Double Pomeron # Exchange from the ISR* (via the Tevatron) to the LHC*

1Mike Albrow (FNAL) DIFF2010 OtrantoDouble Pomeron Exchange from the ISR to the LHC

Double Pomeron# Exchange from the ISR* (via the Tevatron) to the LHC*

Michael AlbrowFermilab

•* Intersecting Storage Rings (1971-1984)•** Large Hadron Collider (2009 - )

p

p

XIP

IP

# “the P-word”

Note: X is independent of nature of colliding hadrons (?)

Same for π+π+ scattering and Ω-Ξ0 scattering (?)

Fundamental in S.I.

frame dependent


pp

pp

p

p

p

p

π+

π-

W+

W-G H

ISR

2.4y

GeV63

BEAM s

6.9y

GeV000,14)7(

BEAM s

LHCy

G = glueball (SI)H = Higgs (WI)

Both:JPC = 0++

No chargeNo color

Exclusive Central Production: p + p p + X + p

t-channel exchange over Δy >~ (3-)4 : only γ or pomeron IP (or odderon O)

Δy

Δy

Δy

Δy

MGA, Coughlan, Forshaw:Review: CEP in hh-collisionsarXiv:1006.1289, PPNP


Triple Regge / Trippple pomeronDouble-Triple Regge / Quintuple pomeron

SDE DPERegge Theory demands double pomeron exchange


Exchange must beQ = 0, Color = 0,J/ α(t=0) >= 1:Pair of gluons:pomeron (Pomeranchukon)or photon γ

Couplings β,g not << 1 so non-perturbative,but Regge calculus “works” to some extent.

Do not think IP emitted like a free particle!Spacelike only.

Both beam particles coherent,xF > 0.95, Δy > (3) 4, IP+IP Xσ(γγ → X) much smaller, & very low t IGJPC(X) = 0+0++, 2++

Q = 0, S = 0 etc.Low-Nussinov IP = {gg} (+…)

So double pomeron exchange is a good “laboratory” for mesonspectroscopy and especially for hunting glue-rich states or “glueballs”

In string model of hadrons:Meson = open stringGlueball = closed string


ISR Phase I (Search for DPE)

|yπ| < 1.0

|yπ| < 1.5

2 gaps Δy > 3

No particle ID but π+π- assumed.M(π+π-) <~ 1 GeV

Later Axial Field Spectrometer: π/K/p ID, better resolution and high statistics.

Before R807: Axial Field Spectrometer


ISR: Axial Field Spectrometer (R807)First sophisticated high-pT spectrometer in pp. Forerunner of p-pbar collider experiments.

Axial Field Magnet(~Helmholtz coils)

Uranium-scintillator full-azimuth calorimeter37%/sqrt(E) hadron showers

ISR (1971-84)Intersecting Storage Rings

pp, ppbar, dd, pd αα,..DC ribbon beams

> 50 amps !!

Central drift chamber half

Jets! When ΣET = 35-40/63 GeV (& UA2, UA1)


Low Mass Central Exclusive Production

ISR = 63 GeVpp p X pX fully measured

p p

+ nothing else

Search for “Glueballs”

{ } as distinct from { }gg qqs

Axial Field Spectrometer (R807)Added very forward drift chambers for p

U-Cal

U-Cal

π

π


Central Exclusive Production (AFS)

)( M

, , , 4K K pp

3Δy GeV, 63s G PC + ++I J =0 even

observed, same M-spectrum,can only be coherent.

f0(980) and f0(1500) seen as dips.

One claim (Ochs and Minkowski):σ = f0(600) is very broad 400-1700 MeV scalar glueball, “cut” at 980 and 1500 MeV by f0’s in destructive interference.

O&M: hep-ph/9811518

Structures not well understoodOnly now being studied at higher (RHIC, Tevatron … LHC)

No ρ0 (980)f

1500

s

s05.0


High statistics Moments of angulardistributions, project out:

~ All S-wave up to 1650 MeV

Small (~6%) D-wave (J=2)at f2(1270)More D-wave ~ 1900-2200 MeV

1

KK

Gluey, but is σ(400-1700) the “Lightest Scalar Glueball”?

1 GeV

1 GeV

J=2 glueball expected~ 2.1 GeV

600

40

S-wave (J = 0) amplitude2

D-wave (J = 2) amplitude2


σ/f0(600) is a very broad scalar resonance in ππ.Has been called “the Higgs boson of the strong interaction”

Γ ~ 1 GeV Lifetime τ ~ ħc/Γ ~ 1/5 fm

It “decays” before exiting the hadronic interaction.NOT like a π or any isolatable meson. NOT really a bound state.Strong S-wave ππ scatteringNOT narrow (as was supposed, from Zweig’s rule) …but αS >~ 1

NB: σ/f0(600) is NOT on the IP trajectory. First state on IP has J = 2 expected at M(G2) ~ 2.1 GeV/c2

Glueball situation still controversial, but never an isolated “hadron”(unless M(G) < 2 m(π) and strong decay forbidden)

Note: The IP does not get “emitted” from the proton either, do not interpret Regge diagrams that way!


Double pomeron exchange at RHIC (STAR)

(Wlodek Guryn’s talk)

p + p p + X + p with p detected, X = low mass hadrons

Work going on to isolate exclusive channels, perhaps more data.

for identifiedhadrons

DPE in UA8 (Schlein et al)But limited stats/resln


ISR – Tevatron -- LHC CM energy: 63 1960 ~ 14,000 GeV

FP420: R&D project; proposing extensions to ATLAS & CMS.In CMS: High Precision Spectrometers, HPSIn ATLAS: ATLAS Forward Protons, AFP

)4,,,( ppKK

pp

pp

p

p

p

p

W

-WG? H?

JetJetΥ,,ψ(2S),J/ψ/,μμ,ee c0

ISR

Tevatron

?,~~

,,,, XllWWHhZ LHC

(eventually)

Moving along:

D IP E


Central Exclusive Production of Higgs

Higgs has vacuum quantum numbers, vacuum has Higgs field.So pp p+H+p is possible.Allowed states:

Process is gg H through t-loop as usualwith another g-exchange to cancel colorand even leave p’s in ground state.If measure p’s:

H

2CEN 1 2 3 4M ( )p p p p

+ - ±Even for H W W l νJJ !

PC ++I J =0 even

J >= 2 strongly suppressed at small p angle (t)

t

4-vectors

( ) 2 GeV per eventHM

0c

0b

u-loop : γγ c-loop : χ

b-loop : χ t-loop: H

...~~

and etcll http://www.fp420.com

+ suppresion of backgrounds


Exclusive Higgs, not via γγ (possible, but σ much too small)

Ht

* gg fusion is the main H production process in hadron-hadron collisions.* If H JJ it’s swamped by QCD background.* Let a 2nd gluon cancel the color, allowing (requiring) both p to stay intact. Possible, but one pays a big price! How much?

Input:gg H (standard)Unintegrated g(x,x’)gg in color singlet C.S.No gluon radiation hadronsNo spectator parton-parton ints.

Large uncertainties

33

x at best

Color Singlet {gg} exchange = pomeron IP

4)(~ xg

~10-5 – 10-4


Q1: Is it really possible to produce a Higgs without any other particles? Can we benefit from p + H + p exclusivity?Q2: If so, is the cross section in reach at LHC?

There are similar reactions that we can measure at the Tevatron,and we have (in CDF).

cχc

0

J/ψ

γ

qγ

χc0 has Q.N.(H)

t cLower Q2

t all qNo final state S.I.Very small x-sn (10-12 σinel)

OBSERVEDCANDID

ATES

π0 π0 b/g ?

γ


Q1: Is it really possible to produce a Higgs without any other particles? Can we benefit from p + H + p exclusivity?

Q2: If so, is the cross section in reach at LHC?

Q3: Will the (non-PileUp) background swamp any signal?

Q4: Can the PU background be “killed”, and how?

Q5: Can suitable detectors (and mechanics) be built?

Q6: Can the forward proton spectrometers be precisely calibrated?

YES : HPS = High Precision Spectrometers (for CMS) AFP = Atlas Forward Protons (for ATLAS)

YES

Probably, it depends!

NO

Largely, timing & kinematics

On paper, yes

YES, if stable


CDF Forward Detectors:

BSC 1 BSC 2,3,4

CLCCherenkov Luminosity Counters

MINIPLUG

BSC important as rap gap detectors.FSC for CMS?


J/ψ

ψ(2S)γγ → μ+μ-

pppp )(

PHOTOPRODUCTION

QED

37 cit.

Ask for γ … find with J/ψ, from χc → J/ψ+γ


pppp )(

nbsyststatboxQED

nbsyststatdy

d

nbsyststatSdy

d

nbsyststatJdy

d

cy

y

y

)(4.0)(3.07.2),(

)(10)(1076)(|

)(10.0)(09.053.0)2(|

)(52.0)(25.092.3)/(|

00

0

0

nb 0.22.18

nb 90

nb 0.46

nb 0.33

Theory

33

0.110.04

QED and photoproduction observed as expected.χc exclusive production observed p+H+p should happen,at rate similar to Durham group prediction, ~ 1-10 fb (SMH) at LHC>>> All χc

0? Want to see χc in other channels (~ 7% hadronic & “clean”)


GAPp

Exclusive Di-Jets in CDF: IP + IP Jet + Jet

(p not seen)

“Almost” exclusive di-jet,Two jets and nothing else

0.8JJ

CEN

M

M

(~ polar angle)

(azimuth) Transverse

Energy TE

JETJET

JET

JET

Detected (Roman pots)

Tests mechanisms, but is B/G toexclusive H → b+bbar (so must b-tag!)


ExHuME: MC with

exclusive di-jets.

JJJJ

X

MR = 1.0

M

Exclusive Dijets (2 central jets + “nothing”) : CDF

pp

J

JXM = total central mass

JJM 40 -150 GeV

detected inferred(GAP)

Cross section agrees with ExHuME MC / 3 (inside uncertainty) based on Durham Gpcalculations.


New Study of DPE in CDF

Without (unfortunately) detecting forward p’s, study central hadronproduction between two large rap-gaps.Difficult to trigger on low mass (<~ 1 GeV/c2) central hadrons.

New CDF data set:All CDF detectors “empty” for 1.1 < |η| < 5.9 both sides. (Δy > 4.8)

In |η| < 1.1 : 2 Electromagnetic showers ET > 0.5 GeV2 EM+Hadronic towers ET > 0.5 GeV1 or 2 tracks pT > 1.5 GeV1 “jet” ET > 3 GeV

in “OR”

Note: this integrates over t1, t2, φ12 and allows low mass dissociation eg p pππ.

Rate is high even at low-Lumi: ~ 2M events in 4 hours


Some (selected) DPE studies of interest in CDF and CMS

)(?!,...

(?),...

.........**

............

?...

...

)(),(.......

0

0

00

00

00

2000

BB

DD

KK

pp

nnKK

KKKK

XfXf

b

c

LL

ss

ii

Low mass exclusives High mass characteristics

dσ/dM(ηmax)nch vs MEvent shapes: Thrust T(M), CircularityJets: 2-jets (gluon jets)…xg

and DPS (2x 22) or 24Drell-Yan & q-qbarBose-Einstein correlations (size of π-emission region)Extremes of n(+-)/n(0) ?

Anything in hadron-hadronexcept the very rare, & …

~ all glue


What: We propose to install a set of scintillation counters around both outgoing beam pipes at CMS, ~ 60m – 120 m

Why: (a) As veto in Level 1 diff. triggers to reduce useless pile-up events. (b) To detect rapidity gaps in diffractive events (p or no-p). (c) Measure “low” mass diffraction and double pomeron exchange. (d) Measure σINEL (if luminosity known, e.g. by Van der Meer) (e) Help establish exclusivity in central exclusive channels (f) To monitor beam conditions on incoming and outgoing beams. (g) To test forward flux simulations (MARS etc.) (h) Additional Luminosity monitor.

Proposal to add Forward Shower Counters FSC to CMS

Also: They may provide valuable tests of radiation environment to be expected for HPS = High Precision Spectrometers

!


2009 JINST 4 P10001

Do not see primary particles, but showers in pipe and other material.

Accessible warm beam pipebetween BMX magnets Can put scintillators at several z-locations

FSC = Forward Shower Counters

FSC


Big discussions: What is a gap?A: I know one when I see one.

No teeth ---- no hadronsCan I be 100% sure? Maybe not, that’s a background or inefficiency


Signal-Noise separationin calorimeters:Hottest PMT in regions:

0-bias with tracks0-bias with no tracks

Central CDF EM Cal:-0.66 < η < +0.66

Noise levels in calorimeters (How gappy is a gap?)

CMS (Nicola Schul)

99% of 0-bias notrackshave no channel > 4.2 GeV

Log(Max ET) (hottest tower/event)Peak at 32 MeV, Cut at 80 MeV

80 MeV

HF = Hadron Forward 4 < η < 5.2

(or no beams or 1 beam)

E in HF, no track events:(Single diffraction e.g.)


What about total inelastic cross section σINEL?And total σTOT if you know σEL ?

Can measure rate of totally empty events, P(0) = exp(-<ninel>)But this misses all the low mass diffraction that give hitsonly with |η| >~ 6, or M <~ 5 GeV/c2

This is many mb!

Nobody can measure σINEL directly, only σTOT - σEL (?)

With FSC, P(0) only faked by events with all particles in cracks(can study with fake cracks) or inefficient regions (small);and inefficient because of noise (can study with data).

FSC fills 2 huge cracks: 5(6) < |η| < 8(9…)

η poor variable here!

Not done at Tevatron!

Control data:No beams, 1 beamBunch Lumi dependenceExclusive l+l-, etc.


Efficiency for detecting forward particles, GEANT (Lamsa, Orava):

Low- : > 20% for > 9.0, > 60% for 9.5 < < 11.5

FSC efficiencies vs η at pT = 0.5 GeV/c (p & n dominate)


>4 hits in FSC or > 1 track in T1/HF or T2/Castor or ZDC(min)

FSC alone

FSC & others

ZDC alone

Efficiency SDE vs Mass:

Generated diffractive mass (PYTHIA/PHOJET) as log(MX), MX in GeV/c2,cf to calculated from rapidity gap edge:(a) full η coverage(b) η < 4.7 (no FSC)

10 GeV


Central events (0-bias trigger) with forward rap-gaps (FSC, ZDC, CASTOR, HF)studied for generic Double Pomeron Exchange processes (~ 0.1 mb)

Low mass DPE:

yFSC hits FSC hits

HF VETO

CENTRALSTATE

Even without seeing quasi-elastic protons, gaps >~ 4 units select D IP E

HF VETO

In β*=90m TOTEM running: p + X + p should be CMS priority!CMS-side trigger = ZDC-FSC-HF veto; TOTEM side = pp (not-elastic)

Low mass DPE in CMS


Change of Subject, Machine, Experiment!

Some pictures of exclusive μ+μ- events in CMS


CMS Exclusive dimuon candidates


Summary, Conclusions

Double Pomeron Exchange DPE is a special kind of interaction:Strong but ~pure glue, constrained quantum numbers, clean.

Exclusive states and hadron (glueball) spectroscopy:

!...,,,),(),(),980(),600( 200 GHXfXff bc

High mass multiparticle states: pomeron structure, jets, …At LHC reaching central masses ~ 200-500 GeV :fn(ηmax)

>> Want maximal forward coverage for gaps : ZDC, FSC +>> Want gaps in Level 1 triggers.


Thank you

Double Pomeron # Exchange from the ISR* (via the Tevatron) to the LHC*

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