LHC Forward Physics

April 23, 2006 DIS2006

XIV International Workshop on Deep Inelastic ScatteringTsukuba, Japan, 20-24/April/2006

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LHC Forward Physics

Jim WhitmorePenn State University

Experiments:ALICEATLASCMSFP420 (R&D project)LHCfTOTEM

April 23, 2006 DIS2006


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LHC Forward Physics

LHC Forward Physics•Total cross-section (and luminosity) with a precision of

1%

•Elastic pp scattering in the range: 10-3 < |t| = (p )2 < 10 GeV2

•Forward Physics:

•Low-x dynamics

•Diffractive phenomena:

•Soft and Hard

•Inclusive and exclusive Double Pomeron Exchange (DPE)

•Leading particle and energy flow in the forward direction

•pA, AA, and p processes (sorry, I will not cover these topics)Many of these topics can be studied best at startup luminosities

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+TOTEM

+LHCf

+FP420

“We are not studying a possibility of

forward physics with LHCb at the moment”

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General philosophy:•Additional detectors near the IP•Proton (Roman Pot) detectors:

•want to detect small scattering angles (~few rad:)•and the beam divergence

•so want large values of *. However, luminosity •want small *

•So expect a selection of * values (0.5-1540 m)•RP detectors at 140-220 m from IP•Need to go to 420 m → the “cold” region

Forward DetectorsForward Detectors

*min *

K

**

*

1L

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Roman Pot acceptanceRoman Pot acceptance

Low *: (0.5m): Lumi 1033-1034cm-

2s-1

220m: 0.02 < < 0.2 300/400m: 0.002 < < 0.02 Detectors in the 420 m region are needed to access the low values

TOTEM(ATLAS)

FP420

- 240 m

M2=12s

= proton momentum loss = p/pReconstruct with roman pots < 0.1 O(1) TeV “Pomeron beams“

(A. d

eR

oeck)

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T1:3.1 << 4.7

T2: 5.3 < < 6.5

T1 T2 CASTOR (CMS)

RP1 (147 m) RP2 (180 m)(later option)

RP3 (220 m)

Experimental Apparatus

Experimental Apparatus

10.5 m~14 m

TOTEM + CMSTOTEM + CMS

CMS Castor 5.25< <6.5

IP5

IP5

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~3 m• 5 planes with measurement of

three coordinates per plane.• 3 degrees rotation and overlap

between adjacent planes• Primary vertex

reconstruction• Trigger with CSC wires

T1 TelescopeT1 Telescope3.1< || <4.7

T2 Telescope

T2 Telescope

Digital r/o pads

Analog r/o circular strips

5.3< ll < 6.5

GEM (Gas Electron Multiplier) Telescope: 10 ½-planes 13.5 m

from IP

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Roman Pot unit:- Vertical and horizontal pots mounted as close as possible- TOTEM at the RP: beam ≈ 80 m- Leading proton detection at distances down to 10beam + d- Need “edgeless” detectors that are efficient up to the physical edge to minimize “d”- Currently two tech. (5-10 m and 40-50 m dead areas)

0

recon

st r

ucte

d t

r ack

Tracks

Roman Pots

Roman Pots

Test beam data:

RP in SPS beam and the detector is measuring the halo

u,vinfo

reconstructedtracks in y

BPMBPM

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Forward Detectors in ATLAS

IP1

Roman Pots at 240 mCerenkov Counter (LUCID)= a lumi monitor at 5.4 << 6.1+ neutral energy at zero degrees

(I. Efth

ym

iopoulo

s)

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ScenarioPhysics:

1low |t| elastic,tot ,

min. bias, soft

diffraction

2diffraction

3large |t| elastic

4hard

diffractionlarge |t| elastic(under study)

* [m] 1540 1540 18 90

N of bunches 43 156 2808 156

N of part. per bunch (x1011)

0.3 0.6 - 1.15 1.15 1.15

Half crossing angle [rad]

0 0 160 0

Transv. norm. emitt. [m rad]

1 1 - 3.75 3.75 3.75

RMS beam size at IP [m]

454 454 - 880 95 200

RMS beam diverg. [rad]

0.29 0.29 - 0.57 5.28 2.4

Peak luminosity [cm-2 s-1]

1.6 x 1028 2.4 x 1029 3.6 x 1032 2 x 1030

Running ScenariosRunning Scenarios

TOTEM

(V. A

vati, M

. Deile

)

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pp total cross section

and luminosity monitor

pp total cross section

and luminosity monitor

TOTEM-CMSATLAS

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pp total Cross-Section


• Measure the total rate (Nel+Ninel) , diff ~ 18 mb and min. bias ~65 mb, with an expected precision of 0.8 % (running for 1 day at L = 1.6 x 1028cm-2s-1).

• Extrapolate the elastic cross-section to t = 0: systematics dominated: 0.5 %(statistical error after 1 day: 0.07 %)

• ρ =Re f(0)/Im f(0) unknown; using COMPETE pred.: 0.2 %

1 %

( = 0.1361±0.0015+0.0058-0.0025

)

pp total cross sectionpp total cross section

221

116

el el tot

t o t o

el ineltot

d dN

dt L dt

N N

L

Luminosity-independent measurement using the Optical Theorem:

02

22

0

/16

1

1

16 /

el ttot

el inel

el inel

el t

dN dt

N N

N NL

dN dt

(M. D

eile

)

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• Current models predictions: 90-130 mb

• Aim of TOTEM: ~1% accuracy (~1 mb)

mb 1.41.2

2.1 5.111 totLHC:

COMPETE Collaboration fits all available hadronic data and predicts:



[PRL 89 201801 (2002)]Cudell et al.

April 23, 2006 DIS2006


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ATLAS’s Plans:ATLAS’s Plans:

ATLAS submitted a Letter of Intent to complement the experiment with a set of forward detectors for luminosity

measurement and monitoring as part of a two stage scenario:

1. Short time scale Roman Pots at 240 m from IP1

• Probe the elastic scattering in the Coulomb interference region

Dedicated detector for luminosity monitoring – LUCID• Used also to transfer the calibration from 1027 1034

Goal: Determine absolute luminosity at IP1 (2-3% precision)

2. Longer time scale Study opportunities for diffractive physics with ATLAS Propose a diffractive physics program using additional

detectors(I. Efthymiopoulos)

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Physics interest -- ATLASPhysics interest -- ATLAS

Luminosity Measurement – Why?Luminosity Measurement – Why?• Important for (precision)

comparison with theory: e.g. bb, tt, W/Z, n-jet, …

cross-section deviations from SM could be a signal for new physics

Systematic error dominated by the luminosity measurement

(ATLAS-TDR-15, May 1999)

(I. Efthymiopoulos)

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pp elastic scatteringpp elastic scattering

TOTEM

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~1.5 GeV2

Elastic scattering – from ISR to Tevatron

Elastic scattering – from ISR to Tevatron

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* = 1540 m

L = 1.6 x 1028 cm-2 s-1

(1)

104 per bin

of 10-3 GeV2

diffractive structure

Photon - Pomeron interference

pQCD

pp 14 TeVBSW model

Multigluon (“Pomeron”) exchange e– B |t|

-t [GeV2]

t p2 2

d/ d

t [m

b / G

e V2 ]

~1 day(1) (3)

wide range of predictions

pp elastic scattering cross-section

pp elastic scattering cross-section

*=18 m

L = 3.6 x 1032 cm-2 s-1

(3)

~ 1/|t|8

BSW = Bourrely,Soffer and Wu

B(s) = B0 + 2P’ ln (s/s0) ~ 20 GeV-2 at LHC

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Observations:

• fwd diffraction cross section increases• • diffractive peak shrinks

• interference dip moves to smaller t

• at –t 1 GeV2:

• d/dt 1/t8 • (3-gluon exchange)• little s dependence

Elastic Scattering Models (eg. Islam et al)

Elastic Scattering Models (eg. Islam et al)

1/t8

BSW

Desgrolardet al

Islam et al

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0.375

Rel = el(s)/tot(s) Rdiff=[el(s) +SD(s) + DD(s)]/tot(s)

0.30

el 30% of tot at the LHC ? SD + DD 10% of tot (= 100-150mb) at the LHC ?

0.2

0.4

0.3

0.2

0.3

0.1

Elastic Scattering- el/totElastic Scattering- el/tot

3 4 53 4 65 6log(s/s0)

(M. D

eile

)

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Low-x at the LHCLow-x at the LHCLHC: due to the high energy can

reach small values of Bjorken-x in structure of the proton F(x,Q2)Processes: Drell-Yan Prompt photon production Jet production W production

If rapidities below 5 and masses below 10 GeV can becovered x down to 10-6-10-7

Possible with T2 upgrade in TOTEM(calorimeter, tracker) 5<< 6.7 !

Proton structure at low-x !!Parton saturation effects?

(A. d

eR

oeck)

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Diffractive physicsDiffractive physics

ALICETOTEMCMSF420 project

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The accessible physics is a function of the integrated

luminosity

2 gluon exchange with vacuum quantum numbers “Pomeron”

X

Double Pomeron exchange:

X

Single diffraction:

p p p X p p p X p

X

Y

Double diffraction:

p p X Y

(M. R

usp

a)

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90% (65%) of all diffractive protons are detected for * = 1540 (90) m

largest acceptance detector ever built at a hadron collider

Ro

ma

n P

ots

TOTEM+CMS

T1,T2 T1,T2

Ro

ma

n P

ots

dN

ch/d

d

E/d

dE/d

Total TOTEM/CMS acceptance

CMS

central

T1

HCal

T2 CASTOR

=90m=90m

RPs

=1540m=1540m

ZDC

Pseudorapidity: = ln tg /2

Energy flux

Charged particles

CMS + TOTEM: AcceptanceCMS + TOTEM: Acceptance

107 min bias events, incl. all diffractive processes, in 1 day with * =1540 m

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Soft Diffractive Event rates

Soft Diffractive Event rates

DPE: pp pXpAcc = 27.8%for detecting both protons (* = 90 m)

ALICE is studying the possibility of implementing a trigger requiring a rapidity gap on both sides of a central region of 1.5 units of rapidity. The selection can include EM energy deposition in the PHOS, protons in the HMPID (RICH), or electrons identified with the TRD, opening the possibility to study heavy flavour production in double diffractive events.

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Measure > 90 (65)% of leading protons with RPs at * = 1540 (90) mand diffractive system X with T1, T2 and CMS.

Events/GeV-day

DPEDPE

Scenario (2) (4)* (m) = 1540 90

Exchange of color singlets (“Pomerons”) rapidity gaps

diffractive system Xproton:p2’

proton:p1’

rapidity gaprapidity gap

min max

2= – ln 1= – ln

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Hard Diffractive EventsHard Diffractive EventsDiffractive events with high pT particles produced

M

M

hard

hard

DoublePomeronExchange

hard

p

pjet 1 (pT 1)jet 2 (pT 2)jet 3 (pT 3)

pgg

u

du

Single diffraction: pp p + 3j

Double pomeron Ex: pp pjjXp= 1 bpT > 10 GeVAcc = 29.3% (for * =90 m, prel.)

(V. A

vati)

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Exclusive Double Pomeron Exchange


TOTEM-CMSFP420(with ATLAS/CMS)

H

p

p

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Quantum numbers are defined for exclusive particle production

Gluonic states c , b , Higgs, supersymmetric Higgs,…..

MX2 = s

Motivation from KMR calculations (e.g. hep-ph 0111078)

• Selection rules mean that central system is (to a good approx) 0++

• H→b-bbar: QCD b-bbar bkgd suppressed by Jz=0 selection rule • If you see a new particle produced exclusively with proton tags you know its quantum numbers• Tagging the protons means excellent mass resolution (~ GeV) irrespective of the decay products of the central system

• Proton tagging may be the discovery channel in certain regions of the MSSM

Trigger studies were discussed by M. Ruspa

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Diffractive: H bbYuk. coupling, MH, 0++

Inclusive: H,A wide bump

mH=

140

mH=

160

=60 fb-1

5

Tasevsky et al

From A. Martin’s parallel session

talk

From A. Martin’s parallel session

talk

SUSY Higgs: h, H, A, (H+, H--)

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From A. Martin’s parallel session talk

From A. Martin’s parallel session talk

(pp p + H + p) ~ 3 fb at LHC for SM 120 GeV Higgs

•L(LHC)~60 fb-1 ~10 observable events after cuts + efficiency

Alan’s Conclusions

There is a very strong case for installing proton taggersat the LHC, far from the IP ---- it is crucial to get the missing mass M of the Higgs as small as possibleThe diffractive Higgs signals beautifully complement theconventional signals. Indeed there are significant SUSYHiggs regions where the diffractive signals are advantageous---determining MH, Yukawa Hbb coupling, 0++ determinn

---searching for CP-violation in the Higgs sector

Higgs needs L ~ 1033 cm-2 s-1, i.e. a running scenario for = 0.5 m:• trigger problems in the presence of overlapping events (see M. Ruspa’s talk)• install additional Roman Pots in cold LHC region (420 m) at a later stage

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The aim of FP420 is to install high precision silicon tracking and fast timing detectors close to the beams at 420 m from ATLAS and/or CMS.

(See B. Cox’s talk in the diffractive parallel session)

FP420 ProjectFP420 Project

FP420 turns the LHC into a glue-glue collider where you know the beam

energy of the gluons to ~ 2 GeV. With nominal LHC beam

optics @ 1033-34 cm-2s-1: • 220 m: 0.02 < < 0.2• 420 m: 0.002 < < 0.02

1 2 s = M2

With √s = 14TeV, MH = 120 GeVon average:

0.009 1%Hence the need for FP420

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Forward physics:connection to cosmic

rays

Forward physics:connection to cosmic

rays

ALICETOTEMLHCf

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Issues in UHE cosmic rays


29th ICRC Pune

1. Spectrum / GZK Cutoff

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2. Composition

Xm

ax(g

/cm

2)

Energy (eV)

Measurements of the very forward energy flux (including diffraction) and of the total cross section are essential for the understanding of cosmic ray events

At LHC pp energy:

104 cosmic events km-2 year-1

> 107 events at the LHC in one day

p

Fe



(O. A

dria

ni)

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UHE Cosmic RaysUHE Cosmic Rays

Interpreting cosmic ray data dependson hadronic simulation programsForward region poorly known/constrainedModels differ by factor 2 or moreNeed forward particle/energy measurements e.g. dE/d…

Cosmic ray showers:Dynamics of the high energy particle spectrum is crucial

p Fe

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Model Predictions: pp at the

LHC Model Predictions: pp at the

LHC

Predictions in the forward region within the CMS/TOTEM acceptance

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• The dominant contribution to the energy flux is in the very forward region

• In this forward region the highest energy measurements of 0 cross section were done by UA7 (E=1014 eV, y = 5÷7)

Simulation of an atmospheric shower due to a 1019 eV proton.

The direct measurement of the production cross section as function of pT is essential to correctly estimate the energy of the primary cosmic rays

(LHC: 1017 eV)

Measurement of Photons and Neutral Pions in the Very Forward Region of LHC

LHCfLHCf(O

. Ad

rian

i)

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INTERACTION POINT Detector II

Tungsten

Scintillator

Silicon strips

Detector I

Tungsten

Scintillator

Scintillating fibers

Beam line

140 m 140 m

Experimental Method:2 independent detectors on both sides of IP

IP1 (ATLAS)

LHCfLHCf

•The vacuum tube contains two counter-rotating beams. The beams transition from one beam in each tube to two beams in the same tube.•Detectors will be installed in the TAN region, 140 m away from the Interaction Point, in front of luminosity monitors•Charged particle are swept away by magnets

•LHCf will cover up to y → ∞

(O. A

dria

ni)

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There are plans at the LHC for a wide range of Forward and Diffractive measurements that can be achieved at a variety of different luminosities:

Measure total cross-section tot with a precision of 1%

Measure elastic scattering in the range 10-3 <|t|< 8 GeV2

A study of soft and hard diffractive physics: semi-hard diffraction (pT > 10 GeV) hard diffraction Inclusive DPE

Studies of Exclusive Double Pomeron Exchange events

Studies of very forward particle production Connection with UHE Cosmic ray phenomena Special exotics (centauro’s, DCC’s in the forward

region)

SummarySummary

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Extra slidesExtra slides

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Elastic Scattering: = Re f(s,0)/Im f(s,0)

TOTEM

Ref+(s,0)/Imf+(s,0)

(analyticity of thescattering amplitude via dispersion relations)

constant/lns with s

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Number of pileup events per bunch crossing =

= Lumi* cross section * bunch time width * total lhc bunches / filled bunches =

= 1034 cm-2 s-1 * 104 (cm^2/m^2) * 10-28 (m2 / b) * 110 mb * 10-3 (b/mb) * 25 (ns) * 10-9 (s/ns) * 3564 / 2808 35

1x1032 0

1x1033 3.5

2x1033 7

Pile-up: numbers!1 mb = 100 events/s @ 10 29 cm-2 s-1

PHOJET: ALL PROCESSES 110 mb NONDIF.INELASTIC 51 mb ELASTIC 33 mb DOUBLE POMERON 1.95 mb SINGLE DIFFR.(1) 7.66 mb SINGLE DIFFR.(2) 7.52 mb DOUBLE DIFFRACT. 9.3 mb

Number of pileup events per bunch crossing =

= Lumi* cross section * bunch time width * total lhc bunches / filled bunches =

= 1034 cm-2 s-1 * 104 (cm^2/m^2) * 10-28 (m2 / b) * 51 mb * 10-3 (b/mb) * 25 (ns) * 10-9 (s/ns) * 3564 / 2808 17

This number is valid in the central detector region, but must be corrected for the elastic and diffractive cross section in the forward region!

Selection of diffractive events with rapidity gap selection only possibleat luminosities below 10 33 cm-2s-1, where event pile-up is absent

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TOTEM Experiment(symmetric about IP5)

T1 & T2

RP

RP

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FP420 Acceptance and Resolution

3 mm

5 mm

7.5 mm

10 mm

3 mm + 3 mm

22 mm

30 mm25 mm

MB apertures

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Planar technology: Testbeam 40 m dead area

Detector 1Detector 1 Detector 2Detector 2

active edges(“planar/3D”)

planar technology CTS(Curr. Termin. Struct.)

50

m

dead

are

a1

0

m d

ead

are

a66 m pitch

Add here photo of RP

Active edges: X-ray measurement

m

Sig

nal

[a.

u.]

5m deadarea

Strip 1 Strip 2

Edgeless silicon detectors for the RP

Edgeless silicon detectors for the RP

10 planes/pot

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Diffraction at * = 1540 m Acceptance

Diffraction at * = 1540 m Acceptance

Diffractive protons are observed in a large -t range: =p/p; t=-(p)2

90% are detected-t > 2.5x10-3 GeV2

10-8 < < 0.1 resolution ~5x10-3

kinematically

excluded

RP at 220 m

acc. < 10%

April 23, 2006 DIS2006


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Diffraction at * = 90 m AcceptanceDiffraction at * = 90 m Acceptance

Resolution in : = 4x10-4

(prel.)L<2x1031 cm-

2s-1

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Diffraction at * = 0.5 m

Diffraction at * = 0.5 m

Documents

LHC Forward Physics