with heavyions Hou Keong Tim Lou Simon Knapen Tongyan Lin and Tom Melia PhysRevLett118171801 a Pb Light Dark Matter 2017 Disclaimer Not Dark Matter Sorry Light Dark ID: 935765
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Slide1
1
Searching for Axion-like particleswith heavy-ions
Hou Keong (Tim) Lou,Simon Knapen, Tongyan Lin and Tom MeliaPhysRevLett.118.171801
a
Pb
Light Dark Matter 2017
*Disclaimer: Not Dark Matter! Sorry!
“Light”? “Dark”?
Matter
Sector 2017
Slide2New Physics @LHC
Must leave no stone unturned!There may be many surprises!750 GeV (false alarm)Can we be missing cousins of 750 GeV?Possibly: What if resonance is lighter?2
lighter?
Slide3Axion-like Particle
Only couple to EMDecay rate Can we improve limits ~ GeV range? (Not DM! sorry!)Existing Constraints3
J. Jaeckel et.al. 1509.00476
Slide4How to look for ALPs
Light ALPsBeam dumps/fixed targetsDecays of mesonsAstrophysicsCosmologyHeavy ALPsMain limits from collidersProduction rates limited by LHCb, CMS, ATLAS, ALICE
p-p, Pb-p, Pb-Pb 4
Slide5Heavy-ion as a
source Can observe LBL scattering!5Old ideaEnhanced production at Heavy-ion collisions (~GeV)QED is strongly coupled!
enhancement
D.
d’Enterria
et.al. 1305.7142
ATLAS 1702.01625
A. Balantekin et.al. 1985,
M. Greiner et.al. 1993…
suppressed processes!!
Slide6Ultra-Peripheral Collisions
6
Pb
Pb
a
Grazing collision, ions do NOT breakup
ALPs are created in the strong EM field of the ions (photons almost on-shell)
Luminosity ~ classical formula
(
lead flashlight!)
Coherence requires photon wavelength
Pb radius / boost
Slide7Photon Luminosity
Photon-photon luminosity: = flux from Pb = probability that no breakup occurs
charge form factor Low energy ~ Requires nuclear physics to get all factors correct
7
a
Pb
Pb
Slide8p-p Collisions
Pb-Pb
CollisionsLuminosity
~ 1000 fb
-1
~ 10
-6
fb-1 (1 nb-1)
Enhancement
None
~ 5
10
7
Max
Energy
~ 1
TeV
(elastic)
~ 170 GeV
Background
Large pile-up background
Clean exclusive events
Regions of sensitivity
~100 GeV
~10 GeV
p-p Collisions
Pb-Pb
Collisions
Luminosity
~ 1000 fb
-1
~ 10
-6
fb
-1
(1 nb
-1
)
None
~ 1
TeV
(elastic)
~ 170 GeV
Background
Large pile-up background
Clean exclusive events
Regions of sensitivity
Proton vs
Pb
8
Proton’s
wrost
nightmare?
when p and
Pb
collide…
Slide99
Slide10Main Background
Light by Light scatteringFake photons / electron brem.Central Exclusive Production10
PbPbPbPb
Pb
Pb
Pb
Pb
Slide11Signal & Background
SignalIntact Pb-Pb ions, no tracks, very little calorimeter activityVeto on tracksTwo ~GeV back to back photons (cut on )Otherwise ions will likely breakupIntact ions may be taggedProminent mass peak!
BackgroundLBL scatteringIrreducibleHas been measured! Can be calculated reliablyElectrons fakes/brem or CEP (photons from QCD)Photons not back to backAll background smoothly falling in !
11
Slide12Search Strategy
Signal SelectionVeto tracks with ( GeV,
) Two photons ( GeV, )
Efficiency ~70% low mass to ~90% at high mass
Signal MC implemented in Starlight
Background:
Analytic approx. for -lumi
ME done analytically / Madgaph5
12
Integrated
lumi. ~ nb
Slide13Results
Standard ALP coupling13p-p collider searches dominated by associated productionPhoton fusion sub-dominant
LEP/CMS/ATLAS comparable8 TeV re-casthigh lumi results will be stronger
Slide14Results
Hypercharge coupling14Introduces coupling
On-shell
Heavy-ion limits comparable to 8
TeV
results
High-Luminosity LHC will likely yield stronger limits
Slide15ATLAS recast
155.02 TeV
480 b-1Current best limit on ALPs with EM coupling!First time heavy-ion yields best limit on BSM physics
Slide16Future Directions ?
New decay channel? decay for light scalar mixing with higgs? Invisible decay? Can we measure the outgoing beam?Exotic decay into hidden sector? e.g. long-lived particles?
New production?New kinds of coherent enhancement (baryon number)?Lighter ALPs? (pair production and off-shell rates are too small)Changes in inclusive elastic cross-sections?16
Slide17Conclusion
Heavy-ion collisions open a new window into ~ GeV ALPs/Hidden sectorATLAS Heavy-ion search places the best constraint for ~ GeV ALPsCMS results forthcomingHidden sector may show up in unexpected places!17
Slide1818
Thank You!
Where are the ALPs?
I think I’ve found it with my lead-flashlight!
Slide19pT
recoil distributionpT ~ virtuality of the photonCorrection beyond equivalent photon approximationALPs: pT ~ 1/R ~ 60 MeVCEP: pT ~ ~ GeVp-p collisions shownPb-Pb requires convolution with breakup factor
19
Slide20Form Factors Effects
20M. Klusek-Gawenda et.al. 1601.07001