Stepanyan JJ symposium · A854 (2017) – based on the engineering runs • “The Heavy Photon Search beamline and its performance”, NIM A859 (2017) First physics publication •

S. Stepanyan (JLAB)John Jaros Symposium

SLAC, May 17, 2019

EXPERIMENT AT JLAB

What is the heavy photon search experiment

• The Heavy Photon Search (HPS) experiment at Jefferson Lab is searching for a new U(1) vector boson ("heavy photon", "dark photon" or Aʹ) in the mass range of 20-

500 MeV/c2.

• An Aʹ in this mass region is natural in hidden sector models of light, thermal dark

matter. It couples to dark matter [the same way as the Standard Model photon to the electric charge], and can couple to SM photon through the kinetic mixing.

S. Stepanyan, Prof. J. Jaros Symposium,

SLAC May 17, 2019

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B. Holdom, Phys. Lett. B 166, 196 (1986).

ε 2 =!αα

a is the fine-structure constant

• Mass of the Aʹ is less constrained, if DM is light and accounts for the relic mass density, the region 1 MeV – 1 GeV is well motivated for dark vector mediator

S. Stepanyan, Prof. J. Jaros Symposium, SLAC May 17, 2019

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Jaeckel and Ringwald, Annu. Rev. Nucl. Part. Sci. 2010.60:405-437

Parameter space for LDMP

Hidden sector photons


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Where and how to search for dark photons?Simply follow the prescription in J.D. Bjorken, R. Essig, P. Schuster, and N. Toro, Phys.

Rev. D80, 2009, 075018 – A’ can be electro-produced the same way as radiative tridents in the fixed target experiments and can decay to SM particles

!A

Kinematics is different from massless photon bremsstrahlung, the heavier product takes most of the beam energy.


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CEBAF

injector

north linacsouth linac

experimental Halls A, B and C

experimental Hall D

FEL

Heavy Photon Search experiment at JLAB

HPS is managed by an international collaboration of more than 60 scientists from USA, France, Italy, UK, and Armenia.


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Resonance search

Displaced decay vertex search

Heavy Photon Search strategies

Parameter space at the time of the proposal

If a’ is small A’ lifetime is long, many will decay downstream of the production vertex

If a’ is large A’ can be seen as a peak on top of copious EM background

Access a unique region of parameter space by exploiting both separated vertex and invariant mass signatures.

S. Stepanyan, Prof. J. JarosSymposium, SLAC May 17, 2019

7And this is how it started• June 2009, Philip’s visit to JLAB and presentation of the dark photon idea at the

CLAS collaboration meeting

• Then an hour long discussion with Philip, and a month later – email from John

• I did not knew John …

First, some crazy ideas


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Possible location for heavy photon search

Photons

Dump

Chicane

CLAS

Then, John’s visit to JLAB in January 2010

After a year of hard work


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HPS proposal, PR12-11-006, was submitted and presented (by John) to JLAB PAC37 (01/2011)

• PAC approved HPS Test run, and conditionally approved (C2) the full experiment, 180 days, conditioned on the success of the test run.

• Test run proposal to DOE for the test run funding was approved few months later

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May 2011, HPS Collaboration is born and nominatedJohn as the chair of the executive committee


Some formalities


October 18, 2011, opening slide from John’s “Overview of HPS” talk


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and the second slide …

A grandiose plan to be completed in less than SIX months

HPS test run)


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… but we pulled if off

John made sure everybody workedand then flooding (7” in Hall-B)


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“The Heavy Photon Search test detector”, NIM A777 (2015)

From John’s presentation to PAC 39 “Test run results demonstrate that the HPS technical approach is sound, and that high rate triggering and DAQ work as required”.

Test run, very last 8 hours of CEBAF 6 GeV


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Space the final frontier. These are the voyages of the starship Enterprise. It's continuing mission, To explore strange new worlds, to seek out new life and new civilizations. To boldly go where no man has gone before.

JLAB the intensity frontier. This is the voyage of the HPS experiment. It's continuing mission, to explore strange new worlds, to seek out new force and new particles. To boldly go where no man has gone before.

My presentation of the test run success

Modern day HPS


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Si Vertex Tracker

e-

PbWO4 Ecal

• Two successful engineering runs, in 2015/2016 with 1.05/2.3 GeV beams

• Fully approved by JLAB in 2016 with requested 180 days of beam time, 39 of which was given “High Impact” status by JLAB PAC-41

• “The HPS Electromagnetic Calorimeter”, NIM A854 (2017) – based on the engineering runs

• “The Heavy Photon Search beamline and its performance”, NIM A859 (2017)

First physics publication• Resonance search results from 2015 run has been published as Rapid

Communication in Physical Review D 98, 091101(R) – article was posted on arXiv 7/30/2018


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• Article has been selected to be a PRD Editors' Suggestion and has been featured on the Physical Review D homepage

And five students who graduated.

Progress in displaced vertex search


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• Omar and Matt S. presented resonance and displaced vertex search results from 2015 run at ICHEP, 4-11 July 2018, Seoul, South Korea.

• A search for displaced A’ decays did not rule out any territory but resulted in a reliable analysis procedure that will probe new, unexplored parameter space with future, higher luminosity runs.

The “optimum interval” method

Preliminary

Maximum detectable A’ after z-cut with 2015 integrated luminosity, 1165 nb-1 (1.5 days)The 90% confidence limit for zero background requires greater than 2.3 A’ events

HPS evolution


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10 years later after the first phone call


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HPS is on the floor for its first long physics run

With upgraded detectors, and high hopes!

Fresh o

ff the

press

S. Stepanyan, Prof. J. Jaros

Symposium, SLAC May 17, 2019

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Parameter space for Heavy Photon Search• Since the first proposal, available parameter space for A’ searches is changed

significantly. Precision measurements on colliders, and experiments on hadron and

electron machines excluded a wide range of masses for e2>10-6

• Theoretical predictions for hidden sector photons have sharpened. Some of original

motivations disappeared, e.g. muon g-2, and new targets have emerged

HPS 2019

S. Stepanyan, Prof. J. Jaros

Symposium, SLAC May 17, 2019

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HPS 2019 4 PAC weeks

• HPS has a unique reach in the

region of parameter space well

motivated by Light Thermal Dark

Matter models

• Using displaced vertex search, HPS

will cover uncharted region of A’

masses from 80 MeV to 200 MeV

and the couplings as low as few

x10-10 with upcoming run in 2019 at

4.55 GeV

• While the main target is the heavy

photon, experiment is sensitive to

any new physics that makes long

lived states and uniquely

positioned to go after other targets

such as SIMPs and True Muonium.

To conclude

• HPS is the most exciting experiment I ever worked on. John really peaked the best [HPS] experiment for last

• It was with John’s exceptional leadership that we built the HPS collaboration and brought 10-years of hard and intense work to success. I hope we will not disappoint him with the first production running this summer and wonderful discoveries

And to John – although you are retired, we hope to continue to enjoy and benefit from your advice, wisdom, and friendship. We promise to keep your membership in the HPS executive committee and the right to vote “right” for years to come


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Documents

Stepanyan JJ symposium · A854 (2017) – based on the engineering runs • “The Heavy Photon Search beamline and its performance”, NIM A859 (2017) First physics publication •