHC 2006-039/G-124

Objective:Carry out a program of diffractive and forward physics as integral part of the routinedata taking at CMS, i.e. at nominal beam optics and up to the highest available luminosities.This program spans the full lifetime of the LHC.

M. Grothe, J. Mnich primaryeditors from CMS side

Areas covered, in addition to diffraction as tool for discovery physics in 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


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


CMS + Totem intend to carry out a joint program on diffractive and forward physics

Unprecedented kinematic coverage

LoI submitted to LHCC Dec 2006

LoI identifies and addresses for the first time at the LHC central experimental

questions for carrying out a program that spans the full lifetime of the LHC

FP420 as possible extension of program currently under review in CMS (and ATLAS), document on results of extensive R&D effort over the past several years in preparation, decision by end of this year

Recap: CMS + Totem (+ FP420) program


Outlook:A Level-1 track trigger for the SLHC


Outlook: L1 track trigger

Tracking in the L1 trigger: CMS ideas Not done at the LHC because of difficulty of high density of low pT tracks in tracker At the SLHC, the increase of luminosity x10, to 1035 cm-2 s-1, will degrade efficiency of LHC algorithms in keeping the L1 output rate under control

Tracking trigger on L1 the solution ?

Example electron trigger: On HLT, matching of Calo electron candidate with pixel detector hits reduces background by a factor 10

Tracking trigger challenge: Find only high pT track stubs and match them with L1 electron and muon objects Because of high occupancy at the SLHC, need to do so while keeping read-out data from detector at a minimum On-detector hit correlator needed to reduce combinatorics

Suggested solution: Stacked pixel layers

rB

rLSearchWindow

A track like this wouldn’t trigger:

<5mm

w=1cm ; l=2cm

y

x

-- C. Foudas &

J. Jones


CorrelatorASIC

CoolingSystem

ThermalEpoxyOptical fibre to

OptoTX card

Kevlar-Carbon FibreLaminate

Support Structure

OpticalTransceiver Flip bonded

sensors

Outlook: L1 track trigger Tracking in the L1 trigger: CMS ideas (II)

• Use closely spaced stacked pixel layers• Angle of track bisecting sensor layers defines pT

• Track stub: Combination of hits in the 2 layers which are at most 1 pixel apart

• Pipelined column-parallel readout architecture where each pixel in a column forms a single cell in the pipeline

• Self-timed, asynchronous system with self-triggering pixels

J. Jones et al, A pixel detector for L1 triggering at SLHC, LECC2005J. Jones et al, Stacked tracking for CMS at SLHC, LECC 2006

• One module of 2 stacked layers a few millimeters apart would allow track stub reco• Two modules. e.g. at 10cm and 20cm from the beam line, would allow full track reco


Grand summary

• Triggering at the LHC is not an easy job

• Pipelined multi-level trigger architecture with algorithms that identify high ET/pT objects

• Extension of the CMS trigger menus:

A dedicated forward detectors trigger stream

• Extension of the CMS baseline physics program:

A joint CMS + Totem (possibly + FP420) program on diffractive and forward physics

• Motivation - Capitalize on diffraction as tool for discovery physics:

Central exclusive Higgs production

• A possible upgrade of the CMS L1 trigger for the SLHC:

Conceptual design for a Level-1 track trigger at the SLHC


Backup



High level triggers strategy

In CMS all trigger decisions beyond Level-1 are performed in a Filter Farm running ~normal CMS reconstruction software on “PCs”

The filter algorithms are setup in several steps

HLT does partial event reconstruction “on demand” seeded by the L1 objects found, using full detector resolution

Algorithms are essentially offline quality but optimized for fast performance


30-40 GeV for or e20 GeV each for

250 GeV jets80 GeV

Trigger cuts determine physics reach!•Efficiency for H and H4 leptons = >90% (in fiducial volume of

detector)•Efficiency for WH and ttH production with Wl = ~85%•Efficiency for qqH with H (1/3 prong hadronic) = ~75%•Efficiency for qqH with Hinvisible or Hbb = ~40-50%

L1 trigger rates


Trigger Mapping onto Cal surface

Area coveredby 1 jet


How does it look in real life ?



•Underground Counting Room–Central rows of racks fortrigger

–Connections via high-speed copper links to adjacent rows of ECAL & HCAL readout racks with trigger primitive circuitry

–Connections via opticalfiber to muon trigger primitive generatorson the detector

–Optical fibersconnected via“tunnels” to detector(~90m fiber lengths)

Rows of Racks containing trigger & readout

electronics

7m thickshielding

wall

USC55


RCT HCAL HTR

Location:USC55 - S2

ECAL TCC

GCT Source Cards

To GCT Source Cards



1 0 1 1 0 0 1 1 0 0 1 0 0 1 1 0 0 1 0 0 1 0 0

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Step 1

Step 2

Step 3

Step 4

Step 1

Step 2

Step 3

Step 4

Step 5

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

0 10 0

128-bit L1 Word

HLT Bits…HL

T A

lgor

ithm

Ste

psP

ath

stop

s w

hen

a se

lect

ion

step

fai

ls e/

2 e/

ME

T

1-Je

t2-

Jet

e+Je

t

HT


High level triggers strategy (II)


Forward physics at the LHC

Forward physics with special LHC beam optics:Elastic scattering: High precision absolute luminosity measurement at ATLAS

Forward physics at nominal LHC beam optics:The CMS + TOTEM (+ FP420) joint program - diffraction - low-x proton structure - Cosmics MC validation


Forward physics:Elastic scattering


Forward physics:Absolute luminosity determination

At ATLAS IP: ALFA near-beam detectors and LUCID luminosity monitor

AT CMS IP: TOTEM


The rate of produced events for a given physics process is given by:

N = L σ

dimensions: s-1 = cm-2 s-1 · cm2

L = Luminosity = cross section

In order to achieve acceptable production rates for the interesting physicsprocesses, the luminosity must be high !

L = 1034 cm-2 s-1 LHC design luminosity, very large !! (1000 x larger than LEP-2, 50 x Tevatron Run II design)

Luminosity depends on the machine:important parameters: number of protons stored, beam focus at interaction region,….

Luminosity

Need to know the luminosity with precision in order to detect new physics effects that may manifest themselves in deviations of the measured from the expected one

Dedicated ATLAS luminosity system aims at precision of 2-3%Means: Elastic scattering in the Coulomb-nuclear interference region


PQCD: 1/t8

“structure”

BS

W -

20

03

Nuclear slope: ebt

Coulomb region: 1/t2

C–N interferenceSensitivity to

Elastic scattering in the CNI region

( )2

2

0

2

4

2 tb

eit

affL

dt

dN EMNC

t

−

≈

++−≈+= ñó

L tot

πππ

Using the optical theorem, the measured elastic rate at small t values can be expressed as

Fit measured t distribution to obtain tot, b and L

p

p

p

p

t: 4-momentum transfersquared between 2 p’s


radGeVa

ffttTOT

EMNC ϑ

5.32468

|)||(| minmin ≤→−×≈≈=−≤

y*

y*

parallel-to-point focusingydet

IP Leff

*,

**det yyeffy Ly ϑϑββ ==

Elastic scattering in the CNI region II

In order to reach CNI region at the LHC

Need special beam opticswith minimal intrinsic beamangular spread at IP:

Displacement ydet is independent of the vertex position:

Need to approach beam with detectorsas closely as possible: “Roman pots”

tracking detectorsRoman Pot

Proton beam line

z-y view x-y view


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 physics:Diffraction


In diffractive events look at the proton constituents through a lens that filters out all parton combinations except those with the vacuum quantum numbers

X

Double Pomeron exchange (DPE):

X

Single diffraction (SD):

central CMSapparatus

central CMSapparatus

Near-beam detectors Near-beam

detectors

Near-beam detectors

IP

IP

IP

rap gap

A new way to probe the proton

2-gluon exchange:LO realisation of vacuum quantum numbers in QCD

pp

pp

IP

If X = anything: Measure fundamental quantities of soft QC

If X includes jets, W’s, Z’s, Higgs (!): Hard processes, calculable in perturbative QCD. Measure proton structure, QCD at high parton densities, discovery physics


TOTEM

xL=P’/Pbeam=

FP420

CMS + TOTEM (+ FP420): Coverage in

Note: Totem RP’s optimized for special optics runs at high β*β* is measure for transverse beam size at vertexTOTEM coverage in improves with increasing β*

At nominal LHC optics, β*=0.5m

Points are ZEUS data

diffractivepeak


Cosmic ray physics

Tune cosmic ray shower models with forward particle flows measured at the LHC

Study of the underlying event at the LHC:

→ Multiple parton-parton interactions and rescattering effects accompanying a hard scatter

→ Closely related to gap survival and factorization breaking in hard diffraction

Heavy-ion and high parton density physics:

Proton structure at low xBj → saturation → Color glass condensates

Photon-photon and photon-proton physics:

Also there protons emerge from collision intact and with very low momentum loss

Multiple connection points to other areas in High-Energy-Physics !

Prospects for diffractive and forward physics

with CMS + TOTEM (+ FP420)


known

Photon-mediated processes:Exclusive μμ production

Calibration process both for luminosity and energy scales of near-beam detectors

Striking signature: acoplanarity angle between leptonsAllows reco of proton values with resolution of 10-4, i.e. smaller than beam dispersion

Expect ~300 events/100 pb-1 after CMS muon trigger

(di-muons) - (true)

rms ~ 10-4


pQCD

No

n p

ertu

rbat

ive

reg

ion

Saturation(Colour glass condensate)

Qs2(x)

1/x

Q2 [GeV2]

Low-x QCD - Saturation

• Steep rise in the gluon density at small x observed at HERA

• Growth cannot continue indefinitely, would eventually violate unitarity

• Growth tamed by gluon fusion: saturation of parton densities

• So far not observed in pp interactions


Low-x QCD: Forward Drell-Yan

Gives access to low-xBJ quarks in proton in case of large imbalance of fractionalmomenta x1,2 of leptons, which are then boosted to large rapidities

CASTOR with 5.3 ≤ || ≤ 6.6 gives access to xBJ~10-7

Measure angle of electrons with T2

Pdf’s known at large xBJ, hence can extract pdf’s at low xBJ

DY pairs suppressed in saturated PDF

saturated PDF

Sensitivity to saturation:


→ Models for showers caused by primary cosmic rays (PeV = 1015 eV range) differ substantially

→ Fixed target collision in air with 100 PeV center-of-mass E corresponds to pp interaction at LHC

→ Hence can tune shower models by comparing to measurements with T1/T2, CASTOR, ZDC

Validation of hadronic shower models in cosmic ray physics


Forward physics covers about 50% of the pp cross section at the LHC

Elastic scattering at special LHC optics used as tool for high precision luminositydetermination (ALFA/LUCID at ATLAS IP, TOTEM at CMS IP)

Joint CMS + TOTEM (+FP420) program foresees rich physics program(hard diffraction, Higgs discovery, low-x proton structure, forward particle flow) at nominal LHC optics and up to the highest luminosities

Possible upgrade of ALFA with Silicon tracking detectors: Capitalize on experience gained with operating detectors near powerful LHC beam Diffractive and forward physics program competitive with the one at CMS + TOTEM Possible Si option: edgeless 3-D Silicon Actively pursued in ATLAS as option for SLHC ATLAS tracking system upgrade

Possible addition FP420: Radiation hard Silicon and fast Cherenkov timing detectors at 420m from the IP R&D complete, discussion in ATLAS and CMS for inclusion as subdetector started


Summary and Outlook (II)

possible upgrade RP220 with Si detectors

possibleaddition

SLHC

Still an opportunity for an original contribution to the LHC detectors !


Experimental situation at the CMS IP Additional option: The FP420 R&D project

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

FP420 R&D fully funded (~1000K CHF) Proposal to ATLAS and CMS in 2007 Detector installation could take place during first long LHC break (~2009)

Technological challenge:420m is in the cryogenic region of the LHC


FP420 project:

How to integrate detectors into the cold section of the LHC

420m from the IP is in the cold section of the LHC !Need to modify LHC cryostat: Use Arc Termination Modulesfor cold-to-warm transition such that detectors can be operated at ~ room temperature

Scattered protonsemerge here

Movable beam-pipe (pipelets)with detector stations attachedMove detectors toward beam envelopeonce beam is stable


FP420 project:

Which technology for the detectors ?3D 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

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

Time-of-Flight detectors:Time resolution of ~10ps would translate in z-vertex resolution of better than 3mm

GASTOF (UC Louvain)Cherenkov medium is a gas

QUARTIC (U Texas Arlington)Cherenkov medium is fused Silica


CRCLouvain-la-NeuveCRCLouvain-la-Neuve

Integration of the moving beampipe and detectors

Benoît Florins, Krzysztof Piotrzkowski, Guido Ryckewaert

ATM

Vacuum Space

BPM

Pockets

ATM

Line X

Bus Bar Cryostat

BPM

Vacuum Space

Transport side

QRLFixed Beampipe


CMS ideas for readout of SLHC track trigger(very preliminary)

Column-wisereadout

Bias generator Timing (DLL)

Diode+’Amp’

Comparator

Local Address Pipe cell

Reset/TransferLogic

Data passesthrough cellin each pixelin column

•At end of column, column address is added to each data element•Data concatenated into column-ordered list, time-stamp attached at front

Inner Sensor Outer Sensor

Column compare

c2c1

• If c2 > c1 + 1, discard c1

• If c2 < c1 – 1, discard c2

• Else copy c2 & c1 into L1 pipeline

This determines your search windowIn this case, nearest-neighbour

L1A Pipeline

L1T Pipeline

•Use sorted-list comparison (lowest column first)

•All hits stored for readout


• Rates calculated using CMS software (ORCA) at 80 MHz double them for 40 MHz.

• No charge sharing has been included. Hence, another factor of at least two to make them realistic. 10 Gb/s/cm2 100 Tb/s

C.Foudas, A. Rose, J. Jones, G. Hall, LECC2005, Heidelberg

CMS ideas for SLHC track trigger: Occupancy(very preliminary)


• Large Factors to be gained also for muons.• Outer tracker subs may be important here.

CMS ideas for SLHC track trigger: Muons(very preliminary)


• Have a stacked pixel detector where the two layers have a radius difference of few mm.

• Require coincidences between the pixels of the two layers to select high Pt stubs

Momentum cut.• Removes all the low pt particles.• See: J. Jones et al. , A Pixel Detector for L1

Triggering at SLHC, LECC 2005

α

SLHC track trigger: Stacked pixel layers (very preliminary)


ComponentOutput

bandwidth per unit

Rate Reduction

Number of units per upstream

component

Total number of

units

Aggregateoutput

bandwidth

Sensor (20cm2)10Gb/s cm2

N/A ~0.4 ~1600 ~140Tb/s

Hit Correlator(5 per 20cm2

stack)~1.6Gb/s X50 ~2 ~2000 ~3Tb/s

Opto TX and SERDES

~3.2Gb/s N/A 12 ~1000 ~3Tb/s

12xSFP to SNAP12 Cable

~40Gb/s N/A 5 ~90 ~3Tb/s

Regional Track Generator

~50Gb/s X4 ~3 ~18 ~1Tb/s

Global Track Generator

~4Gb/s X40 ~6 ~6 ~25Gb/s

Global Track Sorter

~10-20Gb/s

X2? N/A 1 ~10-20Gb/s

SLHC track trigger: Bandwidth requirement(very preliminary)


• By introducing a second double stacked detector one can measure angles and transverse energy of tracks at reasonable resolution.

• See: J. Jones, A. Rose et al., Stacked Tracking with CMS at SLHC• LECC 2006, Valencia.

SLHC track trigger: Two stacked detectors(very preliminary)


SLHC track trigger: Architecture(very preliminary)


= 10-3 – 10-4

PT / PT = 10-2

SLHC track trigger: Two stacked detectors(very preliminary)

pushing the limits: triggering and forward physics at the lhc

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